Abstract
Large longitudinal bedforms (comet marks) occur on the current-swept shelf off southeast Africa. They emanate from tight clusters of low rock outcrops and are as long as 135 m and as wide as 30 m. The low length/width ratio (1:4.5) is explained by lateral coalescence of several narrow tails associated with individual obstacles. They seem to form by removal of sediment from the wake region of the obstacles. Hydrodynamic considerations indicate a high probability for sonic suspension transport, yet no sand shadows occur in the velocity-defect region of the inner wake. It is concluded that shear velocities must exceed the minimal velocity required to sustain sediment transport.
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