Tsunamis are natural events that can be among the deadliest and costliest hazards. Many people associate the word tsunami with a giant sea wave generated from an earthquake, however, this is not the only source. Volcanoes and underwater landslides can also generate tsunamis.
Interestingly, the word tsunami has its origins in Japan: tsu, meaning harbour and nami, wave. The basic mechanism that generates a giant wave is the rapid displacement of a large volume of water.
On average, approximately two tsunamis occur every year somewhere around the world. In the last decade alone, deadly tsunamis have occurred in Chile, Haiti, Peru, Tonga, the Solomons, Indonesia and Japan.
Perhaps, the most notable tsunamis are the one in 2004 in Sumatra, Indonesia and the one in 2011 in Tōhoku, Japan, where, in total, more than 250,000 people died and billions of euros in damage were caused. Such dramatic events shake the global community, which, in turn, demands answers to questions on where and when the next one is going to strike and how the losses can be reduced.
The very first step towards mitigation is awareness. In December 2015, the United Nations General Assembly designated November 5 as World Tsunami Awareness Day, coordinated by the UN Office for Disaster Risk Reduction.
Malta, like any other island in the Mediterranean, is also susceptible to tsunamis. The complex geological environment of the Mediterranean region gives rise to more than one type of tsunamigenic source, such as the subduction of the African plate beneath Greece, volcanic explosions or slope failure of Mount Etna and Mount Vesuvius, large rock falls or sudden submarine landslides.
Historic records show that several tsunamis have occurred in the Mediterranean over the centuries, some causing complete devastation. For example, a volcanic eruption in about 1620 BC on Santorini caused flood waves of up to 60 metres high, submerging the coasts of the entire eastern Mediterranean. In the year 365, a great earthquake caused heavy destruction on Crete followed by a tsunami that destroyed complete coastal regions as far as eastern Sicily and Egypt, killing about 50,000 people in the city of Alexandria.
Malta, like any other island in the Mediterranean, is also susceptible to tsunamis
More recently, on December 28, 1908, an earthquake measuring 7.4 on the Richter scale hit the city of Messina, in Sicily, followed by a tsunami. The earthquake and tsunami killed an estimated 40,000 people in Messina and Reggio di Calabria alone, with some historical documents claiming up to 200,000 victims in total. The earthquake was felt in Malta and the tsunami also reached our shores. Local newspapers such as the Daily Malta Chronicle reported that the sea around Malta became agitated and water rushed up to Msida. Fortunately, there were no casualties.
With the considerable development undergone along Malta’s eastern coast, if a similar tsunami had to strike again today the impact may be more substantial. Though not much can be done to stop an impending wave, monitoring for an approaching tsunami is now feasible.
Seismic networks on land throughout the Mediterranean now enable rapid detection, evaluation and assessment of larger earthquakes within minutes or seconds. In order to have more precise information and confirmation about an approaching tsunami, however, real-time data from tide gauges which monitor the sea level are also necessary.
In the Mediterranean, the Intergovernmental Oceanographic Commission of Unesco (IOC-Unesco) is coordinating the Tsunami Early Warning and Mitigation System in the North-Eastern Atlantic, the Mediterranean and connected seas (NEAMTWS), with the aid of regional tsunami service providers.
Over the past four years, the Seismic Monitoring and Research Group within the Department of Geosciences at the University of Malta has enhanced its real-time seismic monitoring capability and data exchange with other Mediterranean countries through the Simit project.
Now, in a follow-up €2.5 million project called Simit-Tharsy – Tsunami hazard reduction system – the department will enhance its seismic monitoring capabilities and incorporate real-time data from tide gauges to monitor potential tsunamis more accurately. Simit-Tharsy will strengthen the infrastructural systems and the contingency planning systems already present in the Malta-Italy cross-border region and will constitute a new platform for information exchange between civil protection departments in Malta and Sicily and scientific institutions, specifically, addressing monitoring, rapid assessment, alert and rapid intervention in the case of tsunamigenic earthquakes.
Specialised software is being installed to run case-study scenarios providing the national authorities with necessary information for emergency planning and management. These models will provide predictions of the tsunami travel times and expected sea level height across the Mediterranean for a specified earthquake scenario, with special attention on the Maltese islands. Such modelling can help understand how the local bathymetry can affect the wave propagation inside creeks, for example. The recent tsunami that hit the city of Palu, in Indonesia, had an unexpected wave height of six metres instead of the estimated 0.5 metres, probably due to the geographical shape of the bay.
The project partners of Simit-Tharsy are the civil protection departments of Sicily and Malta and the universities of Palermo, Catania and Malta. The local researchers are Sebastiano D’Amico, Pauline Galea, George Bozionelos and the author.
Matthew Agius is a seismologist working on seismic networks to study seismicity and the earth’s interior.
This is a Times of Malta print opinion piece