27. TURBIDITY CURRENTSi 



Bruce C. Heezen 



1. Early Views 



The idea that dense flows of sediment-w^ater mixtures could be of importance 

 in creating subaquatic morphological features, and in transporting sediment, 

 w^as first suggested by F. A. Forel in 1885. Forel, who had studied the mor- 

 phology of the bottom of Lake Leman, discovered that there was a large 

 sublacustrine canyon which ran from the vicinity of the mouth of the upper 

 Rhone River to the flatter floor of the lake. He deduced that repeated flows of 

 watery sediment, emanating from the river, had created the canyon, partially 

 by erosion, but largely by deposition along the lateral margins of the bottom- 

 seeking current. 



This idea was resurrected and championed again by R. A. Daly, whose classic 

 paper published in 1936 encouraged a number of investigations which ultimately 

 led to the verification of turbidity currents as an important submarine and 

 sublacustrine phenomenon. Daly proposed that, during the glacial stages, storm 

 waves breaking on beaches created mixtures of sediment and water which 

 flowed beneath the sea, eroding submarine canyons into the continental slopes. 



At the time Daly made this suggestion there was no experimental evidence 

 for turbidity currents, and although considerable detail was known concerning 

 the morphology of the submarine canyons (largely owing to excellent surveys 

 of the United States Coast and Geodetic Survey) little else was known con- 

 cerning the canyons. It was, however, known, through the work of Stetson and 

 others, that rock cropped out in the canyons. The canyons seemed definitely to 

 have been eroded into the continental slope. 



Kuenen, stimulated by Daly's paper, conducted tank experiments in which 

 he was able to model turbidity currents. Kuenen demonstrated that mixtures 

 of clay, silt and sand introduced at one end of a tank would indeed flow down 

 the sloping tank floor beneath the clear water and deposit a layer of sediment. 

 However, he was unable to demonstrate erosion by such currents. 



Support also came from the work done in reservoirs. Grover and Howard 

 (1938) had observed turbid underflows in Lake Mead Reservoir and had dis- 

 covered that the bottom of the lake immediately behind the dam was being 

 flattened by the deposits of these bottom-seeking sediment flows. However, the 

 density contrast between these weak turbidity currents and the lake water was 

 small, and the velocity of the currents did not exceed a small fraction of a mile 

 per hour. 



It was generally thought that although turbidity currents may be of local 

 importance in the ocean, they jDrobably do not account for submarine canyons, 



1 Lamont Geological Observatory Contribution No. 599. 

 [MS received May, 1961] 742 



