New phenomenon causes concern; the Methane Seep

 This is very interesting and disturbing.  A new term is coming into the specialist literature --  a "methane seep".  You can see several of them in the photo above.  There is a piece on the BBC web site today:

http://www.bbc.co.uk/news/science-environment-18120093

Around the margins of the taiga and in the tundra areas of North America and Siberia there are vast areas where the permafrost has trapped rotting vegetation over millions of years.  This vegetation has been thriving during interglacials, rotting down and accumulating like peat layers, and then "captured" by the permafrost or beneath glacier ice during the glacials.

What is happening now, with global warming, is that the permafrost is melting, and as it does so the methane derived from this rotting material is being released.  Most of the release is invisible, but where the seepage occurs beneath river or lake ice -- or beneath sea ice -- it can cause these circular "melt holes" to appear.  I doubt that there would be enough heat or pressure associated with the methane to melt its way through a thick glacier ice cover -- but we do see similar things in Iceland, where volcanic activity or thermal springs ARE capable of melting their way through to the surface, leaving "ice craters" as evidence of what has happened.