Giant striations at the base of a submarine landslide

A major submarine landslide with a volume >20 km(3) and an area >430 km(2) has been imaged in the subsurface off Angola, using 3D seismic data. The landslide basal surface preserves large 'striations' (similar to9-km long) which appear to record the catastrophic failure and show dramatic evidence for basal erosion over an area >130 km(2). These 'striations' terminate abruptly up-slope at a major growth fault. The landslide head terminates at this fault, and an earthquake or fluid flow associated with that fault may have triggered the failure event. Within the landslide deposit, giant tabular blocks similar to1- to 5-km across and similar to100- to 150-m thick and chaotic debris flow deposit indicate rapid emplacement. The landslide surface geometry reveals block disaggregation and a fully developed debris flow facies less than 5 kin from source. The landslide deposit extends to the SW beyond the study area, so volume and area are underestimated. Volume estimates of the landslide deposit exceed the failure scar volume by a factor of 2 or more, indicating significant seafloor remobilisation during emplacement. Results give new insights into the triggering mechanisms and basal erosion processes of submarine landslide failure. (C) 2004 Published by Elsevier B.V.