Sites 1180 and 1181 were hastily located in an effort to find a spot near Guam suitable for testing the hard-rock reentry system (HRRS or hammer drill). Relocation of the HRRS test was forced by lost time owing to a medical evacuation and the need to obtain a new brake band for the drawworks winch. Transiting to Guam from Japan gave personnel on shore the time to purchase and ship the new part. It also minimized the weather factor; by testing the HRRS near Guam, it was possible to free time for testing that would have gone to contingency because of the transit-time uncertainty resulting from the ever-present tropical storms and typhoons in the region.
Several considerations dictated the choice of HRRS test sites. A hard-rock, preferably igneous, outcrop was sought in moderately shallow water depths (1000-2000 m). Additionally, because the ship had to go to Guam to pick up the new brake band, the location had to be near Guam to minimize transit time. The best option seemed to be to drill on top of one of the arc volcanoes near Guam. After consulting with experts on shore, an unnamed seamount 37 km west of Rota Island was chosen. A dredge from this seamount recovered pumice and basaltic andesite blocks, suggesting that basalt might be found (Dixon and Stern, 1983). Although the precise age of the volcano is not known, it appears to have erupted in recent geologic time but is not currently active. Bathymetry maps also indicated the seamount has a caldera on its western flank with rims slightly deeper than 1000 m (Stern et al., 1989), fitting the sought-after depth profile.
Objectives at Sites 1180 and 1181 were as before for the HRRS test: to attempt spud-in with redesigned ring-type and underreamer bits and to attempt to drill in a casing string. Because of time limitations, it was thought that only one attempt at casing installation and perhaps limited spud-in tests were possible.
1Examples of how to reference the whole or part of this volume can be found under "Citations" in the preliminary pages of the volume.
2Ocean Drilling Program, Texas A&M University, 1000 Discovery Drive, College Station TX 77845-9547, USA. Present address: Conoco, Inc., 600 North Dairy Ashford, PO Box 2197, Houston TX 77252-2197, USA. G.Leon.Holloway@usa.conoco.com
3Shipboard Scientific Party addresses can be found under "Shipboard Scientific Party" in the preliminary pages of the volume.
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