Minimize Landsat 8 highlights from 2019

Landsat-8 Imagery in the period 2019

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References

• December 29, 2019: Since a pilot first noticed Marree Man in 1998, the mysterious work of earthen art has attracted international attention. Etched into a plateau in South Australia, the artwork depicts a hunter with what appears to be a stick or boomerang in his hand. 1)

- Spanning 3.5 kilometers (2.2 miles) from top to bottom, Marree Man is a geoglyph—a design made from earthen materials that is so large it is best viewed from above. An example of an even larger geoglyph is the Nazca Lines in Peru.

- For many years, Marree Man, named after a nearby town, was a prominent feature in Landsat satellite images of the area, but the lines faded over the years. By 2013, they were hardly visible in the natural-color images acquired by OLI on Landsat-8.

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Figure 1: It is unclear who created the giant geoglyph or why, but the large earthen figure has drawn attention to a remote part of South Australia for two decades. OLI on Landsat-8 acquired this image of the feature on June 22, 2019 (image credit: NASA Earth Observatory, image by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Adam Voiland)

- In August 2016, local business owners, concerned about the loss of what had become a tourist draw, decided to restore the fading geoglyph. With accurate GPS coordinates for the original in hand, they used a construction grader to redraw Marree Man over a period of five days.

- The restoration team thinks the updated geoglyph will last longer than the original because they created wind grooves, designed to trap water and encourage the growth of vegetation. Over time, they hope vegetation will turn the lines green.

- Who created the geoglyph and why has long been a topic of controversy and remains unknown, despite the recent announcement of a cash reward for credible information about it. There are indications that an artist living in Alice Springs may have created Marree Man, though other clues suggest that the creator may have been an American.

• December 25, 2019: Off the northwestern coast of Africa, small clusters of land dot the Atlantic Ocean. The archipelagos include the Canary Islands, a Spanish-colonized island chain located just over 100 km west of Morocco. Of the chain’s main islands and numerous islets, Lanzarote is one of the closest to the African mainland. It is also one of the driest and most barren, with rugged terrain that has compelled space agencies to train there. 2)

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Figure 2: The dry, volcanic terrain of this Canary Island is suitable for lichen and crops ... and for training astronauts. OLI on Landsat-8 acquired this image of the island on October 2, 2019. It shows a landscape that is the result of an active volcanic history (image credit: NASA Earth Observatory, image by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Kathryn Hansen)

- One notable eruption event started in 1730 and spanned six years, during which lava erupted from a 14-kilometer (8 mile) long fissure. Lava ultimately spread across 225 square kilometers, or one-third of the island. Another, shorter eruption in 1824 lasted 86 days, but still altered the landscape with new lava flows.

- At times, the eruptions on the island have turned explosive when magma came into contact with cold groundwater. These explosive “phreatomagmatic” eruptions can produce small volcanic cones. One of these more prominent “tuff cones,” Caldera Blanca, measures 1140 meters across and 450 meters high. Its name is derived from its white color, a consequence of a colony of lichens that have taken up residence on its slopes.

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Figure 3: Overview of the Canary Island of Lanzarote, acquired with OLI on Landsat-8 on 2 October 2019 (image credit: NASA Earth Observatory, image by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Kathryn Hansen)

- Caldera Blanca and other volcanic structures are the centerpieces of Los Volcanes Natural Park. With a surface similar to that of the Moon and Mars, the park has been used to train astronauts and to test Mars rovers. It’s an outdoor classroom where astronauts and engineers can learn the techniques of field geology and geo-microbiology.

- The island’s unique landscape has also been shaped by its desert-like climate with sparse rainfall. Because Lanzarote is flatter than the central and western islands in the archipelago, the cool, moist trade winds blowing pass right over it. In contrast, high mountain systems elsewhere in the Canary Islands trap moisture, producing rainfall on their northern coasts and a rain shadow on the leeward side.

- Despite the dry climate and rocky landscape, some areas can support vegetation—mostly with human help. Since the eruption in the 1700s destroyed most of the fertile farmland, people have adapted by digging shallow basins and bordering them with half-circles of stacked lava rock. The figs, grapes, almonds, and other crops planted in the center of these basins receive some protection from the wind and harsh sunlight, and they stay hydrated with the help of mulch—in this case, a moisture-absorbing ash.

• December 24, 2019: “Roads” may bring cars, trucks, and pavement to mind, but the word has a nautical meaning as well. For sailors, roadsteads are sheltered stretches of water near the shore where it is possible to safely drop anchor. This meaning is what originally gave Hampton Roads—the body of water where the James, Nansemond, and Elizabeth Rivers pour into the mouth of the Chesapeake Bay—its name. 3)

- Since early United States history, companies and government entities in Norfolk and Portsmouth have been on the forefront of shipping, trade, and defense. Today, Hampton Roads is the largest coal-exporting port in North America, with much of the coal arriving from Appalachia via rail and passing through the Norfolk Southern’s coal terminal at Lamberts Point.

- Immediately north of Lamberts Point lie the Norfolk International Terminals, the largest container port in the area. The piers are a nexus where ships, trains, trucks, and cranes come together to transfer vast quantities of cargo. Norfolk is typically among the busiest ports in the United States, trailing only New York and Savannah on the East Coast.

- Hampton Roads is also home to the world’s largest naval station. More than 70 ships are based at Norfolk Naval Station, including aircraft carriers, submarines, destroyers, and cruisers. In the wide view of Figure 5, several piers of the naval station are visible at the top of the image.

- For decades, coastal engineers have dredged the channels leading into port to make them deeper and wider. Prior to World War II, much of the dredged material was delivered to open water sites, but in 1946 the U.S. Congress designated Craney Island as a disposal site. In December 2019, dredging began on a new project that aims to make the port the deepest on the East Coast.

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Figure 4: The deep channels through Hampton Roads have made the surrounding cities important hubs of shipping, trade, and defense.

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Figure 5: On November 25, 2019, the Operational Land Imager (OLI) on Landsat-8 captured these images (Figures 4 and 5) showing outflow from the Elizabeth River joining the others in Hampton Roads. The deep, natural channels in this area have defined the character of the region by making it possible for ships to access Norfolk and Portsmouth, Virginia (image credit: NASA Earth Observatory, images by Joshua Stevens, using Landsat data from the U.S. Geological Survey. Story by Adam Voiland)

• December 11, 2019: The Chinese metropolitan area of Shanghai has ranked high on lists of economic and population growth in recent decades. So it is hardly surprising that the city of 24 million people stands out in another way: the amount of new land that people have created, or “reclaimed.” 4)

- Two recently published studies list Shanghai as the world’s leading city for land reclamation, a land-creation process that typically involves dredging and draining shallow coastal areas using ships, pumps, and mud. The studies are based analyses of Landsat satellite imagery.

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Figure 6: While reclaimed land is typically used for ports, industry, and housing, Shanghai stands out for devoting some of its new land to parks, forests, and wetlands. That tendency is visible in this pair of images from 2016 and 2019, acquired by the Operational Land Imager (OLI) on Landsat-8. Nanhui is a newly-built city in Pudong on Hangzhou Bay, about 60 km from downtown Shanghai (image credit: NASA Earth Observatory, images by Joshua Stevens, using Landsat data from the U.S. Geological Survey. Story by Adam Voiland)

- One of the most striking features is Dishui Lake, a circular freshwater lake that engineers constructed between 2003 and 2005 from sediment deposited by the Yangtze River. Within a few years, landscapers planted various shrubs, trees, and other vegetation in the surrounding Green Ring Park—plantings that were designed to improve the fertility of the soil and establish woodlands.

- Since 2016, the vegetation in these parklands has grown thicker. Meanwhile, new patches of green—coastal marshes—have emerged just to the north of the lake on newly reclaimed coastal land. With a combination of marshland, rice paddy, and aquaculture ponds, these areas have become a haven for migratory birds that travel from Australia to Siberia—as well as birdwatchers who follow them.

- With the new land come questions about how to best use it. Some birdwatchers and environmental groups want to keep the new land as marshland, and they have aired concerns about government plans to plant trees, which would make it less hospitable to some types of birds. However, government planners say they need to continue planting trees to meet city-wide standards for forest cover, and they have designated parts of nearby Chongming Island for bird breeding grounds, according to reporting from Caixin.

• December 7, 2019: Fjords and funnel-shaped bays and inlets are often scenes of dramatic tidal changes; the Bay of Fundy is perhaps the world’s most spectacular example. This sloshing of water into and out of basins can produce visible surges of sediment and floating debris, turbulent mixing of fresh and salty waters, and sometimes distinct lines between different water masses. 5)

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Figure 7: That was the case on 2 October 2019 when the Operational Land Imager on the Landsat 8 satellite captured the data for this image of Solway Firth. On that day, the waters along the coast of Dumfries and Galloway, Scotland, and Cumbria, England, were rich with sediment and dissolved organic matter (plant debris, soils, plankton) that was likely stirred up by the tides. The water changes color abruptly offshore where the shallower bay meets deeper waters of the Irish Sea (image credit: NASA Earth Observatory, image by Norman Kuring/NASA's Ocean Color Web, using Landsat data from the U.S. Geological Survey. Story by Michael Carlowicz)

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Figure 8: This image is a blend of art and science. Like a photographer who adjusts lighting and uses filters, Norman Kuring of NASA’s Ocean Biology group works with various software programs and color-filtering techniques to draw out the fine details in the water. The swirls and streamers in Solway Firth are real, but Kuring has separated and enhanced certain shades and tones in the data to make the sediments and dissolved organic matter stand out. Click here for a natural-color view at lower resolution. (image credit: NASA Earth Observatory, image by Norman Kuring/NASA's Ocean Color Web, using Landsat data from the U.S. Geological Survey. Story by Michael Carlowicz)

- On a sandy shoal offshore, a pattern of symmetrical white dots and shadows marks the location of the Robin Rigg wind farm. Sediment plumes make thin lines across the water toward the east-northeast, suggesting either strong winds blowing out of the southwest or the inflow of tidal currents toward the coast. Robin Rigg was Scotland’s first offshore wind farm, coming online in 2010. It can generate up to 174 megawatts of power, enough to supply 117,000 homes.

- Solway Firth is the United Kingdom’s third-largest estuary, and it is lined by beaches, coastal dunes, and salt marshes, a few of which are special conservation areas. The lands around the firth are mostly rural and agricultural. Along with its natural beauty, the region has a touch of history, as the western end of Hadrian’s Wall terminates on its southern shore.

• November 27, 2019: Farmers across the Midwest are in a race to finish harvesting their corn, soybean, and other staples of the Thanksgiving dinner table before the first crop killing freeze sets in. September rains made a late harvest even later. Heavy spring rains flooded millions of acres of cropland around the Mississippi, Wisconsin and Missouri rivers. Some farmers never seeded; others started three weeks behind schedule. 6)

Figure 9: Since 2008, the USDA's (US Department of Agriculture) National Agricultural Statistics Service, or NASS, has drawn on Landsat data to monitor dozens of crops in the lower 48 states as part of NASS's Cropland Data Layer program (video credit: NASA, Matthew R. Radcliff)

- These changes and delays in farmers’ plans this year made the United States Department of Agriculture’s job of tracking and estimating crop production with farmer surveys and ground observations a challenge. To meet it, they turned to the joint NASA - U.S. Geological Survey’s Landsat-8 satellite to fill in the missing pieces.

- “During abnormal growing seasons or natural disasters, satellites shine,” said Rick Mueller, Head of USDA’s NASS (National Agricultural Statistics Service) Spatial Analysis Research Section and manager of the Cropland Data Layer Program in Washington. “Landsat is a robust and independent way to validate what our statistics are telling us.”

- Since 2009, NASS has drawn on Landsat data to monitor dozens of crops, including corn, wheat, soy and cotton in the lower 48 states as part of NASS’s Cropland Data Layer program.

- The Cropland Data layer uses Landsat and similar sensors to identify what is growing where. Separately, NASS uses NASA's MODIS (Moderate Resolution Imaging Spectroradiometer) instruments aboard the Aqua and Terra satellites to monitor daily vegetation health and growth stage, all indicators of crop yield.

- “Landsat has been one of the only ways we can directly measure the global food supply,” said Brad Doorn, program manager for NASA’s Applied Sciences Water Resources and Agriculture Research at NASA Headquarters in Washington.

- However, “It’s not all satellites,” Mueller said.

- During a typical farming year, NASS relies heavily on their ground observations and survey data. Across the country, NASS field officials visit farms, and measure acreage and condition of planted fields throughout the growing season. NASS also receives crop acreage data from the Farm Service Agency (FSA). Farmers are required to self-report crop acreage and land use information to FSA annually. FSA uses the data to determine payment for federal programs such as crop loss due to natural disaster or financial loss from changes in market prices.

- This year was not a typical year. Farmers usually start planting corn, soybean and other crops in May. In Missouri, with 10 percent of the state’s cropland underwater, satellite imagery helped NASS state officials see what fields and areas were most impacted by the floods. They also could see which fields had crops.

- “Satellites helped us fill in the gaps and show what is going on in every region of the state,” said Robert Garino, Missouri State Statistician with the USDA. “The surveys work well at providing estimates for the state as a whole but are not designed to capture what is happening in specific regions within the state.”

- In June, several farmers could not report the amount of acres seeded to Garino’s office. They, were waiting for their fields to dry. In July, the USDA used satellites data to help them revise June production estimates.

- The following month, news stories reported that farmers had doubts about USDA August yield reports. “There was a lot of concern over their accuracy,” said Garino. “The general feeling was that the rain and flooding would cause both a reduction of harvested acreage and a fairly sharp reduction in yield. While harvested acres, especially for soybeans, were significantly reduced, August yield estimates have held up well.”

- NASS will publish the final Cropland Data layer in January 2020 and makes the data available to everyone through the CropScape website. Disaster managers use the site’s historic data to evaluate crop damage from this year’s floods and other natural disasters. Resource managers use historic data to direct crop rotation, study land-use change, and monitor water use.

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Figure 10: Three moments in a tumultuous year for farming north of St. Louis, MO, as seen in NASA-USGS Landsat-8 data. On the left is May 7, 2019, as heavy rains delayed planting for many farms. Sept 12, 2019, in the middle, shows bright green signifying growing vegetation, although with a fair amount of brown, bare fields. On the right, Oct. 14, 2019, the light brown indicates harvested fields while darker brown are fields that have not been seeded or fallow all summer (image credits: NASA)

- New satellites and new data partnerships are helping NASS improve their real-time crop monitoring capability. Currently, computer models use the Cropland Data Layer to calculate monthly yield estimates for corn and soybeans.

- In addition to Landsat-8, launched in 2013, partnerships between the USGS and the European Copernicus constellation provides even more Landsat-like imagery for free.

- “The more satellites, the better we feel,” said Rick Mueller, head of NASS’ Spatial Analysis Research Section and manager of the Cropland Data Layer Program in Washington.

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Figure 11: View of cranberry bogs above Little Trout Lake in northern Wisconsin on Oct. 18, 2018, from NASA-USGS Landsat-8 data. Some of the cranberries have turned bright red and are ready for harvesting (image credit: NASA)

• November 27, 2019: Today’s Image of the Day builds on this story from November 20, 2019. At the same time that scientists were standing on and studying the five-year-old Hunga Tonga-Hunga Ha‘apai island, another island-building event was unfolding just 150 km (90 miles) to the north-northeast in the Southwest Pacific Ocean. An undersea eruption at Lateiki Island in late October 2019 has brought new life to an older island in the Tonga chain. 7)

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Figure 12: An undersea eruption at Lateiki Island in late October 2019 has brought new life to an older island in the Tonga chain. The birth of the island is visible in these images, acquired with OLI on Landsat-8. This image shows the eruption on its third day, October 16, 2019. The false-color image combines shortwave infrared, near infrared, and blue light (bands 7-5-2) to help distinguish the hot spots associated with the eruption (red). Scientists say the emissions were dominated by steam and volcanic gases. (image credit: NASA Earth Observatory, image by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Kathryn Hansen)

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Figure 13: When the plume cleared on November 1, satellites started getting clear views of the new land that had emerged. Landsat-8 acquired the second, natural-color image of Lateiki Island on 17 November. Note that water around the island was still discolored from the eruption’s emissions. The new island measures about 400 meters (1300 feet) long and 100 meters (300 feet) wide (image credit: NASA Earth Observatory, image by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Kathryn Hansen)

- Lateiki’s history of erosion is not unique. Thousands of islands across Earth’s oceans are in a phase of decay. “We rarely see them as ‘newborns’ to watch how they evolve to become what they are,” said NASA scientist Jim Garvin. “Here in Tonga we can now watch and measure how they form and evolve in their childhood years, and compare them with others across the oceans to build better models for their evolutionary stages.”

- Previous eruptions at Lateiki have not been thoroughly documented by satellites, according to Garvin. He noted that this year, scientists are paying close attention to the region with Landsat-8, ESA’s Sentinel-2, and other satellites. “We’re excited because we have looked at this tiny island for the last 20 years,” he said. “Now the old one is gone and we get to watch the new one develop.”

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Figure 14: Lateiki Island, also known as Metis Shoal, is just the tip of a large undersea volcano (seamount) in an extremely active part of the Tonga Archipelago. (Scientists put it in the top ten most active volcanic areas on Earth). Prior to 2019, an eruption in 1995 also produced an island. That island saw considerable erosion and was ultimately destroyed by the 2019 event, which built a new island in its place. Earlier eruptions followed a similar cycle; islands that emerged in 1781, 1854, 1876, 1967, 1979, are all reported to have submerged within months, having succumbed to the erosive lashing of the sea (image credit: NASA Earth Observatory, image by Lauren Dauphin, using Landsat data from the U.S. Geological Survey and using topographic data from the Shuttle Radar Topography Mission (SRTM). Story by Kathryn Hansen, with information courtesy of Taaniela Kula and the government of the Kingdom of Tonga)

- They are particularly interested in seeing how the development and composition of Lateiki compares with Hunga Tonga-Hunga Ha‘apai (HTHH)—an island that appears to be stabilizing instead of eroding, and hence surviving. HTHH grew from an eruption that went through a series of phases over the course of six weeks, including an ash dominated surtseyan phase that built a 120-meter-tall cone, followed by explosive phases that spread material around the vent to grow the 180 hectare (0.69 square-mile) island. In contrast, the volcanic activity at Lateiki was less explosive, with lava piling up around the vent to form the relatively small 3-4 hectare islet.

- “Why they are different is unknown,” Garvin said. “We need to find out so we can predict lifespans of other islands as ‘dip-sticks’ for global environmental change in a time of sea level rise on Earth.”

• November 25, 2019: Many islands dot the bays of the ria coastline of South Gyeongsang Province in South Korea. But around Tongyeong, a city of 140,000 people, satellites observe something else of note in the water—a series of structures that look a bit like the squares of a chess board. In most cases, the squares are areas where oysters are being farmed. 8)

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Figure 15: On November 6, 2019, the OLI on Landsat-8 acquired this natural-color detail image of long-line oyster cultivation near an industrial facility. In this area, oysters are often grown by suspending them from ropes or wires, which are held near the surface with buoys. The technique encourages oysters to grow quickly and develop strong shells (image credit: NASA Earth Observatory, image by Joshua Stevens, using Landsat data from the U.S. Geological Survey. Story by Adam Voiland)

- After China, South Korea is the second-largest oyster producer in the world. Roughly 80 percent of this production comes from Tongyeong, which exports oysters to the United States, Japan, Canada, Hong Kong, and the European Union. Around Tongyeong, the oyster harvesting season begins in the fall, and this year’s haul appears to be unusually large. Downpours in the summer added extra nutrients to water and promoted growth, according to Arirang News.

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Figure 16: Overview image of South Korea’s oyster growing region in the waters of Tongyeong, acquired by OLI on Landsat-8 on 6 November 2019 (image credit: NASA Earth Observatory, image by Joshua Stevens, using Landsat data from the U.S. Geological Survey. Story by Adam Voiland)

• November 15, 2019: Tucked away in the eastern Andes Mountains, more than 5,000 meters above sea level, the town of La Rinconada is the highest permanent settlement in the world. The Peruvian town does not have running water, a sewage system, or garbage disposal. Yet 50,000 people live here amidst the thin air for one valuable resource: gold. 9)

- The town started as a temporary mining settlement more than four decades ago, so no permanent city services (such as sanitation systems) were installed. Male miners were allowed to spend up to thirty days at a time in the mine to collect as much gold as they could. The miners received no wage while in the mine, but there were also no restrictions on how much gold they could haul out.

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Figure 17: This natural-color image was acquired on August 1, 2019, by the Operational Land Imager on Landsat-8. La Rinconada lies in southeastern Peru, near Lake Titicaca and close to the Bolivian border. The town is located on the side of Mount Ananea and below a giant glacier called La Bella Durmiente, meaning “Sleeping Beauty” (image credit: NASA Earth Observatory, image by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Kasha Patel)

- Despite the poor working and living conditions, the population boomed in the 2000s when the market price for gold increased. From 2000 to 2009, the population of La Rinconada reportedly increased by 230 percent. Electricity was finally installed in the 2000s. Residents either burn or bury their trash outside of city limits.

- Besides the prospectors, the town also attracts researchers interested in studying the short-term and long-term effects of oxygen-poor conditions on humans. The thin air—each breath draws in half the amount of oxygen as at sea level—can lead to a syndrome called chronic mountain sickness (CMS). Symptoms of CMS include dizziness, headaches, ringing ears, palpitations, and even heart failure and death. Researchers estimate one in four people in La Rinconada suffer from CMS.

• November 15, 2019: Geoscience Australia’s Alice Springs satellite ground station hosts two 9 meter antennas, a 2.4 meter antenna, and associated infrastructure. The satellite ground station is one of three forming a global Landsat satellite ground station network and has been in operation since 1979. These antennas enable Geoscience Australia to collect data from a number of Earth monitoring satellites, including Landsat 7 and 8, which provide information to detect changes in land use over time and other useful environmental data. This data is used by government, industry, education and research, contributing billions of dollars to the Australian economy. 10)

- The geographic location of this satellite ground station is of strategic importance as it provides satellite reception coverage over the entire Australian continent therefore reducing the need and cost for other installations to provide the same capability in other locations. This ground station allows the US Geological Survey (USGS) Mission Operation Center located at NASA to send command and control signals to current and future Landsat satellites via the facility at Alice Springs, as well as satellite spacecraft telemetry information and 'state of health'.

- 2019 marks the 40th anniversary of Australia’s participation in the USGS Landsat program.

Figure 18: Geoscience Australia has invested more than $4 million to upgrade the Alice Springs antenna, securing Australia’s access to essential satellite data into the future. The antenna collects satellite imagery of the Earth, known as Earth observations from space (EOS) data, which has wide ranging benefits for the Australian community and globally, including significant economic returns. EOS data is used to respond to natural disasters such as bushfires, cyclones and floods, monitor land use, develop agriculture, discover new mineral and energy resources and ensure our water security (video credit: Geoscience Australia)

• November 13, 2019: The Juruá River emerges from highlands in east-central Peru, then winds its way through lowlands in Brazil. By the time it empties into the Amazon River near Fonte Boa, the river course spans more than 3000 km. But as the crow flies, the distance between the river’s source and mouth is only about 1000 km. 11)

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Figure 19: Meanders make up two thirds of the Juruá’s length, making it one of the most sinuous rivers in the Amazon Basin. On May 27, 2019, the Operational Land Imager (OLI) acquired this image of a stretch near Eirunepé, a settlement established in the 1800s as a hub for rubber production. A semicircle of land has been cleared around the city (light green), probably for ranching. Buildings and roads (white) are clustered along the river, which flows through seasonally flooded wetland forests known as várzea (dark green), image credit: NASA Earth Observatory, image by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Adam Voiland

- Note the abundance of oxbow lakes flanking the river. These form when parts of wide, curved meanders—oxbows—grow so close together that the river breaks through the bank and creates a more direct route. This often happens during floods.

- What makes rivers like the Juruá twist and turn so much more than other rivers? It flows through relatively flat terrain, which allows water to change course more readily than in other terrain. But research indicates that a heavy sediment load might be even more important. In analyzing three decades of Landsat images for 20 locations in the Amazon basin, the researchers from Cardiff University found that rivers carrying large amounts of sediment meandered more and had more cutoffs and oxbows than those carrying less sediment. The extra sediment accelerates the growth of point bars — sandy areas along the inside bends of meanders that can change the course of the flow and encourage the formation and lengthening of bends.

- The river has such sediment-rich “whitewater” because it flows through hilly areas in the foothills of the Andes that have soft, easily eroded rock and soil.

• November 6, 2019: For nearly four decades, Mauri Pelto has been studying the advance and retreat of glaciers around the globe. He has watched them succumb, one-by-one, to rising temperatures. Of 250 glaciers that he has watched, all had retreated (or shortened) except one: Taku Glacier. 12)

- Now a new analysis shows that Taku has lost mass and joined the rest of the retreating glaciers. “This is a big deal for me because I had this one glacier I could hold on to,” said Pelto, a glaciologist at Nichols College. “But not anymore. This makes the score climate change: 250 and alpine glaciers: 0.”

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Figure 20: This natural-color image show the glacier on 20 August 2014. The image was acquired by OLI (Operational Land Imager) on Landsat-8 (image credit: NASA Earth Observatory, image by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Kasha Patel)

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Figure 21: This natural color image shows the glacier on 9 August 2019. The image was acquired with OLI on Landsat-8 (image credit: NASA Earth Observatory, image by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Kasha Patel)

- Taku stands north of Juneau, Alaska, and is one of 19 notable glaciers in the Juneau Icefield. (The area also includes the famous Mendenhall Glacier, which has experienced an unusually fast retreat—about one third of a mile in the past decade.) Taku is extremely thick: In fact, it is one of the thickest known alpine glaciers in the world, measuring 4,860 feet (1,480 meters) from surface to bed. It is also the largest glacier in the Juneau Icefield.

- Using satellite imagery, aerial photography, and GPS field mapping, glaciologists with the Juneau Icefield Research Program (JIRP) have been tracking the thickness of Taku’s annual snow layer since 1946. Pelto has personally observed the glacier over a span of three decades, and even spent six months living on the glacier in huts and tents with JIRP in the 1980s.

- In his latest research, he used Landsat imagery to look at changes in the transient snowline—the boundary where snow transitions to bare glacier ice. At the end of the summer, the height of the snowline represents the point where the glacier experienced an equal amount of melting and snow accumulation. If a glacier experiences more melting than snow accumulation in a season, the glacier’s snowline migrates to higher altitudes. Researchers can calculate net changes in glacier mass by tracking the shift of the snow line.

- For half a century, the Taku Glacier was the only glacier in the Juneau Icefield that did not experience a net loss in mass. In fact, Pelto and colleagues found that the glacier was advancing and gaining mass at around 0.42 m/year from 1946-1988. But by 1989, glacier thickening slowed down significantly; eventually, the researchers noticed some thinning. The terminus also slowed its advance and then stalled.

- Usually, glaciers experience a transition period, with decades of terminus stability before switching from an advancing phase to a retreating phase. For instance, the Baird Glacier in nearby Glacier Bay stopped advancing and stood still for three decades before it began showing signs of retreat.

- “We thought the mass balance at Taku was so positive that it was going to be able to advance for the rest of the century,” said Pelto. “A lot of times, glaciers will stop advancing for quite a few years before retreats starts. I don’t think most of us thought Taku was going to retreat so quickly.”

- But it did. Taku Glacier had a short pause (2013-2018), then it began retreating in 2018. That year, Pelto and colleagues observed the highest transient snowline and mass loss in Taku Glacier’s history. The changes coincided with record summer temperatures in Alaska.

- “To be able to have the transition take place so fast indicates that climate is overriding the natural cycle of advance and retreat that the glacier would normally be going through,” said Pelto. “Taku Glacier is being exposed to melting it hadn’t before, which will drive new changes.”

• October 31, 2019: North of the Black Sea, the landscape of southern Ukraine is awash with eye-catching landforms that beg the question: what is that? About 65 km northwest of the colorful Sivash lagoons, the land abruptly turns from forest to sand. This oval-shaped region, known as Oleshky Sands, is the largest expanse of sand in Ukraine and the second-largest in Europe. 13)

- Dunes rise up to 5 m above the surrounding sand and punctuate the landscape. To try and prevent the dunes from encroaching on populated and agricultural areas, dense stands of pine trees were planted around the sandy expanse. Still, an analysis of 30 years of Landsat imagery (1987 to 2017) showed areas where sand had migrated into the forested areas, particularly on the northeastern and southwestern sides.

- Researchers are uncertain what made the area turn to desert. One theory is that the land is a dried riverbed of the Dnieper River (the modern-day course runs north of this image). A common explanation, however, is that millions of sheep that were pastured here in the 18th and 19th centuries initiated the desertification, which has since been sustained by wildfire and wind erosion.

- Episodes of fire continue to arise in the forested area around Oleshky. A notable case occurred in May 2018 when 25 hectares of forest were burned. Smoke from the fire was visible in images from the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra and Aqua satellites.

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Figure 22: The 161 km2 expanse of semi-arid desert is visible in this image acquired on 15 June 2019 by OLI on Landsat-8. At its widest, Oleshky Sands measures about 15 km across (image credit: NASA Earth Observatory, image by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Kathryn Hansen)

• October 30, 2019: On October 23, 2019, a blaze erupted in Sonoma County, California, near the small town of Geyserville. In six days, flames from the Kincade fire spread across more than 75,000 acres (303 km2), becoming the largest wildfire by acreage in California in 2019. As of October 29, the fire had destroyed more than 120 structures and caused at least 2,000 people to evacuate. 14)

- Fierce winds in northern California—known colloquially as Diablo winds—played a large role in quickly spreading the fire. On October 27, wind gusts reached 96 miles (150 km) per hour, which made the fire very difficult to stop. From October 26 to October 28, the fire grew by nearly 48,000 acres.

Figure 23: This animation shows winds over the western United States between October 20 and October 28, 2019. The strongest gusts appear bright yellow; weaker winds are purple. The wind data comes from the Goddard Earth Observing System Model 5 (GEOS-5), an experimental weather model that scientists at NASA use to analyze global weather phenomena. The GEOS model ingests wind data from more than 30 sources, including ships, buoys, radiosondes, dropsondes, aircraft, and satellites (video credit: NASA Earth Observatory)

- Forecasters expect another strong wind event on the night of October 29, which may again fan the flames. Firefighters are working on the ground and from the air to build containment lines around the wildfire. As of October 29, the fire was 15 percent contained.

- The Diablo winds tend to originate in the Great Basin region of Nevada and Utah. The winds are fueled by high-pressure air moving toward lower-pressure areas and lower elevations near the coast. On the way, the air masses pass over California’s mountain ranges and down through valleys, which causes the air to compress, heat up, and dry out. These hot, dry, gusty winds can exacerbate fire conditions and carry embers to the next patch of land. Similar winds—the Santa Anas—occur in southern California and are currently fanning the flames of the Tick Fire.

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Figure 24: This image shows a false-color view of the burn scar from the Kincade Fire as it appeared on October 26, 2019. The image combines shortwave-infrared, near-infrared, and green light from Landsat 8 (OLI bands 7-5-4) to better distinguish between burned vegetation (brown) and unburned vegetation (green). The brightest reds are active fire fronts. - The Kincade fire fits with a trend of larger, more destructive fires in California in autumn; fires in this season are strongly influenced by winds and dry weather. In addition to the impending wind storm, dry weather is expected continue in Northern California for the remainder of the week (image credit: NASA Earth Observatory, image by Joshua Stevens and Lauren Dauphin, using Landsat data from the U.S. Geological Survey and GEOS-5 data from the Global Modeling and Assimilation Office at NASA GSFC. Story by Kasha Patel)

• October 23,2019: When India gained its independence in 1947, it had to import salt to meet its domestic needs. Today, it is the third largest salt producer in the world, exporting surplus salt across regions from Japan to Indonesia. 15)

- The majority of India’s salt production can be traced to one region: the west central-state of Gujarat. With more than 50 percent of salt workers located in Gujarat, the state accounts for almost three-quarters of the country's annual salt production.

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Figure 25: The images of Figures 25 and 26 show the city of Bhavnagar, which is located in one of the major salt-producing districts in the state. They were acquired on February 28, 2019, by OLI on Landsat-8. The colorful rectangles are salt evaporation ponds and often seen in major salt-producing areas, such as the Makgadikgadi Pan in Botswana (image credit: NASA Earth Observatory images by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Kasha Patel)

- India’s main sources of salt are sea brine, lake brine, sub-soil brine, and rock salt deposits. In Gujarat, much of the salt comes from inland lake and marine sources. The Gulf of Khambhat has provided around 24 percent of salt production in the state in the past. Bhavnagar is one of the leading marine salt producers near the Gulf of Khambhat. It is also home to the Central Salt and Marine Chemicals Research Institute, which is one of the world’s leading salt research centers.

- The saltworks in Bhavnagar have also created an important environment for wetland birds. Many wetland species use it as a wintering area, while some water birds use it as a staging ground as they migrate along the coast.

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Figure 26: The west-central state of Gujarat accounts for nearly three-quarters of India’s annual salt production.

• October 9, 2019: The surface of Earth is constantly changing and evolving. Coastal barrier islands demonstrate such change faster than almost any other landscape. 16)

- Assateague Island stretches 37 miles (60 km) from north to south along the Atlantic coast of Maryland and Virginia. As barrier islands go, Assateague is quite dynamic. Longshore currents mostly flow south along this part of the coast, carrying sand to the south. So Assateague Island is steadily, relentlessly losing mass at its north end (near Ocean City, Maryland) and gaining it on the south end near Tom’s Cove.

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Figure 27: This image was acquired by Landsat 5 on June 20, 1985 (image credit: NASA Earth Observatory image by Joshua Stevens, using Landsat data from the U.S. Geological Survey. Story by Michael Carlowicz)

- Assateague also shelters two other islands, Chincoteague and Wallops, in a rare example of overlapping (duplexed) barrier islands. Major storms such as hurricanes and nor’easters sporadically and dramatically move sand from the ocean-facing side of Assateague to its land-facing side, into inlets and bays, and onto the shores of Chincoteague and Wallops. This means all three islands are slowly marching toward a merger with the mainland.

- “This is how Assateague Island has been growing for approximately the past 2,000 years,” said Christopher Seminack, a University of North Georgia geologist who has studied the area. “The island is growing to the south as sand shoals are migrating and welding onto the island. You can see evidence of this from the linear features that appear to be welded onto the most southerly part. And because the southern spit of Assateague acts as a sediment sink—the sediment is deposited there—it starves the barrier islands to the south of sand.”

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Figure 28: This natural color image, acquired with Landsat-8 on 2 June 2019, shows the change to Assateague, Chincoteague, and Wallops islands across three decades. Some of the color differences are related to the different sensors and likely different tidal stages at the time of each image (image credit: NASA Earth Observatory image by Joshua Stevens, using Landsat data from the U.S. Geological Survey. Story by Michael Carlowicz)

- Note the southwestward migration of Assateague Island and especially the substantial growth of vegetation on the southern spit. Just across the inlet, the east side of Wallops Island has bulged markedly. Changes in buildings and infrastructure are a bit more subtle. Activity has increased at NASA’s Wallops Flight Facility in recent decades; a new causeway bridge was built to Chincoteague; and more seasonal property and tourist business has sprung up in the area. But according to census estimates, the year-round population of Chincoteague has actually dropped since the 1980s.

- Through all of the changes, wild ponies have stuck around on the islands for several hundred years as the sand has moved under their feet. Legend has it that some of the original ponies arrived from the shipwreck of a Spanish galleon, though more likely they were left abandoned on the island by settlers and farmers. About 150 feral ponies live on the Maryland portion of Assateague and are kept relatively wild, without much human intervention. Another 150 live on the Virginia side and are owned by the Chincoteague Volunteer Fire Company, which provides medical checkups twice a year and auctions off several ponies each summer to raise money and maintain a steady population. All of the horses have adapted to eating salt marsh grasses and brush.

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Figure 29: NASA Earth Observatory (Photo courtesy of Margaret Landis. Story by Michael Carlowicz)

- “I spend a lot of time going in and out of Chincoteague inlet on my boat, and I have watched the inlet and islands change pretty dramatically over the past 20 years,” said Kyle Krabill, a research engineer at NASA’s Wallops Flight Facility. Krabill, his colleagues, and his father have been observing these shores for decades as they have tested lidar instruments that are ultimately used to study ice. “I have always been interested in these coastal processes and think it's really neat to watch them move around in our timescale.”

• September 25, 2019: After five years of planning and construction and more than three billion dollars in construction costs, one of the world’s longest bridges is complete. Opened in May 2019, the 48 km Sheikh Jaber Al-Ahmad Al-Sabah Causeway is one of the largest construction projects in Kuwait’s history. 17)

- Building the bridge was challenging in the coastal environment, where dangerously high temperatures and varying humidity can create extremely hot and dry conditions. Much of the construction occurred in early morning and after dark, with crews using high-powered lights or sun shields when necessary. The causeway is primarily composed of concrete piles and steel and layered with waterproofing and asphalt.

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Figure 30: OLI on Landsat-8 acquired this image of the causeway on September 8, 2019. Approximately 75 percent of the bridge (36 km) stands over water. It also crosses two artificial islands (Bay Island North and Bay Island South) that were constructed for entertainment and tourism purposes (image credit: NASA Earth Observatory, image by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Kasha Patel)

- Construction companies reported that they tried to take extra care to preserve the ecosystem near the bay, specifically for green tiger shrimp. In one case, they created an alternative breeding area comprised of 1,000 rock and reef blocks in order to draw the shrimp away from the construction site.

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Figure 31: Detail image of Landsat-8 of Kuwait City and the Sheikh Jaber Al-Ahmad Al-Sabah Causeway with Bay Island South (image credit: NASA Earth Observatory, image by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Kasha Patel)

- Named after the late Sheikh Jaber Al Sabah, the causeway was built to help reshape the country into an international trade center, weening it away from an oil-dependent economy. The bridge reduces travel time by nearly an hour from the capital, Kuwait City, to the northern shore of Kuwait Bay and the proposed future site of Madinat Al-Hareer.

- Meaning “Silk City” in Arabic, Madinat Al-Hareer is being proposed as a free trade zone and seaport. With development costs of more than $100 billion, the planned megacity will also include an airport, Olympic stadium, and a tower surpassing Dubai’s Burj Khalifa, currently the world’s tallest building. The causeway and Silk City are just a few elements in Kuwait National Development Plan 2035.

• September 25, 2019: In 1963, the Spanish government under Francisco Franco built the Valdecañas Reservoir in order to bring water and electricity to underdeveloped parts of western Spain. However, the creation of the reservoir flooded some inhabited areas as well as large stone (megalithic) monuments. After fifty years underwater, one of these ancient monuments—the Dolmen of Guadalperal—resurfaced due to dry, hot conditions in 2019. 18)

- Several areas of Europe experienced drought conditions during the summer of 2019. Much of the continent endured two heatwaves with record-breaking temperatures in June and July. Spain, in particular, faced its third-driest June this century, with above average temperatures in July and August. Many crops wilted, affecting many farmers.

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Figure 32: The Dolmen de Guadalperal resurfaced after five decades underwater. OLI on Landsat-8 acquired this image on 25 July 2019. Note the changing water levels and the widening of the tan ring around the shoreline; these lighter colored sediments are the recently exposed lake bottom. A circle marks the area where the remains of the Dolmen of Guadalperal are said to appear (image credit: NASA Earth Observatory, image by Lauren Dauphin, using Landsat data from the U.S. Geological Survey, story by Kasha Patel)

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Figure 33: OLI on Landsat-8 acquired this image of the Valdecañas Reservoir on 24 July 2013 (image credit: NASA Earth Observatory, image by Lauren Dauphin, using Landsat data from the U.S. Geological Survey, story by Kasha Patel)

- The drought conditions were enough to expose the Dolmen of Guadalperal, according to news reports. Dubbed the “Spanish Stonehenge,” the monument is a circle of more than 100 standing rocks dating back to 7,000 years ago. Archeologists believe it was originally constructed as an enclosed space—a large stone house with a cap. The dolmen could have served as a tomb, a site for religious rituals, or a trading hub since it was relatively easy to cross the river at this location. The most recent recorded exploration and excavation of the site was by German archaeologist Hugo Obermaier in the 1920s. By the time Obermaier’s findings were published in the 1960s though, the Valdecañas Reservoir was filled, submerging history with water.

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Figure 34: Since the 1960s, tips of the tallest megaliths have peaked out of the lake as water levels fluctuated. However, the dry, hot conditions in 2019 dropped lake levels to a point where the entire structure for the first time since the reservoir was filled. This photo shows the remains of the standing stones on the Dolmen of Guadalperal on 28 July 2019 (image credit: NASA Earth Observatory, photo used under the Creative Commons Attribution-Share Alike 4.0 International license, courtesy of Pleonr. Story by Kasha Patel)

• September 17, 2019: From a distance, the rows of windmills lined up in the desert seem to be silently performing their wind-to-energy duties. Encounter them up-close, however, and you can hear their striking ‘whoosh-whoosh’ sound. Hikers can have such a close encounter along a 6.5-mile (10 km) section of the Pacific Crest Trail (PCT) in Southern California’s Kern County. 19)

- This segment across Cameron Ridge is just a short stretch of the 2,650-mile (4,265 km) trail across the western United States from Mexico to Canada. But you still need to hike smart and be prepared. The weather can be extreme and, as the wind turbines indicate, typically very windy.

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Figure 35: On 1 July 2019, the Operational Land Imager (OLI) on Landsat-8 acquired this image of Cameron Ridge where the PCT (purple) crosses Tehachapi Pass. The pass divides the Tehachapi Mountains (south) and the Sierra Nevada (north), and forms a narrow connection between the San Joaquin Valley and the Mojave Desert (image credit: NASA Earth Observatory, image by Joshua Stevens, using Landsat data from the U.S. Geological Survey. Story by Kathryn Hansen)

- Note the abundance of wind turbines, connected by both straight and sinuous access roads. The turbine sites were not selected haphazardly; they are positioned to take advantage of the reliable winds, which come off the Pacific Ocean and ultimately get funneled at high speed through a mountain pass toward the southeast. According to a report for the California Energy Commission, the wind speeds through the pass are among the highest in the country, with an annual average of 20 miles (32 km) per hour.

- In 2018, news reports noted that Kern County had the largest concentration of wind capacity in the country, with the potential to generate more than 4,000 MW. The numbers come from a U.S. wind turbine database released by the U.S. Geological Survey and partners. (The database has a web-based tool to let users read up on more than 57,000 wind turbines across the country.)

- The Cameron Ridge area also makes sense for building turbines because Tehachapi Pass is relatively close to energy-hungry cities such as Los Angeles (about 75 miles/120 km away). The proximity also means the hiking trail is a manageable drive and a popular destination for day hikers.

• September 16, 2019: A bed of sea sawdust. A bundle of chopped hay. A pile of sea scum. - The cyanobacteria Trichodesmium spp. has been given many different descriptions, dating back to its first recorded observation in the 1700s by Captain James Cook. In addition to its distinct appearance, these wispy, microscopic filaments also play an important part in sustaining marine life. 20)

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Figure 36: An important player in the nitrogen cycle, Trichodesmium makes a seasonal appearance off the northeast coast of Australia. On 1 September 2019, OLI on Landsat-8 captured an image of what appears to be a bloom of Trichodesmium near the Great Barrier Reef off of northeast Australia. Trichodesmium blooms appear yellowish-brown when the bloom is healthy, green when it starts to decay, and white after the pigments decay (image credit: NASA Earth Observatory, image by Joshua Stevens, using Landsat data from the U.S. Geological Survey. Story by Kasha Patel)

- All aquatic organisms depend on nutrients for growth; one of the most important is nitrogen. Trichodesmium plays an important role in the ocean because it supplies large quantities of this necessary element. Trichodesmium belong to a class of bacteria called diazotrophs, which take nitrogen from the atmosphere and convert it to ammonia—a more usable form of nitrogen for photosynthesizing microbes. Research shows Trichodesmium accounts for about 60 to 80 percent of nitrogen fixation in the ocean.

- Trichodesmium most commonly bloom—grow rapidly in dense patches—in nutrient-poor tropical and subtropical waters in warmer conditions. They are often seen off the coast of Queensland between August and December when the water warms.

• September 11, 2019: Though ice losses from Antarctica and Greenland make up a greater volume and seem more dramatic, the losses from glaciers on Arctic islands and middle-latitude mountain ranges have been quite significant. A NASA-led research team has recently developed a tool to help researchers investigate more than 30 years of ice velocity data from glaciers, a key variable for detecting how Earth’s ice (the cryosphere) is changing. 21)

- Understanding how mountain glaciers change, and how their flow will change in the future, is complicated by the fact that no two glaciers are exactly alike. Malaspina Glacier in southeastern Alaska, for example, may not be moving fast but the motion within the glacier is complex.

Figure 37: This animation was composed from a sequence of false-color images acquired between 1986 and 2003 by the Landsat-5 and -7 satellites. The moving ice appears in shades of blue. Brown lines are moraines—areas where soil, rock, and other debris have been scraped up by the glacier and deposited at its sides. This debris often gets trapped as internal ribbons of rock where two glaciers merge and become one at a confluence (image credit: NASA Earth Observatory, image by Joshua Stevens, using Landsat data from the NASA MEaSUREs program at JPL. Story by Kathryn Hansen)

- Glaciers in this area of Alaska periodically surge, meaning they lurch forward quickly for one to several years. Surging can happen whether a glacier is advancing or retreating. Throughout the animation Malaspina appears to be retreating, and the increased meltwater and retreating ice is causing the lake (bottom-right) to expand. The zigzag pattern of the debris is caused by changes in velocity of the ice.

- “Glaciers all have their own personalities, so a detailed study of a single glacier often doesn’t apply to a region as a whole,” said Alex Gardner, a glaciologist at NASA’s Jet Propulsion Laboratory. “To make progress on understanding sea level rise and adapting large-scale water resources, we need to know the fundamental characteristics of glacier flow that apply over entire regions.”

Figure 38: This set of images are examples of the flow velocity maps that Gardner and colleagues can derive from ITS_LIVE data sets. Comparing velocities in 1997 with those of 2017, you can see that velocity changes along Malaspina are more subtle than for the trio of glaciers to the west, which appear to be surging (image credit: NASA Earth Observatory, image by Joshua Stevens, using Landsat data from ITS_LIVE and the NASA MEaSUREs program at JPL. Story by Kathryn Hansen)

- Gardner and colleagues from the University of Alaska and the University of Colorado have been working on an initiative known as the Inter-mission Time Series of Land Ice Velocity and Elevation, or ITS_LIVE. The core of the project is the comparison of images acquired with Landsat satellites over the past four decades. The researchers developed a highly efficient “feature tracking algorithm” in which high-performance computers track where the information contained within pixels has moved in the time spanned by two images. This is done millions of times between image pairs, resulting in a data set with many millions of estimated ice velocities.

- Data from ITS_LIVE have already revealed that high-mountain glaciers in Asia are flowing more slowly as they thin and melt. As ice thins, there is less gravitational pull tugging it down the mountainsides. “That might sound intuitive, but it is not necessarily so from glaciological point of view,” Gardner said. “Retreating glaciers have more meltwater reaching their beds; this water can act as a lubricant and cause it to speed up. But our data show that is not case in high mountain Asia.”

- Gardner suspects the same will hold true for Alaskan glaciers, but more analysis needs to be done. Can scientists establish a relationship between slowing and thinning ice that holds true for mountain glaciers globally?

- ITS_LIVE data were made publicly available through JPL and the National Snow and Ice Data Center web sites in the summer of 2019. “There is so much data, and we can’t explore it all on our own,” Gardner said. “Our hope is that by making the data easily accessible, researchers can access the tools they need to better understand glacier flow around the world.”

• September 3, 2019: Long recognized as one of the world’s most rapidly retreating glaciers, the Columbia Glacier in southern Alaska has been slowing down in recent years. “The total loss of ice is down substantially,” said Shad O’Neel. “But there is still impressive retreat.” 22)

- O’Neel, a glaciologist at the USGS Alaska Science Center, has kept a watchful eye on Columbia Glacier for years. Since the 1980s, the glacier has lost more than half of its total thickness and volume. Its front has retreated more than 20 km north in Columbia Bay, separating around 2011 into the West Branch (Post Glacier) and the Main Branch. (You can view the retreat from 1986 to present in our World of Change feature.)

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Figure 39: OLI on Landsat-8 acquired this image of Alaska's Columbia Glacier on 21 June 2019. One branch of the Glacier seems to have retreated as far as it can, while the other still has some distance to go (image credit: NASA Earth Observatory, image by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Kathryn Hansen)

- By the time these images were acquired, the West Branch had retreated so far that it had divided into several independent glaciers. O’Neel thinks the branch could be at the limit of its retreat. “I haven’t confirmed that yet from a site visit,” O’Neel said, “but it is unlikely that much, if any, of the glacier bed is below sea level anymore.”

- Meanwhile, the Main Branch has thinned and resumed its retreat, shedding icebergs from its front and retreating again in summer 2019. Ample ice has been lost by volume—from the glacier’s front and surface—but it still has plenty of room to retreat.

- Scientists think the Main Branch could eventually pull back to Divider Mountain. (The mountain’s edge is just visible in the center of the Main Branch along the top-right edge of the satellite images.) The Main Branch could retreat even further if the shape of the fjord and land surface below the glacier allow it.

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Figure 40: This false-color image of the same scene helps to differentiate between snow and ice (bright cyan) and other components of the landscape such as open water (dark blue). Vegetation is green and exposed bedrock is brown, while rocky debris on the glacier’s surface is gray (image credit: NASA Earth Observatory, image by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Kathryn Hansen)

- Analyzing Columbia Glacier’s retreat from beginning to end could help scientists understand what’s in store for the many other tidewater glaciers across southern Alaska. Changes happening along the way can be informative too.

- “Although we don’t usually think of single years as being important to glaciers, the 2019 summer has been so anomalous that it may be driving substantial change at many of Alaska’s glaciers,” O’Neel said.

• August 28, 2019: Today’s Image of the Day is an excerpt from our feature story: Trailing the Pacific Crest from Space. There is no award for completing the walk from Mexico to Canada through California, Oregon, and Washington. But read about the journeys of so-called “thru-hikers” of the Pacific Crest Trail (PCT), and it is clear that the 2,650 mile (4,265 km) hike changes you. Even walking a small segment of trail can connect you with the land, whether you access it in desert, forest, or alpine areas. 23)

- The PCT is not the longest or oldest National Scenic Trail in the United States, but it helped set the standard for trails that followed. The remarkable length of the Pacific Crest Trail, passing through 48 wilderness areas and some extremely demanding terrain, is especially apparent from space. NASA Earth Observatory identified locations along the trail where satellites and astronaut photography offer a unique perspective on this great hike.

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Figure 41: This image, acquired on June 11, 2019, with the Operational Land Imager (OLI) on Landsat-8, shows the PCT route (purple) across the bridge and beyond. The image is draped over topographic data from NASA’s Shuttle Radar Topography Mission (SRTM), image credit: NASA Earth Observatory, image by Joshua Stevens and Robert Simmon, using Landsat data from the U.S. Geological Survey and topographic data from the Shuttle Radar Topography Mission (SRTM). Story by Kathryn Hansen

- The PCT wraps around some of the most majestic peaks in the U.S. West, including some notable volcanoes. Glacier Peak and Mount Adams show up along the route in Washington. And then there’s Mount Rainier.

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Figure 42: By the time thru-hikers reach northern Oregon, they have passed plenty of volcanoes, but they’re not out of the Cascade Arc yet. This is where the trail crosses the flanks of Mt. Hood—the state’s tallest peak. This stratovolcano is shown from the vantage point of an astronaut on the International Space Station (image credit: NASA Earth Observatory, image by Joshua Stevens and Robert Simmon, using the astronaut photograph ISS036-E-23847,provided by the ISS Crew Earth Observations Facility and the Earth Science and Remote Sensing Unit, Johnson Space Center. Story by Kathryn Hansen)

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Figure 43: Towering above the horizon at 14,179 feet (4,322 m), Mount Shasta is sure to catch the eye of hikers. This majestic volcano in Northern California is at least partly visible from the trail for at least 500 miles. The image shows the space-based view of the mountain on November 1, 2013, acquired with the OLI on Landsat-8 and draped over topographic data (image credit: NASA Earth Observatory, image by Joshua Stevens and Robert Simmon, using Landsat data from the U.S. Geological Survey and topographic data from the Shuttle Radar Topography Mission (SRTM). Story by Kathryn Hansen)

- The volcano plays an important role in catching water for the region. Seasonal snowpack replenishes the local water supply that feeds rivers, streams, and nearby Shasta Lake—California’s largest reservoir.

- You can see other prominent PCT landmarks, such as Crater Lake, the Three Sisters volcanoes, and even a windfarm, in our full feature story.

• August 23, 2019: Volcanoes have a lot of dramatic ways to announce their presence: thick plumes of ash and steam; rivers and lakes of molten lava; rockfalls and lahars; earthquakes; even the sudden rising of an island above the water line. One of the more subtle and rarely observed displays is the pumice raft. 24)

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Figure 44: On August 13, 2019, the Operational Land Imager on Landsat 8 acquired natural-color imagery of a vast pumice raft floating in the tropical Pacific Ocean near Late Island in the Kingdom of Tonga (image credit: NASA Earth Observatory, image by Joshua Stevens, using Landsat data from the U.S. Geological Survey. Story by Michael Carlowicz)

- Volcanoes have a lot of dramatic ways to announce their presence: thick plumes of ash and steam; rivers and lakes of molten lava; rockfalls and lahars; earthquakes; even the sudden rising of an island above the water line. One of the more subtle and rarely observed displays is the pumice raft.

- Many of the world’s volcanoes are shrouded by the waters of the oceans. When they erupt, they can discolor the ocean surface with gases and debris. They also can spew masses of lava that are lighter than water. Such pumice rocks are full of holes and cavities, and they easily float.

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Figure 45: NASA’s Terra satellite detected the mass of floating rock on 9 August; the discolored water around the pumice suggests that the submarine volcano lies somewhere below. By August 13, the raft had drifted southwest. As of August 22, the raft had moved north again and was a bit more dispersed, but still visible (image credit: NASA Earth Observatory, image by Joshua Stevens, using Terra data. Story by Michael Carlowicz)

- The Volcano Discovery web site reported that it received an email from a sailor on August 7, 2019, about clouds of smoke on the horizon in the direction of Fonualei volcano. According to a bulletin from the Smithsonian’s Global Volcanism Program (GVP), sailors began reporting sightings of the pumice raft by August 9. The crew of the catamaran Roam encountered the pumice and provided a detailed report on Facebook on August 15. The sailors described a “rubble slick made up of rocks from marble to basketball size such that water was not visible,” as well as a smell of sulfur.

- Volcanologists at the Smithsonian believe the evidence points to an unnamed submarine volcano near Tonga at 18.325° South, 174.365° West. The last report of an eruption at the site occurred in 2001, and the summit of the seamount is believed to stand about 40 m below the water line.

- Volcanologist Erik Klemetti of Denison University wrote: “Pumice rafts can drift for weeks to years, slowly dispersing into the ocean currents. These chunks of pumice end up making excellent, drifting homes for sea organisms, helping them spread... The erupted pumice means this volcano erupts magma high in silica like rhyolite.”

• On August 18, 2019, scientists will be among those who gather for a memorial atop Ok volcano in west-central Iceland. The deceased being remembered is Okjökull—a once-iconic glacier that has melted away throughout the 20th century and was declared dead in 2014. Landsat satellite images show the latter stages of its decline. 25)

- A geological map from 1901 estimated Okjökull spanned an area of about 38 km2. In 1978, aerial photography showed the glacier was 3 km2. Today, less than 1 km2 remains. The satellite images show the glacier during the latter part of its decline, on September 7, 1986 (Figure 46), and August 1, 2019 (Figure 47). The images were acquired with the Thematic Mapper (TM) on Landsat-5, and the Operational Land Imager (OLI) on Landsat-8, respectively.

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Figure 46: TM image on Landsat-5 acquired on 7 September 1986 (image credit: NASA Earth Observatory, image by Joshua Stevens, using Landsat data from the U.S. Geological Survey. Story by Kathryn Hansen)

- The dome-shaped glacier appears in the 1986 image as a solid-white patch, just north of the snow-filled crater. Snow is also visible around the glacier’s edges. In the August 2019 image, only a spattering of thin ice patches remain. Notice the areas of blue meltwater, which are likely associated with the mass of warm air that hit Iceland as it moved from mainland Europe to Greenland in late July.

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Figure 47: OLI image on Landsat-8 acquired on 1 August 2019 (image credit: NASA Earth Observatory, image by Joshua Stevens, using Landsat data from the U.S. Geological Survey. Story by Kathryn Hansen)

- The glacier’s demise is not just a matter of shrinking area. Glaciers form from snow that becomes compacted into ice over time. The ice then creeps downslope under its own weight, helped along by gravity. Okjökull has thinned so much, however, that it no longer has enough mass to flow. According to some definitions, a stagnant glacier is a dead glacier.

- Okjökull, also called Ok (jökull is Icelandic for “glacier”), was part of the Langjökull group—one of Iceland’s eight regional groupings of glaciers. Ice covers about 10 percent of the island, making it an integral part of the landscape. Loss of glacial ice has wide-ranging effects, with the potential to impact water resources, infrastructure, and even the rising of the land as it rebounds under a lighter load of ice.

- Scientists have noted that glaciers have disappeared from Iceland before, although perhaps none as ceremoniously as Okjökull. Anthropologists from Rice University produced a film about the glacier’s demise, and a plaque is set to be installed on the site of the former glacier.

• August 6, 2019: In Iceland, a country rich with compelling geologic phenomena, volcanoes and ice caps abound. Even the country’s rivers are connected to the landscape of fire and ice. 26)

- Iceland’s largest rivers by volume, the Þjórsá and Ölfusá, once flowed toward the coast as one river, joining about 25 kilometers from the modern-day coastline. Then about 8,700 years ago they separated when an eruption deposited the Great Þjórsá lava—the country’s largest lava flow. The rivers today run their separate courses, flowing southwest along the east and west sides of the lava flow.

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Figure 48: The rivers are visible in these images of southwest Iceland, acquired on June 6, 2019, by the Operational Land Imager (OLI) on Landsat-8. The images show the rivers in the summer season when they are ice-free (in winter they are prone to flooding from ice jams). This wide view image shows the river’s locations relative to Reykjavik, Iceland’s capital city (image credit: NASA Earth Observatory, image by Joshua Stevens, using Landsat data from the U.S. Geological Survey. Story by Kathryn Hansen with image interpretation by Emmanuel Pagneux, University of Iceland)

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Figure 49: Detail image of Selfoss: The Ölfusá River is not Iceland’s longest river, measuring only 25 km from its headwaters to the ocean. Yet it moves an average of 423 m3/s of water — more than any other river in the country (image credit: NASA Earth Observatory, image by Joshua Stevens, using Landsat data from the U.S. Geological Survey. Story by Kathryn Hansen with image interpretation by Emmanuel Pagneux, University of Iceland)

- As the river flows by the town of Selfoss, you can see threads of light blue water amid darker areas. Spring water and glacial water feed this part of the river and, given their differences in temperature and density, do not mix well. Dark areas indicate fairly translucent spring water (known as “black rivers” in Iceland). Light blue areas are glacial water, which take on an opaque appearance due to sediments (“glacial flour”) suspended in the water.

- The striking red patch on the river’s eastern shore is dissolved ferrous iron, also known as bog iron. According to Emmanuel Pagneux of the University of Iceland, the bog iron reaches the Ölfusá River via ditches that were once built to drain wetlands and convert them into pastures.

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Figure 50: The Þjórsá River is both Iceland’s longest (230 km) and its second-largest by volume, moving an average of 370 m3/s of water. In this view, we see the river where it meets the Atlantic Ocean at the island’s south side. Before entering the ocean the river becomes braided, as channels of water flow around small, temporary islands of coarse sediment. The dark areas near the river’s mouth are wet volcanic sand. Where the water enters the ocean, the stark contrast in color is again due to two water types that do not mix well: in this case, glacial water and seawater of differing temperatures and densities (image credit: NASA Earth Observatory, image by Joshua Stevens, using Landsat data from the U.S. Geological Survey. Story by Kathryn Hansen with image interpretation by Emmanuel Pagneux, University of Iceland)

• August 6, 2019: If you look at the three largest cities in California by area—Los Angeles, San Diego, and California City—one stands out. Los Angeles has 3.7 million people; San Diego has 1.3 million. California City has a population of just 14,000 people. 27)

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Figure 51: The big dreams of a 1960s real estate developer have not materialized, but that has not stopped California City from pushing forward. Why does such an expansive city have so few people? Satellite images acquired on 18 October 2018 by OLI on Landsat-8 help explain (image credit: NASA Earth Observatory, image by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Adam Voiland)

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Figure 52: Though a large network of perfectly gridded blocks and curving residential streets remain etched into the Mojave Desert, houses are scarce (image credit: NASA Earth Observatory, image by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Adam Voiland)

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Figure 53: Even near the lake and golf courses at the center of town, empty lots abound (image credit: NASA Earth Observatory, image by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Adam Voiland)

- California City was incorporated in 1965 after real estate developer Nat Mendelsohn purchased thousands of acres of open land and started paving roads and laying water pipes for what he envisioned would be a city to rival Los Angeles. But interest from buyers never matched his grand vision, and by 1980, the town had only 2,700 residents.

- Still, an assortment of unusual ventures has kept the city going. Many people who live in California City today work at nearby Edwards Air Force Base, a borax mine, a prison, a vehicle testing facility, or one of the nation’s few spaceports.

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Figure 54: The borax mine is California’s largest open-pit mine, producing about half of the world’s refined borates. Borates are used in fertilizers, in metallurgy, and as components of specialized types of glass, anticorrosive coatings, fire retardants, and detergents (image credit: NASA Earth Observatory, image by Lauren Dauphin, using Landsat data, observed on 18 October 2018, from the U.S. Geological Survey. Story by Adam Voiland)

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Figure 55: Surrounded by solar panels, engineers test automobiles, motorcycles, and ATVs at speeds up to 320 km/hour on the winding roads of the Honda Proving Center (below). The prison (Figure 51), which used to hold people detained by U.S. immigration officials, now houses 2,300 inmates from California (image credit: NASA Earth Observatory, image by Lauren Dauphin, using Landsat data, observed on 18 October 2018, from the U.S. Geological Survey. Story by Adam Voiland)

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Figure 56: The Mojave Air and Space Port lies 25 km (15 miles) to the southwest. In 2004, federal authorities certified the facility as the first spaceport in the United States. Soon after, a private company launched a person into space on the rocket-powered aircraft SpaceShipOne. While experimental aircraft are a common sight, so are planes that are decades old. The air field also hosts a large storage area and boneyard for old planes (image credit: NASA Earth Observatory, image by Lauren Dauphin, using Landsat data, observed on 18 October 2018, from the U.S. Geological Survey. Story by Adam Voiland)

• July 31, 2019: o say the Dead Sea is merely a salt lake is like calling the Great Wall of China a pile of bricks—it does not quite capture how unique it is. 28)

- The Dead Sea is the second-saltiest lake in the world. Its surface and shores stand at the lowest elevation (around 435 meters or 1,430 feet) of any land mass not under water or ice. With a salt concentration above 30 percent, the lake water is nearly ten times saltier than the oceans. Feeling like olive oil mixed with sand, the water is so dense that humans float without effort. The salinity makes it difficult for any plant or animal to survive—hence its name.

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Figure 57: As water levels drop in the Dead Sea, salt is piling up on the lakebed. This image shows the Dead Sea and the Jordan Rift Valley on July 21 2019, as observed by the Operational Land Imager on the Landsat 8 satellite. The green rectangles on the south end of the lake are salt evaporation ponds, which are used to extract sodium chloride and potassium salts for the manufacturing of polyvinyl chloride (PVC) and other chemicals (image credit: NASA Earth Observatory images by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Kasha Patel)

- For the past two to three decades, water levels on the Dead Sea have been dropping at about 1.2 meters per year—an increase from 0.7 meters per year in the 1970s and 1980s. Levels have primarily dropped as water has been diverted from its only tributary, the Jordan River, to serve surrounding communities with water. Lake water also has been pumped to the evaporation ponds.

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Figure 58: As the water level drops, the lake becomes saltier, particularly near the surface. Scientists from the Dead Sea Observatory have discovered that salt has been precipitating out of the water and coating the bottom of the lake. They found the amount of salt on the lakebed (photograph) depended on the season and the various salt densities throughout the lake. The salt layer has been growing about 10 cm thicker every year for the past four decades, showing seasonal alternations of the layers’ properties (image credit: Photograph provided by the Dead Sea Observatory, Geological Survey of Israel. Story by Kasha Patel)

- During the summertime, the lake forms a warm, less dense top layer and a colder, denser bottom layer. When the top of the lake is disturbed by a wave or motion, tiny parcels of warm water—called “salt fingers”—travel down to the colder water. As the warm salt fingers cool on the journey down, the water mass can hold less salt. The salt precipitates out and forms crystals on the lakebed through this process known as double-diffusive convection.

- “In the ocean, the salt fingers might exist, but you’re not going to see them with the naked eye,” said Raphael Ouillon, a fluid dynamics expert at the University of California, Santa Barbara. “What is specific to the Dead Sea is that it’s almost at full saturation of how much salt can be dissolved, so salt precipitates out easily.”

- The Dead Sea is the only salt lake where this “salt fingering” process is known to occur. Scientists think it may be a clue to how salt deposits formed millions of years ago on other ancient sea beds, and specifically, how salt layers are thicker in the central parts of the basins and thin or absent from the shallow parts of these basins. For instance, more than five million years ago, the Mediterranean Sea’s dried out and left thick deposits of salt. Although the sea has since refilled, this salt buildup could have formed through a similar mechanism as currently observed in the Dead Sea.

• July 30, 2019: Plunging deep into the ground, the gaping hole of an open-pit mine is unmistakable from space. People have excavated such pits on every continent except Antarctica. 29)

- Copper mining began at Palabora in 1965, and by 1967 the open-pit mine was fully operational. The hole reached 800 meters down into the Earth before the depletion of resources made it uneconomical to continue mining in the pit. Operations moved underground (below the pit) and mostly out of sight in the early 2000s. The new mining method, known as block caving, involves extracting rock below an ore body, letting the ore break under its own weight, and then hauling the ore back to the surface.

- Three years after the start of underground mining at Palabora, cracks grew in the wall of the pit until the northwest wall collapsed. The image of Figure 60 shows a detailed view of that landslide, which is still visible in 2019. The collapse damaged some infrastructure—roads, power and water lines, and a railway line—but critical mine infrastructure stayed intact and underground mining continues there today.

- The site has become a case study in the challenges in transitioning from surface to underground mining. For example, researchers started using satellite data to improve the models that predict how mining underground will deform the surface.

- People were mining South Africa’s copper and iron resources long before the advent of open pit mines. Some archaeological estimates date mining artifacts back to at least 800 CE. In neighboring Kruger National Park, more than 250 archaeological sites show signs of human occupation back about 1 million years ago.

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Figure 59: The pit near Phalaborwa and Kruger National Park is the most visible sign of a long history of mining in the region. The mine pictured here has been growing vertically and horizontally near Phalaborwa, South Africa, for more than 50 years. The Operational Land Imager (OLI) on Landsat 8 acquired this image of the Palabora mine on July 2, 2019. It is South Africa’s largest open-pit mine, measuring almost 2 km wide. It is about half the width of the world’s largest open-pit mine, which is at Bingham Canyon in Utah (image credit: NASA Earth Observatory image by Joshua Stevens and Allison Nussbaum, using Landsat data from the U.S. Geological Survey and topographic data from the Shuttle Radar Topography Mission (SRTM). Story by Kathryn Hansen)

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Figure 60: A more detailed image of the Palabora mine showing the landslide (image credit: NASA Earth Observatory image by Joshua Stevens and Allison Nussbaum, using Landsat data from the U.S. Geological Survey and topographic data from the Shuttle Radar Topography Mission (SRTM). Story by Kathryn Hansen)

• July 24, 2019: With a series of scalloped bays, terraced sea cliffs, bizarre natural rock sculptures, and clusters of mud volcanoes, the barren landscape of Pakistan’s Makran Coast seems like a geologist’s dreamscape. 30)

- The coastline sits immediately north of an active tectonic plate boundary, a subduction zone where the oceanic crust of the Arabian Plate gets squeezed underneath the continental crust of the Eurasian Plate. In the process, sedimentary rock from the top of the Arabian Plate get scraped off and pile up on the edge of the Eurasian Plate in a convoluted jumble known as an accretionary wedge.

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Figure 61: Striking geology, new ports, and a few hammerhead sharks can be found along Pakistan’s Arabian Sea coast. OLI on Landsat-8 acquired this image of the Ormara peninsula on 15 February 2019. The Landsat data is draped over topographic data from NASA’s SRTM (Shuttle Radar Topography Mission), image credit: NASA Earth Observatory image by Joshua Stevens, using Landsat data from the U.S. Geological Survey and topographic data from SRTM, story by Adam Voiland

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Figure 62: Nadir OLI image of the Ormara peninsula acquired on 15 February 2019 (image credit: NASA Earth Observatory image by Joshua Stevens, using Landsat data from the U.S. Geological Survey, story by Adam Voiland)

- One of the more eye-catching features of the Makran Coast are two hammerhead-shaped peninsulas near the cities of Gwadar and Ormara. Both of the peninsulas are small fault blocks, or horsts— blocks of crust that have been lifted or have remained stationary while land on either side sank. The features, which tilt seaward, are associated with faults that run parallel to the coast.

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Figure 63: Nadir OLI image of the Gwadar peninsula acquired on 27 April 2019 (image credit: NASA Earth Observatory image by Joshua Stevens, using Landsat data from the U.S. Geological Survey, story by Adam Voiland)

- Ormara, which is higher than Gwadar, has elevations of 183 to 305 meters on the seaward side and 427 meters on the inner side. The Gwadar and Ormara horsts both used to be islands. However, the action of waves and drifting sand over time created long sandy spits (tombolos) that connect the islands to the mainland.

- The Makran Coast has an active fishing industry. Some estimates suggest between 8,000 and 10,000 small fishing boats operate in the area, with larger bottom trawlers operating in the region as well.

- The regional emphasis on fishing has had consequences for some of the fish that live in the Arabian Sea. The Arabian Sea has some of the most threatened populations of sharks, rays, and chimaeras in the world, according to a recent study. Hammerhead sharks were among the most vulnerable species in the region, according to the researchers.

- Large port facilities have been built on both of these peninsulas in the past few decades. In Ormara, the Pakistan military began building a naval base in 1994. In Gwadar, construction of a deepwater port on the Demi Zirr harbor began in 2002.

Minimize Landsat-8 highlights from 2019 continued

Landsat-8 Imagery in the period 2019

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References

• December 29, 2019: Since a pilot first noticed Marree Man in 1998, the mysterious work of earthen art has attracted international attention. Etched into a plateau in South Australia, the artwork depicts a hunter with what appears to be a stick or boomerang in his hand. 1)

- Spanning 3.5 kilometers (2.2 miles) from top to bottom, Marree Man is a geoglyph—a design made from earthen materials that is so large it is best viewed from above. An example of an even larger geoglyph is the Nazca Lines in Peru.

- For many years, Marree Man, named after a nearby town, was a prominent feature in Landsat satellite images of the area, but the lines faded over the years. By 2013, they were hardly visible in the natural-color images acquired by OLI on Landsat-8.

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Figure 1: It is unclear who created the giant geoglyph or why, but the large earthen figure has drawn attention to a remote part of South Australia for two decades. OLI on Landsat-8 acquired this image of the feature on June 22, 2019 (image credit: NASA Earth Observatory, image by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Adam Voiland)

- In August 2016, local business owners, concerned about the loss of what had become a tourist draw, decided to restore the fading geoglyph. With accurate GPS coordinates for the original in hand, they used a construction grader to redraw Marree Man over a period of five days.

- The restoration team thinks the updated geoglyph will last longer than the original because they created wind grooves, designed to trap water and encourage the growth of vegetation. Over time, they hope vegetation will turn the lines green.

- Who created the geoglyph and why has long been a topic of controversy and remains unknown, despite the recent announcement of a cash reward for credible information about it. There are indications that an artist living in Alice Springs may have created Marree Man, though other clues suggest that the creator may have been an American.

• December 25, 2019: Off the northwestern coast of Africa, small clusters of land dot the Atlantic Ocean. The archipelagos include the Canary Islands, a Spanish-colonized island chain located just over 100 km west of Morocco. Of the chain’s main islands and numerous islets, Lanzarote is one of the closest to the African mainland. It is also one of the driest and most barren, with rugged terrain that has compelled space agencies to train there. 2)

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Figure 2: The dry, volcanic terrain of this Canary Island is suitable for lichen and crops ... and for training astronauts. OLI on Landsat-8 acquired this image of the island on October 2, 2019. It shows a landscape that is the result of an active volcanic history (image credit: NASA Earth Observatory, image by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Kathryn Hansen)

- One notable eruption event started in 1730 and spanned six years, during which lava erupted from a 14-kilometer (8 mile) long fissure. Lava ultimately spread across 225 square kilometers, or one-third of the island. Another, shorter eruption in 1824 lasted 86 days, but still altered the landscape with new lava flows.

- At times, the eruptions on the island have turned explosive when magma came into contact with cold groundwater. These explosive “phreatomagmatic” eruptions can produce small volcanic cones. One of these more prominent “tuff cones,” Caldera Blanca, measures 1140 meters across and 450 meters high. Its name is derived from its white color, a consequence of a colony of lichens that have taken up residence on its slopes.

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Figure 3: Overview of the Canary Island of Lanzarote, acquired with OLI on Landsat-8 on 2 October 2019 (image credit: NASA Earth Observatory, image by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Kathryn Hansen)

- Caldera Blanca and other volcanic structures are the centerpieces of Los Volcanes Natural Park. With a surface similar to that of the Moon and Mars, the park has been used to train astronauts and to test Mars rovers. It’s an outdoor classroom where astronauts and engineers can learn the techniques of field geology and geo-microbiology.

- The island’s unique landscape has also been shaped by its desert-like climate with sparse rainfall. Because Lanzarote is flatter than the central and western islands in the archipelago, the cool, moist trade winds blowing pass right over it. In contrast, high mountain systems elsewhere in the Canary Islands trap moisture, producing rainfall on their northern coasts and a rain shadow on the leeward side.

- Despite the dry climate and rocky landscape, some areas can support vegetation—mostly with human help. Since the eruption in the 1700s destroyed most of the fertile farmland, people have adapted by digging shallow basins and bordering them with half-circles of stacked lava rock. The figs, grapes, almonds, and other crops planted in the center of these basins receive some protection from the wind and harsh sunlight, and they stay hydrated with the help of mulch—in this case, a moisture-absorbing ash.

• December 24, 2019: “Roads” may bring cars, trucks, and pavement to mind, but the word has a nautical meaning as well. For sailors, roadsteads are sheltered stretches of water near the shore where it is possible to safely drop anchor. This meaning is what originally gave Hampton Roads—the body of water where the James, Nansemond, and Elizabeth Rivers pour into the mouth of the Chesapeake Bay—its name. 3)

- Since early United States history, companies and government entities in Norfolk and Portsmouth have been on the forefront of shipping, trade, and defense. Today, Hampton Roads is the largest coal-exporting port in North America, with much of the coal arriving from Appalachia via rail and passing through the Norfolk Southern’s coal terminal at Lamberts Point.

- Immediately north of Lamberts Point lie the Norfolk International Terminals, the largest container port in the area. The piers are a nexus where ships, trains, trucks, and cranes come together to transfer vast quantities of cargo. Norfolk is typically among the busiest ports in the United States, trailing only New York and Savannah on the East Coast.

- Hampton Roads is also home to the world’s largest naval station. More than 70 ships are based at Norfolk Naval Station, including aircraft carriers, submarines, destroyers, and cruisers. In the wide view of Figure 5, several piers of the naval station are visible at the top of the image.

- For decades, coastal engineers have dredged the channels leading into port to make them deeper and wider. Prior to World War II, much of the dredged material was delivered to open water sites, but in 1946 the U.S. Congress designated Craney Island as a disposal site. In December 2019, dredging began on a new project that aims to make the port the deepest on the East Coast.

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Figure 4: The deep channels through Hampton Roads have made the surrounding cities important hubs of shipping, trade, and defense.

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Figure 5: On November 25, 2019, the Operational Land Imager (OLI) on Landsat-8 captured these images (Figures 4 and 5) showing outflow from the Elizabeth River joining the others in Hampton Roads. The deep, natural channels in this area have defined the character of the region by making it possible for ships to access Norfolk and Portsmouth, Virginia (image credit: NASA Earth Observatory, images by Joshua Stevens, using Landsat data from the U.S. Geological Survey. Story by Adam Voiland)

• December 11, 2019: The Chinese metropolitan area of Shanghai has ranked high on lists of economic and population growth in recent decades. So it is hardly surprising that the city of 24 million people stands out in another way: the amount of new land that people have created, or “reclaimed.” 4)

- Two recently published studies list Shanghai as the world’s leading city for land reclamation, a land-creation process that typically involves dredging and draining shallow coastal areas using ships, pumps, and mud. The studies are based analyses of Landsat satellite imagery.

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Figure 6: While reclaimed land is typically used for ports, industry, and housing, Shanghai stands out for devoting some of its new land to parks, forests, and wetlands. That tendency is visible in this pair of images from 2016 and 2019, acquired by the Operational Land Imager (OLI) on Landsat-8. Nanhui is a newly-built city in Pudong on Hangzhou Bay, about 60 km from downtown Shanghai (image credit: NASA Earth Observatory, images by Joshua Stevens, using Landsat data from the U.S. Geological Survey. Story by Adam Voiland)

- One of the most striking features is Dishui Lake, a circular freshwater lake that engineers constructed between 2003 and 2005 from sediment deposited by the Yangtze River. Within a few years, landscapers planted various shrubs, trees, and other vegetation in the surrounding Green Ring Park—plantings that were designed to improve the fertility of the soil and establish woodlands.

- Since 2016, the vegetation in these parklands has grown thicker. Meanwhile, new patches of green—coastal marshes—have emerged just to the north of the lake on newly reclaimed coastal land. With a combination of marshland, rice paddy, and aquaculture ponds, these areas have become a haven for migratory birds that travel from Australia to Siberia—as well as birdwatchers who follow them.

- With the new land come questions about how to best use it. Some birdwatchers and environmental groups want to keep the new land as marshland, and they have aired concerns about government plans to plant trees, which would make it less hospitable to some types of birds. However, government planners say they need to continue planting trees to meet city-wide standards for forest cover, and they have designated parts of nearby Chongming Island for bird breeding grounds, according to reporting from Caixin.

• December 7, 2019: Fjords and funnel-shaped bays and inlets are often scenes of dramatic tidal changes; the Bay of Fundy is perhaps the world’s most spectacular example. This sloshing of water into and out of basins can produce visible surges of sediment and floating debris, turbulent mixing of fresh and salty waters, and sometimes distinct lines between different water masses. 5)

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Figure 7: That was the case on 2 October 2019 when the Operational Land Imager on the Landsat 8 satellite captured the data for this image of Solway Firth. On that day, the waters along the coast of Dumfries and Galloway, Scotland, and Cumbria, England, were rich with sediment and dissolved organic matter (plant debris, soils, plankton) that was likely stirred up by the tides. The water changes color abruptly offshore where the shallower bay meets deeper waters of the Irish Sea (image credit: NASA Earth Observatory, image by Norman Kuring/NASA's Ocean Color Web, using Landsat data from the U.S. Geological Survey. Story by Michael Carlowicz)

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Figure 8: This image is a blend of art and science. Like a photographer who adjusts lighting and uses filters, Norman Kuring of NASA’s Ocean Biology group works with various software programs and color-filtering techniques to draw out the fine details in the water. The swirls and streamers in Solway Firth are real, but Kuring has separated and enhanced certain shades and tones in the data to make the sediments and dissolved organic matter stand out. Click here for a natural-color view at lower resolution. (image credit: NASA Earth Observatory, image by Norman Kuring/NASA's Ocean Color Web, using Landsat data from the U.S. Geological Survey. Story by Michael Carlowicz)

- On a sandy shoal offshore, a pattern of symmetrical white dots and shadows marks the location of the Robin Rigg wind farm. Sediment plumes make thin lines across the water toward the east-northeast, suggesting either strong winds blowing out of the southwest or the inflow of tidal currents toward the coast. Robin Rigg was Scotland’s first offshore wind farm, coming online in 2010. It can generate up to 174 megawatts of power, enough to supply 117,000 homes.

- Solway Firth is the United Kingdom’s third-largest estuary, and it is lined by beaches, coastal dunes, and salt marshes, a few of which are special conservation areas. The lands around the firth are mostly rural and agricultural. Along with its natural beauty, the region has a touch of history, as the western end of Hadrian’s Wall terminates on its southern shore.

• November 27, 2019: Farmers across the Midwest are in a race to finish harvesting their corn, soybean, and other staples of the Thanksgiving dinner table before the first crop killing freeze sets in. September rains made a late harvest even later. Heavy spring rains flooded millions of acres of cropland around the Mississippi, Wisconsin and Missouri rivers. Some farmers never seeded; others started three weeks behind schedule. 6)

Figure 9: Since 2008, the USDA's (US Department of Agriculture) National Agricultural Statistics Service, or NASS, has drawn on Landsat data to monitor dozens of crops in the lower 48 states as part of NASS's Cropland Data Layer program (video credit: NASA, Matthew R. Radcliff)

- These changes and delays in farmers’ plans this year made the United States Department of Agriculture’s job of tracking and estimating crop production with farmer surveys and ground observations a challenge. To meet it, they turned to the joint NASA - U.S. Geological Survey’s Landsat-8 satellite to fill in the missing pieces.

- “During abnormal growing seasons or natural disasters, satellites shine,” said Rick Mueller, Head of USDA’s NASS (National Agricultural Statistics Service) Spatial Analysis Research Section and manager of the Cropland Data Layer Program in Washington. “Landsat is a robust and independent way to validate what our statistics are telling us.”

- Since 2009, NASS has drawn on Landsat data to monitor dozens of crops, including corn, wheat, soy and cotton in the lower 48 states as part of NASS’s Cropland Data Layer program.

- The Cropland Data layer uses Landsat and similar sensors to identify what is growing where. Separately, NASS uses NASA's MODIS (Moderate Resolution Imaging Spectroradiometer) instruments aboard the Aqua and Terra satellites to monitor daily vegetation health and growth stage, all indicators of crop yield.

- “Landsat has been one of the only ways we can directly measure the global food supply,” said Brad Doorn, program manager for NASA’s Applied Sciences Water Resources and Agriculture Research at NASA Headquarters in Washington.

- However, “It’s not all satellites,” Mueller said.

- During a typical farming year, NASS relies heavily on their ground observations and survey data. Across the country, NASS field officials visit farms, and measure acreage and condition of planted fields throughout the growing season. NASS also receives crop acreage data from the Farm Service Agency (FSA). Farmers are required to self-report crop acreage and land use information to FSA annually. FSA uses the data to determine payment for federal programs such as crop loss due to natural disaster or financial loss from changes in market prices.

- This year was not a typical year. Farmers usually start planting corn, soybean and other crops in May. In Missouri, with 10 percent of the state’s cropland underwater, satellite imagery helped NASS state officials see what fields and areas were most impacted by the floods. They also could see which fields had crops.

- “Satellites helped us fill in the gaps and show what is going on in every region of the state,” said Robert Garino, Missouri State Statistician with the USDA. “The surveys work well at providing estimates for the state as a whole but are not designed to capture what is happening in specific regions within the state.”

- In June, several farmers could not report the amount of acres seeded to Garino’s office. They, were waiting for their fields to dry. In July, the USDA used satellites data to help them revise June production estimates.

- The following month, news stories reported that farmers had doubts about USDA August yield reports. “There was a lot of concern over their accuracy,” said Garino. “The general feeling was that the rain and flooding would cause both a reduction of harvested acreage and a fairly sharp reduction in yield. While harvested acres, especially for soybeans, were significantly reduced, August yield estimates have held up well.”

- NASS will publish the final Cropland Data layer in January 2020 and makes the data available to everyone through the CropScape website. Disaster managers use the site’s historic data to evaluate crop damage from this year’s floods and other natural disasters. Resource managers use historic data to direct crop rotation, study land-use change, and monitor water use.

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Figure 10: Three moments in a tumultuous year for farming north of St. Louis, MO, as seen in NASA-USGS Landsat-8 data. On the left is May 7, 2019, as heavy rains delayed planting for many farms. Sept 12, 2019, in the middle, shows bright green signifying growing vegetation, although with a fair amount of brown, bare fields. On the right, Oct. 14, 2019, the light brown indicates harvested fields while darker brown are fields that have not been seeded or fallow all summer (image credits: NASA)

- New satellites and new data partnerships are helping NASS improve their real-time crop monitoring capability. Currently, computer models use the Cropland Data Layer to calculate monthly yield estimates for corn and soybeans.

- In addition to Landsat-8, launched in 2013, partnerships between the USGS and the European Copernicus constellation provides even more Landsat-like imagery for free.

- “The more satellites, the better we feel,” said Rick Mueller, head of NASS’ Spatial Analysis Research Section and manager of the Cropland Data Layer Program in Washington.

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Figure 11: View of cranberry bogs above Little Trout Lake in northern Wisconsin on Oct. 18, 2018, from NASA-USGS Landsat-8 data. Some of the cranberries have turned bright red and are ready for harvesting (image credit: NASA)

• November 27, 2019: Today’s Image of the Day builds on this story from November 20, 2019. At the same time that scientists were standing on and studying the five-year-old Hunga Tonga-Hunga Ha‘apai island, another island-building event was unfolding just 150 km (90 miles) to the north-northeast in the Southwest Pacific Ocean. An undersea eruption at Lateiki Island in late October 2019 has brought new life to an older island in the Tonga chain. 7)

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Figure 12: An undersea eruption at Lateiki Island in late October 2019 has brought new life to an older island in the Tonga chain. The birth of the island is visible in these images, acquired with OLI on Landsat-8. This image shows the eruption on its third day, October 16, 2019. The false-color image combines shortwave infrared, near infrared, and blue light (bands 7-5-2) to help distinguish the hot spots associated with the eruption (red). Scientists say the emissions were dominated by steam and volcanic gases. (image credit: NASA Earth Observatory, image by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Kathryn Hansen)

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Figure 13: When the plume cleared on November 1, satellites started getting clear views of the new land that had emerged. Landsat-8 acquired the second, natural-color image of Lateiki Island on 17 November. Note that water around the island was still discolored from the eruption’s emissions. The new island measures about 400 meters (1300 feet) long and 100 meters (300 feet) wide (image credit: NASA Earth Observatory, image by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Kathryn Hansen)

- Lateiki’s history of erosion is not unique. Thousands of islands across Earth’s oceans are in a phase of decay. “We rarely see them as ‘newborns’ to watch how they evolve to become what they are,” said NASA scientist Jim Garvin. “Here in Tonga we can now watch and measure how they form and evolve in their childhood years, and compare them with others across the oceans to build better models for their evolutionary stages.”

- Previous eruptions at Lateiki have not been thoroughly documented by satellites, according to Garvin. He noted that this year, scientists are paying close attention to the region with Landsat-8, ESA’s Sentinel-2, and other satellites. “We’re excited because we have looked at this tiny island for the last 20 years,” he said. “Now the old one is gone and we get to watch the new one develop.”

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Figure 14: Lateiki Island, also known as Metis Shoal, is just the tip of a large undersea volcano (seamount) in an extremely active part of the Tonga Archipelago. (Scientists put it in the top ten most active volcanic areas on Earth). Prior to 2019, an eruption in 1995 also produced an island. That island saw considerable erosion and was ultimately destroyed by the 2019 event, which built a new island in its place. Earlier eruptions followed a similar cycle; islands that emerged in 1781, 1854, 1876, 1967, 1979, are all reported to have submerged within months, having succumbed to the erosive lashing of the sea (image credit: NASA Earth Observatory, image by Lauren Dauphin, using Landsat data from the U.S. Geological Survey and using topographic data from the Shuttle Radar Topography Mission (SRTM). Story by Kathryn Hansen, with information courtesy of Taaniela Kula and the government of the Kingdom of Tonga)

- They are particularly interested in seeing how the development and composition of Lateiki compares with Hunga Tonga-Hunga Ha‘apai (HTHH)—an island that appears to be stabilizing instead of eroding, and hence surviving. HTHH grew from an eruption that went through a series of phases over the course of six weeks, including an ash dominated surtseyan phase that built a 120-meter-tall cone, followed by explosive phases that spread material around the vent to grow the 180 hectare (0.69 square-mile) island. In contrast, the volcanic activity at Lateiki was less explosive, with lava piling up around the vent to form the relatively small 3-4 hectare islet.

- “Why they are different is unknown,” Garvin said. “We need to find out so we can predict lifespans of other islands as ‘dip-sticks’ for global environmental change in a time of sea level rise on Earth.”

• November 25, 2019: Many islands dot the bays of the ria coastline of South Gyeongsang Province in South Korea. But around Tongyeong, a city of 140,000 people, satellites observe something else of note in the water—a series of structures that look a bit like the squares of a chess board. In most cases, the squares are areas where oysters are being farmed. 8)

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Figure 15: On November 6, 2019, the OLI on Landsat-8 acquired this natural-color detail image of long-line oyster cultivation near an industrial facility. In this area, oysters are often grown by suspending them from ropes or wires, which are held near the surface with buoys. The technique encourages oysters to grow quickly and develop strong shells (image credit: NASA Earth Observatory, image by Joshua Stevens, using Landsat data from the U.S. Geological Survey. Story by Adam Voiland)

- After China, South Korea is the second-largest oyster producer in the world. Roughly 80 percent of this production comes from Tongyeong, which exports oysters to the United States, Japan, Canada, Hong Kong, and the European Union. Around Tongyeong, the oyster harvesting season begins in the fall, and this year’s haul appears to be unusually large. Downpours in the summer added extra nutrients to water and promoted growth, according to Arirang News.

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Figure 16: Overview image of South Korea’s oyster growing region in the waters of Tongyeong, acquired by OLI on Landsat-8 on 6 November 2019 (image credit: NASA Earth Observatory, image by Joshua Stevens, using Landsat data from the U.S. Geological Survey. Story by Adam Voiland)

• November 15, 2019: Tucked away in the eastern Andes Mountains, more than 5,000 meters above sea level, the town of La Rinconada is the highest permanent settlement in the world. The Peruvian town does not have running water, a sewage system, or garbage disposal. Yet 50,000 people live here amidst the thin air for one valuable resource: gold. 9)

- The town started as a temporary mining settlement more than four decades ago, so no permanent city services (such as sanitation systems) were installed. Male miners were allowed to spend up to thirty days at a time in the mine to collect as much gold as they could. The miners received no wage while in the mine, but there were also no restrictions on how much gold they could haul out.

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Figure 17: This natural-color image was acquired on August 1, 2019, by the Operational Land Imager on Landsat-8. La Rinconada lies in southeastern Peru, near Lake Titicaca and close to the Bolivian border. The town is located on the side of Mount Ananea and below a giant glacier called La Bella Durmiente, meaning “Sleeping Beauty” (image credit: NASA Earth Observatory, image by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Kasha Patel)

- Despite the poor working and living conditions, the population boomed in the 2000s when the market price for gold increased. From 2000 to 2009, the population of La Rinconada reportedly increased by 230 percent. Electricity was finally installed in the 2000s. Residents either burn or bury their trash outside of city limits.

- Besides the prospectors, the town also attracts researchers interested in studying the short-term and long-term effects of oxygen-poor conditions on humans. The thin air—each breath draws in half the amount of oxygen as at sea level—can lead to a syndrome called chronic mountain sickness (CMS). Symptoms of CMS include dizziness, headaches, ringing ears, palpitations, and even heart failure and death. Researchers estimate one in four people in La Rinconada suffer from CMS.

• November 15, 2019: Geoscience Australia’s Alice Springs satellite ground station hosts two 9 meter antennas, a 2.4 meter antenna, and associated infrastructure. The satellite ground station is one of three forming a global Landsat satellite ground station network and has been in operation since 1979. These antennas enable Geoscience Australia to collect data from a number of Earth monitoring satellites, including Landsat 7 and 8, which provide information to detect changes in land use over time and other useful environmental data. This data is used by government, industry, education and research, contributing billions of dollars to the Australian economy. 10)

- The geographic location of this satellite ground station is of strategic importance as it provides satellite reception coverage over the entire Australian continent therefore reducing the need and cost for other installations to provide the same capability in other locations. This ground station allows the US Geological Survey (USGS) Mission Operation Center located at NASA to send command and control signals to current and future Landsat satellites via the facility at Alice Springs, as well as satellite spacecraft telemetry information and 'state of health'.

- 2019 marks the 40th anniversary of Australia’s participation in the USGS Landsat program.

Figure 18: Geoscience Australia has invested more than $4 million to upgrade the Alice Springs antenna, securing Australia’s access to essential satellite data into the future. The antenna collects satellite imagery of the Earth, known as Earth observations from space (EOS) data, which has wide ranging benefits for the Australian community and globally, including significant economic returns. EOS data is used to respond to natural disasters such as bushfires, cyclones and floods, monitor land use, develop agriculture, discover new mineral and energy resources and ensure our water security (video credit: Geoscience Australia)

• November 13, 2019: The Juruá River emerges from highlands in east-central Peru, then winds its way through lowlands in Brazil. By the time it empties into the Amazon River near Fonte Boa, the river course spans more than 3000 km. But as the crow flies, the distance between the river’s source and mouth is only about 1000 km. 11)

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Figure 19: Meanders make up two thirds of the Juruá’s length, making it one of the most sinuous rivers in the Amazon Basin. On May 27, 2019, the Operational Land Imager (OLI) acquired this image of a stretch near Eirunepé, a settlement established in the 1800s as a hub for rubber production. A semicircle of land has been cleared around the city (light green), probably for ranching. Buildings and roads (white) are clustered along the river, which flows through seasonally flooded wetland forests known as várzea (dark green), image credit: NASA Earth Observatory, image by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Adam Voiland

- Note the abundance of oxbow lakes flanking the river. These form when parts of wide, curved meanders—oxbows—grow so close together that the river breaks through the bank and creates a more direct route. This often happens during floods.

- What makes rivers like the Juruá twist and turn so much more than other rivers? It flows through relatively flat terrain, which allows water to change course more readily than in other terrain. But research indicates that a heavy sediment load might be even more important. In analyzing three decades of Landsat images for 20 locations in the Amazon basin, the researchers from Cardiff University found that rivers carrying large amounts of sediment meandered more and had more cutoffs and oxbows than those carrying less sediment. The extra sediment accelerates the growth of point bars — sandy areas along the inside bends of meanders that can change the course of the flow and encourage the formation and lengthening of bends.

- The river has such sediment-rich “whitewater” because it flows through hilly areas in the foothills of the Andes that have soft, easily eroded rock and soil.

• November 6, 2019: For nearly four decades, Mauri Pelto has been studying the advance and retreat of glaciers around the globe. He has watched them succumb, one-by-one, to rising temperatures. Of 250 glaciers that he has watched, all had retreated (or shortened) except one: Taku Glacier. 12)

- Now a new analysis shows that Taku has lost mass and joined the rest of the retreating glaciers. “This is a big deal for me because I had this one glacier I could hold on to,” said Pelto, a glaciologist at Nichols College. “But not anymore. This makes the score climate change: 250 and alpine glaciers: 0.”

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Figure 20: This natural-color image show the glacier on 20 August 2014. The image was acquired by OLI (Operational Land Imager) on Landsat-8 (image credit: NASA Earth Observatory, image by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Kasha Patel)

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Figure 21: This natural color image shows the glacier on 9 August 2019. The image was acquired with OLI on Landsat-8 (image credit: NASA Earth Observatory, image by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Kasha Patel)

- Taku stands north of Juneau, Alaska, and is one of 19 notable glaciers in the Juneau Icefield. (The area also includes the famous Mendenhall Glacier, which has experienced an unusually fast retreat—about one third of a mile in the past decade.) Taku is extremely thick: In fact, it is one of the thickest known alpine glaciers in the world, measuring 4,860 feet (1,480 meters) from surface to bed. It is also the largest glacier in the Juneau Icefield.

- Using satellite imagery, aerial photography, and GPS field mapping, glaciologists with the Juneau Icefield Research Program (JIRP) have been tracking the thickness of Taku’s annual snow layer since 1946. Pelto has personally observed the glacier over a span of three decades, and even spent six months living on the glacier in huts and tents with JIRP in the 1980s.

- In his latest research, he used Landsat imagery to look at changes in the transient snowline—the boundary where snow transitions to bare glacier ice. At the end of the summer, the height of the snowline represents the point where the glacier experienced an equal amount of melting and snow accumulation. If a glacier experiences more melting than snow accumulation in a season, the glacier’s snowline migrates to higher altitudes. Researchers can calculate net changes in glacier mass by tracking the shift of the snow line.

- For half a century, the Taku Glacier was the only glacier in the Juneau Icefield that did not experience a net loss in mass. In fact, Pelto and colleagues found that the glacier was advancing and gaining mass at around 0.42 m/year from 1946-1988. But by 1989, glacier thickening slowed down significantly; eventually, the researchers noticed some thinning. The terminus also slowed its advance and then stalled.

- Usually, glaciers experience a transition period, with decades of terminus stability before switching from an advancing phase to a retreating phase. For instance, the Baird Glacier in nearby Glacier Bay stopped advancing and stood still for three decades before it began showing signs of retreat.

- “We thought the mass balance at Taku was so positive that it was going to be able to advance for the rest of the century,” said Pelto. “A lot of times, glaciers will stop advancing for quite a few years before retreats starts. I don’t think most of us thought Taku was going to retreat so quickly.”

- But it did. Taku Glacier had a short pause (2013-2018), then it began retreating in 2018. That year, Pelto and colleagues observed the highest transient snowline and mass loss in Taku Glacier’s history. The changes coincided with record summer temperatures in Alaska.

- “To be able to have the transition take place so fast indicates that climate is overriding the natural cycle of advance and retreat that the glacier would normally be going through,” said Pelto. “Taku Glacier is being exposed to melting it hadn’t before, which will drive new changes.”

• October 31, 2019: North of the Black Sea, the landscape of southern Ukraine is awash with eye-catching landforms that beg the question: what is that? About 65 km northwest of the colorful Sivash lagoons, the land abruptly turns from forest to sand. This oval-shaped region, known as Oleshky Sands, is the largest expanse of sand in Ukraine and the second-largest in Europe. 13)

- Dunes rise up to 5 m above the surrounding sand and punctuate the landscape. To try and prevent the dunes from encroaching on populated and agricultural areas, dense stands of pine trees were planted around the sandy expanse. Still, an analysis of 30 years of Landsat imagery (1987 to 2017) showed areas where sand had migrated into the forested areas, particularly on the northeastern and southwestern sides.

- Researchers are uncertain what made the area turn to desert. One theory is that the land is a dried riverbed of the Dnieper River (the modern-day course runs north of this image). A common explanation, however, is that millions of sheep that were pastured here in the 18th and 19th centuries initiated the desertification, which has since been sustained by wildfire and wind erosion.

- Episodes of fire continue to arise in the forested area around Oleshky. A notable case occurred in May 2018 when 25 hectares of forest were burned. Smoke from the fire was visible in images from the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra and Aqua satellites.

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Figure 22: The 161 km2 expanse of semi-arid desert is visible in this image acquired on 15 June 2019 by OLI on Landsat-8. At its widest, Oleshky Sands measures about 15 km across (image credit: NASA Earth Observatory, image by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Kathryn Hansen)

• October 30, 2019: On October 23, 2019, a blaze erupted in Sonoma County, California, near the small town of Geyserville. In six days, flames from the Kincade fire spread across more than 75,000 acres (303 km2), becoming the largest wildfire by acreage in California in 2019. As of October 29, the fire had destroyed more than 120 structures and caused at least 2,000 people to evacuate. 14)

- Fierce winds in northern California—known colloquially as Diablo winds—played a large role in quickly spreading the fire. On October 27, wind gusts reached 96 miles (150 km) per hour, which made the fire very difficult to stop. From October 26 to October 28, the fire grew by nearly 48,000 acres.

Figure 23: This animation shows winds over the western United States between October 20 and October 28, 2019. The strongest gusts appear bright yellow; weaker winds are purple. The wind data comes from the Goddard Earth Observing System Model 5 (GEOS-5), an experimental weather model that scientists at NASA use to analyze global weather phenomena. The GEOS model ingests wind data from more than 30 sources, including ships, buoys, radiosondes, dropsondes, aircraft, and satellites (video credit: NASA Earth Observatory)

- Forecasters expect another strong wind event on the night of October 29, which may again fan the flames. Firefighters are working on the ground and from the air to build containment lines around the wildfire. As of October 29, the fire was 15 percent contained.

- The Diablo winds tend to originate in the Great Basin region of Nevada and Utah. The winds are fueled by high-pressure air moving toward lower-pressure areas and lower elevations near the coast. On the way, the air masses pass over California’s mountain ranges and down through valleys, which causes the air to compress, heat up, and dry out. These hot, dry, gusty winds can exacerbate fire conditions and carry embers to the next patch of land. Similar winds—the Santa Anas—occur in southern California and are currently fanning the flames of the Tick Fire.

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Figure 24: This image shows a false-color view of the burn scar from the Kincade Fire as it appeared on October 26, 2019. The image combines shortwave-infrared, near-infrared, and green light from Landsat 8 (OLI bands 7-5-4) to better distinguish between burned vegetation (brown) and unburned vegetation (green). The brightest reds are active fire fronts. - The Kincade fire fits with a trend of larger, more destructive fires in California in autumn; fires in this season are strongly influenced by winds and dry weather. In addition to the impending wind storm, dry weather is expected continue in Northern California for the remainder of the week (image credit: NASA Earth Observatory, image by Joshua Stevens and Lauren Dauphin, using Landsat data from the U.S. Geological Survey and GEOS-5 data from the Global Modeling and Assimilation Office at NASA GSFC. Story by Kasha Patel)

• October 23,2019: When India gained its independence in 1947, it had to import salt to meet its domestic needs. Today, it is the third largest salt producer in the world, exporting surplus salt across regions from Japan to Indonesia. 15)

- The majority of India’s salt production can be traced to one region: the west central-state of Gujarat. With more than 50 percent of salt workers located in Gujarat, the state accounts for almost three-quarters of the country's annual salt production.

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Figure 25: The images of Figures 25 and 26 show the city of Bhavnagar, which is located in one of the major salt-producing districts in the state. They were acquired on February 28, 2019, by OLI on Landsat-8. The colorful rectangles are salt evaporation ponds and often seen in major salt-producing areas, such as the Makgadikgadi Pan in Botswana (image credit: NASA Earth Observatory images by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Kasha Patel)

- India’s main sources of salt are sea brine, lake brine, sub-soil brine, and rock salt deposits. In Gujarat, much of the salt comes from inland lake and marine sources. The Gulf of Khambhat has provided around 24 percent of salt production in the state in the past. Bhavnagar is one of the leading marine salt producers near the Gulf of Khambhat. It is also home to the Central Salt and Marine Chemicals Research Institute, which is one of the world’s leading salt research centers.

- The saltworks in Bhavnagar have also created an important environment for wetland birds. Many wetland species use it as a wintering area, while some water birds use it as a staging ground as they migrate along the coast.

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Figure 26: The west-central state of Gujarat accounts for nearly three-quarters of India’s annual salt production.

• October 9, 2019: The surface of Earth is constantly changing and evolving. Coastal barrier islands demonstrate such change faster than almost any other landscape. 16)

- Assateague Island stretches 37 miles (60 km) from north to south along the Atlantic coast of Maryland and Virginia. As barrier islands go, Assateague is quite dynamic. Longshore currents mostly flow south along this part of the coast, carrying sand to the south. So Assateague Island is steadily, relentlessly losing mass at its north end (near Ocean City, Maryland) and gaining it on the south end near Tom’s Cove.

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Figure 27: This image was acquired by Landsat 5 on June 20, 1985 (image credit: NASA Earth Observatory image by Joshua Stevens, using Landsat data from the U.S. Geological Survey. Story by Michael Carlowicz)

- Assateague also shelters two other islands, Chincoteague and Wallops, in a rare example of overlapping (duplexed) barrier islands. Major storms such as hurricanes and nor’easters sporadically and dramatically move sand from the ocean-facing side of Assateague to its land-facing side, into inlets and bays, and onto the shores of Chincoteague and Wallops. This means all three islands are slowly marching toward a merger with the mainland.

- “This is how Assateague Island has been growing for approximately the past 2,000 years,” said Christopher Seminack, a University of North Georgia geologist who has studied the area. “The island is growing to the south as sand shoals are migrating and welding onto the island. You can see evidence of this from the linear features that appear to be welded onto the most southerly part. And because the southern spit of Assateague acts as a sediment sink—the sediment is deposited there—it starves the barrier islands to the south of sand.”

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Figure 28: This natural color image, acquired with Landsat-8 on 2 June 2019, shows the change to Assateague, Chincoteague, and Wallops islands across three decades. Some of the color differences are related to the different sensors and likely different tidal stages at the time of each image (image credit: NASA Earth Observatory image by Joshua Stevens, using Landsat data from the U.S. Geological Survey. Story by Michael Carlowicz)

- Note the southwestward migration of Assateague Island and especially the substantial growth of vegetation on the southern spit. Just across the inlet, the east side of Wallops Island has bulged markedly. Changes in buildings and infrastructure are a bit more subtle. Activity has increased at NASA’s Wallops Flight Facility in recent decades; a new causeway bridge was built to Chincoteague; and more seasonal property and tourist business has sprung up in the area. But according to census estimates, the year-round population of Chincoteague has actually dropped since the 1980s.

- Through all of the changes, wild ponies have stuck around on the islands for several hundred years as the sand has moved under their feet. Legend has it that some of the original ponies arrived from the shipwreck of a Spanish galleon, though more likely they were left abandoned on the island by settlers and farmers. About 150 feral ponies live on the Maryland portion of Assateague and are kept relatively wild, without much human intervention. Another 150 live on the Virginia side and are owned by the Chincoteague Volunteer Fire Company, which provides medical checkups twice a year and auctions off several ponies each summer to raise money and maintain a steady population. All of the horses have adapted to eating salt marsh grasses and brush.

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Figure 29: NASA Earth Observatory (Photo courtesy of Margaret Landis. Story by Michael Carlowicz)

- “I spend a lot of time going in and out of Chincoteague inlet on my boat, and I have watched the inlet and islands change pretty dramatically over the past 20 years,” said Kyle Krabill, a research engineer at NASA’s Wallops Flight Facility. Krabill, his colleagues, and his father have been observing these shores for decades as they have tested lidar instruments that are ultimately used to study ice. “I have always been interested in these coastal processes and think it's really neat to watch them move around in our timescale.”

• September 25, 2019: After five years of planning and construction and more than three billion dollars in construction costs, one of the world’s longest bridges is complete. Opened in May 2019, the 48 km Sheikh Jaber Al-Ahmad Al-Sabah Causeway is one of the largest construction projects in Kuwait’s history. 17)

- Building the bridge was challenging in the coastal environment, where dangerously high temperatures and varying humidity can create extremely hot and dry conditions. Much of the construction occurred in early morning and after dark, with crews using high-powered lights or sun shields when necessary. The causeway is primarily composed of concrete piles and steel and layered with waterproofing and asphalt.

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Figure 30: OLI on Landsat-8 acquired this image of the causeway on September 8, 2019. Approximately 75 percent of the bridge (36 km) stands over water. It also crosses two artificial islands (Bay Island North and Bay Island South) that were constructed for entertainment and tourism purposes (image credit: NASA Earth Observatory, image by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Kasha Patel)

- Construction companies reported that they tried to take extra care to preserve the ecosystem near the bay, specifically for green tiger shrimp. In one case, they created an alternative breeding area comprised of 1,000 rock and reef blocks in order to draw the shrimp away from the construction site.

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Figure 31: Detail image of Landsat-8 of Kuwait City and the Sheikh Jaber Al-Ahmad Al-Sabah Causeway with Bay Island South (image credit: NASA Earth Observatory, image by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Kasha Patel)

- Named after the late Sheikh Jaber Al Sabah, the causeway was built to help reshape the country into an international trade center, weening it away from an oil-dependent economy. The bridge reduces travel time by nearly an hour from the capital, Kuwait City, to the northern shore of Kuwait Bay and the proposed future site of Madinat Al-Hareer.

- Meaning “Silk City” in Arabic, Madinat Al-Hareer is being proposed as a free trade zone and seaport. With development costs of more than $100 billion, the planned megacity will also include an airport, Olympic stadium, and a tower surpassing Dubai’s Burj Khalifa, currently the world’s tallest building. The causeway and Silk City are just a few elements in Kuwait National Development Plan 2035.

• September 25, 2019: In 1963, the Spanish government under Francisco Franco built the Valdecañas Reservoir in order to bring water and electricity to underdeveloped parts of western Spain. However, the creation of the reservoir flooded some inhabited areas as well as large stone (megalithic) monuments. After fifty years underwater, one of these ancient monuments—the Dolmen of Guadalperal—resurfaced due to dry, hot conditions in 2019. 18)

- Several areas of Europe experienced drought conditions during the summer of 2019. Much of the continent endured two heatwaves with record-breaking temperatures in June and July. Spain, in particular, faced its third-driest June this century, with above average temperatures in July and August. Many crops wilted, affecting many farmers.

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Figure 32: The Dolmen de Guadalperal resurfaced after five decades underwater. OLI on Landsat-8 acquired this image on 25 July 2019. Note the changing water levels and the widening of the tan ring around the shoreline; these lighter colored sediments are the recently exposed lake bottom. A circle marks the area where the remains of the Dolmen of Guadalperal are said to appear (image credit: NASA Earth Observatory, image by Lauren Dauphin, using Landsat data from the U.S. Geological Survey, story by Kasha Patel)

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Figure 33: OLI on Landsat-8 acquired this image of the Valdecañas Reservoir on 24 July 2013 (image credit: NASA Earth Observatory, image by Lauren Dauphin, using Landsat data from the U.S. Geological Survey, story by Kasha Patel)

- The drought conditions were enough to expose the Dolmen of Guadalperal, according to news reports. Dubbed the “Spanish Stonehenge,” the monument is a circle of more than 100 standing rocks dating back to 7,000 years ago. Archeologists believe it was originally constructed as an enclosed space—a large stone house with a cap. The dolmen could have served as a tomb, a site for religious rituals, or a trading hub since it was relatively easy to cross the river at this location. The most recent recorded exploration and excavation of the site was by German archaeologist Hugo Obermaier in the 1920s. By the time Obermaier’s findings were published in the 1960s though, the Valdecañas Reservoir was filled, submerging history with water.

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Figure 34: Since the 1960s, tips of the tallest megaliths have peaked out of the lake as water levels fluctuated. However, the dry, hot conditions in 2019 dropped lake levels to a point where the entire structure for the first time since the reservoir was filled. This photo shows the remains of the standing stones on the Dolmen of Guadalperal on 28 July 2019 (image credit: NASA Earth Observatory, photo used under the Creative Commons Attribution-Share Alike 4.0 International license, courtesy of Pleonr. Story by Kasha Patel)

• September 17, 2019: From a distance, the rows of windmills lined up in the desert seem to be silently performing their wind-to-energy duties. Encounter them up-close, however, and you can hear their striking ‘whoosh-whoosh’ sound. Hikers can have such a close encounter along a 6.5-mile (10 km) section of the Pacific Crest Trail (PCT) in Southern California’s Kern County. 19)

- This segment across Cameron Ridge is just a short stretch of the 2,650-mile (4,265 km) trail across the western United States from Mexico to Canada. But you still need to hike smart and be prepared. The weather can be extreme and, as the wind turbines indicate, typically very windy.

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Figure 35: On 1 July 2019, the Operational Land Imager (OLI) on Landsat-8 acquired this image of Cameron Ridge where the PCT (purple) crosses Tehachapi Pass. The pass divides the Tehachapi Mountains (south) and the Sierra Nevada (north), and forms a narrow connection between the San Joaquin Valley and the Mojave Desert (image credit: NASA Earth Observatory, image by Joshua Stevens, using Landsat data from the U.S. Geological Survey. Story by Kathryn Hansen)

- Note the abundance of wind turbines, connected by both straight and sinuous access roads. The turbine sites were not selected haphazardly; they are positioned to take advantage of the reliable winds, which come off the Pacific Ocean and ultimately get funneled at high speed through a mountain pass toward the southeast. According to a report for the California Energy Commission, the wind speeds through the pass are among the highest in the country, with an annual average of 20 miles (32 km) per hour.

- In 2018, news reports noted that Kern County had the largest concentration of wind capacity in the country, with the potential to generate more than 4,000 MW. The numbers come from a U.S. wind turbine database released by the U.S. Geological Survey and partners. (The database has a web-based tool to let users read up on more than 57,000 wind turbines across the country.)

- The Cameron Ridge area also makes sense for building turbines because Tehachapi Pass is relatively close to energy-hungry cities such as Los Angeles (about 75 miles/120 km away). The proximity also means the hiking trail is a manageable drive and a popular destination for day hikers.

• September 16, 2019: A bed of sea sawdust. A bundle of chopped hay. A pile of sea scum. - The cyanobacteria Trichodesmium spp. has been given many different descriptions, dating back to its first recorded observation in the 1700s by Captain James Cook. In addition to its distinct appearance, these wispy, microscopic filaments also play an important part in sustaining marine life. 20)

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Figure 36: An important player in the nitrogen cycle, Trichodesmium makes a seasonal appearance off the northeast coast of Australia. On 1 September 2019, OLI on Landsat-8 captured an image of what appears to be a bloom of Trichodesmium near the Great Barrier Reef off of northeast Australia. Trichodesmium blooms appear yellowish-brown when the bloom is healthy, green when it starts to decay, and white after the pigments decay (image credit: NASA Earth Observatory, image by Joshua Stevens, using Landsat data from the U.S. Geological Survey. Story by Kasha Patel)

- All aquatic organisms depend on nutrients for growth; one of the most important is nitrogen. Trichodesmium plays an important role in the ocean because it supplies large quantities of this necessary element. Trichodesmium belong to a class of bacteria called diazotrophs, which take nitrogen from the atmosphere and convert it to ammonia—a more usable form of nitrogen for photosynthesizing microbes. Research shows Trichodesmium accounts for about 60 to 80 percent of nitrogen fixation in the ocean.

- Trichodesmium most commonly bloom—grow rapidly in dense patches—in nutrient-poor tropical and subtropical waters in warmer conditions. They are often seen off the coast of Queensland between August and December when the water warms.

• September 11, 2019: Though ice losses from Antarctica and Greenland make up a greater volume and seem more dramatic, the losses from glaciers on Arctic islands and middle-latitude mountain ranges have been quite significant. A NASA-led research team has recently developed a tool to help researchers investigate more than 30 years of ice velocity data from glaciers, a key variable for detecting how Earth’s ice (the cryosphere) is changing. 21)

- Understanding how mountain glaciers change, and how their flow will change in the future, is complicated by the fact that no two glaciers are exactly alike. Malaspina Glacier in southeastern Alaska, for example, may not be moving fast but the motion within the glacier is complex.

Figure 37: This animation was composed from a sequence of false-color images acquired between 1986 and 2003 by the Landsat-5 and -7 satellites. The moving ice appears in shades of blue. Brown lines are moraines—areas where soil, rock, and other debris have been scraped up by the glacier and deposited at its sides. This debris often gets trapped as internal ribbons of rock where two glaciers merge and become one at a confluence (image credit: NASA Earth Observatory, image by Joshua Stevens, using Landsat data from the NASA MEaSUREs program at JPL. Story by Kathryn Hansen)

- Glaciers in this area of Alaska periodically surge, meaning they lurch forward quickly for one to several years. Surging can happen whether a glacier is advancing or retreating. Throughout the animation Malaspina appears to be retreating, and the increased meltwater and retreating ice is causing the lake (bottom-right) to expand. The zigzag pattern of the debris is caused by changes in velocity of the ice.

- “Glaciers all have their own personalities, so a detailed study of a single glacier often doesn’t apply to a region as a whole,” said Alex Gardner, a glaciologist at NASA’s Jet Propulsion Laboratory. “To make progress on understanding sea level rise and adapting large-scale water resources, we need to know the fundamental characteristics of glacier flow that apply over entire regions.”

Figure 38: This set of images are examples of the flow velocity maps that Gardner and colleagues can derive from ITS_LIVE data sets. Comparing velocities in 1997 with those of 2017, you can see that velocity changes along Malaspina are more subtle than for the trio of glaciers to the west, which appear to be surging (image credit: NASA Earth Observatory, image by Joshua Stevens, using Landsat data from ITS_LIVE and the NASA MEaSUREs program at JPL. Story by Kathryn Hansen)

- Gardner and colleagues from the University of Alaska and the University of Colorado have been working on an initiative known as the Inter-mission Time Series of Land Ice Velocity and Elevation, or ITS_LIVE. The core of the project is the comparison of images acquired with Landsat satellites over the past four decades. The researchers developed a highly efficient “feature tracking algorithm” in which high-performance computers track where the information contained within pixels has moved in the time spanned by two images. This is done millions of times between image pairs, resulting in a data set with many millions of estimated ice velocities.

- Data from ITS_LIVE have already revealed that high-mountain glaciers in Asia are flowing more slowly as they thin and melt. As ice thins, there is less gravitational pull tugging it down the mountainsides. “That might sound intuitive, but it is not necessarily so from glaciological point of view,” Gardner said. “Retreating glaciers have more meltwater reaching their beds; this water can act as a lubricant and cause it to speed up. But our data show that is not case in high mountain Asia.”

- Gardner suspects the same will hold true for Alaskan glaciers, but more analysis needs to be done. Can scientists establish a relationship between slowing and thinning ice that holds true for mountain glaciers globally?

- ITS_LIVE data were made publicly available through JPL and the National Snow and Ice Data Center web sites in the summer of 2019. “There is so much data, and we can’t explore it all on our own,” Gardner said. “Our hope is that by making the data easily accessible, researchers can access the tools they need to better understand glacier flow around the world.”

• September 3, 2019: Long recognized as one of the world’s most rapidly retreating glaciers, the Columbia Glacier in southern Alaska has been slowing down in recent years. “The total loss of ice is down substantially,” said Shad O’Neel. “But there is still impressive retreat.” 22)

- O’Neel, a glaciologist at the USGS Alaska Science Center, has kept a watchful eye on Columbia Glacier for years. Since the 1980s, the glacier has lost more than half of its total thickness and volume. Its front has retreated more than 20 km north in Columbia Bay, separating around 2011 into the West Branch (Post Glacier) and the Main Branch. (You can view the retreat from 1986 to present in our World of Change feature.)

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Figure 39: OLI on Landsat-8 acquired this image of Alaska's Columbia Glacier on 21 June 2019. One branch of the Glacier seems to have retreated as far as it can, while the other still has some distance to go (image credit: NASA Earth Observatory, image by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Kathryn Hansen)

- By the time these images were acquired, the West Branch had retreated so far that it had divided into several independent glaciers. O’Neel thinks the branch could be at the limit of its retreat. “I haven’t confirmed that yet from a site visit,” O’Neel said, “but it is unlikely that much, if any, of the glacier bed is below sea level anymore.”

- Meanwhile, the Main Branch has thinned and resumed its retreat, shedding icebergs from its front and retreating again in summer 2019. Ample ice has been lost by volume—from the glacier’s front and surface—but it still has plenty of room to retreat.

- Scientists think the Main Branch could eventually pull back to Divider Mountain. (The mountain’s edge is just visible in the center of the Main Branch along the top-right edge of the satellite images.) The Main Branch could retreat even further if the shape of the fjord and land surface below the glacier allow it.

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Figure 40: This false-color image of the same scene helps to differentiate between snow and ice (bright cyan) and other components of the landscape such as open water (dark blue). Vegetation is green and exposed bedrock is brown, while rocky debris on the glacier’s surface is gray (image credit: NASA Earth Observatory, image by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Kathryn Hansen)

- Analyzing Columbia Glacier’s retreat from beginning to end could help scientists understand what’s in store for the many other tidewater glaciers across southern Alaska. Changes happening along the way can be informative too.

- “Although we don’t usually think of single years as being important to glaciers, the 2019 summer has been so anomalous that it may be driving substantial change at many of Alaska’s glaciers,” O’Neel said.

• August 28, 2019: Today’s Image of the Day is an excerpt from our feature story: Trailing the Pacific Crest from Space. There is no award for completing the walk from Mexico to Canada through California, Oregon, and Washington. But read about the journeys of so-called “thru-hikers” of the Pacific Crest Trail (PCT), and it is clear that the 2,650 mile (4,265 km) hike changes you. Even walking a small segment of trail can connect you with the land, whether you access it in desert, forest, or alpine areas. 23)

- The PCT is not the longest or oldest National Scenic Trail in the United States, but it helped set the standard for trails that followed. The remarkable length of the Pacific Crest Trail, passing through 48 wilderness areas and some extremely demanding terrain, is especially apparent from space. NASA Earth Observatory identified locations along the trail where satellites and astronaut photography offer a unique perspective on this great hike.

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Figure 41: This image, acquired on June 11, 2019, with the Operational Land Imager (OLI) on Landsat-8, shows the PCT route (purple) across the bridge and beyond. The image is draped over topographic data from NASA’s Shuttle Radar Topography Mission (SRTM), image credit: NASA Earth Observatory, image by Joshua Stevens and Robert Simmon, using Landsat data from the U.S. Geological Survey and topographic data from the Shuttle Radar Topography Mission (SRTM). Story by Kathryn Hansen

- The PCT wraps around some of the most majestic peaks in the U.S. West, including some notable volcanoes. Glacier Peak and Mount Adams show up along the route in Washington. And then there’s Mount Rainier.

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Figure 42: By the time thru-hikers reach northern Oregon, they have passed plenty of volcanoes, but they’re not out of the Cascade Arc yet. This is where the trail crosses the flanks of Mt. Hood—the state’s tallest peak. This stratovolcano is shown from the vantage point of an astronaut on the International Space Station (image credit: NASA Earth Observatory, image by Joshua Stevens and Robert Simmon, using the astronaut photograph ISS036-E-23847,provided by the ISS Crew Earth Observations Facility and the Earth Science and Remote Sensing Unit, Johnson Space Center. Story by Kathryn Hansen)

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Figure 43: Towering above the horizon at 14,179 feet (4,322 m), Mount Shasta is sure to catch the eye of hikers. This majestic volcano in Northern California is at least partly visible from the trail for at least 500 miles. The image shows the space-based view of the mountain on November 1, 2013, acquired with the OLI on Landsat-8 and draped over topographic data (image credit: NASA Earth Observatory, image by Joshua Stevens and Robert Simmon, using Landsat data from the U.S. Geological Survey and topographic data from the Shuttle Radar Topography Mission (SRTM). Story by Kathryn Hansen)

- The volcano plays an important role in catching water for the region. Seasonal snowpack replenishes the local water supply that feeds rivers, streams, and nearby Shasta Lake—California’s largest reservoir.

- You can see other prominent PCT landmarks, such as Crater Lake, the Three Sisters volcanoes, and even a windfarm, in our full feature story.

• August 23, 2019: Volcanoes have a lot of dramatic ways to announce their presence: thick plumes of ash and steam; rivers and lakes of molten lava; rockfalls and lahars; earthquakes; even the sudden rising of an island above the water line. One of the more subtle and rarely observed displays is the pumice raft. 24)

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Figure 44: On August 13, 2019, the Operational Land Imager on Landsat 8 acquired natural-color imagery of a vast pumice raft floating in the tropical Pacific Ocean near Late Island in the Kingdom of Tonga (image credit: NASA Earth Observatory, image by Joshua Stevens, using Landsat data from the U.S. Geological Survey. Story by Michael Carlowicz)

- Volcanoes have a lot of dramatic ways to announce their presence: thick plumes of ash and steam; rivers and lakes of molten lava; rockfalls and lahars; earthquakes; even the sudden rising of an island above the water line. One of the more subtle and rarely observed displays is the pumice raft.

- Many of the world’s volcanoes are shrouded by the waters of the oceans. When they erupt, they can discolor the ocean surface with gases and debris. They also can spew masses of lava that are lighter than water. Such pumice rocks are full of holes and cavities, and they easily float.

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Figure 45: NASA’s Terra satellite detected the mass of floating rock on 9 August; the discolored water around the pumice suggests that the submarine volcano lies somewhere below. By August 13, the raft had drifted southwest. As of August 22, the raft had moved north again and was a bit more dispersed, but still visible (image credit: NASA Earth Observatory, image by Joshua Stevens, using Terra data. Story by Michael Carlowicz)

- The Volcano Discovery web site reported that it received an email from a sailor on August 7, 2019, about clouds of smoke on the horizon in the direction of Fonualei volcano. According to a bulletin from the Smithsonian’s Global Volcanism Program (GVP), sailors began reporting sightings of the pumice raft by August 9. The crew of the catamaran Roam encountered the pumice and provided a detailed report on Facebook on August 15. The sailors described a “rubble slick made up of rocks from marble to basketball size such that water was not visible,” as well as a smell of sulfur.

- Volcanologists at the Smithsonian believe the evidence points to an unnamed submarine volcano near Tonga at 18.325° South, 174.365° West. The last report of an eruption at the site occurred in 2001, and the summit of the seamount is believed to stand about 40 m below the water line.

- Volcanologist Erik Klemetti of Denison University wrote: “Pumice rafts can drift for weeks to years, slowly dispersing into the ocean currents. These chunks of pumice end up making excellent, drifting homes for sea organisms, helping them spread... The erupted pumice means this volcano erupts magma high in silica like rhyolite.”

• On August 18, 2019, scientists will be among those who gather for a memorial atop Ok volcano in west-central Iceland. The deceased being remembered is Okjökull—a once-iconic glacier that has melted away throughout the 20th century and was declared dead in 2014. Landsat satellite images show the latter stages of its decline. 25)

- A geological map from 1901 estimated Okjökull spanned an area of about 38 km2. In 1978, aerial photography showed the glacier was 3 km2. Today, less than 1 km2 remains. The satellite images show the glacier during the latter part of its decline, on September 7, 1986 (Figure 46), and August 1, 2019 (Figure 47). The images were acquired with the Thematic Mapper (TM) on Landsat-5, and the Operational Land Imager (OLI) on Landsat-8, respectively.

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Figure 46: TM image on Landsat-5 acquired on 7 September 1986 (image credit: NASA Earth Observatory, image by Joshua Stevens, using Landsat data from the U.S. Geological Survey. Story by Kathryn Hansen)

- The dome-shaped glacier appears in the 1986 image as a solid-white patch, just north of the snow-filled crater. Snow is also visible around the glacier’s edges. In the August 2019 image, only a spattering of thin ice patches remain. Notice the areas of blue meltwater, which are likely associated with the mass of warm air that hit Iceland as it moved from mainland Europe to Greenland in late July.

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Figure 47: OLI image on Landsat-8 acquired on 1 August 2019 (image credit: NASA Earth Observatory, image by Joshua Stevens, using Landsat data from the U.S. Geological Survey. Story by Kathryn Hansen)

- The glacier’s demise is not just a matter of shrinking area. Glaciers form from snow that becomes compacted into ice over time. The ice then creeps downslope under its own weight, helped along by gravity. Okjökull has thinned so much, however, that it no longer has enough mass to flow. According to some definitions, a stagnant glacier is a dead glacier.

- Okjökull, also called Ok (jökull is Icelandic for “glacier”), was part of the Langjökull group—one of Iceland’s eight regional groupings of glaciers. Ice covers about 10 percent of the island, making it an integral part of the landscape. Loss of glacial ice has wide-ranging effects, with the potential to impact water resources, infrastructure, and even the rising of the land as it rebounds under a lighter load of ice.

- Scientists have noted that glaciers have disappeared from Iceland before, although perhaps none as ceremoniously as Okjökull. Anthropologists from Rice University produced a film about the glacier’s demise, and a plaque is set to be installed on the site of the former glacier.

• August 6, 2019: In Iceland, a country rich with compelling geologic phenomena, volcanoes and ice caps abound. Even the country’s rivers are connected to the landscape of fire and ice. 26)

- Iceland’s largest rivers by volume, the Þjórsá and Ölfusá, once flowed toward the coast as one river, joining about 25 kilometers from the modern-day coastline. Then about 8,700 years ago they separated when an eruption deposited the Great Þjórsá lava—the country’s largest lava flow. The rivers today run their separate courses, flowing southwest along the east and west sides of the lava flow.

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Figure 48: The rivers are visible in these images of southwest Iceland, acquired on June 6, 2019, by the Operational Land Imager (OLI) on Landsat-8. The images show the rivers in the summer season when they are ice-free (in winter they are prone to flooding from ice jams). This wide view image shows the river’s locations relative to Reykjavik, Iceland’s capital city (image credit: NASA Earth Observatory, image by Joshua Stevens, using Landsat data from the U.S. Geological Survey. Story by Kathryn Hansen with image interpretation by Emmanuel Pagneux, University of Iceland)

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Figure 49: Detail image of Selfoss: The Ölfusá River is not Iceland’s longest river, measuring only 25 km from its headwaters to the ocean. Yet it moves an average of 423 m3/s of water — more than any other river in the country (image credit: NASA Earth Observatory, image by Joshua Stevens, using Landsat data from the U.S. Geological Survey. Story by Kathryn Hansen with image interpretation by Emmanuel Pagneux, University of Iceland)

- As the river flows by the town of Selfoss, you can see threads of light blue water amid darker areas. Spring water and glacial water feed this part of the river and, given their differences in temperature and density, do not mix well. Dark areas indicate fairly translucent spring water (known as “black rivers” in Iceland). Light blue areas are glacial water, which take on an opaque appearance due to sediments (“glacial flour”) suspended in the water.

- The striking red patch on the river’s eastern shore is dissolved ferrous iron, also known as bog iron. According to Emmanuel Pagneux of the University of Iceland, the bog iron reaches the Ölfusá River via ditches that were once built to drain wetlands and convert them into pastures.

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Figure 50: The Þjórsá River is both Iceland’s longest (230 km) and its second-largest by volume, moving an average of 370 m3/s of water. In this view, we see the river where it meets the Atlantic Ocean at the island’s south side. Before entering the ocean the river becomes braided, as channels of water flow around small, temporary islands of coarse sediment. The dark areas near the river’s mouth are wet volcanic sand. Where the water enters the ocean, the stark contrast in color is again due to two water types that do not mix well: in this case, glacial water and seawater of differing temperatures and densities (image credit: NASA Earth Observatory, image by Joshua Stevens, using Landsat data from the U.S. Geological Survey. Story by Kathryn Hansen with image interpretation by Emmanuel Pagneux, University of Iceland)

• August 6, 2019: If you look at the three largest cities in California by area—Los Angeles, San Diego, and California City—one stands out. Los Angeles has 3.7 million people; San Diego has 1.3 million. California City has a population of just 14,000 people. 27)

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Figure 51: The big dreams of a 1960s real estate developer have not materialized, but that has not stopped California City from pushing forward. Why does such an expansive city have so few people? Satellite images acquired on 18 October 2018 by OLI on Landsat-8 help explain (image credit: NASA Earth Observatory, image by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Adam Voiland)

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Figure 52: Though a large network of perfectly gridded blocks and curving residential streets remain etched into the Mojave Desert, houses are scarce (image credit: NASA Earth Observatory, image by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Adam Voiland)

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Figure 53: Even near the lake and golf courses at the center of town, empty lots abound (image credit: NASA Earth Observatory, image by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Adam Voiland)

- California City was incorporated in 1965 after real estate developer Nat Mendelsohn purchased thousands of acres of open land and started paving roads and laying water pipes for what he envisioned would be a city to rival Los Angeles. But interest from buyers never matched his grand vision, and by 1980, the town had only 2,700 residents.

- Still, an assortment of unusual ventures has kept the city going. Many people who live in California City today work at nearby Edwards Air Force Base, a borax mine, a prison, a vehicle testing facility, or one of the nation’s few spaceports.

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Figure 54: The borax mine is California’s largest open-pit mine, producing about half of the world’s refined borates. Borates are used in fertilizers, in metallurgy, and as components of specialized types of glass, anticorrosive coatings, fire retardants, and detergents (image credit: NASA Earth Observatory, image by Lauren Dauphin, using Landsat data, observed on 18 October 2018, from the U.S. Geological Survey. Story by Adam Voiland)

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Figure 55: Surrounded by solar panels, engineers test automobiles, motorcycles, and ATVs at speeds up to 320 km/hour on the winding roads of the Honda Proving Center (below). The prison (Figure 51), which used to hold people detained by U.S. immigration officials, now houses 2,300 inmates from California (image credit: NASA Earth Observatory, image by Lauren Dauphin, using Landsat data, observed on 18 October 2018, from the U.S. Geological Survey. Story by Adam Voiland)

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Figure 56: The Mojave Air and Space Port lies 25 km (15 miles) to the southwest. In 2004, federal authorities certified the facility as the first spaceport in the United States. Soon after, a private company launched a person into space on the rocket-powered aircraft SpaceShipOne. While experimental aircraft are a common sight, so are planes that are decades old. The air field also hosts a large storage area and boneyard for old planes (image credit: NASA Earth Observatory, image by Lauren Dauphin, using Landsat data, observed on 18 October 2018, from the U.S. Geological Survey. Story by Adam Voiland)

• July 31, 2019: o say the Dead Sea is merely a salt lake is like calling the Great Wall of China a pile of bricks—it does not quite capture how unique it is. 28)

- The Dead Sea is the second-saltiest lake in the world. Its surface and shores stand at the lowest elevation (around 435 meters or 1,430 feet) of any land mass not under water or ice. With a salt concentration above 30 percent, the lake water is nearly ten times saltier than the oceans. Feeling like olive oil mixed with sand, the water is so dense that humans float without effort. The salinity makes it difficult for any plant or animal to survive—hence its name.

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Figure 57: As water levels drop in the Dead Sea, salt is piling up on the lakebed. This image shows the Dead Sea and the Jordan Rift Valley on July 21 2019, as observed by the Operational Land Imager on the Landsat 8 satellite. The green rectangles on the south end of the lake are salt evaporation ponds, which are used to extract sodium chloride and potassium salts for the manufacturing of polyvinyl chloride (PVC) and other chemicals (image credit: NASA Earth Observatory images by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Kasha Patel)

- For the past two to three decades, water levels on the Dead Sea have been dropping at about 1.2 meters per year—an increase from 0.7 meters per year in the 1970s and 1980s. Levels have primarily dropped as water has been diverted from its only tributary, the Jordan River, to serve surrounding communities with water. Lake water also has been pumped to the evaporation ponds.

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Figure 58: As the water level drops, the lake becomes saltier, particularly near the surface. Scientists from the Dead Sea Observatory have discovered that salt has been precipitating out of the water and coating the bottom of the lake. They found the amount of salt on the lakebed (photograph) depended on the season and the various salt densities throughout the lake. The salt layer has been growing about 10 cm thicker every year for the past four decades, showing seasonal alternations of the layers’ properties (image credit: Photograph provided by the Dead Sea Observatory, Geological Survey of Israel. Story by Kasha Patel)

- During the summertime, the lake forms a warm, less dense top layer and a colder, denser bottom layer. When the top of the lake is disturbed by a wave or motion, tiny parcels of warm water—called “salt fingers”—travel down to the colder water. As the warm salt fingers cool on the journey down, the water mass can hold less salt. The salt precipitates out and forms crystals on the lakebed through this process known as double-diffusive convection.

- “In the ocean, the salt fingers might exist, but you’re not going to see them with the naked eye,” said Raphael Ouillon, a fluid dynamics expert at the University of California, Santa Barbara. “What is specific to the Dead Sea is that it’s almost at full saturation of how much salt can be dissolved, so salt precipitates out easily.”

- The Dead Sea is the only salt lake where this “salt fingering” process is known to occur. Scientists think it may be a clue to how salt deposits formed millions of years ago on other ancient sea beds, and specifically, how salt layers are thicker in the central parts of the basins and thin or absent from the shallow parts of these basins. For instance, more than five million years ago, the Mediterranean Sea’s dried out and left thick deposits of salt. Although the sea has since refilled, this salt buildup could have formed through a similar mechanism as currently observed in the Dead Sea.

• July 30, 2019: Plunging deep into the ground, the gaping hole of an open-pit mine is unmistakable from space. People have excavated such pits on every continent except Antarctica. 29)

- Copper mining began at Palabora in 1965, and by 1967 the open-pit mine was fully operational. The hole reached 800 meters down into the Earth before the depletion of resources made it uneconomical to continue mining in the pit. Operations moved underground (below the pit) and mostly out of sight in the early 2000s. The new mining method, known as block caving, involves extracting rock below an ore body, letting the ore break under its own weight, and then hauling the ore back to the surface.

- Three years after the start of underground mining at Palabora, cracks grew in the wall of the pit until the northwest wall collapsed. The image of Figure 60 shows a detailed view of that landslide, which is still visible in 2019. The collapse damaged some infrastructure—roads, power and water lines, and a railway line—but critical mine infrastructure stayed intact and underground mining continues there today.

- The site has become a case study in the challenges in transitioning from surface to underground mining. For example, researchers started using satellite data to improve the models that predict how mining underground will deform the surface.

- People were mining South Africa’s copper and iron resources long before the advent of open pit mines. Some archaeological estimates date mining artifacts back to at least 800 CE. In neighboring Kruger National Park, more than 250 archaeological sites show signs of human occupation back about 1 million years ago.

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Figure 59: The pit near Phalaborwa and Kruger National Park is the most visible sign of a long history of mining in the region. The mine pictured here has been growing vertically and horizontally near Phalaborwa, South Africa, for more than 50 years. The Operational Land Imager (OLI) on Landsat 8 acquired this image of the Palabora mine on July 2, 2019. It is South Africa’s largest open-pit mine, measuring almost 2 km wide. It is about half the width of the world’s largest open-pit mine, which is at Bingham Canyon in Utah (image credit: NASA Earth Observatory image by Joshua Stevens and Allison Nussbaum, using Landsat data from the U.S. Geological Survey and topographic data from the Shuttle Radar Topography Mission (SRTM). Story by Kathryn Hansen)

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Figure 60: A more detailed image of the Palabora mine showing the landslide (image credit: NASA Earth Observatory image by Joshua Stevens and Allison Nussbaum, using Landsat data from the U.S. Geological Survey and topographic data from the Shuttle Radar Topography Mission (SRTM). Story by Kathryn Hansen)

• July 24, 2019: With a series of scalloped bays, terraced sea cliffs, bizarre natural rock sculptures, and clusters of mud volcanoes, the barren landscape of Pakistan’s Makran Coast seems like a geologist’s dreamscape. 30)

- The coastline sits immediately north of an active tectonic plate boundary, a subduction zone where the oceanic crust of the Arabian Plate gets squeezed underneath the continental crust of the Eurasian Plate. In the process, sedimentary rock from the top of the Arabian Plate get scraped off and pile up on the edge of the Eurasian Plate in a convoluted jumble known as an accretionary wedge.

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Figure 61: Striking geology, new ports, and a few hammerhead sharks can be found along Pakistan’s Arabian Sea coast. OLI on Landsat-8 acquired this image of the Ormara peninsula on 15 February 2019. The Landsat data is draped over topographic data from NASA’s SRTM (Shuttle Radar Topography Mission), image credit: NASA Earth Observatory image by Joshua Stevens, using Landsat data from the U.S. Geological Survey and topographic data from SRTM, story by Adam Voiland

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Figure 62: Nadir OLI image of the Ormara peninsula acquired on 15 February 2019 (image credit: NASA Earth Observatory image by Joshua Stevens, using Landsat data from the U.S. Geological Survey, story by Adam Voiland)

- One of the more eye-catching features of the Makran Coast are two hammerhead-shaped peninsulas near the cities of Gwadar and Ormara. Both of the peninsulas are small fault blocks, or horsts— blocks of crust that have been lifted or have remained stationary while land on either side sank. The features, which tilt seaward, are associated with faults that run parallel to the coast.

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Figure 63: Nadir OLI image of the Gwadar peninsula acquired on 27 April 2019 (image credit: NASA Earth Observatory image by Joshua Stevens, using Landsat data from the U.S. Geological Survey, story by Adam Voiland)

- Ormara, which is higher than Gwadar, has elevations of 183 to 305 meters on the seaward side and 427 meters on the inner side. The Gwadar and Ormara horsts both used to be islands. However, the action of waves and drifting sand over time created long sandy spits (tombolos) that connect the islands to the mainland.

- The Makran Coast has an active fishing industry. Some estimates suggest between 8,000 and 10,000 small fishing boats operate in the area, with larger bottom trawlers operating in the region as well.

- The regional emphasis on fishing has had consequences for some of the fish that live in the Arabian Sea. The Arabian Sea has some of the most threatened populations of sharks, rays, and chimaeras in the world, according to a recent study. Hammerhead sharks were among the most vulnerable species in the region, according to the researchers.

- Large port facilities have been built on both of these peninsulas in the past few decades. In Ormara, the Pakistan military began building a naval base in 1994. In Gwadar, construction of a deepwater port on the Demi Zirr harbor began in 2002.