What causes a tsunami?

Question

What causes a tsunami?

Answer 1

What causes a tsunami?... A tsunami is a large ocean wave that is caused by sudden motion on the ocean floor. This sudden motion could be an earthquake, a powerful volcanic eruption, or an underwater landslide. The impact of a large meteorite could also cause a tsunami. Tsunamis travel across the open ocean at great speeds and build into large deadly waves in the shallow water of a shoreline.

Subduction Zones are Potential Tsunami Locations

Most tsunamis are caused by earthquakes generated in a subduction zone, an area where an oceanic plate is being forced down into the mantle by plate tectonic forces. The friction between the subducting plate and the overriding plate is enormous. This friction prevents a slow and steady rate of subduction and instead the two plates become "stuck".

Earthquake Causes Tsunami

Energy accumulates in the overriding plate until it exceeds the frictional forces between the two stuck plates. When this happens, the overriding plate snaps back into an unrestrained position. This sudden motion is the cause of the tsunami - because it gives an enormous shove to the overlying water. At the same time, inland areas of the overriding plate are suddenly lowered.

Answer 2

Tsunamis are a series of extremely long waves that are created after a large volume of water is displaced.  But what is a large volume?  And how is it displaced?

Although there is no calculated volume of water that constitutes a standardized quantity that will generate a tsunami, the amount displaced must be significant enough to create waves underwater in the vast ocean.  Waves are formed as the displaced water mass moves under the influence of gravity to regain its equilibrium and radiates across the ocean like ripples on a pond.  The larger the displacement, the larger the wave generated.        

A tsunami can be generated by four general ways: (1) an undersea earthquake; (2) landslide; (3) volcanic eruption; or (4) an extraterrestrial collision.  

(1)An Undersea Earthquake - is the most common form of tsunami formation, typically generating the most destructive tsunamis.  The earth is constantly moving on large tectonic plates.  When these tectonic plates move past each other, collide and/or slide under one another (subduction), an earthquake results.  This is what happened with the recent tsunami that devastated Southern Asia.  Here, a massive earthquake in the Indian Ocean measuring 10.0 on the Richter scale jolted the seabed causing the sudden displacement of a very large volume of water.  The earthquake temporarily produces a fluctuation in the mean sea level of a specified area.  Waves quickly form as the displaced water tries to recapture equilibrium by filling the vacuum that was created.  It should be noted that not all earthquakes generate tsunamis.  Usually, it takes an earthquake with a Richter magnitude exceeding 7.5 to produce a destructive tsunami.

(2)Landslides – resulting in rockfalls, icefalls, or underwater (submarine) landslides or slumps can generate displacement of water to create a tsunami.  More often than naught, submarine landslides are often caused by earthquakes, large and small, therefore strengthening the force of an earthquake induced tsunami.  The most notable example of a landslide-induced tsunami can be traced to Southern France in the 1980’s where the movement of a significant amount of earth for the construction of an airport triggered an underwater landslide, which resulted in destructive tsunami waves hitting the harbor of Thebes.        

(3)Volcanic Eruption - Although relatively infrequent, violent volcanic eruptions represent also impulsive disturbances, which can displace a great volume of water and generate extremely destructive tsunami waves in the immediate source area.    Volcanic disturbances can generate waves by the sudden displacement of water caused by a volcanic explosion, by a volcano's slope failure, or more likely by a phreatomagmatic explosion and collapse and/or engulfment of the volcanic magmatic chambers.  The majority of tsunamis that occur in the Pacific Ocean happen around the “Ring of Fire” Area surrounding the Hawaiian Islands.  The periphery has also been dubbed the 'Ring of Fire' because of the extraordinarily high number of active volcanoes and seismic activity located in the region.  Since 1819, over 40 tsunamis have struck the Hawaiian Islands.  One of the largest and most destructive tsunamis ever recorded was generated in August 26, 1883 after the explosion and collapse of the volcano of Krakatoa (Krakatau), in Indonesia.  This explosion generated waves that reached 135 feet, destroyed coastal towns and villages along the Sunda Strait in both the islands of Java and Sumatra, killing 36, 417 people.  

(4)Extraterrestrial Collision – Tsunamis caused by extraterrestrial collision (i.e. asteroids, meteors) are an extremely rare occurrence.  Although no meteor/asteroid induced tsunami have been recorded in recent history, scientists realize that if these celestial bodies should strike the ocean, a large volume of water would undoubtedly be displaced to cause a tsunami.  Scientists have calculated that if a moderately large asteroid, 5-6 km in diameter, should strike the middle of the large ocean basin such as the Atlantic Ocean, it would produce a tsunami that would travel all the way to the Appalachian Mountains in the upper two-thirds of the United States.  On both sides of the Atlantic, coastal cities would be washed out by such a tsunami.  An asteroid 5-6 kilometers in diameter impacting between the Hawaiian Islands and the West Coast of North America, would produce a tsunami which would wash out the coastal cities on the West coasts of Canada, U.S. and Mexico and would cover most of the inhabited coastal areas of the Hawaiian islands.

Answer 3

usually an earthquake, under the sea

Answer 4

A tsunami can be generated when the plate boundaries abruptly deform and vertically displace the overlying water. Such large vertical movements of the Earth’s crust can occur at plate boundaries. Subduction earthquakes are particularly effective in generating tsunami.

Tsunami are surface gravity waves that are formed as the displaced water mass moves under the influence of gravity and radiates across the ocean like ripples on a pond.

Answer 5

A tsunami is caused by tetonic plates rubbing up against themselves or pusing against eachother causing high vibrations in the underwater (in this instance) sea floor and having the shockwaves push against the water molecules resulting in a gigantic wave called a tsunami.

Answer 6

When God is angry with human invasion of Sea. We have enough land to live, cultivate and grow our food still we are invading into sea by occupying it. We call it reclamation but it is purely against the nature. As if there is no land to build and live the Dubai Government has encroached into the Arabian Sea for miles. The same thing else where in Bombay, New York and all other places. These causes in-balance of space on earth and things like tsunami happens to settle the scores. The so called environmentalists make a big hue and cry about Global warming but what the h**l they are doing about this type of messing with the nature?

Answer 7

earthquackes or tremors,on the sea bottom ,

and mega tsunamis are cause by large landslides that fall into the  sea ,there is one coming from the philipines ,but nobody knows when ,but it will cause a 25 meter high wave that will hit the east coast of the USA.

Answer 8

Usually it is caused by an earthquake that occurs in the ocean.

Answer 9

Earthquakes off the shore can cause a tsunami.

Answer 10

Normally a tsunami can be generated when the plate boundaries abruptly deform and vertically displace the overlying water. Such large vertical movements of the Earth’s crust can occur at plate boundaries. Subduction earthquakes are particularly effective in generating tsunami.

Tsunami are surface gravity waves that are formed as the displaced water mass moves under the influence of gravity and radiates across the ocean like ripples on a pond.

In the 1950s it was discovered by that larger tsunami than previously believed possible could be caused by landslides, explosive volcanic action, and impact events when they contact water. These phenomena rapidly displace large volumes of water, as energy from falling debris or expansion is transferred to the water into which the debris falls. Tsunami caused by these mechanisms, unlike the ocean-wide tsunami caused by some earthquakes, generally dissipate quickly and rarely affect coastlines distant from the source due to the small area of sea affected. These events can give rise to much larger local shock waves (solitons), such as the landslide at the head of Lituya Bay which produced a water wave estimated at 50 – 150 m and reached 524 m up local mountains. However, an extremely large landslide could generate a “megatsunami” that might have ocean-wide impacts.

The geological record tells us that there have been massive tsunami in Earth's past.

Answer 11

A tsunami is a large ocean wave that is caused by sudden motion on the ocean floor. This sudden motion could be an earthquake, a powerful volcanic eruption, or an underwater landslide. The impact of a large meteorite could also cause a tsunami. Tsunamis travel across the open ocean at great speeds and build into large deadly waves in the shallow water of a shoreline.