Glaciers and volcanoes combine to release large amounts of methane

Volcanoes and glaciers can combine to form a surprisingly robust source of methane, a powerful greenhouse gas.

New analysis of the Sólheimajökull glacier, a volcanic glacier in Iceland, suggests methane production is fueled by the unique combination of wet, low oxygen conditions and geothermal warmth found where ice and volcano meet.

"Sólheimajökull glacier is frequently visited by tourists and is renowned as a rather smelly, gassy place, with the distinctive eggy whiff of hydrogen sulphide in the air for much of the year," Hugh Tuffen, a volcanologist at Lancaster University, told UPI in an email.

Ten years ago, Lancaster geochemist Peter Wynn began visiting Sólheimajökull to investigate the gassy volcanic glacier. His efforts were aided by Rebecca Burns, who -- as part of her PhD work -- measured remarkably high concentrations of dissolved methane in Sólheimajökull's meltwater.

"That was when we realised something very interesting is going on," Tuffen said.

Follow-up investigations revealed Sólheimajökull's main meltwater river releases approximately 41 metric tons of methane every day during the summer months. That's the equivalent of 136,000 flatulent cows. For some perspective, there are 1.9 million dairy cows living in the United Kingdom.

Volcanoes are known to produce significant amounts of methane and CO2 on their own, but Tuffen and his colleagues determined the methane being released by Sólheimajökull's meltwater isn't directly produced by Katla, the volcano that lies beneath.

"The carbon and hydrogen isotopes in the methane tell us that the gas was generated by microbes, rather than coming straight from underground magma," Peter Wynn told UPI. "These microbes live in the wet, low oxygen sediments underneath the glacier and give off methane in a similar way to how yeast gives off carbon dioxide."

Researchers collected sediments from beneath the glacier and watched in the lab as microbes living in the sediment samples produce significant amounts of methane.

"Other researchers have shown that microbes make methane much more rapidly when they are warm, and so we suspect that the geothermal heat from Katla volcano, hidden beneath the ice, is accelerating the methane production," Wynn said.

The lack of oxygen is an important part of the unique methane factor found beneath Sólheimajökull. When oxygen is present, methane is easily converted into CO2. But very little oxygen is able to penetrate beneath the layers of glacial ice, allowing methane to become dissolved in the glacier's meltwater and drained before eventually bubbling out into the atmosphere.

Researchers found the glacier's methane emissions fluctuate with the seasons.

"In winter it's mostly trapped beneath the ice in isolated cavities, but in the summer there's a lot more meltwater around, these cavities connect, and the methane-rich water is quickly discharged to the glacier snout before the methane can all be converted to CO2," Tuffen said.

The new research, published Tuesday in the journal Scientific Reports, suggests volcanic glaciers could be responsible for an under appreciated source of greenhouse gases.

"The amount of methane emitted from Sólheimajökull during the summer months is more than all known methane emissions from European volcanoes put together, and 15 percent of estimates of the combined total of European volcanic and geothermal emissions," Wynn said. "We have increasing evidence for large zones of geothermal heat beneath the world's biggest ice sheets in Antarctica and Greenland, so there could be a large amount of methane being produced there."

And while Sólheimajökull is producing prodigious amounts of methane, new research suggests the volcano beneath is releasing significant quantities of CO2 into the atmosphere.

"Katla has just been discovered to be a huge emitter of CO2 -- it's number three on the league table of volcanoes globally," Tuffen said.

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