Huge Underwater Eruptions Blasted Craters into Arctic Seafloor

[Judi Lynn]

By Stephanie Pappas, Live Science Contributor | June 1, 2017 02:16pm ET

Craters as wide as 12 city blocks on the Arctic seafloor were put there by giant eruptions of underground methane gas.

Some of these craters had been discovered in the early 1990s, but only now have scientists mapped the features in detail. Researchers have discovered that there are many more craters than first believed — more than 100 giant ones and perhaps thousands of smaller pockmarks — and that these features probably formed about 11,600 years ago. This happened as the retreat of ice sheets destabilized frozen gas under the seafloor. Some mounds of frozen gas exploded, creating the craters still seen today.

"It's an analog for events that could take place in the future around contemporary ice sheets," said study researcher Karin Andreassen, a marine geologist and geophysicist at the Arctic University of Norway in Tromsø. Methane is a potent greenhouse gas, Andreassen said, so studying these undersea eruptions is important for understanding how they might affect the climate. [8 Ways Global Warming Is Already Changing the World]

Frozen methane

Andreassen and her colleagues were funded through the Research Council of Norway with grant money earmarked for understanding methane release from the seafloor. It's well-known that methane bubbles up from the sediments under the ocean in the Arctic, Andreassen told Live Science, but these small seeps don't reach much higher than 650 feet (200 meters) into the water column above the ocean bottom. The gas dissolves back into the ocean water before it can reach the atmosphere.

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