Molten magma can survive in Earth`s upper crust for hundreds of millennia
Washington: Silica-rich magma reservoirs can persist in Earth`s upper crust for hundreds of thousands of years without causing an eruption, according to a new research.
The new University of Washington modeling research shows that an area known to have experienced a massive volcanic eruption in the past, like Yellowstone National Park, could have a large pool of magma festering beneath it and still not be close to going off as it did 600,000 years ago.
Recent research models have suggested that reservoirs of silica-rich magma, or molten rock, form on and survive for geologically short time scales - in the tens of thousands of years - in the Earth`s cold upper crust before they solidify.
They also suggested that the magma had to be injected into the Earth`s crust at a high rate to reach a large enough volume and pressure to cause an eruption.
But Sarah Gelman, a UW doctoral student in Earth and space sciences and her collaborators took the models further, incorporating changes in the crystallization behavior of silica-rich magma in the upper crust and temperature-dependent heat conductivity.
They found that the magma could accumulate more slowly and remain molten for a much longer period than the models previously suggested.
There are two different kinds of magma and their relationship to one another is unclear. Plutonic magma freezes in the Earth`s crust and never erupts, but rather becomes a craggy granite formation like those commonly seen in Yosemite National Park.
Volcanic magma is associated with eruptions, whether continuous "oozing" types of eruption such as Hawaii`s Kilauea Volcano or more explosive eruptions such as Mount Pinatubo in the Philippines or Mount St. Helens in Washington state.
The new work suggests that molten magma reservoirs in the crust can persist for far longer than some scientists believe. Silica content is a way of judging how the magma has been affected by being in the crust, Gelman said. As the magma is forced up a column from lower in the Earth to the crust, it begins to crystallize.
Crystals start to drop out as the magma moves higher, leaving the remaining molten rock with higher silica content.
Gelman said that even if the molten magma begins to solidify before it erupts it is still a long process.
As the magma cools, more crystals form giving the rock a kind of mushy consistency. It is still molten and capable of erupting, but it will behave differently than magma that is much hotter and has fewer crystals.
The research has been published in Geology.
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