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A river of lava flowing down the side of a volcano

A river of pahoehoe lava in Hawaii.

When a volcano is your lab bench

By Linda Raab

From eNews, June 9, 2005

When Mount St. Helens in Washington state showed signs of volcanic unrest in fall 2004, scientists watched and waited to see if there would be an eruption as devastating as the one that occurred there 24 years before. In 1980, a magnitude 5.1 earthquake occurred after two months of increased seismic activity--spawning an explosive eruption. Within 10 minutes, debris from a magma avalanche spread more than 15 miles, uprooting trees and killing most wildlife in its path.

Ultimately, Mount St. Helens did erupt again in 2004. Fortunately, that eruption was an effusive eruption, meaning it was dominated by an outpouring of lava onto the ground, rather than an explosive eruption, which is characterized by the violent sky-high fragmentation of molten rock.

Although scientists cannot yet predict whether a particular eruption from the same volcano will be explosive or effusive, studying the geologic fluid mechanics of the volcano's magma (molten rock beneath the Earth's surface) increases their understanding of the problem. In the U's Department of Geology and Geophysics, newly arrived assistant professor Martin Saar is conducting such studies. Saar uses field work, laboratory experiments, and computer simulations to examine fluid flow in geologic settings. The research he performs has implications for geothermal energy exploration, volcanic and seismic hazard assessment, water management, construction of reservoirs, and the remediation of environmental contamination.

In one aspect of his current research, Saar is looking at the characteristics of magma and lava (molten rock when it erupts onto the Earth's surface)--both of which typically contain crystals and bubbles of suspended gases.

"If magma can lose [its gas] bubbles while ascending within the volcano, the magma pressure [will decrease] similarly to a shaken soda bottle that has been opened slowly," says Saar. "This [degasing phenomenon] may be one of the most important factors for determining if an eruption will be explosive or effusive." When the bubble and crystal content of magma change, its fluid characteristics (such as viscosity and permeability) change. As a result, its likely association with an explosive eruption or its lava's flow velocity and distance characteristics will also change.

Saar is also interested in the transition between two well-characterized types of lava, commonly known by their Hawaiian names, pahoehoe, which has a smooth or ropy surface, and a'a, which has a rough, blocky surface. An understanding of how these types of lava change and travel is important in populated regions because such knowledge is key to saving or protecting life and property.

Magma and lava are difficult to study both in nature and in the laboratory due to the high melting temperature of rocks (magma exists between 650 and 1200 degrees Celsius). For his laboratory studies, Saar creates artificial lava using corn syrup with other materials, such as bubbles and particles (poppyseeds), mixed in. To test some of the findings derived from his experiments with artificial lava and computer simulations, Saar currently has a proposal pending to study the physics of fluid flow on actual molten rock samples.

As part of his new post, Saar is forming a new hydrogeology and geofluids research group within his department. "We hope that what comes out of our labs will be applied in the fields of groundwater resource management, geothermal energy exploration, or volcanic hazard assessment," he says.

To read a longer version of this story, including other geological studies conducted by Saar, see Gateway story.

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