Deep Water Multibeam Sonar Surveys on the Hawaiian Ridge

The Japan Marine Science and Technology Center (JAMSTEC) sponsored four collaborative cruises by Japanese and US scientists, in 1998, 1999, 2001, and 2002, to build a greater understanding of deep marine geology around the Hawaiian Islands. These cruises have surveyed over 600,000 km² of the seafloor with a multibeam seafloor mapping sonar system (Seabeam 2112), made robotic and manned submersible dives, collected dredge and piston core samples, and performed single channel seismic, gravity, and magnetic surveys. The JAMSTEC sonar surveys are the most comprehensive synoptic dataset for the Hawaiian Islands since the lower-resolution GLORIA surveys by the U.S. Geological Survey in the 1980's. The Seabeam system produces wide-swath contiguous contour maps and acoustic backscatter images. The surveys generated detailed maps of previously known features and imaged some features for the first time. The new surveys determined block distribution, orientation, and structure of the enormous Nuuanu and Wailau landslides, which lie just north of the islands of Oahu and Molokai. Many of the volcanic rift zones were surveyed; the Puna, Hilo and Hana ridges in their entirety. Slumped flanks of several islands and rift zones were mapped, including Hilina, South Kona, Laupahoehoe, and Pololu (Hawaii Island), Hana (Maui), and Clarke's landslide (SW of Lanai). The detailed bathymetry confirms involvement of a compressional component at the toes of some slumps. Most of the large North Arch volcanic field, first located by GLORIA, was mapped, and many low-relief lava flows and vents were imaged. The SW Oahu volcanic field was surveyed in detail for the first time; it consists of both flat-topped and steep-sided cones and low-relief lava flows. The transitional-stage chemistry of the field makes it distinct from alkalic lava fields on the North and South Arch.