6) Tectonics case studies volcanos

6) Tectonics case studies volcanos

1. Volcanic eruption Montserrat

   • Impacts
     • Economic Impacts
       • The total loss in value of peoples homes and investments was estimated to be about 1 billion. over 20 villages and 2/3's of homes on the island were destroyed by pyroclastic flows. Tourists stayed away and businesses were destroyed disrupting the economy. However, tourism on the island is now increasing to see the volcano. Schools, hospitals, the airport and the port were destroyed.
     • Social Impacts
       • 19 people died and 7 were injured. Hundereds of people lost their homes. Fires destroyed many buildings e.g local government offices, the police headquaters and petrol stations. the population has declined 8000 of the islands 12000 inhabitants have left since the eruptions began in 1995. around 4000 came to the UK.
     • Environmental Impacts
       • Large areas were covered with volcanic material- the capital city Plymouth was covred under 12m of mud and ash. Vegetation and farmland were destroyed. volcanic ash from the eruption however has since improved soil fertility.
   • Context
     • The Soufriere hills Volcano is a composite volcano in monsterat. it is above a destructive plate margin where the North American plate is being forced under the caribbean plate. In 1995, Earthquakes , small eruptions and Lahars started. this lasted intil 1997. then on June 25th 1997, there was a series of small earthquakes followed by pyroclastic flows (fast flowing streams of hot volcanic material and gases)
   • Responses
     • The responses for the eruption were long term and short term. People evacuated from the south to safe areas in the north. the 1st evacuations took place in 1995. Shelters were built to house evacuees. Temporary infrastructure was also built e.g roads and electricity supplies.
     • Local emergancy services provided support units to search for and rescue survivors. A risk map was created and an exclusion zone is in place. the suth of the island is off limits while the volcano os still intermittently active. The UK has provided 41 million of long term aid to develop the north of the island. this included new docks, an airport and houses. these have been built with this.
   • Little managment
     • Scientists had studied the volcano in the 1980s but thier report wasn't given a lot of attention. There was no disaster managment plan for a volcanic eruption so when the volcano started erupting, the responses were slow. Also in the 1990s, key infrastructure had been built in risk area so when the volcano erupted, it was destroyed. this futher hampered the response.

2. Mt St Helens

   • Context
     • Mount St Helens in washington (USA) is one of several volcanic peaks in Cascade Muntains. The Cascade mountains are above a destructive plate margin where the Juan de Fuca plate is being forced under North American Plate.
     • Mount St helens is a composite volcano. From March 1980, there were signs that an eruption could happen soon- there were small earthquakes, a bulge appeared on the side of the volcano and ash and steam were released On 18th may, 1980 there was a large earthquake of magnitude 5.1 followed by a massive eruption of volcanic material- including rocks, ash, hot gases, steam and lava.
     • The eruption covered a 600 km fan-shaped area north of the volcano (blast zone) almost all vegetation and buildings were destroyed in the blast zone which reached up to about 30km away. The pyroclastic flows, lahars and floods (due to material being dumped in revers and lakes, displacing water( were caused by the eruption. then shortly after,there was another eruption of ash and steam. about 540 million tonnes of ash were deposited over an area of 57,000 km
   • Impacts
     • Economic
       • The total cost of damage was $1.1 billion. Over 200 homes and cabins were destroyed and many more were damaged.
       • Airports were temporarily closed (some for up to 2 weeks because of reduced visibility. (over 1000 comercial flights were canceled. A lot of money was spent clearing ash from roads and runnaways e.g it cost $2.2 million to clear ash in Yakima (a city 135 km from the volcano.
       • 27 bridges, 24 km of railways and around 300km of roads were destroyed, river traffic and shipping was disrupted and 31 ships were stranded because mudflows dumped huge amounts of sediment in rivers. the timber industry was severly affected by the destruction of the forrest.
     • Social
       • 57 people were killed-mostly by inhaling volcanic ash. Hundereds of people lost their homes. Unemployment rose tenfold at 1st (although this did return to normal once clean up operations began
       • Social facilities and recreational sites were destroyed. some people experienced emotional stress.
     • Environmental
       • Almost 240 km of forest was destroyed. Wildlife suffered- around 7000 big game animals (e.g Bear deer and elk) many thousands of birds and small mammals were killed. Around 12 million young salmon were killed.
       • Sediment dumped inspirit lake raised the lake bottom by over 90 m and the water level by over 60m water quality was temporarilyt reduced.
   • Responses
     • Responses included emergency shelters and Ash Clearance.Emergency responses were cordinated by FEMA and involved both national organisations (e.g the US Army corps of engineers) and local services)
     • Facemasks were distrubuted in some areas to protect people from breathing in ash. Emergency shelters were set up ffor stranded and homeless people. Ash clean up operations were organised- around 900,000 tones of Ash were removed from buildings, roads and airports.
     • Shipping channels were cleared of sediment to restore shipping and some new channels were cut. 45,500 acres of land have been re planted with more than 18.4 million trees. Domestic water supplies were monitored so they weren't contaminated.
   • Good managment
     • When the earthquakes began in march, the USGS (United States Geological Survey) started a round the clock monitoring system. It included gathering seismic data and measuring the rate of bulge growth ground temperature and sulfur dioxide gas emissions. Volcanic and seismic activity reports were issued daily. USGS Scientists issued warnings to people living in the area and made recommendations about the location of hazardous zones.
     • Based on these recommendations, In March access to the volcano was restricted and the evacuation of around 2000 people started. Despite the monitoring data, scientists couldn't accurately predict the eruption- on the day of the eruption, there were no unusual changes that could be taken as warning signs.