Joey Diaz, age 13, of Santee, Calif., for his question:

WHAT CAUSES A TIDAL WAVE?

Destructive tidal waves are caused by undersea earthquakes, called seaquakes, or by hurricanes far out in the ocean.  Tidal waves are not related to true tides. Many scientists call them tsunami, the Japanese word for storm wave.

Seismographsare used by scientists to predict almost exactly when a tidal wave will arrive at a given seacoast. An earthquake off the Aleutians, for example, might cause a tidal wave that will hit the coast of Hawaii.

In 1755, a tidal wave 50 feet high hit Lisbon, Portugal. Great damage was suffered in Galveston, Texas, when a tidal wave hit in 1900. More than 200,000 were killed when a cyclone and tidal wave struck Bangladesh in 1970.