The Younger Dryas Impact Theory describes an asteroid impact in Northern America, possibly the eastern part of Hudson Bay, which contributed to the end of the last ice age.

If a comet strikes a glacier, would it make a print on the land below? If specifically the comet that made this impact crater in Hudson Bay, and a glacier that was maybe comparable to Antarctica so 2 km thick.

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    $\begingroup$ It likely depends on how large the comet is. $\endgroup$ – probably_someone Jul 8 '17 at 4:38
  • $\begingroup$ if specifically the comet that made this impact crater in Hudson Bay, ottawa-rasc.ca/wiki/images/thumb/5/57/… and a glacier that was maybe comparable to Antarctica so 2 km $\endgroup$ – mumin Jul 8 '17 at 5:12
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    $\begingroup$ @mumin Please edit that comment answer into your question. Question should contain all relevant information; comments may disappear. $\endgroup$ – user1569 Jul 8 '17 at 10:22
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    $\begingroup$ Related question here: earthscience.stackexchange.com/questions/6723/… Also "would it leave an impact under ice" is Earth science, not Astronomy. Comets & Meteors are Astronomy. Geological and other evidence of past impacts on Earth (during an ice age) - Earth Science. $\endgroup$ – userLTK Jul 8 '17 at 13:17

While it's a clever suggestion, the answer is almost certainly that they are not related because the Nastapoka Arc "crater" is too big. It's 450 km in diameter. By comparison, the Chicxulub crater is 180 km. Even if an impact through mile of ice could, somehow, spread the impact out wider, the proposed Younger Dryas Impact object was almost certainly too small to leave a 340 km crater.

There's also the problem that glacial ice carves the landscape and a neat circular crater is unlikely, even if the size had been a closer fit, an impact crater that was run over by a glacier should look disturbed by the glacier, not a neat circle visible on the surface.

What geological evidence might remain for a large impact on a glacier is an interesting question given that the ice would significantly buffer any impact and continue to reshape the landscape below it as the glacier moves and/or melts and possibly floods the region.

Mile high ice glaciers are relatively rare events, both localized and periodic, and large meteor impacts are also rare events. A combination of the two, large enough to leave clear evidence through the ice, would at best, be a hugely rare event and there's a good possibility that the right combination of impact and ice hasn't happened at all over the last 2.5 million years (northern Hemisphere) or on Antarctica (3% of the surface area of the earth) - last 20-30 million years.

I think the safer bet is that there's no impact crater from the proposed Younger Dryas impact specifically because of the thickness of the glacier. It remains a debated hypothesis, so there's some uncertainty, but Ice should significanly buffer all but the largest impacts.

For Younger Dryas, there should be other physical evidence such as debris from the impacting meteor or comet, but debris cast over a glacier that first re-freezes over and later melts can be spread very far and be very hard to identify. Much of it could have washed into the ocean. A somewhat related example, it took 105 years before debris from the Tunguska event was identified.

(and this question should probably be moved to Earth Science).

  • $\begingroup$ I was thinking something along the lines: asteroids are burning hot, the melting point of ice is quite low compared to for example continental crust, and so perhaps an asteroid would, to some extent, slice through glaciers. $\endgroup$ – mumin Jul 8 '17 at 16:13
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    $\begingroup$ They're not hot, but they do release a lot of energy so when they hit things tend to heat up. But there would be no slicing, just blasting. $\endgroup$ – James K Jul 8 '17 at 16:17
  • $\begingroup$ @mumin actually ice is very hard to melt. The melting temperature is comparatively low but the energy required to melt ice is quite high. It would be a collision impact, not a hot knife through butter (so to speak). $\endgroup$ – userLTK Jul 8 '17 at 17:06
  • $\begingroup$ so an impact on 2 km thick glacier by an asteroid 10km or so in width, wouldn't leave much of an impact crater on the ground below? $\endgroup$ – mumin Jul 8 '17 at 17:50
  • $\begingroup$ @mumin 10 km impacts happen very rarely. There's been only one in the last 66 million years and it didn't impact a glacier. But to answer your question, yes, a 10 km asteroid impact onto a glacier would likely leave a detectable impact crater, even millions of years later. 10 km is enormous for an impactor. It would be a global extinction level event. $\endgroup$ – userLTK Jul 8 '17 at 22:32

"If a comet strikes a glacier, does it make a print on the land below?"

This would depend upon the depth of glacial ice, the nature of soil beneath it, and size-composition-velocity of the comet.

Being made of 'dirty ice' a comet's density is much less that an asteroid's so even though their velocity is much grater as a rule they would leave only a small cater at their target and likely no permanent mark where they hit deep ice. However, prominent lateral imprints were formed by a relatively recent earth impact as debris within the ice was ejected at extreme velocity by explosive vaporization.

Asteroids striking deep glacial ice are an entirely different matter Their fireball vaporized a tunnel though deep glacial ice by radiant heat and their cold core penetrated poorly consolidated sediment for many miles in some cases before explosive vaporization occurred to create a wide variety of crater configurations in the 24 'recent' events I've identified since '98.

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    $\begingroup$ I've never heard of of this. Can you give references or suggest search terms? $\endgroup$ – Keith McClary Mar 22 '18 at 5:02
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    $\begingroup$ I'm skeptical of a fireball "tunneling through" a glacier due to heat. Comet or asteroid impacts tend to behave like explosions. The ice would be blown up and a crater in the ice created, similar to a crater on land. After the fact, some melting would likely take place, but "tunneling through" - I'm highly skeptical. $\endgroup$ – userLTK Nov 20 '19 at 23:18

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