A trio of mysterious gaping holes in northern Siberia has spawned many theories about the craters' origin, but scientists have suggested some concrete explanations.
In mid-July, reindeer herders stumbled across a crater that was approximately 260 feet (80 meters) wide, on the Yamal Peninsula, whose name means "end of the world," The Siberian Times reported. Since then, two new chasms — a 50-foot (15 m) crater in the Taz district and a 200- to 330-foot (60 to 100 m) crater in the Taymyr Peninsula — have also been reported.
Neither aliens nor meteorites caused the strange cavities, as some had speculated, but the true explanation could be exciting nonetheless. Russian scientists have launched an investigation to find out more. [How Weird! The Top 10 Unexplained Phenomena]
Helicopter video footage of the first hole shows it is surrounded by a mound of loose dirt that appears to have been thrown out of the hole.
"My personal opinion is it's some type of sinkhole," said Vladimir Romanovsky, a geophysicist who studies permafrost at the University of Alaska Fairbanks. Sinkholes are pits in the ground formed when water fails to drain away.
The water likely came from melting permafrost or ice, said Romanovsky, who has spoken with the Russian scientists investigating the site. But whereas most sinkholes suck collapsed material inside, "this one actually erupted outside," he told Live Science. "It's not even in the literature. It's pretty new what we're dealing with," he added.
Early on, polar scientist Chris Fogwill of the University of New South Wales, in Australia, suggested the first hole was created by the collapse of a pingo, a large, earth-covered mound of ice that usually forms in Arctic and subarctic regions.
Kenji Yoshikawa, an environmental scientist also at the University of Alaska Fairbanks, said he also thinks that a drained, collapsed pingo pond is the most likely explanation for the Yamal Peninsula pit. In Alaska, similar pingos exist in the Northern Seward Peninsula and near the city of Nuiqsut.