Mount Hood, Oregon
Seismic Activity, September 2001

Submitted at 15:40 PDT, September 14, 2001

Volcanoes in the Cascade Range are all at normal levels of background seismicity. These include Mount Baker, Glacier Peak, Mount Rainier, Mount Adams, and Mount St. Helens in Washington State; Mount Hood, Mount Jefferson, Three Sisters, Newberry, and Crater Lake, in Oregon; and Medicine Lake, Mount Shasta, and Lassen Peak in northern California.

A minor earthquake swarm has been underway at Mount Hood, Oregon, since late on September 9. Up to the time of this report, about 25 events have been detected by the Pacific Northwest Seismograph Network ranging up to M=2.9. Epicenters of the events cluster near the village of Government Camp, about 8 km (5 mi) SSW of the volcano's summit. Depths of well-located events range from about 1 to 7 km (0.5 to 4 mi). Swarms such as this are common at Mount Hood and occur once or twice per year. For more information about past earthquakes at Mount Hood see: http://www.geophys.washington.edu/SEIS/PNSN/HOOD/info.hood.html

Information about the recent detection of a slight uplift of a broad area west of South Sister volcano can be found in the update of May 8, 2001.

USGS Cascades Volcano Observatory, the Pacific Northwest Seismograph Network at the University of Washington, and the USGS Northern California Seismic Network and Volcano Hazards Team in Menlo Park, California, monitor the major volcanoes in the Cascade Range of northern California, Oregon, and Washington.