Nearshore Sand Bars on Western Mediterranean Beaches

Abstract

Turbidity currents in the submarine seascape are what river flows are in terrestrial landscapes. While rivers transport sediment from the mountains through valleys towards the sea, turbidity currents transport sediment from the shallow marine realms through canyons towards the deeper abyssal plains. The large scale architecture of both systems is remarkably similar. Yet, there are some fundamental differences between rivers and turbidity currents, the most fundamental one being their density difference; the density of river water is thousand times denser than its surrounding air, while the density of a turbidity current can never be more than twice as dense as its ambient water. In addition, rivers do not depend on their sediment load to flow, while turbidity (density) currents do need the sediment derived excess density to flow. These physical differences change their morphodynamics on the bedform scale. Present day high-resolution seafloor observations show that turbidity current path ways are covered with bedforms that are fundamentally different from those that occur in river channels. In this chapter we point out these differences and present a 3D bedform stability diagram for turbidites.