Mt. St. Helens

Introduction

After being inactive for 123 years, Mt. St. Helens erupted on May 18, 1980. The first sign that Mt. St. Helens was waking up happened when a earthquake with a magnitude of 4.2 shook the earth beneath the volcano. There would be hundreds of smaller earthquakes that would follow in a very short period of time. Within seven day the first steam-explosion would break a 250 foot crater through the ice cap. By April an area one mile long and half a mile wide bubbled outward 450 feet. The outward bulge was caused by a rise in molten rock into the volcano.

Geologic Processes

Mt. St. Helens is located on an ocean-continent subduction boundary. The boundary is where the Juan de Fuca plate is sub ducting under the North American plate. It is believed the the eruption was caused by a body of magna moved into the shallow part of the volcano between the earthquakes and the minor eruptions in March. Then by May 18th so much pressure had built up that the north face of the mountain failed and the magna was able to erupt. The failure of the north face of the mountain was aided by a earthquake with a magnitude of 5.1 one mile under the mountain.

Impacts

The eruption flattened 230 square miles of forest in only three minutes. The rates at which the landslide swept across the land was 500 miles per hour. The landslide was the largest in recorded history removing 1,300 square feet from the summit. The mountain dropped from 9,677 feet to 8,363 feet. The mountain was the 9th highest peak in Washington state before the eruption. Then after the eruption it dropped to the 30th highest mountain in Washington state. The eruption instantly turned more than 70 percent of the glacial ice and snow on the mountain into water. The gases and molten rock streams uprooted trees as far as six miles from the mountain. The top soil was completely striped away and all that was left was bare rock. The wild life in the area surrounding the mountain was killed. The eruption killed an estimated 5,000 black-tailed deer, 1,500 roosevelt elk, 200 black bears, 15 mountain goats, and many more small game animals. Also the eruption killed 57 people. The other damage that the eruption had was on the industries around the mountain. Some 60,000 acres of trees used for logging were destroyed.

Recovery

The land and the animals are slowly recovering from the eruption. Though most of the recovery has been left to mother nature. The logging industry has planted more that 18.4 million trees by hand. This re-planting has been hard because the volcanic ash has had to be moved to allow the root to be planted into the rich soil that was covered. Other than that the area around the mountain has been named a National Volcanic Monument. People are not to interfere with the recovery of the land so how the land recovers can be study.

Literature Cited

http://vulcan.wr.usgs.gov/Volcanoes/MSH/description_msh.html

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Copyright © 2004 Earlham College. Revised April 20, 2004 . Send corrections or comments to smithti@earlham.edu