Volcano case study Flashcards
what plates involved in the mount st helens volcanic eruption
Lies close to a destructive plate boundary where the smaller Juan de Fuca plate is being forced into the mantle by the larger North American plate
dates/duration of Mount St Helens eruption
18th May 1980
more than nine hours
stratovolcano
timeline of events for mount st Helens eruption
- march 1980, shallow earthquakes on north side of volcano, recognized to be different due to their harmonic tremor
- ash eruptions followed for few weeks and north flank started to bulge
- may 18th north flank broke open and fell downhill in a massive 2.3km cubed landslide, leaving new horseshoe shaped crater, 2km wide, 3km long and 600m deep
- landslide stopped moving** 22km from volcano** its water content together with melted ice/snow to form destructive lahars
- hot pyroclastic flows drained rapidly down volcanoes side covering 550km
environmental effects of Mt St Helens
- debris reached Columbia river that ocean-going ship could not sail on it because the previously 200m wide, deep channel was reduced to less than 70m wide and 3m deep
- Ash had to be cleared from roads
social effects of Mt St Helens
- 57 dead
- 200 homes destroyed
- destructive lahars ripped out eight bridges and cut evacuation routes
- PTSD
- $1.1 billion damage
responses to mt st helens
Helicopters rescued more than 100 people, and only 57 died, including a geologist monitoring the hazard and people who refused to leave the area.
prediction/planning and management for mt st helens
- Ground deformation was monitored using lasers in 1980, enabling fairly accurate predictions of eruptions
- In march 1980, shallow earthquakes on north side of volcano recognized to be different (Harmonic tremor) to normal ones so extra seismographs were installed and emergency services, guided by hazards maps, started to work on plans to evacuate
- People were not allowed within 13 km of summit and most property owners moved away
- Emergency evacuation plans were made for communities further down the valleys
mount Pinatubo volcano key details
- developing country
1991
North east of Philippines on island of Luzon
strato volcano
primary/secondary hazards of mount pinatubo volcano
Primary: ash cloud and pyroclastic flow
Secondary: lahars and flooding
development of mount pinatubo eruption
- Eurasian (continental) plate was being subducted beneath Philippine plate
- when oceanic plate subducted it is melted and forced away. Molten magma is pushed up through small cracks and explodes out through a volcano
- 2 weeks before 15th june there were small magma and ash eruptions as well as earthquakes
- 15th of june = ash cloud 34km
- eruption lasted 3 hours
impact of primary hazards
Ash cloud:
- 34km cloud covered 125,000 km squared and brought darkness to Luzon
Ash/pumice from pyroclastic flow:
- smothered 80,000 hectares of land
- 800 km squared of agricultural land destroyed
- 847 killed by collapsing roofs
- 1.2 million homeless
- pyroclastic flow travelled 16km
- cost $89 million
impact of secondary hazards of mount pinatubo
Lahar:
- caused by ash mixed with rainfall from typhoon Yungha
- 100 killed
- indigenous moved to gov organised homes = fragmented society
- manila airport closes - stopping import/exports
prediction for mount pinatubo eruption
- united states geological service helped to predict
- lahar detectors and hazard mapping
- constantly monitored
- satellite images
- warning signs like gas, steam looked for
modifying event for mount pinatubo eruption
- not much done
- did not help that the houses were flimsy and easily destructible
- dykes that were built for lahars failed and they were washed away
modifying vulnerability for mount pinatubo eruption
- alert systems were in place to warn of eruption
- 75000 evacuated within 30km radius
- USA air force helped
- aid was pre organised
modify loss of mount pinatubo eruption
- red cross provided food and blankets in refugee camps
- us government officially helped advise
- raised 600 millionplate
h in aid - new houses built on stilts so lahars will not bury
