What is a Tsunami?

  • A tsunami is a series of ocean waves generated by sudden displacements in the sea floor, landslides, or volcanic activity. In the deep ocean, the tsunami wave may only be a few inches high. The tsunami wave may come gently ashore or may increase in height to become a fast moving wall of turbulent water several meters high.
  • Although a tsunami cannot be prevented, the impact of a tsunami can be mitigated through community preparedness, timely warnings, and effective response.

What types of earthquakes generate a tsunami?

  • Tsunamis can be generated when the sea floor abruptly deforms and vertically displaces the overlying water. Tectonic earthquakes are a particular kind of earthquake that are associated with the earth's crustal deformation; when these earthquakes occur beneath the sea, the water above the deformed area is displaced from its equilibrium position. Waves are formed as the displaced water mass, which acts under the influence of gravity, attempts to regain its equilibrium. When large areas of the sea floor elevate or subside, a tsunami can be created.

How are tsunami's dectected?

  • Deep-ocean tsunami detection buoys are one of two types of instruments used by the Bureau to confirm the existence of tsunami generated by undersea earthquakes. These buoys observe and record changes in sea-level out in deep ocean.

How are tsunami's generated?

  • Volcanic eruptions can also produce tsunamis. The rules are similar to the rules for earthquakes. In order for a volcano to produce a tsunami you need:
  • A volcano near the coast
  • An eruption that sends a large enough volume of material into the water to displace a significant volume of water.
  • If a large eruption sends a great volume of material into the water, it creates the vertical disturbance necessary to make a tsunami. This is one of reasons the Cumbre Vieja volcano is worrisome: either an eruption or a landslide from a flank collapse could produce a tsunami.

Where do tsunami's happen most?

Tsunamis happen most often along areas of the Pacific Rim. This is the area from New Zealand, Indonesia, and Asia. About eighty percent of all tsunamis happen in the Pacific Ocean.

What are the warning signs of a tsunami's?

  • If there was a large earthquake in the vicinity, the groundshaking is a clue to move to higher ground. In the great Tsumami in the indian ocean the classic sign was a rapidly recceeding sea before the tidal wave stikes. If the tide goes out unexpectedly and rapidly, head for higher ground. Third world countries don't have the tools to warn folks.

How far inland can tsunami waves travel?

  • There are various factors that determine how far inland a tsunami can go. Here is a list of factors involved:
  • The terrain of the land and the height of the tsunami wave. If the land is mountainous the tsunami would probably not go very far; however, if it is lowland, it may wash inland for several kilometers.
  • Another important factor in a tsunami is the volume of water displaced. It is not the height of a tsunami that gives it momentum over land, but the length.
  • The angle at which the tsunami reaches land and the geographical shape of the coastline: A concave coastline will suffer more damage than a convex coastline that can deflect the water movement.
  • Land forms slow them down considerably. The distance travelled inland is directly related to the change in elevation.

Where and when were the last 5 largest tsumami's recorded?

1. 1883 Krakatoa tsunami

In 1883, the volcanic island of Krakatoa erupted in Indonesia. The blast destroyed two-thirds of the island and sent 130-foot-high waves surging across the Indian Ocean, killing 36,500 people from Indonesia to India.

According to the US National Geophysical Data Center, an air pressure wave from the blast traveled around the Earth seven times.

2. 1498 Japan tsunami

For the same reason Japan is famous for its hot springs, it's also known for its tsunami-causing earthquakes. It sits near where several continental and oceanic plates meet in the Pacific Ocean, and in 1498 those plates shifted.

The resultant 8.6-magnitude earthquake triggered a 56-foot-high wave, according to the US National Geophysical Data Center. The wave hit the Japanese coast at Meiƍ Nankai, killing 31,000 people. The Nankai region is particularly known as an earthquake region, according to the Journal of Earth and Planetary Science Letters.

3.1755 Lisbon tsunami

In 1755, a massive 9-magnitude earthquake in the Atlantic Ocean caused a 400-foot-high wave to come crashing down on Lisbon, the capital of Portugal.

It killed an estimated 60,000 people and resulting fires destroyed two-thirds of the city, according to the US National Geophysical Data Center. Waves were seen as far away as Ireland.

4. 1908 Messina tsunami

In 1908, an earthquake off the coast ofMessina, Italy, triggered a large tsunami that claimed more than 75,000 lives, according to the US National Geophysical Data Center. A PBS report says the tsunami reduced the city's population to the mere hundreds and the death toll may have been as high as 200,000 people.

5. 2004 Indian Ocean tsunami

The 2004 Indian Ocean tsunami killed more than 300,000 people, according to the US National Geophysical Data Center. The deadliest tsunami in recorded history was triggered by the second-largest earthquake in recorded history, at magnitude 9.3, in the ocean near Indonesia's Sumatra island. The wave measured higher than 80 feet, which is still much lower than the 1,742-foot-high Lityua Bay tsunami of 1958, considered the tallest-ever.

Amid the devastation, the Monitor reported how 59 people in Aceh, Indonesia, weresaved by a veritable Noah's Ark. "In water up to their necks, they embraced, prayed and said their goodbyes. Then the boat came flying through the air and, with a sound like a thunderclap, crashed to a halt on top of the building."

None of these tsunamis listed, however, wiped out an entire culture. That responsibility goes alone to the tsunami of 1628 BC, which submerged the entire eastern Mediterranean coast and is believed to have destroyed Minoan culture, according to the National Geophysical Data Center.

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