In 2014, a large crater suddenly appeared on the Yamal peninsula in north-west Siberia, sparking a scientific mystery. The 50-metre-deep hole, surrounded by debris, was clearly the result of an explosion. Over the years, several more craters were discovered on the Yamal and nearby Gydan peninsulas, prompting a range of theories from meteor impacts to natural gas explosions.
A new study has now identified the cause. Researchers found that under the seasonally frozen soil lies a thick clay permafrost layer. Between the soil and permafrost are unusual metre-thick ponds of very salty water known as cryopegs. Beneath these are crystallised methane-water solids, kept stable by high pressure and low temperature.
The study, published in Geophysical Research Letters, reveals that warmer temperatures and longer summers have caused the soil layer to defrost more deeply. When the thaw reaches a cryopeg, the pressure from added meltwater forces cracks to open in the soil above. This sudden drop in pressure destabilises the methane hydrate, releasing an explosive bubble of methane gas.
While such explosions are infrequent, they release large amounts of methane, a potent greenhouse gas, and could have a significant warming impact.
