Eight giant craters with a depth of about 50 meters were discovered in Siberia. Scientists claim to have found a plausible explanation for their formation - but it is very worrying.
Methane warms over time, causing the frozen layer to thaw from below, while climate change thaws it from above. In places where the permafrost layer has become very thin, the accumulated gas pressure at its base can trigger a sudden collapse. This "champagne effect" can cause clods of soil to "explode", leaving behind huge holes.