|  The
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.
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