HR: 1330h
AN: OS23B-04    [Abstracts]
TI: Insights about the processes associated with the origin and evolution of Rippled Scour Depressions based on multibeam sonar imagery
AU: * Ferrini, V
EM: ferrini@ldeo.columbia.edu
AF: Columbia University - LDEO, Lamont Doherty Earth Observatory of Columbia University 61 Rt. 9W, Palisades, NY 10964 United States
AU: Flood, R D
EM: rflood@notes.cc.sunysb.edu
AF: Marine Science Research Center, Stony Brook University, Stony Brook, NY 11794-5000 United States
AB: We present observations of the textural and morphological characteristics of Rippled Scour Depressions (RSDs) identified during high-frequency multibeam sonar surveys at three inner shelf environments. RSDs are evident as distinct bathymetric depressions that are associated with high acoustic backscatter intensity and contain coarse sediment formed into shore-parallel ripples. Elongate shore-normal RSDs identified near Grays Harbor, Washington, are associated with a larger-scale bathymetric undulation upon which they are superimposed. Repeat bathymetric surveys indicate that the large-scale undulation with which these RSDs are associated was propagated in the alongshore direction by 10s of meters over 2 years indicating that they are driven by shore-parallel processes. Other RSDs, not associated with larger-scale bathymetric patterns, identified near Grays Harbor and off the South Shore of Long Island, exhibit along-shore textural asymmetry suggesting that they are transverse sorted bedforms. Smaller amorphous RSDs that are not associated with larger-scale bathymetric patterns can be created and destroyed over time-scales of less than 1 year, and do not appear to be sorted bedforms. The shore-parallel ripples contained within all of these features, and observations of shoreward evolution, indicate that RSDs are modified by shore-normal processes. We propose a classification of RSDs and a conceptual model that describes their creation and evolution based on their morphologic and textural characteristics and the larger-scale seabed patterns associated with them. By comparing RSDs observed at different sites we can begin to address the non-local significance of these features and gain important insight about the mechanisms associated with their creation and evolution.
DE: 3000 MARINE GEOLOGY AND GEOPHYSICS
DE: 3045 Seafloor morphology and bottom photography
SC: Ocean Sciences [OS]
MN: 2005 Joint Assembly