Transient River Networks
From UNC Tectonic Geomorphology
River incision into bedrock connects tectonic uplift to erosion of landscapes by translating base level through a mountain range. This project aims to understand how the pattern and rate of river incision is established across a mountain landscape, and how these parameters adjust to changing tectonic and base level boundary conditions. Basement-cored uplifts of the Kyrgyz Tien Shan exhume a regional pre-Cenozoic erosion surface that acts as a marker of erosion depth. Because rocks beneath this surface are much more resistant than the rocks above, exhumation of the surface effectively resets the landscape, yielding a unique laboratory to study river incision patterns.
Two field sites are presently under study. Gory Baybieche, in central Kyrgyzstan, consists of a single tilted slab of bedrock capped by the pre-Cenozoic erosion surface on its north side. Denudation of the Naryn basin is gradually exhuming this surface from beneath its Miocene sedimentary cover. River incision into this surface progresses systematically as the surface is exhumed and as channels gather catchment area upstream. The interplay of these processes determines how deeply channels are incised into the erosion surface.
The second site of field study is the Kyrgyz Range, located in northern Kyrgyzstan and the site of a parallel study of alpine landscape evolution. Rivers working in tandem with glaciers at higher altitude carve deeply incised bedrock channels into the Kyrgyz Range. Recent field work has documented that significant lateral migration of bedrock stream channels does occur, even though these streams appear to have reached an equilibrium graded profile. These findings have important implications for how mountainous landscapes can adjust over time and why regular patterns of river networks emerge. Further testing of these ideas is presently underway using GIS-enabled analysis and comparison of river networks in Kyrgyzstan and other orogenic settings.
