Geophysicists say a network of electrical sensors is giving them a picture of the deep underground volcanic plumbing containing molten rock under some of North America's most active and dangerous volcanoes.
The network, acting like a giant metal detector, has helped in understanding the process that brings magma from as deep as 50 miles below the earth to volcanoes such as Mount Rainier in Washington state, the scientists reported.
Such findings could help improve early warnings of possible eruptions, they say.
Mount Rainier and Mount St. Helens, the Northwest's most active volcano and also located in Washington, are among scores in the Cascade Range, stretching down the West Coast of North America from British Columbia in Canada to Northern California. Mount St. Helens erupted in May 1980, killing more than 50 people and spreading ash across 11 states.
As part of a study reported in the journal Nature, researchers presented a detailed picture of the magma pipes and chambers under the active Mount Rainier.
The majority of the volcano's molten magma forms deep in the Earth's mantle, then a gigantic column of it rises approximately straight up and aimed at the surface, collecting in a magma reservoir underneath the volcano's 14,000-foot peak, the researchers found.
The network of sensors helped settle the question of whether the melted magma "goes up through a network of cracks, or whether it gets dragged up in little bits, or rises in diapirs," says lead study author R. Shane McGary from the Woods Hole Oceanographic Institute.
Diapirs, the geophysicist explained, are "just like what you would see in a lava lamp: a blob that gets heated up and rises."
Mount Rainier is on top of an impressively massive "chimney" of melted magma, the researchers said, a configuration not seen on some other adjacent volcanoes in Oregon.
That's evidence that even volcanoes that are close neighbors can possess different dynamics driving potential eruptions, they said.
"I would regard Mount Rainier as a much more serious short-term threat than Mount Jefferson in Oregon, which lacks a flow path," McGary said, although he added that eruptions are not seen as imminent.
The sensor network under Mount Rainier can map the underground movements and positions of magma by monitoring fluctuations in electric and magnetic conductivity caused by changes in underground geologic structures, the researchers said.
Molten rock shows up especially well using such sensors, McGary said, suggesting similar studies at other West Coast volcanoes could yield vital information.
"I would be really interested in seeing what Mount St. Helens looks like using this technique," McGary said.
