4 Effects of Waves and Currents
We have seen that the morphology of the ocean margins is largely determined by
tectonics and sediment supply (Chap. 2), and we have reviewed the various types of
sediment~ which are involved (Chap. 3). We now tum to the all-important role of
water motion in determining the distribution of sediments on the sea floor. A first
impression of this role can be gained from contemplating Fig. 4.1 which illustrates
the redistribution of sediment supplied by a river in a setting typical for southern
California. The water motions indicated are not the only ones that need to be considered, as we shall see.
Fig. 4.1. Redistribution of sediment on the continental margin, by water motion . The drawing
reflects a West Coast geographic setting ; note river input , longshore transport (powered by wave
energy), interception by submarine canyon. Fine sediment bypasses the shelf, and comes to rest on
slope or deeper. Note starved beaches and rocky shelf beyond canyon. [Based on a drawing in D. G.
Moore, 1969, Geol. Soc. Am . Spec. Pap. 107: 142]