Tsunami is a Japanese word that means “harbour wave.” They are large and powerful ocean waves that grow in size as they reach the shore. What happens after that is a tragedy.
Imagine yourself sitting on a beautiful beach enjoying a lovely day, when out of the blue, alarm blasts from your phone and reads “Tsunami warning.” What do you do next and where do you go? What if you aren’t at a place where there are alarms, would you know the signs of an approaching tsunami?
A tsunami is a series of ocean waves that sends surges of water, sometimes reaching heights of over 100 feet (30.5 meters), onto land. These walls of water can cause widespread destruction when they crash onto the shore.
What causes a Tsunami?
These awe-inspiring waves are typically caused by large, undersea earthquakes at tectonic plate boundaries. When the ocean floor at a plate boundary rises or falls suddenly, it displaces the water above it and launches rolling waves that will become a tsunami.
Most tsunamis–about 80 percent–happen within the Pacific Ocean’s “Ring of Fire,” a geologically active area where tectonic shifts make volcanoes and earthquakes common.
Tsunamis may also be caused by underwater landslides or volcanic eruptions. They may even be launched, as they frequently were in Earth’s ancient past, by the impact of a large meteorite plunging into an ocean.
Tsunamis race across the sea at up to 500 miles (805 kilometres) an hour—that’s as fast as a jet airplane. At that pace, they can cross the entire expanse of the Pacific Ocean in less than a day. And their long wavelengths mean they maintain much energy along the way.
In the deep ocean, tsunami waves may appear only a foot or so high. But as they approach the shoreline and enter shallower water they slow down and begin to grow in energy and height. The tops of the waves move faster than their bottoms do, which causes them to rise precipitously.
What happens when it hits land?
A tsunami’s trough which is the low point beneath the wave’s crest often reaches shore first. When it does, it produces a vacuum effect that sucks coastal water seaward and exposes the harbour and sea floors. This retreating of seawater is an important warning sign of a tsunami because the wave’s crest and its enormous volume of water typically hit shore five minutes or so later. Recognizing this phenomenon can save lives.
The best defense against any tsunami is an early warning that allows people to seek higher ground. The Pacific Tsunami Warning System, a coalition of 26 nations headquartered in Hawaii, maintains a web of seismic equipment and water level gauges to identify tsunamis at sea. Similar systems are proposed to protect coastal areas worldwide.
There may not be time to wait for an official warning, so it is important to be able to recognize natural tsunami warnings. These include strong or long earthquakes, a loud roar (like that of a train or an airplane) coming from the ocean, and a sudden rise or fall of the sea level that is not related to the tide. Be prepared to respond immediately to any tsunami warnings. Move quickly to a safe place by following posted evacuation signs. If you do not see an evacuation route, go to high ground or as far inland as possible.
Rushing water from waves, floods, and rivers are incredibly powerful. Just six inches of fast-moving water can knock adults off their feet, and twelve inches can carry away a small car. Tsunamis can be particularly destructive because of their speed and volume. They are also dangerous as they return to the sea, carrying debris and people with them.
Stay out of the tsunami hazard zone until local officials tell you it is safe, as the danger may last for hours or days.
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