'MRI' reveals huge magma reserve under Mount Rainier

'MRI' reveals huge magma reserve under Mount Rainier
Map shows, in purple and pink, the west-east line of magnetotelluric sensors that were placed north of Mount Rainier. Photo: R. Shane McGary / Woods Hole Oceanographic Institution
Washington’s famous volcanoes have recently become targets for researchers mapping their inner workings. Mount Rainier was the latest subject.

University of Utah geophysicist Phil Wannamaker, as well as researchers from Massachusetts, New Jersey and Norway, captured detailed images of Rainier’s volcanic plumbing system. The study, published July 16 in the science journal Nature, focuses on the path that a subducting plate takes as it melts and becomes a part of Mount Rainier’s reservoir for eruptions.

This study used seismic imaging and magnetotelluric measurements to show how the rocks and liquids affect electrical and magnetic fields. According to Wannamaker, this is the most detailed image yet of a volcanic system in the Cascade Range.

This image “captures the melting process that feeds magma into a crustal reservoir that eventually is tapped for eruptions,” Wannamaker said in a news release. “But it does not provide any information on the timing of future eruptions from Mount Rainier or other Cascade Range volcanoes.”

The magma reservoir lies five miles underneath Rainier and, according to Wanamaker, appears to be five to 10 miles thick and five to 10 miles wide from east to west. The north-to-south dimensions can’t be determined because the researchers took only a sliced view of the system.

The image also shows that part of the reservoir extends up to 10 miles northwest of Mount Rainier. Wannamaker said this could be a lobe extending from Rainier’s main reservoir.

The new image doesn’t detail the ways in which the magma reservoir is connected to Mount Rainier, but instead shows that molten rock and water are introduced as the oceanic tectonic plate dives underneath the continental plate.

Rainier got a lot of attention from researchers but it isn’t the only Washington mountain to get this type of attention.

Geophysicists from the University of Washington, Rice University and more will be conducting a combined ultrasound and CAT scan of Mount St. Helens’ internal systems next week.

The goal of this research is to help improve early warning systems at volcanoes like Mount St. Helens.