Accession Number:

ADA499122

Title:

High-Resolution Mapping of Mines and Ripples at the Martha's Vineyard Coastal Observatory

Descriptive Note:

Journal article

Corporate Author:

NAVAL RESEARCH LAB STENNIS SPACE CENTER MS MARINE GEOACOUSTICS DIV

Report Date:

2007-01-01

Pagination or Media Count:

18.0

Abstract:

High-resolution multibeam sonar and state-of-the-art data processing and visualization techniques have been used to quantify the evolution of seafloor morphology and the degree of burial of instrumented mines and mine-shapes as part of the U.S. Office of Naval Research ONR, Arlington, VA mine burial experiment at the Marthas Vineyard Coastal Observatory MVCO, Edgartown, MA. Four surveys were conducted over two years at the experiment site with a 455-kHz, Reson 8125 dynamically focused multibeam sonar. The region is characterized by shore-perpendicular alternating zones of coarse-grained sand with 5-25-cm-high, wave orbital-scale ripples, and zones of finer grained sands with smaller 2-5-cm-high an orbital ripples and, on occasion, medium scale 10-20-cm-high, chaotic or hummocky bedforms. The boundaries between the zones appear to respond over periods of days to months to the predominant wave direction and energy. Smoothing and small shifts of the boundaries to the northeast take place during fair-weather wave conditions while erosion scalloping of the boundary and shifts to the north-northwest occur during storm conditions. The multibeam sonar was also able to resolve changes in the orientation and height of fields of ripples that were directly related to the differences in the prevailing wave direction and energy. The alignment of the small scale bedforms with the prevailing wave conditions appears to occur rapidly on the order of hours or days when the wave conditions exceed the threshold of sediment motion most of the time for the fine sands and particularly during moderate storm conditions. During storm events, erosional windows to the coarse layer below appear in the fine-grained sands. These window features are oriented parallel to the prevailing wave direction and reveal orbital-scale ripples that are oriented perpendicular to the prevailing wave direction.

Subject Categories:

  • Hydrology, Limnology and Potamology
  • Land Mine Warfare

Distribution Statement:

APPROVED FOR PUBLIC RELEASE