Debris-covered glaciers: assessing dynamics of European Alpine and Nepalese Himalayan examples

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 thesis aims to investigate temporal and spatial changes in the dynamics of debris-covered glaciers in the European Alps and the Himalayan Manaslu region. A range of in situ data collection methods and remotely sensed data was analysed to further understand debris-covered glacier evolution and future response to climatic change. Glacier surface evolution was mapped at Miage Glacier, Italian Alps, over the period 1952 – 2018 and at three easterly-flowing glaciers in the Manaslu region of the Nepalese Himalaya from 1970 to 2019; namely Punggen Glacier, Hinang Glacier and Himal Chuli Glacier. Surface elevation change was quantified over the 28-year and 49-year time periods respectively based on digital elevation model (DEM) differencing, in addition to surface velocity analysis. Bathymetric and ground-based photogrammetry surveys were undertaken to assess glacial lakes (inclusive of supraglacial ponds and ice-marginal lakes) and adjacent ice cliff evolution at Miage Glacier in 2017 and 2018, and at Hinang Glacier in 2019. Sustained negative mass balance observed at both Miage Glacier (−0.86 ± 0.27 m w.e. a−1 from 1990 – 2018) and the Manaslu glaciers (mean of −0.29 ± 0.05 m w.e. a−1, 1970 – 2019) has coincided with similar stages of debris-covered glacier evolution regarding increased in debris-cover extent, limited reduction in terminal position, substantial reductions in surface velocity (−46%) and increasing development of supraglacial ponds and ice cliffs. Supraglacial ponds and ice cliffs have important roles in overall ablation at all surveyed glaciers accounting for up to eight times the mean surface lowering rates. Despite these broad similarities between regional responses, nonlinear variability was observed at both Miage Glacier and the Manaslu glaciers, which showed highly variable patterns of surface elevation change and dynamic flow behaviour. Glacier hypsometry and local variability in precipitation in addition to topographic controls, which regulate ice flux, are considered to account for individual glacier response providing further uncertainties when modelling future debris-covered glacier response to climatic change. The inconsistency of these glacier dynamics highlight the complex, nonlinear changes of debris covered glaciers over differing spatial and temporal scales. The results of this thesis add to the current knowledge base and offer a unique and valuable insight into the variability of debris covered glacier evolution in two comparatively different environmental settings