On the morning of January 23, a magnitude 7.9 earthquake struck the Gulf of Alaska some 175 miles southeast of Kodiak, Alaska. The tremors triggered fears of tsunamis throughout the Pacific, but as of 7:35 a.m. U.S. Eastern, the U.S. Tsunami Warning Center has canceled all tsunami watches and warnings.
A tsunami advisory remains in effect for some portions of southern Alaska and the Alaska Peninsula. Observed tsunami waves have not exceeded heights of 2.3 feet (0.7 meters but nevertheless pose dangers. (Read the advisory.)
A tsunami is a series of ocean waves that sends surges of water, sometimes reaching heights of over 100 feet (30.5 meters), onto land. These walls of water can cause widespread destruction when they crash ashore.
What Causes a Tsunami?
These awe-inspiring waves are typically caused by large, undersea earthquakes at tectonic plate boundaries. When the ocean floor at a plate boundary rises or falls suddenly, it displaces the water above it and launches the rolling waves that will become a tsunami.
Most tsunamis–about 80 percent–happen within the Pacific Ocean’s “Ring of Fire,” a geologically active area where tectonic shifts make volcanoes and earthquakes common.
Tsunamis may also be caused by underwater landslides or volcanic eruptions. They may even be launched, as they frequently were in Earth’s ancient past, by the impact of a large meteorite plunging into an ocean.
Tsunamis race across the sea at up to 500 miles (805 kilometers) an hour—about as fast as a jet airplane. At that pace, they can cross the entire expanse of the Pacific Ocean in less than a day. And their long wavelengths mean they lose very little energy along the way.
In deep ocean, tsunami waves may appear only a foot or so high. But as they approach shoreline and enter shallower water they slow down and begin to grow in energy and height. The tops of the waves move faster than their bottoms do, which causes them to rise precipitously.
What Happens When It Hits Land
A tsunami’s trough, the low point beneath the wave’s crest, often reaches shore first. When it does, it produces a vacuum effect that sucks coastal water seaward and exposes harbor and sea floors. This retreating of sea water is an important warning sign of a tsunami, because the wave’s crest and its enormous volume of water typically hit shore five minutes or so later. Recognizing this phenomenon can save lives.
A tsunami is usually composed of a series of waves, called a wave train, so its destructive force may be compounded as successive waves reach shore. People experiencing a tsunami should remember that the danger may not have passed with the first wave and should await official word that it is safe to return to vulnerable locations.
Some tsunamis do not appear on shore as massive breaking waves but instead resemble a quickly surging tide that inundates coastal areas.
The best defense against any tsunami is early warning that allows people to seek higher ground. The Pacific Tsunami Warning System, a coalition of 26 nations headquartered in Hawaii, maintains a web of seismic equipment and water level gauges to identify tsunamis at sea. Similar systems are proposed to protect coastal areas worldwide.
Tsunami is a Japanese name for 'harbour waves' generally called tidal waves but actually tsunami has nothing to do with tides. Tsunami is generated when ocean floods shift vertically, usually due to an earthquake. When a shift in the ocean floor displaces the water above, the water body travels as a huge wave to regain equilibrium. Actually tsunami is generated as a result of a sudden rise or fall of section on the earth's crust under the ocean.
A seismic disturbance can displace the water column creating a rise or fall in the level of the ocean above. This rise or fall in sea level is the initial formation of tsunami wave.
Unlike surface waves that affect only a shallow amount of water, a tsunami stretches all the way to the sea floor, as rises to the land, so does the wave. Arriving at shore, such waves can grow suddenly by dozens of feet. The satellite imaging did not provide a depth for the waves that hit ashore. In deep water, a tsunami can travel at 700 km per hour.
But in shallow water near coast, it get slower and water mass rises up to 50 meters. A tsunami is very much destructive. It can strip coasts of land, uproot trees, wipe out towns. The records of tsunami deaths or disaster are generally not available as they are commonly fixed with earthquake deaths.
In the year 1755 on 1st Nov. a colossal earthquake destroyed Libson, Portugal and rocked much of Europe, a tsunami followed, killing more than 60,000. August 27,1883 was another day of disaster. The eruptions from Krakatoa volcano fuelled a tsunami that drowned 36,000 in western Java and southern Sumatra. On 23rd August, 1976 a tsunami in southern west Philippines killed 8,000.
In another tsunami disaster waves as high as 100 feet, spawned by an earthquake, swept the east coast of Japan in which 27,000 people died.
In the latest tsunami on 26th December, 2004 in Indian Ocean caused because of an undersea disturbance which was the result of an 8.9 magnitude earthquake, just off the northern tip of Indonesia's Sumatra Islands. This created a havoc in Indonesia, Hong Kong, Sri Lanka and India. It is estimated that more than 1 million people lost their lives and more than this are missing and the total loss must be of hundred of crores.
Tsunami affected India's southern part. The most affected areas were Tamilnadu and Andaman & Nicobar Islands. Joggers on the Marina Beach in Chennai and fishermen all over the Tamil Nadu coast got a jolt of their lives as these deadly waves lashed these coastal areas within seconds and washed away over 25,000 people, leaving equal number untraceable.
Tsunami struck India for the first time in the recorded history. The country 3 still coming to grips with nature and scale of disaster. The worst affected . ere the 45,000 people of Car Nicobar and Greater Nicobar where a earthquake of 7.5 magnitude hit the area in the morning.
In Indonesia, Sri Lanka and Hongkong thousands of people lost their lives and up to five million people have been displaced by the divesting tsunami that pummeled large areas of Asia. Three millions out of these affected are in Indonesia alone and another one million in Sri Lanka. The rest were spread between India, Maldives and other nations hit by tsunami waves.
But the most surprising is that wildlife in Sri Lanka's biggest national park survived the December's tsunami, but it was probably keen senses and the lay of the land rather than any mysterious instinct danger enabled animals to scamper to safety. It was a acute natural senses such as hearing that helped animal’s times to flee. It is an ancient belief that animals have a sixth sense for danger and this sense must have a med animals of tsunami's approach.
Geography and planning saved Maldives from these deadly tsunami. While standing on the highest point rock of the Maldives and looking down the Indian Ocean less than 3 meters below, it is easy to see why this nation of low-lying atolls fears rising sea-levels will one day wipe it off the map. When a giant tsunami crushed fishing villages and tourist resorts across Asia became a reality the day after Christmas.
It was combination of geography and planning the death toll in the Maldives stands at just 80 in a disaster that claimed more than 1,50,00 from Indonesia. Many the Maldives 1,200 tiny palm-fringed coral islands 800 km off the toe India were swamped by these tsunami waves about a meter high.