MAPPING THE BATHYMETRY AND GEOLOGY OF YELLOWSTONE LAKE: AN ESSENTIAL TOOL FOR MANAGING NATURAL RESOURCES AND ASSESSING POTENTIAL HAZARDS

Discoveries from multi-beam sonar, seismic-reflection, and submersible surveys of Yellowstone Lake provide new insight into post-caldera volcanism and active hydrothermal processes in a large lake environment above a magma chamber. Yellowstone Lake has an irregular bottom covered with dozens of features directly related to hydrothermal, tectonic, volcanic, and sedimentary processes. Detailed bathymetric, seismic reflection, and magnetic evidence reveals that rhyolitic lava flows underlie much of Yellowstone Lake and control lake bathymetry and localization of hydrothermal activity. We have identified several previously unknown features including over 250 hydrothermal vents, several large hydrothermal explosion craters, many small hydrothermal vent craters, domed lacustrine sediments related to hydrothermal activity, elongate fissures cutting post-glacial sediments, siliceous hydrothermal spires, sublacustrine landslide deposits, submerged former shorelines that may relate to caldera inflation/deflation cycles, and a recently active graben. These features and processes constitute potentially significant geologic hazards. Potentially toxic elements, such as Hg, As, Sb, W, and Mo, derived from hydrothermal processes also may adversely affect the Yellowstone ecosystem. Mapping in Yellowstone Lake extends the subaerial geologic mapping, allowing the lake basin to be understood in the geologic context of the rest of the Yellowstone region. Rhyolitic lava flows contribute greatly to the geology and morphology of Yellowstone Lake, as they do to the subaerial morphology. Our data suggests that islands in the lake are underlain by large-volume rhyolitic lava flows and that these flows are mantled by late Pleistocene glaciolacustrine sediments. The margin of the Yellowstone caldera passes through the central part of the lake and northward along the lake’s eastern edge. Postcaldera rhyolitic lava flows are present along much of the caldera margin beneath Yellowstone Lake. Active faults, young fissures, hydrothermal explosion craters, landslide deposits, and numerous hydrothermal sediment domes are potentially hazardous features on the lake bottom that will be assessed and monitored under the aegis of the new Yellowstone Volcano Observatory.