Even though not many people know much about tsunamis, they can be very devastating to the people who have experienced them.  Tsunamis also known as tidal waves, are not actually caused by tides. Tsunamis are destructive waves caused by earthquakes under the sea or large storms at sea such as hurricanes, and cyclones.  They can also be caused by volcanoes.  Tsunamis caused by undersea earthquakes are called seismic sea waves.  These earthquakes can create waves that can travel at speeds up to 500 miles (800 kilometers) per hour.  Tsunamis often don't reach land and go unnoticed, but when they do reach land they can pile up into walls of water 1.8 meters (6 feet) to 18 meters (60feet) high.  The earthquakes that cause tsunamis are called seaquakes. To predict seaquakes and other earthquakes scientists use seismographs, a machine that picks up seismic waves and tells where and how bad they are.
    Tsunamis can also be caused by stoms at sea.  These tsunamis are called storm surges. Storm surges are usually caused by hurricanes or cyclones,but they can be caused by other large storms at sea.  Storm surges are especially destructive when they hit at high tide.
    Some examples of tsunamis are: Libson,Portugal-1775; Galveston,Texas-1900; Hilo,Hawaii-1946; Bangladesh-1970; and another one in Bangladesh in 1985. Also,many tsunamis have occured in Japan.