I NSIDE E ARTH : V OLCANOES Section 1: Volcanoes and Plate Tectonics

W HAT IS A VOLCANO ? Volcano - weak spot in the crust where molten material, or magma, comes to the surface Magma - molten mixture of rock, gasses, and water from the mantle Lava - magma that reaches the surface

L OCATION OF VOLCANOES There are about 600 active volcanoes on land. Many more lie below the sea. Ring of Fire: a major volcanic belt formed by many volcanoes at the rim of the Pacific Ocean Most volcanoes occur along diverging plate boundaries, such as the mid-ocean ridge or in subduction zones around the edges of oceans

V OLCANOES AT D IVERGING P LATE B OUNDARIES Volcanoes form along the mid-ocean ridge, which marks a diverging plate boundary. Most of this is located underwater, except for places such as Iceland and the Azores Islands in the Atlantic Ocean.

V OLCANOES AT C ONVERGING B OUNDARIES Many volcanoes form near the plate boundaries where the oceanic crust returns to the mantle (subduction) Subduction causes ocean crust to sink into the mantle forming a trench. The crust melts and forms magma, which then rises back towards the surface. Continental plate and oceanic plate collide, oceanic plate dives under the continental plate Produced the volcanoes of the Andes Mountains in South America and volcanoes of the Pacific Northwest in the United States

Many volcanoes occur on islands, near boundaries where two plate collide. The resulting volcanoes create a string of islands called an island arc.

H OT S POT V OLCANOES Some volcanoes result from “hot spots” in Earth’s mantle. A hot spot is a weak spot where magma from deep in the mantle melts through the crust like a blow torch. Hot spots often lie in the middle of continental or oceanic plates far away from plate boundaries.

Can gradually form a series of volcanic islands, for example the Hawaiian Islands, which formed one by one over millions of years as the Pacific plate drifted over a hot spot.

They can also form under the continents. An example of this is Yellowstone National Park in Wyoming, which marks a major hot spot under the North American plate.

W RITING IN S CIENCE Travel Brochure – As a travel agent, you are planning a Pacific Ocean cruise that will visit volcanoes in the Ring of Fire and Hawaii. Write a travel brochure describing the types of volcanoes the group will see and explaining why the volcanoes formed where they did.