2-1. Nuuanu and Wailau landslide @[J.G. Moore and E. Takahashi]

The pair of adjacent landslides on the north side of Oahu (Nuuanu) and Molokai (Wailau) together form the largest landslide complex in the Hawaiian Islands and rank amaong the largest on Earth. These, like the dozens of other giant Hawaiian hotspot which built these volcanoes so rapidly that they became gravitationally unstable, and large sectors failed repeatedly producing the landslides. Not only do these landslides modify the slopes of the volcanoes and adjacent sea floor, but they no doubt also interact with the magmatic plumbing system of the volcanoes modulating to some extent the volcanic processes that engendered them. Moreover, the landslides are linked with geologic hazards, including major earthquakes associated with slope failure (such as the 1975 Kilauea mag 7.2 earthquake [Tilling et al., 1976] , large scale submergence and emergence of shorelines and massive tsunamis [Moore and Moore, 1988].

In the JAMSTEC cruises of 1998 and 1999 the first detailed multibeam map of the greater landslide area was prepares and a series of Rov and submersible dives were conducted on the more proximal regions of the landslides [Smith et al., 2001]. In addition four piston cores were taken of sediment within the landslide area [Kaqnamatsu et al., 2001]. Based on geologic observations on the landslide blocks from Seabeam bathymetry [Moore and Clague, 2001], those by submersibles [Yokose, 2001], petrologic and geochemical description of recovered rock samples [Shinozaki et al., 200;Tanaka et al., 2001; Clague et al.,2001] and glass chemistryin the piston cores [Sherman et al., 2001], the nature of the landslide blocks and the original position of material that has now moved out in the form of the landslide blocks have been established. These works also established the relative age relations between the two landslides, and provided information on the absolute ages of major turbidities which may be related to landsliding.

The focus of work on the 2001 cruise is to explore in more detail the distal parts of the landslides by means of dredging blocks out to 160 km from land, taking piston cores of sediment out to 410 km from land, and making single channel seismic profiles of sediment outboard of the landslides to appraise the nature of processes that have deposited the uppermost 10 m of sediment in the region beyond the toes of the landslides.

Such investigations are directed toward such questions as: What is the sources and age of major turbidities and how are they related to landslides? What are the boundaries and thickness of the mapped landslides? How important are these major landslides in the life history of the volcanoes, and what part of the sedimentary filling of the Hawaiian Deep is attributable to landsliding? What is the likely periodicity of major landslides with their attendant hazards? The answers to these questions remain elusive, but systematic marine investigations of this kind are the best way to provide some answers.

References
Clague, D.A. Moore, J.G. and Davis, A.S., 2001 Volcanic breccia and hyaloclastite in blocksfrom the Nuuanu and Wailau landslides, Hawaii, In Evolution of Hawaiian Volcanoes: (Ed. E. Takahashi et al.), AGU Monograph, in press.
Moore, G.W. and Moore, J.G., 1988, Large-scale bedforns in boulder gravel produced bygiant waves in Hawaii: Geol. Soc. Americ Spec. Pap. 229, p. 101-110.
Moore, J.G. and Clague, D.A., 2001, Mapping the Nuuanu and Wailau landslides in Hawaii,In Evolution of Hawaiian Volcanoes: (Ed. E. Takahashi et al.), AGU Monograph, in press.
Tilling, R.I. Koyanagi, R.Y., Moore, J.G. and Swanson, D.A., 1976, Earthquakes and related catastrophic events, Island of Hawaii: U.S.Geol. Survey Circ. 740, p. 33.
Sherman, S.B., M.O. Garcia and E. Takahashi, 2001, Geochemistry of volcanic glasses from piston cores taken north of Ofahu and Molokai islands, Hawaii. In Evolution of Hawaiian Volcanoes: (Ed. E. Takahashi et al.), AGU Monograph, in press.
Shinozaki, K., Z.-Y. Ren and E. Takahashi, 2001, Geochemical and petrological characteristics of Nuuanu and Wailau landslide blocks. In Evolution of Hawaiian Volcanoes: (Ed. E. Takahashi et al.), AGU Monograph, in press.
Takahashi, E and Nakajima, K., 2001, Melting processes in the Hawaiian plume: an experimental study. In Evolution of Hawaiian Volcanoes: (Ed. E. Takahashi et al.), AGU Monograph, in press.
Tanaka, R. E. Nakamura and E. Takahashi, 2001, Geochemical evolution of Koolau volcano ,Hawaii. In Evolution of Hawaiian Volcanoes: (Ed. E. Takahashi et al.), AGU Monograph, in press.
Yokose, H., 2001, Landslides on the windward flanks of Oahu and Molokai, Hawaii: SHINKAI 6500 submersible investigations. In Evolution of Hawaiian Volcanoes: (Ed. E. Takahashi et al.), AGU Monograph, in press.