When Karin Andreassen set out for the Barents Sea, she knew she would find a lot of methane. The cold, shallow body of water just north of where Norway meets Russia is home to oil and gas fields, and methane—the main component of natural gas—naturally seeps out of the seafloor here. Andreassen, a marine geologist at UiT The Arctic University of Norway, also knew from surveys in the 90s that she’d find some underwater craters.
But she did not expect to find so many craters (hundreds!) and so many huge ones (half a mile wide).
“They were giant,” she says, “and they were next to these huge mounds.” The mounds ended up being a clue to the craters’ origins. In a new study, Andreassen and her colleagues lay out a unified theory for how the craters and mounds formed as the Barents Sea itself changed over thousands of years. It all goes back to methane.
Methane can form deep underground, where heat and pressure transform ancient organic material into methane gas. Fifteen thousand years ago during the Ice Age, when the Barents Sea was not yet a sea but an ice sheet, methane that migrated up through bedrock would have hit solid ice. It couldn’t go anywhere so it froze in place as methane hydrate. But as ice sheets melted to form a now liquid Barents Sea, the hydrates also began to turn back into methane gas. Pressure from this gas lifted the seafloor to create the giant mounds. With enough pressure, the mounds could blow, creating those giant craters.