The Eruption of Mount Pinatubo

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The Eruption of Mount Pinatubo

• By Anh Phi
• Prof. Terry Swanson
• ESS 315

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Statistics

• Date June 15, 1991
• Location Island of Luzon, Philippines
• Precursor 7.8 magnitude earthquake 100 km NE of
  Pinatubo region on July 16, 1990
• Volcano Type Subduction Volcano (composed of
  andesite and dacite) from Philippine Plate
  sliding under Eurasian Plate
• Type of Eruption Plinian (forms huge clouds,
  ex Mt. Vesuvius)
• Volcanic Explosivity Index (VEI) 6 (2nd
  largest terrestrial eruption of the 20th century)
• Ash Cloud Extent 34 km height, 400 km width,
  125000 km2 area
• Volcanic Material Expelled 10 billion metric
  tonnes magma and 20 million tons SO2
• Eruption Duration 9 hours

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Eruption Photos
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Aftermath
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Complications

• Typhoon Yunya (75 km north of Mt. Pinatubo)
• The mixing of rain torrents and volcanic
  materials resulted in massive lahars
• Most of the casualties caused by roofs collapsing
  under the weight of accumulated wet ash
• Annual flooding and lahars during wet season,
  remains a public hazard even all this time

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Why Did Pinatubo Erupt This Way?

• Mt. Pinatubo is an andesitic/dacitic volcano
• Viscosity (liquids tendency to resist flow) is
  dependent upon
• Temperature of liquid
• Chemical Composition of liquid ( SiO2 )
• Explosiveness of eruption is dependent upon
• Viscosity of magma
• Gas Content of magma
• This is why Mt. Pinatubos eruption was explosive
  compared to a basaltic lava flow in Hawaii.
• Andesitic and dacitic magma are lower temperature
  and more silicate-rich compared to basalt (higher
  viscosity) and also have higher gas content,
  therefore their eruptions are more explosive

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Economic Social Effects

• Casualties 800 dead and 100,000 left homeless
• 364 communities and 2.1 million people affected
  by eruption
• 8,000 homes completely destroyed, additional
  73,000 damaged
• Cost of billions of pesos to restore damaged
  infrastructure
• Agriculture disrupted 800 km2 farmland
  destroyed, 800,000 head of livestock and poultry
  killed, cost 1.5 billion pesos
• The gross regional domestic product (GRDP) of the
  Pinatubo area had been growing at 5 annually
  pre-eruption but fell to 3 afterwards

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Climate Change

• 20 million tons of sulfur dioxide gas expelled by
  eruption
• Sulfur dioxide mixes with water and oxygen in the
  atmosphere to form sulfuric acid, which depletes
  the ozone
• The ejected ash plume and aerosols (suspended
  solid particles or liquid droplets in gas)
  resulted in
• Decrease in incident light reaching Earths
  surface by 10
• Decrease in global temperature by 0.5 oC (1.1 oF)
  for 3 years
• Record level depletions of ozone layer

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• Questions?