The Sahara Slide Complex in Northwest Africa is a giant submarine landslide with an estimated run-out length of ~ 900 km. We present newly acquired high-resolution multibeam bathymetry, sidescan sonar, and sub-bottom profiler data to investigate the seafloor morphology, sediment dynamics and the timing of formation of the upper headwall area of the Sahara Slide Complex. The data reveal a ~35 km-wide upper headwall opening towards the northwest with multiple slide scarps, glide planes, plateaus, lobes, slide blocks and slide debris. The slide scarps in the study area are formed by retrogressive failure events, which resulted in two types of mass movements, translational sliding and spreading. Three different glide planes (GP I, II, and III) can be distinguished approximately 100 m, 50 m and 20 m below the seafloor. These glide planes are widespread and suggest failure along pronounced, continuous weak layers. Our new data suggest an age of only about 2 ka for the failure of the upper headwall area, a date much younger than derived for the landslide deposits on the lower reaches of the Sahara Slide Complex, which are dated at 50-60 ka. The young age of the failure contradicts the postulate of a stable slope off Northwest Africa during times of relative stable sea-level highstands. Such an observation suggests that submarine-landslide risk along the continental margin of Northwest Africa should be reassessed based on a robust dating of proximal and distal slope failures.

The Sahara Slide Complex in Northwest Africa is a giant submarine landslide with an estimated run-out length of ~ 900 km. We present newly acquired high-resolution multibeam bathymetry, sidescan sonar, and sub-bottom profiler data to investigate seafloor morphology, sediment dynamics and the timing of formation of the upper headwall area of the Sahara Slide Complex. The data reveal a ~ 35-km wide upper headwall,opening towards the northwest, with multiple slide scarps, glide planes, plateaus, lobes, slide blocks and slide debris. The slide scarps were generated by retrogressive failure events associated with two types of mass movements: translational sliding and gravitational spreading. As a result of this evolution, three different glide planes (GP I, II, and III) can be distinguished approximately 100 m, 50 m and 20 m below the seafloor. These glide planes are widespread and suggest failure along pronounced, continuous weak layers. Our data suggest an age of only about 2 ka for the failure of the upper headwall area, a date much younger than that derived for landslide deposits on the lower reaches of the Sahara Slide Complex, which are dated at 50–60 ka. The young age of the failure contradicts the postulate of a stable slope offshore Northwest Africa during sea-level highstands. Such an observation suggests that submarine-landslide risk along the continental margin of Northwest Africa should be reassessed based on a robust dating of proximal and distal slope failures.

Acoustic data reveal giant submarine slides offshore Senegal. The most prominent slide, named Dakar Slide, shows a headwall with a length of at least 100 km in water depths of 2,000-3,100 m. The slide is situated between two canyons, the Dakar Canyon in the north and the Diola Canyon in the south. Seismic data indicate a complex interaction of mass wasting and canyon evolution during the formation of this part of the continental margin. The northern sidewall of the Dakar Slide crosses the distal part of the Dakar Canyon, which was repeatedly destroyed and. filled by slide deposits. The area above the headwall does not show major mass-wasting events though the slope gradient there is significantly steeper. The Dakar Slide is underlain by multiple giant mass transport deposits reaching back to Oligocene times.

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 km2 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.

The Sahara-Slide complex (NW-Africa) is a mega slide with a length of ∼ 700km and an estimated volume of ∼ 600km3. The morphology and evolution of the headwall area of the Sahara-Slide complex was investigated during a Poseidon-Cruise in early 2010 by means of acoustic data and gravity coring. The bathymetric and sidescan data show a slab type failure with multiple headwalls and at least two glide planes. Some areas are characterized by elongated blocks, which have not moved far, while other areas are characterized by quickly disintegrating sediment masses. Seismic data show older mass transport deposits and giant elongated mound-like features, which are aligned with the sidewalls. We speculate that migrating fluids in the mound-like features control the location of the failure. Previous investigations of the distal deposits of the Sahara Slide yield an age of 50–60 ka for the main slide event, which is a period of global sea level rise. Major slides off NW-Africa are all dated at periods of global sea level rise. This observation is challenged by new observations made during the Poseidon-cruise in early 2010. Numerous cores taken beneath the upper headwall complex suggest an age of only 1 – 2 ka for this major failure. We are currently investigating whether this age represents a major re-activation of an existing headwall or a major failure of undisturbed slope sediments. The young age of this slide calls for a re-assessment of the risk potential of this margin.

In this study we aim on a reconstruction of mechanisms and kinematics of slope-failure and mass-movement processes along the northeastern slope of Crete in the Hellenic forearc, eastern Mediterranean. Here, subsidence of the forearc basin and the uplift of the island of Crete cause ongoing steepening of the slope in-between. The high level of neotectonic activity in this region is expected to exert a key role in slope-failure development. Newly acquired reflection seismic data from the upper slope region reveal an intact sediment cover while the lower slope is devoid of both intact strata and mass-transport deposits (MTDs). In a mid-slope position, however, we found evidence for a ∼4-km³-sized landslide complex that comprises several MTDs from translational transport of coherent sediment bodies over short distances. Morphometric analysis of these MTDs and their source scars indicates that this part of the northeast Cretan slope can be characterized as a cohesive slope. Furthermore, we reconstruct retrogressive development for this complex and determine a critical slope angle for both pre-conditioning of failure and subsequent landslide deposition near source scars. Consequently, data imply that the investigated shallower slope is stable due to low angles in the order of 3°, whereas 5°-inclined mid-slope portions favour both slope destabilization and landslide deposition. The failed mid-slope parts are dominated by sediment truncations from faults almost correlating with the orientation of head- and sidewalls of scars. We suggest that cohesive landslides and MTDs are generated and preserved, respectively, in such critical slope regions. If once generated, cohesive landslides reach the lower slope further downslope that exceeds the threshold gradient for MTD deposition (∼5°), they are transported all the way down to the foot of the slope and disintegrate to mass flows. From these observations we suggest that the mass-wasting history of the investigated Cretan slope area over a longer period of time is characterized by repeated sediment erosion and transport into the deeper Cretan Sea basin. The relocation of the critical slope portion in upslope direction and therefore recurrence of mass-wasting events is thereby likely controlled by the progressive steepening of the slope. This mechanism and restriction of sediment failure to narrow, critically-inclined and relocating slope portions likely explains how such an active margin setting can exhibit only scarce findings of MTDs on the slope despite an expected, extensive and widespread mass wasting.

New multichannel seismic data were collected in spring 2009 offshore NW Africa. Two study areas were located at the continental slope west of Cape Yubi and Cape Blanc, both under the influence of the eastern boundary Canary Current and a northward directed undercurrent. The seismic data from both study areas reveal features like terraces, erosional surfaces, and drift deposits, suggesting that contour currents have a major impact on shaping the slope in this region

The continental margin off Northwest Africa is largely shaped by a complex interplay of sediment transport processes directed both downslope and along-slope. During Meteor-Cruises M58/1 and M65/2 we investigated the sediment transport processes between 12 and 22 N off Senegal and Mauritania by means of geophysical, sedimentological, and geochemical methods. Bathymetric and high-resolution seismic data were used to study the areal extent and the internal structure of redeposited sediments. Based on these measurements sediment cores were taken for sedimentological and geochemical analyses.