I like the second hypothesis which you set out, where "permafrost" is relieved of its water. That's pretty much what I said at first - though you have to remember that unlike on Earth, the "permafrost" also contains very high CO2 concentrations.

It's the working fluid where you and I disagree. In this case I don't think it's magma - it's CO2/water instead. Maybe that CO2/water has been freed by a very deep hot spot where magma rises to meet the lower levels of the stratified debris. Maybe the release was simply due to gravitational compacting and local density differences.

Who knows? I just find it relaxing to contemplate the images. And there's over 100,000 images, with more coming every day.

ep