September 2008

Mapping a Volcano’s History

BY BETH LEFEBVRE

It’s difficult to believe that the smoky, lush slopes of the Blue Ridge Mountains that dominate the southwestern Virginia landscape were once the site of an ancient volcanic explosion, the magnitude of which dwarfs the 1980 eruption of Mount St. Helens.

Such violent volcanic activity is a rarity in the Appalachian Mountain range and throughout the East Coast. GW Associate Professor of Geology Richard Tollo and three geology students are unlocking the mysteries of the explosion and the “basement” rocks below. These rocks include some of the oldest in the southern Appalachians, dating back to the Precambrian Age, 1.3 billion years ago, long before major life on Earth appeared.

“Nearly a quarter of Earth’s history is right here,” Tollo says, pointing to the layers of rock jutting from the mountainside. “There’s no other Precambrian rock at this latitude above the surface until you hit Denver.”

Tollo, along with GW sophomore Allie Rubin and seniors Maureen Logan and Chris Parendo, spent the summer mapping a 400-square-mile section of the Jefferson National Forest near Mount Rogers, a large volcanic complex where eruptions once sent thick lava and a turbulent mixture of gas and rock fragments oozing throughout the mountains at extremely high temperatures. These violent bursts did not come from a typical volcanic cone but from a caldera, a volcanic feature formed by the collapse of land following an eruption.

“Calderas are extraordinarily rare. A similar age eruption hasn’t happened anywhere else in the East, and we’re trying to understand why,” says Tollo, who was named a 2007 Professor of the Year by the Council for Advancement and Support of Education.

Tollo and the students were hired by the U.S. Geological Survey to complete mapping that the agency began in the 1960s. The project is part of the agency’s Educational Geologic Mapping Program, which gives students firsthand experience in field-based research.

The students alternated between fieldwork in Virginia and the laboratory at GW, as they collected evidence, prepared samples, compiled maps, and analyzed data to determine how and when rocks were formed and how lava erupted in the area. Their work involved cracking open rocks to uncover historical details inside and using isotopic dating to determine the age of basement rocks and lava.

The students will transform the map data and chemical compositions into a complete history of Mount Rogers: a largely unknown story of volcanism that followed an earlier episode of heating and deformation of the crust. Together, these processes gave rise to the much-visited, much-photographed, much-sung-about Blue Ridge landscape.

“It’s great to be involved in a project this complex and interesting,” says Parendo, a Luther Rice Undergraduate Research Fellow for 2008-09, who also spent summer 2007 working with Tollo.

While research was the primary goal of their work, Tollo used the fieldwork as a constant learning opportunity. He held roadside question-and-answer sessions with students and delivered his “habitual” lectures while driving from one site to another, pointing out the Jeep window to roadside rock formations. “This was so much different than learning from a textbook,” says Rubin.
Tollo says, “When they are out there, they are not students, they are geologists. It’s amazing.”

The results of their work range from promoting regional stewardship by providing the information needed for good land-use decisions to helping scientists better understand volcanic eruptions worldwide.

“Our hope is that people will develop a better understanding of the Earth,” says Tollo. “With geology, the past, present, and future are often inextricably linked.”

Send feedback to: bygeorge@gwu.edu