While such tsunamis in these areas may be devastating locally, their energy decays rapidly with distance. Usually, they are not destructive a few hundred kilometers away from their sources. That is not the case with tsunamis generated by great earthquakes in the North Pacific or along the Pacific coast of South America.
On the average of about half-a-dozen times per century, a tsunami from one of these regions sweeps across the entire Pacific, is reflected from distant shores, and sets the entire ocean in motion for days. For example, the Chilean tsunami caused death and destruction throughout the Pacific. Hawaii, Samoa, and Easter Island all recorded runups exceeding 4 m; 61 people were killed in Hawaii. In Japan people died. Although not as frequent, destructive tsunamis have been also been generated in the Atlantic and the Indian Oceans, the Mediterranean Sea and even within smaller bodies of water, like the Sea of Marmara, in Turkey.
In , a large earthquake along the North Anatolian Fault zone, generated a local tsunami, which was particularly damaging in the Bay of Izmit. In the last decade alone, deadly tsunamis have occurred in Chile , , Haiti , Indonesia , , , , Japan , Peru , Samoa - American Samoa - Tonga , Solomons Of these, only Indonesia and Japan caused deaths at distant shores. In the deep ocean, tsunami wave amplitude is usually less than 1 m 3. The crests of tsunami waves may be more than a hundred kilometers or more away from each other.
Therefore, passengers on boats at sea, far away from shore where the water is deep, will not feel nor see the tsunami waves as they pass by underneath at high speeds. The tsunami may be perceived as nothing more than a gentle rise and fall of the sea surface. There are three factors of destructions from tsunamis: inundation, wave impact on structures, and erosion. Strong, tsunami-induced currents lead to the erosion of foundations and the collapse of bridges and seawalls.
Flotation and drag forces move houses and overturn railroad cars. Considerable damage is caused by the resultant floating debris, including boats and cars that become dangerous projectiles that may crash into buildings, break power lines, and may start fires. Fires from damaged ships in ports or from ruptured coastal oil storage tanks and refinery facilities, can cause damage greater than that inflicted directly by the tsunami.
Of increasing concern is the potential effect of tsunami draw down, when receding waters uncover cooling water intakes of nuclear power plants. Destruction of Hilo, Hawaii harbor pier during Aleutians Islands tsunami.
Once a tsunami has been generated, its energy is distributed throughout the water column, regardless of the ocean's depth. 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. The period of the tsunami waves may range from 5 to 90 minutes. The wave crests of a tsunami can range from a few to a hundred kilometers or more apart as they travel across the ocean.
As the waves approach the coast, their wavelength decreases and wave height increases. On the open ocean, the wavelength of a tsunami may be as much as two hundred kilometers, many times greater than the ocean depth, which is on the order of a few kilometers. In the deep ocean, the height of the tsunami from trough to crest may be only a few centimeters to a meter or more - again depending on the generating source.
Tsunami waves in the deep ocean can travel at high speeds for long periods of time for distances of thousands of kilometers and lose very little energy in the process. The deeper the water, the greater the speed of tsunami waves will be. At such high speeds, a tsunami generated in Aleutian Islands may reach Hawaii in less than four and a half hours.
In , great tsunami waves generated in Chile reached Japan, more than 16, km away in less than 24 hours, killing hundreds of people. Tsunami wave height increase as they reach the shore due to the shallowing of seafloor. The following is a position paper that was issued by the Tsunami Society concerning the occurrence of Mega-Tsunamis:. The mission of the Tsunami Society includes "the dissemination of knowledge about tsunamis to scientists, officials, and the public".
We have established a committee of private, university, and government scientists to accomplish part of this goal by correcting misleading or invalid information released to public about this hazard.
We can supply both valid, correct and important information and advice to the public, and the names of reputable scientists active in the field of tsunami, who can provide such information. Most recently, the Discovery Channel has replayed a program alleging potential destruction of coastal areas of the Atlantic by tsunami waves which might be generated in the near future by a volcanic collapse in the Canary Islands.
They like to call these occurences "mega tsunamis". We would like to halt the scaremongering from these unfounded reports. We wish to provide the media with factual information so that the public can be properly informed about actual hazards of tsunamis and their mitigation. Here are a set of facts, agreed on by committee members, about the claims in these reports:. The Discovery program does not bring out in the interviews that such volcanic collapses are extremely rare events, separated in geologic time by thousands or even millions of years.
Carefully performed numerical and experimental model experiments on such events and of the postulated Las Palma event verify that the relatively short waves from these small, though intense, occurrences do not travel as do tsunami waves from a major earthquake.
Volcanoes on La Palma Mader, in Science of Tsunami Hazards, Vol. Moore and D. Clague, in the Geologic Society of America Bulletin, , For general and educational material on tsunamis, check: www. Current Warnings Most Recent Tsunami. Also Tsunami Sources Icosohedron Globe. What to Do? Are Tsunamis Dangerous? What is a tsunami? How do earthquakes generate tsunamis? By far, the most destructive tsunamis are generated from large, shallow earthquakes with an epicenter or fault line near or on the ocean floor.
These usually occur in regions of the earth characterized by tectonic subduction along tectonic plate boundaries. Basically, a tsunami is triggered by some under sea disturbance after which follows a series of water waves. The deadly waves are caused by the displacement of a large volume of water, usually an ocean. However, tsunamis can also occur in large lakes. Basically, tsunamis can be generated when the sea floor abruptly moves and displaces water. A tsunami can occur in any tidal state and even at low tide it can still inundate coastal areas.
Tsunamis are a frequent occurrence in Japan; approximately events have been recorded. Earthquakes, volcanic eruptions, landslides and other underwater explosions all have the potential to trigger a tidal wave or tsunami.
More than 48, people were forced to flee their homes, and over aftershocks have struck the region. Even though the water has receded, conditions on the ground are still treacherous. Tinggi tsunami sekitar 3 meter.
Permukiman di sekitar pantai hancur disapu tsunami. Earthquakes in the ocean can trigger tsunamis as vertical underwater movements shift columns of water, causing massive waves to propagate.
These waves can travel upward of miles per hour in the deep ocean. As they roar toward coastal waters, the waves slow down while getting taller. One common sign a tsunami is barreling toward a shoreline is the water receding abnormally far. Text message alerts failed to send since cell towers collapsed during the earthquake. Indonesia has a tsunami early warning system with tidal gauges, accelerometers, and seismic broadband stations. Another factor in the devastation is the geography of the region.
Palu is about 50 miles south of the epicenter of the earthquake, nestled inside an elongated bay. The bay served to channel the massive tsunami toward the city, as you can see in this map:. The Donggala Regency , located near the mouth of the bay, was also hammered by the tsunami. Officials have also struggled to enforce building codes that make buildings more resilient to earthquakes. But the rumbling earth is a fact of life in Indonesia.
Back in , the third-largest earthquake on record triggered waves up to feet high, killing more than , people across 14 countries, with the bulk of the casualties in Indonesia.
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