The Mediterranean Sea is widely recognized as having a low tsunami risk. History and recent modeling techniques show that destructive waves have already hit the coast of France and may do so again. The results of projects carried out in Nice and along the Cote d’Azur demonstrate why predictive and preventive evacuation measures are the only truly effective means of saving lives.
Tsunamis were once known as high waves. tsunami France? tsunami In Italy, these are one of the most destructive natural phenomena. Caused by earthquakes, underwater landslides, and volcanic eruptions, they quickly spread over long distances and then release energy near the coast in the form of sudden flooding and very powerful currents.
This flood is generally characterized by multiple waves, ranging from a few centimeters to several meters, and the first wave is not necessarily the largest. The speed of tidal currents can put pressure on coastal infrastructure of several tons per square meter.
Since 1970, tsunamis have claimed more than 250,000 lives around the world, most notably the 2004 Boxing Day tsunami in the Indian Ocean and the March 11, 2011 tsunami in Japan.
Not such a far-fetched risk after all
In the collective imagination, tsunamis have long been associated with the Pacific and Indian Oceans. The risk of tsunamis off the coast of the Mediterranean has been considered to be minor, but this in itself can be misleading. UNESCO, which works to improve global tsunami risk awareness among coastal communities, declared in June 2022:
“Statistics show that there is a 100% chance of a tsunami over 1 meter high in the Mediterranean in the next 30 years.”
The Mediterranean Basin has recorded the highest number of tsunamis in history after the Pacific Ocean, some of which have affected France’s Côte d’Azur coastline.
According to available data, around 20 outbreaks have been reported in waters along the French Riviera from the 16th century to the early 2000s, with waves often exceeding 2 meters.
Evacuation time is often very short
The sources of Mediterranean tsunamis can be local or remote. In some scenarios, the initial wave rise time can be less than 10 minutes, especially when underwater landslides or earthquakes occur near the coast, such as in the Ligurian Sea between Corsica and the Italian coast. Conversely, a tsunami originating further from France, such as off the northern coast of North Africa, could reach the French Riviera in less than 90 minutes.
The May 21, 2003 Boumerdes earthquake (Algeria) caused havoc throughout France’s Mediterranean coast. Field investigations showed that eight marinas on the Côte d’Azur experienced significant sea level drops (from 50 cm to 1.5 m), basin cleansing, strong eddies and currents, and boat damage, consistent with port resonance events. Effects were observed on the French Riviera coastline 1 hour and 4 minutes after the earthquake.
Of a more local origin, the Nice tsunami of October 16, 1979, caused by the underwater collapse of part of the construction site of Nice’s new commercial port (Alpes-Maritimes) adjacent to the airport, caused eight deaths and significant damage in Antibes, Cannes, and Nice. This phenomenon was observed in Antibes for about 30 minutes.
Another scenario that could occur near the coast is the earthquake tsunami that hit the Ligurian Sea on February 23, 1887, following an underwater earthquake of 6.5 to 6.8 on the Richter scale. Accounts from the time describe how the sea suddenly receded by about 1 meter in Antibes and Cannes, leaving fishing boats high and dry before waves reaching nearly 2 meters arrived and covered the beaches.
These events remind us how completely surprised we are and how such short periods of time have shown the limits of traditional warning systems. It will be important for coastal communities to be able to evacuate quickly.
Alarm system operating in France
France has a national tsunami warning system. Tsunami warning center (Cenalt) has been implemented since July 2012 in cooperation with the international system coordinated by UNESCO in the Mediterranean. The system enables the rapid detection of earthquakes that can cause tsunamis and the transmission of warnings to the Interdepartmental Crisis Management and Operations Center (Cogic) and overseas warning centers within 15 minutes.
It is then up to the authorities to distribute warning messages to the public, especially through the FR-Alert platform, which can send notifications to the mobile phones of people in danger zones.
However, this global system only targets tsunamis caused by distant earthquakes and is less effective in the case of local tsunamis or tsunamis caused by underwater landslides, where the time it takes for a tsunami to reach the shore may be shorter than the warning time. This is why it is important to raise awareness among coastal residents about detecting warning signs such as felt earthquakes, unusual sea movements, and receding seawater that often precedes tsunami run-up.
NICE – The Côte d’Azur coastline is in extreme danger
Along France’s entire Mediterranean coast, evacuation zones have been established by government agencies and the University of Montpellier based on altitude, distance from the sea and historical data. This applies to coastal areas less than 200 meters from the sea and less than 5 meters above sea level. Along the river estuary, this distance extends up to 500 meters from the estuary.
At least 1,700 kilometers of coastline, including Corsica, 187 towns on France’s Mediterranean coast, and at least 164,000 residents will be affected. At the height of summer, an estimated 835,000 beach users need to be accounted for in the event of a tsunami.
The Nice-Côte d’Azur metropolitan area is vulnerable for a variety of reasons, including dense urbanization, strong tourist attraction, and very crowded beaches. Our photo analysis and modeling work allowed us to estimate that tens of thousands of people are present in the evacuation area during periods of high visitor numbers (between 10,000 and 87,000 people are present on the coast, depending on the season and time of day).
Evacuation in preparation for a tsunami: planning for Nice and surrounding coastal areas
In the face of a tsunami, evacuation is the only effective means of ensuring civilian safety. International experience shows that rapid and well-prepared evacuation procedures can save the majority of exposed populations. For example, when a massive tsunami hit the Tohoku coast on March 11, 2011, post-evacuation measures saved 96% of Japan’s residents.
In the Nice-Côte d’Azur region, a comprehensive evacuation strategy has been developed and supported by scientific research led by the Institute of Geography and Land Planning at the University of Montpellier. It is based on an optimized walking route that takes into account slopes, obstacles, travel speed, and congestion points. Evacuation sites in “out of reach” locations were identified and verified by local authorities, and evacuation routes were devised using an algorithm to find the fastest route.
In total, nearly 100 evacuation sites have been planned and incorporated into evacuation plans to quickly guide people to safety.
From science to action: preparing the public
Raising tsunami awareness requires not only the creation of evacuation maps, but also the gradual introduction of safety drills, especially evacuation drills in schools, and public warning signs. Contribute to promoting responsible behavior. Some of these initiatives are also being carried out in Nice through a project with students from Montpellier.
In Nice, a publicly accessible information platform with interactive maps allows users to find evacuation zones, routes and instructions in the event of a warning. These tools contribute to the development of a true tsunami risk culture.
Transition to the realm of “tsunami preparedness”
This information portal is applicable beyond the French Côte d’Azur coastal region to other coastlines in France and Europe where tsunami run-up times can be similarly short, both in the Mediterranean and abroad.
The initiatives being implemented in Nice are in line with UNESCO regulations. Prepare for tsunami International Recognition Program (TRRP). This 12-point program aims to identify areas that can predict tsunami risk, prepare residents and coordinate appropriate responses.
The first towns to receive this label and benefit from the scientific and technical support of our team are Deshayes and Cannes in Guadeloupe, and Nice will also join this program in the near future.
There is no doubt that being prepared to evacuate will make a big difference when faced with a wave that can arrive within minutes.
This article was written in collaboration with Louis Monnier, Monique Gherardi, Matthieu Péroche and Noé Carles, Paul Valéry, University of Montpellier..
