1. Volcanoes

2.
Volcano – opening in Earth’s surface that often forms a mountain when layers of lava and volcanic ash erupt and build up.

3. Dormant volcano - volcano that is not “active”

4. Where volcanoes occur
1. Divergent Boundaries- location where two plates are moving apart
Long deep cracks are present and lava flows up and quickly cools

5. Where volcanoes occur
2. Convergent Boundaries - location where plates are moving together
One plate may slide under the other and partially melt = subduction zone
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The magma may then get forced upward and form a volcano
Ex. Pacific Ring of Fire (Mt. Saint Helens)

7. 3. Hot Spots
Occur because mantle is hotter in some areas than others and the magma is closer to the crust and can sometimes melt the Earth’s crust.
Ex. Hawaiian Islands

8. Two factors that determine if an eruption will be explosive or quiet:
1. Amount of water vapor and other gases that are trapped in the magma.
2. If the magma is basaltic or granitic
Basaltic (dark) magma contains less silica and is very fluid
Granitic (light) magma contains higher levels of silica and is very thick

9. Forms of Volcanoes
The type of volcano is determined by the type of eruption
The type of eruption is determined by the type of magma
There are three types of volcanoes.

10. Composite/Stratovolcanoes
Formed by eruptions that vary between quiet and explosive.
Made from andesitic lava
Composed of layers of tephra and lava.
Tall, steep-sided cones
Ex: Mt. Saint Helens & Mt. Vesuvius

11. Cinder Cone Explosive eruptions
Composed of tephra – volcanic material (ash, cinders, rocks, lava bombs)
Small, steep-sided cone
Ex: Paricutin, Mexico

12. Shield Volcano Gently sloping sides Basaltic lava Quiet eruptions
Ex. Hawaiian Islands