Our Window on Nature

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Voice of a Volcano

Filed under: Geology — Lowell Christie -- December 8, 2006 @ 6:10 am

Mount St. HelensYears ago we were hiking high on Mount Ranier in Washington State when we saw a plume rising from Mount St. Helens far in the distance. It had to be some time after 1980, because that is when the volcano become active once again. Our first thought was of another eruption. Training our binoculars on the volcano, we finally decided it must be dust from a rockfall inside the dome.

The original eruption in 1980 reduced the height of Mount St. Helens by 1,314 feet, removing 3.7 billion cubic yards of material. But now the volcano is growing again, and it is the upward pressure that is causing the present tremors.

The volcano became active most recently in September of 2004, and since that time there have been many small earthquakes, each with a magnitude of less than 2.0 on the Richter scale. Now there are multiple quakes each day. Scientists say they don’t think an eruption is likely at the present time, but no one can tell for sure. Locally the small quakes are being called drumbeats, and the cause of the minor shaking is part of an ongoing dispute.

One group thinks that a “plug” is being pushed up — then released, and that rock rubbing against rock is causing the quakes. Another argues that it is steam inside the volcano and they say

vibrations in a steam-filled horizontal fracture about 330 feet (100 meters) beneath the crater floor are causing the drumbeats. There’s plenty of water in the ground, and there’s plenty of heat.

When the weather warms up, you can actually visit Mount St. Helens, but in the meantime (or if you don’t want to get that close), here is a WebCam view of the volcano. Just don’t bother looking at night, since the view is live.

P1206


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