Glacial erosion and mountain denudation over the last glacial cycle: Case studies from the NE Atlantic margin

Abstract

Mountain development is dynamic and spans significant temporal (103 to 106 years) and spatial (single valley to mountain range) scales. Understanding and quantifying the fundamental processes which govern the growth and denudation of mountains is important as these provide context for and influence rates of modern climate change. This thesis investigates the glaciological drivers of mountain denudation with specific focus on the mountains of Wicklow, Ireland and the Pyrenees, France/Spain, and the coupling of glacial and hillslope erosion over the last glacial cycle. These mountain ranges represent end-members on a glaciological spectrum between (i) ice cap and (ii) ice field and alpine style glaciation. Chapter 3 introduces and tests novel geochronological techniques to permit widespread dating of glacial and hillslope deposits and to investigate sub-aerial weathering rates; a proxy for baseline erosional efficiency. In Chapter 4, these techniques are applied to glacial landforms, with results analysed in the context of recalibrated surface exposure ages (10Be, 36Cl). These data reveal complex patterns of ice advance/recession, with variable ice residence times and glacier configurations; complexity which places a first-order control on the magnitude and spatial focusing of erosion during glacial cycles. Chapter 5 presents a database of rock slope failure deposits (RSFs) to investigate the timing and significance of post-glacial slope instability. These data indicate that high-frequency, low magnitude RSFs (103 - 105 m3) can contribute significantly to mountain denudation, with a pulse in paraglacial erosion after deglaciation (127 - 148 mm ka-1), while the frequency and magnitude of interglacial RSFs is closely coupled to climatic drivers. In Chapter 6, cirque and geomorphometric analyses indicate that glacier configurations and the relative duration of maxima and marginal glacial conditions control mountain range morphology through the spatial focusing of erosion, with contrasting rates of valley and cirque incision between the studied regions. Chapter 7 assesses the long-term signature of glacial erosion, incorporating a range of geochronological, geomorphological and geomorphometric analyses. In turn, these data show that while glacial erosion has profoundly shaped the Wicklow Mountains, the morphological significance of glacial erosion in the Pyrenees wanes at large spatial scales and at low elevations; a trend which reflects the size, longevity and erosional efficiency of Quaternary glaciers. These results address the fundamental processes which control the efficiency, timing and focusing of mountain range denudation.

Date of Award	31 Dec 2019
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Philip Hughes (Supervisor) & Jonny Huck (Supervisor)