Large-Scale Mass Wasting on the Northwest African Continental Margin: Some General Implications for Mass Wasting on Passive Continental Margins

The continental margin off Northwest Africa is shaped by a complex interplay of sediment transport processes, directed both downslope and alongslope. During several recent cruises, sediment transport processes between 12\textdegreeN and 29\textdegreeN off Senegal, Mauritania, and Western Sahara were investigated by means of geophysical and sedimentological methods. Sediment transport on the Northwest African continental margin operates with different rates and styles: some sections of the margin show a large concentration of upper slope canyons but no indication for significant mass wasting, whereas other sections are characterized by large-scale mass wasting with no canyons or gullies. Four mega-slides, each affecting over 20,000 km 2 of seafloor, have been identified along the continental slope off Northwest Africa. All slides are complex in morphology and show a stepped headwall pattern typical for retrogressive failure. Several buried mass transport deposits are seismically imaged beneath all near-surface slides indicating a long history of mass wasting for some sections of the margin. Two of the mega-slides show headwalls at atypically large water depths, deeper than 3,000 m.