Triggering and evolution of a giant submarine landslide, offshore Angola, revealed by 3D seismic stratigraphy and geomorphology

The source area of a large submarine landslide complex has been imaged in the subsurface off Angola using 3D seismic data. The 3D seismic data reveal erosional slide scars, landslide blocks, and debris flows involving > 20 km(3) material, affecting an area > 430 km(2). The basal and internal structure is imaged in detail showing basal erosion and evidence for at least three phases of landslide failure. Landslide internal structure reveals evidence for seafloor remobilization during the initial phase of submarine landslide failure. Missing strata and downslope-trending striations 15 m deep and 9 km long on the basal sliding surface record the initial failure over an area > 130 km(2). The basal striations originate from and extend downslope from a major growth fault trending NW-SE. We speculate that fluid flow or seismicity associated with this growth fault triggered landsliding. The landslide deposit consists of large blocks (similar to 1 to > 5 km across and similar to 100 to 150 m thick) which have slid, rotated, and deformed in the landslide within a chaotic debris-flow matrix. A smoother debris-flow morphology extends from the erosional scars and blocks to the SE beyond the boundaries of the survey area. A rough estimate of landslide geometry indicates that the deposit volume is double the volume of erosional slide scars within 5 km of source. The observations from this study are summarized in a process-oriented landslide model. Results provide insight into the triggering, evolution, and runout potential of giant submarine landslides.