Li, Wei, Alves, Tiago M., Urlaub, Morelia , Georgiopoulou, Aggeliki, Klaucke, Ingo , Wynn, Russell B., Gross, Felix, Meyer, Mathias, Repschläger, Janne, Berndt, Christian and Krastel, Sebastian (2017) Morphology, age and sediment dynamics of the upper headwall of the Sahara Slide Complex, Northwest Africa: Evidence for a large Late Holocene failure. Marine Geology, 393 . pp. 109-123. DOI 10.1016/j.margeo.2016.11.013.

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Abstract

Highlights

• The upper headwall region of Sahara Slide is mapped for the first time.
• The upper headwall region comprises multiple slope failures.
• Slope failure occurred on pronounced glide planes at different stratigraphic levels.
• Failure is young (~ 2 ka) contradicting the hypotheses of a relatively stable continental margin at present.
• This young age requires a reassessment of slope instability and associated risks off NW Africa.

Abstract

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.

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