A MECHANISM FOR THE FORMATION AND MAINTENANCE OF SHORE-OBLIQUE SAND RIDGES ON STORM-DOMINATED SHELVES

A remarkable set of shore-oblique sand ridges occupies the inner porti on of the storm-dominated Middle Atlantic and South Atlantic Bights, o ff the east coast of the United States of America. A mechanism for pre sent-day formation and growth of these distinctive geological features follows from a linearized analysis of the stability of alongshore-per iodic topographical perturbations, based on a depth-averaged fluid dyn amical model with a simple representation of sediment transport. The a nalysis indicates exponential growth of shore-oblique features as a re sult of offshore deflection of storm-driven alongshore flows at ridge crests, which leads to a convergence of sediment flux because the effe ctive carrying capacity decreases with increasing distance offshore. T he analysis indicates a set of conditions required for ridge growth. M odel solutions for topography under conditions favorable for ridge gro wth are strikingly similar to the observed sand ridges.