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What Causes a Tsunami?



One of the most destructive powers on Earth is water. It can cut rock, erode mountains, smash buildings, and leave utter devastation in its wake. Tsunamis have historically been some of the worst natural disasters human communities have faced, and there’s not a lot we can do to soften the blow when they strike. To understand more about them, let’s look at what causes a tsunami in the first place:



1. When the earth moves, a domino effect is triggered.
The trigger for a tsunami can be an earthquake, volcanic eruption, or an underwater landslide. Each of these events involves earth moving suddenly and with force. Earthquakes that happen under the ocean floor can generate massive waves, as can volcanic eruptions when they dump large volumes of material into the ocean. These waves then turn into tsunamis.

2. The ocean presents a wide expanse where momentum can gather.
How exactly does one event create a wave that can decimate a city? Think about the open ocean. It stretches for miles not only from coast to coast, but also from the surface to the deep. There are no obstructions that take momentum away from the building wave, allowing it to grow to incredible sizes.



3. When a wave reaches a shoreline, it breaks.
The growing wave will continue to gain energy until it finds an island, where the sea floor rises. This rise causes the tsunami wave to gain amplitude (height) in order to conserve energy, resulting in the huge and powerful waves we associate with tsunamis.
 
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Jan 24, 2020
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One of the most destructive powers on Earth is water. It can cut rock, erode mountains, smash buildings, and leave utter devastation in its wake. Tsunamis have historically been some of the worst natural disasters human communities have faced, and there’s not a lot we can do to soften the blow when they strike. To understand more about them, let’s look at what causes a tsunami in the first place:



1. When the earth moves, a domino effect is triggered.
The trigger for a tsunami can be an earthquake, volcanic eruption, or an underwater landslide. Each of these events involves earth moving suddenly and with force. Earthquakes that happen under the ocean floor can generate massive waves, as can volcanic eruptions when they dump large volumes of material into the ocean. These waves then turn into tsunamis.

2. The ocean presents a wide expanse where momentum can gather.
How exactly does one event create a wave that can decimate a city? Think about the open ocean. It stretches for miles not only from coast to coast, but also from the surface to the deep. There are no obstructions that take momentum away from the building wave, allowing it to grow to incredible sizes.



3. When a wave reaches a shoreline, it breaks.
The growing wave will continue to gain energy until it finds an island, where the sea floor rises. This rise causes the tsunami wave to gain amplitude (height) in order to conserve energy, resulting in the huge and powerful waves we associate with tsunamis.
i know how tsunmai's are formed there are many ways they are formed but the most comon way is an earthquake.
 
Jan 27, 2020
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Tsunamis happen most frequently in the Pacific Ocean because of the many large earthquakes associated with subduction zones along the margins of the Pacific Ocean basin. This area is called the “Ring of Fire” and about 90% of the world's earthquakes occur in this location, while about 72% of all tsunamis are generated by earthquakes.. There are subduction zones with associated deep-sea trenches off the coasts of Chile, Alaska, Japan, and Indonesia, that have produced large earthquakes and devastating tsunamis, many of which caused damage and loss of life in the Hawaiian Islands and Alaska.

Earthquakes that generate tsunamis most often happen where Earth’s tectonic plates converge, and the heavier plate dips beneath the lighter one. The lighter seafloor snaps upward when the tension is released. This column of seawater is pushed upward, creating an enormous bulge in the ocean. As this bulge of water collapses, giant ripples race outward through the ocean at nearly the speed of a jet aircraft. Interestingly, from an observation standpoint, in mid-ocean the tsunami waves may only create an inch or two rise in the sea level. However, it is when this enormous energy reaches the shallow coastal waters that the huge waves appear. You must also remember that water cannot be compressed, so any violent action on water will result in its immediate propagation outwards.

Huge sub-surface landslides, which often occur during a large earthquake, can create a tsunami. During a sub-surface landslide, the seawater is displaced by huge amounts of sediment moving along the sea floor. Gravitational forces then propagate the tsunami after the initial perturbation of the sea level. Similarly, a violent marine volcanic eruption can create an impulsive force that displaces the water column and generates a tsunami. Landslides and meteors disturb the water's surface. The falling debris displaces the water from its position of equilibrium and produces a tsunami. Unlike ocean-wide tsunamis caused by some earthquakes, tsunamis generated by non-seismic mechanisms usually dissipate quickly and rarely affect coastlines far from the source area.

However, the meteor which created the Chixculub crater, which has a diameter of some 93 miles, off the Yucatan Peninsula and ended the reign of the dinosaurs, generated a massive tsunami. The initial height of this tsunami created by the blast wave from the meteor strike has been estimated to have been some 4,000 feet high.

In 2019, researchers, led by Kliti Grice, a geochemist at Curtin University in Australia, analyzed samples of the peak ring (see illustration below) of the Chicxulub crater core, searching for molecules such as polycyclic aromatic hydrocarbons (PAH), which are organic compounds containing carbon and hydrogen. ("Aromatic" does not refer to the molecules' smell, but their ring like chemical bonds.) In the samples, the scientists looked for a PAH called perylene, which comes from pigment made by wood-degrading fungi.

The compound's presence suggests that a returning tsunami several hundred feet (or meters) high "flooded the crater within days of the asteroid impact," Grice said. "The abundance of perylene within the crater is the result of it being transported there by the soil and land plant debris carried by the (second incoming) tsunami."

As the reporter said in Howard Hawk's original 'The Thing', "Watch the skies, watch the skies."
 

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