It's a pingo that had its ice plug popped out by gas pushing up from below.
I know, I know, I also wish it were Cthulhu, but pingos are pretty cool too...
They're a feature in the tundra, where ice builds up under the layer of earth on top of permafrost and forms a thing that is, essentially, a big ice-pimple. When the permafrost is covering the world's largest natural gas field, I guess they also occasionally pop like pimples too.
But what both of these do look like is the work of a pingo - a natural geological process that experts have theorized formed the first hole after the initial on-site investigation. According to the British Society for Geomorphology, pingos occur when elevated temperatures cause rising ground water to build and push a mass of ice towards the surface. Once the ice pops like a cork from a Champaign bottle, it melts away, leaving a very deep hole and ice water.
Still, that doesn't mean that experts should simply ignore the accounts of excited locals, no matter how fantastical they may seem. A bright flash? An explosion? It's possible considering the second hole discovered is relatively close to a huge natural gas extraction plant.