Volcano watchers study Three Sisters

Scientists from the 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.

Two local information sharing sessions for the public have also been scheduled. A Sisters session is set Tuesday, October 2, from 7 to 9 p.m. at the Sisters Fire Hall, 301 South Elm, Sisters.

Dr. William Scott, a USGS scientist studying the uplift, will present the most recent information, and U.S. Forest Service representatives will provide an overview of current land management of the area and what management scenarios would look like in the event that the uplift grows.

The work by USGS is part of an ongoing program to track 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.

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.

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.