Mount St Helens

?

Location, Cause And Date Of Eruption

On May 18th 1980 at 0833 Mount St Helens (Cascade mountain range, Washington, USA) erupted following a period of activity which began in March 1980. Mount St. Helens is located in the Northern Hemisphere in the continent of North America. It is in the mountain range the Rockies. It is located on a destructive plate boundary. The Juan de Fuca plate (oceanic crust) moves eastwards towards the North American Plate (continental crust), and is forced downwards. This movement creates friction which produces earthquakes and due to an increase in temperature destroys the oceanic crust.

(The Plate Boundaries)

It triggered an earthquake measuring 5.2 on the Richter scale and the north face of the mountain collapsed in a massive landslide which is the largest landslide ever recorded. The landslide was 200 meters thick in the upper Toutle valleys. At the same time, a giant cloud of ash rose 15 miles (24km) into the sky in just 15 minutes. Then hot ash, pumice and gas known as pyroclastic flows poured out of the crater. The heat melted the snow, which created mudflows in all the major river valleys. When it erupted, it permanently changed the surrounding landscape. Westerly winds bowed millions of tons of ash across the United States turning blue skies grey as far as Spokane, Washington - 250 miles (400km) away.

Before The Eruption

Before Mount St .Helens erupted the volcano went through 3 months of seismic activity as magma rose within the mountain. As the magma rose, a large bulge grew on the north flank of the volcano. This was due to a blockage in the main vent resulting in the growth of a crypto dome (mound of viscous lava) in the side of the volcano. There was also an earthquake in March measuring 4.0 on the Richter scale. US Geological survey team monitored at different camps called Coldwater 1, Coldwater 2 and Swift creek and the most expensive equipment was used. On the 28th March 14 residents had to be evacuated from their homes because of how close they were to the volcano. Harry Truman an elderly local resident refused to leave his home because he believed Mount St. Helens was apart of him because he grew up there, he later died in the blast. Also on the 28th march police closed up roads and 2 days later Red Zones were set up 3-8 miles from the volcanoes summit. 5 mile exclusion was then set up around the volcano. People were also warned via television broadcasts from 3rd April onwards, reporters were air lifted to the volcano. Before the eruption the area around Mount St. Helens had forests of cedar and fur. It was the last untouched forest in the United States and the eruption blew and buried nearly 230 square miles of forest. The eruption lasted 9 hours but Mount St. Helens and he surrounding landscape where automatically changed within seconds.

(Forests of Cedar & Fur)

(Harry Truman)

Primary Effects

Primary effects were logging camps and forests where destroyed by hot ash, gas and dust. Around 57 people were killed mainly by poisonous gasses. A resident called Harry Truman and a photographer also died. Buildings, property and farmland were damaged and destroyed. Ash raced down Mount St. Helens at 300 miles per hour destroying communication signals, transport, electricity and telephone lines. The heat of the eruption melted the ice cap sending 46 billion gallons of water down the mountain creating a Lahar into Toutle valley at 90mph and 91°C. Spirit Lake was filed with the debris. The ash reached 200 miles away and trees where uprooted 19 miles away from the volcano.68, 000 acres of commercial timber worth $400 million was destroyed.

Secondary Effects

Secondary effects were that Ash blocked rivers destroying popular fishing sites. Lots of flooding occurred. This in turn destroyed crops and livestock. Flooding destroyed communications such as road and railway bridges. Sediment carried downstream ruined barge transport on the Columbia River. Shortages of food, water and shelter, spread of diseases from contaminated water was also a huge problem. Economic problems started to arise from the cost of rebuilding and planning for stronger materials to help prevent such a magnitude of damage again. Loss of farmland, factories and tourism also contributed to the economic downfall. Social problems within families began to arise because of the loss of loved ones which caused allot of stress and time off of work. However the eruption did not only produce negative