What have you experienced or seen of a tsunami or its aftermath?
Tsunami
When an earthquake happens under an ocean, it may push the ocean floor up and then drop it again, creating a pulse in the water above it, and passing its energy to that wave. If so, waves may be created that head both for the shore and away, and the latter can travel long distances. Volcanic eruptions and meteorite impacts can also cause tsunamis. As many earthquakes and volcanoes are near a mainland coast and/or island chains, the waves can reach the nearest coast with little or no warning (Alaska, the Philippines, Japan and the U.S. West Coast are at risk from this).
Unlike ordinary waves, the distance between 2 crests of tsunami waves can be more than 100km (60 miles), and an hour, apart. Most tsunamis originate in the Pacific, around the "Ring of Fire". Tsunamis can cross the Pacific in a day. The speed of a tsunami varies with the square root of the water depth. Tsunamis can travel as fast as a jet plane, at to 800kph (500mph). They travel faster in deep water than in shallow water. The December 26 2004 tsunami took 7 hours to travel from Indonesia to Somalia in East Africa.
Tsunamis may not be very noticeable mid-ocean (only a few feet high), but they change as they approach the shore. They slow down in shallow water but get higher and higher, occasionally reaching 30m (100 feet) high. The tsunami resulting from the Krakatoa Volcanic Eruption on Aug. 27, 1883 reached 38 metres (125 feet) high. An April 1 1946 tsunami destroyed the U.S. Coast Guard's steel-reinforced concrete Scotch Cap lighthouse on Unimak, which stood about 90 feet above sea level. Tsunamis arrive with great force, devastating beaches and any towns or villages within reach. They tend not to break like ordinary surf, but to act like very strong tides or currents.
The behaviour of the wave at the coast can be quite complex, varying with the geography, and often the first wave to arrive on shore is not the largest. A sudden withdrawing of water from the coast is a warning that a tsunami is about to arrive, but this does not always happen.
In 1960 the world's biggest recorded (i.e. 20th century) earthquake occurred off the coast of Chile, sending tsunamis around the Pacific Rim and killing people 10,000 miles (16,000km) away. 56 died in Hawaii, 32 in the Philippines, and 138 in Japan. Historically, Japan has suffered most from tsunamis. One in 1896 killed an estimated 27,000. An Alaskan Earthquake in 1964 generated a deadly tsunami that struck Alaska, Oregon and California.
If a tsunami remains near the earthquake that triggered it, like the July 1993 tsunami that remained within the Sea of Japan and affected only Japan, Korea and Russia, it is called a "local event". Other local tsunamis took place in Nicaragua (1992), Indonesia (1992, 1994) and the Philippines (1994). Often the tsunamis arrive only minutes after the earthquake has been felt.
The deadliest tsunami for at least a century occurred on December 26 2004 not in the Pacific Ocean, but in the Indian Ocean. It killed around 276,000 and left over 2 million displaced. Over 100,000 of those were in Indonesia, where 50,000 are known to have died in previous tsunamis. The Krakatoa tsunami is believed to have killed over 36,000 people.
Strong quake hits confidence in India's Andamans,
Earthquake Hits India's Nicobar Islands
A 7.3 earthquake shook the Andaman Islands on Sunday. It caused no damage and no tsunami, but after last December's 9.15 earthquake and tsunami it left the people shaken. The quake was actually off the Nicobar Islands just to the south of the Andamans. Some mainland residents and ships took precautions when they heard of the quake. A tsunami warning was triggered in Thailand.
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