The Rabat and Larache boulder fields; new examples of high-energy deposits related to storms and tsunami waves in north-western Morocco

The coastal areas of south-west Iberia and north-west Morocco host numerous megaclast accumulations thought to have been emplaced by high-energy waves, namely by the major tsunami related to the 1 November 1755 AD earthquake. New observations were carried out along several transects from Rabat and Larache areas, using statistical methods applied to boulder size. The main results are (a) the boulders belong to two or three sources located within the Pleistocene–Holocene formations of both areas, but only from a single source at Harhoura; (b) the boulders in Larache are generally small, thin and show a normal polarity, whereas those of Rabat are much larger and are often overturned; (c) the directions of inclination of imbricate boulders are variable at Rabat (N, NW and W), whereas they are constant in Larache (WNW); (d) the blocks were displaced for distances up to 150 m in Rabat, while the displacement of the Larache boulders was stopped by the MHW cliff; (e) the hydrodynamic equations suggest that tsunami waves, with maximum amplitudes of 5–11 m in Rabat and 4.5 m in Larache, were responsible for the displacement of the largest boulders, whereas storms may have displaced smaller ones.