When the earth’s tectonic plates shift, the earth shakes and quakes. This shaking causes a number of events to occur. The tsunami is one nature’s most dramatic damaging phenomenon. It is the result of an earthquake shaking the oceans and seas around the world. The force and volume of water displaced in a tsunami is difficult to describe. The damage that results is all too vivid.
The day after Christmas, 2004, the second largest earthquake ever recorded occurred happened off the coast of Sumatra, Indonesian. Measuring a magnitude9.1, this earthquake lasted more than 8 minutes. It was so strong and lasted so long it quite literally shook the entire earth. It triggered earthquakes as far away as Alaska. It also triggered a series of tsunamis that spread death and destruction around the rim of the Indian Ocean. A death toll reaching nearly a quarter of a million people with property damage superseding 7 billion dollars.
Tsunami, tidal wave and seiche are terms that refer to the same phenomenon, a massive ocean wave that strikes land with a surge of up to 100 feet. Tsunami is a Japanese word for “harbor wave.” It better describes this particular event than tidal wave. A seiche is a small scale tsunami. A seiche can be formed by atmospheric conditions where tsunami are the result of under ocean earthquakes. This phenomenon much be compared to moving a pan of water. The normal sloshing from a gentle movement such as moving the container slowly along a counter surface is best seen as a seiche. The effects of this type of movement limited to a near by area and the amount of spill is easily cleaned up with a paper towel. A tsunami would be a rapid and violent move of this container. The water sloshes over the sides splashing water across the counter and on to the floor needing a roll of paper towels to absorb the mess.
Tsunami are caused by an earthquake. More than 80% of tsunamis occur in the pacific “Ring of Fire.” Earthquakes are caused by movements of the earth’s tectonic plates. As these plates slide, movements cause the earth to shake- an earthquake! Some of these movements are so slight that they often go unnoticed except by seismograph measurements. Earthquakes centered on land cause buildings to collapse. Earthquakes that happen under water, move the water causing a wave.
The tsunami wave forms when the plate rises or sinks causing seawater to be displaced. Waves have a crest and a trough. The crest is the high part of the wave and the low part is the trough. Tsunami waves characteristically have a long distance between the crests of waves. As a result, there is very little energy lost. In open water, the wave may only be a foot high. But as the wave moves into shallower water near land, the waves slow and energy is compacted. The crest is moving faster causing the wave to grew in height. As the crest nears the shore, the wave creates a vacuum that draws water along the shoreline out. Within minutes, the wall of water strikes the shoreline. The energy of the wave pushes off the shoreline destroying standing structures and carrying anything in its path deep inland. The results are devastating.
Shortly after the end of World War II, the Pacific Tsunami Warning System was established in Hawaii. Today 26 nations cooperate and coordinate efforts to provide warnings of tsunamis. There was no warning system in the Indian Ocean like this to prepare the unsuspecting natives and tourists that stood in the path the 2004 tsunami that wreaked such shocking devastation. Not all earthquakes create tsunami but with the possibility that it could, preparation can be made.
