Volcano under Antarctic ice sheet

Volcano under Antarctic ice may erupt, accelerate melting

NBC,

17 November, 2013

A newly discovered volcano rumbling beneath nearly a mile of ice in Antarctica will almost certainly erupt at some point in the future, according to a new study. Such an event could accelerate the flow of ice into the sea and push up the already rising global sea levels.

When the volcano will blow is unknown, "but it is quite likely" to happen, Amanda Lough, a graduate student in seismology at Washington University in St. Louis, Mo., told NBC News. 

"At some point, it is going to erupt," she said. "Is it going to erupt in any of our lifetimes? That is not something that we can pinpoint."

And when it does erupt, she added, "there would be an increase in melting around the area. … You would add water to the system beneath the ice sheet … and that could cause that ice stream to speed up."

In other words, global warming likely isn't the only factor causing sea levels to rise, and the discovery of a subglacial volcano adds another layer of complexity for scientists trying to model how polar ice sheets move as the world gets warmer. But what overall impact this might have on global sea levels is unknown — and up for debate.

"The implication of large amounts of under-ice water accelerating ice flow, ice discharge and, thus, raising sea levels is 'permissible,' but remains highly speculative," Robert Bindschadler, an expert on glacial ice dynamics and emeritus NASA scientist now living in Quilcene, Wash., told NBC News in an email. "The actual processes involved are still very much topics of research."

Bindschadler was not involved in the new research, which Lough and colleagues discuss in a paper published Sunday in the journal Nature Geoscience. 

Surprise discovery
Hints of the unnamed volcano's existence first appeared in seismic data collected by an array of instruments strung across the West Antarctic Ice Sheet. Lough's job was to analyze the data for earthquakes. "I found this grouping of events that kept being located at the same location over and over again," she said. "And when you see something like that, you want to go see what is causing it."

She typed the quakes' location into Google Earth to look for any features that could explain the shaking. She saw a group of nearby mountains, but ruled them out as the source since they were not an exact match. But as more and more earthquakes popped up in the seismic data, her team revisited the mountains.

"We realized they are actually a chain of volcanoes that date younger as they go south and the earthquakes were south of the volcanoes," Lough said. A subsequent examination of the bedrock topography made with airborne radar revealed a slight rise above the source of the weak, low-frequency quakes.

Intrigued, Lough shipped her seismic data off to a volcano seismologist who said the signature was consistent with a type of earthquake caused by magma coursing through the Earth's crust. Though these quakes could also be caused by the movement of glacial ice, they occurred between 15 and 25 miles beneath the surface of the ice, much too deep to be related to the pile of ice not quite one mile thick.

The final clue came from a distinct layer of ash dated to about 8,000 years ago in the vicinity of the earthquake cluster. At first, Lough said, she and her colleagues thought it was from an earlier eruption of the suspected volcano, though they later concluded it was more likely from Mount Waesche, a known existing nearby volcano that, in geological terms, erupted recently.

"All of the lines of evidence just fell together nicely," Lough said. The clusters of earthquakes "are indicative of magma movement in the crust and that this area is still quite active."

Eruption consequences uncertain
The earthquakes, Lough noted, are "not necessarily a precursor" to an imminent eruption. "Any volcano that is still not extinct, that still has an active magma chamber, is going to be showing seismicity whenever you have the magma moving around in the crust."

Given the nearly mile-thick pile of ice covering the volcano, any eruption anytime soon would unlikely vent to the surface, according to Lough. Rather, the heat from the eruption would melt the surrounding ice, which would lubricate the flow of the overlying ice sheet. 

"All of these processes could lead to accelerating ice mass loss in West Antarctica," John Behrendt, a geophysicist at the University of Colorado's Institute of Arctic and Alpine Research, wrote in an accompanying article in Nature Geoscience.

Whether that will happen, Bindschadler noted, is debatable. 

"In my opinion, it boils down to whether the excess water would flow under the ice as a sheet or within a more confined channel," he said, adding that sub-glacial water flow typically evolves from sheets to channels. "I think, in this volcanic case, the water would start local and form a channel to get to the ocean. This would produce a minimal change to the ice sheet dynamics."

Bindschadler cautioned, however, that this is just his "reading of the tea leaves." 

So little is known about the bottom of the West Antarctic Ice Sheet that models of ice motion over it are unable to reliably predict what to expect from a subglacial eruption, noted Slawek Tulaczyk, a glaciologist at the University of California, Santa Cruz.

However, the new paper, he added in an email to NBC News sent from Antarctica, "serves as an important reminder that, in addition to climate changes, one-off events such as volcanic eruptions or subglacial lake floods may influence the rate at which Antarctica looses ice to the ocean."