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Geologic Map
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Generalized Geologic Map of the Conterminous United States
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  The North American Tapestry of Time and Terrain

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Aleutian Islands


Close up of the Aleutian Island chainThe strike-slip plate motion found at the San Andreas and Denali faults runs along most of the Pacific Coast of North America. However, at the Pacifc plate's northern edge, along the southwestern coast of Alaska, the strike-slip behavior gives way to subduction. This means the Pacific plate is plunging under the North American plate, rather than grinding against it. As the crust is pulled deep into the earth, it starts to melt and some of the melted crust rises back to the surface, penetrating it in the form of volcanoes. In this region, an arc of volcanic islands have formed. Called the Aleutian arc, it stretches over 2,500 km (1,550 miles), extending from western Alaska to Russia's Kamchatka Peninsula. The volcanoes here are highly active, and have had negative economic consequences as the smoke and ash they produce interferes with the airplanes that follow Asia-North America-Europe flight paths overhead.

photograph of mount gilbert volcano
This photograph, taken by Chris Nye of the Alaska Division of Geological and Geophysical Surveys, shows the volcanic Mount Gilbert on the northern end of Akun Island in the eastern Aleutians. For more information on the volcanoes of Alaska, see the Alaska Volcano Observatory. This image was obtained from the USGS's Volcanoes of the Alaska Peninsula and Aleutian Islands--Selected Photographs.