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"In Catalonia the tsunami risk is low but not zero"

Japan's devastating earthquake and subsequent tsunami have set off alarms across much of the planet. Can a catastrophe of this magnitude take place in the Mediterranean? Are we prepared for it? University of Barcelona professor Miquel Canals, a marine geosciences expert, provides the answers to these pressing questions

Miquel Canals is a professor of Marine Geoscience at the University of Barcelona. He has participated in the European project Transfer, which aims to improve current knowledge on tsunamis and, in particular, on the probability of one affecting Europe. Under Transfer, Canals has participated in the study Tsunami Risk and Strategies for the European region.

What is the risk of a tsunami in the Mediterranean?
The area most prone to tsunamis is the Eastern Mediterranean and Adriatic and Tyrrhenian Seas. In the Western Mediterranean they are not as common but they do occur. The catalog of tsunamis that have affected Spanish coasts kept by the Spanish National Geographic Institute (IGN) lists a dozen such events from the early eighteenth century. A part of them affected the Alboran Sea and the Balearic Islands, but overall, the fluctuations in sea level and flood heights were very small, on the centimeter level.

That doesn’t sound very worrisome.
A very notable exception was the tsunami of May 21, 2003, that struck the coasts of the Balearic Islands with a flood height of two meters according to the IGN and was classified as “strong” according to the Ambraseys scale of tsunami intensity *. This tsunami was caused by the Boumerdès- Zemmouri earthquake in northern Algeria, where there were many casualties and considerable material damage. In the Balearic Islands, the waves caused damage to some coastal and port facilities, and sank or destroyed dozens of boats. The formation of so-called edge waves and resonance phenomena in some ports were the ultimate cause of much of the damage, as in the case of the Port of Palma. In Valencia, there was also some damage but it was very minor in nature. There was no loss of life in the Balearics or in Valencia.

What about Europe’s Atlantic coasts?
They are also prone to tsunamis. In fact, one of the great catastrophes of human history was the earthquake and tsunami in Lisbon in 1755. The material damage and loss of life in what was then one of the world’s great capitals were very high. The lasting impact of the disaster on Portuguese society was enormous. Ignoring the distances, it was comparable to the tsunamis that hit Indonesia on December 26, 2004, and the one that hit Japan on Friday. The Lisbon tsunami struck the coasts of much of the North Atlantic, including the Bay of Cadiz and the coast of Galicia in northwestern Spain.

What is the risk for Catalonia?
In Catalonia, the tsunami risk is low but not zero. Seismogenic tsunami sources with the potential to reach the Catalan coast are located on the continental edges with high levels of seismic activity, such as the North African edge, especially in Algeria, the Betic margin, from Andalusia to Alicante, and the margins of the Tyrrhenian Sea, the Ligurian Sea and Sicily. However, Catalonia is protected by a series of natural shields, such as the Balearic Islands, which block tsunamis coming from northern Africa, and Corsica and Sardinia, which are in the path of tsunamis coming from from the Tyrrhenian Sea. These natural shields would absorb most of the energy of the tsunami before it reached the Catalan coast.

Are earthquakes the only source of tsunamis?
Another potential source of tsunamis is underwater landslides, for which evidence has been found in many parts of the seabed between Catalonia and the Balearics. In the event of a tsunami from a deep-sea landslide on the slope of the Ebro Delta, it would reach the northern coasts of the Balearics before the Catalan and Valencian coasts due to the braking effect the wide continental shelf of the Ebro Delta would have on the wave.

Why is there more risk of tsunamis in the Pacific?
It is because of its geodynamic composition. It has many edges of tectonic plates, which continually rub and collide with one other. The heavier plate slides under the lighter one along the so-called subduction zones. This action means the plates gather stress and strain. If this tension is not released in a gradual and frequent manner, it can reach very high levels.

The tsunami wave travels on the surface at high speed, up to almost 1,000 kph This tension is what causes tsunamis?
When the tension passes a certain physical threshold it produces a sudden release of energy which produces a rupture of the lithosphere and the transfer of momentum and energy into the body of water. The result of this process is the tsunami. When the waters are deep, the tsunami wave travels on the surface at high speed, up to almost 1,000 kph, so it arrives to the coast shortly after being generated.

Are there forecasts of an increased risk of tsunamis in the Mediterranean?
An increase in tectonic or volcanic activity or underwater landslides could increase the risk of a tsunami. But right now there is no known evidence that such an increase is taking place.

Could climate change be a trigger?
It has been speculated that global warming and the gradual increase in temperature of deep waters could contribute to melting of gas hydrates (compounds composed mainly of methane that remain in solid form under conditions of high pressure and low temperatures like those found in deep sea areas) on the continental edges, thus inducing the destabilization of the sedimentary cover and an increase in the frequency of landslide tsunamis. This, if it were to occur, would mainly affect the northern margins of Europe.

Are there other risks?
You can also have episodes of heavy rainfall. Together with subsequent rise of coastal aquifers, combined with the building of embankments on the coast, heavy rains could cause displacement and thereby generate tsunamis, usually local in scope. This is the case of the airport in Nice, in southern France, which occurred in October 1978. Fjords are also more conducive to the generation of tsunamis, often resulting from the combination of earthquakes and landslides. In fact, the megatsunami with the tallest waves on record (524 meters) occurred in the fjord of Lituya Bay, Alaska, in 1958.

"We are not at all prepared to adequately respond to a tsunami" Are we prepared to fight a tsunami?
A tsunami cannot be fought, it is unstoppable. The only thing to do is to mitigate the damage and, above all, the loss of human life as much as possible. And if the question is whether we are prepared to respond adequately to a tsunami, the answer is no, not at all.

Can we do something to lessen its effects?
To start, we can encourage more scientific research on the processes behind tsunamis, which also would include the identification and simulation of flood scenarios.

And on a more applied level?
We need to work on the installation of detection and early warning systems. We can also reduce our vulnerability as much as possible, depending on available financial resources and investment priorities. In addition, we can educate the population located in vulnerable areas, and establish evacuation plans in the case of a tsunami warning. Finally, there exist anti-tsunami constructions like typhoon shelters, which are especially useful when there is sufficient time between the warning and the arrival of the tsunami.

What is your opinion on the nuclear situation in Japan?
It certainly does not seem to be good practice to locate nuclear sites in vulnerable areas since the nuclear risk is added to the effects of the earthquake and tsunami. This idea applies to any potentially dangerous facility and should be enforced worldwide.

* The Ambraseys intensity scale for tsunamis has six levels. Level four is “strong,” characterized by the flooding of the beach to a certain height, slight erosion of the man-made land areas, damage to piers and docks, damage to light structures near the beach, minor damage to solid structures on the coast and the dragging of large sailboats and small ships offshore.

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Marina 15/11/2011
Estoi haciendo un trabajo sobre este tema, sobre si seria possible que llegara un tsunami a mi ciudad (por Barcelona), y agradeceria mucho si pudiera contactar de alguna manera con Miquel Canals para que me resolviera algunas dudas. Grácias.

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