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.

Wannamaker cautioned in a press release that the data won’t enable scientists to predict when Mount Rainier will erupt again. But gaining knowledge about the inner workings of a volcano conceivably might contribute someday to the development of such a warning system.

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The scientists’ equipment included a device that uses sound-wave tomography, in a fashion similar to how medical centers use CT scans to see the inside of the body. They also used equipment that maps rock and fluids in the earth by utilizing their varying ability to conduct magnetic fields and electricity.

Meanwhile, Nature reports that in another research project, a different team of scientists is probing the underground network beneath Mount St. Helens, whose May 1980 eruption killed 57 people and blanketed much of the western United States in ash.