Rachel Speller

Previous bedform research has described different ripple types forming in varying hydrodynamic conditions and used ripple geometry within sedimentary rocks to infer the paleoenvironmental conditions during the ripple formation. During the 1997 SandyDuck97 nearshore dynamics experiment at the U. S. Army Engineers Waterways Experiment station’s field research facility at Duck, North Carolina, rotary fan beam sonar was used to collect images of the characteristics of the sea floor. In these images, curious depressions were observed to form in the seabed during storm growth and decay. These “pock marks” have horizontal scales of 10-30cm and appear to form in a specific range of wave orbital velocity amplitudes, and in particular, during both the growth and decay phases of individual storm events. The purpose of this investigation is to determine the relationship between pock marks and their hydrodynamic forcing conditions. This was accomplished by studying their spatial and temporal characteristics such as size, shape, number per unit area, and lifetime, and relating these to flow energy. Also studied is the mode of formation of the pock marks (i.e. shell/pebble nucleus) and their connection to lunate megaripple genesis.

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Pages: 72
Supervisor: Alex Hay