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.