How does a tsunami travel across the ocean so fast?

Unlike ordinary surface waves, tsunamis involve the motion of the entire water column from the seafloor upward. In the deep ocean their wavelength is enormous and wave height is usually small, which is why they can be hard to notice at sea. Their speed depends on ocean depth, so they travel faster in deeper water and slow down near shore. As they approach land, the wave energy compresses, the wave height increases, and destructive flooding can occur. Tsunamis are commonly triggered by undersea earthquakes, but they can also result from landslides or volcanic eruptions.