Glacial Landscape Evolution
From UNC Tectonic Geomorphology
The elevation of pleistocene glaciation and temperate mountain ranges are strongly correlated, suggestive that glacial erosion is the ultimate control of mountain range height. Although the impact of glaciation on alpine landscapes is obvious, it remains poorly understood how glacial erosion processes are distributed through a landscape, and thus how these landscapes may be expected to have evolved over time. This study seeks to calibrate glacial erosion processes from the form of progressively eroded alpine landscapes.
Field studies of alpine landscape evolution is presently focussed on the Kyrgyz Range of the western Tien Shan, central Asia and the Sierra Nevada of California. Several characteristics of the Kyrgyz Range lend its alpine landscapes uniquely suited to measuring glacial erosion processes. The range encompasses 4 km of relief from its permanently glaciated peaks at 4800 m elevation to the Chu basin on its northern margin at 800 m elevation. Thermochronology and structural geology indicate uplift and denudation rates of ~1 mm/yr over the range. Eastward propagation of the Kyrgyz Range uplift has progressively exhumed a pre-Cenozoic erosion surface bevelled onto resistant Paleozoic bedrock. The rocks beneath this surface remain virtually free of denudation until reaching the zone of pleistocene glaciation, whereupon glaciers incise and remove bedrock in a systematic and interpretable manner. This research, recenlty published in Geology, documents that the primary mechanism of intitial glacial erosion is via cirque retreat. Ongoing field studies of the Sierra Nevada take advantage of the high degree of preservation of glacial flow features to investigate and test models of the flow field within cirques to try to further understand the pattern of erosion there.
