Mass balance and surface evolution of the debris-covered Miage Glacier, 1990–2018

Many glaciers in high-mountain regions exhibit a debris cover that moderates their response to climatic change compared to clean-ice glaciers. Studies that integrate long-term observations of debris-covered glacier mass balance, velocity, surface debris evolution and geomorphological changes (such as ponds and ice cliffs) are relatively few. This study used satellite imagery, ground-based photogrammetry and bathymetry to assess such changes at Miage Glacier, Italian Alps, over a 28-year time period (1990–2018). Over this period, Miage Glacier experienced sustained negative mass balance (−0.86 ± 0.27 metres per year water equivalent [m w.e. a−1]), a substantial reduction in surface velocity (−46%), and increased debris-cover extent (+8.5% of the total glacier area). Since 1990, supraglacial ponds and ice cliffs have become more prevalent; whilst only covering 1.2–1.5% of the glacier area, they account for up to 8 times the magnitude of the average glacier surface lowering. Subsequently, Miage Glacier has entered a phase of enhanced decay since 1990. Miage Glacier is expected to continue to slow and thin, although any further accelerations in its decay will depend upon whether or not the tributary glaciers become disconnected from the main trunk, which would reduce ice flow, promote stagnation, flatten the longitudinal profile, and facilitate more widespread development of supraglacial ponds and so enhance ablation.