Three Sisters, Oregon
Information Statement - September 12, 2001

Scientists from U.S. Geological Survey's Cascades Volcano Observatory and Central Washington University, in cooperation with staff from the Willamette and Deschutes National Forests, will make surveys of ground deformation and gas emissions in the Three Sisters region of the central Oregon Cascade Range during the week of September 17, 2001. The work is part of an ongoing USGS program to track activity in the broad area of crustal uplift detected by satellite techniques last spring. Scientists interpret the slight ground uplift and weak gas emissions in the area as evidence that a small amount of magma, or molten rock, may have been intruded deeply under the area. For more information, see: http://vulcan.wr.usgs.gov/Volcanoes/Sisters/WestUplift/.

The purpose of the upcoming work is twofold.

• Measure ground deformation: A helicopter will support field operations and move crews and equipment to selected spots on South Sister and the surrounding area. Crews will reoccupy level lines and benchmarks around South Sister that were installed in 1985 in order to provide baselines for assessing future ground deformation. Resurveys using leveling equipment and Global Positioning System (GPS) receivers will determine the amount of deformation since 1985 and provide confirmation of the satellite results. Crews will also install several new benchmarks to cover the entire area of the uplift.

• Measure gas emissions: A helicopter carrying several instruments will fly over the area of the uplift at low altitude in order to repeat a gas-monitoring survey done in May 2001 that measured slightly elevated values of atmospheric carbon dioxide.

Information contact:

U.S. Geological Survey, Cascades Volcano Observatory, Vancouver, Washington
(360) 993-8900
http://vulcan.wr.usgs.gov