ECOLOGICAL IMPACT OF POSTGLACIAL HYDROTHERMAL EXPLOSION EVENTS IN YELLOWSTONE NATIONAL PARK INFERRED FROM YELLOWSTONE LAKE SEDIMENTS

Yellowstone National Park contains the largest concentration of terrestrial hydrothermal features on Earth, and Yellowstone Lake is a key hydrothermal basin within the system. Hydrothermal explosion events are a catastrophic response to conditions wherein subsurface fluids flash to steam; they were particularly common in the Yellowstone Caldera during deglaciation. The timing of hydrothermal explosions can be reconstructed through breccia deposits preserved in Yellowstone Lake sediments. The objective of this study is to assess the effect of past hydrothermal explosions on lake and watershed dynamics. An 11-meter sediment core collected near the center of hydrothermal activity in northern Yellowstone Lake featured three hydrothermal explosion deposits. Diatom, pollen and charcoal records were examined to assess pre- and post-explosion conditions for the three large events. Directly after hydrothermal explosions, diatom productivity diminishes and increased turbidity and silica input is reflected by changes in diatom community composition. In contrast, the explosions resulted in little change in watershed vegetation or fire activity. Thus, localized hydrothermal explosion events in Yellowstone Lake had short-term effects on the aquatic community likely through increasing both turbidity and silica availability. Impacts on the surrounding landscape were not apparent in the sediment record. Future research includes assessing the impact of hydrothermal explosions on smaller lake basins in the region where the effects on local vegetation and fire history may be more detectable.