Tepexitl is a volcano in east-central Mexico that appears as a crater rather than the more traditional cone-shaped volcano.
Photo by Allison Austin

Northern Arizona University geology graduate student Allison Austin figures the best way to understand a certain type of volcanic explosion is to re-create it.

Austin’s master’s thesis focuses on a volcano in east-central Mexico, where magma flashed groundwater to vapor, creating an explosion that left a large hole in the ground.

With support from a 10-month J. William Fulbright Foreign Scholarship, Austin will travel to Wuerzburg, Germany, in September to work in the only laboratory in the world equipped to take rocks from the Mexican volcano, re-melt them and mingle the melted rock with water to trigger an explosion. The lab is associated with the University of Wuerzburg.

Austin will compare characteristics of the fragments produced by explosions in the German laboratory with fragments from the Mexican volcano, called Tepexitl, to determine if she successfully reproduces the explosions.

“No one has ever done this type of work with magmas of the composition with which she is working—and only one study has done it with any magma at all—so this is scientifically quite exciting,” saidMichael Ort, Austin’s faculty advisor at NAU.

NAU geology graduate student Allison Austin will travel to Wuerzburg, Germany, in September on a Fulbright scholarship to reproduce a volcanic explosion in a laboratory in hopes of ultimately better predicting eruptions of maar craters.
NAU geology graduate student Allison Austin will travel to Wuerzburg, Germany, in September on a Fulbright scholarship to reproduce a volcanic explosion in a laboratory in hopes of ultimately better predicting eruptions of maar craters.


Tepexitl is a maar crater. “Maar craters are not volcanoes in the traditional sense,” Austin explained. “Instead, they look like meteor impact craters. Cinder cones like Sunset Crater (east of Flagstaff) are the most common volcanic landform on Earth. Maars are the second most common.”

Maars are relatively small—between about 1,000 feet and two miles in diameter—and the short-lived eruptions last from a few days to a few years. But they can pack a wallop.

“These eruptions are highly explosive but less intense than some of the larger eruptions that you hear about in Alaska or Indonesia,” Austin said. “Maar eruptions can cause devastation for a one- to eight-kilometer radius from the vent and can have columns of ash that go up to 15 kilometers high.”

Austin said that predicting maar eruptions is complicated because so many variables come into play. One of the variables is the type of magma involved. Tepexitl is composed of rhyolite magma, which contains a lot of silica, so it moves like honey, as opposed to basalt magma, which contains less silica and moves more like water. Ort explained that most magmas ascend through water-saturated rocks near the surface, but only some interact explosively, and scientists don’t know why.

“The ultimate goal of all this work is to understand this interaction process and what triggers the explosions, so we can predict an eruption,” Ort said.

The NAU graduate student, who earned a geology degree from Guilford College in Greensboro, N.C., plans to defend her thesis in May 2007.

Established in 1946, the Fulbright Program aims to increase mutual understanding between the United States and other countries through the exchange of people, knowledge and skills.