“Volcanoes” What is a Volcano? Volcano - A hole in the earth’s surface that often forms mountains from eruptions of lava and/ or volcanic ash. B. What causes a volcano? 1. Rock has to melt into magma. 2. Magma is forced upward because it is less dense than the rock layers around it. 3. When magma and other gases reach the surface it turns to lava or volcanic ash. 4. That forms the volcano. “Volcanoes” I. What is a Volcano? A. Volcano - A hole in the earth’s surface that often forms mountains from eruptions of lava and/ or volcanic ash. B. What causes a volcano? 1. Rock has to melt into magma. 2. Magma is forced upward because it is less dense than the rock layers around it. 3. When magma and other gases reach the surface it turns to lava or volcanic ash. 4. That forms the volcano.

C. Where do volcanoes occur? 1. A volcano can occur in one of three places. A.) Where plates move apart. B.) Where plates move together. C.) “Hot Spots” 2. Divergent Plate Boundaries - The area where plates move apart. A.) When plates move apart they form large cracks in the crust called rift zones. B.) Lava flows out of the rift zone. C.) This builds up a volcano.

Where volcanoes occur cont. D.) Examples: Volcanoes of Iceland (On the Mid Atlantic Ridge). 3. Convergent Plate Boundaries - The area where plates collide into each other. A.) When plates collide one plate is pushed downward. B.) This area is known as a subduction zone. C.) The heat and pressure of the plate being downward forms magma.

Where volcanoes occur cont……. D.) A volcano forms when the magma reaches the surface. E.) Examples: Ring of Fire volcanoes in the Pacific (Mt. St. Helens, Mt. Pinatubo). 4. Hot Spots - Areas of the mantle that are warmer than other areas. A.) Rock melts in these areas. B.) The magma reaches the surface and forms a volcano. C.) Example: Hawaiian Islands.

II. Eruptions & Volcanoes: A. What causes a violent eruption? 1. Two things determine if a volcano erupts violently or quietly. a.) The amount of water and gas trapped in the magma. b.) The type of magma. B. Amount of water and gases trapped: 1. Water and gases in magma act like soda in a can.

B. Amount of water and gases trapped cont. 2. If you shake the can and open it the gases explode out of the can. 3. Gases in magma also try to escape. 4. When the gases escape the volcano explodes.

C. The Type of Magma: 1. Basaltic magma has a low viscosity. 2. Viscosity - The ability of a substance to flow or the thickness of a substance. 3. Gases are released easily. 4. This causes nonviolent eruptions like Mt. Kilauea in Hawaii. 5. Granitic magma has a high viscosity. 6. Gases build up huge amounts of pressure before being released. 7. This causes violent eruptions like Mt. St. Helen's in Washington.

D. Forms of Volcanoes: 1. The form depends on if it was a nonviolent or violent eruption. 2. There are three basic types: A.) Shield Volcanoes B.) Cinder Cone C.) Composite 3. Shield Volcanoes - a broad volcano with gently sloping sides, built by nonviolent eruptions of basaltic magma. A.) Example: Hawaiian Islands.

Forms of Volcanoes Cont. 4. Cinder Cone - Volcano that forms from volcanic material that is violently erupted and piles up into a steep sided cone mountain. A.) Tephra - lava and or other volcanic material that harden into ash, cinders or bombs. B.) Example: Paricutin in Mexico (Corn Field Volcano). 5. Composite Volcano - Volcano that alternates between violent tephra eruptions and nonviolent lava eruptions. ANIMATIONS

ASH CINDER LAPILLI BOMBS BLOCK RETICULITE (SCORIA) OBSIDIAN

Forms of Volcanoes Cont. A.) Composite volcanoes are the most violent. B.) Example: Mt. St. Helens, Mt. Pinatubo.