Plate tectonics volcano case studies

Plate tectonics volcano case studies

1. Mount St. Helen's (1980)

   • Physical factors
     • Cascade mountain range - USA
     • Subduction
       • Juan de Fuca plate under North American plate
     • Explosive volcano
       • Pyroclastic flows
     • 9,677 feet high
   • 'However' moments
     • Located in a National Forest
       • Low population density surrounding volcano
     • Lateral blast (northwards)
       • Did not follow expected pattern
       • Acres of timber, bridges, roads and camp lands destroyed
       • Low population density minimised the deaths
   • Before the eruption
     • Had erupted many times before
       • Winter 1979 - changes below ground
         • March 20th - 4.1 magnitude earthquake
           • Predictions made
             • Forest area surrounding volcano closed - ranger stations closed
               • Gadgets used to detect any changes
             • Mad of predicted flooding
             • Bulge noticed on north face of volcano
   • Effects of the eruption
     • Moving NWW at 5ft per day
     • Mountain covered in snow
       • Flooding - following the topography
     • May 18th - 8.32 am - 1m3 of rock and ash erupted
       • NE wind
     • Rescue mission
       • Largest in the history of NW
       • Helicopters kicked up too much ash - rescuers released by cable to reach survivors who were reeled up
     • Lower Columbia River closed
       • Impact on trade
     • 61 people died
       • Only 3 within the exclusion zone
     • Masses of vegetation destroyed
       • All vegetation up to 20 miles away had been destroyed or stripped of leaves
     • Eruption lasted 9 hours
   • Management of consequences
     • Recovery and planning scheme surveyed the damage
     • Attempts to rehabilitate land

2. Navado Del Ruiz (1985)

   • Physical factors
     • In Pacific ring of Fire
     • Subduction - Mazca plate under South American PLate
   • 'However' moments
     • Composition of mud meant people could float
       • Reduced death toll
     • Mud could not support rescue equipment or heavy machinery
       • People rescued by helicopter
         • Shortage of helicopters
           • Rescue teams sent in from other countries
     • Huge lahar created by melting glacier
   • Before the eruption
     • Increased seismic activity
       • Increased sulphur emissions
       • Bursts of steam eruptions
     • USGS - noticed cluster of small earthquakes before eruption
       • Was not recognised as a precursor to an eruption
     • Columbia had no equipment to monitor the volcano
       • Expertise came from other countries
     • Money from UN - help map the areas at greatest risk
       • Almero identified as high risk
     • Report of map and volcanic hazards finished on October 7th
       • Only 10 copies distributed
   • Effects of the eruption
     • Local health services, civil defence and the Red Cross - helped injured
     • Armero
       • 30 miles East
       • Built on mudflow from eruption 400 years ago
       • 85% destroyed by lahar
         • Only 1/4 of population survived
           • 23,000 people died due to mudflow
       • Mud flow reached the city at 25 mph
         • 1 mile wide
     • 50 schools destroyed
     • Cost 20% of country's GDP

3. Mount Pinatubo (1991)

   • Before the eruption
     • Surveillance flights over volcano
     • June 10th - evacuation
       • 100s of 1000s of people
       • Only 1500 security force remained
       • Eruption 48 hours after
   • 'However' moments
     • Typhoon - Tropical Storm Yunya
       • Effected poorer parts
         • Poorer housing in shanty towns etc.
         • Work in agriculture
           • 1/2 livestock died
           • Lahars lasted for years
       • Meant the ash spread further than the evacuation zone
     • Clark Airforce Base - US MIliraty
       • Very organised
       • Ended their 100 year presence in the Philippines
   • Effects
     • Communities 50 miles away showered with ash and sand
     • Ash sent 100 ft into the air
     • Eruption 10 miles wide
     • Pyroclastic flow seen 15 miles away
     • Creates lightning as part of own weather system
     • Angeles
       • Buried in 10 feet of ash
       • 500 deaths from this city
     • Evacuation kept death toll under 800
     • 1/2 regions farm animals died
     • Increased average global temperatures by 1 degrees C for up to 5 years
       • Ash circling the globe
     • 1/4 million displaced
     • Lahars and mud flows - effect lasted for years
     • 650,000 lost jobs
     • 50,000 families lost homes
     • 100,000 became homeless
     • 1/2 billion dollars in property and economic damage

4. Mt Nyiragongo (2000)

   • Physical factors
     • Constructive margin
     • African Rift Valley
     • Main crater - 250 m deep and 2km wide
     • Democratic Republic of Congo
   • Before the eruption
     • Unexpected but warnings of lava flows meant many were evacuated
   • Effects of the eruption
     • Opened a fissure 13 km long
     • Destroyed 1/3 Goma, a town with 200,000 inhabitants
       • Unemployment
       • Loss of infrastructure
     • Lava covered 3rd runway at Goma airport
     • 147 died
     • More than 350,000 fled the area
     • Earthquakes (magnitude 5) caused building damage
     • 'Red Alert' after eruption
       • Evacuation kept the death toll low
     • Aid from UN
     • Camps set up by UN
     • £15 million - aid and housing for refugees
   • 'However' moments
     • Petrol station exploded while it was being looted
       • People were looting in order to be able to sell the petrol for food
       • 200 killed
     • Sulphurous lava entered Lake Kiivu, polluting the lake, which is a major source of drinking water in the area

5. Mt Etna (1991 - 1993)

   • Physical factors
     • Stratovolcano
     • Truncated by several small calderas
     • Constructed over an old shield volcano
   • During the eruption
     • End of 1991 - lava began to pour from vents on the Eastern flank
     • Large earth barrier constructed across the end of the Val Calanna
       • Several tens of meters high
       • More than 400 meters long
       • Held back the lava for several months
       • Slow lava advance temporarily while other protective measures were put in place
       • 1992 - lava began to spill over the barrier and into the valley
         • Smaller barriers erected across the valley
           • Overwhelmed by the lava
           • Concrete blocks dropped from helicopters in an attempt to block the primary feeder channel
             • 1992 - holes blasted in the side of the lava tube to try and encourage another direction of flow
               • Stopped the lava flow advancing on Zafferana
                 • Eruption ended 10 months later in 1993

6. Soufriere Hills - Montserrat (1995 - 1997)

   • During the eruption
     • Began to erupt on July 1995
     • Early activity - ash emission, steam explosions and earthquakes
       • Ash and steam reached 2500m height
     • After a quiet period, high ash cloud and small pyroclastic flow in March 1996
     • June 25th - main exlosion
       • Extensive pyroclastic flows
         • 4 -5 million m3 of material
         • Most flowed down northern flank
           • Damaging houses and killing some inhabitants
     • Only 40 km2 of the 100 km2 island was safe to live on
       • Southern island was uninhabitable
     • Plymouth (capital) - covered in 10 m of ash and mud
   • Management
     • Aid by the British government
       • Spent more than £100 millon
         • Assisting migration
         • Restoring services, agriculture and employment
     • Exclusion zones set up
     • Evacuation of 7,000 of the island's 11,000 inhabitants
       • Went to neighbouring countries (e.g. Antigua) or for resettlement in the UK
     • Resettlement of some of the population from the south to the safer north of the island
     • Temporary shelters set up in the north
     • New permanent housing set up
     • Capital moved from Plymouth to Salem
     • Montserrat Volcano Observatory set up
       • Monitor Soufriere Hills activity
   • Long term responses
     • Attempts to restore the tourist industry
     • Return of some refugees from the UK and elsewhere
     • Gerald's - new airport built
       • Opened in 2005
       • Cost £11 million
     • New football pitch constructed
       • Funded by FIFA