. The Earth beneath the sea : History. Ocean bottom; Marine geophysics. SECT. 3] BEACH AND NEAKSHORE PROCESSES 509 wliicli they enter the sea-bed zone, is straightforward in theory but difficult in practice. In common with the very similar problem of j)redicting the ground destination of fall-out from a nuclear explosion it requires a detailed knowledge of the speed and direction of the sea currents in every fluid layer. The fall velocity of a quartz-density cobble 10 cm in diameter which might be rafted out to sea by an iceberg and loosed into deep water is about 150 cm/sec or 5 ft/sec. It wo
. The Earth beneath the sea : History. Ocean bottom; Marine geophysics. SECT. 3] BEACH AND NEAKSHORE PROCESSES 509 wliicli they enter the sea-bed zone, is straightforward in theory but difficult in practice. In common with the very similar problem of j)redicting the ground destination of fall-out from a nuclear explosion it requires a detailed knowledge of the speed and direction of the sea currents in every fluid layer. The fall velocity of a quartz-density cobble 10 cm in diameter which might be rafted out to sea by an iceberg and loosed into deep water is about 150 cm/sec or 5 ft/sec. It would fall to a depth of 10,000 ft in less than an hour and would drift but little during its fall. On the other hand, since the fall velocity of fine grains decreases as the square of their size, very small particles may drift immense distances. The fall velocity of a solid quartz particle 10 [x in diameter. FALL VELOCITY IN CM/SEC Fig. 1. Fall velocities in water at 20°C of quartz-density grains of average natural shape. is 10~2 cm/sec, approximately; and the particle would take 10^ h to reach the 10,000-ft depth. A graph giving the fall velocities in water at 20°C of natural quartz grains of average shape is shown in Fig. 1. 3. Transport of Sediment over the Sea Bed The transport of sediment over a gravity bed by the combined action of fluid flow and of a gravity component parallel to the bed surface is a phenomenon which occurs in nature under many different conditions. It appears in such varied guises that, until recently, no common characteristics have been looked. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Hill, M. N. (Maurice Neville), 1919-. New York : Interscience Pub.
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