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What causes tsunamis?

2021-08-24 00:00:00.0 太阳报-世界新闻原网页

TSUNAMIS are among the most terrifying and dangerous of natural disasters.

But what exactly is a Tsunami and how can you survive one? Here's all you need to know...

In open water they can easily go unnoticed as they sometimes don't rise more than 30cm above the water level Credit: Alamy What is a tsunami?

A tsunami, also called a seismic wave, is a series of waves caused by the movement of a large body of water.

The term tsunami means "big wave in the port" in Japanese - and it was coined by fishermen after they returned to shore to find their villages devastated by a giant wave they had not seen at sea.

The killer waves can sometimes only be 30cm high in the open ocean, so go unnoticed by sailors.

But as it reaches shallower waters, the wave is slowed and the top of it moves faster than the bottom, causing the sea to dramatically rise.

Tsunamis can cause the sea levels to rise by as much as 30 metres, although they usually cause a rise averaging three metres.

The enormous energy of a tsunami can lift boulders, flip cars and plough down buildings.

The tallest ever in 1958 was caused by a quake and massive rockfall in Alaska - sending an enormous wave down the bay and stripping millions of trees up to a height of 1,720ft above sea level.

The devastation after a tsunami can be huge Credit: Reuters How is a tsunami formed?

A tsunami can be formed in a number of different ways, but usually there are three things that have to happen.

An earthquake must measure at least 7.0 on the Richter scale, the sea bed must be lifted or lowered by the earthquake, and the epicentre of the earthquake must be close to the Earth's surface.

Earthquakes, volcanic eruptions, underwater explosions, landslides, meteorite impacts and other disturbances above or below water can potentially generate a tsunami.

While normal waves are caused by the winds as well as the Moon and the Sun, a tsunami is always caused by the displacement of a large body of water.

Tsunamis are sometimes called tidal waves, although this term is not popular among experts as they are not actually influenced by the tides at all.

How to survive a tsunami? Be ready

If you are traveling to an area known as a tsunami hotspot be prepared.

Have an emergency kit packed and easy accessible in case of an occurrence.

In your emergency kit you should have food, water, climate-appropriate clothing, and if possible a small first aid kit.

However its essential that you pack light as you never know when you’ll need it and for how long you will need to carry it.

Know that it's coming

There are three signs that you can use to know when a tsunami is coming

shakes and tremors underfoot The water recedes If you hear a loud roar from the ocean

It is also vital that you are alert to any announcements and warnings made by local authorities.

Evacuation

It is very important that you listen to any guidance that governments and local authorities give you.

If they say to evacuate - then evacuate.

Abandon any unnecessary belongings and get away from the danger zone.

Tsunami hazard zones usually have signs to direct you to safety.

Get to high ground

As soon as it is safe to move, go to higher ground.

High ground is the safest place to be during a tsunami.

Avoid downed power lines and weakened bridges and over passes.

If you are outside of a tsunami hazard zone, stay where you are.