A late Holocene record of marine high-energy events along the Atlantic coast of Morocco: new evidences from the Tahaddart estuary

Abstract

The Atlantic coast of Morocco has been exposed to marine submersion events from storm surges and tsunamis which have resulted in human and economic losses. The absence of long term records for these hazards makes it difficult to trace their behavior through time, which is the first step to prepare proactive adaptation strategies for events that may happen in the future. In this paper, we present a late Holocene record of marine submersion events along the Atlantic coast of Morocco using a 2.7 m sediment core sampled from the Tahaddart estuary. The sedimentological and geochemical analyses conducted on this geological archive showed a mud-dominated sequence with 14 allochthonous sandy layers (E1-E14) left by marine high-energy events. The deposition age of three layers (E1, E13 and E14) has been determined using conventional dating methods (210Pbex, 137Cs and 14C). The first layer, introduced as E1 seems to fit with the great Lisbon tsunami in 1755 CE (Common Era), an event dated for the first time along the Atlantic coast of Morocco. The other two layers, referred to as E13 and E14, were dated between 3464 and 2837 cal BP (calibrated years Before Present) and chronologically correlated with marine high-energy deposits found on the Spanish Atlantic coast. This correlation confirms the existence of another regional event around 3200 BP.

Quantitative risk assessment in El-Jadida (Northern Atlantic Coast of Morocco) for a tsunami scenario equivalent to that of the 1755 Lisbon earthquake

“…Several attempts to model the effects of these events and to estimate the risk to human life and goods, show that the region is widely exposed if similar events were to recur (Omira et al 2010;Atillah et al 2011;Renou et al 2011;Mellas et al 2012;Moussaoui et al 2017;Ramalho et al 2018). In addition to historical documents, material evidence (geomorphic and sedimentary indices) for tsunamis or high energy events in Morocco have been found in many sites alongside the Moroccan Atlantic coast: (1) in Larache and Rabat (Medina et al 2011), (2) Tahadart estuary (Talibi et al 2016;Khalfaoui et al 2020) and (3) close to the Loukkos river mouth, (Mhammdi and Medina, 2015). According to Soyris (1755), the Lisbon earthquake of 1755, the intensity of which reached VIII-XI on the Mercali scale, produced a large tsunami wave that affected northern Morocco, with El-Jadida city being one of the most impacted (Levret 1991).…”

Storm surge and tsunami deposits along the Moroccan coasts: state of the art and future perspectives

“…Usually, the DeltaR value can be estimated by comparing 14 C dates obtained on pairs of contemporary marine and continental organisms, collected for example at the same depth in the same sediment core (or trench), or found at the same coastal archaeological site. In the Tahaddart estuary (NW of Morocco), Khalfaoui et al (2020) tried to estimate this value using a pair of contemporary wood and marine shell, collected from the same depth in one of the studied cores. The authors found a value of -75±20 years, which is relatively close to the one obtained by Martins and Soares (2013) for the Andalusian coast in Spain (-108 ± 31 years).…”

“…The authors found a value of -75±20 years, which is relatively close to the one obtained by Martins and Soares (2013) for the Andalusian coast in Spain (-108 ± 31 years). However, the value obtained by Khalfaoui et al (2020) There is a great need to work in partnership with local historians and archaeologists to better understand the impact of these extreme events on the local population, which has occupied the Moroccan coasts since the Neolithic phase. During the Roman period, trade activities, based on fishing, salt and garum production were probably affected by these disasters.…”

“…Over the last 10 years, several coastal sites were investigated for sedimentary traces left by marine submersions, in the hope of dating them and filling the information gap regarding these natural hazards. Multiple sites with sedimentary evidences of these events were identified along the Moroccan coasts, in the form of boulders (Medina et al 2011) and fine-grained sediments (typically sand-sized) (Mhammdi et al 2015;Raji et al 2015;El Talibi et al 2016;Khalfaoui et al 2020). Despite this effort, the number of studies is still low compared to the nearby Iberian coasts, which are confronted with the same natural disasters.…”

Storm surge and tsunami deposits along the Moroccan coasts: state of the art and future perspectives

“…Over the last 10 years, several coastal sites were investigated for sedimentary traces left by marine submersions, in the hope of dating them and filling the information gap regarding these natural hazards. Multiple sites with sedimentary evidences of these events were identified along the Moroccan coasts, in the form of boulders (Medina et al 2011) and fine-grained sediments (typically sand-sized) (Mhammdi et al 2015;Raji et al 2015;El Talibi et al 2016;Khalfaoui et al 2020). Despite this effort, the number of studies is still low compared to the nearby Iberian coasts, which are confronted with the same natural disasters.…”