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However, the local time is also given as a reference for what local residents experience.

unless, of course unusual activity takes place that suggests a different time sequence is needed to better interpret that activity.

Here are links to some of the descriptive web pages provided by the Cascade Volcano Obervatory. Helens More information about the 1980 eruption More information about the 1980-1986 eruption More information about the 2004-2008 eruption The Cascades Volcano Observatory and the PNSN cooperatively operate 21 seismometers on or near Mount St. On average, we locate 4 to 14 earthquakes within 10 km of the volcano each week. For lots of detail on the past seismicity at Mount St. Most earthquakes are located at a shallow depth directly under the volcano; however there is a St.

Helens Seismic Zone (SHZ) that extends north and south of the volcano on which some earthquakes take place.

During eruptions and eruption precursor periods earthquakes are even shallower.

There have been a few times during the past thirty years that there have been many earthquakes in the depth range 1-7 km.

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