Mount Hood study suggests dormant volcanoes quickly become active

February 18, 2014 – GEOLOGY – New research by UC Davis and Oregon State University may soon lead to new forecasts into how soon volcanoes are ready to erupt. Geologists from both schools, publishing a paper online in the journal Nature, have found that in order for an eruption to occur, molten rock under the volcano must be sufficiently mobile. The evidence comes from a study of Oregon’s 11,249-foot-high Mount Hood. The team found that the magma located roughly three miles beneath the surface of the volcanic mountain has been stored in near-solid conditions for thousands of years. However, they say that it takes just a significantly short period – perhaps as little as a few months – for said magma to liquefy and potentially lead to an eruption. Kari Cooper, lead author and an associate professor in the Department of Earth and Planetary Sciences at UC Davis, said that people typically believe there is a big reservoir of liquid magma under a volcano, but the evidence shows that this is not always true. The study team said that mobility of the magma depends on the amount of crystallization. When it is more than about 50 percent crystalline, it becomes immobile. Crystallization, in turn, depends on the temperature of the rock. If the temperature of the solid rock rises to more than 1,328 degrees F, which can happen when hot magma rises up from deeper within the Earth’s crust, an eruption may be imminent. It is exactly this that occurred in Mount Hood’s last two eruptions – 220 and 1,500 years ago, said USO geologist Adam Kent, coauthor of the paper. “If the temperature of the rock is too cold, the magma is like peanut butter in a refrigerator,” Kent said in a statement. “It just isn’t very mobile. For Mount Hood, the threshold seems to be about 750 degrees (C) – if it warms up just 50 to 75 degrees above that, it greatly increases the viscosity of the magma and makes it easier to mobilize.”

Until this study surfaced, volcanologists have not known how common it is for magma to be crystalline compared to being mobile and eruptible. The new research shows that Mount Hood’s magma is mobile much less than 10 percent of the time. For the study, Cooper, Kent and their colleagues studied rocks ejected from Mount Hood’s previous eruptions. By analyzing the radioactive isotopes and the distribution of trace elements, the team was able to reconstruct the history of the rocks and the conditions they were exposed to before the volcano erupted. The results of their findings could make it much easier for volcanologists to assess when a volcano is ready to blow its top. If eruptible magma is indeed relatively rare, then when it does appear, the risks of an eruption are much higher, Cooper noted. If Mount Hood does become eruptible again, Kent said there is some good news. Past events have shown that the volcano’s eruptions are not particularly violent. Instead of exploding, the magma had oozed out of the peak in previous eruptions. A previous study by Kent and OSU postdoctoral researcher Alison Koleszar found that magma mixing is both a trigger for an eruption and a constraining factor on how violent the eruption will be. “What happens when they mix is what happens when you squeeze a tube of toothpaste in the middle,” said Kent. “A big glob kind of plops out the top, but in the case of Mount Hood – it doesn’t blow the mountain to pieces.” The research team hopes to apply the techniques used in studying Mount Hood with other, larger volcanoes to determine their crystalline behaviors. If the evidence holds true for other volcanoes, then it could lead to better eruption forecasting. –Red Orbit