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Magma can survive in Earth’s upper crust for hundreds of millennia, study finds

According to new modeling research from the University of Washington, silica-rich magma reservoirs can exist in the upper crust of Earth for millennia, without causing the violent volcanic eruptions for which this particular type of magma is responsible.  That is good news for geologists monitoring the Yellowstone Caldera, which erupted some 600,000 years ago, as the new modeling suggests that a large reservoir of magma may be bubbling beneath it without coming close to its previous eruption.

According to Sarah Gelman, a University of Washington doctoral student in Earth and space sciences, “You might expect to see a stewing magma chamber for a long period of time and it doesn’t necessarily mean an eruption is imminent.“

Gelman is the lead author of a scholarly paper published in the July edition of Geology, in which she and co-authors Francisco Gutiérrez – a former UW doctoral student with Universidad de Chile in Santiago – and Olivier Bachmann – a former UW faculty member with the Swiss Federal Institute of Technology in Zurich – extrapolated existing models and found that magma may accumulate more slowly and persist longer than was previously thought possible.

Two types of magma exist in the Earth’s crust: plutonic magma and volcanic magma.  Plutonic magma solidifies in the Earth’s crust and never erupts, instead becoming a granite-like formation such as that which is commonly seen in Yosemite National Park.  Volcanic magma is commonly associated with volcanic eruptions, such as those seen on Mount Kilauea and Mount St. Helens.

The recent study suggests that molten magma reservoirs in the crust can persevere for much longer than previously thought. According to Gelman, silica content is a way of ascertaining how the magma has been influenced by being in the crust.  As the magma rises lower in the Earth to the crust, it begins to crystallize.  These crystals then start to deposit into the surrounding rock as the magma rises progressively higher, which gives the molten rock that remains higher silica content.

“If you see melt in an area, it’s important to know how long that melt has been around to determine whether there is eruptive potential or not.  If you image it today, does that mean it could not have been there 300,000 years ago? Previous models have said it couldn’t have been. Our model says it could.  That doesn’t mean it was there, but it could have been there,” Gelman concluded.