Depositional Characteristics of a Submarine Debris Flow

An example of a recently active delta-front fjord landslide has been extensively studied using side-scan sonar, subbottom profiler, piston coring, and submersible observations. The resulting sea-floor morphology and sediments have many characteristics similar to terrestrial debris flows. Analysis of cores, including physical properties and X-ray radiographs, is correlated with survey data to interpret the debris flow deformational processes and to categorize the debris flow sediments. Deformational mechanisms include delta-front sliding, downslope loading and mixing, translational shearing and remolding, and distal-lobe block gliding over weak, high-water-content fjord bottom sediments. A major part of the debris flow apparently involves remolding and deformation of fjord bottom sediments. These mechanisms result in distinctive sediment properties and structures. The data and interpretations provide a basis for comparison with other marine sedimentary sequences where slope instability processes are suspected.