ABSTRACT
Most large tsunamis arise around the rim of the Pacifi c Ocean and the Indian Ocean, along seafl oor faults called subduction zones, where colliding tectonic plates trigger large earthquakes (Folger 2012). Waves spread in opposite directions from the fault and within minutes crash onto nearby land, as in Japan in 2011; within hours crossing the ocean and in this case sweeping a California man out to sea. Landslides and volcanic eruptions can launch tsunamis in lakes and rivers. A warning system consisting of a network of 53 detector buoys, most in the Pacifi c Ocean, now tracks the movement of tsunamis, alerting people on distant shores. Major tsunamis occur at the rate of once a year globally, with records of thousands killed in Chile, Portugal and Sumatra-with one predicted for the Cascadia subduction zone extending along the Pacifi c coast of North America (Folger 2012).
