Measuring the topography and motion of rock glaciers in the Cordillera Principal, Argentina

Abstract

GPS and digital photogrammetry were used to obtain topographic and motion data for the El Altar, QDM, and Los Azules Rock Glaciers in the High Dry Andes of Argentina. A total of 21 survey stations (8 at El Altar, 3 at QDM, and 10 at Los Azules) were monitored between AD 2010 and 2017 at various intervals as allowed by funding and weather conditions at the study locales. Rates of motion were compared with elevation, local slope, and rock glacier thickness at each station. Results suggest that all three landforms or portions of the glaciers are active rock glaciers, but no single correlation explains the nature of movement for all the study landforms. El Altar’s motion is correlated with elevation and not slope and suggests an upper portion moving approximately 2 to 5 times faster than motion along the terminal margin (ca. 0.16 m yr-1 vs. 0.2 m yr-1). Those rates, coupled with the lack of ice or melt water at the margin suggests much of this landforms motion likely occurs as creep much slower than velocities of typical ice rich glacial forms. This indicates the upper portion is likely active, whereas the lower portion is likely inactive. The QDM rock glacier, where ice has been identified within a few meters of the terminus, shows a significant correlation (R2 = 0.97, Figure 18b) between local slope and rate of motion. Los Azules, despite having a known ice rich margin, shows little down-valley movement at rates of 0.04 m yr-1. This slow movement is difficult to explain but may be a result of the multiple accumulation areas that are generally transverse to the valley in which they accumulate. This results in a landform that is poorly organized topographically, with hummocky topography and slow rate of motion. These results emphasize that these landforms have a complex response to both internal ice and surface topography. Our results, most of which would be impossible without high resolution topographic data, underscore the value of coupling aerial imagery with sparse data like the GPS measurements to provide insight for future analyses focused on ice presence and volume.