It has been about 11,600 years since the last one of the huge mounds exploded, releasing its methane gas, and there are literally hundreds of the craters to be seen on the floor of the Barents Sea, according to a study published in the journal, Science on June 1, 2017.
The cold and shallow body of water just a little north of Norway meets Russia and is home to oil and gas fields. Methane, the primary component of natural gas naturally seeps out of the seafloor in this region. Karin Andreassen, the lead author of the study is a marine geologist and geophysicist at the Centre for Arctic Gas Hydrate, Environment, and Climate in Tromsø, Norway.
She knew the research team would find some craters on the seafloor when they began the study in the Barents Sea, however, she didn’t realize just how many craters the team would find or how massive many of them turned out to be.
They were giant,” she says, “And they were next to these huge mounds.” But the mounds turned out to be the clue to the craters’ origins, and it all goes back to the end of the last Ice Age some 12,000 years ago. During the last Ice Age, what we now call the Barents Sea was an area of solid ice.
Methane forms deep inside the Earth, where organic material is turned into methane by heat and pressure. Any methane that bubbled up through the bedrock would have hit the thick layer of ice that covered the region during the Ice Age. Naturally, having no place to go, the gas froze into what is called methane hydrate.
As the Earth began warming, the glaciers and ice sheet retreated forming the Barents Sea, and some of the methane hydrates began thawing, turning back into methane gas. The pressure of the warming gas lifted the seafloor, creating huge mounds called pingos, as they pushed up towards the surface.
The researchers used seismic data that revealed fractures in the seabed and identified deep sources of hydrocarbons that could feed the area. Acoustic surveys identified over 600 spots on the seabed where methane was still seeping.
“The data set is beautiful,” says Carolyn Ruppel, a geophysicist who heads the US Geological Survey’s Gas Hydrates Project in Woods Hole, Massachusetts. She praised the Research team, adding, “I think they really have nailed this area very well.”
Speaking to Gizmodo, Andreassen said methane explosions are the best explanation for the craters. “We have numerically modeled the evolution of methane hydrates through the last Ice Age up until today, and the methane hydrates became unstable at the time estimated for crater formation,” she said.
The findings in this study are relevant to today’s concerns over greenhouse gasses and how they influence climate change. As Andreassen points out, we could have these explosions today. And the Arctic isn’t the only place where massive seeps of methane have been found.
Besides the finding of methane leaks on the Atlantic Coast of the U.S., in another study conducted in 2015, scientists mapped one of the longest active methane seeps on the planet—a strip extending from British Columbia to Northern California.
