760 



HEEZEN 



[chap. 27 



the heads of submarine canyons by Shepard (1948), Zenkovich (1958), Heezen 

 (1956) and others. 



It was found that cable faihu'es in the submarine canyon of the Magdalena 

 (Heezen, 1956) occurred after prominent changes had taken place in the depth 

 and shape of the river mouth (Fig. 13). These changes in turn had occurred 

 only during the highest flood stages of the river. A similar pattern was also 

 observed off the Congo. Both rivers have a common characteristic in their lack 



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Fig. 15. Log of core A179-3 from the Colombia Abyssal Plain. Sediment in this core 

 presumably caine from the month of the Magdalena River through the action of 

 turbidity currents, which carried this sediment nearly all the way across the Colombia 

 Basin. Note that many of the beds contain up to 90°o of plant debris. Other cores in 

 this general area were found to be extremely rich in plant debris. (After Heezen, 1 956a.) 



of a modern subaerial delta. The delta sediments in both cases are to be found in 

 the alluvial cones at the mouths of their submarine canyons; and, indeed, 

 exploration in both areas has disclosed graded beds containing a large propor- 

 tion of terrestrial organic remains as well as tree leaves and wood (Figs. 14 and 

 15). A dramatic fact associated with the 1935 cable failure off the Magdalena 

 was recorded when grass, still green, was brought up wrapped around the 

 damaged cable which lay in 750 fm, 12 miles seaward from the river mouth. 



