Deep-Sea Channels, Topography, and Sedimentation

The type and distribution of much of the minor topography in the northeastern Pacific basin can be correlated with the accessibility of a given area to deposition from turbidity currents. Deep-sea areas separated from North America by basins or troughs, which act as sediment traps for turbidity currents, are characterized by a highly irregular relief of a few hundred feet. Other areas connected to the continent by a gradual continuous slope are characterized by very smooth plains like those of the North Atlantic sea floor. These plains slope out from the continent except in the vicinity of long ridges on the sea floor. The plains slope around the ridges because the slopes are formed by turbidity currents and the ridges act as dams to deflect the currents to one side. Roug -bottomed basins thousands of feet deep are found in the regions of smooth plains, but with one exception all are inaccessible to turbidity currents because they are surrounded by mountains, or lie on the "lee" side of ridges relative to the general direction of flow of turbidity currents. The exceptional basin is in a seismically active area, and it may have formed too recently to be filled by turbidity-current deposition. Turbidity currents have formed deep-sea fans at the mouths of many submarine canyons, and deep-sea channels cross most, if not all, of the fans. All twelve of the channels which have been explored in any detail hook sharply to the left across the fans. This left hook can be explained as a secondary effect of the action of Coriolis force on the turbidity currents which formed the channels. Without channels, this type of flow would have no tendency to hook left. Unchannelized turbidity currents are required to form the fans.