Tsunamis vs. Tidal Waves: Understanding the Key Differences Between These Devastating Waves

Those who live in coastal areas around the world fear the tsunami warning. This alert warns populations when the waves are still far from the shore so that they have time to take shelter. Tsunami alerts have already been issued in France, even though this phenomenon most often originates in the Pacific Ocean.

Tidal waves are also capable of creating enormous damage when a giant wave crashes onto the shores. This is why the terms tsunami and tidal wave are often confused. They may be incorrectly used as synonyms.

A tidal wave does not form in the same way as a tsunami

In reality, they are two very distinct phenomena. They are not created in the same way. The tidal wave is caused by the gravitational interaction between the Earth, the Moon and the Sun. This is sort of the extreme version of low and high tides that occur daily in coastal areas.

Tides are highest when the Moon is between the Earth and the Sun and when the Earth is between the Moon and the Sun. So most areas experience high tide twice every 24 hours and 50 minutes. Low tides occur in areas that are neither the furthest nor the closest to the Moon.

You should also know that tidal waves can extend over several thousand kilometers, but they are generally small. They can take on gigantic proportions depending on the geography.

For example, river mouths and narrow coves can create huge, devastating waves. However, this has nothing to do with the destructive force of tsunamis. They are all the more dangerous because they are largely unpredictable.

A tsunami can travel at 800 km/h in the open sea

According to UNESCO, the probability of a tsunami wave more than one meter high in the Mediterranean in the next 30 years is “close to 100%”. Many populations around the world are therefore affected by tsunamis.

Unlike tidal waves, tsunamis occur following a sudden event such as an underwater earthquake, landslide, volcano eruption and even meteorite impact.

All of these events can cause a sudden movement of a large body of water. Giant and destructive waves then form near the coasts. You should know that tsunamis created in the open sea move very quickly, but they have a relatively low height.

So, even if they reach several hundred kilometers per hour (up to 800 km/h), they generally go unnoticed.

Shallow tsunamis are the most dangerous

It is when approaching the coast when the depth of the water decreases that the waves gain height. They are then extremely dangerous. Moreover, tsunamis can occur either close to where the waves hit the coastline or thousands of kilometers away.

Generally speaking, earthquakes of magnitude 6.5 or higher that occur at relatively shallow depths and uplift the Earth's crust are most likely to cause tsunamis.

As Costas Synolakis, director of the University of Southern California's Tsunami Research Center, explains for LiveScience, volcanic eruptions and landslides that move large quantities of magma and rock can go unnoticed. for detection systems.

It is therefore more difficult to detect the formation of these tsunamis in advance. Residents of vulnerable coastal areas therefore sometimes have only a few minutes to evacuate.

The DART tsunami monitoring system is not yet perfect

Today, tsunamis are closely monitored by the Deep-ocean Assessment and Reporting of Tsunamis (DART) system. It is a network of offshore buoys that capture signals from pressure sensors on the ocean floor.

The buoys in turn transmit the signals to satellites which directly inform the warning centers. However, the DART system is not yet perfect worldwide.

“The problem is that currently there are around fifty DARTs covering the Pacific and Indian Oceans. About half of them are working at any given time. We need at least 150 spread across the world's oceans to have an effective system with targeted alerts,” explains Costas Synolakis.

Source: LiveScience