20. SUBMARINE CANYONS 



F. P. Shepard 



1. Introduction 



Submarine canyons have been discussed extensively in the hterature during 

 the past 30 years. Field investigations, however, have lagged and have been 

 confined to a very few individuals and to a few localities. This is regrettable 

 because the studies that have been made have indicated both that the canyons 

 of the sea floor are of amazingly large pro]^ortions and that they play a very 

 important role in sedimentary processes. 



Most of the information available on submarine canyons comes as the result 

 of coastal charting operations, particularly those of the U.S. Coast and Geodetic 

 Survey. Detailed scientific studies have been largely centered around the 

 canyons of southern California and Lower California, coming from the opera- 

 tions of Scripps Institution (Shepard and Emery, 1941, pp. 51-161 ; Shepard, 

 1949, 1951, 1961; Shepard and Einsele, 1962) and the Hancock Foundation 

 (Emery, 1960, pp. 40-50). Several of the canyons off the eastern United States 

 have been investigated by the Lamont Geological Observatory (Ericson et al., 

 1951: Heezen. Tharp and Ewing, 1959) and by Woods Hole Oceanographic 

 Institution (Stetson, 1930). French scientists have studied some of the Mediter- 

 ranean canyons and the Japanese have collected some samples from the canyons 

 off Japan. Otherwise the numerous submarine canyons found along the coasts 

 of many parts of the world are known only from rather inadequate soundings. 



Recently some decided advances have been made in canyon studies. These 

 have come from aqualung explorations of the shallow canyon heads particularly 

 off California. Also, Precision Depth Recorders used by the oceanographic 

 laboratories have given much more detail concerning the configuration of a 

 number of the submarine canyons. 



2. Classification of Submarine Valleys 



If we define canyons as deeply incised V-shaped valleys with steep walls, 

 we find that many of the valleys of the sea floor to which the name "canyon" 

 has been applied do not fit the definition. For exam])le, the large valley off the 

 Ganges Delta is more ap]iropriately called a trough because of its broad flat 

 floor ; whereas the deep outer continuations of true submarine canyons, like 

 those of Monterey Bay, resemble river channels with raised levees on the sides 

 and therefore should be referred to as channels. Realization of the existence 

 of decidedly different types of submarine valleys, which has come partly from 

 the study of Precision Depth Recorder (P.D.R.) profiles, has now made it 

 possible to subdivide submarine valleys and, hence, to discuss their origins 

 separately rather than throwing them all into the same pot. 



The types of submarine valleys which extend down the continental slopes 

 can be divided into: (1) true submarine canyons which have winding courses, 

 V-shaped profiles, steep walls with many rock outcro]is, numerous entering 

 tributaries, and virtually continuous outward-sloping floors ; (2) trough-shaped, 



[MS received March, 1960] 480 



