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. 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: 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

4. What Controls the Type of Magma and Eruption Style? - The viscosity of the magma What effects viscosity? 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. Magma is a liquid, less dense than surrounding material. Gases within magma rise to surface Gases within magma rise to surface Low viscosity lava: gases easily rise and are gently released Low viscosity lava: gases easily rise and are gently released High viscosity lava: gases build up – explosive eruptions High viscosity lava: gases build up – explosive eruptions

6. III. Types of Magma Characteristic Basaltic Magma (Mafic) Andesitic Magma Rhyolitic Magma (felsic) Silica content ≤ 50% ≈ 60% ≈ 70% Gas content LeastIntermediateMost ViscosityLeastIntermediateMost Type of eruption Rarely explosive Sometimes explosive Usually explosive Melting temperature HighestIntermediateLowest Location Rifts, oceanic hotspots Subduction boundaries Continental hotspots

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 formed under water

11. B. Solid Pyroclastic Material: 1. Ash – microscopic solids 1. Ash – microscopic solids Cinders – pea-sized Cinders – pea-sized 2. Lapilli – walnut size 2. Lapilli – walnut size 3. Blocks/Bombs – football size or bigger 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 Cinder Cone: steep- sided, formed by explosive eruption of cinders Small height, short lived Small height, short lived Sunset crater, Arizona Sunset crater, Arizona

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

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

15. Caldera Crater-shaped basin formed after top of a volcano collapses Crater Lake, Oregon

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

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

18. Lahars Volcanic mudflow often formed when hot ash mixes with water from melted snowand ice or a crater lake. 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 Duration of shaking Distance from epicenter Distance from epicenter Type of bedrock material Type of bedrock material Amount of slippage along faults Amount of slippage along faults

20. 2. Building Collapse Earthquakes don ’ t kill people, buildings kill people.

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

22. 4. Landslides and Ground Subsidence Damage from the 1964 Alaskan Earthquake – a massive earthquake where over 200 acres of land slid toward the ocean.

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

25. 6. Ring of Fire Earthquakes 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. Geologic Hazards and Emergency Preparedness Millions live in hazardous areas Millions live in hazardous areas Many have no choice Many have no choice Many choose to live there Many choose to live there Risks and Benefits: volcanic ash creates fertile soil Risks and Benefits: volcanic ash creates fertile soil tourists tourists geothermal energy geothermal energy Scientists try to predict hazards in advance - Monitoring escaping gas, - increased magma temperature, - animal behavior

29. Good planning reduces the effects of the hazard Monitoring – warning Monitoring – warning Emergency supplies Emergency supplies Families can organize Families can organize Local emergency services be prepared Local emergency services be prepared Information available Information available Buildings and roads designed to cope. Buildings and roads designed to cope.