A segment of seafloor the size of the state of California moved upward and seaward by more than 30 feet, displacing huge amounts of water.
The Indonesian 9.0 earthquake in 2004 released more energy than all the earthquakes on the planet in the last 25 years combined. The force of the tsunami backwash can be just as strong and in some cases stronger than the initial impact. The speed as it moves inland changes dramatically depending on the slope of the beach and the shore environment. When a tsunami crashes into coastal areas, it is typically moving at about 22 mph (35 km/hr). Tsunami means “harbor wave” in Japanese ( tsu = harbor + nami = wave), reflecting Japan’s tsunami-prone history. Wind is the most common cause of seiches. They are usually smaller and less harmful than tsunamis. Seiches (SAYSH uhz) are like tsunamis, but instead of occurring in seas and oceans, they occur in enclosed bodies of water, such as lakes or inland seas. If caught by a tsunami wave, it is better not to swim, but rather to grab a floating object and allow the current to carry you. People often die after the first tsunami wave because they return to their homes too soon or go to the beach to help stranded people or animals, only to be engulfed by another tsunami wave. A mega-tsunami occurred at Lituya Bay, Alaska, in 1958, creating the tallest tsunami ever recorded at 1,700 feet (534 m) high. A “mega-tsunami” is a tsunami with extremely high waves and is usually caused by a landslide. The lighter colored areas near the sides of the bay are where the megatsunami stripped away trees A tsunami will generally not form if the tectonic plates instead split apart or slide past each other. This rise and fall of the ocean level above the earthquake generates a tsunami. The sudden rise or fall of the ocean floor displaces the entire overlying water column. Earthquake-induced tsunamis are created along subduction zones, or when a lighter tectonic plate is forced above a heavier plate. The tsunami that resulted is theorized to have been approximately 600 feet (180 m) high. Scientists believe that an asteroid struck the Indian Ocean about 4,800 years ago. While waves generated by wind may travel anywhere from around 2 to 60 miles (3.2 to 97 km) per hour, tsunami waves can travel at speeds of 600 miles (970 km) per hour, the speed of a jet plane. While no one has witnessed a tsunami caused by a meteorite, many scientists think that a meteorite may have created a tsunami that wiped out life on Earth more than 3.5 billion years ago. Fifteen hours later, tsunami waves struck Hawaii and, finally, 22 hours after the earthquake, the tsunami struck Japan-10,000 miles from where the earthquake took place. Just 15 minutes after the 9.5 quake, 80-foot waves struck the coast. One of the largest earthquakes in history occurred over 100 miles off the coast of Chile on May 22, 1960. at greatest risk for tsunamis are Hawaii, Alaska, Washington, Oregon, and California. The withdraw of the water is called the “drawback” and is the trough of the tsunami reaching the shore. Up to half an hour before a tsunami strikes, the ocean can (but not always) suddenly appear to drain away. People are often confused when a tsunami drawback occurs and are unaware of the impending catastrophe Consequently, anyone in a coastal area who feels a strong earthquake should take that as a natural warning that a tsunami may be imminent and leave low-lying coastal areas. Approximately 99% of all tsunami-related fatalities have occurred within 160 miles (250 km) of the tsunami’s origin or within 30 minutes of when the tsunami was generated. Sailors may not even realize that tsunami waves are passing beneath them. In the deepest part of the ocean, tsunami waves are often only 1 to 3 feet tall. Greek historian Thucydides (460–395 B.C.) in his History of the Peloponnesian War was the first to associate tsunamis with underwater earthquakes. The first wave is usually not the strongest, and later waves, such as the fifth or sixth, may be significantly larger. #Tsunam irecorder series#
A tsunami is not just one big wave, but a series of waves called a “wave train.” The time period between waves is called the “wave period” and can be between a few minutes and two hours. A tsunami is usually caused by an earthquake but can also be caused by a volcanic eruption, landslide, rapid changes in atmospheric pressure, or a meteorite.
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