Other volcanic features

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Other volcanic features

• Flood basalts
• Largest volcanic events in terms of volume
• Volatiles, viscosity are low, so not very
  explosive
• Cover large areas w/ thick layers of lava
• Lava domes
• Hardened dome/plug of magma cools quickly
• Can form in hours, continue for years, decades

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Flood Basalts
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Lava Domes
Lava Dome, Mt. St. Helens
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Volcanic Hazards
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Outline

• Types of volcanic hazards

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Volcano Classification

• Active currently erupting or has erupted in
  historical time
• Dormant presently inactive but may erupt again
  (examples Cascades)
• Extinct not active, not expected to be active
  for long time in future

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Cumulative Deaths Due to Volcanic Hazards in past
2000 years
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Causes of Deaths
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How bad can it be?

• 1815 Indonesia 92,000 died
• 1822 Indonesia 5,500 killed
• 1826 Indonesia 3,000 killed
• 1883 Indonesia 36,417 killed
• 1902 Martinique 29,025 killed
• 1902 Guatemala 6,000 killed
• 1919 Indonesia 5,110 killed
• 1951 New Guinea 2,942 killed
• 1982 Mexico 1,700 killed
• 1985 Columbia 23,000 killed

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Pyroclastic Flow

• Most deadly of all hazards
• Superhot, fast moving cloud of volcanic gas,
  steam, debris
• 200-700 degrees C, 80 km/hr (hurricane speeds!)

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Generation of pyroclastic flow

• Eruption column collapse
• Dome collapse
• Directed blasts

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Pyroclastic flows
Mayon, Philippines, 1984
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Effects of Pyroclastic Flows

• Destroys nearly everything in path
• Structures
• Burial of sites
• Burn forests, crops, structures
• Melt snow to form lahars

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Building destruction
Remnant of building after eruption of El Chichon,
Mexico in 1982 Note reinforcement rods bent in
direction of flow
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Effects of pyroclastic flows
Mt. St. Helens - forest destruction
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Effects on people

• Physical impact
• Burns
• Inhaling superhot gases
• Usually quick death

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Examples

• Many examples of devastating pyroclastic flows
• Unzen, Japan
• Chichon, Mexico
• Mt. Pelee, Caribbean

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Mt. Pelee

• 1902-1903, 1929-1932 significant pyroclastic
  flows
• Many from directed blasts, deadliest in 1902
• Viscous magma filled crater
• May 1902, several pyroclastic flows, traveling
  190 km/hr
• Destroyed St. Pierre (30,000 people) and other
  towns in area

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Mt. Pelee
Large area affected by 1902 pyroclastic flows
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Eruption Debris

• Includes cloud, bombs, ash fall
• Bombs kill small of people every year
• Clouds
• Planes fly into cloud - dangerous
• Over 25 years, 60 jets damaged
• Ash fall
• Bury cities

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Ash fall hazards
Roof collapse
Mid-Afternoon - daylight gone
Water systems can clog
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Cloud Hazard
Kamchatka eruption, seen by space shuttle
Ash from Mt. Spurr traveled around for days
(satellite image)
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Example - Mt. Vesuvius 79 AD

• Cause of volcano subduction
• Region near Pompeii also had earthquakes, but
  city of 20,000 people not deterred to move
• Significant volume of material erupted (4 km3) in
  first wave
• Pompeii buried by ash/pumice 3 m deep
• Later pyroclastic flows continued to bury city

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Vesuvius
Remains of Pompeii after 79 AD eruption
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Tsunami

• Wave caused by undersea vertical displacement
  (like earthquakes)
• Volcanic eruption can also cause tsunami
• Pyroclastic flow or lava dome avalanche
• Collapse of cone or crater

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Example - Krakatau 1883

• Stratovolcano between Java and Sumatra
• Subduction zone
• Collapse led to tsunami 35 m (115 ft)
• Death toll 36,000
• New cone appeared in 1927

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Collapse of Krakatau
Anak Krakatau
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Lahars

• Mudflow of volcanic debris, produced when
  pyroclastic debris or lava mix with rain, snow,
  ice, lakes
• Can travel quickly (40 mph) and significant
  distances (10s of miles)

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Dark pathways - lahars triggered by Mt. St.
Helens eruption, 1985
Cloud upriver lahar traveling down riverbed in
Guatemala
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Home destroyed from lahar - Mt. Unzen, Japan lava
dome collapse and later rains, 1993
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Example - Nevado del Ruiz 1985

• Colombian volcano, small glacier on top
• Small eruption caused melting, sending mud down
  the mountain
• Covered most of town of Armero with 26 ft thick
  mud
• Killed 22,000

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Nevado del Ruiz, 1985
River valley with lahar remains
Town of Armero
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Famine

• Indirect hazard
• Eruptions change climate
• Can harm plants, animals

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Iceland eruption, 1783

• Fissure eruption of basalt
• Released gas rich in SiO2 and fluorine
• Slowed grass growth and added significant amounts
  of fluorine to grass
• Killed significant population of livestock
• 20 of Iceland population died due to famine

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Tambora, 1815

• Indonesian volcano, most violent eruption in last
  200 years
• Significant Plinian eruption
• Next pyroclastic flows (12mi3 of material)
• Deaths in region 90,000 (10 during eruption,
  90 later)
• 1816 - year without summer
• Affected global climate

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Gas

• Gas can escape from basaltic magmas
• CO2 gas is common
• Depending on gas, can kill plants in region
• Can also be trapped in water

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Example - Lake Nyos, Cameroon

• Area of failed rifts with some remaining volcanic
  activity
• 1986 - gas burp from the lake
• Sent rivers of gas down into valleys 25 km (16
  mi)
• Effects - 1700 deaths, no animals alive
• Plants ok though

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Why?

• CO2 gas leaking out of basaltic magma
• Dissolved in bottom waters of lake (held down by
  pressure)
• Some event caused overturn
• Eruption, earthquake, landslide, temp change all
  possible triggers
• Gas release river 50 m thick

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Lake Nyos
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Lake Nyos
Efforts to pump water, gas out of lake
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Continued hazard?

• YES!
• Still some gas remaining
• Continues to build up
• Possible ways to pump gas out to reduce risk

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Lava Flows

• Not big hazards in terms of fatalities
• Moves too slow to kill people
• Can destroy towns, villages

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Kilauea, HI

• Few lives lost
• Mostly structural losses

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1973 Flows in Iceland

• Lava flows threatened town, harbor
• Built diverters to control flow
• Sprayed water to harden flows, move to flow in
  other direction away from harbor

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Man vs. volcano!
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Actually gained land and improved harbor
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Next Time

• U.S. volcanoes and related hazards