Coastlines
Tsunamis
Natural Disasters

How do tsunamis happen?

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March 25, 2015 11:07AM

A tsunami (Japanese for harbor wave) can be caused when a large volume of water in a sea or ocean is displaced. Tsunamis can happen most anywhere that there is an ocean or giant body of water. They especially happen where major natural events like underwater earthquakes or volcanoes can happen.

A tsunami can be generated when convergent or destructive plate boundaries abruptly move and vertically displace the overlying water. There is usually a movement underwater, like an earthquake, where the earth's plates push together, or a landslide, which causes a wave to be generated. When tectonic plates slide on each other, that's when an earthquake may happen. Because they can slide under the ocean, the impact can make the water form a giant wave. This wave is massive - nothing like what a surfer seeks. The wave can be meters high, and as it rushes closer to the coast it gains enough momentum to wreak massive damage on land. The momentum slows upon reaching land, but it is still a major force.

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.

Tsunamis can be caused from different kinds of events, including, but not limited to:

Sea bed earthquake, displacing water (the most likely cause).Distance landslides into the ocean or sea.Tropical storms or hurricanes.Volcanic disruption.Meteor striking the ocean or sea. More details

Most tsunamis 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 account for most tsunamis. This will cause shock waves to be radiated out of the epicenter. There will be a rise or fall of the seabed. This displacement will create a wave which cannot be clearly detected from shore. These waves can travel at speeds up to 700 mph (i.e. the speed of sound in 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.

Tsunamis can also occur because of landslides. When land subsides into water bodies (usually extremely large landslides), they can create a wave that resembles a tsunami. The wave of these kinds of tsunamis will not be very high, unless a huge volume of rock or ice is involved.

Tsunamis can also occur when asteroids fall into the water bodies. This is extremely rare, and they must be extremely 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.

Some meteorological storm conditions such as deep depressions causing cyclones, hurricanes, strong winds and other similar occurrences can generate a storm surge, which can be several metres above normal tide levels. This is due to the low atmospheric pressure within the centre of the depression. As a storm surge comes ashore, it can resemble a tsunami, inundating vast areas of land.