Almost 100 small earthquakes were detected by the Pacific Northwest Seismograph Network beneath the south flank of Mount Hood between February 2 and 5. Sixty-five were large enough to be located; the largest event (M 2.6) on February 5 was located at a depth of 7.4 kilometers. Since the late 1970's when seismic monitoring became routine, earthquakes beneath Mount Hood have occurred in swarms (several to tens of earthquakes) of small events (<M3.5) lasting only a few days. The earthquakes are located chiefly beneath the south flank and summit at depths of less than 11 kilometers. ( MAP VIEW | CROSS SECTION )

Typically, 1 to 3 earthquake swarms and several discrete events are recorded each year. Like other earthquake swarms, this most recent one was not accompanied by any other observed changes at the volcano. These intermittent earthquake swarms and discrete events seem to characterize Mount Hood's "normal" level of seismic activity. Any departure from this usual activity would be closely watched as it could represent an early warning that the volcano might be heading towards renewed voclanic activity.

The most recent significant eruption of Mount Hood occurred in the late 1700's. Based on it's earlier eruptions, a report published in 1997 explains how future volcanic activity of Mount Hood is likely to affect nearby communities and recreation areas.

The Pacific Northwest Seismograph Network is operated jointly by the University of Washington, University of Oregon, and Oregon State University and is funded by the US Geological Survey (USGS), the Department of Energy, and the University of Washington.

URL of this page: http://volcanoes.usgs.gov/About/What/Highlights/MtHood/MtHood_Swarm.html