  Several mysterious large craters, with anomalously high concentrations of
methane, have formed in the Yamal and Taymyr peninsulas of Siberia since 2014.
While the thawing of the permafrost in the Arctic owing to climate warming may
promote methane releases, it is unknown how such release might be associated
with violent explosion and crater formation. In this study we demonstrate that
a significant volume of surface ice-melt water can migrate downward driven by
the osmotic pressure associated with a cryopeg, a lens of salty water below. We
show that the overpressure reached at depth, caused by this water accumulation
in the reservoir, can exceed the fracture strength and cause the frozen soil to
crack. If such fractures propagate to the surface, a rapid reduction of
pressure at depth can result in methane hydrate decomposition, methane gas
release, and mechanical explosion. This phenomenon may also be the cause of
seafloor pockmarks in fine-grained sediments such as silts and clays. This
unforeseen mechanism may therefore accelerate significantly the decomposition
of methane hydrates transported from depth to the surface, with implications
for the climate.
