Mount St. Helens

1. Mount St. Helens By Annie Crutchley

2. Location and background history • Mount St. Helens is an active strata volcano in Washington, in the Pacific North West region of the United States. It is a composite volcano. • It is located 96 miles South of the city of Seattle, and 53 miles North East of Oregon. • Mount St. Helens is part of the Pacific Ring Of Fire that includes over 600 active volcanoes. • This volcano is best known for its ash explosions and pyroclastic flows. • This volcano is famous for its eruption on May 18th 1980. • This was the deadliest and most economically destructive volcanic event in the history of the United States. • 57 people were killed, 250 homes, 47 bridges, 15 miles of railways and 185 miles of highway were destroyed.

3. Continued ....... • The eruption caused a major debris avalanche reducing the elevation of the mountains summit from 9,600 ft to 8,000 feet. • Other eruptions in the history of Mt St Helens have been: • 1480 – several times larger than the eruption in 1980. • 1482 – another large one rivalling the 1980 eruption. • 1800 – about the same size as the 1980 eruption although did not case as much destruction. • 1831 to 1857 – small eruptions of ash

4. Main Causes Of The Eruption • Mt St Helens erupted after many months of build up activity including a massive bulge growth on the side of the mountain. • The main cause of the eruption however was a moderate earthquake. Even though this earthquake was minor (4.2 on the Richter scale) it caused the whole North flank of the mountain to bulge. May 18th had another earthquake occur and this caused the largest landslide in the history of Mt St Helens. • The magma inside Mt St Helens burst forth into a large scale pyroclastic flow that flattened vegetation and buildings. • There were some human impacts that contributed to the eruption of the volcano in May 1980.

5. Main Events Of The Eruption • March 20th 1980 – Helens experienced a magnitude 4.2 earthquake. • March 27th – steam venting occurred. • End of April – North side of mountain started to bulge. • May 18th – another earthquake occurred at 5.1 on the Richter scale causing a massive collapse of the North side of the mountain which also made an avalanche occur. This mixed with ice, snow and water which created Lahars.

6. Short Term Impacts ..... • One short term effect of the Mount St. Helens eruption is that 1300 feet was blasted off the top of the mountain. This would have a great effect because that would all break up into ash and encircle the Earth, which would stop heat and light from the sun coming into the atmosphere. • Power supplies were cut off and that ash got into water supplies. Consequently, it would have led to contamination of the water and the spread of disease. • 230 square miles of forest burned and got destroyed. This would have a great effect on the logging industry because there would not be as many trees for them to cut down. In addition to this it would have a great effect on wildlife as 1000s of animals' homes would have been destroyed.

7. Long Term Impacts ..... • A long term effect of the Mount St. Helens eruption is that lodges would have had to be closed down. This would have an impact on the economy because if the lodges were closed down then there would be nowhere for tourists to come and stay there for they would lose money. • Another long term effect of the Mount St .Helens eruption is that 57 people died. This would have lead to lots of families being devastated. • Ash settled 15cm deep this would have an effect because when it rained you would get lots of mud flows and it will but growing trees or crops for next year very hard.

8. Prediction And Monitoring • The first inkling that something was going on were some small explosions and earthquakes that occurred in March of 1980. These alerted scientists to the possibility of an eruption. After that they put in more seismometers and lots of other devices for measuring the deformation of the volcano. Nobody was able to predict the exact time and date of the eruption, but by the time it did occur they figured that it was close. • Scientists are now monitoring St Helens with Seismology to try and prevent more devastation.

9. Activity Since The Main Eruption? • From December 7th 1989 to January 6th 1990 and from November 5th 1990 to February 14th 1991 – the mountain erupted with some huge clouds of ash. • October 11th 2004 – magma reached the surface of the volcano resulting in the growth of a lava dome. • July 2nd 2005 – the tip of the dome broke off. • March 8th 2005 – showed significant activity. • October 22nd 2006 - magnitude 3.5 earthquake that broke loose Spine 7. There was a collapse and avalanche of the lava dome that sent an ash plume 2,000 feet over the western rim of the crater; the ash plume then rapidly dissipated • December 19th 2006 - large white plume of condensing steam was observed.