Geography - The Restless Earth - Volcanoe - Mt St Helens CASE STUDY

Mt St Helen CASE STUDY

Background · Mt St Helens is one of the 5 volcanoes in the Cascade Range in Washington State, USA. · Like these others it had been dormant for many years · In March 1980 there were signs of an impending eruption. These included: Earth tremors, gas and steam release and visible selling of the mountain. · An 8km (5mile) exclusion zone was set up in preparation for an eruption. · The eruption took place on May 18th at 8:33am

Causes · Mount St. Helens is a volcano which lies near to a destructive plate boundary where the small Juan de Fuca Plate is being sub-ducted underneath the North American Plate. · The Juan de Fuca Plate is sub-ducted into the mantle where increased heat and friction cause the plate to melt. · The magma produced in the melting rises up through the North American Plate via crack, forming Mount St. Helens. · The trigger stimulus was a magnitude 5 earthquake underneath Mount St. Helens on the 18th of May at 8:32am. · This caused a bulge on the North face of the volcano to become unstable and collapse as an avalanche. · The volcano then went on to erupt ash and produce pyroclastic flows – currents of hot gas and ash.

Facts · 540 million tonnes of ash was produced · 1300ft was lost from the mountains summit · 8000 million tonnes of rock was blown from the mountain

Primary effects Economic · It was the most economically destructive volcanic eruption in the history of the USA. · 15km2 timber was destroyed ruining the timber industry in the area · Agriculture downwind of the volcano suffered. Fields were covered in ash and 12 million salmon dies when ash entered the rivers and their hatcheries were destroyed. Social · 57 people died, all but 3 were outside of the exclusion zone. · 200 homes were destroyed · 300km of main roads were destroyed. Environmental · 60,000km2 covered with volcanic debris · Wildlife (deer, elk, bear, birds and small mammals) damaged – estimated 7000 big game killed. · All living things 27km north of the crater were wiped out due to a sideways blast of pulverised rock, glacier ice and ash. · The surrounding landscape was said to be “more desolate than the moon”.

Secondary effects Economic · Overall cost was estimated to be $1.1million to fix the damages · Tourism trade dipped · Commercial flights were cancelled from nearby airports for 2 weeks due to the ash · Timber industries suffered · Jobs were lost in the area · However in the long term tourism to see the volcano has created some jobs Social · People moved away from the neighbourhood. · Residents were left without some amenities for a while (eg, water treatment, electricity and sewage removal were damaged) · Residents suffered emotional trauma and stress Environmental · Local ecosystems were left damaged and unbalanced · Water was polluted by volcanic debris · Much of the landscape is still scarred today · However the soil in the surrounding area is now more fertile

Immediate Responses · Search and rescue helicopters were mobilised to rescue stranded people, · Shelters were provided for those who had lost their homes or been forced to evacuate · Medical aid was given to those who were injured. · Ash masks were distributed so people didn’t breath in the ash · The authorities were able to mobilise many people and much equipment quickly to help in these operations. · The aid operation rescued 198 people. · Unfortunately, the landscape had changed so much that maps were no longer accurate, this slowed down the rescue efforts.

Long Term Responses · A million tonnes of ash was removed from roads, buildings and airports. This cost over $1million in the town of Yakima and it took ten weeks. � · Millions of trees were replanted because there was a huge loss of timber which would cost $300million. � · Compensation was given to farmers because what they produced on their farms was destroyed by being covered by ash. This cost about $70million. � · New tourist facilities were built because there were less tourists, meetings and conferences in the area after the eruption. It was important to get these people back as they input a lot of money into the economy. � · A channel was dredged to remove logs and levees were rebuilt to reduce floods which could happen in the future. This is because the Columbia River shipping channel was closed. This caused the port of Portland $3million per month in lost trade. � · A new highway was built and major repairs were undertaken because 250km of roads and 25km of railways were damaged, costing $7million. � · Money was given to rebuild houses after 200 homes were destroyed. � · Money was given to redevelop the salmon hatcheries after 12 million baby salmon were killed.