Volcanoes Case Study: Mount Saint Helens, 1980

National 5 Geography Global Issues- Environmental Hazards- Case StudyVolcano: Mount Saint Helens 1980 Cause Mount Saint Helens Erupted on the 18th May 1980.The volcano is located in the Rocky Mountains, near the west coast of the USA, in the state of Washington.Mount Saint Helens lies above the boundary of two tectonic plates, at a destructive plate boundary. The small, oceanic Juan de Fuca plate and the continental North American plate move towards each other, causing the heavier oceanic plate to be pulled beneath the North American plate in a process known as subduction. This creates friction, preventing the plates from moving. Eventually, the build up of pressure is too great and the oceanic plate is pushed downwards, causing the crust to melt. Some of this new molten rock is then forced to the surface, forming a volcano.The volcanic eruption was triggered by an earthquake, measuring 5.0 on the Richter Scale, which occurred at 8:32am. This caused a bulge on the north side of the volcano to become unstable, and fall as an avalanche. The volcano then went on to erupt ash and pyroclastic flow.ImpactNegativePeople57 people were killedAround two hundred people had to be rescued15cm of ash fell, causing airline and traffic chaos (in some areas, ash was as deep as 2 feet)Ash damaged car engines and farm machinery and destroyed crops, costing farmers £100 millionElectricity supplies and telephone lines were knocked outTourists no longer visited the area, damaging the local economyThe timber industry was destroyed as trees were flattenedBuildings, bridges, railway lines and roads were destroyedLandscapeThe eruption blew away the top of the mountain, reducing its height by 400 metresA crater 500 metres deep formedEvery form of plant and animal life, for a distance of 25 kilometres north of the volcano, was killedApproximately 7000 animals died and every tree within 30km of the volcano was flattenedThe mudflow choked rivers with sediment, killing all fish and water life and completely filling Lake Spirit12 million salmon diedThe harbour at Portland was completely clogged up as the mud emptied itself into itPositivePeopleFive visitor centres were builtA sediment retention dam to prevent ash and sediment from flowing, while still allowing water to pass, was built to prevent the harbour at Portland from becoming clogged up after any future eruptions A new earthquake and eruption proof road was built, allowing access to Mount Saint HelensThe blast zone was declared a National Volcanic Monument by President Ronald Reagan, creating 110,000 acres dedicated to research, recreation and educationThis also created many new jobs and boosted the economy Landscape120 new lakes formedAmerica's youngest glacier formed in the crater of Mount Saint HelensThe roots of plants were still alive beneath the ash, so many plants grew back naturallyGophers were underground at the time of the eruption, so survived. They mixed old soil (containing seeds and roots) with ash, facilitating germinationWhere ash had been washed away, sprigs of roots began to resproutThe ground was cold and wet, and there was snow on the mountain as it was May. This vital timing meant that plants were dormant, so survived Management PredictionFrom March 1980, there had been several minor earthquakes, which were recordedThe earthquakes increased in frequency and intensity as time went onSmall eruptions of ash and steam indicated that an eruption was imminentA bulge developed on the north side of the volcano and it increased in size at a rate of five feet per dayPlanningAuthorities set up an exclusion zone, based on a previous eruptionResidents, tourists and forestry workers were strongly advised to evacuate the area, but not everyone took the adviceEmergency services, including helicopters and aeroplanes were on stand by, ready for the eruptionHowever, scientists could not give a precise date for the eruption, so some people did not leave their homesShort Term AidStranded people rescuedShelter was provided for those who had lost their homesMedical supplies were provided to the injuredOne million tonnes of ash was removed from roads, buildings and airportsElectricity was restoredThe clean up operation gave work to 200,000 people who had been temporarily put out of work by the eruptionHowever, due to the extent that the landscape had changed due to the eruption, maps were no longer accurate, which slowed down rescue effortsLong Term AidMillions of trees were replanted to restore the timber industry, which suffered a loss of $300 millionFarmers were provided with compensation, as they lost an estimated $70 millionNew tourist facilities were built, to provide the area with an income. Now, 3 million tourists visit Mount Saint Helens annuallyA channel on the Columbia river shipping channel was dredged to remove logs and a sediment retention dam was built to prevent the Portland Port from becoming clogged up after any future eruptionsMajor repairs, including the construction of a new highway, were undertaken to rebuild the 250km of roads, and 25km of railways that were damagedThe government provided money to the owners of the 200 homes that were destroyedMoney was given to redevelop salmon hatcheries as 12 million baby salmon died