What regions of France are the most at risk?

“We are never sure of anything” in terms of tsunami, recalls Johnny Douvinet, professor of geography at the University of Avignon. In recent years, this academic has been working on alerts to populations, including tsunamis.

If the peaceful and Indian ocean are frequently affected by tsunamis, such as this Wednesday, July 30, 2025 after an earthquake off the coast of Kamchatka, France could, or even should, one day face such a phenomenon.

A risk close to 100 % in the Mediterranean

During the United Nations Conference on the Oceans in Lisbon, in 2022, Unesco alerted the risk of tsunami in the Mediterranean in the next 30 years.

Statistics show that the probability of a tsunami wave of more than 1 meter in the Mediterranean in the next 30 years is close to 100 %.

The Atlantic and the Channel could also be affected.

According to the Ministry of Ecological Transition, “the most exposed coastlines concern: the Côte d’Azur (from Cannes to Nice), La Ciotat in Toulon, the Côte des Maures, the Perpignan coast, part of the northwest coast of Corsica (from Calvi to Galéria)”.

Up to 850,000 people to evacuate

Contacted by actu.frJohnny Douvinet explains that in the Mediterranean, two scenarios are feared.

“The first is an important earthquake in the Liguria Sea (Italy),” begins the professor. In this case, “a significant wave could touch Nice in ten minutes. And Marseille in 1 hour. »»

The second scenario, “is that of an earthquake in a North Algerian fault. There, all the Mediterranean periphery could be affected in 1 h 20, 1 h 40, “said the academic.

During the summer, this represents 800 to 850,000 people to be evacuated.

Damage, even without 10 m wave

And, “if it all depends on the intensity of the earthquake, the authorities are considering a wave of up to 1m50, 2m“, According to Johnny Douvinet. It is therefore not a 10 m high wave that would fall on the Mediterranean coast. But in terms of tsunami, the height is not everything.

“A wave of one meter can generate significant material damage,” insists the professor. “A number of platforms can be overwhelmed, boats in ports can be carried away. »»

The Japanese rescue association, whose country is used to the risk of tsunami, explains the possible consequences depending on the size of tsunamis:

• 0 to 30 cm: an adult can stand up, but cannot work;
• 30 to 50 cm: cars start to float, an adult can stay standing, clinging;
• 50 to 70 cm: water becomes powerful, even an adult can be carried away.
• 70 cm to 1 m: Impossible to remain motionless. The probability of death in the event of a collision with a large floating object is close to 100 %.

Station at speed

“More than the height is the wave arrival speed” which is important, says Johnny Douvinet.

It is also “the wave trainWhich is important. Here, understand the sequence of waves. Because a tsunami is not just a wave, it is a chain.

As a reminder, “78 % of tsunamis are due to seismic activity, 10 % to volcanic activity and landslides, and 2 % to weather activity”, explains UNESCO.

A tsunami is made up of several waves that will flood the coast in general every 10 to 30 minutes, sometimes for several hours. The first wave is often not the most important.

The populations ready?

Hence the importance of knowing ” Signals before a tsunami“, Specifies Johnny Douvinet. “A rapid fall in sea level or rapid withdrawal of the sea are natural signs before the imminent arrival of tsunami waves,” writes the Cenalt.

To read also on

The other question is whether the populations and the authorities are ready, “because the preparation and awareness phase saves lives,” notes the academic.

“The authorities are aware of the risk, and a priori, We can prepare without knowing the date, ”recalls Johnny Douvinet. On January 19, 2024, a FR-Alert notification had been sent to the smartphones of the inhabitants of nine departments in the Southeast to prevent them from a risk of tsunami. It was obviously an exercise: a way of doing prevention.

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