The Mediterranean seems almost always a calm sea but, as several recent studies have warned, the risk of major catastrophes is by no means ruled out. And one of the possible natural tragedies is a tsunami reaching the Mediterranean coasts, for example following an earthquake or a volcanic eruption.
In June 2022, during the presentation of the International Tsunami Ready system, the Secretary of Unesco’s Oceanographic Commission (IOC), Vladimir Ryabinin, recalled that there is a high probability of tidal waves in the Mediterranean over the next 30 years that could be considered tsunamis. In fact, several scientific teams have studied the risk and possible consequences of this type of phenomenon on our coasts, such as the model presented in 2015 by experts from Italy and Greece.
A new historical review study now shows that the danger is not new, meaning that it could be repeated.
Specifically, this new contribution has been published in the Journal of Iberian Geology and its authors are Javier Lario, Professor of External Geodynamics at the Faculty of Sciences of the UNED, Chris Spencer (UWE Bristol) and Teresa Bardají (UAH).
In this work, based on deposits found at Cabo Cope, Murcia, the researchers have recorded an event, dated between approximately 800 and 1,400 years ago, which caused large accumulations of blocks in this region of the Murcian coast. From the results, it is clear that “catastrophic tsunamis have also occurred on the Spanish Mediterranean coast, phenomena that could be repeated today”, the UNED said in an information note.
Javier Lario pointed out that, knowing these data, the need to “implement warning plans in the coastal areas of the southern Mediterranean to educate the population and raise awareness is even more justified.”
“We applied the methodology we had developed to see if it could be due to large storms or tsunamis, as the Murcia area can have tectonic earthquake activity”, Javier Lario said, “and we have seen that it could be the result of a tsunami”.
Although the waves of a large storm can be larger than those of a tsunami, they would not have the capacity to drag these blocks up to 4 metres above sea level, which reach 17.7 tonnes.
With their work, Lario and his colleagues are mainly trying to distinguish between these two types of phenomena. “It is interesting to differentiate between them because with climate change we are seeing an increase in large storms and even hurricanes, which have a similar geological record,” said the geologist.
On the other hand, they seek to focus on the risk that exists in the western Mediterranean off the Spanish coast.
“It is true that the geological record is very local,” said Lario, “but for that geological record to remain, it had to be more regional. In fact, in the northern part of Castellón, colleagues have found deposits of the same type”.
Although this coastal region differs from other more active areas further east in the Mediterranean – such as volcanically active Italy or Turkey – there are active faults, especially in the Alboran Sea.
“Through the studies, what we are trying to show is that, although in the instrumental period no high-risk tsunamis have been recorded in the area, there is a nearby geological record that tells us that they have occurred”, explained Javier Lario. Thanks to these records, recurrence periods can be established that allow the authorities to be alerted to possible phenomena similar to the historic Lisbon tsunami that devastated the Andalusian coast.
“We are talking about 70 per cent of the population being on the coasts. If it were to hit in summer, the floating population in coastal areas is much higher than in winter. Clearly a tsunami now would have a very big impact,” says Javier Lario. “The population tends to be in the lower areas associated with riverbanks or near beaches, which are easier to urbanise.”
Cities such as Huelva and Cadiz have started to create evacuation plans, but Lario explained that it would be necessary to implement them in the coastal areas of the southern Mediterranean in order to educate the population and raise awareness.
But the absence of a major tsunami in the historical memory of this region makes its implementation more complicated. In addition, human-induced coastal erosion and degradation could greatly affect the severity of a potential tsunami.
“The processes of sea level rise or erosion of the beach and the natural protection of the coastline make it more vulnerable in the event of a tsunami. If we have lost sand or coastal area and the water can penetrate further inland, when a tsunami comes, the effect will be worse,” warned the geologist.
The Spanish Interior Ministry, together with the National Geographic Institute and the Directorate General of Civil Protection, has developed a State Tsunami Plan.
Through the analysis of the danger of tsunamis on the Spanish coasts, this plan is a starting point for autonomous communities and localities to implement their own action plans for tsunami inundation risks that could occur within their territories.
It informs society of the data extracted from research such as that carried out by the geologist Javier Lario and also facilitates the dissemination of knowledge of general interest, such as the causes and consequences of events of this type.
Additional reporting by Maria Ortega