Cascade Range Current Updates
September 2009

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: The swarm of small earthquakes beneath Mount Rainer that started on the morning of September 20, 2009, continued until September 23. The seismicity rate dropped significantly towards the end of Sept. 20 and again early on Sept. 22, with the last swarm event occurring Sept. 23 at 10:35 PDT. Most of the swarm earthquakes located at a depth of 2-3 km (1-2 miles) and were centered ~1 km (0.5 miles) northeast of the summit. According to the Pacific Northwest Seismic Network (PNSN), the largest event was a M 2.3 on Sept. 20.

Seismic swarms are concentrations of earthquakes that typically are not initiated with a mainshock, and are common features at volcanoes. The vast majority of volcanic swarms are not associated with eruptive activity. Rainier itself has had several such swarms: in the past 7 years there have been days-long swarms in 2002, 2004, and 2007, two of which (2002 and 2004) included M 3.2 earthquakes. We consider the September 20-23, 2009, swarm to be within the realm of normal activity at Mount Rainier. The USGS and PNSN continue to closely monitor seismicity and other geophysical parameters at Mount Rainier

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.

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: No significant changes in activity occurred during the past week. Fieldwork includes mapping at Mount St Helens and Medicine Lake, teacher training at Rainier, field instrumentation at Rainier and Mount St. Helens, and field surveys around Mount St. Helens and Mount Hood. On Wednesday two micro earthquakes occurred under Mount St. Helens of magnitudes 1.3 and 2.8 about eight hours apart. This is normal background activity.

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: No significant changes in activity occurred during the past week. At Mount St. Helens, field crews: (1) repaired and did standard maintenance on monitoring equipment, (2)surveyed channel cross-sections, and (3) continued geologic mapping of the volcanic edifice. Last week, CVO field crews finished a successful GPS campaign at Newberry volcano to monitor potential ground deformation.