The Valu Fa Ridge (VFR) in the southern Lau Basin--located behind the westward-dipping Tonga-Kermadec subduction zone-- was one of the earliest targets to be explored for hydrothermal activity in the southwestern Pacific Ocean (Figure 1). In 1989, the French-German dive program NAUTILAU (Nautile-Lau) discovered active hydrothermal fields venting high-temperature fluids with high acidity accompanied by massive ore deposits in this area [Fouquet et al., 1993]. In September-October 2004, the SWEEP VENTS (SouthWestern Edge of Pacific hydrothermal vents) expedition explored and sampled the hydrothermal systems of the VFR using the deep submergence research vehicle (DSRV) Shinkai 6500. The 2004 Shinkai dives focused on the geobiological and geochemical character of the deep-sea hydrothermal vent ecosystems of the Valu Fa Ridge and shed new light on these hydrothermal fields 15 years after their discovery. These 2004 dives were the first to revisit this area, and have been followed by further dive programs and continued research.