Tentative data on flow resistance in suspension currents

Abstract

The efficiency with which turbidity currents have carried large volumes of sand for great distances on slight slopes of the deep-sea floor is remarkable. This seems to argue against high flow resistance by 'Jostle" viscosity and floor impacting. The grading of the deposits is inexplicable by thin, dilute currents because these would have to be fed at the origin over a period of a dozen hours or longer, to supply the observed volume of larger beds, and with decreasing grain size. High densities (over 1.16) seem more probable than great thicknesses (over 100 m). Experiments on viscosity of suspensions showed moderate values up to densities of 1.2 for clay and 1.5 for mainly sandy mixtures. Eddies large in comparison with the grain size do not meet serious obstruction by jostling. Measurements in a circular flume of bottom drag for suspension currents indicate that resistance is less than for clear water on a cohesive rough bottom of the same grain size and less than 2 X that of clear water on a smooth hard floor. These results, although of a tentative nature and without refinement by considerations of scale or of the paddle turbulence, appear to show that densities over 1.16 up to 1.5 as deduced from velocity cum thickness of the currents and from grading in the turbidites, ale not contradicted by flow resistance. True experimental turbidity currents are being studied to gain further insight.