20 



PRICE 



Figure 11 . The Three Hydrologic Regimes. We have seen a series of characteristic 

 profiles of the continental shelf of the northern half, and a portion of the southern half of the 

 Gulf of Mexico. We found that the profiles are concave near the shore, and that there are var- 

 ious obstacles farther off which stand above the projected line of that concavity. Seaward from 

 these obstacles the profiles show a general convexity at the edge of the continental shelf. This 

 convexity merges quickly with the steep continental slope. 



Comparing the shelf profile with that of the river, which is well-known, and that of the 

 submarine canyon, which is beginning to be known through the work of Maurice Ewing and 

 others, I find we can make a generalization that sedimentary particles moving from the moun- 

 tain top or slope to the oceanic abyss, must pass through three— possibly in some cases only 

 two— hydrologic regimes. 



First the particle comes down the river, descending the steeply concave slope of the 

 upper river profile, very much exaggerated here; then the middle and lower courses through 

 the plain; then the delta. 



The delta extends into the Gulf and overlaps the profile of the next regime, that of the 

 continental shelf. This drawing is approximately to scale so that the shelf is shown very short. 

 (The shelf profile is shown enlarged on the next figure.) At the outer margin of the shelf is a 

 convexity which usually occurs except in badly deformed shelves. Clay is found here. It is in 

 this convex portion that you find the heads of the average type of submarine canyon. 



Last month Kuenen presented a classification of submarine canyons. He calls his com- 

 mon type the New England type. Study of the New England type of canyon shows the head to lie 

 commonly just at the inner side of the outer shelf convexity, where it joins the nearly horizontal 

 section or its built-up portions. 



o 5 



o 

 o 

 o 



10 



20 



RIVER 



REGIME 



MOUNTAIN PLAIN 



^ SHELF H^ 

 REGIME- 



RAPIDS 

 FALLS 



DELTA 



SUBMARINE CANYON 

 REGIME 



TURBIDITY CURRENT 

 DELTA 



ABYSSAL 

 PLAIN 



TROUGH 

 sea level 



OF 

 BEACH 



/^ 



OF 

 DELTA 



C 



SHOREFACE 



SUBMARINE 

 CANYON 



OF DELTA, 



OF BEACH, 

 BETWEEN 

 DELTAS 



SHELF^-^V 

 SLOPE 



NATURAL UEVEES 

 CHANNEL 



TURBIDITY 

 CURRENT 

 FILL 



ABYSSAL PLAIN 



100 



300 



400 600 

 MILES 



600 



700 



800 



900 



Figure 11. The three hydrologic regimes of sediment transport and 

 erosion, true proportions diagrammatically sho\wn. 



