A tsunami is a series of ocean waves caused by a sudden displacement of water. Tsunamis are most often caused by earthquakes, but they can also be caused by other events, such as volcanic eruptions and meteorites.
Tsunamis are waves of energy that radiate from the source at great speeds. If you imagine throwing a rock into a lake, you get some sense of how the tsunami's energy radiates from its source. In the deep ocean, this energy might barely make a ripple on the surface, but as it gets closer to shore, that energy becomes compressed, which can result in large, destructive waves.
The word tsunami is made up of the two Japanese characters tsu, which means "harbor," and nami, which means "wave." So, in Japanese, tsunami means "harbor wave."
Though a "harbor wave" might sound unexceptional, tsunamis rank quite high on the devastation scale. The National Oceanic and Atmospheric Administration (NOAA) reports that, since 1850, tsunamis have been responsible for the deaths of over 420,000 people. (Tornadoes, by contrast, have taken the lives of approximately 23,000 people during the same period.)
One of the reasons tsunamis are so destructive is that a single tsunami can affect areas hundreds of miles apart. For example, a tsunami on December 26, 2004, claimed the lives of 130,000 people who lived near the earthquake that caused it as well as another 58,000 lives on farther shores.
Because tsunamis are caused by unpredictable events, they are also unpredictable, but scientists are continually working on tsunami measurement and early-warning systems, called tsunameters. Although such devices won't be able to tell when a tsunami will happen, they can warn those in its path of its imminent arrival, giving them time to evacuate to a safer distance.
