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Quack Chats explores the insides of the world’s great volcanoes

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Posted May 20, 2019

Most people know what the outside of a volcano looks like, but not many can describe what they’re like on the inside.

That’s something that has captivated Emilie Hooft, a physicist-turned-geologist who uses seismic imaging techniques to map the deep system of pathways that transport magma to the earth’s surface.

The magma storage region beneath Greece’s Santorini islands and caldera system can be seen in red in this digital model. The yellow star represents a small amount of magma that was added during a period of volcano inflation in 2011-12. Image credit: University of Oregon

The magma storage region beneath Greece’s Santorini islands and caldera system can be seen in red in this digital model. The yellow star represents a small amount of magma that was added during a period of volcano inflation in 2011-12. Image credit: University of Oregon

“What exactly does the plumbing system beneath a volcano look like?” Hooft wonders. “How are things organized underground? Is it a big vat? A flat thing? A long column? A bunch of layers of magma sills? To some extent that’s all up for grabs. It used to be that people thought there were big magma chambers under volcanoes, but it turns out they are often quite small.”

In her talk, Hooft will detail her cutting-edge research techniques — which she likens to a CAT scan for volcanoes — and zero in on two recent projects: one involving seismic instruments set on land around Central Oregon’s Newberry Volcano and one requiring a floating research vessel and underwater seismometers on the floor of the Aegean Sea covering Greece’s Santorini volcano.

Hooft has studied all kinds of volcanoes — everything from arc volcanoes like the ones in the Oregon Cascades to midocean ridges where volcanic melt is rising to fill a gap to deep mantle plumes like the volcanoes of Hawaii or Iceland. She likes to say, simply, that she studies volcanoes and she uses physics to do so.

The seismic techniques Hooft employs do require a firm understanding of physical properties. By sending sound waves into the earth and measuring their rate of travel, she is able to turn sound into visuals. If the rocks are hot, or broken, sound travels more slowly and vice versa.

She captures that data, interprets its meaning and creates three-dimensional models of the nooks and crannies in the subsurface, sometimes with the aid of digital artists.

The techniques also differ widely, depending on the volcano. In the case of the Newberry volcano, she relied on almost a hundred instruments set in 300- and 800-meter increments across the land to record one explosive charge. In Santorini, her team submerged 90 instruments on the seafloor and, as a sound source, used massive compressors on the National Science Foundation’s largest and most advanced research vessel.

“The value of the research is that you can better understand, from a societal or hazards point of view, what’s there underground,” Hooft said. “If you have more information about what’s underground you can try to predict what might happen when the volcano becomes restless.”

Additionally, the research helps scientists better understand how the earth functions, how big magma systems assemble themselves, and how they reset and regrow after major volcanic episodes.

“These volcanoes are where most of the continental crust is actually cooked and made,” Hooft said. “But even as scientists are getting a better idea of the chemical steps that form the continental crust, we still don’t really know in what kinds of vessels these reactions are happening.”

Source: University of Oregon

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