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Full Version: City Sized Crater Found Under Greenland Beneath 0.6 Miles Of Ice
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Today, an international team of scientists describes what they say is a huge new impact crater that lies under northwestern Greenland’s Hiawatha Glacier. If confirmed, it would be the first impact crater on Earth discovered under ice, the team reports in the journal Science Advances. At an estimated 19 miles wide, it is larger than Washington, D.C., and would rank among the top 25 known craters in the world.

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To find out more, the Danish scientists reached out to MacGregor, who is the chief scientist for the IceBridge project. To get more high-resolution scans of the Hiawatha Glacier, the team also enlisted the Alfred Wegener Institute in Germany, which provided them with additional surveying flights in May 2016 carrying newer, more sensitive instruments. They also sent a ground team in July 2016 to map surrounding structures on the surface and collect samples of sediments that had drained out from under the glacier.
With the precise radar data, the team was able to more completely work out the shape of the proposed crater. The walls of the circular rim are roughly 1,050 feet above the floor of the crater, they found. The team also identified an uplifted area 164 to 230 feet high in the center of the crater, which Kjær says is an expected feature and is the result of the force of the strike.

In the sediment samples, the researchers found grains of what's known as shocked quartz—a rare form of the ubiquitous mineral that has been deformed in a characteristic way by very high-energy events, such as in a large impact. Some of the grains also showed a brown color known as toasting, again a sign of intense energy release. Other minerals showed signs of shock metamorphism, to the point of turning into glass.
Based on the size of the crater, the team estimates that the asteroid would have been around 0.75 miles across and would have weighed 11 to 12 billion tons as it entered the atmosphere. And based on their mineral analysis, they believe it was an iron-rich space rock—the same type of rock as the meteorite fragment in the museum, although more tests would need to be done to establish a firm link, Kjær notes.

Now that he knows the circular depression is there, Kjær adds that he can even see its outline on the surface of the ice.

Cite: https://www.nationalgeographic.com/scien...nland-ice/

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.

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“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.
The researchers plan to continue their work in this area, addressing remaining questions on when and how the meteorite impact at Hiawatha Glacier affected the planet.

Cite: https://scitechdaily.com/nasa-discovers-...nland-ice/

Full Throttle

Excellent info, One of several catastrophic, and life ending events in the history of the planet. A bombardment from space by rocks really takes it's toll on things. Plus the aftermath of it all, probably worse.