Volcano case study Flashcards
(25 cards)
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: signs of an impending eruption as first earth quakes occured and then steam filled with ash exploded onto the summit of the mountain.
- residents told to leave/not allowed within 8km of crater
- eruption on 18th May at 8:32 am: earthquake of 5.1 caused landslide - biggest ever recorded and wiped out all life within 27km radius
environmental effects of Mt St Helens
- mountain reduced from height of 2950m to 2560m as eruption created largest landslide ever recorded
- all plant/animal life within 25km radius of volcano killed
- mudflows poured down valleys choking rivers
social effects of Mt St Helens
- 61 dead: would have been more but sunday so noone working at logging camps
- 198 rescued
- 200 homes destroyed
- destructive lahars ripped out eight bridges and cut evacuation routes
- PTSD
- ash caused £100 million damage to farm machinery/crops
- shipping stopped on Columbia river/vessels stranded
responses to mt st helens
Helicopters rescued more than 100 people, and only 61 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
- Philippine plate plate was being subducted beneath Eurasian (continental)
- 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
mount pinatubo 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
- new houses built on stilts so lahars will not bury
montserrat key details
- Antilles Island
- boundary between the Caribbean and North American plates - destructive - composite volcano
details of montserrat eruption
- 18th July 1995, first since 19th century
Timeline: - 18 July 1995: First signs of eruption after centuries of dormancy – ash venting and steam explosions
- 25 June 1997: Major eruption with pyroclastic flows that killed 19 people in the Streatham village area (officially evacuated)
- island’s airport directly in the path of the main pyroclastic flow - completely destroyed
primary hazards of montserrat
- Pyroclastic Flows:
- over 400 degrees and speeds of up to 80 km/h
- killed 19 people in 1997 and buried capital Plymouth under up to 12 metres of ash/debris - Ash falls:
- columns of volcanic ash rose up to 9000 metres into atmosphere
- made roofs collapse - Lava domes/dome collapses:
- lava dome began growing 1995 at summit and when collapsed triggered pyroclastic flow
secondary hazards of montserrat
- Lahars:
- more than 10 years after initial eruption
- destroyed key infrastructure: recovery
- 15km of agricultural land buried
Primary effects of Montserrat
- 2/3 island covered in ash = impossible to get aid to people - roads blocked
- airport destroyed in Plymouth
- 19 died from pyroclastic flow
- Plymouth capital destroyed
- ash caused respiratory problems, collapse of roofs and eye/skin irritation
- 2/3 population evacuated: many to shelters in north others permanently e.g UK
secondary impacts of Montserrat
Economic:
- ash covered fields killed crops = year of failed harvest/no income for families
- tourism suffered - only visitors coming from cruise ships to look at volcano (issues of not staying locally)
- 80% of economy destroyed when Plymouth was
Social:
- loss of population: decline of about 5000
- limits to housing/development options: 60% of island became uninhabitable (Exclusion zones)
what is the hazard management used in montserrat?
- extensive seismograph network established around volcano to measure earthquake strength/depth
- earthquake deformation meters/tiltmeters put in place show signs of ground swelling
- satellite location GPS used to check ground movements
- pH rainwater monitored - indicate magmatic gas content
- geologists regularly flew into dangerous area to check growth of dome
Unsustainability of management of Montserrat eruption 1997
Social:
- just finished recovering from Hurricane hugo in 1989 when volcano erupted
- 2/3 population left after eruption -loss of community/brain drain
- tourism: people still visiting volcano (also mainly on cruise ships) but it is still active - hazard
- inequality between those who could evacuate/those who couldn’t: lack of space for people
- overcrowding in temporary shelters such as Salem
Economic:
- significant loss of workforce = difficult for recovery
- 70% rise in rent for accommodation: issues of inequality
- reliance on British aid: around 400 million since 1995
- fishing industry limited by exclusion zones and limited economic diversification = vulnerable (only agriculture and tourism)
