Tsunamis, giant waves that sometimes travel across entire oceans, are triggered by underwater earthquakes or volcanic eruptions. In the open ocean, tsunamis can be barely noticeable, but as they approach land, the waves increase in height, sometimes flooding the landscape with devastating results.
A tsunami is technically a series of waves. They can travel at up to 500 miles per hour on the open ocean and may only be a foot high. As the waves approach land, they enter shallower water and tend to bunch up, gaining in both strength and height. Some tsunamis reach 100 feet in height before they inundate a shoreline.
Before a tsunami hits, seawater retreats, exposing parts of the sea floor not normally seen. It is the same physical action seen on ocean beaches, where a wave comes in, the water retreats and then the next wave comes in. The more the water retreats, the bigger the wave is. Before the adaptation of tsunami early warning systems, this was often the only warning coastal communities had before a tsunami hit. A large earthquake could also be a warning, but not all earthquakes produce tsunamis.
The National Oceanic and Atmospheric Administration, or NOAH, mans a National Data Buoy Center. Scientists can predict when and where a tsunami will hit using strategically placed buoys anchored to the sea floor. The waters around Hawaii, for example, have underwater buoys deployed in a grid system. Bottom pressure and water displacement are constantly monitored, with information going to a satellite transmitter.