48 



Physiography 



REDONDO DEEP CH 

 V X 12.5 



STATUTE MILES 



Figure 47. Detailed profiles across fan at mouth of Redondo Canyon, showing two deep channels extending across 

 the upper part of the fan down toward San Pedro Basin. 



(Dana, 1863, pp. 441-442) than on the Pacific 

 coast of the United States, but description 

 of the Atlantic canyons (Lindenkohl, 1885, 

 1891) and the Pacific ones (Davidson, 1887, 

 1897) was almost simultaneous. Immedi- 

 ately there arose conflicting opinions on 

 their origin. During later years these opin- 

 ions have been modified and new ones added 

 at a rate exceeding the rate of accumulation 

 of new facts about the canyons. It is note- 

 worthy that few of the men who have writ- 

 ten about this subject have taken either 

 soundings or samples from the canyons. In 

 the following pages no attempt will be made 

 to exhaustively treat the morass of opinions 

 of origin; this has previously been done by 

 Johnson (1938-1939), Shepard (1948, pp. 

 207-251; Shepard and Emery, 1941), Daly 

 (1942, pp. 111-157), Umbgrove (1947, pp. 

 120-139), and Kuenen (1950, pp. 480-531). 

 The general similarity of the submarine 

 canyons to large youthful river valleys in 

 plan, profile, and cross section led Dana 

 (1890), Le Conte (1891), Lindenkohl (1891), 

 Fairbanks (1897), and Spencer (1903) to con- 

 sider them products of subaerial erosion 

 during a brief time when local uplifts brought 

 the continental shelf and slope high above 

 sea level. Later, canyons were discovered 

 elsewhere in the world (although nearly half 

 the presently known ones are off the United 



States where marine surveying has been rela- 

 tively intense), requiring something more 

 than local uplift as an explanation. At this 

 stage the opinions of origin progressed down 

 two contemporaneous but separate paths: 

 (1) subaerial erosion owing to world-wide 

 causes and (2) submarine processes. 



The world-wide distribution of canyons, 

 the Pleistocene age of some of them, and the 

 presence of some off mouths of large rivers 

 naturally led to the hypothesis that they were 

 cut by streams flowing across the former sea 

 floor during the Pleistocene Epoch when 

 much of the water that evaporated from the 

 ocean was temporarily stored on land in the 

 form of glacier ice. This hypothesis, advo- 

 cated by Shepard in a long series of papers 

 beginning in 1932, was so completely ac- 

 cepted by Veatch and Smith (1939) that in 

 areas of their charts of the Atlantic conti- 

 nental slope where soundings were lacking 

 they drew subaerial-type valleys with numer- 

 ous tributaries to depths exceeding 1200 

 fathoms as the most probable topographic 

 form. The hypothesis, however, is opposed 

 by estimates (Flint, 1947, pp. 429-437; 

 Kuenen, 1950, pp. 535-540) of much too 

 smafl an ice volume and by the probable 

 drastic biological effects that would have 

 been produced by the resulting increase of 

 salinity of the remaining ocean. The re- 



