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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 50 (1966)

Issue: 3. (March)

First Page: 627

Last Page: 627

Title: Turbidity-Current Experiments: ABSTRACT

Author(s): Gerard V. Middleton

Article Type: Meeting abstract


Experiments were performed in the W. M. Keck Laboratory, California Institute of Technology, using a lucite channel 5 meters long, 50 cm. deep, and 15.4 cm. wide. Turbidity-current "surges" were produced by releasing suspensions of plastic beads from a lock at one end of the channel. The bottom of the flume was horizontal and before release of the suspension the water level was the same within the lock and the main channel; the experimental results may therefore be compared with the results obtained by Keulegan (1958) for saline surges. Experiments were performed at two depths (20 and 30 cm.), and two suspension concentrations (about 25% and 45% concentration by volume) were used. The sediment consisted of perfectly spherical plastic beads with a density of 1.52 and an av rage size of 0.18 mm. The results show that the shape of the Previous HitheadNext Hit, the initial velocity, and the relation between the velocity of the Previous HitheadNext Hit and its thickness and density are very similar to those reported for saline surges. The velocity of the Previous HitheadNext Hit is given by the equation


where g^prime = g^Dgre/e, d2 is the thickness of the Previous HitheadNext Hit, and C is a coefficient with a value of 0.75. In another series of experiments, with saline density currents, it was found that C varies little with increase in slope of the bottom, up to a slope of 0.04.

The velocity (u) of the water near the bottom, at a distance x in front of the Previous HitheadNext Hit, was found to be given by the equation


Two types of graded bed were formed, depending on the concentration of the suspension used. The "normal" type of graded bed, formed by surges with low sediment concentration, shows continuous grading within the bed at nearly all percentiles. The "coarse-tail" type of graded bed, formed by high-concentration surges, shows little grading through most of the bed, except for the coarsest 2-5 per cent of the size distribution. The differences between the two types of grading can be related to the depositional mechanics, which are revealed by slow-motion movies. In low-concentration flows, the bed is deposited Previous HitlayerNext Hit by Previous HitlayerNext Hit. In high-concentration flows, most of the bed is deposited first as an expanded or "quick" bed which continues to shear and to be disturbed by Previous HitwavesNext Hit which form at the i terface between the bed and the flow above. As the bed comes to rest, the Previous HitwavesTop disappear and the upper surface becomes perfectly flat.

A 300-foot color movie of the experiments will be shown.

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