Debris-Covered Glaciers in the Sierra Nevada, California, and Their Implications for Snowline Reconstructions

Abstract

Ice-walled melt ponds on the surfaces of active valley-floor rock glaciers and Matthes (Little Ice Age) moraines in the southern Sierra Nevada indicate that most of these landforms consist of glacier ice under thin (ca. 1 - 10 m) but continuous covers of rock-fall-generated debris. These debris blankets effectively insulate the underlying ice and greatly reduce rates of ablation relative to that of uncovered ice. Such insulation explains the observations that ice-cored rock glaciers in the Sierra, actually debris-covered glaciers, are apparently less sensitive to climatic warming and commonly advance to lower altitudes than do adjacent bare-ice glaciers. Accumulation-area ratios and toe-to-headwall-altitude ratios used to estimate equilibrium-line altitudes (ELAs) of former glaciers may therefore yield incorrect results for cirque glaciers subject to abundant rockfall. Inadvertent lumping of deposits from former debris-covered and bare-ice glaciers partially explains an apparently anomalous regional ELA gradient reported for the pre-Matthes Recess Peak Neoglacial advance. Distinguishing such deposits may be important to studies that rely on paleo-ELA estimates. Moreover, Matthes and Recess Peak ELA gradients along the crest evidently depend strongly on local orographic effects rather than latitudinal climatic trends, indicating that simple linear projections and regional climatic interpretations of ELA gradients of small glaciers may be unreliable.

Modeling debris-covered glaciers: response to steady debris deposition

“…Because debris strongly influences glacier length, independent of climate change, debris should be considered amongst temperature and precipitation as primary controls of paleoglacier lengths (e.g., Clark et al, 1994;Scherler et al, 2011b). The effect of debris on paleoclimate estimates can be minimized by avoiding de-glaciated catchments with high-relief headwalls, supraglacially sourced moraine sediments, or by using a debris-glacier-climate model to estimate the effect of debris on glacier extent.…”

A quantification of the glacial imprint on relief development in the French western Alps

“…In the presence of significant debris cover, the THAR may reach values of 0.6 -0.8, while the AAR would be reduced to values 0.1 -0.4 (Clark et al, 1994).…”

Internal Structure and Current Evolution of Very Small Debris-Covered Glacier Systems Located in Alpine Permafrost Environments

“…This insulating layer confers specific behavior to heavily debris-covered glaciers. Because ice melt is limited in the ablation area, they have smaller accumulation area ratios than other glaciers (typically 0.1-0.4 instead of 0.6-0.7; Clark et al, 1994). They can thus have a positive mass balance with a restricted accumulation area, reach lower elevation and advance when neighboring bare-ice glaciers are retreating (Scherler et al, 2011;Deline et al, 2012;Carturan et al, 2013).…”