Monitoring and modelling cryosphere processes using high resolution surveys

This thesis aims to study the recent and past behaviours of the lowermost Italian glacier, a very small glacier (<0.5 km2) known as Ghiacciaio Occidentale del Montasio (Julian Alps), which is located far below the regional equilibrium-line altitude. Glacier elevation changes, mass balances, surface displacements and change in surface cover were monitored using high resolution techniques (in particular Structure from Motion Multi-View Stereo, SfM-MVS) and reconstructing Digital Elevation Models (DEMs) from historical images and maps. Glacier changes were correlated to air temperature and precipitation trends to better characterise and understand its climatic response. The first object of the thesis was to investigate the reliability of the SfM-MVS technique for monitoring elevation changes in debris covered areas such as the lower half of the Montasio Glacier. The technique was tested over easy-to-access riverbeds with different morphologies and patterns, to point out critical aspects and minimise errors in the acquisition and processing phases. SfM-MVS proved to have high repeatability with unchanged acquisition setup, while surveys performed with different sensors might introduce systematic errors in the elevation change detection analysis. Overall, this technique was considered adequately accurate and precise for monitoring small debris covered areas, such as the Montasio Glacier. Bases on these results, the focus moved to the recent (2006-2019) dynamics of the Montasio Glacier. Data acquired with both SfM-MVS and laser scanning (terrestrial and aerial) techniques were used to analyse the annual mass balance of the glacier. The study confirmed a complex relationship between the glacier mass balance and the extent of the debris-covered area. It also highlighted the unusual behaviour of this glacier, characterised by: i) a remarkably lower imbalance compared to others Alpine reference glaciers, ii) a nonsignificant correlation of mass balance with air temperature, and iii) a high sensitivity to precipitations during the accumulation season. The analysis of the recent dynamics opened new questions regarding the long-term climatic sensitivity of the glacier and its relationship with the debris cover, at the secular time scale. Therefore, an historical analysis was performed reconstructing glacier DEMs for five different years (1920,1948,1982,2006,2020), which enabled the calculation of the geodetic mass balance rate in the last century. The Montasio Glacier behaviour was comparable with the other alpine glaciers trough the 20th Century until the early 1980s. In the recent decades, however, it progressively decoupled from the typical response of alpine glaciers, showing increasing departure and much lower imbalance. The progressively increase in thickness and extent of the debris layer observed after the 1940s, in association with the avalanche feeding and the shadowing effect of the Mt. Jof di Montasio, were confirmed as the main causes of the current minor imbalance and low sensitivity to air temperature fluctuations. This thesis demonstrates that high-resolution SfM-MVS represents a cost-effective method, which can be successfully adopted for monitoring the response of glaciers with characteristics similar to the Montasio Glacier.The study provides a full characterisation of the current and past dynamics and behaviour of the Montasio Glacier, from both climatic and glaciological perspectives. Based on the results of this study, it can be assumed that a transition to periglacial conditioning (i.e.transformation to a rock glacier) is improbable, and that the glacier should not quickly disappear in the near future.