One of Iceland’s largest and most active volcanoes sits below a massive ice cap covering nearly 595 square kilometers (230 square miles) of the Nordic nation. Though a seemingly unlikely duo of fire and ice, new research published in Scientific Reports suggests the two make a rather dynamic methane-producing team.

Descending from the Mýrdalsjökull ice cap, we find an 8-kilometer-long (5-mile) outlet glacier called Sólheimajökull that flows from the nearby ice-covered Katla volcano. Here, geothermal activity creates an ideal environment for the growth of microbes that remain locked in by the glacier during the colder months but is released when the ice melts in the summertime. With the release comes the greenhouse gas methane in enormous amounts – up to 41 tonnes of methane every day, or the equivalent of more than 136,000 belching cows.

"This is a huge amount of methane lost from the glacial meltwater stream into the atmosphere," said biochemist and study author Peter Wynn in a statement, adding that methane has a global warming potential of 28 times that of carbon dioxide. "It greatly exceeds average methane loss from non-glacial rivers to the atmosphere reported in the scientific literature. It rivals some of the world's most methane-producing wetlands, and represents more than twenty times the known methane emissions of all Europe's other volcanoes put together."

To measure the release of methane, the team took samples from the edge of a meltwater lake in front of the glacier during the summer between 2013 and 2017 and compared these levels to those in sediments and other rivers in the area. They found that the greatest concentrations of methane occur where the river upwells from below the glacier and flows into the lake. Normally, methane converts to carbon dioxide when it comes into contact with oxygen, but in Sólheimajökull’s glacial environment, meltwater comes into contact with gases produced by the volcano. This can lower the oxygen content of the water, dissolving some of the methane into the river water and then transporting the gas out into the environment.

Together, the results present the “strongest evidence yet” that glaciers release methane.

"There has been a lot of speculation about whether or not glaciers can release methane. The beds of glaciers contain the perfect cocktail of conditions for methane production – microbes, low oxygen, organic matter, and water – along with an impermeable cap of ice on the surface trapping the methane beneath,” explained Wynn.

Like Iceland, Antarctica also has active geothermal systems and volcanoes. The authors note that understanding how methane is produced under ice caps will help further inform climate change models and emissions predictions, particularly as glaciers and ice sheets are “rarely accounted for as methane contributors.”