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Mt. Rainier is experiencing an earthquake swarm that hasincluded a 3.2 earthquake a mile beneath the surface, thatis the largest earthquake ever recorded under the mountain.

Volcanologists do not believe that the current earthquakeswarm is being caused by the movement of magma beneath thevolcano, but nevertheless the earthquakes are unusualenough to have caused scientific concern.

Scientists are watching for earthquake swarms close to thevolcano’s surface and the seismic signature of fluid movingthrough rocks. Such clues might signal an eruption.

Mt. Rainier is considered the most dangerous of the Cascadevolcanoes, because it is so close to the large metropolitanareas of Seattle and Portland.
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US Geological Survey volcanologists raised the alert levelat Mt. St. Helen’s to the highest possible and warned that amajor eruption appeared to be “imminent.”

The tremor this morning lasted 25 minutes, and is anindication that the volcano is moving toward an additionaleruption. There was a release of steam on Saturday thatattracted the largest crowd ever to the volcano’s visitorcenter.

While scientists anticipate a major eruption, they expectthat it will be smaller than the May 18, 1980 explosion thatkilled 57 people and ejected millions of tons of ash intothe atmosphere, which rained down across the PacificNorthwest for weeks.
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At 3:00PM PDT on September 26 the US Geological Survey Cascades Volcano Observatory issued a Notice of VolcanicUnrest for Mt. St. Helens. This advisory was issued becauseof pattern of earthquakes that are consistent with movementof magma within the volcano.

A swarm of very small, shallow earthquakes that began on themorning of September 23, peaked on September 24, thensubsided on Saturday morning, and it was initially thoughtthat they might be due to rainwater seeping into hot areaswithin the volcano.

Since then, however, the swarm has change to include morethan ten large earthquakes, the most in a 24-hour periodsince the October, 1986 eruption. These quakes are of a typethat suggests the involvement of pressurized water andsteam, and possibly magma.
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