The recently released documentary movie "La Gran Ola" (The Great Wave), with its apocalyptic scenarios makes one sit up and think. According to this film there is great danger of tsunamis in the Mediterranean and adjacent waters. We talk to Alexander Rudloff who contributed to several projects related to Tsunami Early Warning Systems
GFZ: Is the situation really that serious?
Alexander Rudloff: Yes, absolutely. The described scenarios are partly quite dramatic - for example, individual regions can indeed be cut off from the supply for days on end following a tsunami and thus further worsening the emergency situation.
And the scenes are based on real facts. In the movie, a number of experts who are well known and highly appreciated at the GFZ through joint research projects speak on tsunamis. Generally, the threat is no news – we have actually been aware of potential tsunami sources in the Mediterranean and neighboring areas for many years.
GFZ: How can the dangerous tidal waves develop?
Rudloff: Tsunamis are mainly triggered by earthquakes, but can also result from volcanic eruptions and landslides on underwater slopes. For the Mediterranean, the number of these submarine slopes is significantly higher than in comparable regions such as the Indian Ocean. We estimate that between a quarter and a third of all tsunamis in the Mediterranean Sea are triggered by mass movements; this is below ten percent in other seas. These landslides are often also associated with volcanic eruptions. An example: The collapse of the island of Santorini as a result of a volcanic eruption in 1613 BC presumably produced a tidal wave up to twelve meters high. Also today, we know of smaller tsunamis caused by volcanic activity such as around Stromboli.
GFZ: Are there further examples from history?
Rudloff: The best known example was a combination of an earthquake and a tsunami on 1 November 1755 in Lisbon. As a result, the city, then a world metropolis, was almost completely destroyed, several tens of thousands of people died. However, it is important to keep in mind that due to All Saints Day large amounts of candles were lit in churches and this would have been the reason for extensive fires that caused devastating damage. Another example is the earthquake of 28 December 1908 in the Strait of Messina, which led to a tsunami - both events led to the loss of tens of thousands of lives. From the recent past, we should mention a tsunami of 31 May 2003 which was triggered by an earthquake off the coast of Algeria. After just 30 minutes the waves arrived at the Balearic Islands causing extensive damage to the marinas.
GFZ: How can you protect yourself?
Rudloff: Tsunami cannot be prevented. But early warning systems can help ensure that as many people as possible are informed in a timely manner and can thus reach safety. At the northern and eastern borders of the Mediterranean Sea there are early warning systems that by now function well. On the North African coasts the instrumentation is generally capable of development. This applies both to earthquake stations as well as to GPS measuring instruments and coastal gauges.
GFZ: How does a tsunami early warning system actually work?
Rudloff: Computer programs continuously evaluate data from a wide range of sensors installed at numerous different points and which are all connected with each other within a network: first of all, seismometers that register seismic waves, secondly, GPS stations that also register minimum movements of the mainland, and thirdly, tide gauges that identify noticeable changes on the surface of the water even if the wave has not yet towered to a major tsunami.
In the ideal case the software from these data can actually detect a tsunami, many minutes before it hits the mainland. This provides time to warn the population so that they can get to safety. On a side note, the GFZ was also involved in advising on the early warning systems in the Mediterranean. For example, the GFZ provided the software for analysis of the seismic data as well as our experience from the Tsunami Early Warning System GITEWS which was established in the Indian Ocean under the leadership of the GFZ.
GFZ: What else can be done in addition to a monitoring of the sea?
Rudloff: A further protective measure is to make people conscious of the danger so that they live in awareness of this situation. In this respect, appropriate emergency drills are carried out in the respective countries where a complete tsunami scenario from the first alerting of the people through to evacuation is fully acted out. Israel did this last year, other countries could do more.
GFZ: What do I have to consider as a tourist?
Rudloff: For holidaymakers who travel, for example, to the Mediterranean, it is recommended to prepare for such an event, for example by studying the tsunami data sheets which we have compiled at the GFZ. Immediately after arrival, it is advisable to familiarize yourself with the local conditions: Are evacuation routes and assembly points for evacuations or safe places identified? Where are they located, and how can I get to safety in the case of emergency, for example at an elevated location across from the beach? This should be best clarified during daytime when you have a good overview of the location and a clear mind. Natural catastrophes always come at an unsuitable moment. The better you are prepared, the better your chances of survival.
GFZ: Would it then actually be wiser not to travel to these regions?
Rudloff: That would be exaggerated. In effect the individual risk of being hit by a tsunami is far less than being harmed, for example, when traveling. Still the danger of a tsunami for the Mediterranean Sea and adjacent seas, even for the Atlantic, is real and should not be underestimated. This should be kept in mind.
GFZ: For a long time, the early warning in the Mediterranean region was considered capable of development. What is the current state?
Rudloff: Progress has been made in this respect. Since autumn 2016 there are four existing “Tsunami Service Providers” in the region: In Greece, Turkey, Italy, and France. In the respective countries, early warning centers exist and they exchange information between centres. According to established criteria, linked for example to a certain magnitude of an earthquake and its location, a tsunami alarm is triggered. Portugal and Spain, which are addressed in the film "La Gran Ola", have not yet progressed this far. The Spanish Mediterranean coast is largely covered by the French early warning system, but there is a clear need for improvement as far as the Atlantic coast is concerned.
GFZ: Is the risk in Spain and Portugal underestimated?
Rudloff: No. As I said, many experts who speak in "La Gran Ola" are well-known experts who are involved in joint research projects such as ASTARTE (Assessment, STrategy and Risk Reduction for Tsunamis in Europe). But bureaucracy is sometimes cumbersome. The further development of an early warning system in these countries is progressing slowly.
This does not mean nothing is happening. For example, there is an exemplary evacuation point on the city beach in the Algarve in the port of Lagos, where there is a clear sign posting from the water line to an assembly point. However, right next door on the large neighboring beach with many tourists there is no signposting at all. Especially for such places it makes sense for holidaymakers to be prepared and to know how to behave in the case of a tsunami.
The interview was led by Ralf Nestler