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High-Resolution Multibeam Survey of the Insular Shelf and Slope of Windward and Southern Oahu, Hawai'i

Field, M.E.1, Gardner, J.V.1, Mayer, L.A.2, Hughes-Clarke, J.E.2 Benumof, B.3, and Cochran, S.A1,3

1) U.S. Geological Survey, Menlo Park, California, USA; 2) University of New Brunswick, Fredericton, NB, Canada; 3) University of California, Santa Cruz, California, USA

American Geophysical Union 1998 Fall Meeting, San Francisco, CA, December 1998


ABSTRACT

The insular shelf and slope of windward and southern Oahu, Hawai'i were surveyed in 1998 using a Konsberg Simrad EM300 multibeam system. The two margins have contrasting structural and sedimentologic morphologies that reflect their recent volcanic and landslide framework, island drainage systems, and modern sedimentary regimes. Both margins show evidence of late-stage post-erosional volcanic eruptions. Basaltic edifaces on the slope off Mokapu Peninsula (verified by submersible dives), Koko Head, and possibly off Diamond Head, are evident in these new maps. A large landslide, possibly triggered by a post-erosional volcanic phase off Diamond Head, is a prominent feature of the southern margin. By combining seafloor relief with backscatter (as a proxy for hardness), the multibeam maps also provide useful information for mapping benthic fish habitats.

The windward slope is characterized by several large dendritic drainage systems composed of slope channels merging into canyons. The presence of these large drainage networks here and nowhere else in areas that have been surveyed in Hawai'i may reflect erosion and transport processes that followed the large landslide that removed much of the Koolau Range, as well as the high sediment yield from the windward basins of the island.

The southern margin is largely covered by large volumes of sediment, possibly reflecting long-term drainage from the Koolau and Waianae Ranges through the southern coastal plain. The relatively smooth sediment cover is molded into large north-south striking bedforms spaced 10's to 100's of m apart and several m high that record periodically strong westward bottom flows. The location of material dredged from Honolulu and Pearl Harbors and dumped onto the seafloor at 450 m is accurately mapped both by backscatter patterns and small-scale relief.

For more information, please contact:
Michael E. Torresan
U.S. Geological Survey
400 Natural Bridges Drive
Santa Cruz, CA 95060
(831) 460-7425

U.S. Department of the Interior | U.S. Geological Survey | Western Coastal & Marine Geology
URL: http://walrus.wr.usgs.gov/reports/field98.html
maintained by Laura Zink Torresan
Last modified: 20 Aug 2001(lzt)