Analysis of Heat Flow and Groundwater Flow in the South Dakota Geothermal Anomaly

Abstract

A geothermal anomaly with heat flow values ranging from 80 mW m-2 about 130 mW m-2 extends over an area of about 40,000 km centered in southern South Dakota. The anomaly is caused by the thermal effects of a complex groundwater flow system which is driven by eastward sloping hydraulic gradients. Heat advection occurs due to upward fracture leakage near major stream valleys an due to confined, up dip groundwater flow that has persisted for about 65 m.y. Analysis of temperature depth and gradient depth curves from heat flow hole sin the anomalous area indicates that upward fracture leakage may be significant only near gaining streams. Energy flux calculations suggest that the positive heat flow anomaly equals the heat sink caused by recharge of the regional groundwater system.