The summit crater of Vailulu'u Seamount, the youngest volcano in the Samoan chain, hosts an active hydrothermal system with profound impact on the ocean water column inside and around its crater (2 km wide and 407 m deep at a 593 m summit depth). The turbidity of the ocean water reaches 1.4 NTU, values that are higher than in any other submarine hydrothermal system. The water is enriched in hydrothermal Mn (3.8 ppb) and 3He (1 × 10?11 cc/g) and we measured water temperature anomalies near the crater floor up to 0.2°C. The hydrothermal system shows complex interactions with the ocean currents around Vailulu'u that include tidally-modulated vertical motions of about 40–50 m, and replenishment of waters into the crater through breaches in the upper half of the crater wall. Inside and outside potential density gradients suggest that hydrothermal venting exports substantial amounts of water from the crater (1.3 ± 0.2 × 108 m3/day), which is in good agreement with fluxes obtained from a tracer release experiment inside the crater of Vailulu'u (0.8 × 108 m3/day [Hart et al., 2003]). This mass flux, in combination with the differences in the inside and outside crater temperature, yields a power output of around 760 megawatts, the equivalent of 20–100 MOR black smokers. The Mn output of 300 kg/day is approximately ten times the output of a single black smoker.