Abstract

The surficial sand sheet seaward of Diamond Shoals on the North Carolina shelf is molded into a series of coast-parallel ridges as much as 10 m high and 5 km apart. An older cohesive substrate is exposed in the troughs. Fields of sand waves as much as 7 m high occur on the ridges and in the troughs. Their crests are normal to the ridges. Sand size varies across the sea floor in sympathy with the ridge topography. The gently inclined landward flanks are coarser grained; the steeper seaward flanks are finer grained.

There is evidence to indicate that the sand ridges, like the sand waves with which they are associated, are responses to flow. However, it is not possible to demonstrate the nature of coupling between fluid motion and substrate morphology on the basis of the existing data.

The landward part of the study area is subjected to a southward water drift that during winter is punctuated by intense southward pulses associated with storms. The seaward part experiences a strong, predominantly northward flow throughout most of the year, and the zone of shear appears to migrate back and forth across the study area. Regional considerations suggest a southward sand transport. However, during the period of observation, water flow and bedform asymmetry indicated northward transport. It seems probably that the transport direction reverses with time.

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