As they flew over the sweeping Siberian tundra, a Russian TV crew recently spotted an intriguing feature: a crater more than half a football field deep gouged from the frozen ground. Blocks of ice and dirt lay hundreds of feet away from the crater, flung from the deep scar on the surface.

This is just the latest in a series of such curious craters discovered in the Siberian Arctic, after the first was identified in 2014. Scientists believe they form from blasts of methane and carbon dioxide gas trapped within mounds of dirt and ice—a phenomenon that may be increasingly common as the climate warms. But much remains uncertain.

“We still don’t know what’s going on,” says Sue Natali,