MOSCOW — A natural phenomenon first observed by scientists just six years ago and now recurring with alarming frequency in Siberia is causing the ground to explode spontaneously and with tremendous force, leaving craters up to 100 feet deep.
When Yevgeny Chuvilin, a Moscow-based geologist with the Skolkovo Institute of Science and Technology, arrived this summer at the rim of the latest blast site, called Crater 17, “it left quite an impression,” he said.
The pit plunged into darkness, surrounded by the table-flat, featureless tundra. As Mr. Chuvilin stood looking in, he said, slabs of dirt and ice occasionally peeled off the permafrost of the crater wall and tumbled in.
“It was making noises. It was like something alive,” Mr. Chuvilin said.
While initially a mystery, scientists have established that the craters appearing in the far north of western Siberia are caused by subterranean gases, and the recent flurry of explosions is possibly related to global warming, Mr. Chuvilin said.
Mr. Chuvilin said the conditions causing the explosions, which are still not fully understood, are probably specific to the geology of the area, as similar craters have not appeared elsewhere in Siberia or in permafrost zones in Canada and Alaska that are also affected by global warming.
The explosions occur underneath small hills or hummocks on the tundra where gas from decaying organic matter is trapped underground.
Contained beneath a layer of ice above and permafrost all around, the gas creates pressure that elevates the overlying soil. The explosions occur when the pressure rises or the ice layer thaws and breaks suddenly.
Where the gas comes from is a matter of debate, said Mr. Chuvilin, one of Russia’s leading experts on permafrost, the jumbled layer of soil, ice, prehistoric plants and the occasional frozen mammoth that covers 67 percent of Russia’s land surface. Permafrost also extends under the Arctic Ocean in some place.
“In Russia, we have a lot of experience studying permafrost,” said Mr. Chuvilin, who graduated from the Department of Permafrost at Moscow State University, one of the few universities to have such a specialty.
From this icebox of the Arctic, bits or even whole frozen mammoths, musk ox, woolly rhinoceroses, prehistoric horses, wolves and other ancient beasts wash out from the banks of rivers. But Mr. Chuvilin said he found no animal parts in the debris field of frozen mud the explosions threw out.
The strata of perpetually frozen soil are usually a few hundreds of yards deep, but they go down almost a mile in some places in Siberia. Each summer, a portion near the surface, known as the active layer, thaws.
With warmer summers, the active layer is deepening, potentially melting and weakening the ice over the gas deposits.
The gases causing the explosions, said Mr. Chuvilin, may have built up to their current pressure tens or hundreds of thousands of years ago as the organic components of the permafrost partially decayed, before freezing.
Another possibility is that methane trapped in deeper layers of the permafrost in a crystalline, ice-like form known as methane hydrates is reverting to its gaseous state, possibly because of effects of global warming. In this theory, rising pressure rather than thawing on the surface is causing the gas pockets to burst.
“It goes off like a bottle of champagne,” Mr. Chuvilin said.
The most recent to blow, at Crater 17 site on the Yamal Peninsula, was one of the more dramatic.
A reindeer herder was near enough to hear the blast but was unhurt. The Russian scientific expedition arrived by helicopter about a month later, in August. The crater was at least 100 feet deep.
Though the Russian government is encouraging oil, natural gas and mining ventures in the far north, the area is still too sparsely populated for the explosions to pose much risk, Mr. Chuvilin said.
Reindeer herder communities had passed along tales of such eruptions before 2014, said Mr. Chuvilin, but Soviet and later Russian scientists had not documented any instances in earlier years. They have likely been rare occurrences until recently. Global warming is heating the Arctic faster than the rest of Earth.
“The permafrost is actually not very permanent, and it never was,” Mr. Chuvilin said.
Within a year or two of erupting, the craters fill with water and appear no more suspicious than small lakes.