HR: 13:55h
AN: T33D-02    [Abstracts]
TI: Co-evolution of spatial patterns of precipitation and topography
AU: * Anders, A M
EM: andersa@u.washington.edu
AF: University of Washington Department of Earth and Space Science, Box 351310, Seattle, WA 98195-1310 United States
AU: Roe, G H
EM: roe@ess.washington.edu
AF: University of Washington Department of Earth and Space Science, Box 351310, Seattle, WA 98195-1310 United States
AU: Durran, D R
EM: durrand@atmos.washington.edu
AF: University of Washington Department of Atmospheric Sciences, Box 351640, Seattle, WA 98195-1640 United States
AU: Montgomery, D R
EM: dave@ess.washington.edu
AF: University of Washington Department of Earth and Space Science, Box 351310, Seattle, WA 98195-1310 United States
AU: Hallet, B
EM: hallet@ess.washington.edu
AF: University of Washington Department of Earth and Space Science, Box 351310, Seattle, WA 98195-1310 United States
AB: A necessary step towards understanding the coupled climate-tectonics-erosion system is learning how, on geologic timescales, patterns of climatic forcing create patterns of erosion. Precipitation patterns in mountainous landscapes are strongly related to topography, while at the same time, precipitation fundamentally affects the ability of rivers and glaciers to erode, thus directly influencing topographic development. We present observations that reflect significant and robust connections between topography and precipitation and numerical models that show significant landscape modifications resulting from these feedbacks. Mesoscale numerical weather prediction via MM5 and field measurements in the Olympic mountains of Washington state reveal a sustained 2-4 fold enhancement of precipitation on ridges relative to valleys separated by horizontal distances of ~10 km and elevation differences of ~500 m. These strong gradients in precipitation are observed on annual, seasonal, and individual event timescales despite variability in wind speed, direction and temperature. In the Matheny ridge area, field measurements of rain and snow support numerical predictions of the location and amplitude of spatial gradients in precipitation. Incorporation of a linear precipitation model that reproduces, for the Olympics, the observed locations and magnitudes of spatial gradients in precipitation in the CASCADE landscape evolution model allows for exploration of the influence of spatial patterns of precipitation on topographic development. We present simulations of the co-evolution of precipitation and topography with a distribution of atmospheric conditions meant to simulate climatic variability. Additionally, we have modeled this co-evolution with several different imposed uplift patterns. Topography that co-evolves with precipitation is distinct from topography created under uniform precipitation conditions in several ways. First, on the windward side, precipitation is enhanced on ridges relative to valleys and results in smaller ridge-valley elevation differences and higher channel concavities than predicted by simple erosion laws. In addition, the topographic divide is shifted down wind and highest topography is shifted even farther down wind than the divide. On the lee side, rivers are deeply entrenched between high ridges and the ridge-valley elevation difference is more extreme while channel concavities are lower than predicted by erosion laws.
DE: 3394 Instruments and techniques
DE: 3309 Climatology (1620)
DE: 1815 Erosion and sedimentation
DE: 1824 Geomorphology (1625)
DE: 1894 Instruments and techniques
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting