News Release

Another cascade range volcano may be coming to life

Peer-Reviewed Publication

Geological Society of America

South Sister volcano in Oregon’s Cascade Range is beginning to show signs of awakening after several thousand years of slumber. Although indications are that an eruption is not likely to occur anytime soon, scientists are increasing their vigilance of the volcano, located approximately 22 from miles from Bend, Oregon.

Geoscientists will share results of their research as well as their perspectives on changes at South Sister at the Geological Society of America Cordilleran Section meeting this week at Oregon State University in Corvallis. The session titled “Hazards and Risks from Cascade Volcanoes” takes place Wednesday morning, May 15.

About a year ago, scientists at the U.S. Geological Survey (USGS) detected a bulge in the Earth's crust near the base of South Sister volcano. Using high-precision radar data from satellites, Charles Wicks (Menlo Park, CA) and colleagues found that the ground west of South Sister swelled about 4 inches since 1996. Wicks will discuss how this swelling has continued at a rate of about 1 inch every year.

In addition to the ground swelling, Terry Gerlach and his colleagues at the USGS Cascades Volcano Observatory in Vancouver, WA, measured the chemistry of gasses in the air and springs around the bulging area. This chemistry shows that small amounts of gas from molten rock are showing up in some spring waters around the bulge.

The swelling near South Sister could be caused by the slow accumulation of molten rock around 4 miles beneath this area. William Evans and his coworkers in Menlo Park and at the Lawrence Berkeley National Laboratory in Berkeley, CA, will present models that combine the geochemical and satellite data. These models suggest that molten rock is now accumulating beneath South Sister at a faster rate than in the past.

Using information from these studies and new geologic dates for South Sister’s eruptive history by Andrew Calvert and Wes Hildreth, William Scott will discuss how the U.S. Geological Survey is responding to these changes at South Sister volcano. Additional investigations are planned and ongoing to help determine if the crustal bulge indicates an eruption could occur anytime soon.


Geological Society of America
Cordilleran Section Meeting
May 13-15, 2002
Oregon State University, Corvallis, OR

For information and assistance during the meeting, please call the GSA registration desk at 541-737-6453.

To view a list of all presentations in this session and to access abstracts of presentations described above visit

To view all sessions and presentations go to

Additional Contact Information:

Patricia Jorgenson, Public Information Officer
U.S. Geological Survey, Menlo Park, CA

Charles W. Wicks
Menlo Park, CA

Terrence M. Gerlach
Vancouver, WA

William C. Evans
Menlo Park, CA

William E. Scott
Vancouver, WA

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