Geothermal heat flux from hydrothermal plumes on the Juan de Fuca ridge

Abstract

Estimates of the heat output of hydrothermal vents, identified along the Endeavor and Southern Segments of the Juan de Fuca Ridge, are used to evaluate the total heat flux associated with hydrothermal circulation for the ridge segment. An array carried by D/V ALVIN sampled the temperature and velocity structure of hydrothermal plumes from individual vents . The maximum heat flux calculated for a single vent is 50 MW, but the average vent output is only 13 MW per vent for 31 vents. The estimates for any given vent may vary over an order of magnitude. This uncertainty is due mainly to the difficulty of locating the centerline of the plume relative to the point of measurement, although the uncertainty in determining the constants from the appropriate equations based on laboratory experiments contributes a significant share to the net error. For the Endeavor Segment, the minimum total geothermal heat flux due to hydrothermal circulation exceeds 70 MW. The minimum estimate for the Southern Segment is 16 MW. The maximum estimate is probably closer to the total heat flux (236 MW and 66 MW respectively) . The estimated heat flux density is 3300 W/m2 for the Endeavor vent field and 39 W/m2 for the Southern vent field. Focused hydrothermal venting accounts for only a small fraction of the heat available according to steady-state predictions of conductive heat flux; however, other hydrothermal phenomena (e.g., diffuse flow) account for the greater share of the total hydrothermal heat flux.