A tsunami is made up of a series of very long waves. The waves will travel outward on the surface of the ocean in all directions away from the source area, much like the ripples caused by throwing a rock into a pond. The wavelength of the tsunami waves and their period will depend on the generating mechanism and the dimensions of the source event.
If the tsunami is generated from a large earthquake over a large area, its initial wavelength and period will be greater. If the tsunami is caused by a local landslide, both its initial wavelength and period will be shorter. From the beginning the animation shows all coastlines covered by colored points.
These are initially a blue color like the undisturbed ocean to indicate normal sea level, but as the tsunami waves reach them they will change color to represent the height of the waves coming ashore, and often these values are higher than they were in the deeper waters offshore. Details Permalink to Details. Added to the Catalog 7 March View this area in EO Explorer. In March , a magnitude 9.
Acquired in March and February , these images document the recession of flood waters after the Tohoku tsunami. The earthquake was one of the most powerful of the last 35 years and had a magnitude of 8. After the initial quake, coastal residents witnessed a sudden draw-down of the ocean and knew a tsunami was imminent.
They had less than 20 minutes to reach higher ground before the tsunami hit. Waves as high as 8 meters came in four destructive surges reaching as far as 1. Thousands of buildings were destroyed, and the combined earthquake and tsunami killed as many as people. Image of the Day Land. Acquired March 18, , this natural-color image shows agricultural fields near Sendai, Japan, covered with either snow or flood water.
The Indian Ocean tsunami of December caused waves as high as 30 feet 9 meters in some places, according to news reports. In other places witnesses described a rapid surging of the ocean.
Flooding can extend inland by a thousand feet meters or more. The enormous energy of a tsunami can lift giant boulders, flip vehicles, and demolish houses. They may be more like a very rapidly rising tide. This may be accompanied by much underwater turbulence, sucking people under and tossing heavy objects around. Entire beaches have been stripped away by tsunamis. More than , people lost their lives, many of them washed out to sea. The most damaging tsunami on record before was the one that killed an estimated 40, people in following an earthquake in the South China Sea.
In some 36, people were killed by tsunamis in the South Java Sea, following the eruption of Indonesia's Krakatoa volcano. In northern Chile more than 25, people were killed by a tsunami in But tsunamis have been generated in other bodies of water, including the Caribbean and Mediterranean Seas, and the Indian and Atlantic Oceans.
North Atlantic tsunamis include the tsunami associated with the Lisbon earthquake , which killed as many as 60, people in Portugal, Spain, and North Africa. This quake caused a tsunami as high as 23 feet 7 meters in the Caribbean. Some were generated locally and others were the result of events far away, such as the earthquake near Portugal. The combined death toll from these Caribbean tsunamis is about 9, If you feel a strong quake do not stay close to shore.
If you hear of an earthquake be aware of the possibility of a tsunami and listen to the radio or television for additional information. Remember that an earthquake can trigger killer waves thousands of miles across the ocean many hours after the event generated a tsunami. If you see the ocean receding unusually rapidly, that's a good sign that a tsunami may be on its way.
Go to high ground immediately. Many people were killed by the Indian Ocean tsunami because they went down to the beach to view the retreating ocean exposing the seafloor.
Experts believe that a receding ocean may give people as much as five minutes' warning to evacuate the area. The danger from a tsunami can last for several hours after the arrival of the first wave.
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