Researchers at a pair of Western US universities report they have uncovered a key factor in predicting volcanic eruptions.
Geologists from the University of California-Davis and Oregon State University have found that in order for a volcanic eruption to occur, molten rock under the volcano must be sufficiently mobile. This occurs when the temperature of rock below the volcano rises to more than 1,328 degrees Fahrenheit.
“The team found that the magma located roughly three miles beneath the surface of Mount Hood has been stored in near-solid conditions for thousands of years,” according to RedOrbit. “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.”
The belief that there is a big reservoir of liquid magma under an active volcano is not always true, said Kari Cooper, lead author and an associate professor at UC Davis.
“The study team said that mobility of the magma depends on the amount of crystallization,” according to RedOrbit. “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,” the online publication added.
“If the temperature of the rock is too cold, the magma is like peanut butter in a refrigerator,” Oregon State University professor Adam Kent said in a statement. “It just isn’t very mobile. For Mount Hood, the threshold seems to be about 750 degrees (C) [1,328 Fahrenheit] – 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.”
Mount Hood has had at least four major eruptive periods during the past 15,000 years. The last three occurred within the past 1,800 years. The last of these took place around 170-220 years ago, shortly before the arrival of the Lewis and Clark Expedition in 1805, according to the website www.mounthoodhistory.com.
For the study, researchers 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, according to RedOrbit.
The results of their findings could make it much easier for volcanologists to assess when a volcano is ready to explode. If eruptible magma is indeed relatively rare, then when it does appear, the risks of an eruption are much higher, Cooper noted.
(Top: Oregon’s Mount Hood, part of the Cascade Range.)