Refined Geomorphologic Interpretation of Glacial Deposits using Combined Soil Development Indices and LiDAR Terrain Analysis

Abstract

Core Ideas Soil derived information can aid age discrimination of glacial deposits. Profile development indices proved to be an effective tool for age discrimination of glacial deposits. Geomorphic reconnaissance of glacial deposits in forested catchments can be greatly improved by using LiDAR technologies. The ages of glacial deposits in the Lake Tahoe Basin (LTB) have been poorly constrained. Recent absolute cosmogenic dates and a newly delivered light detection and ranging (LiDAR) dataset for LTB, have revived interest for the age interpretation of these glacial deposits. In this study, we combined field geomorphic reconnaissance, terrain analysis, and soil development indices to discern the timing of glaciation for three Quaternary moraine complexes (Meeks Creek, General Creek, and McKinney Creek) in the western LTB. Tahoe‐age deposits displayed significantly more relaxed and wider crests and lower flank slopes than Tioga‐age deposits. However, these parameters cannot resolve the relative ages of Tahoe I from Tahoe II and Tioga I from Tioga II. The interpretation of various soil development indexes combined with terrain analysis improved relative age assignment, especially for Tahoe I and II. Among the best soil parameters for age discrimination were: textural separates, amount of rock fragments, and elemental composition (C, Al, Fe, Si). Other parameters, including sand‐size ratios or soil selective dissolutions, failed to separate relative ages. In addition, we combined multiple soil properties into a soil profile development index (PDI), which clearly showed that soil development tends to increase with age and that this overall trend was independent of the moraine complex. Our results showed that this combined approach can greatly aid moraine age discrimination, especially for these densely forested catchments.