A glacier in transition: Surface elevation change, ELA and geomorphic evolution of a very small glacier in the Dolomites (S-E Alps)

Small glaciers of temperate mountain regions are suffering significant reduction, with ice mass losses reaching unprecedented melt rates in the very last years. On the other hand, several glacial bodies experienced increasing debris inputs since the end of the Little Ice Age, transitioning from rather clean ice to debris-covered and, sometimes, to rock glaciers. Here we present the recent surface elevation change (2006-2022) of the Popera Alto glacier, a very small debris-covered glacier in the Sesto Dolomites (S-E European Alps), retrieved from a combination of airborne LiDAR and Structure from Motion surveys. We analyse the glacier evolution in terms of surface cover and geomorphic processes, reconstructing its palaeo-volume and -extent from geomorphological evidence. The environmental Equilibrium Line Altitude (envELA) based on climatic data is compared to the effective ELA (effELA), discussing the role of local topography in the evolution of small debris-covered glaciers. Popera Alto glacier lost 0.35 m w.e. yr(-1) in the last 16 years, with its surface cover actively modified by geomorphic processes. Debris and local topography feedback allowed the resilience of the glacier, with marked difference between the current envELA of the area, 3480 m a.s.l., and the effELA of the glacier, 2550 m a.s.l. As such, Popera Alto glacier shows evidence of transitioning from a glacial to a periglacial landform.

Automated summary

Small glaciers in temperate mountain regions have experienced significant reduction and unprecedented melt rates in recent years. Some glaciers have transitioned from clean ice to debris-covered or even rock glaciers. This study examines the surface elevation change of the Popera Alto glacier in the Sesto Dolomites using LiDAR and Structure from Motion surveys, and analyzes its evolution in terms of surface cover and geomorphic processes. The glacier has lost an average of 0.35 m water equivalent per year over the past 16 years, with active modification of its surface cover by geomorphic processes. The role of debris and local topography feedback has allowed the resilience of the glacier, leading to a marked difference between the current environmental equilibrium line altitude (envELA) and the effective ELA (effELA) of the glacier.