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Volcanoes and Seismic Hazards

Volcanoes and Seismic Hazards. Volcanoes. I. What is a volcano ? Opening in Earth ’ s 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.

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Volcanoes and Seismic Hazards

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  1. Volcanoes and Seismic Hazards

  2. Volcanoes I. What is a volcano? • Opening in Earth’s 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 earth’s surface through which volcanic material is extruded. Magma Chamber – reservoir of magma in the shallow part of the lithosphere

  3. II. Magma Formation:

  4. 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.

  5. 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

  6. III. Types of Magma

  7. Basaltic Magma: Kilauea

  8. Andesitic Magma: Mt. St Helens

  9. Rhyolitic Magma: Yellowstone Caldera (rim)

  10. 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

  11. 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

  12. V. Volcanic Landforms • Cinder Cone: steep-sided, formed by explosive eruption of cinders • Small height, short lived • Sunset crater, Arizona

  13. 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

  14. Shield VolcanoGentle slope, resembles a warriors shield, quiet eruptions of fluid lava flows (basaltic), largest landforms on earth Mauna Loa

  15. CalderaCrater-shaped basin formed after top of a volcano collapsesCrater Lake, Oregon

  16. 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

  17. Mt Ruapehu, New Zealand • A cone volcano – • Very active • Last erupted in 1995

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

  19. 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

  20. 2. Building CollapseEarthquakes don’t kill people, buildings kill people.

  21. 3. FirePhotograph showing the great fire following the 1906 San Francisco Earthquake – magnitude 8.1-8.2.

  22. 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)

  23. Liquefaction- Stable ground turns into fluid not capable of supporting structures

  24. 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

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

  26. 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)

  27. 1953 Tangiwai disaster

  28. Mt. St, Helens Mudflow and Pyroclastic Blast

  29. Seismic Risk Map (USA)

  30. 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

  31. 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.

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