Tsunamis

Large tsunamis have occurred in the United States and will undoubtedly occur again.
NOAA maintains the U.S. Tsunami Warning Centers, which work in conjunction with USGS seismic networks to help determine when and where to issue tsunami warnings.
Tsunamis are ocean waves triggered by large earthquakes that occur near or under the ocean, volcanic eruptions, submarine landslides, and by onshore landslides in which large volumes of debris fall into the water.
Although earthquake magnitude is one factor that affects tsunami generation, there are other important factors to consider. The earthquake must be a shallow marine event that displaces the seafloor.
Although both are sea waves, a tsunami and a tidal wave are two different and unrelated phenomena. A tidal wave is a shallow water wave caused by the gravitational interactions between the Sun, Moon, and Earth.