Massive Crater Discovered Under Greenland Ice
An international team of researchers, including a NASA glaciologist, has discovered a large meteorite impact crater hiding beneath more than a half-mile of ice in northwest Greenland. The crater — the first of any size found under the Greenland ice sheet — is one of the 25 largest impact craters on Earth, measuring roughly 300 m deep and more than 31 km in diameter, an area slightly larger than that inside Washington's Capital Beltway, or corresponding to an area bigger than Paris. 1) 2)
The group, led by researchers from the University of Copenhagen's Center for GeoGenetics at the Natural History Museum of Denmark worked for the past three years to verify their discovery, which they initially made in 2015 using NASA data. Their finding is published in the 14 November issue of the journal Science Advances. 3)
"NASA makes the data it collects freely available to scientists and the public all around the world," said Joe MacGregor, a NASA glaciologist at Goddard Space Flight Center in Greenbelt, Maryland, who became involved in the investigation in its early stages. "That set the stage for our Danish colleagues' 'Eureka' moment."
Figure 1: Two views of the Hiawatha crater region: one covered by the Greenland Ice Sheet, the other showing the topography of the rock beneath the ice sheet, including the crater (image credit: NASA/Cindy Starr)
The researchers first spotted the crater in July 2015, while they were inspecting a new map of the topography beneath Greenland's ice sheet that used ice-penetrating radar data primarily from NASA's Operation IceBridge — a multi-year airborne mission to track changes in polar ice — and earlier NASA airborne missions in Greenland. The scientists noticed an enormous, previously unexamined circular depression under Hiawatha Glacier, sitting at the very edge of the ice sheet in northwestern Greenland.
Using satellite imagery from the Moderate Resolution Imaging Spectroradiometer instrument on NASA's Terra and Aqua satellites, MacGregor also examined the surface of the ice in the Hiawatha Glacier region and quickly found evidence of a circular pattern on the ice surface that matched the one observed in the bed topography map.
To confirm their suspicions, in May 2016 the team sent a research plane from Germany's Alfred Wegener Institute to fly over the Hiawatha Glacier and map the crater and the overlying ice with a state-of-the-art ice-penetrating radar provided by the University of Kansas. MacGregor, who is an expert in radar measurements of ice, helped design the airborne survey.
Figure 2: Radar data from an intensive aerial survey of the Hiawatha crater in May 2016 is shown here in aqua-colored curtains. A blue arrow points to the central peak of the crater (image credit: NASA/Cindy Starr)
"Previous radar measurements of Hiawatha Glacier were part of a long-term NASA effort to map Greenland's changing ice cover," MacGregor said. "What we really needed to test our hypothesis was a dense and focused radar survey there. The survey exceeded all expectations and imaged the depression in stunning detail: a distinctly circular rim, central uplift, disturbed and undisturbed ice layering, and basal debris — it's all there."
The crater formed less than 3 million years ago, according to the study, when an iron meteorite more than half a mile wide smashed into northwest Greenland. The resulting depression was subsequently covered by ice.
"The crater is exceptionally well-preserved and that is surprising because glacier ice is an incredibly efficient erosive agent that would have quickly removed traces of the impact," said Kurt Kjær, a professor at the Center for GeoGenetics at the Natural History Museum of Denmark and lead author of the study.
Kjær said that the crater's condition indicates the impact might even have occurred toward the end of the last ice age, which would place the resulting crater among the youngest on the planet.
In the summers of 2016 and 2017, the research team returned to the Hiawatha Glacier to map tectonic structures in the rock near the foot of the glacier and collect samples of sediments washed out from the depression through a meltwater channel.
Figure 3: Map of the bedrock topography beneath the ice sheet and the ice-free land surrounding the Hiawatha impact crater. The structure is 31 km wide, with a prominent rim surrounding the structure. In the central part of the impact structure, an area with elevated terrain is seen, which is typical for larger impact craters. Calculations shows that in order to generate an impact crater of this size, the earth was struck by a meteorite more than 1 km wide (image credit: The Natural History Museum of Denmark, Ref. 2)
Figure 4: An international team of scientists came together to unravel the mystery of Greenland's Hiawatha Crater. This video shows how that discovery came together (image credit: NASA/Jefferson Beck)
1) "International Team, NASA Make Unexpected Discovery Under Greenland Ice," NASA Release 18-099, 14 November 2018, URL: https://www.nasa.gov/press-release/international-
2) Faculty of Science - University of Copenhagen, "Massive impact crater from a kilometer-wide iron meteorite discovered in Greenland," Science Daily, 14 November 2018, URL: https://www.sciencedaily.com/releases/2018/11/181114160042.htm
3) Kurt H. Kjær, Nicolaj K. Larsen, Tobias Binder, Anders A. Bjørk, Olaf Eisen, Mark A. Fahnestock, Svend Funder, Adam A. Garde, Henning Haack, Veit Helm, Michael Houmark-Nielsen, Kristian K. Kjeldsen, Shfaqat A. Khan, Horst Machguth, Iain McDonald, Mathieu Morlighem, Jérémie Mouginot, John D. Paden, Tod E. Waight, Christian Weikusat, Eske Willerslev, Joseph A. MacGregor, "A large impact crater beneath Hiawatha Glacier in northwest Greenland," Science Advances, Vol 4, No. 11, 14 November 2018, eaar8173, DOI: 10.1126/sciadv.aar8173, URL: http://advances.sciencemag.org/content/