THE GROWTH AND DISAPPEARANCE OF AN INTER-FIELD MARINE SANDWAVE AND THE ASSOCIATED ANTI-ASYMMETRY MIGRATION OF NEIGHBORING CRESTS

A series of high resolution multibeam echo sounding surveys offshore of San Francisco, CA indicates the occasional migration of marine sandwave crests in the direction opposite to that indicated by the shape asymmetry of the individual sandwaves, in contrast to all previous observations of the relationship between bedform shape asymmetry and migration. We hypothesize and provide observational support that the unusual migration is due to the genesis of a new sand wave within the large and relatively stable, nearly two-dimensional field. The sandwaves in the vicinity of the new crest are found to migrate away from the new crest regardless of their shape asymmetry. Upon the later disappearance of the new crest, the neighboring sand waves migrate back toward the vacated crest location. This field-scale accommodation migration occurs for sandwaves up to several wavelengths away from the new crest. The new sandwave appears in the vicinity of “defects” in the nearly two-dimensional field. The precise dynamic mechanisms for the field-scale accommodation are unknown, but the process appears robust and is probably relevant to a wide variety of bedform fields on earth and other planets.