Huge, mysterious gaping holes in Northern Siberia may not be such a mystery anymore. One scientist has pinned down a cause and, spoiler alert, it’s not aliens or weapons testing, as had been theorized.

The first hole discovered in the Yamal Peninsula, which is 260 feet wide, is likely a sinkhole caused by melting ice or permafrost, University of Alaska geophysicist Vladimir Romanovsky tells LiveScience.

Plants around the crater suggests the hole is several years old, but closer inspection is needed to determine the exact age. Romanovsky thinks climate change played a role, which means “we will probably see this happen more often now,” he says.

But questions remain, notes LiveScience: Where did the natural gas come from, and why is the hole so even and round? (Click to read about a burning crater that’s been on fire for more than 40 years.)