113 



Effect of Waves 



Vening Meinesz (in Kuenen, 1939) reports that submarines 

 are moved considerably by waves at depths of 60 m (200 ft.) 

 during rotigh weather and he showed how waves approaching 

 shelves have their energy concentrated near the break in 

 slope, Kuenen, therefore, believes this accounts for the 

 common concentration of coarse sediments at the edge of many 

 continental shelves. 



Dietz and Menard (1951b), in discussing the origin of 

 continental shelves and slopes, state that "effective erosion" 

 does not exceed 5 fathoms (30 feet). Buffington (1956) takes 

 exception to this view and gives information collected during 

 more than 5,000 dives by Geological Consultants of San Diego. 

 He says that when a diver moves from a depth of about 150 feet 

 to water 90 to 100 feet in depth, there is little or no evi- 

 dence of disturbance caused by currents or waves. The only 

 exception to this is around headlands and points where bottom 

 currents are occasionally observed. At a depth of 70 to 80 

 feet there is frequently a noticeable bottom water movements 

 or surge. This implies that bottom motion extends to a depth 

 of at least 80 feet and perhaps occasionally to more than 

 200 feet. 



Long period waves or storm waves may generate sufficient 

 bottom motion to carry sediments off the shelf. These waves 

 arrive so rarely that they have not been observed in Santa 

 Monica Bay directly. However, bottom photographs taken off 

 Osborn Bank near Catalina Island show a series of large 

 partially destroyed ripple marks. These ripple marks were 



