How and where?
- Volcanoes are found at destructive and constructive plate margins
- At destructive plate margins, the oceanic plate subducts under the continental plate as it is more dense (which also creates an ocean trench)
- The oceanic plate is melted and destroyed in the magma
- A pool of magma forms
- The magma rises through cracks in the crusts and erupts onto the surface, forming a volcano.
- At constructive plate margins, the magma rises up into the gap created by the plates moving apart an forms a volcano
Types of Volcano
Composite - Mount Fuji, Japan
Made of ash and lava that has erupted and cooled into layers. The lava is thick and flows slowly. It hardens quickly to form a steep-sided volcano.
Shield - Mauna Loa, Hawaiian Islands
Made up of only lava. The lava is runny, flows quickly and spreads over a large area, forming a low, flat volcano.
Dome - Mount Pelee, the Caribbean
Made up of only lava. The lava is thick, flows slowly and hardens quickly, forming a steep-sided volcano.
Case Study - Soufriere Hills, Montserrat
The Soufriere Hills volcano in Montserrat erupted on June 25th 1997 (smaller eruptions started in June 1995). It was very large with 4-5 million metres cubed of rocks and gas released. 19 people were killed.
Montserrat is on a destructive plate margin (Atlantic plate forced under the Caribbean plate). Magma rose through weak points in the Soufriere Hills, forming an underground pool of magma. The rock above the pool collapsed and formed a vent, causing the eruption.
Case Study - Primary Impacts
- Large areas of the island were covered with volcanic material - The capital city (Plymouth) was buried under 12m of mud and ash.
- Over 20 villages and 2/3 of homes on the island were destroyed by pyroclastic flows (fast-moving clouds of super-heated gas and ash).
- Schools, hospitals, the airport and the port were destroyed.
- Vegetation and farmland were destroyed.
- 19 people died and 7 were injured.
Case Study - Immediate Response
- People were evacuated from the south to safe areas in the north.
- Shelters were built to house evacuees.
- Temporary infrastructure was also built e.g. roads and electricity supplies.
- The UK provided £17 million of eergency aid (Montserrat is an overseas territory of the UK).
- Local emergency services provided support units to search for and rescue survivors.
Case Study - Secondary Impacts
- Fires destroyed many buildings including local governement offices, the police headquarters and the town's central petrol station.
- Tourists stayed away and businesses were destroyed, disrupting the economy.
- Population decline - 8000 of the island's 12000 inhabitants have left since the eruptions began in 1995.
- Volcanic ash from the eruption has improved soil fertility.
- Tourism on the island is now increasing as people come to see the volcano.
Case Study - Long-term Response
- A risk map was created and an exclusion zone is in place. The south of the island is off-limits while the volcano is still active.
- The UK has provided £41 million to develop the north of the island - new docks, an airport and houses have been built in the north.
- The Montserrat Volcano Observatory has been set up to try and predict future eruptions.