Europe’s largest meteorite impact crater is pumping out methane and nobody knows why

New research in Sweden has uncovered perplexingly high methane emissions coming from the largest meteorite crater in Europe.

The Siljan Ring is a prehistoric impact structure in central Sweden that measures around 52 km in diameter. There are several lakes in the region, the largest of which is Siljan on the southwestern edge.

Every winter, thick ice forms over Lake Siljan - except in a few strange, recurring spots. These open patches, known as "ice wakes," baffled locals for years. Why did they always appear in the same places? What kept these holes free of ice, even in bitter cold?

Now a new study by scientists at Sweden’s Chalmers University of Technology has found that these open spots are releasing astonishingly high levels of methane.

“The natural methane emissions from the Siljan Ring lakes appear to be far more extensive than previously known,” explains Johan Mellqvist, professor of optical remote sensing at the university. “At certain sites, we recorded emission rates up to 300 times higher than what is typically seen in lakes.”

The decay of organic matter underwater produces methane in all water bodies. What’s unusual about the situation at Siljan is the highly concentrated nature of the emissions discovered.

Usually, methane in lakes occurs as ‘bubble emissions,’ scattered leaks that pop up here and there on the surface. However, the results from Siljan suggest much stronger and localised leaks, forming detectable gas plumes in the air.

"It's unusual—and quite strange—that the emissions were so extremely localised,” says Mellqvist. “To our knowledge, this kind of tightly concentrated methane leak has never been measured in a lake before. And we've only examined a small part of the Siljan Ring lakes so far. It's