MASS FLUX MEASUREMENTS OF HOT SPRINGS IN YELLOWSTONE NATIONAL PARK USING DEUTERIUM OXIDE DOPING METHOD

Estimates of hydrothermal heat flux from the Yellowstone Caldera have largely been calculated using chloride flux in drainages as a proxy for heat flow from hydrothermal fields. Although this is a powerful tool for estimating heat flux from a large area, it relies on several assumptions that can lead to the potential for error. Measuring the thermal discharge for single hot springs could lead to more precise estimates of the overall heat flux at Yellowstone. Here, a new method is described that uses spring discharge, calorimetry, and ground temperature measurements, to estimate both advective (calculated from hot spring surface/subsurface discharge) and diffusive heat flow. Hot spring discharge can be measured using a time-series spring temperature response related to atmospheric conditions. Tracer-decay experiments have been carried out in four isolated hot springs in the Lower Geyser Basin at Yellowstone to test the application of the time-series method. Relatively small amounts of nearly pure deuterium oxide (D₂O) were added to four hot springs in the Merry Mountain Springs area. The springs’ temperatures ranged from 74° to boiling at 95°C. D₂O was used to limit the ecological and visual impacts inherent in other common tracers (NaCl, fluorescein dyes, etc.). Hot spring volumes were estimated in the field in order to calculate how much D₂O was needed to increase each hot spring’s background δD value from around -140‰ to approximately 90‰. D₂O (14 to 600 mL depending on spring volume) was mixed into the hot springs at t=0. Samples were then collected over a time series with intervals of a few minutes to several hours. Initial results indicate clear exponential decay of δD values over time for each of the four hot springs. All of the hot springs re-equilibrated to background values several hours to days after t=0. Springs with no visible surface discharge decayed to background values at similar rates as those that had strong visible surface drainage, suggesting that advective flow out of the shallower parts of the hot spring walls is an important heat and mass flux process.