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1.3.2.apt.wavThe plates that make up the earth's surface are of two types: lighter continental plates, like the North American Plate, and heavier oceanic plates. Continental plates contain the land that rides on top of them, while oceanic plates are composed entirely of the ocean floor.
These plates are not stationary. New seabed is constantly being created in the middle of the oceans. As this new ocean crust is pushed up from the earth's interior, it sets in motion all the earth's plates. These plates move at speeds of between 1 to 4 inches every year, about the speed at which fingernails grow. As the plates move, intense geologic activity occurs at the plate edges as they slide past, dive under, or collide with each other. Plate tectonics is the name given to the study of plate movements and how they create landforms.
All of Alaska's land is on the North American Plate. But Alaska's geology is also affected by another plate, the oceanic Pacific Plate. The Pacific Plate is moving slowly northward at about three inches a year and colliding into the North American Plate. While three inches a year may seem small, remember that the landscape forms over millions of years. So, three inches a year means three million inches over a million years! And that is enough to make mountains. This slow-speed collision is responsible for many of the landforms of modern Alaska, especially those of southern Alaska.
Direction of primary plate movement
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