Volcanoes and Plate Tectonics A volcano is a

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/2 _10. swf