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Tectonic Plates
by Leslie Whitaker

Tectonic plates are the name given to the sections of the Earth’s crust which move about very slowly. Some are continental plates and some are oceanic plates. When you look at the coast line of Africa and South America, you might think that they look like the two sides of a piece of paper torn apart on a jagged curving line. Well, I thought the same thing when I was a child, but I was taught that it was just a coincidence. After all, these continents are separated by thousands of miles of Atlantic Ocean. At that time, we did not understand the theory of plate tectonics. Since then, scientists have learned that the surface of the Earth, its crust, is actually composed of a set of plates which float on the surface of the molten mantle. These plates can rub against one another as they move. They may slide side by side like the plates along the coast of California, or they may crash into one another like the Indian subcontinent is crashing into Asia, or one plate may sink under the edge of the other plate. In the Cascade mountains, the small Juan de Fuca plate is being forced under the North American plate beneath these mountains. This is called a subduction zone. At the subduction zone, the rock of the sinking plate is heated and turns into magma. In addition, the friction and the stress of two plates rubbing together causes weak spots and tears in the plate where underlying magma from the mantle can come to the surface.

The Ring of Fire is the result of the large Pacific plates interaction with all the plates around its perimeter.

Introduction - Magma, Lava, and Mountain Formation - Predicting Volcanoes - Tectonic Plates - Mt. St Helens - Mount St. Helens Recovery - Volcanoes: Good, Bad or Both