Seismic Trace of Mt. St. Helens

March 19, 2005


Referred by: Noah Newman
Summary authors & editors: Noah Newman

This trace comes from the U.S.Geological. Survey, Pacific Northwest Seismograph Network -- it was made on Oct. 2, 2004. On this date, scientists were very alert, as Mt. St. Helens was showing the most activity since its explosive eruption in 1980, nearly 25 years ago. Each horizontal line on the trace represents 10 minutes of time. The colors were added to make it easier to distinguish between the seismic tremors and the harmonic resonance. Minor earthquakes were occurring every few minutes or so for several days, until around 12:30 local time. At that point, the volcano stopped shaking and started "humming". For almost a full hour, Mt. St. Helens displayed something scientists call harmonic resonance. Similar to the pipes in your own home, when the water pressure is just right, the pipes make a loud humming sound. Here, instead of water, lava was shooting upwards towards the dome creating this unique image from a nearby seismograph. The alert level was raised, and some visitors were evacuated. Since then, the volcano has simmered down for now, but scientists will be keeping a close eye on it for years to come.

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