A study published today in Nature gives what may be the most detailed view so far of the natural plumbing under a volcano.
University of Utah geophysicist Philip Wannamaker and colleagues from three other institutions used electrical and seismic imaging technology to explore Washington state's Mount Rainier, an 14,000-foot-tall active volcano that has erupted numerous times over the past 11,000 years, though the last such event was in 1894.
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The scientists traced the flow of the volcano's supply of semi-molten rock, or magma. They found that it starts 50 miles down in the Earth and ends up in a vast underground reservoir about five miles beneath the surface. From there extends horizontally for as far as 10 miles to the west of Mount Rainier.
Fifty miles down where the flow begins, water and hot rock from the mantle rises up through a rift between two of the plates that form the Earth's crust, one of which is sliding under the other. The magma then rises straight up in a column to the underground reservoir, where it pools until it eventually erupts.