Hydrogeological and Hydrochemical Investigations in West Nymph Creek Thermal Area, Yellowstone National Park, USA

Fast changing geothermal features characterize the Yellowstone National Park, USA. Highresolution aerial images were taken to map the hydrothermal study area. The combination of a digital camera and a low flying (< 100 m) helium balloon was a cost and time effective method to get a status quo of the feature’s form and size. The resulting aerial overview has a resolution of 2.5 cm and is presented in a multilayer digital atlas, providing a basis for further surveying. Ground survey included mapping and on-site hydrochemistry of 18 major hydrothermal features. Arsenic concentrations are known to be elevated in Yellowstone (1.7 ± 2 mg/L) - therefore, beside trace element analysis with ICP-AES, three techniques for As speciation were applied: HG-AAS, HPLC-ICP-MS, and on-site SPE with GF-AAS. Surprisingly low total As concentrations made an evaluation of the different methods difficult. Grouping the water samples revealed two water types: steam heated waters (type I) and waters with a deep thermal origin (type II). Thus, a known hydrogeological model (White et al. 1988) is checked for its applicability to the study area.