The recorded evidence of AD 1755 Atlantic tsunami on the Gibraltar coast

Abstract

Evidence of the AD 1755 tsunami consisting of the same type of accretions produced by the re-deposition of earlier sediments, has been recorded at three different height along the coast of Gibraltar: Along a shallow sandy shore, the tsunami wave reached a run-up of 2-3 m, whereas along steep, cliff-lined shores (Rosia Bay) it surpassed 5 m. An overwash deposit was also identified at the bottom of a lagoon (The Inundation), at 0.5 m b.s.l., on the isthmus that joins the Rock with the mainland. Southern submerged platforms (Vladi's Reef) were also affected by the erosional backwash to a depth of 22 m. The tsunamigenic sediments exhibit a bimodal granulometry, mainly composed of sands with a coarser fraction composed of marine faunal shells remains, together with larger clasts derived from the rocky substrate. All remobilized sediments were dated by historical methods and radiocarbon dating.Keywords: Lisbon earthquake, AD 1755 tsunami, run-up, sedimentary record, radiocarbon dating, Gibraltar ResumenSe han registrado evidencias del tsunami de 1755 localizadas a tres alturas diferentes a lo largo de la costa de Gibraltar, todas ellas como resultado del mismo tipo de acreción producida por el re-depósito de sedimentos previos. A lo largo de las costas bajas y arenosas estudiadas, la ola del tsunami alcanzó una altura de 2 a 3 m, mientras que en litorales acantilados y con fuertes pendientes ISSN (print): 1698-6180. ISSN (online): 1886-7995

Environmental conditions and geomorphologic changes during the Middle–Upper Paleolithic in the southern Iberian Peninsula

“…Obtained dates and extensive fieldwork were used to determine the timing of local seismic activity that resulted in the geomorphological changes summarized in Table 3 and Fig. 2 (Mattey et al, 2008;Rodríguez-Vidal et al, 2008). The regional paleoseismic evolution is based on data from the Bay of Cádiz and Upper Pleistocene beach deposits published in Gracia et al (2008).…”

Consideraciones paleogeográficas en la bahía de Algeciras. Acerca de un posible tsunami en la Carteia romana (San Roque, Cádiz)

“…También el hallazgo de bloques de tamaños considerables, desplazados de su lugar original, han sido interpretados en otros casos como posibles productos de remociones por tsunamis; tal y como los observados en los acantilados gaditanos (Alonso et al, 2004). Incluso, en plataformas sumergidas y cavidades próximas al Peñón de Gibraltar, Rodríguez Vidal et al (2011) estudiaron depósi-tos sobre estas morfologías que eran anteriores al evento histórico de 1755 -el conocido terremoto y tsunami de Lisboa-y observaron que en algunas plataformas, que ya existían, sufrieron retoques erosivos por la retirada de la ola, siendo pues tipificadas como evidencias del tsunami.…”

Evidence of MIS 5 sea-level highstands in Gebel Mousa coast (Strait of Gibraltar, North of Africa)

“…revealing lower Quaternary tectonic uplift compared to the results obtained in the study area. Likewise, in eastern positions of the opposite Iberian shore (Rock of Gibraltar) an uplift value of 0.05 ± 0.01 mm/yr is calculated for the last 200 kyr (Rodríguez-Vidal et al, 2004, 2007b on the basis of uplifted marine terraces located at +1.5 to +2 and +5 m asl (MIS 5a and MIS 5e, respectively). Finally, near Tetuan and Malaga, in the Moroccan and Spanish Mediterranean coasts, MIS 5 terrace heights range from +3 to +6 m asl (Zazo et al, 1999(Zazo et al, , 2003Bardají et al, 2009a and references therein;El Kadiri et al, 2010 and references therein) indicating a very similar uplift rate in both regions.…”

“…According to phreatic overgrowths studies in coastal caves located in Mallorca in the western Mediterranean, sea-level was ~1.5-3 m above present sea level (m asl) during MIS 5e and ~1-1.9 m asl during MIS 5a (Fornós et al, 2002;Tuccimei et al, 2006;Dorale et al, 2010). For the Rock of Gibraltar, Rodríguez-Vidal et al (2007a, 2007b described several marine terraces and coastal sedimentary deposits at heights between 1,5 and 5 m asl. More recently, Dabrio et al (2011) described small-scale, short-lived fluctuations and rapid sea-level changes recorded during the second MIS 5e highstand in the southeastern coast of the Iberian Peninsula.…”