The number of mystery craters appearing in Siberia is growing, prompting a call for investigations over how and why the phenomenon is occurring. 

"I would compare this with mushrooms: when you find one mushroom, be sure there are few more around," professor Vasily Bogoyavlensky, deputy director of the Moscow-based Oil and Gas Research Institute, told the Siberian Times. "I suppose there could be 20 to 30 craters more."

International interest in the craters has grown since the discovery last summer of a massive sinkhole on the Yamal Peninsula in Russia, commonly referred to as the "end of the world." Researchers speculate that the craters may be caused by gas explosions, as residents near one of the new craters said they saw a flash before its appearance. With new satellite photos of the region showing more evidence of the phenomenon, curiosity has given way to concern. 

"Years of experience has shown that gas emissions can cause serious damage to drilling rigs, oil and gas fields and offshore pipelines," Bogoyavlensky said. "Yamal craters are inherently similar to pockmarks. We cannot rule out new gas emissions in the Arctic and in some cases they can ignite."

Some researchers believe the recent unusually warm summers in Siberia are directly responsible for the craters, with thawing permafrost collapsing and releasing dangerous gas. According to Nature, tests conducted last year near the bottom of the Yamal crater showed extremely high concentrations of methane. 

"We need to answer now the basic questions: what areas and under what conditions are the most dangerous?" Bogoyavlensky said. "These questions are important for safe operation of the northern cities and infrastructure of oil and gas complexes."

Video of a November 2014 expedition inside one of the craters is below.