28-09-2026 | Posted by Joaquín Martí
Tsunamis are among the most devastating natural disasters, capable of causing widespread destruction on shores and coastal communities over large distances. These massive ocean waves may be generated by underwater earthquakes, volcanic eruptions or landslides, displacing vast amounts of water and sending waves racing across the ocean at high speeds.
A typical tsunami is triggered by a seismic event that involves large vertical displacements of the ocean floor. Thus, subduction zones, where one tectonic plate is progressively sinking under another, are common places for generating tsunamis.
The changes in elevation of the water surface are initially rather small (say 20 or 30 cm) but they travel fast: their speed of propagation is (gh)1/2, where g is the acceleration of gravity and h is the water depth (with ocean depths of 4000 m they travel at some 720 km/h). In mid ocean, ships do not notice that a tsunami is passing by but, as the waves approach the shore, the water depth decreases and so does the wave propagation velocity while the wave amplitude increases.
Distance from the source helps to reduce the effects, but only moderately. If the fault rupture extends over many hundreds of kilometres, geometry will help little until the distance to the source is considerably larger than the fault rupture length. And the other dissipation mechanism, viscosity, plays only a small role because of the relatively small water motions involved in the propagation. The 2004 Sumatra–Andaman earthquake, which featured a fault rupture spanning some 1,300 km and killed almost a quarter of a million people, is a recent example of a large seismically generated tsunami.
Other natural phenomena, such as volcanic eruptions and landslides, whether occurring underwater or on coastal cliffs, can also lead to the formation of very large tsunamis. But even if they are large near the origin, the local character of the source leads to their dissipation with increasing radial distance. Examples of modern tsunamis of this kind include that associated with the 1883 volcanic eruption of Krakatoa and the 1958 Lituya Bay (Alaska) coastal landslide, which caused an initial wave of 524 metres.
The Spanish shores have been affected by various tsunamis over the years. The Mediterranean coasts are not very problematic, but seismic events on the Azores-Gibraltar fault have a greater potential. Indeed, the more significant tsunami experienced in historical times in Spain primarily affected Huelva and Cádiz, and to a lesser extent Galicia, and was caused by the 1755 Lisbon earthquake. It is estimated that sea level rises in Andalucía exceeded 10 m, as indicated in the tsunami catalogue of the National Geographic Institute.
Principia has studied the tsunami hazard and risk in various areas of the world and for a variety of purposes. For example, Principia participated in a study of the tsunami hazard along the Spanish coastline for the General Directorate for Civil Protection and Emergencies, within the Ministry of the Interior.
And we have also conducted this type of studies for other facilities like liquefied natural gas (LNG) plants, refineries, hotels, etc., in places like Algeria, Peru, the Caribbean, or the Andaman Islands, next to where the Sumatra–Andaman earthquake mentioned earlier occurred. All these projects have led us to accumulate a considerable amount of experience in analysing the tsunami hazard and in designing strategies to mitigate the associated risk.
