Abstract
AbstractThe ice-cored Galena Creek Rock Glacier, Wyoming, USA, has been the subject of a number of studies that sought to determine the origin of its ice. We present new observations of the rock glacier's internal structure from ground-penetrating radar to constrain ice and debris distribution and accumulation. We imaged dipping reflectors in the center of the glacier that are weak and discontinuous, in contrast to strong reflectors toward the edge of the cirque beneath large debris-avalanche chutes. These reflectors form a network of concave-up, up-glacier dipping layers. We interpret these as englacial debris bands formed by large debris falls buried by subsequent ice and snow accumulation. They are discontinuous where ice outpaces debris accumulation, but with sufficient debris accumulation an interleaved pattern of ice and debris layers can form. We propose a model in which the ice in these interleaved layers is snowfall preserved by debris-facilitated accumulation. Large debris falls that occur in early spring bury sections of the snowpack, which are then preserved through summer and incorporated into the rock glacier body over time. This study highlights the importance of sequential accumulation of ice and debris for understanding the dynamics of rock glaciers and debris-covered glaciers.
Highlights
Galena Creek Rock Glacier is a site of great importance in the rock glacier scientific literature, being a touchstone in the historical debate around rock glacier origins (Potter and others, 1998)
Motivated by the goal of constraining ice and debris accumulation history at Galena Creek Rock Glacier, we present a Groundpenetrating radar (GPR) survey performed at the site designed to image the rock glacier’s internal structure
We described through thermokarst exposure observations and GPR data the presence of englacial debris layers produced by large debris falls buried in Galena Creek Rock Glacier
Summary
Galena Creek Rock Glacier is a site of great importance in the rock glacier scientific literature, being a touchstone in the historical debate around rock glacier origins (Potter and others, 1998). Hypotheses of rock glacier formation generally fall into two categories: those maintaining that many rock glaciers are cored with snowfall-derived glacial ice (Potter, 1972) and those maintaining that rock glaciers are exclusively periglacial features with interstitial ice sourced from refreezing of meteoric water and snow/ice melt (Barsch, 1987). In their seminal survey of 200 rock glaciers in the Alaska Range, Wahrhaftig and Cox (1959) presented the periglacial model, in which observed interstitial rock glacier ice is accumulated by the refreezing of snowmelt and rainwater percolated into talus debris in periglacial environments. Outcalt and Benedict (1965) studied a number of rock glaciers in the Colorado rockies and drew a distinction between two types: (1) tongue-shaped cirque floor rock glaciers containing pure ice cores that they hypothesized are the debris-covered snouts of former glaciers and (2) apron-shaped valley wall rock glaciers containing interstitial ice that they hypothesized is avalanche snow buried by debris fall
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