Right before a volcano erupts, molten rock, known as magma, is moving around underneath the surface. New research suggests this liquid magma is very rare. That’s an important finding for researchers trying to predict when a volcano may erupt.
Geologists from University of Califonia, Davis, and Oregon State University studied Mount Hood and have found that magma is often too cold to move around so much. And cold, here, is a relative term.
"We can tell it was below about 750 degrees Celsius, so it's still pretty hot. You wouldn't touch it," said Adam Kent, co-author of the study.
So, why is the temperature of magma important? If it’s cold, the magma is immobile. And if it’s immobile, that means a volcanic eruption is not likely to happen right away. The time it takes to liquefy and potentially erupt is perhaps as little as a couple of months, according to the report.
"[Magma] is like peanut butter or honey. If you warm it up, it becomes much runnier and easier to spread on your toast. If it's cold, like if you put your peanut butter in the fridge, it gets really hard to spread. So the analogy with magma is: if it's hot, it's easy to mobilize. And that means it's easy to bring up to the Earth's surface, which is what you need for an eruption," Kent said.
Until now, researchers didn’t know how often magma is in the immobile, or cold, state. Oregon State University’s Kent said magma moves around under Mount Hood's surface less than 10 percent of the time over thousands of years.
Knowing how often magma turns to liquid can help researchers predict how close a volcano is to erupting.
“And so if then you were able to image a magma chamber that had a lot that was hot and in this eruptible state, the inference is that maybe an eruption is going to happen sooner rather than later,” Kent said.
Magma is about 3 miles below Mount Hood, Kent said. The last time it erupted was about 220 years ago, when Lewis and Clark noted some of the eruption's effects.
Kent said magma under other volcanoes may be similar to the Mount Hood study. The study was funded by the National Science Foundation and published in the journal Nature.