to disrupt normal processes of erosion and sedimentation. 

 Surfaces of targets are cleaned or smoothed by the fine- 

 grained materials falling through the water column. Iso- 

 microroughness values continue largely unchanged for 

 hundreds of square miles. 



3. Whatever its origin, the magnitude of the roughness 

 eventually reaches an equilibrium value. 



4. There are many causes of microrelief, but they are 

 of less importance acoustically than an ability to delineate 

 the shape or pattern of the relief for a particular environ- 

 ment at a specific time. 



5. Microroughness in deeper water is largely caused 

 by infauna churning in clays and silts where organic matter 

 is scarce. 



6. Microroughness in shoaler areas, in contrast, is 

 influenced mainly by the presence of rock outcrops and the 

 effects of epifauna attached to hard surfaces. Ripple marks 

 are present because of the greater occurrence of sandy 

 sediments. Churning is highly variable in nearshore sedi- 

 ments because of the great influence of inflowing subaerial 

 sediments, light, and plant life. The acoustic effects of 

 nearshore sediment roughness are predictable. Sediment 

 changes occur faster than in deeper water. 



Microrelief Interrelationships and Distribution 



Figures 32A through 32E have been prepared as an 

 aid to the study of the origin and distribution of microrelief, 

 and the interrelationships of different types of microrelief. 



Figure 32A shows the distribution of sea floor 

 roughness according to the numerical scale of table 3, 

 and general zones of isoroughness. Figures 32B through 

 32E similarly show the distribution of ripple marks and 

 bedrock, manganese nodules, benthonic organisms, and 

 biological churning, respectively. A close relationship 

 naturally exists between figures 32D and 32E. Exposure 



56 



