One tsunami it is a giant wave hitting the coast. It is usually caused by a earthquake or from an underwater landslide (often also caused by an earthquake). In the sea the wave is barely perceptible, but when it is slowed down by a shallow area, such as near the coast, it becomes steeper and can reach a height of tens of meters, with an enormous destructive force. Imagine that a medium-sized building suddenly appears at the water's edge and falls onto the beach. Now imagine that the building is made of water and as wide as the eye can see, if not more. You certainly don't want to be below this building!
Realistically, the only way to survive a moderate to large tsunami is to not be present in the flood zone when it arrives. Fortunately, if it's detected by local warning systems or if you know what to look for before you can see it, you'll likely have at least several minutes to walk away before it hits.
The tsunamis
If the epicenter of an earthquake is under the ocean or a large lake, the earthquake will displace huge amounts of water. Even a small earthquake can cause an underwater landslide, with similar effects. The tsunami risk depends on the direction in which the water is moved. In the worst case, such as when the edge of a tectonic plate moves up or down along the plate boundary, the water will move more or less in a coordinated direction, causing a wave. The wave can be small (even smaller than a normal wave) or huge. There may be one, but there will likely be more than one. The former is not always the largest. And earthquake aftershocks are common, which means subsequent tsunamis are also common.
Tsunamis can strike the coast from minutes to hours after an earthquake, depending on the distance from the coast to the epicenter. Furthermore, tsunamis can travel very far from their point of origin. For example, the 2004 Indian Ocean tsunami was caused by an earthquake north of Sumatra, but it also wreaked havoc on the East coast of Africa several hours later. An earthquake near one side of the Pacific Ocean can cause a tsunami both locally and on the opposite side of the ocean. This means that you may not feel the earthquake that triggered the tsunami.
Tsunamis can travel as fast as a commercial jet and are often invisible before it's too late, as they only grow in height when they hit shallower waters near the coast. It is not possible for a human to overcome a tsunami once you can see it.
Natural alert system
If you find yourself in the unlikely situation of a tsunami where there is no warning infrastructure, there are usually what are called "natural warning signs": nature itself says a tsunami is on the way. If an earthquake occurs right on the coast, you may only have a few minutes to escape, then do not hesitate to evacuate. Some obvious natural warning signs are:
- Water that recedes and exposes the ocean floor which is usually always submerged. This is a clear indication that a larger tsunami is imminent and you have, at best, a couple of minutes to escape from this point onwards. The more the water comes out, the more of it will suddenly come back to kill anyone who stopped to take photos or explore newly revealed shells instead of stepping out of the tsunami's path.
- Notable tremors of an earthquake off or near the coast. If you are on the coast and you feel an earthquake, don't wait for official warnings, but go ahead immediately inwards and on higher ground.
- Loud or unusual noises coming from the sea.
During a tsunami
During a tsunami warning, follow designated escape routes and pay close attention to what the authorities say. Especially in countries with a Pacific coast line, they are usually well aware of the nature of a tsunami and have refined their contingency plans with previous events. The most important thing during a tsunami is of course arrive on a rise. However, trees and even house roofs are a poor alternative to mountains, as the enormous force of the water could simply make you fall off the tree or destroy the house you are seeking refuge in (in the roof).
Under no circumstances should you rely on your ability to swim against such a powerful current! Even the best swimmers drown when they are unconscious, and by the time it hits you, that wall of water will be filled with a surprising number of deadly objects, such as trees, boulders, and vehicles that were parked near the beach. If you get carried away by the water, try to hold onto a piece of floating debris and wait for rescue.
Never go to the coast to see or witness a tsunami! This is a surprisingly popular way for people to accidentally die. Hundreds of people have been killed by tsunamis over the years - sometimes dozens at once - because they heard the early warning systems, thought they knew a safe place near the coast by getting some photos of the event, and were blown away or crushed by the tsunami.
After the tsunami
Keep in mind that there may be more than one tsunami wave and they can occur up to 24 hours after the initial wave, so stay away from the coast until officials tell you it's safe to return.
When returning to the buildings, be aware that floodwaters may have caused severe infrastructure damage. Flood water can also be contaminated with sewage.
Avoid sightseeing and travel only if necessary. If you have made travel arrangements with an airline or otherwise, it is best to contact them for advice.
