INTRODUCTION

On the Cascadia continental margin offshore central Oregon, Hydrate Ridge (Figs. F1, F2) has been the focus of numerous geologic and geophysical investigations for nearly two decades. During the mid-1980s, its location within the lower slope of the accretionary wedge initially prompted investigations of seafloor fluid flow and the dewatering processes associated with accretionary wedge deformation and development and resulted in one of the first discoveries of chemosynthetic biological communities (Suess et al., 1985; Kulm et al., 1986; Ritger et al., 1987). By the early 1990s this early work was supplemented by Ocean Drilling Program (ODP) drilling (Fig. F2; Sites 891 and 892), during which gas hydrates were first recovered (Westbrook, Carson, Musgrave, et al., 1994), and detailed structural investigation (MacKay et al., 1992; Goldfinger et al., 1992, 1996). Subsequent work, including numerous sea-floor observation and sampling expeditions since the late 1990s (e.g., Suess et al., 1999, 2001) and more recently a gas hydrate–dedicated ODP leg (Tréhu, Bohrmann, Rack, Torres, et al., 2003; and Tréhu et al., this volume) (Fig. F2; Sites 1244–1252), focused on the surface and shallow subsurface gas hydrate system, seeking to characterize the distribution, concentration, and behavior of gas hydrates in an active margin setting.

In this paper we integrate our recent work on

The history of deformation, constrained by structures interpreted from seismic reflection data and core biostratigraphy;
The record of fluid venting, as imaged on sidescan sonar data;
The surface and subsurface gas hydrate distribution, constrained by seafloor observations and ODP coring; and
Records of slope failure, interpreted from piston cores and ODP cores in the Hydrate Ridge region.

Together, these data suggest that variability in structural style may strongly influence the distribution and concentration of fluids and gas hydrates in the subsurface and the susceptibility of accretionary ridges to slope failure.