F-28 



The attempt to map outcrop and erosion patterns from 

 our field study data should be considered preliminary. Near 

 bottom side-scan sonar is a much more appropriate mapping tool 

 than vertical incidence profiling. We would expect that 

 side-scan surveys would reveal greater plan-view detail 

 and more variability in the outcrop pattern. An important 

 conclusion to be drawn from our preliminary mapping, which we 

 believe would also be supported by side-scan surveying, is 

 that outcrop is not pervasive throughout the entire canyon 

 system. In fact, it is probable that less than 20% of the 

 canyon area exposes either outcrop or contemporary erosional 

 surfaces. 



All three east coast canyons studied are active in the 

 sense that they are bypass routes for traction transported 

 sediments. Parts of the canyon walls are being kept free of 

 sediment by contemporary currents. We would not expect to 

 see a major difference in the way the three canyons distri- 

 bute material injected by offshore development activities. 

 We would anticipate that materials which enter from the 

 margins would eventually become entrapped in the second and 

 third order tributaries. Hereon it would await further down- 

 slope transportation, most likely confined to the small V- 

 shaped valleys. We would not expect these materials to come 

 in contact with the steep outcrop belts lining the central 

 thalweg unless they were injected as suspensions. Materials 

 entering the canyon head should rapidly pass into the cen- 

 tral thalweg and then eventually bypass the entire canyon 



