SECT. 3] 



TURBIDITY CURRENTS 



745 



full-scale experiment in erosion, transportation, and deposition of marine 

 sediments by a turbidity current in which the submarine telegraph cables 

 served to measure its progress and to give tangible evidence of its force". 



Following this earthquake, which shook the continental slope south of New- 

 foundland, all the submarine telegraph cables lying downslope (south) of the 

 epicentral area were broken in sequence from north to south (Fig. 1). According 

 to Heezen and Ewing's explanation each successive cable was broken by a 

 turbidity current which had originated as a series of slumps in the epicentral 



50 100 150 200 250 300 



Distance from (00:59) break measured 

 along deepest portion of bight 



350 



Fig. 3. Time-distance graph of the 1929 Grand Banks turbidity current. (After Heezen 

 and Ewing, 1952.) 



_ /^--:i 



area. The current travelled down and across the continental slope, continental 

 rise and ocean basin floor, and, continuing far out onto the abyssal plain, 

 reached a limit well over 450 miles from its source area on the continental slope 

 (Fig. 2). 



On the continental slope where the bottom gradient is 1:10 to 1:30 the 

 velocity of the current exceeded 50 knots; and out on the abyssal plain where 

 the gradient is less than 1 : 1500 its velocity, although diminished, still exceeded 

 12 knots (Fig. 3). Subsequent exploration of the area with the piston corer 

 revealed a one-meter thick, uppermost bed of graded silt containing shallow- 

 water microfossils (Heezen, Ericson and Ewing, 1954) overlaying abyssal lutite 



