23 



GEOLOGIC PROBLEMS 



Marine geological processes have direct bearing on some types of cur- 

 rents as well as being affected in turn by the current systems. Since the recent 

 visit of Professor Philip Keunen to the United States, there has been more gen- 

 eral interest in his turbidity current hypothesis published nnore than a decade 

 ago (Geol. Mag. , 1938). The geologic record in cores and in marine deposits 

 exposed on land contains examples of vertically and horizontally graded coarse 

 materials deposited conformally on fine materials. In many cases these can be 

 explained as load deposited far from land by turbidity currents. It would be of 

 great interest to measure a turbidity current and then to sample the deposits it 

 has produced. 



It has been suggested that a number of buoyant spheres be anchored at 

 intervals along the foot of the continental slope so that if a turbidity current 

 were to pass one or more of these they would break loose and float to the sur- 

 face. If found on shore, the floats would call attention to a suitable area for bot- 

 tom sampling and coring. 



More immediate information might be gained from one or a succession 

 of electrical cables laid parallel to the foot of the continental slope at intervals 

 of perhaps 100 kilometers seaward. A turbidity current cutting each of these 

 cables in turn would give a succession of signals indicating its speed of advance 

 and an estimate of the distance run. If the cable were moved but not parted, a 

 measurable voltage would be developed which is proportional in magnitude to the 

 speed and in its sense to the direction of the cable's motion through the magnetic 

 field of the earth. One long cable would indicate when a turbidity current 

 passed but would not indicate what part of its length had become involved. Short- 

 er cable loops would localize occurrences better. While not ideally placed, 

 there are already a number of commercial cables across the ocean floor. The 

 full force of motional potentials derived from the displacement of a cable in a 

 turbidity current would either mask or disrupt telegraph service. Commerical 

 cable companies may have records available for research or might offer oppor- 

 tunities for more suitable recording of the signals now regularly received. 



In studies of more localized geological processes controlled by currents, 

 movable-bed hydraulic nnodels may serve to clarify problems of sediment trans- 

 port by longshore currents and the sorting of the coarser materials over the bot- 

 tom. This particular use of models would require development. Engineering 

 use of movable-bed models is traditionally concerned with the topography of the 

 bottom rather than the structure of sedimentary deposits produced by moving 

 water. 



ESTUARINE CIRCULATION 



Studies of currents in coastal and estuarine areas is one of the tradition- 

 al concerns of oceanographers. Despite the time that has been spent on the 

 subject, very little significant progress has been made in methods for measur- 

 ing of these complex current systems. The complexity of the circulation 

 arises from the fact that there are many strong influences at work simultane- 

 ously. Broadly, these influences may be grouped as hydrologic, meteorologic, 

 and oceanographic in nature. These groups of active forces work in confined 

 situations so that for every parcel of water set in motion there may be simulta- 

 neously or eventually a corresponding parcel moving in reaction. The nature 

 of the reactive motions depends to a large extent on the submarine topography 

 of the region. The interplay of the active and reactive forces generally pro- 

 duces very complex circulation systems which may vary significantly from place 



