Evolution of the debris-covered Miage Glacier

Glaciers in high-mountain regions typically exhibit a debris cover that moderates their response to climatic change. Here we present an integrated study that integrates long-term observations of debris-covered glacier mass balance, velocity, surface debris evolution and geomorphological changes (such as ponds and ice cliffs) of Miage Glacier, Italian Alps over the period 1952 – 2018. Analysis of the evolution of Miage Glacier highlighted a reduction in glacier activity associated with a period of sustained negative mass balance (-0.86 ± 0.27 metres per year water equivalent [m w.e. a^-1]) and a substantial reduction in surface velocity (-46%). Ice mass loss of Miage Glacier was quantified using satellite imagery and derived digital elevation models (DEMs) applying the geodetic approach over a 28-year time period, 1990 – 2018. Temporal analysis highlighted an increase in surface lowering rates from 2012 – 2018. Further, the increase in debris-cover extent, supraglacial ponds and ice cliffs was evident since the 1990s. Supraglacial ponds and ice cliffs accounted for up to 8 times the magnitude of the average glacier surface lowering, whilst only covering 1.2 – 1.5% of the glacier area.

Ground-based photogrammetry and bathymetry surveys undertaken in 2017 and 2018 indicated the total volume of water storage at Miage Glacier increased by 46%, however, intermittent drainage events suggest this is highly variable over both seasonal and annual timescales. All ice cliffs underwent substantial vertical retreat upto a maximum rate of -8.15 ma^-1 resulting in ice loss of 39,569 m³. Thus, ice loss from supraglacial ponds and ice cliffs are important to account for and have the potential to substantially impact future glacier evolution.