Methane 'kitchens' in Siberia's permafrost form mounds that can erupt, creating giant craters

Mysterious "frost mounds" dotted across Siberia sometimes burst to form giant craters — and now, scientists have taken a step closer to discovering what makes these strange humps pop.

Frost mounds are areas of the permafrost that bulge as fluids accumulate beneath the surface. According to ongoing research at the Siberian Branch of the Russian Academy of Sciences (SBRAS), two distinct "systems" can lead to this bulging: open and closed. In an open system, water and gas pooling beneath the permafrost move around and leak to the surface through cracks. But in a closed system, water and gas are trapped in a pocket that iNFLates, putting increasing pressure on the permafrost.

The open system is similar to an idea researchers put forward earlier this year. In a preprint review published Jan. 12 to the EarthArXiv database, the scientists argued that natural gas moving between the bedrock and overlying permafrost leads to melting from below. This melting creates pockets in the permafrost where fluids can accumulate, but these are not completely sealed off from the gas beneath or from the surface. The pockets grow as more gas flows into them, leading to more melting and a rise in pressure, which causes the ground to swell.

The gas is mostly thermogenic methane, which likely forms continuously as a by-product when organic matter heats up. "We call it a kitchen [down there], because it's kind of like cooking, and it's creating gas," Helge Hellevang, a professor of environmental geosciences at the University of Oslo in Norway and lead author of the preprint review, told Live Science.

In a closed system, gas and water come from deep within the bedrock. The fluids rise and form a pocket inside the permafrost that is "surrounded by frozen rocks on all sides," according to SBRAS researchers, and therefore does not leak out.

Related: Underwater robot in Siberia's Lake Baikal reveals hidden mud volcanoes — and an active fault

Despite the distinction between open and closed systems, there is nothing to stop one from morphing into the other as the permafrost evolves, Hellevang said. An open system may even need to become closed before it can form a crater, he said.