| U.S. Geological Survey, Vancouver, Washington University of Washington, Pacific Northwest Seismic Network, Seattle, Washington U.S. Geological Survey, Northern California Seismic Network, Menlo Park, California CASCADES VOLCANO OBSERVATORY WEEKLY UPDATE Sunday, September 20, 2009 12:53 PDT (Sunday, September 20, 2009 19:53 UTC) Cascade Range Volcanoes Volcano Alert Level: NORMAL Aviation Color Code: GREEN Activity Update: All volcanoes in the Cascade Range are at normal levels of background seismicity. These include Mount Baker, Glacier Peak, Mount Rainier, Mount St. Helens, and Mount Adams in Washington State; Mount Hood, Mount Jefferson, Three Sisters, Newberry Volcano, and Crater Lake, in Oregon; and Medicine Lake volcano, Mount Shasta, and Lassen Peak in northern California. Mount St. Helens has been at Volcano Alert Level NORMAL (Aviation Color Code GREEN) since July 10, 2008. Recent Observations: A swarm of small, shallow earthquakes occurred beneath the summit of Mount Rainier on Sunday, September 20, 2009, starting at ~0920 PDT. According to the Pacific Northwest Seismic Network (PNSN), the largest event at 0945 PDT has a preliminary magnitude of M 2.2 with a depth of 1.8 km, located 1 km NNE of the summit. The swarm also featured many small events that were too small to be located, and lasted for several hours before gradually waning. Such swarms have happened several times in the past decade. One example is the swarm on November 7, 2004, that included a M 3.2 event. We consider the September 20, 2009, swarm to be within the realm of normal activity at Mount Rainier. The U.S. Geological Survey and University of Washington continue to monitor these volcanoes closely and will issue additional updates and changes in alert level as warranted. For additional information, background, images, and other graphics: http://vulcan.wr.usgs.gov For seismic information on Oregon and Washington volcanoes: http://www.pnsn.org/WEBICORDER/PNSN/welcome.html For seismic information on California volcanoes: http://earthquakes.usgs.gov/eqcenter/recenteqsus/Maps/special/California_Nevada.php For a definition of alert levels: http://vulcan.wr.usgs.gov/Volcanoes/Cascades/CurrentActivity/volcano_warning_scheme.html For a webcam view of Mount St. Helens: http://www.fs.fed.us/gpnf/volcanocams/msh/ |