Styles of Eruptions and Volcanic Hazards

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Styles of EruptionsandVolcanic Hazards
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Styles of volcanic eruptions

• Some volcanoes may erupt only once - monogenetic
  (Diamond Head)
• Other volcanoes erupt many times - polygenetic
  (Kilauea)
• Some erupt very gently (Kilauea)
• Others are very violent and explosive (Mt. St.
  Helens, Mt. Pinatubo)
• How come?

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Explosive volcanoes found associated with
subduction zones

• Explosiveness is a function of magma viscosity
  (resistance to flow)
• Magmas that generate the explosive volcanoes are
  much more viscous than the non-explosive magmas
• More silica, cooler magma, more gas

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Hawaiian magmas

• Not very explosive
• Not very viscous
• Low silica, hot magma, moderate gas content

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Eruptive styles are

• Classified by level of eruption explosiveness

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I. Flood eruptions

• Least explosive eruptions
• Very fluid basalt erupted in very large
  quantities VERY FAST
• Lavas erupted over large areas
• Thought to develop as hot spots burn thru crust

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Columbia Plateau
More than 420,000 cubic km of lava
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Flood basalts
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II. Hawaiian-type eruptions
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Hawaiian-type eruptions

• The next least explosive kind of eruption
• Fluid magmas with small amounts of gas
• Eruptions relatively gentle
• Periodically have a violent eruption but very
  rare - Drive in volcanoes

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Hawaiian-type eruptions Build shield volcanoes
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Styles of explosive volcanism
Modified from Julia Sable
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III. Strombolian eruptions

• Named for volcanic island off coast of Italy
• Characterized by less fluid lavas
• Moderate explosive activity
• Tephra common
• Lots of ash blankets country side
• Basalt and andesite common
• Large steep-sided composite volcanoes built by
  repeated Strombolian eruptions

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More explosive eruptions Build composite cones
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Mt. Shasta, California
Aa flows
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IV. Vulcanian eruptions

• Characterized by more viscous lavas
• Stubbly flows are common
• Lots of ash
• Andesite most common

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Arenal Volcano, Costa Rica
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V. Peléan eruptions

• Named for 1902 eruptions of Mount Pelée on
  Martinique in the Caribbean

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Mt. Peléeruption

• Almost 30,000 people were killed instantly

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Peléan eruptions

• Lavas highly viscous, very explosive
• Explosive eruption of highly gas-charged lava
  leads to nuée ardente (glowing avalanche) or
  pyroclastic flow which move at 60 kph and are
  300deg C inside
• Dont outrun these guys!!!

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Pyroclastic flows formed during 1968 eruption of
Mt. Mayon Ash cloud is 30,000 fthigh Flows
caused by ash cloud collapse or lava dome
collapse
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VI. Plinian Eruption most powerful eruption

• Named for Roman naturalist killed in explosion of
  Mt. Vesuvius in 79 A.D
• Very destructive
• Accompanied by major collapse

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Plinian Eruption

• Mt. St. Helens is good example

before
during
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Plinian most powerful eruption

• Crater Lake in Oregon formed by similar explosive
  eruption
• Ash from this volcano (Mt. Mazama) found all over
  the Pacific Northwest as far east as the
  Mississippi River!

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Plinian most powerful eruption

• Greatest Plinian eruptions of modern times
• 1813 explosion of Tambora volcano (eastern
  Indonesia)
• 1883 explosion of Krakatau (Sunda Strait between
  Java and Sumatra)
• Explosion heard in northern Australian, 2400 km
  away

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Other Recent Eruptions

• Pinatubo Vulcanian-type eruption
• Mt. Unzen (Japan,1991) -- generated a number of
  lava domes that collapsed, sending pyroclastic
  flows down the side of the volcano, so it can be
  classified as a Peléan eruption

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Volcanoes Plate Tectonics

• OK. So, where do you find all these volcanic
  eruptive styles?
• Flood eruptions - atop hot spots
• Hawaiian - at hot spots along MOR
• All the rest are associated with subduction!

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Styles of explosive volcanismWhat are the
hazards?
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Volcanic Hazards

• 1. Lava
• Flows

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Volcanic Hazards

• 2. Falling Tephra
• Like one sees at the beginning of the movie
  Dantes Peak.

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• Falling tephra in Yakima, Washingtonduring Mt.
  St. Helens eruption

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More Volcanic Hazards

• Pyroclastic flows
• Mudflows - Lahars
• Toxic volcanic gases

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Hazards in Hawaii

• Lava flows

Note The next few slides are courtesy of GG
graduate student Chris Gregg
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Lava Flow Hazard Zone Map of Hawaii
Historic Eruptions Mauna Loa 33 flows
since 1843 5 reached ocean in Kona Hualalai
3 flows since 1800 2 reached ocean in
Kona
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Steep slopes gt 6 Hualalai gt50 Mauna Loa
35 Kilauea lt5
Fast transit times

• lt 24 hours

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Lava FlowsFrom Hualalai and Mauna Loa That Have
Affected Kailua-Kona
1877
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Hualalais last eruptions (c. 1800-1801)
Resorts
Airport
Subdivision
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MAUNA LOAs Radial Vents (33) and Rift Zones
Historic radial vent eruptions 1843, 1859, 1877,
1935
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Typical Mauna Loa Eruptions Summit followed by
fissure eruptions
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What Controls the Flow Paths of Lava Flows?
TopographyWhat Controls the Speed of Lava
Flows? Slope angle, surface roughness, eruption
rate, lava type (viscosity)
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1950 Eruption Flow velocities 16-48 km/hr
Note that all of these hazards are associated
with the big island! How come?
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Worst volcanic hazards often occur after major
eruptions

• Ash covers sides of volcano
• Ash becomes unstable during heavy rain
• Ash mud flow - LAHARS
• 10 years after Pinatubo eruption, mudflows were
  still killing people

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LAHAR - ASH MUD FLOW
LAHAR - ASH MUD FLOW
LAHAR - ASH MUD FLOW
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Volcanic gases

• Very dangerous
• CO2, CO, SO2, H2S, HCl and HF

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Hawaiian volcanoes

• Do not usually emit enough gas to harm people
• Except for Vog which forms as volcano erupts and
  as lava enters the ocean (Even reaches Oahu with
  Kona wind)

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Attempts to control flows

• In the past, people have tried to control, direct
  lava flows by
• Diverting the flow with barriers built with
  bulldozers
• Diverting by bombing one or all of the following
  locations - the vent, edge of a flow, tube
  entrance
• Water the flow front - not very successful!

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Avoiding volcanic hazards

• Predict them
• Volcanologists getting good at predicting
  eruptions of dangerous volcanoes
• Mt. St. Helens, Unzen and Pinatubo
• But, missed 1993 Mayon eruption

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Predictions eruptions

• Mostly made based on monitoring
• Seismic activity increases
• Ground tilting
• Increased heat flow
• Increase in sulfur in volcanic gas
• Because magma is moving into shallow levels under
  volcano!

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Cyclic nature of Kilauea eruptions
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Waianae Volcano
Koolau Volcano
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Thurston Lava Tube
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Meteorites have struck the Earth in the past.
Many meteorites are made of iron and nickel.
We think this represents material of planets
similar to Earth.
Earths interior (core) is probably also
composed of iron and nickel.
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The end!