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The term tsunami comes from the Japanese language and means "harbor" (tsu) and "wave" (nami). A tsunami (pronounced tsoo-NAH-mee) is a series of waves generated when a body of water, such as an ocean, is rapidly displaced on a massive scale. Earthquakes, landslides, volcanic eruptions, and large meteorite impacts all have the potential to generate a tsunami. The effects of a tsunami can range from unnoticeable to devastating. Tsunamis, unlike normal wind-generated waves, are shallow-water waves. Tsunamis have a very long wavelength — up to 100 kilometers (62 miles) — and extremely long periods — up to several hours. This allows them to travel transoceanic distances with limited energy losses and at very high speeds. Contrary to popular belief, the idea of the tsunami as a "huge tidal wave" is not true. A tsunami actually looks like an endless fast-coming wave that breaks its way through any obstacles. The real damage caused by a tsunami is due to the huge mass of water traveling behind it. The smashing water is enough to reduce buildings to their foundations, and cars and boulders can be tossed several miles inland before the water resides. It can erode beaches that took years to form. Out in the open water, the height of a tsunami is around 1 meter (3.3 feet), which is unnoticeable to people on ships, but because of its incredible wavelength, the wave mobilizes the ocean beneath it. The wave travels at an average speed of 800 kilometers (497 miles) an hour. As it nears the shore and the water becomes shallow, the wave slows down, causing it to pile up and increase in size. That is why, while it traveled at a height of 1 meter in the ocean, by the time it reaches the coast, a tsunami can reach a height onshore of 30 meters (98 feet), which is more than ten stories high! How Tsunamis Are Generated Tsunamis can be generated when the sea floor abruptly deforms and vertically displaces the overlying water. This happens because of shifts in the layers of the crust. When this happens, the displaced mass of water forms waves, and if a large enough mass of water is displaced, a tsunami may be formed. Submarine landslides, as well as submarine volcanoes, can also cause tsunamis by the disturbance of the overhead column of water thus leading to the displacement of large amounts of water. Meteorites or shoreline landslides can also cause disturbance from outside that can create a tsunami. This type, however, usually dissipates quickly and is not as damaging as one created by earthquakes or underwater disturbances. Tsunami Warning System
Tsunamis cannot be prevented or precisely predicted, but there are some warning signs of an impending tsunami and there are many systems being developed and in use to reduce the damage from tsunamis. The earliest warning system was animals. Animals seem capable of detecting danger earlier and fleeing to high ground, a few minutes or even hours before a tsunami strikes. This has led scientists to speculate on whether animals can detect the subsonic Rayleigh waves, which are a type of surface wave produced by earthquakes and subterranean movement of magna. Also, in tsunami-prone countries, several protection systems have been used to reduce the damage from the wave. Japan, for example, has been building an extensive system of tsunami walls up to 4.5 meters (14.8 feet) high to protect heavily populated coastal regions. The effectiveness of this, however, is argued because the wave can be much higher than that. While a tsunami wall may slow down the wave and break its height a little, it might not be enough to prevent major damage and loss of life. The effect of a tsunami can also be reduced drastically by nature itself. A wall of trees in the 2004 Indian Ocean tsunami saved the Tamil Nadu region in India from much damage because the trees broke the speed and force of the wave. Now, in light of the 2004 tsunami in the Indian Ocean, the deadliest recorded tsunami ever, UNESCO and several other world bodies called for the establishment of a global tsunami warning system that would prevent loss of life through early detection of tsunamis. The system is divided into two parts. The first is concerned with a network of sensors and detectors to determine tsunamis early, while the second component is a communication infrastructure to spread warnings early enough to allow for evacuation. As a first step towards an international early warning program, the UN meeting in Japan agreed to form the Indian Ocean Tsunami Warning System (IOTWS), which became active late June 2006. It consists of 25 seismographic stations relaying information to 26 national tsunami information centers, as well as three deep-ocean sensors. However, UNESCO warned that further coordination between governments and the ability of the different centers to relay information to civilians were critical for the success of the system. The Pacific Ocean The rim of the Pacific Ocean still remains the area most prone to tsunamis. This is because around the margins of the Pacific Ocean, denser oceanic plates tend to slip under continental plates in a process called subduction. This sometimes brings the lip of the continental plate with it. Eventually, the high pressure on the lip causes it to snap back, sending shockwaves through the earth's crust that cause an underground earthquake. The resulting subduction earthquakes are particularly effective in generating tsunamis. The Pacific Ocean and Indian Ocean alone are recorded to be the site of around eight major tsunamis in the past century, in addition to several smaller-scale tsunamis that have not been as damaging or may have gone undetected. These include tsunamis in Asia, such as the 2004 Indian Ocean tsunami, or ones in the United States such as the infamous Chilean tsunami that struck Hawaii in 1960. The 2004 Asia tsunami has brought the world's attention to the danger posed by this devastating natural phenomenon with a death toll in the 300,000 range. Much work has gone into early warning and control to prevent the repeat of such misery. But as with all natural disasters, no protective measure is 100 percent safe. Even with UNESCO's ambitious plan of protection, much will come down to the governments and the people to prevent as much loss as possible if events are repeated. |
PADANG, Indonesia – A second powerful earthquake rocked western Indonesia on Thursday as rescuers struggled to reach survivors of the previous day's quake, which killed more than 500 people and left thousands trapped under collapsed buildings.
The death toll from Wednesday's 7.6-magnitude earthquake off Sumatra island was expected to rise as rescuers dig through the rubble, sometimes by hand, in heavily populated cities. The latest, 6.8-magnitude quake damaged hundreds of additional buildings, and communications remained cut in some areas.
"Let's not underestimate (the disaster). Let's be prepared for the worst. We will do everything we can to help the victims," President Susilo Bambang Yudhoyono said in Jakarta before flying to Padang.
A total of 529 people were confirmed dead and 440 were seriously injured, the Social Affairs Ministry's crisis center said. It said 376 deaths occurred in Padang, a coastal city of 900,000 and capital of West Sumatra province. The rest were in four surrounding districts.
Thousands were believed trapped, said Rustam Pakaya, head of the Health Ministry's crisis center. A foot could be seen sticking from one pile of rubble.
The president ordered the military to deploy all its crisis centers in Jakarta, West Sumatra and North Sumatra provinces and said the military will provide earth-moving equipment to clear the rubble.
Padang became the immediate focus of rescue efforts. At least 500 buildings in the city collapsed or were badly damaged in Wednesday evening's quake, which also set off fires, said Disaster Management Agency spokesman Priyadi Kardono.
Terrified residents who spent a restless night, many sleeping outdoors, were jolted by the new quake Thursday morning.
The U.S. Geological Survey said the quake hit about 150 miles (240 kilometers) south of Padang. It damaged 1,100 buildings, including mosques and homes, in Jambi, according to Mayor Hasfiah, who uses only one name like many Indonesians. He said there were no deaths but dozens of people were injured.
In Padang, collapsed or seriously damaged buildings included hospitals, mosques, a mall and a school. TVOne network footage showed heavy equipment breaking through layers of cement in search of more than 30 students it said were missing from the school, where they were taking after-school classes.
Parents of missing students stayed up all night, waiting for signs of life.
"My daughter's face keeps appearing in my eyes ... my mind. I cannot sleep, I'm waiting here to see her again," a woman who identified herself only as Imelda told TVOne, tears rolling down her face. She said her 12-year-old daughter Yolanda was in the school for science lessons.
"She is a good daughter and very smart. I really love her. Please, God help her," she said.
At least 80 people were missing at the 5-story Ambacang hotel in downtown Padang, said Indra, a paramedic who uses only one name. Rescuers, working in heavy rain, found two survivors and nine bodies in the rubble.
Thousands fled Wednesday's quake in panic, fearing a tsunami. The shaking was so intense that people crouched or sat on the street. Children screamed as thousands of frantic residents fled in cars and motorbikes, honking horns.
The quake caused buildings to sway hundreds of miles (kilometers) away in Malaysia and Singapore.
The quake severed roads and cut off power and communications to Padang, and the extent of damage in surrounding areas was still unclear.
Indonesia, a poor, sprawling nation, sits on a major geological fault zone and is frequently hit by earthquakes. The latest quakes were along the same fault line that spawned the 2004 Asian tsunami that killed 230,000 people in a dozen nations.
Geologists said the Indonesia quakes were not related to another deadly quake Tuesday that hit islands in the South Pacific.
Padang's mayor appealed for assistance on Indonesian radio station el-Shinta.
"We are overwhelmed with victims and ... lack of clean water, electricity and telecommunications," Mayor Fauzi Bahar said. "We really need help. We call on people to come to Padang to evacuate bodies and help the injured."
Finance minister Sri Mulyani said the government has allocated $25 million for a two-month emergency response. She said the earthquake will seriously affect Indonesia's economic growth, because West Sumatra is a main producer of crude palm oil.
"This region has been damaged seriously, including its infrastructure," Mulyani said.
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Associated Press writers Ali Kotarumalos and Niniek Karmini in Jakarta contributed to this report.
