Submarine spreading : dynamics and development

Abstract

Spreading is a pervasive type of ground failure in subaerial environments, but its occurrence has hardly been documented in submarine settings. However, recent advances in seafloor imaging techniques show that repetitive extensional patterns of parallel ridges and troughs, oriented perpendicular to the direction of mass movement and typical of spreading, are widespread offshore. A spread develops via the failure of a surficial sediment unit into coherent blocks. These blocks are displaced downslope along a quasi-planar slip surface. Two modes of failure can be identified: retrogressive failure of the headwall, and slab failure and extension. Mechanical modelling indicates that loss of support and seismic loading are the main triggering mechanisms. The extent of displacement of the spreading sediment is controlled by gravitationally-induced stress, angle of internal friction of sediment, pore pressure escape and friction. The resulting block movement patterns entail an exponential increase of displacement and thinning of the failing sediment with distance downslope. A deeper insight into submarine spreading is important because of the widespread occurrence of ridge and trough morphology in numerous submarine slides, particularly in the vicinity of submarine infrastructures.