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.
Highlights
Driven by climate change, glaciers in most high mountain ranges around the globe are receding and losing mass rapidly (Jomelli et al, 2011; Davies and Glasser, 2012; Zekollari et al, 2019; Davaze et al, 2020; Hugonnet et al, 2021)
Our results for the investigated glaciers in Monte San Lorenzo agree with this assertion, since we found a continuous increase in the debris-covered ice area and a steady shift of the upper altitudinal limit of the ice cliff area toward higher elevations during the study period
In this study we have reconstructed the evolution of surface features and morphology, debris cover, and a superficial flow velocity of Río Oro, Río Lácteo, and San Lorenzo Sur glaciers in Patagonia, which, taken as a whole, covers a time span of over 60 years
Summary
Glaciers in most high mountain ranges around the globe are receding and losing mass rapidly (Jomelli et al, 2011; Davies and Glasser, 2012; Zekollari et al, 2019; Davaze et al, 2020; Hugonnet et al, 2021). Debris cover on glacier surfaces accounts for ∼7% of the mountain glacier area worldwide (Herreid and Pellicciotti, 2020), and is relevant from a surface energy balance point of view, as the distribution and thickness variability of debris layers can alter glacier melt rates (Nicholson et al, 2018; Fyffe et al, 2020). Length adjustments and overall response times of debris-covered glaciers to climate variability are often delayed compared to debris-free glaciers. This delayed signal can occur as ablation rates decrease when debris layers are thicker than the effective thickness (i.e. the thickness above which glacier ice is sheltered and insulated from solar radiation, commonly
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