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Comment by mehrdadn | Hacker News Reader

How/why is it such an incredibly "clean" and round hole?

It might be similar to the reason sinkholes are usually round [1].

[1] https://io9.gizmodo.com/why-are-sinkholes-round-1614203510

Interesting. Relevant quote from that link: "When a void occurs in sediment that has a certain amount of cohesion ('stickiness' among sediment grains), the most stable configuration of the roof of the void is a dome, like the dome of the U.S. Capitol building. If that dome collapses, the vertical sides may remain upright, and the open hole will be circular."

Why are bubbles round?

A sphere has the lowest ratio of surface area to volume.

Bubbles are round because of air pressure. But that doesn't really apply to large holes in the ground. The ground is a lot more difficult to move than a thin soap film is. Most caves aren't round. Most mountains aren't round, and when they are, it's for different reasons.

The holes in the ground appear to have been caused by air pressure (expanding methane gas), so perhaps the bubble analogy is apt.

tundra is peat

peat of made of decaying moss

moss is permeable like a sponge

sponges can hold stuff

stuff can change state with changes in temp/pressure

stuff in a new state can occupy increased volume

increased volume can cause increased pressure

increasing pressure increases temperature

changing the state of more stuff ...

(wavefront) path of least resistance contains most square inches with least circumference

HN's formatting engine requires two newlines between paragraphs.

That way you can separate points and make them more readable (punctuation also helps).

Caves are not created due to gas pressure neither are mountains. The former are the result of water flowing and solving weak rock, while mountains are the front of colliding tectonic plates.

In this case you have gas and mud.

The article hints that it's formed from gas pressure:

> The craters appear because ‘gas-saturated cavities are formed in the permafrost…

> "In a literal sense, a void space filled with gas with high pressure. The covering layer distends, the thickness of which is 5-10 metres approximately."

> Explosions have happened in swelling pingos, or mounds in the tundra which erupts when the gas builds up under a thick cap of ice.

Perhaps because it's caused by an eruption of methane gas. Perhaps the bubble analogy is apt.

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