Magma sitting 2-3 miles under the surface of Oregon's Mount Hood has been stored in "near-solid conditions" for thousands of years, but the time it takes to liquefy and eventually erupt can take place in just a month or two. according to a study published in the journal Nature.

The detection of large quantities of liquid magma in a volcano mean eruption is likely "imminent," according to one of the co-authors of the study, Dr. Adam Kent, of Oregon University.

"Until now, people monitor volcanoes looking for changes in the temperature of gases or water, and the number of earthquakes, to indicate the magma is ready to erupt," said Kent, according an Oregon State University press release. "Our work gives some extra insight into how to interoperate results from geophysical and seismic studies which identify large bodies of liquid magma."

Kent, along with co-author Dr. Karl Cooper, of the University of California, based their conclusion on a study of the thermal history at the magma reservoir of Mount Hood, an active volcano in Oregon's Cascade Mountains, according to the press release.

"We've been trying to understand how hot magma is when it's stored," said Kent. "Magma needs to be at temperatures of over 750°C to have sufficiently low viscosity to erupt."

The study is important since the conditions which magma is stored has an influence over the process that eventually leads to volcanic eruptions.

The researchers studied solidified magma from two Mount Hood eruptions, an event known as Old Maid which occurred 220 years ago, and one known as the Timberline eruption, which took place 1500 years ago, according to the press release.

"Most volcanoes aren't erupting all the time, many have magma or the cooled remains of magma, stored underground for long periods, sometimes hundreds of thousands of years," said Kent. "At Mount Hood you have cool and rigid magma about five kilometres below the volcano. All of a sudden some new, hotter magma rises and mixes with it, heating the whole thing up, making it easier to move up fractures to the surface."

By using radioactive decay dating techniques, the researchers figured out that the crystals that erupted in the Mount Hood magma were approximately 100,000 years old, according to the press release.

Kent and Cooper were able to decide how long the crystals were growing based on the size of the crystals and known growth rates.

"We've done a little preliminary work by looking at data from other volcanoes, and it looks like the pattern is pretty common, so we can infer that other volcanoes work in a similar way most of the time," said Kent.

Research was funded by the National Science Foundation.

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