What causes a tsunami to erupt?

Answer 1

Take a look at the video in the related links section. That was when the tsunami hit Thailand in 2004, it started when there was an earthquake in the Indian ocean. They can be very destructive, and deadly.

Answer 2

THE CAUSES OF TSUNAMI

A short explanation of causes:

Tsunami (pronounced su-nah'-me) are huge ocean waves caused by natural forces like underwater earthquakes. Tsunami are caused when the forces of these phenomena rapidly displace large amounts of water.

Most tsunami occur when there is an earthquake or volcanic eruption in the sea or ocean. This is caused when there are plate boundaries that are meeting in plate tectonics processes. This will cause shock waves to be radiated out of the epicenter. This natural event will cause a rise or fall of the seabed. This will create a wave deep in the ocean (or less frequently in other large body of water).

Tsunami can also be caused by landslides, such as a cliff-side of a mountain near shore that falls into a large body of water or ocean.

Powerful bombs, like nuclear bombs, are tested, dropped, or detonated in the sea or ocean and can cause shock waves to be radiated out that move the ocean waters in waves as described above.

They also occur when large asteroids fall into the water. This is extremely rare, and the asteroids must be very large to cause a large water displacement to form a tsunami wave. But they are known to have occurred. Meteorites will not cause high waves as they are usually much smaller than asteroids by the time they have been burned in the atmosphere on the way to the surface.

A longer, more in depth answer:

The huge waves called tsunami are caused by the abrupt vertical displacement of a large volume of a body of water, usually from natural sources of kinetic energy (such as the force of large earthquakes near the shore or underwater). These forces produce a wave that shifts not just a few meters of surface water, but the entire column of water from the floor to the surface. They contain enormous amounts of energy. Earthquakes that cause tsunami often occur offshore at tectonic plate subduction zones. As the sea floor snaps up in response to the tectonic plate movement and subsequent earthquake, the tsunami wave is formed and moves out from the source of the displacement. The wave increases in height as it enters more shallow waters close to land.

They can occur in any large body of water, even in large lakes. An example is the mega-wave that formed when the volcano erupted at Mount St. Helens in the US in 1980. The eruption caused a massive landslide into Spirit Lake and that caused the mega-wave.

To better understand how a tsunami forms, try this experiment:

Get in a pool or the bath tub and put your hand a good ways down and then pull it up quickly but not out of the water, pull up strong but don't break the surface and watch the result. Not exactly a tsunami, but a simple version of the science.

SUMMARY:

Most tsunami occur when there are underwater seismic events such as an underwater earthquake or volcanic eruption. This normally occurs along plate boundaries. Subduction in convergent boundaries accounts for most tsunami. Subduction occurs when one plate dives under another that is blocking its movement. This will cause shock waves to be radiated out of the epicenter. There will be a rise or fall of the seabed. This displacement of the sea floor will create a wave which cannot be clearly detected from shore at first. These waves can travel at speeds up to 700 mph (i.e. the speed of sound in water) deep in the ocean or other large body of water. As the wave gets nearer to the shore, the wave will compress and gain height in the shallower water. The waves can be up to 100 ft. (30 m) or more when they come ashore.

Tsunami can also occur because of landslides or when asteroids (or very large meteorites) fall into large bodies of water. This is extremely rare, and they must be very large to cause a large enough water displacement to form a massive tsunami wave.

DETAILS:

Natural Causes

Besides earthquakes, these waves can also be caused by the forces of other natural phenomena and seismic events that move the tectonic plates, or that directly move the undersea water, or smash into the water surface from above in such a way as to rapidly displace the water.

When it happens in a sea, the sea floor may be deformed from below pushing the water up, or the water can be displaced from an impact coming down on the sea surface from above. Some of the natural causes, other than tectonic plate movements resulting in earthquakes, are huge landslides and other mass movements above or below the water. Sometimes a small underwater earthquake will trigger a landslide that causes a tsunami.

Volcano eruptions in or near the ocean can produce water displacement from underwater or from impacts from above by huge pieces of falling debris from explosions as a volcano erupts along a coastline or near a large lake.

Another cause from natural events is an ocean impact by rare large meteorites or asteroids. This is extremely rare, and they must be very large to cause a large water displacement to form a wave. Meteorites will not cause high waves as they are usually much smaller than asteroids.

Since these natural phenomena can be the causes, it means that tsunami have the potential to be formed anywhere in any large body of water at unpredictable times and without time for any warnings.

Unnatural Causes

An unnatural event with potential to cause tsunami is the detonation of underwater explosions (including detonations of underwater nuclear devices).

STILL MORE DETAILED INFORMATION ABOUT TSUNAMI:

The name

The word tsunami is a Japanese term. Japan is one of the most common locations for tsunami. The literal translation in English is "wave harbor" meaning "harbor wave". This name came from the fact that they only become visible as huge waves after arriving in shallower waters near shores and harbors, and therefore, they were originally believed to have originated in the harbor. The word tsunami has been used long enough that it has been adopted into most languages rather than being translated.

The Japanese word does not have a plural form and tsunami is used both for singular and plural in English in many locations. However, it has become accepted over time to say "tsunamis" for the plural in English.

Many early geological, geographical, and oceanographic texts refer to tsunami as "seismic sea waves."

They are sometimes mistakenly called "tidal waves," but tsunami have no relationship to the tides other than looking similar but smaller and generating some similar effects on land with flooding and devastation.

Tsunami are also sometimes incorrectly called "storm surges", which are also different wave phenomena. Tsunami have no relationship to weather. They are not caused by storms, cyclones, hurricanes, or high winds.

Tectonic plate action

Tsunami are commonly caused by seismic activity of tectonic plates (most often earthquakes). As such, they are often found around the Pacific Rim, a region of high tectonic activity in the Pacific Ocean.

A Tsunami can be caused when a tectonic plate in the earth's crust is subducted by another plate, which releases a lot of tensive (potential) energy, in an earthquake. Movement of tectonic plates can cause an earthquake that sends out jolts of seismic activity. Large vertical movements of the earth's crust can occur at plate boundaries. This will cause shock waves to be radiated out of the epicenter. These jolts then can push a tectonic plate under the sea floor, or over or under another plate. The earthquakes can form anywhere there is stress in a tectonic plate, but notably on plate boundaries. Plates interact along these boundaries called faults. Seismic activity is not, however, limited to boundaries of these plates. Tsunami can be formed if there is a very big earthquake any place in a plate that disrupts a water column in a large body of water.

Subduction in the convergent plate boundaries is said to account for most of the tsunami. This natural event will cause a rise or fall of the seabed. When large areas of the sea floor elevate or subside, a tsunami can be created.

This will create a wave deep in the ocean which cannot be clearly discerned from shore. This massive underwater wave transforms when it hits the shoreline and has nowhere else to go but up. This then pushes the water on the surface up, forming the massive wave.

Earthquakes

The Greek historian Thucydides was the first to relate tsunami to submarine earthquakes.

Subduction earthquakes are particularly effective in generating tsunami. In the case of earthquake-generated tsunami, there is a major disturbance under water causing the water column to rise as the earthquake uplifts or causes subsidence of the sea floor.

When the sea bed is lifted as a result of an earthquake, the water is also lifted. The size of the wave depends on how high and over how big an area the seabed was lifted. Some say the earthquake size must be at least 6.0 on the Richter scale to create a tsunami.

Landslides

Tsunami can be caused by very large landslides either falling into the water from above or by an underwater landslide pushing a column of water from below the surface. These mechanisms causing submarine slumps of material, or landslides of huge parts of a mountain or cliff side near shore, can occur without an earthquake, or at least without a significant one. Super marine landslides and cosmic-body impacts disturb the water from above as momentum from falling debris is transferred to the water into which the debris falls. Generally speaking, tsunami generated from these mechanisms, unlike the Pacific-wide tsunami caused by some earthquakes, dissipate quickly and rarely affect coastlines distant from the source area.

Submarine landslides, which often accompany large earthquakes, as well as resulting collapses of volcanic edifices, can also disturb the overlying water column as sediment and rock slump down-slope and are redistributed across the sea floor.

Another type of landslide that can produce tsunami involves the debris delta from a river system that eventually becomes unstable and slides off, thus displacing a large body of water. The rebound to this can cause a large enough surge to be a tsunami, and one with little warning.

Other similar causes in the colder oceans are huge avalanches or glacier calving.

Volcanoes

Tsunami can be generated when a violent volcano eruption on land occurs near a large body of water. Sometimes huge chunks of solid rock burst out of a volcano and fall into the nearby ocean or lake making a tsunami. Similarly, volcano eruptions can cause tsunami when they explode undersea. A violent submarine volcanic eruption can create an impulsive force that uplifts the water column and generates a tsunami.

Asteroids

Tsunami can also occur when large asteroids fall into the water. This is extremely rare, and the asteroids must be huge to cause a large enough water displacement to form a tsunami wave. But they are known to have occurred. Some geologists believe as recently as the early 1700s an asteroid impact off the Pacific Northwest coast of North America may have created a tsunami that reached Japan.

These produce a wave that shifts not just a few meters of surface water, but the entire column of water from the floor to the surface. They contain enormous amounts of energy. Tsunami caused by an asteroid impact could be a much higher and more devastating wave, depending on the asteroid's size. Fortunately such occurrences don't happen as frequently as those caused by earthquakes, volcanoes and underwater landslides.

Meteors

An even more rare cause is a meteorite hitting Earth. Meteorites will not cause waves as high as those caused by asteroids since they are usually much smaller bodies. There are estimates that the space rocks would have to have a diameter of between about 165 feet (50 meters) and 490 feet (150 meters). Any smaller and the rock would have exploded before hitting Earth or Earth's waters.

Underwater Explosions

Tsunami can also occur when powerful bombs, like nuclear bombs, are tested, dropped, or detonated in the sea or ocean or above the ocean waters. There have been tests done in various parts of the world. This was done with nuclear bombs in the area of the Bikini Atoll and resulted in tsunami. A top secret New Zealand program to experiment with tsunami caused by explosions was known as Project Seal, in the 1940's.

Size

This wave is massive - nothing like what a surfer seeks. The waves can be as high as 100 ft. tall when they near shore. They initially will create a series of waves deep in the ocean, that are only a few feet tall. They cannot be clearly discerned from shore or ships until they get to the shallows close to shore and then can be identified too late to allow warning and people to escape.

The largest recorded tsunami was in Lituna Bay Alaska at 1720 feet (524.25600 meters).

Speed

Tsunamis move faster than a human being on shore and can not be "outrun". These waves can travel under water at great speeds, up to hundreds of mph. They can travel as shallow waves at 500 mph deep under the sea. Close to the shore, this speed reduces to 30 to 40 mph. Although the momentum slows upon reaching land, it still hits with a major force.

How the waves move

The waves travel in all directions from the area of disturbance, much like the ripples that happen after throwing a rock into water.

The crests of the tsunami waves can be as much as a hundred miles apart. They can cross the entire ocean in less than a day without losing much energy. Tsunami waves can be as long as 60 miles and be as far as an hour and 100 miles apart. They destroy vast cities and developments on land, but at the same time don't destroy ships as they travel beneath them on the way to shore. They can pass right under the ships unnoticed. That's because the height of a tsunami wave might be only a foot or two at those depths. Or they might be noticed but not given any special attention because they seem harmless as they travel under the ocean surface.

The situation changes dramatically when the waves come closer to shore. As they enter shallow waters, they begin to decelerate and gain height as the wave becomes compressed and the seafloor rises in height.

Tsunami travel through water, and therefore can reach areas not located near the epicenter of the earthquake. Reflection and diffraction can change the regions affected. This was seen in the 2004 Boxing Day tsunami, whereby the wave front diffracted around the tip of India and Shri Lanka and hit the western coast of India, a section of coastline that was not in the direct line of the tsunami.

This wall of water travels underwater until it reaches the shore. Once a tsunami reaches the shallow water near the coast, it slows down. The top of the wave moves faster than the bottom, causing the sea to rise dramatically. It will uplift and form the huge wave and as the water gets more and more shallow, it rises and rises until it is at its maximum height.

Interestingly, a tsunami will cause the water along the shore to pull away from shore into the oncoming tsunami, adding more and more water to the "big wave" on its way in. This displacement pulls water back from the shore, causing the wave to build in size and intensity. Depending on whether the leading element of the tsunami is a trough or a crest (it can be either) there may be an eerie ebbing or pulling back of the water along the shore; it must appear to observers like an unnatural pulling back of the tide. This would happen if the leading element is a trough.

Many people get so mesmerized by the unusual sights at the shoreline that they don't recognize the impending danger. Tsunami kill a lot of people because of the fierce strength of the initial wave, subsequent waves, and the undertow created by gallons of rushing water.

Storm Surge vs Tsunami

Tsunami are not caused by storms or wind or other weather phenomena. Those would be storm surges which are different waves.

Some meteorological storm conditions, such as deep weather depressions that cause cyclones, hurricanes, strong winds and other similar occurrences, can generate a storm surge, which can be several meters above normal tide levels. This is due to the low atmospheric pressure within the center of the weather depression. As these storm surges come ashore, the surge can resemble a tsunami, inundating vast areas of land. But they are not one and the same.

Results and devastation of tsunami

As we have seen from the 2004 tsunami of Southeast Asia and the 2011 Japanese tsunami, the effects can be devastating. A tsunami has great energy, and can carry waves far inland. The power of the water can knock down buildings and crush vehicles. People usually die from being smashed against something, rather than drowning. Tsunami can push huge amounts of water over islands and coastal regions causing the deaths of hundreds of thousands or millions of people, and they can cause millions or even billions of dollars worth of damage.

They can move up the rivers and streams leading to the ocean. Flooding can reach land 1000 feet (300 meters) from the coastline and the dangerous waves have enough force to lift giant boulders, flip vehicles, and demolish houses. Tsunami kill a lot of people because of the fierce strength of the initial wave, subsequent waves, and the undertow created by gallons of rushing water.

Tsunami will definitely cause damage, casualties, and injuries. Fires can break out from gas line breaks that are ignited. Tsunami, as they reach closer to shore, will wash fishing boats and other boats, such as cruisers, onto shore, and onto streets, railroads, and buildings. Airports are destroyed, roads are impassable. The boats will be stuck on shore and usually wrecked from the force of the wave. Cars, trucks, airplanes and trains can be washed through the coastal areas damaging structures and people in their wake.

Entire coral reefs and the plants and animals that depend on them for habitat can be devastated. Once the reefs are destroyed, the protection they provided for the coastal areas from hurricanes, storms and other damage is lost along with the barrier reefs.

People and livestock can be caught in the wave and carried away inland and back into the sea with all the debris from the devastation. The waves will also cause fish to be washed onto the shore and stuck there to die. They flood the lands near the shore, causing entire buildings to be inundated. They are identified too late for most people in the coastal areas to escape and avoid death from them. They will damage the crops and cause nearby buildings to collapse. Some people might be trapped under the buildings and die. They uproot trees too, causing them to fall on houses and people.

Lastly, they cause economic decline as countries have to spend billions of dollars rebuilding and recovering from the damage. Millions of people can be homeless without food, clean water, and proper sewage disposal and without electricity. Hospitals that may be still operating are overwhelmed, injured people may not receive timely medical care. Access to medical supplies, pharmacy supplies, and maintenance medications may not be available for months or more. People cannot find loved ones and family members and there are little, if any, means of communication immediately following the tsunami. Factories and jobs are eliminated and many never rebuild in the area again. Tourist industries collapse for even years afterward.

Tsunami "Season" ?

There is no tsunami season, they are unrelated to weather, so they can occur at any time just like the things that cause them can happen any time of year… plate subduction, earthquake, volcano, etc.

Tsunamis can take place at any time; night or day.

Where they occur

Tsunami could occur anyplace there is a large body of water (even large lakes). They can move up the rivers and streams that connect with the body of water of the tsunami, causing further destruction and flooding.

They often hit along the coasts of the "Ring of Fire," around the margins of the Pacific Ocean. In the US: California, Washington, Oregon, and Hawaii and the Japanese coastlines are all potential areas where denser oceanic plates slip under continental plates in the process mentioned above known as tectonic plate subduction. One in Chile sent tsunami warnings ino the pacific. Thailand is in a circle where tsunami hit a lot. There is a well known spot in Alaska where a Mega Tsunami hit, Lituna Bay. There was the tsunami in the Bay of Bengal in 2004.

There was one on October 7, 2009 , originating from an underwater earthquake near the Vanuatu Islands in the southwest Pacific. The wave affected other islands, including Hawaii and Fiji, as well as Alaska and California. This tsunami, however, was weak and insubstantial compared to a devastating tsunami on December 26, 2004, also known as the Sumatra-Andaman earthquake. The wave itself was up to 100 feet (30 meters) high in places. At the time it was considered the fifth worst natural disaster in recorded history, and the deadliest tsunami ever, possibly more than four times worse than the next deadliest tsunami (in terms of death toll, rough estimates range from 229,866 to 443,929 people killed).

Mega Tsunami

Mega earthquakes (measuring 9.0 and above on the Richter Scale) are said to produce Megatsunami (also known as Iminami) which are much more destructive than normal tsunami. They can reach heights of up to 300-500+ meters, and reach about 25 km inland. They are said to be able to cross the Atlantic (Transatlantic).

As mentioned above, an example of a mega-tsunami happened on the 9th of July in 1958 in Lituna Bay in Alaska, generating the largest recorded tsunami. An earthquake measuring 7.7 on the Richter scale caused 90 million tons of rock to fall directly into the sea. It caused a wave 524 meters high (1720 feet).

The wave from the collision of the KT Event 65 million years ago (an asteroid) is believed to have been up to 1.5 kilometers high.

When Cumbre Vieja in La Palma eventually collapses into the Atlantic it could generate a 2000 foot high wave rushing across the Atlantic at 500 mph.

Predictions, warnings, and animal behavior

Scientists are not yet able to predict them just as volcano eruptions and earthquakes can't be predicted. Seismic activity could signal a warning, however, and this is under study.

Animals often recognize the danger and run inland. One explanation of this is that animals can sense the movement of the air and hear changes in the waves much faster than humans recognize these.

Answer 3

A tsunami is a large ocean wave caused by sudden motion on the ocean floor. This sudden motion could be an earthquake, powerful volcanic eruption, or an underwater landslide.

Answer 4

An earthquake can spawn a tsunami at its epicenter. Also, seafloor spreading can cause them.

Answer 5

An underwater earthquake or volcanic eruption

Answer 6

Earthquakes seem to be the main reason.

Answer 7

An underwater earthquake.