Volcanoes and Plate Tectonics

• A volcano is a weak spot in the Earth’s crust where molten material, or magma, comes to the surface.

• Magma is a mixture of rock forming substances, gasses, and water from the mantle

• Lava is magma that has reached the Earth’s surface.

Volcanoes and Plate Boundaries

• Volcanic belts often form along plate boundaries.– The Ring of Fire is a volcanic belt that follows

the rim of the Pacific Ocean.

Diverging Boundaries

• Mid-ocean ridges are a series of active volcanoes that occur along diverging plate boundaries.

• Continental rift valleys also contain volcanoes.

Converging Boundaries

• When subduction occurs along a plate boundary the rock on top of the subducting plate melts and forms magma.– Because the magma is less dense than the

surrounding rock it rises to the surface of the Earth forming volcanoes.

• Island arcs form along oceanic plate boundaries where subduction occurs.

• The volcanoes of the Pacific Northwest are also formed from subduction.

Hot Spot Volcanoes

• Hot spots are volcanoes that form above area where magma from deep in the Earth’s mantle rises and melts.– A hot spot can be found in the middle of a

plate.• Yellowstone National Park, and the Hawaiian

Islands are examples of hot spots.• http://www.wwnorton.com/college/geo/egeo/flash/

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