The cross-sectional characteristics of glacial valleys and their spatial variability

Glacial valleys are fundamental large-scale geomorphological landscape features that dissect mountain ranges. Their cross-sectional shape is recognised as distinct from fluvial valleys. They develop into the typical glacial ‘U-shaped’ valley as a consequence of the intensity and duration to which the valley has been exposed to glacial processes. Factors in such ‘U’ development have been related to climate, lithology and tectonic settings. This thesis presents a semi-automated GIS-based method for systematically measuring valley cross-sections over large areas such as across mountain divides and small mountain ranges like the Pyrenees. When compared to the traditional hand-drawn transect method the semi-automated method produced an equivalent of 857,781 transects; a 1,000 fold increase in data previously reported. Descriptive statistics are provided on cross-sectional area, form ratio and a measure of the tendency to a parabolic form (b-value) for 21,412 valleys sampled from Patagonia, the Southern Alps, New Zealand and the Pyrenees. By measuring the actual shape and size of valley cross-sections in large quantities and relating the data to proxies for ice residence time and flux, as well as landscape characteristics such as valley floor slope, climatic effects, tectonic uplift and lithology, insights into glacial processes and valley development were gained. To further understand how relationships varied spatially, Geographical Weighted Regression (a local scale statistical technique) was used in the sample areas. Results show that more intense and prolonged glaciation yields large, wide parabolic valley cross-sections, in contrast to predominant paradigm of valley deepening. A major finding was a link between valley cross-sectional widening and the flattening of the valley longitudinal profile.