DETERMINING THE SOURCE OF HEAT IMPACTING THERMAL SPRINGS IN THE WARM SPRINGS VALLEY OF BATH AND ALLEGHANY COUNTIES, VIRGINIA

The source of heat that warms waters issuing from thermal springs in Bath and Alleghany counties, Virginia, has been studied for many years but is still poorly understood. This region contains the warmest thermal waters east of the Mississippi River and has some of the youngest igneous activity (Eocene aged) found in the eastern United States. To date, researchers have been unable to positively link the thermal nature of these waters with this igneous activity. Instead, the most commonly accepted explanation for the origin of these thermal waters is that they are the result of shallow meteoric water flowing through permeable thrust faults which is then transported to the surface by vertical fracturing located in the center of valleys in the study area.

We have attempted to investigate the origin of heat in six thermal springs in Bath and Alleghany counties, Virginia with basic physical and chemical hydrologeologic techniques. Preliminary drainage basin and spring discharge analysis suggests that long term discharge cannot be sustained from only a shallow water source as previous works have suggested. Bulk water chemistry indicates that these thermal spring waters are 1) chemically similar, 2) high TDS, and 3) supersaturated with respect to numerous mineral phases. These geochemical characteristics are common in relatively deep aquifer waters. Additionally, ³He and ⁴He analyses (courtesy of Lawrence Berkeley National Laboratory) from 2 of these springs produce R/Ra values substantially greater than 1.0, which leads us to the conclusion that these waters show an unambiguous influence of mantle derived water. As a result of these physical and chemical hydrologic analyses, we believe the source of heat for these thermal waters is ultimately deeper than previous workers have suggested and may be in part from the mantle.