Mount St.Helen Eruption The eruption of Mount St. Helens occurred on May 18, 1980. It was the most significant eruption of the volcano in continental U.S. throughout the history. Today, most of geologists agree that the initial build up of magma, underneath the volcano, which resulted in eruption, was caused by the the movement of Earth’s continental plates. The Mount St. Helens is located at the edge of Pacific plate, therefore the original seismic activity in volcano’s vicinity, prior to eruption, can be directly attributed to it.
The most important geological event, which occurred approximately 2 months, before the eruption, is without the doubt an earthquake that took place on March 20, 1980. According to the Richter scale, the earthquake was rated 4.2 and its center was located immediately underneath the north face of St. Helens. This was an indication of volcano coming to the active state, after 120 years of being inactive. On March 27, two phreatic eruptions had radically changed the morphology of the old crater, since they covered it with about 1 meter of smashed rock and ash, while resulting in creation of two new craters. This geological event coincided with the formation of east-trending fracture system, which was estimated to be 5 kilometers long. These geological process were being accompanied by continuous seismic activity, there were at least 10.000 earthquakes recorded in the period, which we now refer to as buildup stage.
A tsunami is a series of water waves caused by the displacement of a large volume of a body of water, generally an ocean or a large lake. Earthquakes, volcanic eruptions and other underwater explosions(including detonations of underwater nuclear devices), landslides, glacier calvings, meteorite impacts and other disturbances above or below water all have the potential to generate a tsunami. ...
They were the main contributing factor, along phreatic eruptions, to cause two small mudslides. It also need to be mentioned that the shape of the whole mountain was being altered, during the buildup period. Its cheer volume was increased by 125.000.000 m3, within two months. The height of St. Helens was increasing by 1.5 meters a day, within the same period. Thus, we can say that, prior to eruption, Mount St.
Helens went through very a dramatic geological restructuring, which would normally take thousands and thousands of years. Yet, because of this restructuring, the geologists were able to link the increasing seismic activity with coming eruption, thus saving the lives of many people. The most immediate geological result of the eruption on May 18, was the removal of the entire north face of St. Helens, which also reduced the height of this mountain by 400 meters. It is considered to be the largest landslide in the recorded history and also, probably the fastest one, as it traveled with the speed of 175-250 kilometres per hour. The landslide moved 13 miles down Toutle River, filling river’s valley with avalanche debris, which in some places reached the depth of 180 meters. The newly formed crater was 3 km wide, in diameter.
Hundreds of thousands tonnes of volcanic material was being lifted up in the air. Its deposits, in form of underground sediments, were being found as far away as Texas. In all, the area of about 62 km2 was the most heavily affected by the eruption, in geological sense of the word. Also, the rising temperature resulted in numerous volcanic mudslides, which dramatically altered the landscape. The first mudslide occurred in 20 minutes, after the initial eruption, it proceed 20 kilometers down the south slope of the mountain, while completely removing the alluvial sediments on its path. It is estimated that the beds of all water reservoirs, in volcano’s vicinity, were being elevated by 5 meters, due to the intense deposition of volcanic ash. As a matter of fact, all the water in lake Spirit was being temporarily displaced by landsliding debris, creating the waves of 10 metres high, which crashed into the north ridge of the lake and caused more debris to settle onto the lakebed.
... p. 369-396 Geological Survey Professional Paper 1249 (1982) Volcanic Eruptions of 1980 at Mount Saint Helens-The First 100 Days ... excellently (Chester 1992). As a result of the Mount Saint Helens eruption, the government officials on the Indonesian ... Helens, situated in the volcanic region of the Cascade Mountains in Washington State, USA, began mainly in the late 1930's by Verhoogan (Geological ...
Volcano’s eruption also forced numerous spring creeks to change their course. This, in its turn, resulted in creation of completely new water reservoirs. The geological impact of St. Helens eruption can be hardly underestimated. It won’t be an exageration to say that its violent force had litterally moved the mountains. It provided geologists with the rare opportunity to witness volcanic landscaping in making.
Bibliography: 1980 Eruption of Mount St. Helens. 2006. Wikipedia. 7 Apr. 2006. http://en.wikipedia.org/wiki/1980_eruption_of_Moun t_St._Helens#Direct_results The Many Faces of Mount St. Helens.
17 Apr. 2005. Valerie’s Home Page. 7 Apr. 2006. http://www.olywa.net/radu/valerie/StHelens.html.