Abstract: Currents in Submarine Canyons and Their Relation to Deep-Sea Fans

F. P. Shepard, N. F. Marshall

Vast quantities of sediments from land are being transported to the deep sea along the axes of submarine canyons. The nature of canyon currents has been based largely on theory. During the past 8 years we have obtained current-meter records from a variety of canyon types with a total of about 840 days of recording. These data provided information that shows the nature of ordinary canyon currents along with some clues as to the unusual but vitally important turbidity currents.

Normal canyon currents are found to flow almost continuously along canyon floors. Most flows alternate between upcanyon and downcanyon in cycles that range from less than an hour in some canyon heads to approximately 12½ hours at greater depths. Velocities of these ordinary currents often exceed the 18 cm/sec thought necessary to initiate and transport fine sands. Stronger currents more commonly are downcanyon, and are about as common in the deep canyons as in their shallow heads. Thus, these ordinary currents are important in carrying sediments down the continental slopes to the deep ocean. We also have established the presence of much more powerful currents that develop in canyons heading near the coast during strong onshore winds or during times of high swell. The velocities of these turbidity currents are still conjectural, although we have a few records and at times have lost our current meters because of the current strength. Future plans include the use of transducers held by cables high above the canyon floors. These should give the speed of advance of clouds of sediment during turbidity currents.

AAPG Search and Discovery Article #90972©1976 AAPG-SEPM Annual Convention and Exhibition, New Orleans, LA