Active fluid venting was observed for the first time along the Aleutian convergent margin during RV SONNE cruise 97. These subduction-induced cold vents were subsequently investigated in detail during cruise SO 110 in the summer of 1996 using the Canadian remotely operated vehicle, ROPOS. Active sites of dewatering were found at the youngest deformation structure adjacent to the decollement zone. High concentrations of reduced gases in the escaping fluids provide the nutritional and energy basis for the observed chemosynthetic communities in which clams and tubeworms dominate. Further evidence for fluid venting comes from the mineral precipitates of barite and carbonates
