Detrending—a new trend in geomorphology? Unravelling erosional processes at the base of submarine landslides

Abstract Erosion at the base of submarine landslides remains poorly understood, despite being a critical threat for the stability of valuable seabed infrastructures such as communication cables and offshore renewable energy installations. Clues about its genesis are often preserved at the basal surface of landslides in the form of elongated scours aligned in the direction of landslide transport. However, these features are commonly concealed by the overlying landslide mass, and when visible, the overprint of slope gradient often masks their structural complexity. This research applies detrending algorithms to remove slope-induced overprint from exceptionally well-imaged landslide basal surfaces mapped using high-quality 3D seismic reflection data. Detrending revealed the morphological characteristics of prominent scour fields, providing new insights into the erosional mechanisms operating at the base of submarine landslides. The results indicate that distinct basal erosion processes create morphometrically diagnostic scour features. For example, basal block tooling produces steep and symmetric scours with increased erosion depth at their downslope termination, suggesting enhanced material removal at the base of blocks as these progressively sink within a decelerating landslide. Erosion might also occur by the action of longitudinal flow vortices at the boundary layer of gravity flows, with the latter generated from the disaggregation of landslides evacuating further upslope. These scours are spatially detached from landslide headscarps and initiate where seabed irregularities ignite secondary flow vorticity. The termination of this type of scours where bathymetric breaks occur suggests changes in flow dynamics and suppression of vorticity at those locations. Recognising different scour morphologies is key to reconstructing failure dynamics and better assessing hazards posed by submarine landslides. The detrending method presented here offers a powerful tool able to unravel complex geomorphic features, with potential applications across marine, terrestrial, and planetary environments.