As the weight of melting ice is lifted off volcanos, eruptions will become more common and more violent, according to a new study of volcanos in Chile’s Patagonia region, reports the Smithsonian magazine.

Since the start of the century, the world’s glaciers have lost some 5% of their collective mass. That is equivalent to about 8,500 gigatonnes, (8.5 quadrillion kilograms, or 8.5 x 10¹⁵ kg) based on United Nations’ Intergovernmental Panel on Climate Change (IPCC) estimates of glacier mass.

That is the same as a third of all the water in Lake Baikal, the biggest lake in the world, twice the volume of Lake Michigan and 95 times that of Lake Geneva. That amount of ice is very heavy indeed. So heavy that it puts enough pressure on volcanos to prevent them erupting. Now the ice is gone, that snowy cap on volcanos is disappearing too.

Scientists from the University of Wisconsin-Madison, Dickinson College and the University of La Frontera presented their findings on July 8 at the Goldschmidt Conference on geochemistry in Prague. The study shows that as glacial ice melts, the immense weight it once exerted on tectonic plates is reduced, which in turn decreases the pressure on magma chambers beneath the Earth's surface and makes eruptions more likely.

“When you take the load off, it’s just like opening a Coca-Cola bottle or a champagne bottle,” said Brad Singer, geoscientist at the University of Wisconsin-Madison, in comments to Inside Climate News. “It’s under pressure, and the dissolved gasses in the melt come out as bubbles.”

The team focused its research on six volcanoes in Chile’s Patagonia region, including Mocho-Choshuenco, using argon dating and crystal analysis. During the last Ice Age, between 26,000 and 18,000 years ago, glaciers in the area formed a reservoir of magma ten miles underground. As the ice sheet retreated, pressure was released, and the compound stratovolcano system took shape.

“Glaciers tend to suppress the volume of eruptions from the volcanoes beneath them. But as glaciers retreat due to climate change, our findings suggest these volcanoes go on to erupt more frequently and more explosively,” said Pablo Moreno Yaeger, a graduate student at the University of Wisconsin-Madison who presented the research.

The study draws parallels with Iceland, where volcanic eruptions increased up to 50-fold after the last Ice Age. Scientists warn that similar dynamics may now be unfolding in other glaciated volcanic regions.

All eyes are now on Antarctica, where over 100 active volcanoes lie beneath the West Antarctic Ice Sheet. A 2023 study in Nature Climate Change predicted that this ice sheet is on track to melt significantly by the end of the century, even under aggressive emission reductions. A surge in volcanic activity could release heat and greenhouse gases, further accelerating ice loss and contributing to a global feedback loop.

The researchers note that the implications extend far beyond the Southern Hemisphere. A 2020 paper in Global and Planetary Change found that 245 active volcanoes worldwide are within five kilometres of ice. Further research published in Communications Earth & Environment last November indicated that glaciers near volcanoes are retreating 46% faster on average than those located farther away.

“Other continental regions, like parts of North America, New Zealand and Russia, also now warrant closer scientific attention,” Yaeger said.