Evidence discovered in Lanzarote of the impact on the Canary Islands of the 1755 Lisbon tsunami

A team of scientists has identified on the western coast of Lanzarote, in the Timanfaya National Park, evidence of the impact that the tsunami caused by the great Lisbon earthquake in 1755 had on the Canary Islands, which caused tens of thousands of deaths.

The study is signed by Inés Galindo, Nieves Sánchez and Juana Vega, from the Geological and Mining Institute; Carmen Romero, from the Department of Geography of the University of La Laguna; Esther Martín, from the Museum of Natural Sciences of Santa Cruz de Tenerife; and Javier Lario, from the Faculty of Sciences of the UNED.

The work is based on the identification of deposits of large blocks of basalt, some up to three meters long, transported inland by an extreme wave event.

The researchers suggest that these deposits could only have been caused by a strong storm or, more likely, by a tsunami.

Through the application of different equations for the study of wave heights, flow velocity and depth necessary to mobilize these blocks, they rule out that the extreme storm conditions recorded in the area were sufficient to form these accumulations of blocks in Punta del Cochino and Punta del Volcán Nuevo.

By dating the pebbles from geological and geomorphological mapping of volcanic lava flows, they have determined that they were formed in the period between the end of the Timanfaya eruption in 1736 and September 3, 1824, when the lava flows emitted from the Volcán Nuevo del Fuego entered the sea through Punta del Volcán Nuevo.

In this interval of time, the 1755 Lisbon earthquake generated a tsunami that spread through the Gulf of Cádiz and the North Atlantic, being recorded on the northeastern coasts of Africa, the northwest coast of America and even in several locations scattered throughout the North Atlantic.

The authors of the study emphasize that there are records of the effect of this tsunami in most of the Macaronesian islands, and specifically in the case of the Canary Islands, and Lanzarote itself, there is evidence and historical documentation that records the arrival of the tsunami to them.

Based on all these data, they conclude that the presence of pebbles on the north coast of Timanfaya has been interpreted as a consequence of waves associated with the 1755 tsunami.

It is estimated that the waves reached heights of more than 2.1/2.7 meters, accompanied by flow velocities of more than 2.8 meters per second, sufficient to initiate the movement of the rocks.

In addition, it is estimated that the flood distance extended at least 188 meters from the coast.

Although the historical record of this event is documented in the Canary Islands, this is the first evidence of the geological record of the 1755 tsunami in the islands, the authors of the study emphasize.

This discovery, they add, not only helps to understand the geological past of the Canary Islands, but also "is fundamental to assess the frequency of these destructive events in the islands and also plan prevention and protection measures."