http://www.newsweek.com/ocean-crater-permafrost-thaw-methane-seafloor-1687735

Enormous craters measuring 90 feet in depth have appeared on the seafloor of the Arctic Ocean.

The craters, scientists say, are forming as a result of thawing submerged permafrost on the edge of the Beaufort Sea in northern Canada, with retreating glaciers from the last ice age driving the change.