Causes of Tsunamis
There are several ways tsunamis are produced. One way is by regional uplift or subsidence of the seafloor during an earthquake. Tsunamis started this way can travel long distances and cause destruction thousands of miles from where the wave was generated. Underwater landslides are another cause of tsunamis but these are less common, infrequently by submarine volcanic eruptions and very rarely by a large meteorite impact in the ocean. Submarine volcanic eruptions have the potential to produce truly awesome tsunami waves. Destruction in Seward, Whittier, and Valdez, and other places in 1964 were from underwater landslides which is a very good example. These tsunamis are localised. Above water landslides can also cause local tsunamis if they enter a body of water.
Diagram:
