NO. 1 



EMERY AND HtJLSEMANN: SUBMARINE CANYONS 



Below the canyon edge, the profiles show steep slopes — too steep in 

 fact for completely satisfactory use of an essentially non-directional echo 

 sounder. The measured slopes are minimal ones; still, as shown by the 

 left-hand part of the top panel of Figure 16, the indicated slopes of the 



WIRE DEPTH MINUS CORRECTED SONIC DEPTH 



-25 



q: 



LJ 



LU 5001- 



I 



0. 

 UJ 



a 



LJ 



orioooh 



25 



♦50 



♦75 



♦100 



♦125 



1500 



F'ig. 2. — Plot of difference between wire depth and sonic depth 

 corrected for sound velocitj'. The dominantly shallower 

 sonic depth is the result of echoes from steep canyon 

 walls which obscure the echo from directly beneath the 

 ship. The sounding differences at sites in canyon axes 

 and on canyon side walls are similar. 



walls nearest the heads of the canyons are 10° to 40°. Observations 

 made by divers in shallower waters reveal yet steeper, even vertical to 

 overhanging walls. These parts of the submarine canyons probably rep- 

 resent the steepest areas of the sea floor. 



