Massive seabed craters caused by retreating ice and methane blow-outs

There are many ways to make a crater – asteroids, volcanoes – but the way that large indentations on the Arctic sea floor formed may have concerning implications for the future, according to a new study published in Science.

Karin Andreassen from the Centre for Arctic Gas Hydrate, Climate and Environment (CAGE) in Norway has shown that these holes – many up to a kilometre wide – are the result of methane blow-outs that occurred after the last ice age, roughly 12,000 years ago.

Andreassen explains that this process began as methane leaked up from deep hydrocarbon reservoirs in the Earth to pool underneath some 2000 metres of ice on the sea floor.

Trapped, the methane was stored as gas hydrate in the sediment and placed under increasing pressure as more and more was pushed up from underground.  

When the ice sheets rapidly retreated after the last ice age, the hydrates concentrated in mounds, and gradually started to melt and expand. 

Eventually the pressure build-up became too much and an uncontrolled release of methane occurred – think of an overheated pressure cooker, but on a much grander scale.

Andreassen notes that the processes that caused these craters still pose a risk in a warming world, and should be monitored closely. Methane is currently leaking from at least 600 sites around the Arctic craters and more large blow-outs could occur with the retreat of modern ice sheets.