Figure 34. The U.S. EEZ Hawaii I Southeastern Hawaiian Ridge area GLORIA sidescan-sonar mosaic.

Background

Survey of the southeastern Hawaiian Ridge was the fifth major segment of the U.S. EEZ mapping program to have been initiated. Data acquisition for this region required approximately a total of 6 months and data were acquired during eight cruises during a four year period from 1986 through 1989, skipping 1987. At the conclusion of the surveys 29 50 m mosaics of a 2-degree by 2-degree area were completed for the region. The completed GLORIA image of this area covers approximately 1,068,000 sq km of seafloor.

The first two cruises (F-5-86-HW and F-6-86-HW) were completed concurrently over a six week period. The first cruise running from October 13 to November 4, 1986 and the second cruise from November 5 to November 26, 1986. The 1986 surveys covered the EEZ surrounding the Island of Hawaii at the southeastern end of the Hawaiian chain (Normark and others, 1987).

In 1988, five more cruises, four of which were held concurrently, were completed. The first 1988 survey (F-3-88-HW) was of short duration and was carried out from March 11-16, 1988. After a quick port stop in Honolulu, that survey was followed immediately by the second 1988 survey (F-4-88-HW) from March 17 through April 5, 1988. The operation area for these surveys were an area along the flank of the Hawaiian Ridge along Maui, Molokai, and Oahu (Normark and others, 1989).

The fifth cruise (F5-88-HW) was from April 7 to May 2, 1988. The area surveyed during this cruise was west of the Island chain, from southwest of the island of Hawaii north to Niihau and to the 200 nautical mile limit (Torresan and others, 1989).

Two final 1988 GLORIA surveys (F-6-88-HW and F-10-88-HW) completed the imaging of the "state" waters (the area around the islands between Hawaii and Kauai, as far west as Necker Island). F-6-88-HW was completed from May 4 - 26, 1988 and F-10-88-HW from September 20 to October 22, 1988 (McGregor and others, 1991). The F-10-88-HW cruise surveyed on the leeward side of the Hawaiian Ridge south of the island of Kauai, from the Molokai fracture zone on the east to Necker Ridge on the west, and abutted the images collected during cruise F-5-88-HW to the east. The survey began at the seaward edge of the EEZ and progressed northward to the Hawaiian Ridge to join the images collected on Leg 6 (F-6-88-HW) north of Kauai on the windward side of the islands.

The final cruise to complete the southeastern Hawaiian Ridge area (F-12-89-HW) was done from November 3-26, 1989. The area surveyed during this cruise was on the north side of the Hawaiian Ridge between Nihoa Island and St. Rogatien Bank. With the completion of F-12-89-HW, the EEZ around the major islands of the State of Hawaii have been imaged (Torresan and others, 1991).

Two cruises (F-10-88-HW and F-12-89-HW) were only partial surveys of the southeastern Hawaiian Ridge. The surveys overlapped with the adjacent central Hawaiian Ridge.

Figure 35. Map showing field activities for GLORIA sidescan-sonar data collection in the U.S. Exclusive Economic Zone (EEZ) Hawaii Southeastern Hawaiian Ridge area.