DISCRETE AND DIFFUSE HEAT-TRANSFER AT ASHES VENT FIELD, AXIAL VOLCANO, JUAN-DE-FUCA-RIDGE

Heat fluxes of discrete and diffuse components of hydrothermal discharge are estimated from submersible measurement in the ASHES vent field located in the caldera of Axial Volcano on the central Juan de Fuca Ridge. The discrete component comprises discharge from individual vents and the diffuse component comprises seepage from large areas of the seafloor. The investigation centered on the high-temperature portion of the field, a 100 x 100 m area of fractured lobate and sheet lava flows encompassing discrete discharge (less-than-or-equal-to 326-degrees-C) from seven individual vents and diffuse flow from intervening areas. A total of 4.4 +/- 2 x 10(6)W was estimated for the discrete heat flux based on measurements of effluent temperature, flow rate and orifice diameter at all the known individual vents by D.S.V. Alvin in September 1987. A total of 15-75 x 10(6)W was calculated with a standard plume model for the diffuse flux based on a grid of temperature measurements at altitudes of 1 m and 20 m above the study area using a 1 m long vertical array of temperature sensors mounted at the front of Alvin's instrument platform. The study indicates that (1) the diffuse component rises separately from the discrete component of hydrothermal discharge and is laterally advected by a prevailing current below the discrete component, and that (2) the diffuse component of convective heat flux is approximately an order of magnitude greater than the discrete component in the high-temperature portion of the ASHES vent field.