There is a new article in Nature Geosciences published in May 2012 about 'Geologic methane seeps along boundaries of Arctic permafrost thaw and melting glaciers'by Katey M. Walter Anthony, Peter Anthony, Guido Grosse and Jeffrey Chanton

The full article can be found at http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo1480.html

The picture shows slow bubbling from superficial seeps that produces distinctbubble patterns and occasionally small holes (0.01–0.3 m2) that remainice-free for several days to weeks following freeze-up