ABRUPT CHANGE IN SLOPE CAUSES VARIATION IN THE DEPOSIT THICKNESS OF CONCENTRATED PARTICLE-DRIVEN DENSITY CURRENTS

Abstract

Abrupt changes in slope occur frequently in some marine environments. Laterally confined laboratory experiments show that when dense surge-like particulate flows travel over abrupt slope reductions their deposits may have an asymmetric bell-shaped thickening near the break of slope. This thickening is herein called a slope-break deposit and is related to the change in kinetic energy of the flow. Slope-break deposits are particularly pronounced under relatively high-velocity flows. In our experiments these are flows with high particle concentrations (c=5-10% by volume silicon carbide) moving down slopes steeper than 3°. The experiments were designed such that currents generated by a lock-exchange mechanism flowed down a slope (variable slope angle) onto a flat surface. The bodies of the flows became thicker and slower just downstream of the slope break. Because the flow body slows very rapidly, particles are dumped forming the slope-break deposit. The peak in sediment thickness of the slope-break deposit is downstream of the break in slope because falling particles continue to move forward in the flow during settling. The slope-break deposits may be several tens of percent thicker than deposits from an equivalent flow in which no change in slope occurred. The parameters of the slope-break deposit correlate with slope angle change.