PARIS, September 13 — UNESCO has warned that the probability of a tsunami wave exceeding 1 meter somewhere in the Mediterranean over the next 30 years is close to 100 percent. The organization stated this on June 22, 2022, and the estimate concerns an event somewhere in the Mediterranean basin over the following three decades, roughly through 2052.
According to the statement, the figure is not a prediction of an imminent disaster, a guarantee that the French Riviera would be struck, or a forecast that every Mediterranean coastline would experience the same waves. The Mediterranean is often treated as an unlikely setting for a tsunami.
UNESCO has warned against that assumption.
Why the basin can produce dangerous waves
The region has the ingredients needed to generate dangerous tsunamis. Earthquakes can occur along active faults in the Ligurian Sea, near the French and Italian coasts. Farther south, the movement of the African and Eurasian plates creates another source of potentially powerful earthquakes off North Africa.
Underwater landslides provide an additional, sometimes much more local, trigger. A tsunami begins when a large volume of water is suddenly displaced, often by an earthquake, landslide, or volcanic eruption.
The disturbance spreads outward, potentially traveling long distances before reaching the coast. Historically called tidal waves, raz-de-marée in France or maremoti in Italy, tsunamis can bring both sudden flooding and extremely powerful currents. They do not always resemble the towering wall of water people imagine.
A tsunami can appear as a rapid rise or retreat of the sea, followed by repeated surges. Flooding can range from centimeters to several meters, while fast currents can exert forces equivalent to several tons per square meter against coastal structures.
The first wave is not necessarily the largest. Italy’s National Institute of Geophysics and Volcanology notes that a tsunami with an amplitude of just 50 centimeters can be dangerous because of the energy and sustained movement of the water, which can behave more like a rushing torrent than ordinary surf. Globally, tsunamis have killed more than 250,000 people since 1970.
The December 26, 2004, Indian Ocean disaster and the March 11, 2011, tsunami in Japan account for much of that devastating toll.
The Mediterranean’s recorded history
Montpellier researchers describe the Mediterranean as having the largest historical tsunami record after the Pacific. Along the French Riviera, they cite roughly 20 reported events between the 16th century and the early 2000s, including waves exceeding two meters. On February 23, 1887, an earthquake in the Ligurian Sea, with an estimated magnitude between 6.5 and 6.8, triggered a tsunami along the coast.
Historical accounts describe the sea falling by about one meter in Antibes and Cannes, leaving fishing boats stranded. Waves approaching two meters then swept over the beaches.
On October 16, 1979, part of the construction site for a new commercial port in Nice (Alpes-Maritimes), beside the airport, collapsed into the sea. The resulting landslide and tsunami caused eight deaths, according to a reconstruction published in Natural Hazards. Effects were reported in Nice, Antibes, and Cannes, with disturbances observed in Antibes for about half an hour.
The later study found that water reached elevations of 3.5 meters locally and flooded as far as 150 meters inland. The May 21, 2003, Boumerdès earthquake in Algeria demonstrated that the trigger could also lie across the Mediterranean.
Its effects reached the Riviera about 75 minutes later. Investigators documented abrupt sea level drops of from 50 centimeters to 1.5 meters, partially emptied harbor basins, swirling water, strong currents, and damaged boats in eight marinas. Harbor resonance, in which the shape of a basin reinforces the water’s oscillations, helped explain why neighboring ports experienced different effects.
On December 4, 2022, a flow of hot volcanic material entered the sea at Stromboli and generated a small tsunami, activating the island’s warning system. Italy’s geological institute reported no damage, but the event provided another reminder that the region’s tsunami activity is real and ongoing.
Warning systems and the race to the coast
France has operated its national tsunami warning center, the Centre d’alerte aux tsunamis (Cenalt), since July 2012. Working within the international system coordinated by UNESCO, it monitors earthquakes that could generate tsunamis and sends initial messages to French emergency authorities and other warning centers. The warning then has to reach the public. In France, the chain includes the interdepartmental crisis management operational center (Cogic), followed by authorities responsible for issuing instructions. One channel is FR-Alert, which can send notifications to mobile phones in the threatened area.
Detecting an earthquake and getting people moving are therefore separate steps. Distance makes a crucial difference. A tsunami generated off North Africa may take less than 90 minutes to reach the French Riviera. On the French Riviera, a tsunami could arrive before a warning reaches people on the beach. In some local scenarios,
