Yesterday I was at a workshop where someone presented evidence of an impact crater under Antarctica that's 500 km wide, but yeah, I guess this 30 km one is cool too...
The crater was first noted by scientists looking at NASA data taken as part of the Program for Arctic Regional Climate Assessment and Operation IceBridge from 1997 to 2014. This was radar data taken by airplanes that fly over the ice; the radar can penetrate the ice and get reflected by the rock underneath. The crater outline was in the data, but not quite sharply enough to be sure (the researchers have also noted that if you know what you’re looking for, the rim can be seen from the air, and the surface of the ice at that location shows a dip as well).
The region is covered by the Hiawatha glacier, and there’s a subglacial river that comes out there. Samples of sediment from the river were collected, and brought back to a lab to examine. And that’s where the scientists hit the jackpot: They found quartz grains that showed clear evidence of a specific disturbance in their crystalline structure — a deformation caused by an intense pressure wave slamming into them. This is called shocked quartz, and is a smoking gun when it comes to impacts. Even huge volcanic explosions can’t create it. It takes the massive and energetic collision of an asteroid with Earth to make these structures in quartz.
The well-preserved structure of the crater strongly implies it’s geologically young, and the scientists estimate it’s no older than about 3 million years. But it could be substantially younger. Moving ice tends to erode structures underneath pretty rapidly. There are several layers of ice over the crater, including one that goes down to a depth of 700 meters from the surface that appears pretty clean and smooth. Beneath it is a layer that is disturbed and mixed with a lot of debris, which is what you’d expect for ice over a crater. If the crater were very old, this ice would have equilibriated, reached some sort of balance with the crater under it. It hasn’t, again indicating youth.
The researchers conclude the ice could — stress could — be as young as 12,000 years.
https://www.syfy.com/syfywire/deep-freeze-impact-scientists-find-a-huge-asteroid-impact-crater-under-greenlands-ice
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