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

Abstract

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.