HR: 0800h
AN: H31A-1278    [Abstracts]
TI: Transient fluvial incision in the upper reaches of the Yellow River: Base-level fall or differential rock uplift?
AU: * Harkins, N
EM: nharkins@geosc.psu.edu
AF: Penn State University, Department of Geosciences, Deike Building, University Park, PA 16802 United States
AU: Kirby, E
EM: ekirby@geosc.psu.edu
AF: Penn State University, Department of Geosciences, Deike Building, University Park, PA 16802 United States
AU: Heimsath, A
EM: arjun.heimsath@dartmouth.edu
AF: Darmouth College Department of Earth Sciences, 6105 Fairchild Hall, Hanover, NH 03755 United States
AU: Kline, K
EM: worldonmyfinger@hotmail.com
AF: Penn State University, Department of Geosciences, Deike Building, University Park, PA 16802 United States
AB: Fluvial incision into bedrock may be a consequence of locally high rates of rock uplift, changes in sediment supply and bed state, or upstream propagation of incision driven by downstream changes in baselevel. Deconvolving these effects is critical to interpretation of rates and patterns of active deformation from landscape morphology. Here we combine observations of fluvial channel profiles extracted from SRTM data with field measurements of erosion rate to place constraints on the incision history along the upper reaches of the Yellow River. As the Yellow River drains northward from its headwaters on the Tibetan Plateau (Qinghai and Gansu provinces) to lower elevation regions of northeastern Tibet, it transitions from a wide, low gradient alluvial river to a narrow, steep river inset in a 2km deep bedrock gorge. These differences in channel form and inferred incision rate might be attributed to differential rates of rock uplift along the Yellow River. Analysis of trunk and tributary channel profiles, however, reveal systematic spatial patterns in channel gradient; tributary channels exhibit strongly convex, steep lower reaches immediately above their junctions with the Yellow River. The upstream extent of these convex reaches depends on tributary size and position along the Yellow River. Cosmogenic isotope concentrations in sediment collected from first and second-order tributaries indicate relatively slow erosion rates (~0.1-0.2 mm/yr) above convex channel reaches and increased erosion rates (~0.4-0.5 mm/yr) adjacent to convex reaches. Together, these data suggest that the Yellow River experienced a recent increase in incision rate and that tributary profiles are transient. The cause of this recent incision remains uncertain; possibilities include evacuation of Tertiary basin fill downstream of the mountain range and/or a recent change in rock uplift rates. Radiometric dating of terrace surfaces along the Yellow River (in progress) will allow reconstruction of the spatial distribution, timing, and rate of incision along the river. Together with analysis of channel profiles these data should help resolve driving mechanisms for transient fluvial incision within northeastern Tibet.
DE: 1822 Geomechanics
DE: 1824 Geomorphology: general (1625)
DE: 8175 Tectonics and landscape evolution
DE: 8177 Tectonics and climatic interactions
SC: Hydrology [H]
MN: Fall Meeting 2005