BAY MOUTH BARS, LOOP BARS, AND RECURVED SPITS IN YELLOWSTONE LAKE: NORTH AMERICA’S HIGHEST ELEVATION “COASTAL” LANDFORMS

Yellowstone Lake (Yellowstone National Park, USA) is among the world’s largest high-altitude lakes (elevation 2,357 m above MSL). A reconnaissance survey of the lake’s perimeter identified a number of landforms more commonly associated with coastal environments (bay mouth bars, loop bars, recurved spits). Though similar features may commonly be observed along the shorelines of large lakes, they are generally unknown from alpine lakes. As such, the “coastal” landforms of Yellowstone Lake represent a unique yet unstudied aspect of Yellowstone geomorphology and are the highest elevation “coastal” landforms in North America. Many of the best developed accretionary bay mouth bars, loop bars, and spits appear to correspond to the axis of maximum uplift within Yellowstone caldera. This suggests that resurgent uplift of the caldera associated with Yellowstone hot spot dynamics provides a littoral shelf where sediment derived from erosion of unconsolidated volcanic agglomerates along the lake shore may be transported by longshore drift forming large sedimentary bodies. A transect across the best developed bay mouth bar in the West Thumb arm of Yellowstone Lake indicates that it displays several subtle progradational ridges as well as evidence of sediment transport resulting from overwash. Future detailed studies of “coastal” landforms of Yellowstone Lake could provide insights into the geologic history of lake level variations related to episodic inflation-deflation of the central caldera.