Magma, climbing from beneath the Earth's crust, has been mapped traveling up to the base of Mount Rainier. A second study is examining the volcanic plumbing of Mount Saint Helen's. Those two volcanoes are among the most dangerous in the nation.
An eruption of Mount Rainier could cause glaciers on the mountain to melt. This would possibly trigger massive mudflows, called lahars, that might flood metropolitan areas of Seattle and Tacoma.
As the North American continental plate moves westward, the Juan de Fuca plate, under the Pacific Ocean, is moving beneath the continental plate, in a process called subduction. It is this action which gives rise to the Cascade volcanoes, which include Mount Saint Helens and Rainier.
The Juan de Fuca plate is moisture-rich from its time beneath the water. As it is pressed beneath the North American plate, the rock deforms as the temperature and pressure rises. This releases water from the plate, which begins to rise. This lowers the melting point of the rocks, creating magma.
Magnetic and electrical conductivity changes during the subduction process. In 2006, a team of researchers measured these fluctuations. A seismic study was also undertaken at the same time, allowing investigators the ability to determine the boundary between solid rock and magma.
As hot water rises from the Juan de Fuca plate roughly fifty miles underground, it causes the formation of magma, which travels toward the surface. About 25 miles underground, the mixture is joined by additional water, also squeezed from the rock. This then rises like an elevator shaft, heading to the base of Mount Rainier. Strangely, this shaft is west of the mountain, toward the coast. When it reaches 12 miles beneath the surface, the structure suddenly turns east, toward the volcano.
"I don't think anyone knows why volcanoes don't form directly above [the rising magma], but this seems to be the characteristic of subduction zones," Shane McGary, geophysicist at the College of New Jersey, told the press.
Investigation of Mount Saint Helens will involve setting off small explosions around the mountain, in order to study the seismic waves the blasts produce. Researchers say these vibrations will not be as strong as earthquakes that regularly happen at the mountain, and pose no risk of triggering an eruption.
"This will tell us where the pathways of the magma are, and the geologic structures through which they're moving," said director John Vidale, from the University of Washington.
Mapping paths taken by magma through volcanoes could help researchers predict eruptions with a greater degree of accuracy.
Volcanic mapping of Mount Rainier was detailed in the journal Nature.