Magma spends most of its existence as sludgy mush

Crystals open window into volcanic depths

8:00am, February 18, 2014

UNDER THE VOLCANO  Mount Hood looms over Oregon’s White River Valley. A study of magma that poured into this valley around 220 years ago shows that the magma spent most of its long existence under the mountain in a cold, semisolid state.

When red-hot magma spews from a volcano, it is clearly flowing like a liquid. But before erupting, that same magma may have spent hundreds of thousands of years in a chunky state resembling cold porridge, a new study finds. The discovery suggests that hot, liquid magma pools may be useful as an indicator of impending eruptions.

Volcanic magma, the molten mix of rock and gas below Earth’s surface, leads a sort of double life: It spends some time as a hot liquid and some as a colder, rocky “crystal mush.” Scientists have long known that magma is mostly liquid only above 750° Celsius, and that in its colder state, it is too viscous to flow.  Whether magma spends much of its existence in the hot, largely liquid state or heats up briefly before erupting has been a mystery.

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