Turbidity Currents on the Ocean Bottom.

The ocean bottom turbidity currents flow downslope, under the influence of gravity and by virtue of the fact that the density of their entrained turbulent suspension is greater than that of water. Turbidity currents originate in upslope sedimentary reservoirs. Initiated by some trigger mechanism, the sediment fails and starts to slump. As all or parts of the slump are transformed into a suspension of higher density than the surrounding water, a resulting turbidity current flows downslope with increasing velocity often through channels until it reaches lower gradients, where it further spreads out and decreases in velocity. The current can pick up new material from the sea bed in the path of motion if the velocity and turbulence are sufficient to retard the settling of entrained particles. Turbidity currents can flow for several thousand kilometers, moving out to the extremes of a sedimentary depression. As the current slackens, suspended sediment is deposited vertically and laterally in graded beds known as turbidites. Depending upon the properties of the initial suspension, the grain size of the entrained particles, and the steepeness of the downhill slope, the velocities of turbidity currents range from about 10cmsec to over 50 knots 2,500 cmsec. The basal portion of the average turbidite bed may be deposited on the basin floor in a few hours. Author