But tsunamis are caused by energy originating underwater, from a volcanic eruption, a submarine landslide, or most commonly, an earthquake on the ocean floor caused when the tectonic plates of the Earth's surface slip, releasing a massive amount of energy into the water. This energy travels up to the surface, displacing water and raising it above the normal sea level, but gravity pulls it back down, which makes the energy ripple outwards horizontally.
Thus, the tsunami is born, moving at over miles per hour. When it's far from shore, a tsunami can be barely detectable since it moves through the entire depth of the water.
But when it reaches shallow water, something called wave shoaling occurs. Because there is less water to move through, this still massive amount of energy is compressed.
The wave's speed slows down, while its height rises to as much as feet. The word tsunami, Japanese for "harbor wave," comes from the fact that it only seems to appear near the coast.
There was no single year of the period that was free of tsunamis. Note: The Indian Ocean tsunami is now reported to be one of the strongest in the world over the past 40 years. General questions about tsunamis links to the web site of the International Tsunami Information Center, Honolulu :.
Current Warnings Most Recent Tsunami. Also Tsunami Sources Icosohedron Globe. What to Do? Frequently Asked Questions On this page we provide answers to frequently ased questions about the Indian Ocean Tsunami. Q: "Can you tell whether there will be a similar tidal wave coming in the future from today, when and what will be the magnitude" A: Unfortunately, scientists cannot predict when the next large earthquake will occur, what its size will be, and whether a tsunami will be generated.
Q: Has a tsunami hit the Indian Ocean before? As the coastal ocean waters recede from the shore, it often leaves large portions of the sea floor exposed.
Individuals who do not recognize this as a common precursor to tsunami waves often find themselves gravitating toward the exposed shore. Unfortunately, they often perished as they rush to gather fish left high and dry on the exposed beach or to view never before seen rock and reef formations — only to be hit moments later by the incoming wall of water.
This cycle may be repeated several times as successive wave crests arrive five minutes to an hour apart. But tsunamis have been generated in other bodies of water, including the Caribbean and Mediterranean Seas, and the Indian and Atlantic Oceans. North Atlantic tsunamis included the tsunami associated with the Lisbon earthquake that killed as many as 60, people in Portugal, Spain, and North Africa.
This quake caused a tsunami as high as 23 feet 7 meters in the Caribbean. Some were generated locally and others were the result of events far away, such as the earthquake near Portugal. The combined death toll from these Caribbean tsunamis is about 9, If you feel a strong quake do not stay in a place where you are exposed to a tsunami. If you hear of an earthquake be aware of the possibility of a tsunami and listen to the radio or television for additional information.
Remember that an earthquake can trigger killer waves thousands of miles across the ocean many hours after the event generated a tsunami. If you see the ocean receding unusually rapidly or far it's a good sign that a big wave is on its way. Go to high ground immediately. Many people were killed by the Indian Ocean tsunami because they went down to the beach to view the retreating ocean exposing the seafloor. Apparently they were unaware that this phenomenon precedes a killer wave.
Experts believe that a receding ocean may give people as much as five minutes' warning to evacuate the area. An approaching tsunami is not something to be admired unless you are safely on high ground.
The danger from a tsunami can last for several hours after the arrival of the first wave. A tsunami wave train may come as a series of surges that are five minutes to an hour apart. The cycle may be marked by a repeated retreat and advance of the ocean.
Stay out of danger until you hear it is safe. Survivors of the Indian Ocean tsunami reported that the sea surged out as fast and as powerfully as it came ashore. Many people were seen being swept out to sea when the ocean retreated. Do not assume that because there is minimal sign of a tsunami in one place it will be like that everywhere else. Stay away from rivers and streams that lead to the ocean as you would stay away from the beach and ocean if there is a tsunami. Tsunami, earthquake, hurricane—an emergency can develop with little or no warning.
Tsunamis can cause rapid changes in water level and unpredictable, dangerous currents in harbors and ports. Boat owners may want to take their vessels out to sea if there is time and they are allowed to do so by port authorities.
People should not stay on their boats moored in harbors. Unlike typical wind-caused waves and swells which arrive on the order of every 10 to 20 seconds, tsunami surges are usually many minutes apart and sometimes more than an hour can pass between successive crests.
Tsunamis can trick you. They are irregularly spaced in time and just when you might think a tsunami is over, larger surges may arrive. The arrival time of the first surge in a tsunami can be accurately predicted within minutes as it only depends on where the source is located and the distance and sea floor depths to coastal areas. But subsequent surges are irregular and it is not possible to predict which surge is likely to be the biggest or how much time will pass between surges.
In some coastal locations like Crescent City, tsunami energy is trapped in the harbor and can continue for many days. Our recommendation — never return to coastal areas after a tsunami until authorities give you the all clear. In about half of tsunami cases, the initial wave arrival at the coast is a trough, meaning that the water will draw down and appear to retreat, exposing the sea floor over a much larger area that an extremely low tide.
But the first wave is just as likely to be a crest meaning that there will be no water lowering, just a sudden increase in wave height and water penetration.
Whether the first arrival is negative drawdown or positive wave increase depends on the source characteristics and where your are relative to the source. If you suddenly notice that the water has gone out much further than normal, treat this as a warning that the water could suddenly rush back in and evacuate.
The majority of historic tsunamis have been located in the Pacific Ocean basin. Redwood Coast Tsunami Work Group rctwg humboldt. Skip to main content. Toggle navigation Menu.
About Tsunamis. Frequently Asked Questions:.
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