Evolution of Surface Characteristics of Three Debris-Covered Glaciers in the Patagonian Andes From 1958 to 2020

Abstract

A number of glaciological observations on debris-covered glaciers around the globe have shown a delayed length and mass adjustment in relation to climate variability, a behavior normally attributed to the ice insulation effect of thick debris layers. Dynamic interactions between debris cover, geometry and surface topography of debris-covered glaciers can nevertheless govern glacier velocities and mass changes over time, with many glaciers exhibiting high thinning rates in spite of thick debris cover. Such interactions are progressively being incorporated into glacier evolution research. In this paper we reconstruct changes in debris-covered area, surface velocities and surface features of three glaciers in the Patagonian Andes over the 1958–2020 period, based on satellite and aerial imagery and Digital Elevation Models. Our results show that debris cover has increased from 40 ± 0.6 to 50 ± 6.7% of the total glacier area since 1958, whilst glacier slope has slightly decreased. The gently sloping tongues have allowed surface flow velocities to remain relatively low (<60 m a−1) for the last two decades, preventing evacuation of surface debris, and contributing to the formation and rise of the ice cliff zone upper boundary. In addition, mapping of end of summer snowline altitudes for the last two decades suggests an increase in the Equilibrium Line Altitudes, which promotes earlier melt out of englacial debris and further increases debris-covered ice area. The strongly negative mass budget of the three investigated glaciers throughout the study period, together with the increases in debris cover extent and ice cliff zones up-glacier, and the low velocities, shows a strong linkage between debris cover, mass balance evolution, surface velocities and topography. Interestingly, the presence of thicker debris layers on the lowermost portions of the glaciers has not lowered thinning rates in these ice areas, indicating that the mass budget is mainly driven by climate variability and calving processes, to which the influence of enhanced thinning at ice cliff location can be added.

Controls on Ice Cliff Distribution and Characteristics on Debris‐Covered Glaciers

“…While models accurately simulate the energy and mass balance contribution of individual ice cliffs (Buri et al., 2016; Kneib et al., 2022), their application at large spatial scales is limited by our understanding of the controls of ice cliff distribution. Indeed, estimates of ice cliff density are difficult to make (Anderson, Armstrong, Anderson, & Buri, 2021; Herreid & Pellicciotti, 2018; Kneib et al., 2020) and vary widely in time and space, between 1% and 15% of the debris‐covered area (e.g., Falaschi et al., 2021; Kneib et al., 2021; Loriaux & Ruiz, 2021; Sato et al., 2021; Steiner et al., 2019; Watson, Quincey, Smith, et al., 2017). Remote sensing studies have shown that cliffs are often associated with ponds (Steiner et al., 2019; Watson, Quincey, Carrivick, & Smith, 2017), hinting at a preferential location of ice cliffs where lower glacier longitudinal gradient and surface velocities promote surface ponding (Bolch et al., 2008; Quincey & Glasser, 2009; Quincey et al., 2007; Racoviteanu et al., 2021; Reynolds, 2000; Sakai & Fujita, 2010; Salerno et al., 2012).…”

Modelled sensitivity of Monte San Lorenzo ice cap, Patagonian Andes, to past and present climate

“…Glaciar Calluqueo terminates on bedrock, but drains into the large, 3.5 km long proglacial Lago Calluqueo, which discharges into Rio Salto to the north. Glaciar Rio Lacteo in the east and Glaciar San Lorenzo are largely debris covered (Falaschi et al, 2021), and terminate in proglacial lakes. Glacier velocity mapping by Millan et al (2022) indicates that the tongue of Calluqueo Glacier reaches velocities of up to 350 m a −1 , with slower flow of ~100 m a −1 in the tongue's tributaries in the accumulation area.…”

Sub-seasonal variability of supraglacial ice cliff melt rates and associated processes from time-lapse photogrammetry

“…These limitations highlight the need for detailed and quantitative observations of cliff melt and evolution during the melt season. This is particularly challenging as ice cliffs are dynamic features which can grow, shrink, appear or disappear within the course of a single season (Sato et al, 2021;Kneib et al, 2021), which results in the ice cliff area regularly changing by up to 20 % from year to year (Kneib et al, 2021;Watson et al, 2017a;Steiner et al, 2019;Falaschi et al, 2021;Sato et al, 2021;Anderson et al, 2021). This high variability can be explained by the strong influence of local processes such as pond undercutting, filling and drainage (Kraaijenbrink et al, 2016;Watson et al, 2017b), stream undercutting (Mölg et al, 2020), and debris redistribution (Moore, 2018;Westoby et al, 2020).…”