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Volcanoes Case Studies Mount St Helens – May 18 1980 What Where Mount St Helens is on the plate boundary between the Juan de Fuca plate and North American plate. When it erupted it permanently changed the surrounding landscape It is one of five volcanoes in the cascade range in Washington An Earthquake of 5.0 on the Richter scale triggered the eruption Huge lateral (sideways) blast of hot volcanic gases team dust and rock fragments released at over 100mph Some lava erupted but mainly as pyroclastic (lava bombs and pumice stones) Glaciers melted Huge quantities of ash, steam and gas released Biggest ever landside of soil, snow and rock ran down the mountainside and filled Spirit Lake - led to a huge mudslide Located in Washington state, NW USA, the Rocky mountains Located on a destructive plate boundary N. American Plate (continental crust) and Juan de Fuca plate (Pacific plate(oceanic crust) collided – a subduction zone Pacific plate is sub ducted and pressure/heat causes rock to "melt" into magma increased pressure caused Mt St Helens to erupt above the magma hot spot The area around the mountain is a National Park which is mainly used for tourism, forestry, salmon farming and some agriculture – therefore the population density of the area is relatively low The USA is an MEDC (and was in 1980) – with a GDP per capita of over $25,000 (in 1980) Mt. St. Helens is a typical composite cone volcano - formed on a destructive plate margin where the Juan de Fuca plate is being Effects Short term Social Ash and mud blocked roads, chocked rivers Many injuries and 61 people died mainly after choking on hot volcanic ash and burns and poisonous gas Many people left homeless after 200 log cabins destroyed Flooding destroyed communications such as road and railway bridges. Sediment carried downstream ruined barge transport on the Columbia River Lahars (mudflows of ash and water) covered an extensive area surrounding the volcano. Helicopters used to search for survivors Air conditioning systems cleaned as clogged by Ash Masks ordered (2 million) to protect lungs 2000 people evacuated. The National Guard issued clean water for Economic Environmental Livestock, 520km of pine wildlife and forests flattened crops destroyed up to 20km away many killed e.g. from the deer, bear and eruption – birds landscape totally changed Ash blocked rivers destroying Ash deposited popular fishing over a huge area sites and causing (over 1cm deep flooding. This in 120km away at turn destroyed Yakima) crops and Ash cloud took livestock. 17 days to travel round the world The national park was closed as Swirling ash partly destroyed triggered so loss of tourism lightening which Prime farm land started many covered in ash so forest fires no production of When it erupted crops (Nuée it permanently ardente (hot ash changed the and gas surrounding Massive loss of landscape. commercial Caused biggest logging land and landslide ever trees destroyed recorded. Local tourism The sideways disrupted i.e. blast of camp sites, pulverised rock, subducted under the North American plate people to drink. Cause The eruption on Mount St Helens was caused by an earthquake caused by the feeble north face, which made the volcano to release its underground pressure. Series of earthquakes that initially took place at a rate of 15 per hour. Each of these earthquakes was of a different magnitude and they took place beneath the volcano. The northern flank of the mountain then began to slide downward and a series of steam eruptions followed. When May 18 1980 at 8.30am (had not erupted for 100 years before) From the spring of 1980, scientist started to record 100s of small earthquake tremors coming from the mountain. In March there were small eruptions of stream and ash from the volcano. These events attracted a large number of news reporters and tourist to the area. By early May there was a visible bulge on the northern flank of the volcano where magma was being pushed to as a result of a volcanic plug that had formed in the main vent. At 8:32 am on Sunday 18th May 1980 the eruption began .As well as the landslide, lateral blast, pyroclastic flows and ash cloud, the heat from the eruption melted snow which covered the mountain creating lahars (as secondary hazard) Long Term The Volcano is now more closely monitored Drains cleared to prevent flooding. More people employed in tourism. hotels etc. Huge compensation issue as flights were cancelled etc. Some positives souvenir ash trays/T-shirts made a lot of income and the site became an even bigger tourist attraction some financial compensation Buildings and bridges and roads rebuilt – allow tourism Farming community and locals suffered huge losses-land, property Overall cost of destruction and damage estimated at $1.1 billion Tourism increased – local economy helped. Many tourist centres. glacier ice and ash wiped out all living things up to 27km north of the volcano Trees replanted (over 10 million) Fertile soil after a time due to ash adding nutrients Rapid natural recovery Mount Pinatubo – 3 June 1991 What Where Pinatubo lies near a subduction zone and has been inactive for 600 years The first formal evacuations were ordered from the 10 km (6.2 mi) zone on April 7. Followed by ones on June 7, 13 and 15. Ten times larger than the eruption of Mount St. Helens in 1980, Pinatubo’s eruption threatened the lives of millions of people. A giant ash cloud rose 35 kilometres into the sky Typhoon Yunya, coincidentally, occurred the same time as the eruption and also saved many lives. The typhoon brought heavy rain, which saturated accumulating tephra and stopped its spread. Second largest eruption this century – Not erupted for 4 centuries. Mount Pinatubo is a stratovolcano found in the north east Philippines. It formed where the Eurasian plate is being subducted beneath the Philippine plate. One of the 22 active volcanoes dotting the Philippines Mount Pinatubo is one of a chain of composite volcanoes that constitute the Luzon volcanic arc. It is among the highest peaks in west-central Luzon, in the Philippines. Effects Social Short term 847 people killed 300 by collapsing roofs, 100 from mud flows (lahars) and rest from disease including measles. Ash and pumice destroyed 42,000 homes 58,000 people had to be evacuated from a 30km radius of the volcano 100 people killed by lahars Manila airport closed (houses and bridges destroyed). Electricity went off 200000 people relocated Red Cross, Action Aid and Oxfam provided food and blankets in evacuation camps 23 USGS personnel helped advise the community and government officials for 8 weeks Lack of clean water (as contaminated) Aviation problems Economic Environmental Ash cloud covered 125000km2 bringing darkness to central Luzon. Volcanic ash smothered 80000 hectares of land. 150km2 of reforestation projects destroyed. Water was contaminated Fast flowing volcanic mudflows (lahars) because severe river bank erosion, undercut bridges etc. Until June 1991, Mount Pinatubo rose 1,745 metres above sea level. The new summit elevation of Pinatubo is approximately 1,485 metres above sea level. Huge avalanches of hot ash, gas, with fresh volcanic deposits as much as 200 metres thick. The eruption removed so much magma and rock from below the volcano that the summit collapsed to form a large volcanic depression or caldera Weight of the rain caused roofs to collapse. 5 billion cubic meters of ash and pyroclastic debris were ejected from its fiery bowels producing eruption columns 18 kilometres wide at the base and heights reaching up to 30 kilometres above the volcano’s vent. When Cause 15th March 1991 earthquakes felt Earthquakes of increasing intensity for the next 2 weeks. 2nd April 1991 phreatic eruptions along a 1.5km fissure on the summit. Small eruptions of volcanic ash over the next few weeks. 3rd May first eruption of magma. 7th June Large explosion generated an ash column 7km high. 12th June more violent eruptions with small earthquakes producing ash columns 24km high. 15th June ash was ejected 34km into the atmosphere. The eruption lasted for 3 hours. A series of earthquakes that lasted over two weeks caused Mount Pinatubo to erupt. Mount Pinatubo erupted because the Philippine plate started to slide underneath the Eurasian plate. This caused the lave to be pushed to the surface and causing a big explosion A build-up of pressure due to tectonic movement over time. Long Term 500 people died from diseases such as measles in refugee camps Many indigenous Aeta people had to move into government organised resettlement areas because their homes were destroyed. This caused the Aeta society to become fragmented. President Ramos created the Mount Pinatubo Commission to raise 10 billion Filipino pesos in aid. Overseas Filipino Workers provided clothing for victims The volcano continues to be a major hazard to the people who have returned to the area around the volcano. 1.2 million people lost their homes and had to migrate to shanty towns in Manila Telephone links cut and communications were damaged or destroyed by pyroclastic flows Heavy rainfall from Typhoon Yunga causes buildings to collapse New houses have been built on stilts so future lahars will not bury them. Road links destroyed More than 8,000 houses were completely destroyed, and a further 73,000 were damaged. Full economic recovery cost £10 billion. Norway and UK government sent millions in aid 5 billion pesos spent on used to build dykes for lahars (later washed away by the lahars) Farmland destroyed by falling ash and pumice, unusable for years, the 1991 harvest was destroyed 800km2 agricultural land destroyed and 800000 livestock and poultry killed costing 1.5 billion pesos. 650,000 workers lost jobs Total losses in 1991 and 1992 alone were estimated at 10.6 and 1.2 billion pesos respectively, including damage to public infrastructure estimated at 3.8 billion pesos. Lahars caused severe erosion to rivers. Global cooling caused by the ash. Temperatures dropped by 0.5°C. Acid rain due to the 22million tonnes of SO2 erupted. Since the climactic 1991 eruption, ash deposits have also been remobilised by monsoon and typhoon rains to form giant “lahars