Heat Flux From a Vapor-Dominated Hydrothermal Field Beneath Yellowstone Lake

We report results from 149 heat flux measurements made over n similar to 2-year interval at sites in and around a vapor-dominated geothermal field located at water depths of similar to 100-120 m in Yellowstone Lake, Wyoming. Measurements of both in situ temperature and thermal conductivity as a function of depth were made with a 1 m probe via a remotely operated vehicle, and are combined to compute the vertical conductive heat flux. Inside the similar to 55.5 x 10(3) m(2) bathymetric depression demarcating the vapor-dominated field, the median conductive flux is 13 W m(-2), with a conductive output of 0.72 MW. Outside the thermal field, the median conductive flux is 3.5 W m(-2). We observed 49 active vents inside the thermal field, with an estimated mass discharge rate of 56 kg s(-1), a median exit-fluid temperature of 132 degrees C, and a total heat output of 29 MW. We find evidence for relatively weak secondary convection with a total output of 0.09 MW in thermal area lake floor sediments. Our data indicate that vapor beneath the thermal field is trapped by a low-permeability cap at a temperature of similar to 189 degrees C and a depth of similar to 15 m below the lake floor. The thermal output of the Deep Hole is among the highest of any vapor-dominated field in Yellowstone, due in part to the high boiling temperatures associated with the elevated lake floor pressures.