How tsunamis form

A tsunami or tidal wave is a wave or a group of giant waves with great energy, created by sudden movements that occur on the seabed. The term tsunami is of Japanese origin and means “big wave in the port or bay”.

There are many that have been formed throughout history, but there is no doubt that the most recent ones have been really terrible natural disasters . We refer to those mentioned at the beginning, the one that occurred in Sumatra and Sri Lanka, in December 2004, and the one that occurred in Japan in March 2011.

Find out more details about the effects of the 2011 Japan earthquake and tsunami with AgroCorrn .

First of all, to explain how tusnamis are formed , we must bear in mind that the Earth’s surface is made of huge plates, called tectonic plates. Some of them form the continents and others the bottom of the oceans. These plates move and slide slowly over the soft rocks of the mantle, located under the earth’s crust. There are occasions in which these plates due to their movement separate, and occasions in which they come together until they collide. These movements are the cause of phenomena such as earthquakes, volcanic eruptions or landslides.

Now, what does all this have to do with tsunamis? It is simple, when these movements that we discussed earlier are movements that occur in the oceanic plates , that is, at the bottom of the sea, marine earthquakes can form and, therefore, trigger a tsunami.

If you want to know the process in more detail, we will describe it below, take note.

Tsunamis evolve in three general phases :

Tsunami generation

This phase refers to the previous section in which the disturbance of the seabed occurs. The height that the waves can reach depends on various factors, such as the magnitude and duration of the disturbance, the speed or the depth of the sea.

In the case of the Sumatra tsunami, the plates gave way, causing the seabed to deform abruptly, producing an uplift that pushed the water upwards, forming a column 3 meters high when it formed.

Spread

In this stage, the energy that has been generated on the seabed due to the disturbance is propagated to the coast. On the surface, tsunami waves advance at great speed, which depends on the depth of the ocean; deeper, faster. Again taking the Sumatra tsunami as an example, as this one originated at 4,000 meters deep, its waves reached a speed of 700 km / hour.

Something characteristic of tsunamis is that as they approach the coast, the sea becomes shallower and the water recedes, leaving a hole in front of the water column. The waves grow in height and thickness, becoming giant waves .

Flood

The waves have reached their maximum size, 20 meters in the Sumatra tsunami. These reach the coast leaning towards it to later break and penetrate up to several hundred meters inland devastating everything in its path . Tsunami waves can arrive several minutes out of phase with each other.

For our “peace of mind”, and we highlight it in quotation marks because when faced with phenomena of this caliber, our peace of mind lies in being able to detect them in time and be safe , since they cannot be avoided ; in the Pacific Ocean there are facilities dedicated to the detection of these tsunamis to limit the effects that may occur. These facilities to detect tsunamis have:

• A detector placed on the ocean floor that can detect a rise in the ocean surface of a few centimeters.
• Broadcast buoys anchored to the ocean floor to collect detector signals and send them to the satellite.
• The satellite, which captures the information provided by the buoy and transmits it to the tsunami warning center in Hawaii.
• A tide gauge that detects ocean level changes so that when the water recedes before the tsunami hits, it sounds the sirens.
• The seismological station: It is a laboratory equipped with seismographs that detect earthquakes. All stations are connected to the alert center.
• The Tsunami Warning Center, located on the island of Hawaii. All the information collected by seismographs, underwater detectors or tide gauges reaches this center. At the slightest sign of a tsunami, warning reports are sent to all countries exposed to the tsunami.
• Dams: In some islands of Japan these structures have been built to attenuate the energy of the waves of tsunamis.

Two other important points when it comes to protecting yourself against tsunamis are:

• Mangroves, areas planted with mangroves (woody shrubs or trees) that form a very dense vegetation along the coast and that play an important role when the waves break, slowing their force a little.
• Prepare the population. As soon as the sirens sound or the alert is notified by radio, the inhabitants flee inland, that is, away from the coast or go to high places.

After the Sumatra tsunami, the countries decided to create a warning center in the Indian Ocean. The first detection buoys were placed in July 2005.