Since 2017, Northwest Siberia has experienced 17 ground explosions, resulting in holes that are more than 20 feet across by 65 feet deep and filled with dark, peaty water. Speculation about the cause of these so-called black holes ranges from weapons testing and meteorites to sinkholes. A team lead by the University of Oslo, in Norway, theorized that the holes are craters caused by warming Arctic temperatures, which weaken the frozen soil so much that fossil pockets of gas explode through its surface.

While thawing ice was long suspected as a cause, this theory explains why the holes are found only in specific areas of Russia, over the remains of some of the oldest continental crust found on Earth. In those areas, hot natural gas seeps up through geological faults that had been trapped by sediment caps of old frozen lakes. As the temperatures in Siberia have warmed, these caps are more likely to rupture, causing sudden gas explosions that could have formed the craters.