Experiments in connection with Daly's hypothesis on the formation of submarine canyons

Abstract

Shepard has made us familiar with the shape and various properties of submarine gorges and in a number of publications he has shown the great importance to earth-science of these wonderful features of the sea floor.\nVarious hypotheses have been brought forward to explain the formation of submarine canyons. The only hypothesis to which there are no grave objections, is that suggested by Daly. During the low sea levels of the ice age mud was stirred up on the shallowing shelves and the dense water ensuing, flowed down the continental slopes, gradually eroding the gorges. This theory can be substantiated by experiments. These proved that a suspension will flow down a slope without being much diluted by mixing, that such a flow will concentrate in slight depressions in the flat and follow a rut down the slope, that the current will begin to form ripple marks in sand at a velocity of 10—20 cm/sec and that the speed varies with the root of the density and probably also roughly with the root of the depth.\nRough estimations, based on the data of one of the Georges Bank canyons, show that the velocity in nature should be somewhat less than that of larger rivers, but encreasing as it proceeds and catches up more sediment. At the lower end the suspension has gained 6 times the (effective) density and two to three times the velocity it started with. At this stage the amount of sediment has caught up the average of most larger rivers and reached that of the most muddy major rivers. Some 10.000 flows must have occurred, or one every 5 years, each eroding as much sediment as the Mississippi carries to sea in two or three weeks. The current lasted many hours and its discharge was several times the average of the Mississippi. The relatively large percentage of materials carried by the currents is a consequence of its having slumped down the sides of the gorge before the current picked it up.\nHowever rough these figures may he, they show that no preposterous assumptions have to be made to arrive at reasonable relations between velocities, am