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Time Scales and Processes of Shoreline Formation in Pluvial Lakes of the Great Basin, Western USA
AuthorAbramson, Noah Forrest
AdvisorAdams, Kenneth D
Geological Sciences and Engineering
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This study examines historical beach deposits formed in Walker Lake, Winnemucca Lake, and Lake Tahoe to characterize the processes that lead to the construction of beach ridges along lacustrine shorelines and compares the volume of individual shoreline features to the lengths of time under which they formed. Maximum fetch distances of < 50 km limit waves generated in these basins. Waves that are capable of significant geomorphic work are generated during events that achieve wind speeds > 10 m/s for 3 or more hours. A 30-year wind record from the Dead Camel Mountains, NV indicate these wind events occur 5-24 times per year. Modeled maximum total wave swash elevations for the observed significant wind events range from 0.93- 1.93 m across the three lakes studied, which is in general agreement with heights of observed beach ridges. Total incident wave energy delivered to the shorelines of interest for the years 1999, 2007, and 2017 ranged from 0 - 2.5x108 J/m across the three basins, indicating total wave energy delivered per year can be highly variable. The volumetric analysis of historical beach ridges at Walker Lake showed a strong correlation between time of formation and increased volume, therefore, the individual volumes of beach ridges can be used as an indicator to infer relative durations of lake-level stability. By applying the volume vs. time of formation relationship developed on the historical shorelines, we estimate lake levels were sustained at 1262 m elevation for ~4.5 - 5.5 years in Walker Lake during the late Holocene highstand around 3500 cal yr. BP. When used to estimate durations of time of lake-level stability, volumetric analysis of beach ridges presents a new technique to further refine pre-historic lake-level curves on an annual to decadal timescale. However, given large variability in shoreline volumes and rates of development across basins, it is important to acknowledge differences in sediment supply, wind conditions, wave energy, shoreline equilibrium, and other parameters relating to beach ridge formation before applying volumetric relationships from one lake to another.