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KILLER: pronounced "soo-NAH-mee"
Many people have grown up fearing tidal waves. In the past, students might have rattled off the term "tidal wave" in a list of natural disasters including hurricanes, forest fires, blizzards, and tornadoes. What many people are learning now is that "tidal wave" is a vague and general term and that tsunamis actually have nothing to do with tides. Tsunami is the Japanese word for "harbor wave" and these waves may reach devastating heights of 100 feet or more.
Unlike storm surges, which are caused by hurricanes, tsunamis are usually caused by earthquakes in the ocean. These waves can be formed at any time, without warning, and have been known to lift heavy trucks off the ground when they hit the coast. They move as fast as 150 to 200 miles per hour. One famous tsunami that wiped out the town of Hilo, Hawaii in the summer of 1958 killing one hundred fifty-nine people, was caused by an earthquake-triggered landslide 2,500 miles away in the Aleutian Islands of Alaska. The displacement of water from that landslide sent the tsunami rolling half way across the Pacific until it hit something that could slow it down.
You only have to live in a coastal area in order to worry about tsunamis. The earthquakes that cause them occur on the sea floor, sending energy through the water that creates small seismic waves. These otherwise unremarkable waves do not grow and become dangerous until they come into contact with the shallow waters of coastlines, harbors, or bays.
Some scientists have used the comparison of throwing a pebble into a still pond as an example of how tsunamis work. If the pebble were a meteorite, the ripples that travel away from the point of impact would be like the energy that could create a tsunami in shallow coastal waters. It is also possible for island volcanoes in the Pacific to cause tsunamis near the coastlines of continents. Pacific rim volcanoes have particularly explosive eruptions and their ash and lava can cause landslides in the ocean that can lead to tsunamis.
It is impossible to tell how high a tsunami will be until it hits the shore, which they do with little or no warning. Although researchers have estimated that a major tsunami only strikes the West Coast of the United States every 300 to 400 years, the last was estimated to have been caused by an earthquake in the 1700's and experts say that coastal towns in states like California are totally unprepared today and at high risk.
Common safety tips for dealing with tsunamis include heading for higher ground or the upper stories of high rises or even climbing trees if you have time. You should not rely on roads for evacuation because highways can become flooded or get backed up with traffic. The best way out may be on foot. Most importantly, if you're in a coastal area and you survive an earthquake, you may want to prepare for a tsunami as soon as the quake has passed. Also remember that tsunamis can occur as a series of waves. After Hilo was hit by another tsunami in 1960, many people went back to their houses and got hit by a second wave that came six hours later. It was this second tsunami, incidentally, that destroyed the town's power plant.
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