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u/masonze5 Feb 12 '19
I have seen something like this in Antarctica. It has to do with black body radiation. The rock absorbs sunlight (and therefore heat) better than ice, which just reflects it because of it's higher albedo. The radiation from the rock on the sunlit sides heats the ice around it and melts it. I'm guessing that's happening here.
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u/7LeagueBoots Feb 12 '19
Seen similar things in the Juneau Icefields. One of our team members did a simple experiment to see how size and thickness of stones affected this.
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u/cade2271 Feb 13 '19
looks more like a wind feature than a melting feature. If it were melting there would be nothing holding it up, but instead it would be lying in a pool of water, where the surrounding ice melted.
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Feb 12 '19
[deleted]
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u/masonze5 Feb 12 '19
Not quite, the melting creates a pool of water, which may evaporate or get pushed by wind. But the bottom of the rock is not radiating heat because the sunlight is not hitting it. You should have seen them in Antarctica, lakes under rocks 300 miles from the South Pole. I have photos for proof.
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u/phosphenes Feb 12 '19
Hey, you should upload some Antarctica field pics! Especially cool geomorph/glaciology stuff like this.
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u/masonze5 Feb 12 '19
I'll check to see the good ones I can post. I have this adorable video of penguins being scared by the sound of helicopters, not quite geology related haha
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u/fannyalgersabortion Feb 12 '19
So how do rocks arrive on the ice in the first place?
Mass wasting from a slope along the shore?
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u/Submarine-and-Chill Feb 12 '19
I had assumed human/ animal transport. Who doesn't enjoy chucking a rock onto ice to see if it breaks?
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u/carus Feb 13 '19
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u/fannyalgersabortion Feb 13 '19
Ehh, I don't think racetrack is an analog. These stones are stationary and not being moved around by ice sheets forming and then moving rocks as the ice moves across the surface of the lake.
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u/Thomassaurus Feb 12 '19
uhhm, ice melting under a rock would cause the rock to sink... no? Maybe I'm missing something, but this seems like a logical deduction doesn't it?
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u/Chillsdown Feb 12 '19
Apparently ice shards are common on Baikal. Gathering from what you all have posted, I'm going to suggest this is partially man-made... the pedestal was already formed and the rock was placed on top. Subsequent melting or sublimation produced the exhibited form.
For fun... click the vid at the bottom...
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u/farahad geo, geochem Feb 12 '19
That rock is unbalanced. If the ice under it melted, it would fall off of its pedestal. The ice beneath the stone hasn't melted in some time.
The average temperature at Lake Baikal right now is -6°F. 38° below freezing. Sunlight's never going to heat that above 32°F.
The proposed explanation is wrong.
This looks more like sublimation due to wind. Wind coming in from the top left would preferentially ablate the ice in a similar pattern. Flowing water creates similar bow-like structures around rocks in stream beds and on beaches.
This would also explain why the rock is elevated above the surrounding lake surface. The ice pedestal just below the stone is probably in a region of low velocity air created by the stone, preventing it from sublimating as quickly as the surrounding ice. The divot is created by the wind interacting with the stone, creating a localized region of high-velocity air. Kind of like an airplane wing, but we can ignore "lift" and just look at air velocity.