Origin of shallow submarine mass movements and their glide planes-Sedimentological and geotechnical analyses from the continental slope off northern Norway

• Published in: Journal of geophysical research. Earth surface 2014-11, Vol.119 (11), p.2335-2360
• Main Authors: Baeten, Nicole J., Laberg, Jan Sverre, Vanneste, Maarten, Forsberg, Carl Fredrik, Kvalstad, Tore J., Forwick, Matthias, Vorren, Tore O., Haflidason, Haflidi
• Format: Article
• Language: English
• Subjects: Continental slope; geotechnical analysis; Glide; glide plane; hazard potential; Landslides; Landslides & mudslides; mass movement; Mass transport; Mathematical models; Movements; Physical properties; Planes; Pore pressure; seafloor stability; sedimentary processes; Sedimentology; Sediments; Shear strain; Slabs; Slopes; Stratigraphy
• ISSN: 2169-9003; 2169-9011
• DOI: 10.1002/2013JF003068

Submarine landslides are often characterized by a basal surface of rupture parallel to the stratigraphy, in which downslope movement is initiated. However, little is known about the sedimentology and physical properties of the sediments within these surfaces. In this study, we present a multiproxy analysis of the sediments collected from a giant piston core penetrating a shallow submarine mass transport deposit, in combination with high‐resolution seismoacoustic data to identify and characterize the basal glide plane and the weaker sediments in which movement was initiated. The initial phase of instability consists of a single fracture that formed due to the downslope movement of a mostly intact slab of sediments. The 16 m long core, comprising mostly undisturbed massive and laminated ice‐rafted debris‐rich clay penetrated this slab. The base of the slab is characterized by a high‐amplitude semicontinuous reflection visible on the subbottom profiler data at about 12.5 m depth, interpreted to originate from the glide plane on top of a plumite deposit. This plumite has dilative behavior with pore pressure decrease with increasing shear strain and high undrained shear strength. Movement probably started within contouritic sediments immediately above the glide plane, characterized by higher sensitivities and higher water contents. The occurrence of the mass movements documented in this study are likely affected by the presence of a submarine landslide complex directly downslope. The slide scar of this landslide complex promoted retrogressive movement farther upslope and progressive spreading of strain softening along the slide base and in the slide mass. Numerical models (infinite slope, BING, and retrogressive slope models) illustrate that the present‐day continental slope is essentially stable and allow reconstruction of the failure processes when initiated by an external trigger. Key Points An initial phase of shallow mass movements was targeted by a 16 m long coreA plumite interval was interpreted to have acted as the basal glide planeMovement was inferred to have started within contouritic sediments above