Quantitative Analyses of Warm Spring Waters at the Hot Creek Fish Hatchery, Mammoth Lakes, California

Abstract

Springs at the Hot Creek Fish Hatchery, within the volcanically active Long Valley caldera in east-central California and contain mixtures of thermal and non-thermal groundwater. The average temperature in the westernmost AB spring group (17°C) is some 6°-7°C higher than temperatures in more dilute cold springs around the caldera margin. Hatchery spring temperature and chemistry data at AB suggest variable mixtures of about 5% thermal and 95% non-thermal groundwater. Periodic fluctuations in temperature and thermal-water mixing ratio have been observed over the monitoring period 1988-2003 described here. These fluctuations occur primarily in response to seasonal and annual variations in snow-melt generated recharge. Measured temperature variations are well-matched with power-law (exponential) relations of the form T = AQ-B, where T = spring temperature, Q = spring flow rate, and A and B are constants determined from regression analysis. In contrast, computations based on measured chemical flux values for boron and chloride show significant overestimates of spring temperature changes. In this paper, we show that consideration of a temperature-buffering process involving heat conduction between the mixed water aquifer and the surrounding rocks explains the over-estimation of temperature changes computed from chemical-flux data and yields estimates of spring temperatures as functions of flow rate that are in agreement with the results of power-law relations.