Quaternary climate forcing on Alpine glacier dynamics and subglacial erosion patterns: insights from morphometrics and numerical modelling

Guedes Magrani, Fabio José (2021). Quaternary climate forcing on Alpine glacier dynamics and subglacial erosion patterns: insights from morphometrics and numerical modelling. (Dissertation, University of Bern, Philosophisch-naturwissenschaftlichen Fakultät)

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During the last 2.6 million years of the Quaternary, multiple glacial/interglacial periods have taken place following climatic oscillations, mostly triggered by orbital changes, tectonics and fluctuations in patterns of oceanic and/or atmospheric circulation. Quaternary glaciations have left remarkable imprints at the Earth’s surface, especially in Alpine regions where lakes, hanging waterfalls and steep mountain valleys offer evidences of the impact of glacial dynamics on landscapes. Climate is probably one of the main controlling mechanisms in alpine landscape evolution, significantly influencing denudation rates throughout the Quaternary. In this thesis, I quantitatively investigate the connections between climate and glacier dynamics, with a focus on subglacial erosion, aiming to comprehend modern to paleoglacial systems and involved physical processes acting in alpine settings. Despite scientific efforts over the last decades, the spatial patterns of (sub)glacial erosion and the timescales over which they develop are still under debate and poorly constrained. To address this issue, I used a combination of geoprocessing tools, numerical simulations (based on the ice-flow model iSOSIA) and geochronological dating to explore ice dynamics and the complex patterns of (sub)glacial erosion in relation to climatic forcing and other potential controlling factors such as bedrock resistance, topographic/drainage settings and subglacial hydrology, between the different sectors of a temperate alpine glacier. I also extracted morphometric data from Quaternary overdeepenings (ODs) in the Swiss Alpine foreland, which are major erosional features in paleo-glaciated regions, and compared ODs metrics with predictions from numerical experiments in order to better understand their distribution and evolution in space and time. Outcomes from ice-flow simulations highlight the role of subglacial hydrology in dictating patterns of subglacial erosion, while erosion magnitudes and ice geometry are conditioned by ice flux and climate inputs (temperature and precipitation forcing). Significant differences were observed between the accumulation and ablation zones of the glacier, both in terms of glacier geometry and subglacial erosion, evidencing contrasting impacts of climate forcing on the accumulation/ablation areas. My results also suggest that ice-flow context and bedrock lithology play a major role in controlling the development of subglacial erosional features, with larger, wider and shallower overdeepenings within low-resistance bedrock of the foreland region. Besides, both ODs data and numerical simulations support headward subglacial erosion, with ODs initiating from multiple small nested valleys and evolving into bigger and connected features, driven by either changes in climate and/or over multiple glaciations. The original approach with combined methodologies and the results presented in this thesis are providing new insights into our understanding of the complex patterns and mechanisms of (sub)glacial erosion, with potential implications for landscape evolution (including development of overdeepenings) and paleo-climate reconstructions.

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