Volcanoes%20and%20Seismic%20Hazards

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Volcanoes and Seismic Hazards
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Volcanoes

• I. What is a volcano?
• Opening in Earths crust through which molten
  rock, gases, and ash erupt.
• Volcano Formation
• Crater a basin-like rimmed structure at top or
  on flanks of a volcanic cone.
• Vent opening at earths surface through which
  volcanic material is extruded.
• Magma Chamber reservoir of magma in the shallow
  part of the lithosphere

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II. Magma Formation
3 conditions that allow magma to form Example of location this would occur
Decrease in pressure lowers melting temperature of materials in asthenosphere Rift valley at mid-ocean ridge
Temperature increase can cause materials to melt Asthenosphere at a hot spot
Increase in amount of water in asthenosphere can lower melting temperature of materials there Asthenosphere at subduction boundaries
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What Controls the Type of Magma and Eruption
Style?

• - The viscosity of the magma
• What effects viscosity?
• - Temperature of magma hotter, lower viscosity,
  more fluid
• - Composition of magma (amount of silica) more
  silica, higher viscosity, more resistant to flow.

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What Makes Magma/Lava Erupt?

• Magma is a liquid, less dense than surrounding
  material.
• Gases within magma rise to surface
• Low viscosity lava gases easily rise and are
  gently released
• High viscosity lava gases build up explosive
  eruptions

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III. Types of Magma
Characteristic Basaltic Magma (Mafic) Andesitic Magma Rhyolitic Magma (felsic)
Silica content 50 60 70
Gas content Least Intermediate Most
Viscosity Least Intermediate Most
Type of eruption Rarely explosive Sometimes explosive Usually explosive
Melting temperature Highest Intermediate Lowest
Location Rifts, oceanic hotspots Subduction boundaries Continental hotspots
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Basaltic Magma Kilauea
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Andesitic Magma Mt. St Helens
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Rhyolitic Magma Yellowstone Caldera (rim)
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IV. Ejected Material

• A. Lava liquid molten rock
• 1. Pahoehoe ropelike lava
• 2. Aa crumbly lava
• 3. Pillow lava thought to have
• formed under water

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B. Solid Pyroclastic Material

• 1. Ash microscopic solids
• Cinders pea-sized
• 2. Lapilli walnut size
• 3. Blocks/Bombs
• football size or bigger
• 4. Pyroclastic flow avalanche of burning ash

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V. Volcanic Landforms

• Cinder Cone steep-sided, formed by explosive
  eruption of cinders
• Small height, short lived
• Sunset crater, Arizona

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Composite Volcano (Stratovolcano)

• Steep-sided, built by lava flows and pyroclastic
  deposits (tephra)
• alternating layers, intermediate composition
  (andesitic), most dangerous
• Osorno volcano in the Chilean Andes

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Shield VolcanoGentle slope, resembles a warriors
shield, quiet eruptions of fluid lava flows
(basaltic), largest landforms on earth Mauna Loa
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CalderaCrater-shaped basin formed after top of a
volcano collapsesCrater Lake, Oregon
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Match description to type of eruption and volcano

• 1. Thin mafic lava flows, gentle slopes of
  hardened lava layers shield.
• 2. Felsic thick lava flows, much pyroclastic
  debris/steep slope composite
• 3. Small steep-sided, formed by explosive
  eruption of cinders cinder cone
• 4. Mt. St. Helens composite volcano
• 5. Mt. Pinatubo part of a chain of composite
  volcanoes
• 6. Mt. Fuji stratovolcano or composite
• 7. Kilauea shield
• 8. Craters on the Moon lava flow field with
  cinder cones

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Mt Ruapehu, New Zealand

• A cone volcano
• Very active
• Last erupted in 1995

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Lahars

• Volcanic mudflow often formed when hot ash mixes
  with water from melted snowand ice or a crater
  lake.

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Earthquake Destruction

• 1. Ground Shaking
• There are several controls to amount of damage
  any area may sustain
• Duration of shaking
• Distance from epicenter
• Type of bedrock material
• Amount of slippage along faults

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2. Building CollapseEarthquakes dont kill
people, buildings kill people.
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3. FirePhotograph showing the great fire
following the 1906 San Francisco Earthquake
magnitude 8.1-8.2.
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4. Landslides and Ground SubsidenceDamage from
the 1964 Alaskan Earthquake a massive
earthquake where over 200 acres of land slid
toward the ocean. (9.4)
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Liquefaction- Stable ground turns into fluid not
capable of supporting structures
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5. Tsunami Harbor Wave

• Most triggered by subduction-zone earthquake and
  earthquake induced landslides.
• Wall of water is pushed up from the ocean floor
• Can travel across ocean as a series of waves

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6. Ring of FireEarthquakes and volcanoes are
not distributed randomly they occur in specific
regions- usually along zones. where plate
boundaries meet.
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7. Volcanic Hazards

• Lava ash is deadly
• Mudflows (Lahars) are deadly
• Toxic gases
• Pyroclastic bombs,
• Cause acid rain
• Landslides
• Even though violent often results in fertile
  soil
• (Ruapehu Lahar emergency)

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1953 Tangiwai disaster
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Mt. St, Helens Mudflow and Pyroclastic Blast
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Seismic Risk Map (USA)
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Geologic Hazards and Emergency Preparedness

• Millions live in hazardous areas
• Many have no choice
• Many choose to live there
• Risks and Benefits volcanic ash creates fertile
  soil
• tourists
• geothermal energy
• Scientists try to predict hazards in advance
• Monitoring escaping gas,
• increased magma temperature,
• animal behavior

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Good planning reduces the effects of the hazard

• Monitoring warning
• Emergency supplies
• Families can organize
• Local emergency services be prepared
• Information available
• Buildings and roads designed to cope.