Ice cave research finds connection between heat, gas and pressure




Scientist Aaron Curtis descends into Sauna Cave on Mount Erebus. Curtis is conducting an ongoing survey of the dozens of ice caves along the flanks of the volcano. Research on the caves has linked the vents that feed into the subterranean structures to being a major source of carbon dioxide. Photo Credit: Nial Peters

Peter Rejcek, Antarctic Sun Editor: The discovery of a lava lake on Mount Erebus 40 years ago offered a window into the "plumbing" of Antarctica's southernmost active volcano.

It turns out there are scores of peepholes into the volcano's inner workings through the ice caves and towers that form where fissures on the flanks of Mount Erebus vent gas and steam. Recent research into these steam-carved structures has found they are an important source of carbon dioxide gas emissions from the volcano.

"I think there's far more gas coming out of the edifice of Erebus as opposed to coming out of the lava lake than we think," said Aaron Curtis, a PhD student at New Mexico Tech .

Curtis was the lead author on a paper published last year in Geophysical Research Letters that used temperature data in the ice caves as a proxy for how much gas was being emitted from the fumaroles, or fissures, that feed into the caves and towers that dot the upper flanks of Mount Erebus. The research also suggested a link between changes in barometric pressure and temperature - and, consequently, gases like CO2.

"Understanding how gas comes out of the flanks of volcanoes is something that volcanologists, in general, are really interested in lately," Curtis said. In 2006, for example, on the ski resort Mammoth Mountain, three ski patrol members died after they were overcome by toxic fumes after falling through the snow into an ice cave.

Curtis made use of the first-ever temperature measurements on an active volcano using a distributed temperature sensing (DTS) instrument, which records temperature along a fiber optic cable. The temperatures dropped as the barometric pressure rose, and as the pressure dropped, the temperature rose, suggesting barometric pumping of the gas vents.

"These results enable the use of [ice cave] temperature as a proxy for flank degassing rate on Erebus, and represent the first application of DTS for monitoring an active volcano," wrote Curtis and co-author Phil Kyle , principal investigator on the Mount Erebus Volcano Observatory program.

The coupled nature of the heat and gas spewing out of the discrete vents is important for not only understanding how the volcano works, but also improving safety to prevent accidents like the one that occurred on Mammoth Mountain.

"It's important for monitoring the volcano," Curtis said.

The ice caves are networks of passages melted into the base of the snowpack, where geothermal heat and warm gases vent through fumaroles. Fumarolic ice towers reaching up to 10 meters high cover many of the ice cave entrances.

For the last three years, Curtis has spent much of his time on the 3,794-meter-high volcano near McMurdo Station mapping the ice caves and towers. A geographical database -- still a work in progress -- contains about 120 caves that have been visited, maybe half of all that exist on Mount Erebus.

"There are certainly a lot of caves that no one has been in," Curtis said.

His work is the first methodical survey of the ice caves on Erebus, though the unique subterranean system is also drawing interest from biologists who want to study the unique microbial communities that live in these extreme environments. The increased activity has necessitated the creation of a code of conduct to protect the scientific values represented by the caves.

"I was amazed at how little work had been done [on the caves] when I started," Curtis said.

The only previously published work on the ice caves dates back to the 1970s by New Zealand scientist Werner Giggenbach , who explored a site known as the Camp Cave system. Jean Wardell, a former NMT graduate student, more recently worked on gas emissions associated with the caves, through her research focused on degassing at the cave entrances. Camp Cave has since collapsed, according to Curtis.

"I would love to go back to that cave, because it's the only one that anything has been published about before my work and Jean Wardell's work," he said.

Curtis said such collapses appear to be the exception rather than the rule.

"I don't think that [the] caves so much appear or disappear, but they change, and entrances tend to appear and disappear," he explained. "We do see a huge amount of change between field seasons. ... They're very dynamic."

NSF-funded research in this story: Philip Kyle and Clive Oppenheimer, Mexico Institute of Mining and Technology (New Mexico Tech), Award No. 1142083 .

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