LARGE BOULDERS ALONG THE RABAT COAST (MOROCCO); POSSIBLE EMPLACEMENT BY THE NOVEMBER, 1st, 1755 A.D. TSUNAMI

The rocky coastline south of Rabat (Morocco) shows a large number of boulders lying upon the lithified dune system. The boulders, of 4-100 tons, may be single, in imbricated sets, or forming clusters and ridges. Several of the boulders were lifted and overturned, thus showing pool apertures downwards. Transport distance is generally decametric because of the surface roughness, but it can reach 300 m in flat areas. All boulders have been detached from their initial position at the fractured front of the active cliff. Quantification with the help wave hydrodynamics and rock displacement mechanics shows that dislodgement and transport of these boulders were accomplished rather by tsunami than by storm waves. Although no dating was attempted, post- emplacement bio-erosion by littorinids and the absence of any erosional features below the boulders suggests that they were emplaced during the 1st November 1755 AD Lisbon tsunami.