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Volcanic Hazards p. 138-140, web reading

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Title: Volcanic Hazards p. 97-99, web reading Author: Dept. of Geology and Geophysics Last modified by: saar Created Date: 2/6/2004 1:02:17 AM Document presentation ... – PowerPoint PPT presentation

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Title: Volcanic Hazards p. 138-140, web reading


1
Volcanic Hazardsp. 138-140, web reading
  • Volcano Facts
  • Volcano Hazards
  • Fall processes
  • Flow processes
  • Other types
  • Predicting Volcanic Eruptions

2
Giant Caldera Volcano Yellowstone
3
Toba, IndonesiaThe Biggest Eruption?
  • 75,000 years ago

4
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

5
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
6
Volcanic Hazards
Fall Processes Flow Processes
Web reading
7
Lava Flows
Basaltic lava (low viscosity) Usually slow moving
(lt10 mph) Rarely life threatening
8
Nyiragongo volcano, Congo Goma, Jan. 19, 2002
9
Nyiragongo volcano, Congo Goma, Jan. 19, 2002
10
Pyroclastic Flows
High density mixture of hot ash, rock, and hot
gases Temp. gt500C Velocity gt 80-100 mph
11
Pyroclastic Flows
12
Mt Unzen, Japan
  • Pyroclastic flows
  • Eruption in June, 1991, killed 40 journalists and
    3 experienced volcanologists

13
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
14
Ash fall in Rabaul, Papua New Guinea, 1994
15
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
16
Poisonous Gas Emissions
CO2, SO2, HCl, HF H2S
17
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
18
Volcanic Landslides
Mt. St. Helens May 18, 1980 Debris Flow 2.3 km3
of material
Largest debris landslide in recorded history
19
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.
20
Mt. St. Helens May 18, 1980
Figure 5.10
21
Mt. St. Helens
22
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
23
Nevado del RuizNov. 13, 1985
  • Canyon that channeled the lahar that destroyed
    Armero and killed 23,000 people

24
Town of Armero
The November 13, 1985 lahar from Nevado del Ruiz
25
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26
Volcano Monitoring and Prediction
Goal Prevent a Volcanic Crisis from turning into
a Volcanic Disaster
27
Volcanoes of the Lower 48
28
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
29
Volcano Monitoring and Prediction
Short Term systematic observations of volcanos
visible and subsurface activity
Seismicity Ground tilt Gas emissions
30
Rising Magma
  • Ground Deformation
  • Rising magma and increasing pressure exerted by
    gases often cause volcanoes to deform, or swell,
    before an eruption

31
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
32
Forecasting Volcanic Activity
  • Ideal Forecast includes
  • Location
  • Timing
  • Character of eruption and magnitude

33
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
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