1. Ch. 18 Volcanoes

2. Ch. 18 Vocabulary Viscosity Tepha Vent Hot Spot Caldera
Cinder-Cone Volcano
Composite Volcano
Pyroclastic Flow
Shield Volcano
Crater

3. Magma
Proves that earth is geologically active
Magma formed deep within earths surface
Temperatures must be high enough to melt rock oC
Temperatures increase with depth
Pressure increase with depth
Increase Pressure – Decrease melting point
B/C Magma is less dense than surrounding rock, Magma rises to surface

4. Magma Composition Viscosity Silica content Water content
Resistance to flow
Hotter the magma, lower the viscosity
Silica content
Determines viscosity
High content – high viscosity
Water content
High amounts of water will evaporate, build pressure
More explosive
Three Types of Magma

5. Magma Types Basaltic Andesitic Rhyolitic Low Viscosity (50% Silica)
Quiet Eruptions
Andesitic
Intermediate Viscosity (60% Silica)
Intermediate Eruptions
Rhyolitic
High Viscosity (70% Silica)
Great Eruptions

6. Volcano Locations: Ring of Fire

7. Anatomy of a Volcano Vent Cone (1 km wide) or Caldera (50 km wide)
Magma reaches the surface and lava erupts out of a vent
Lava solidifies and builds up mountain around vent
Cone (1 km wide) or Caldera (50 km wide)

8. Types of Volcanoes Shield Broad gently sloping sides
Layer upon layer of basaltic lava accumulation (non-explosive)
Low viscosity

9. Types of Volcanoes Cinder Cone
Material exploded high into the air and comes back to earth
Steep side from explosive eruptions
More viscous lava contains more gases which fuel more explosive eruptions

10. Types of Volcanoes Composite
Volcanic fragments and lava eruptions – most common
Contains large amounts of silica, water, and gases
Potentially dangerous to people and environment

11. Other locations for Volcanoes
Hot Spots
Located away from plate boundaries
High temperature mantle plumes rise towards the surface
Hawaiian Islands