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: 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?
- 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 ≤ 50% ≈ 60% ≈ 70% Characteristic
Basaltic Magma (Mafic)
Andesitic Magma
Rhyolitic Magma (felsic)
Silica content
≤ 50%
≈ 60%
≈ 70%
Gas content
Least
Intermediate
Most
Viscosity
Type of eruption
Rarely explosive
Sometimes explosive
Usually explosive
Melting temperature
Highest
Lowest
Location
Rifts, oceanic hotspots
Subduction boundaries
Continental hotspots

7. Basaltic Magma: Kilauea

8. Andesitic Magma: Mt. St Helens

13. Rhyolitic Magma: Yellowstone Caldera (rim)

17. 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

18. 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

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

21. 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

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

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

24. 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

25. Mt Ruapehu, New Zealand A cone volcano – Very active
Last erupted in 1995
Looks like a partly collapsed cone, but its sprawling mass was formed by at least six craters along its 3 km length, one usually becoming activa after another.
Pinnacle ridge was the main vent 200,000 ya but activity has now moved to the southern end of the mountain.
Only one vent is active today, filled with the acidic waters of the almost circular crater lake, some 500 m across.

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

27. 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
Seismic Hazards – There aremany types of hazardous conditions resulting from earthquakes.
Write notes on Seismic Hazards

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

29. 3. Fire Photograph showing the great fire following the 1906 San Francisco Earthquake – magnitude

30. 4. Landslides and Ground Subsidence Damage from the 1964 Alaskan Earthquake – a massive earthquake where over 200 acres of land slid toward the ocean. (9.4)

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

32. 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
– on land appears like a fast rising high (or low) tide.
(speed is same as jumbo jet)

33. 6. Ring of Fire Earthquakes and volcanoes are not distributed randomly – they occur in specific regions- usually along zones. where plate boundaries meet.
Earthquakes and volcanoes are not distributed randomly- they occur in specific regions- usually along a zone where plate boundaries meet
Ring of Fire-zone along the Pacific Ocean that rings it, where earthquakes and volcanoes are the most common/active

34. 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)

35. 1953 Tangiwai disaster

37. Mt. St, Helens Mudflow and
Pyroclastic Blast

38. Seismic Risk Map (USA)

39. 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

40. 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.
Question – in what way can the effects of the hazards be reduced?