With Speed and Violence Fred Pearce - Global Commons Institute

Meanwhile, pockmarks are turning up on the seabed almost everywhere that
clathrates are found: from the tropics to the poles, from the Atlantic, the
Pacific, and the Arctic to the Indian and Southern Oceans. Evidence of when
methane was released from the ocean floor remains sketchy, but the signs
are of major releases. At Blake Ridge, off the eastern U.S., marine geologists
have found pockmarks 700 yards wide and up to 30 yards deep, like huge
moon craters. And drilling studies suggest that the ridge may still have
around 15 billion tons of frozen methane hidden beneath the craters, with at
least as much again trapped as free gas in warmer sediments beneath the
frozen zone. European researchers have found pockmarks just as big in the
Barents Sea southeast of Svalbard. The widely quoted estimate that 1 to 10
trillion tons of methane is trapped down there remains a bit of a stab in the
dark, but the scale sounds right.
The lattice structures that hold methane clathrates survive only at low
temperatures and high pressures, so sightings are rare. Occasionally they
survive briefly at the ocean surface. Fishing nets bring lumps to the surface
from time to time. They fizz away on the ship's deck, releasing their methane.
Alarmed fishermen usually throw them back fast. Researchers have found
white clathrate chunks "the size of radishes" sitting in the mud on the
bottom of the Barents Sea; sometimes they track small plumes of methane
rising from the seabed to the surface. Russian researchers have reported
clathrates bursting out of the Caspian Sea and igniting "like a huge
blowtorch, producing flames that rise several hundred metres high." But
these events are mild curiosities compared with the evidence being pieced
together of major catastrophic events caused by methane releases from