Landsat image of the East Kyrgyz Range. The white areas are glacier-capped peaks, and the broad eroded upland area southeast of these peaks is an exhumed pre-Cenozoic erosion surface.
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.
Small Late Pleistocene cirque cut into the pre-Cenozoic erosion surface.
Field study of alpine landscape evolution is presently focussed on the Kyrgyz Range of the western Tien Shan, central Asia. 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 project seeks to interpret and model the processes responsible for this pattern of glacial and related fluvial erosion and sediment transport.
Enhanced frost weathering as the erosion surface is advected to high altitude overwhelms the landscape with hillslope debris.
Detailed field studies in 2002 and 2003 have revealed a complex interplay of glacial, fluvial, and periglacial processes. In addition to a significant impact of glacial erosion, insufficient sediment transport out of the alpine landscape was discovered to play a key role in limiting deep incision of bedrock. Even before rocks reach the zone of glaciation, periglacial intensification of hillslope weathering significantly alters the balance between fluvial erosion and transport.
Deeply incised Ala Medin canyon, central Kyrgyz Range.
Eventually, fluvial incision 'catches up' to the glacially modified landscapes, carving deeply incised canyons in the central Kyrgyz Range. Progressive evolution of these canyons, as revealed by comparison to more youthful parts of the Kyrgyz Range, supports significant lateral adjustment of bedrock stream courses through time that gradually leads to formation of an optimal channel network over probably several million years.