114 



possibly formed by long southerly swell in the summer and 

 then reworked by bottom dwelling organisms (see photographs 

 of Emery, 1952, p. 8 ), 



It is noteworthy that sediments are coarser along the 

 edges of the shelves in Santa Monica Bay as shown in Figure 

 20. It is possible, therefore, that waves (or tidal currents) 

 may concentrate their force along the edge of the shelf and 

 cause this distinct coarsening. However, it is improbable 

 that they result in nondeposition on the shelf, for the 

 area extends from the edge of the shelf near Santa Monica 

 Canyon far to the south and landward. 



Possible Effect of Tsunamis 



Shepard iisregards tsunamis as a caust for nondeposition 

 off the southern California coast. Although one or two tsunami? 

 large enough to do any damage have reached the eoait off Cali- 

 fornia in historic time, they are so rare and generally are 

 so reduced in force that they are probably not important in 

 causing nondepositional surfaces in this region. 



Effects of Tidal Currents 



Strong tidal currents form when large volumes of water 

 flow through a relatively small outlet. Velocities of tidal 

 currents may also increase at the break in the slope or over 

 any rise above the general level of the sea floor, Fleming 

 (1938) found a pronounced increase in the velocity of tidal 

 currents in the Gulf of Panama. Revelle and Shepard (1939), 

 on the other hand, found little evidence indicating tides to 

 be aji important role in producing nondeposition off southern 



