Temporal and Spatial Variation in Temperature and Geochemistry of the Thermopolis Geothermal System

After Yellowstone National Park, the Thermopolis Geothermal System (TGS) is the largest hydrothermal system in Wyoming. Located in the southern portion of the Bighorn Basin, the TGS consists of two major active springs (Big Spring, White Sulfur Spring) that are currently precipitating two series of travertine terraces along the Bighorn River. Past TGS activity is evident from at least eight ancient deposits, each over 15 m thick, that occur at distinct geologic units at varying elevations within the basin. The placement of these deposits indicates that the hot springs periodically dry-up and/ or migrate, suggesting a sensitivity to regional hydrology and, therefore, the potential for these deposits to provide a detailed paleo-hydraulic record for the Bighorn Basin. However, to interpret paleoenvironmental conditions from the TGS travertine deposits, a better understanding of the currently active springs and terraces is needed.

Initial assessment of the temperature profile for the TGS was made by flying an Unmanned Aerial Vehicle (UAV, Parrot Bebop 2 Pro-Thermal) with a FLIR Thermal Imaging Camera over the whole system to map the temperature gradient from source (Big Spring), across the travertine terraces, to where waters from the TGS entered the Bighorn River. These images showed that temperatures cooled quickly from the source (~50°C) to the travertine pools (~30°C). Temperature of waters within the pools remained relatively stable (25-30°C) and did not decline further until flowing out of the lowest pool (21°C) and entering the river. UAV temperature data were compared with field measurements made at 10 spots spaced along a transect from source to river. Along with temperature, measurements of flow depth, flow speed, and pH were taken at each spot and water and travertine samples were collected for later isotopic measurements. Temperatures measured by UAV showed excellent agreement with those determined by field measurement, demonstrating the usefulness of UAV thermal-imaging data collection for rapid, spatially-extensive readings for large hydrothermal systems.