An extreme wave event in Timanfaya National Park: Possible first geological evidence of the 1755 Lisbon tsunami in Lanzarote, Canary Islands

Abstract

The identification of extreme wave events' deposits is of the main importance in the contexts of global warming and coastal geohazards. Specifically, improving the knowledge of this phenomenon is extremely relevant for high populated volcanic oceanic islands. In this paper, we analyse two extreme wave event deposits located on a coastal platform formed by lavas from the 1730–1736 Timanfaya eruption in Lanzarote Island (Spain). The first one consists of a boulder ridge parallel to the coast of approximately 750 m in length and 7 m asl in elevation. These are accumulations of non‐cemented large boulders and sands that extend about 150 m inland from the intertidal zone. The boulders are of basaltic composition, heterometric, sub‐rounded to angular, and they reach sizes up to 3 m of major axis. They are imbricated both inland and seaward, indicating a strong inundation and backwash. The second deposit is a small outcrop of boulders of equal composition and sizes up to 1 m of major axis, reaching an elevation up to 6 m asl, and has been correlated with the former deposit. Here, the boulders were also deposited on the Timanfaya lavas and later covered by lava flows extruded during the 1824 eruption. Therefore, both deposits could be related with a chronologically well‐contrasted event, between 1736 and 1824. The origin of these deposits could be interpreted as an extreme storm or a tsunami. There are no historical records of extreme storms in the Canary Islands for this period, but there is documentary evidence of the tsunamis of 1761 and 1755. Moreover, for the latter, there is documentation that indicates its impact on coastal infrastructures in the Canary Islands, including the western slope of Lanzarote, and therefore, we propose these deposits as the first sedimentary evidence of the 1755 tsunami in the Canary Islands.