Bathers along southern California who haven't given a thought to these giant waves should think again. Scientists had thought tsunamis occur rarely and are generally triggered remotely. Nations rely on an efficient Pacific-wide alert system to give timely warnings. Costas Synolakis from the University of Southern California at Los Angeles told the geophysics meeting that scientists have changed their minds. Several research teams reported that many giant waves are caused locally by offshore underwater landslides.
Earthquakes can trigger the the slides.
Ground water oozing through underwater sediment banks can also cause slumping. Garry Greene from the Monterey Bay Aquarium Research Institute showed maps of at least two slope failures in the central Santa Barbara channel. This is a new risk to be managed. A wall of water up to 50 feet high sweeping over a highly developed coastline could be devastating. Scientists reporting the danger said that local warning systems could be established that would give bathers and beach house residents the few minutes they would need to escape to higher ground.