New View on Volcanic Plumbing Systems

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Researchers from three universities say massive features such as Yosemite’s El Capitan form as part of a ‘reverse energy cascade’ that traps rising magma in the crust. To mountaineer Alex Honnold, El Capitan was something to be climbed without safety gear last month.

To UO geologist Leif Karlstrom, the giant, rocky landmark at California’s Yosemite National Park is like an airliner’s black box, filled with data about magma trapped in the Earth’s crust.

“You have magma that is generated deep in the earth and somehow it gets to the surface carrying heat and volatiles, such as carbon dioxide. How that happens is through the crustal magma transport system,” said Karlstrom, a professor in the Department of Earth Sciences and a member of the UO’s volcanology cluster.

Most of the magma, from 50 to 90 percent, never breaches the surface.

In a new paper, Karlstrom and colleagues suggest that structures such as El Capitan contain the historical record — dating to tens to hundreds of millions of years ago — that doesn’t explode as Mount St. Helens did in 1980.

Such structures are called magmatic intrusions. They form and grow gradually from small pulses of magma that cool and crystalize some 3 to 12 miles underground. Those seen today have been uplifted and exposed by erosion.

The research, which was supported by three National Science Foundation grants, published online July 10 by the journal Nature Geoscience. It provides a new framework for understanding the structure of magma plumbing systems.

“Granitic landscapes in the Yosemite Valley in California and in the North Cascades are iconic, huge cliffs with exposed rock,” Karlstrom said. “If you look closer, the structure of that landscape shows all kinds of intrusive bodies that record different pulses of magma coming into the crust. Our findings hopefully allow you to stare up at El Capitan and make sense of it in some new way.”

For the research, Karlstrom, Scott R. Paterson of the University of Southern California and A. Mark Jellinek of the University of British Columbia examined more than a decade of measurements of size distributions of igneous rock intrusions in the North American Cordillera, the mountain chain that includes the Cascade and Sierra Mountains.

Magma rising in active volcanic regions in places such as the Cascades, Hawaii and Iceland, Karlstrom said, often occurs as narrow, sheet-like intrusions commonly called dikes and sills. This occurs as a cracking process in brittle crustal rocks.The iconic El Capitan at Yosemite National Park in California contains a long-running record of magma injections that never breached the surface, instead freezing into the Earth’s crust.