The southern part of Alaska is composed of a series of terranes that have been pushed against the North American landmass by the action of plate tectonics . The Pacific Plate moves northwestward relative to the North American Plate at about to per year , meeting the continental landmass in the Gulf of Alaska . The Pacific Plate subducts under the Alaskan landmass , compressing the continental rocks and giving rise to a series of mountain ranges . Terranes or island arcs carried on the surface of the Pacific Plate are carried against the Alaskan landmass and are themselves compressed and folded , but are not fully carried into the Earth 's interior . As a result , a series of terranes , collectively known as the Wrangellia composite terrane , have been pushed against the south coast of Alaska , followed by the Southern Margin composite terrane to the south of the Border Ranges fault system . A byproduct of the subduction process is the formation of volcanoes at some distance inland from the subduction zone . At present the Yakutat Terrane is being pushed under material of similar density , resulting in uplift and a combination of accretion and subduction . Nearly all of Alaska is composed of a series of terranes that have been pushed against North America . The coastal region is seismically active with frequent large earthquakes . Major quakes occurred in 1899 ( four between magnitudes 7 and 8 ) and 1958 ( 7.7 ) , followed by the 1964 Alaska earthquake ( 9.2 ) . The 1979 St. Elias earthquake reached magnitude 7.9
1964 Alaska earthquake
1964 Alaska earthquake
Wrangell–St. Elias National Park and Preserve