Tsunamis are giant, powerful waves most often caused by earthquakes beneath the ocean floor. Their incredible power can destroy entire communities, then drag the debris out to sea. This video shows what causes tsunamis and the importance of evacuating any area under a tsunami alert. | National Geographic TV

Tsunamis are long-wavelength ocean waves caused by the sudden displacement of large volumes of water. Most are triggered by undersea earthquakes, but volcanic eruptions, landslides, and meteor impacts can also generate them. Unlike normal wind-driven waves, tsunamis move through the entire water column, allowing them to travel at jet-aircraft speeds across deep oceans. In open water they may be barely noticeable, but as they reach shallow coastlines, the waves slow down, compress, and dramatical