What is a tsunami?
From the Japanese word for harbor wave
A series of huge waves that happen after an undersea disturbance, like an earthquake or volcano eruption.
The waves travel in all directions from the area of disturbance, sort of like the ripples that happen after throwing a rock in a pond or lake.
Tsunami can also be caused by underwater landslides and can even be started by the impact of a large meteorite plunging into the ocean. This was common in Earth’s ancient past.
The waves can travel in the open sea as fast as 600
miles per hour.
As the big waves approach the shallow waters along the coast they grow very tall and smash into the shore. They can be as high as 100 feet.
They are sometimes mistakenly called "tidal waves," but tsunami have nothing to do with the tides. Where do tsunamis happen?
About 80 percent of tsunamis happen within the
Pacific Ocean’s “Ring of Fire,” an active area where plate shifts make volcanoes and earthquakes common.
In the United States, Hawaii is the state at greatest risk for a tsunami. They get about one a year, with a damaging tsunami happening about every seven years.
Alaska is also at high risk. California, Oregon and
Washington experience a damaging tsunami about every 18 years.
How do we know when a tsunami might happen?
Tsunami Warning Centers in Honolulu Hawaii and Palmer
Alaska monitor disturbances that might trigger tsunami.
When a tsunami is recorded, the center tracks it and issues a warning when needed.
The National Oceanic and Atmospheric Administration
(NOAA) has a system of buoys that are called the DeepOcean Assessment and Reporting of Tsunami, or DART.
The sensing devices on these buoys contain pressure sensors for determining a wave's size by gauging the weight of the water column passing over it. This information is relayed to the surface buoy and then to a satellite. The satellite then beams the information to the two Tsunami
Warning Centers in Alaska and Hawaii.
The low point between the wave’s crest is called the trough. The trough of a tsunami often reaches the shore first. When this happens, it causes a vacuum effect that sucks the coastal water out toward the sea and exposes harbor and sea floors. This is an important warning sign of a tsunami, because the wave’s crest and its enormous volume of water usually hit the shore about five minutes later. Recognizing this can save lives.
A tsunami is usually made up of a series of waves, called a wave train, so its damaging force may become more destructive as each wave reaches shore. People experiencing a tsunami should remember that the danger may not have passed with the first wave and should await official word that it is safe to return to at risk locations.
Some tsunamis do not appear on shore as massive breaking waves but instead look like a quickly surging