Ocean Drilling Program (ODP) Leg 200 had two distinct objectives:
In order to understand the nature of the Earth, it is extremely important to study both spatial and temporal changes. Traditional sea-going expeditions primarily study spatial variations, which because of seafloor spreading can be used as a proxy for processes over geological timescales. On the other hand, submarine cabled observatories enable real-time temporal monitoring of oceanographic, biological, chemical, geological, and geophysical processes. The U.S. Ocean Research Interactive Observatory Network (ORION) project (ORION, 2004), the Japanese Geophysical and Oceanographical TransOcean Cable (GeO-TOC) project (Kasahara et al., 1998), and the Japanese Versatile Eco-monitoring Network by Undersea-cable System (VENUS) project (Kasahara, 2000; Kasahara et al., 2001, 2003) are examples of projects targeted at real-time acquisition. A broad range of seafloor measurements either require, or are improved by, borehole installations (Stephen et al., 2003), and borehole observatories are a natural complement to cabled observatories.
The second objective of Leg 200 was to drill a hole in the Nuuanu Landslide to explore the nature of the gigantic Koolau Landslide. Bathymetric surveys and piston core samples taken east of Oahu show that Koolau Volcano on Oahu experienced a gigantic collapse of the northeast part of the volcano ~2 m.y. ago (Figs. F2, F3). This collapse generated the Nuuanu Landslide, which we found was actually a series of landslides. The turbidite deposits caused by these landslides are found 200 km away from Oahu, and it was estimated that turbidites could be found even farther away. It was planned to study the size and the age of the gigantic landslides by drilling 300 km from Oahu where the units would be thin enough to achieve total penetration.