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°N and 29°N 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.