Just big gas bubble “sploops”, like a large scale version of a geothermal mudpot or where sand wells out with water when a confining layer is breached. Here the surface has probably softened enough that a void which has collected a lot of gasses bursts out like a big earthy zit.
Re Giant arctic hole:
Couldn’t find anything about sinking poles. 17th hole was interesting. Who knows what will bubble up from beneath the Earth’s crust? The scientist in the article says he found interesting stuff, but won’t reveal it yet!