AN EMPIRICAL MODEL OF SHORELINE CHANGE AT YELLOWSTONE LAKE, 1954-2002

Decadal changes in the position of the Yellowstone Lake shore were documented from aerial photographs of West Thumb arm (1954, 1976, 1989, 1994, 2002). Photos were orthorectified and georeferenced and the lake shore delineated on each photograph using GIS to determine shore recession or advance. A digital terrain model (DTM) was developed to simulate shore position from 1954-2002 responding to surface elevation changes due to caldera deformation and lake level oscillations. Surface tilting in the model was driven by caldera deformation estimated from all available data (historic leveling surveys, INSaR data, and U. of Utah continuous GPS observations). Following deformation of the DTM, “shoreline” was determined using historic lake elevation data and compared to the shore position observed on aerial photographs. The shore on the DTM was deformed until it most closely matched shores observed on aerial photographs. Modeling results demonstrated that lake level variation alone was not sufficient to achieve reasonable fit between the DTM “shore” and observed shore positions of northern West Thumb arm. The best fit between modeled/observed lakeshore was achieved by combining corrected lake levels with surface tilting (5-10 times more deformation than documented from various measures). In contrast, the southern shore of West Thumb experiences very little surface deformation, yet lake level variations alone also failed to reproduce historic shore changes. Best fit of modeled/observed shores for southern West Thumb were achieved using historic lake elevation +/- lake level change comparable in magnitude to surface deformation along the north shore. This simple empirical model demonstrated that (1) caldera deformation is a primary controlling factor on shoreline change at Yellowstone Lake and (2) shoreline changes can be modeled on the lake over decadal to multi-decadal time scales from empirical data.