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there are a lot of different throries presented

but top me that looks like a cave staft or aven has been dramatically uncovered :

sireria crater by andyj23uk1, on Flickr

Depends on whether we are really looking at eroded rock.

The most popular current theory is that these are craters formed by gas eruptions or even explosions. It has been theorized that the release of gas hydrates could be accelerated by global warming and create a runaway effect with large quantities of methane being release into the atmosphere. Quite worrying.

Yet the markings are suggestive of scallops caused by a massive swallet with a 'swirl effect', like a bath plughole?