So far, only eight craters have been documented since 2014, but each one has stunned scientists and locals with its scale and geological drama. Some explanations suggested warming permafrost was to blame – including the growth of liquid salt water pockets called cryopegs, which can expand and create cavities or gas-filled chambers. The Yamal and Gydan peninsulas sit on vast gas reserves – with fault lines running through the rock below. The scientists argue that these fault lines allow for gas and heat to move up from below the permafrost. Where these fault lines intersect with lakes and rivers, the thick frozen ground is thinned by taliks, or areas of year-round unfrozen soil.