Ice expands as it freezes. We also know water under pressure will super cool and not freeze but it will still expand. Take a pop bottle and fill it with water without putting the cap on and set it in the freezer. It will spill out the top. Put the cap on it and it will simple expand the plastic bottle (or break a glass bottle)
Now imagine a hole in the ground or a pocket of water just under the surface of the ground. It freezes, pushes up, and brings the ground with it a bit. It's under pressure so it doesn't all freeze but exerts force in pretty much a radius. The relief point is up until the weight of the column of water finds another relief point (a crack in the earth leading to sea or something.) If you look at the craters again, you will not find enough material around the edges to correct for the amount missing from the hole.
Now there is something called geothermal flux which is more or less changes in the heat within the ground. It is already being blamed for some of the permafrost melting. And we know there are perforations within the permafrost in the sea beds off the coast which are letting methane release. It's could have aided in the release and removal of material assuming water under pressure was in fact not frozen in these areas.
The pictures do not look like sink holes can be ruled out. What would likely rule sink holes out would be the depths of the permafrost as well as when it was originally established (the last ice age I believe).