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=3.1 Volcanoes and Plate Tectonics (pg. 78)=

Vocabulary

 * Volcano:** A place where the crust is weak, and there is magma on the surface.
 * Magma:** Molten rock combined with rock substances from gases in the mantle.
 * Lava:** Places where the magma reaches Earth's crust.
 * Island Arc:** The places when volcanoes create a line of islands.
 * Hot Spot:** An area where magma (form the mantle) melts through the crust.
 * Ring of Fire:** One serious volcanic belt.

What is a Volcano?

 * Volcano eruptions- very dangerous
 * Cooled lava can form islands

Location of Volcanoes

 * About 600 active volcanoes on land
 * Most occur on diverging plate boundaries/hot sptos
 * Volcanoes occur in Belts
 * Major belt- Ring of Fire
 * Forms along boundaries

Volcanoes at Diverging Plate Boundaries

 * Form along mid- ocean ridge- volcanoes
 * some places mid-ocean ridge extends above surface

Volcanoes at Converging Plate Boundaries

 * When subduction happens at ocean floor, crust falls and rises as magma
 * Oceanic crust falls into asthenosphere and turns hot and melts to form magma
 * This is because surrounding rock is denser, magma seeps upward through cracks
 * Finally it breaks though ocean floor, creating volcanoes
 * These volcanoes make island arcs (see definition)

Hot Spot Volcanoes
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 * A hot spot is when magma is very large/dense (like a blow torch)
 * Hot spots create lots of volcanoes