Glacial pressure likely holding back Alaska eruption | Polarjournal
An arc of ice and fire (Map: Frontiers in Earth Science)

Predicting volcanic eruptions is not a perfect science, but it is a science nonetheless. Improved sensing equipment and a better understanding of how volcanoes work has made volcanic activity if not predictable then at least foreseeable. And it is precisely for that reason that scientists were left scratching their heads when Alaska’s Westdahl Peak did not erupt as expected in 2010. The most probable explanation — the layer of ice that sits atop its peak — may be of interest to anyone who flies. 

Westdahl Peak may be far less known than some of America’s other volcanoes. In part that is because of where it lies; located along the Aleutian Island chain in western Alaska, it is about as remote as a volcano can be in America. Fewer than 500 people live within 100km, according to the USGS, a science agency. But while that means few people would be in immediate danger in the event of an eruption, Westdahl Peak lies on a major transport route between Asia and America. Were it to erupt, the volcanic ash it threw up into into the atmosphere would be a hazard to jet engines, potentially disrupting air travel. The closed airspaces resulting from the 2010 eruption of Iceland’s Eyjafjallajökull is a good example of the sort of chaos that ensues when this happens.

If you were looking to get a better understanding of what makes volcanoes tick and their potential consequences, Westdahl Peak would be a good place to start. In part, this is because the Alaska Volcano Observatory, joint federal and state monitoring programme, keeps a close eye on it with a tight net of sensing devices. The fact that it is overdue for an eruption suggests that, if you look hard enough, you may find something new to report. And, if you do, it will likely help to improve eruption forecasts for the volcanoes like it that lie along other airline routes that passing through the North.

Notyetajökull (Photo: Alaska Volcano Observatory)

Indeed, a paper, published on 29 April by Frontiers in Earth Science, has done just that, and concludes that the reason why Westdahl Peak did not erupt on schedule was, to put it in simple terms, because it could not overcome the weight of the ice that covered its peak. “Volcanic forecasting involves a lot of variables, including the depth and size of a volcano’s magma chamber, the rate at which magma fills that chamber and the strength of the rocks that contain the chamber, to name a few,” the paper’s lead author, Lilian Lucas, of the University of Illinois Urbana-Champaign, said. “Accounting for overlying pressure from polar ice caps is another critical, yet poorly understood, variable.” 

To determine how pressure from polar ice can affect the timing of eruptions, the research team created computer simulations of how various sizes and shapes of magma reservoirs acted on the volcano. Key to their understanding was how the magma that enters the volcano system from below pushes on the surrounding rock. When the pressure of that magma exceeds the strength of the rock, the resulting failure leads to an eruption.

The results of the study suggest that the presence of ice on Westdahal peak increases the stability of the magma system and delays the eruption date by approximately seven years. “More specifically, the models without the presence of the confining pressure off the ice cap calculated a time to eruption of about 93 years. Adding a kilometer-thick ice cap to the model then increases the eruption date to approximately 100 years,” Ms Lucas said.

Previous studies have considered how seasonal changes such as annual snow cover might affect the eruption interval of volcanoes. But, when compared with the total overlying load that the magma chamber must overcome to erupt, the small seasonal variations they cause are unlikely to a role for most volcanoes.

Though Ms Lucas cautioned that the simulated results are not the same as a forecast for when Westdahal Peak finally will erupt, the paper concluded that glacial ice should be considered when making predictions for when it or other volcanoes could erupt. In general, the study results indicated that ice thicknesses of 1 to 3 kilometers can delay eruptions for years to decades. That is insignificant on a geological time scale, but it is potentially relevant for humans, not to mention anyone who flies.

Kevin McGwin, PolarJournal

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