1. Essential Question
How do volcanoes shape the earth?

2. Volcanoes
Openings in the Earths Crust That Lets Magma Through and Often Forms a Mountain.

3. Parts of a Volcano
Vent: opening through which magma reaches the surface.
Crater: Steep depression around the vent.
Mountain: made of lava flows or tephra (dust, ash, cinders, bombs)
Magma Chamber: area of magma below volcano

4. Where Volcanoes Form Divergent Boundaries
Plates spread apart and magma flows to surface
Mid-ocean Ridge / East African Rift
Convergent Boundaries / Subduction Zone
Subduction melts one plate, melted material reaches surface.
Mount St. Helens
Hot Spots
Area of super heated mantle that a plate moves over.
Hawaii

5. Hot Spot Video

6. Types of Magma Granitic Magma Andesetic Basaltic Magma
High Silica content
Intermediate
Low Silica content
Thick
Runny
Traps lots of gases
Water vapor
Little trapped gases
Pressure builds
Small pressure build up
Explosive
Ash eruption
Fairly explosive
Ash and lava eruption
Non-explosive
Lava flow eruption

7. Three Types of Volcanoes
Shield Volcanoes
Cinder Cones
Composite Volcanoes

8. Shield Volcano Hot Spots / divergent plate boundaries
Basaltic magma: runny, little silica, little trapped gases.
Built by layer upon layer of lava flows.
Lava oozes and flows.
Non-explosive.
Broad flat gentle slopes.
Usually wider than is tall.

9. Hawaiian Island Shield Volcano

10. Cinder Cone Subduction Zones / Hot spots
Granitic magma: Thick, high silica, lots of trapped gases.
Built by piles of tephra (dust, ash, cinders, bombs).
Explosive.
Steep sides and not very tall.

11. Cinder Cone Video

12. Composite Volcano Subduction Zones
Has things in common with both cinder cone and shield volcano.
Alternating layers of lava flows and tephra.
Very tall and dormant for years
Cooling lava can seal vent and build pressure.
Mount Rainier
Andesetic Magma

13. Composite Volcano Video