Geologic Cutaway of Tectonic Plates

The earth's surface is a network of large interlocking plates, like the pieces of a puzzle. The plates move in relationship to one another. We live at the edge, where the Pacific Plate slides under the North American Plate, about 2½ to 3 inches a year. As it curves beneath the Kenai Peninsula, the Pacific Plate descends to a depth of 30 miles. When it reaches the west side of Cook Inlet, it is 60 miles below the surface. Subduction, the process whereby one plate dives under another, produces the volcanoes west of Kachemak Bay. Eight percent of all active volcanoes on earth are found in Alaska.

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