Heat Flow Measurements in Lake Wakatipu, South Island, New Zealand: A Warm Monomictic Lake

Abstract

Rapid uplift and erosion can result in elevated surface heat flows and shallow low temperature geothermal resources of regional extent. In order to investigate the potential of geothermal energy and provide constraints for tectonic modeling, we made a series of heat flow measurements in warm, monomictic glacial lakes on the South Island. Measurement in water depth below 300 m in Lake Wakatipu (290 km2) indicate that bottom water temperatures increase downstream but mean heat flows decrease downstream from the middle arm though a transition area to the south arm. Focusing of heat flow by the glacial valley can enhance the surface heat flow by 40%. Without property geologic constraint, modeling of advection or erosion can account for heat flow highs in the middle arm. To explain low heat flows in the south arm, post glaciation sedimentation rate exceeding 5 mm/years must be invoked. More likely, high heat flows result from rising warm water along a yet to be confirmed fracture zone beneath the middle arm of the invested "z" shaped Lake Wakatipu.