Volcanic Hazards p. 138-140, web reading

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Volcanic Hazardsp. 138-140, web reading

• Volcano Facts
• Volcano Hazards
• Fall processes
• Flow processes
• Other types
• Predicting Volcanic Eruptions

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Giant Caldera Volcano Yellowstone
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Toba, IndonesiaThe Biggest Eruption?

• 75,000 years ago

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Toba, IndonesiaThe Biggest Eruption?

• Caldera diameter 100x35 km
• Volume erupted 2,800 km3
• 10 cm of ash fell in India, 3000 km away
• Volcanic winter for a decade
• With global cooling 3-5C
• Might have affected human evolution

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Volcanic Eruptions over the last 10,000 years

• 1300 active volcanoes
• 550 eruptions (lt 2000 yrs)
• lt10 potentially destructive volcanoes have been
  studied in detail

800 million people worldwide _at_ risk gt50 of
worlds volcanoes in nations with per capita GDP
lt20 US
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Volcanic Hazards
Fall Processes Flow Processes
Web reading
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Lava Flows
Basaltic lava (low viscosity) Usually slow moving
(lt10 mph) Rarely life threatening
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Nyiragongo volcano, Congo Goma, Jan. 19, 2002
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Nyiragongo volcano, Congo Goma, Jan. 19, 2002
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Pyroclastic Flows
High density mixture of hot ash, rock, and hot
gases Temp. gt500C Velocity gt 80-100 mph
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Pyroclastic Flows
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Mt Unzen, Japan

• Pyroclastic flows
• Eruption in June, 1991, killed 40 journalists and
  3 experienced volcanologists

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Ash Falls (Tephra Falls)

• can cover large areas for days to weeks
• ash will last on the ground for months to years
• making land and water unusable
• provide material for future hazards (lahars)

Mount Pinatubo, Philippines June 1991
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Ash fall in Rabaul, Papua New Guinea, 1994
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Volcanic AshDanger to Aircraft
Volcanic ash can be a serious hazard to aviation
even thousands of miles from an eruption.
Airborne ash can diminish visibility, damage
flight control systems, and cause jet engines to
fail. USGS
Part of a 747 engine
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Poisonous Gas Emissions
CO2, SO2, HCl, HF H2S
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Poisonous Gas EmissionsLake Nyos, Cameroon (1986)
Controlled degassing, 1995
Lake Nyos
River of CO2 50 m thick layer
Bottom of lake Saturated in CO2
CO2 gas from Magma
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Volcanic Landslides
Mt. St. Helens May 18, 1980 Debris Flow 2.3 km3
of material
Largest debris landslide in recorded history
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The avalanche traveled approximately 15 miles
downstream at a velocity exceeding 150 mph. It
left behind a hummocky deposit with an average
thickness of 150 feet and a maximum thickness of
600 feet.
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Mt. St. Helens May 18, 1980
Figure 5.10
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Mt. St. Helens
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Lahars (Mudflows)

• A mixture of volcanic fragments and water
• Mudflows are channeled along valleys on the
  flanks of volcanoes.
• Mudflows have the consistency of wet concrete and
  move at high speeds (up to 20-60 mph).

Pinatubo
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Nevado del RuizNov. 13, 1985

• Canyon that channeled the lahar that destroyed
  Armero and killed 23,000 people

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Town of Armero
The November 13, 1985 lahar from Nevado del Ruiz
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Volcano Monitoring and Prediction
Goal Prevent a Volcanic Crisis from turning into
a Volcanic Disaster
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Volcanoes of the Lower 48
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Volcano Monitoring and Prediction
Long-Term based on Historical Records and
Geologic History Age-dating of volcanic
deposits ? Eruption Frequency Types and amounts
of eruption products ? Size of Eruption
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Volcano Monitoring and Prediction
Short Term systematic observations of volcanos
visible and subsurface activity
Seismicity Ground tilt Gas emissions
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Rising Magma

• Ground Deformation
• Rising magma and increasing pressure exerted by
  gases often cause volcanoes to deform, or swell,
  before an eruption

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Rising Magma
Moving Magma and Volcanic Fluids Trigger
Earthquakes
High pressure causes rocks to break, triggering
earthquakes
Rising magma and volcanic gases exert pressure
Magma rises into reservoir beneath volcano
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Forecasting Volcanic Activity

• Ideal Forecast includes
• Location
• Timing
• Character of eruption and magnitude

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Forecasting Volcanic Activity

• Ideal Forecast includes
• Location
• Timing
• Character of eruption and magnitude

• Effective Forecasting involves
• Scientists
• Public officials
• News media
• Informed Public

Friday Video Path of a Killer Volcano Mt.
Pinatubo eruption of 1991