Volcanism and Volcanic Hazards

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Volcanism and Volcanic Hazards

• Bill Menke
• September 21, 2005

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Questions to think about

• Which is the most dangerous volcano in the world?
• What group of people are most endangered by
  volcanoes

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Summary

• What is a volcano?
• Where does lava come from and why do volcanoes
  erupt?
• How is size quantified?
• Where are volcanoes occur?
• How frequently do volcanoes erupt?
• How do volcanoes cause damage?

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What is an volcano ?

• An volcano is a mountain from which lava and hot
  gasses erupt

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But I have a semantic problem here

• But I dont like the word mountain, because
  sometimes lava erupts from places that have
  little, if any, topographic relief
• And I dont like the definition leaving out the
  notion of temporal persistence, that the eruptive
  activity is long-lasting

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So maybe I should use the phrase Volcanic Center

• A region of the earth in which lava and hot
  gasses have persistently erupted from the ground
  over many thousands, or even millions, of years.
• A single volcanic center may include several
  related and closely-spaced volcanoes, or it may
  contain none.

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Why do Volcanoes Erupt ?
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What is Magma ?

• Molten rock with in earth
• Chemical composition matters!
• Low silica rocks (e.g. basalts) very fluid
• High silica rocks (e.g. rhyolites) very viscous
• Concentration of gasses (main H20 and CO2)
  matters!
• Gasses under pressure cause explosions
• Gasses are poisonous

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Volcano Size The Volcanic Explosivity Index, or
VEI, was proposed in 1982 as a way to describe
the relative size or magnitude of explosive
volcanic eruptions. It is a 0-to-8 index of
increasing explosivity. Each increase in number
represents an increase around a factor of ten.
The VEI uses several factors to assign a number,
including volume of erupted pyroclastic material
(for example, ashfall, pyroclastic flows, and
other ejecta), height of eruption column,
duration in hours, and qualitative descriptive
terms.
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VEI Description Plume Height Volume Classification How often Example
0 non-explosive lt 100 m 1000s m3 Hawaiian daily Kilauea
1 gentle 100-1000 m 10,000s m3 Haw/Strombolian daily Stromboli
2 explosive 1-5 km 1,000,000s m3 Strom/Vulcanian weekly Galeras, 1992
3 severe 3-15 km 10,000,000s m3 Vulcanian yearly Ruiz, 1985
4 cataclysmic 10-25 km 100,000,000s m3 Vulc/Plinian 10's of years Galunggung, 1982
5 paroxysmal gt25 km 1 km3 Plinian 100's of years St. Helens, 1981
6 colossal gt25 km 10s km3 Plin/Ultra-Plinian 100's of years Krakatau, 1883
7 super-colossal gt25 km 100s km3 Ultra-Plinian 1000's of years Tambora, 1815
8 mega-colossal gt25 km 1,000s km3 Ultra-Plinian 10,000's of years Yellowstone, 2 Ma


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Global distribution of Volcanoes
About 1500 volcanoes worldwide
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How long do eruptions last?

• Most eruptions last 10 - 1000 days
• Less than 20 over within 72 hours
• Median is 7 weeks (1176 hours)

1000
600
Eruptions
200
0.1
1
10
100
1000
10000
Duration (days)
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How Often do Eruptions Occur?
Cumulative number of eruptions With eruptive
volumes equal to or Greater than the given amount
Eruptions obey Gutenberg-Richter Statistics lots
of small ones, just a few big ones. The graph at
the left are for Explosive eruptions in
Kamchatka During the last 10,000 years
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Divergent Plate Boundaries

• Mid-ocean ridges
• strong mantle upwelling to fill in hole, so
  lots of basaltic magmatism (almost all of which
  is under water)
• Continental Rifting
• Thicker crust suppresses mantle melting
  somewhat, but can add volatiles

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Convergent Plate Boundaries

• Subduction Zones
• dewatering of subducted lithosphere (string at
  100-150 km depth) suppresses the melting point of
  mantle rock to produce basaltic magma
• Continental Collision
• Strong thickening of crust can cause
  once-shallow, water-rich crustal rocks to be
  buried. They can heat up and melt to produce
  granitic melts

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Mantle Plumes

• Oceanic Hotspots
• rising mantle plumes lead to melting that
• produces basaltic magmas and Hawaii-type
  volcanic islands
• Continental Hotspots
• Thick lithosphere leads to greater degree of
  chemical variability, broader range of lava types.

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Hazard 1 Lava Inundation(rare, but it happens)

• Case of Goma, Congo
• a city with a population 500,000, located near
  Rwanda border, on shore of Lake Kivu, affected by
  lava from Nyiragongo Volcano
• Jan 17, 2002, 45 people died, 50,000 displaced.
  Eruptions with deaths in 1977, too.

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African Rift Valley Continental Divergent Plate
Boundary
Nyiragongo Volcano
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City of Goma
Lake Kivu
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Lava from Nyiragongo volcano, inundates Goma,
Congo
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Goma airport closed by lava flow
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Reasons for deaths

• Burns from coming in contact with lava or hot
  rock, or from buildings set afire.
• High concentrations of poison gases that are
  being emitted from the lava.
• Destruction of infrastructure that supplies vital
  services (water, etc)

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Hazard 2 Mudflow Lahar
Mt. Rainier, Washington State Lots of water
locked up in that summit glacier
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Crate Lake, Oregonlots of water in that lake ...
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If all that iceon Mt. Ranier suddenly melted,
where would the water and mud go?
Tacoma, Wa
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Armero, Columbia

• Town of 27,000 people on the flank of Nevado del
  Ruiz Volcano
• Much of the town in a river valley subject to
  Lahars
• Nov 13, 1995 23,000 people died on when the town
  was innudated by 15 meters of mud

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Nevado del Ruis Volcano Note glacier at summit,
valley that channels water
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Part of town that was in river valley Was
innundated by several meters of mud
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Reason for Deaths

• Being buried alive in thick, gooey mud

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Hazard 3 Pyroclastic Flow Nuee Ardente

• Hot gasses and dust burp out of the volcanos
  summit and cascade downhill at speeds of 50-100
  mph.

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St. Pierre, Martinique

• Town of 29,000 people on the shore of a volcanic
  island in the Carribean
• May 8, 1902 Pyroclastic flow from Mt. Pele
  volcano destroys the entire town, leaning only 1
  survivor (a guy in jail)

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Martinique
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May 8, 1902 Pyroclastic flow Destroying
the town of St. Pierre
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St. Pierre After the Pyroclastic flow
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(Aside) The famous Pelean Spine, 350 meters
high, was a rock spire that was pushed up out Of
the crater of Mt. Pele in 1902 as new lava rose
beneath the volcano.
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Hazard 4 Tsunami

• Explosive volcanism at volcanic island caused a
  tsunami in nearby water
• Local tsunamis, like the one following the
  Krakatau eruption, are the most common. But
  ocean-crossing tsunamis are possible. The ca.
  1625 BCE eruption of the Agean island of Thera is
  an example.

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Krakatau
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Note location of volcano island in center of
narrow straight between two populated land
masses, Java and Sumatra
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• August 27, 1883
• extremely large explosion
• collapse of the volcanic edifice
• 30 meter high tsunami hits coast of
• Java and Sumatra, killing
• 36,000 people
• 165 villages totally destroyed

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Steamship washed Inland by 1883 tsunami
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Reasons for Deaths

• drowning
• Being crushed by floating debris

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Hazard 5 Ash Fallsvolcanic ash fine rock
particles

• Ash falls over broad area, like snow
• weight of ash collapses house
• ash makes road impassible
• ash-covered grass poisonous
• to livestock (e.g. Iceland, 1783)
• larger chucks of rock (bombs) also fall

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Luzon, Phillipines

• Near Mt Pinatubo
• 800 people killed by housing collapse when ash
  covered their houses
• Plenty of warning, but ash does not initially
  appear all that dangerous. But wait till its a
  meter thick! An it becomes very heavy and slick
  during the rain!

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Ash Plume from Mt. Pinatubo
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Ash covered houses near Mt. Pinatubo
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Hazard 6 Global Cooling
Aerosols (particularly sulfate) injected high is
the atmosphere reflect sunlight back to space,
resulting in net cooling of the Earths
surface Unseasonably cold temperatures case crop
failures
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1816 The Year without a Summer June 9-10, 1816
On the 9th, frost was reported as far south as
Worcester, Massachusetts and on the 10th to East
Windsor, Connecticut. July 6, 1816
Temperatures in the 40s F range were reported in
Connecticut at both Hartford and New Haven.
Robbins in East Windsor noted temperatures almost
cold enough for a frost.
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Tambora volcano (Sumbawa, Indonesia) Extremely
large VEI6 eruption in 1815. May have been
the Largest in 10,000 years Perhaps 90,000
people Died worldwide, from starvation
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People and Volcanoes

• Very local hazards
• Lava inundation
• pyroclastic flow
• regional hazards
• mudflow
• Explosion induced tsunami
• global hazards
• Global cooling
• Chemical pollution by ash
• Island collapse

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Questions to think about

• Which is the most dangerous volcano in the world?
• Versuvio, because of its proximity to Naples,
  Italy
• And because of the very large eruption that
  occurred in 79 CE
• What group of people are most endangered by
  volcanoes
• Volcanologists I know several of whom have
  died, and nearly all of us have had close calls