The United States spans an extraordinary range of tectonic settings, from the Pacific coast, where the Pacific and North American plates grind past each other along the San Andreas Fault, to the Cascadia subduction zone of the Northwest and the Yellowstone hotspot in the continental interior. Alaska and Hawaii add subduction and mantle-plume volcanism, making the country one of the most seismically and volcanically diverse on Earth.
California's San Andreas produced the devastating 1906 San Francisco earthquake, while Alaska's 1964 Good Friday quake, magnitude 9.2, remains the largest ever recorded in North America. The nation's active volcanoes range from Mount St. Helens, whose 1980 eruption reshaped the Cascades, to Kīlauea in Hawaii and the vast Yellowstone caldera, a supervolcano closely monitored by scientists.