HR: 17:00h
AN: H34B-04    [Abstracts]
TI: Determining the Topographic Manifestation of Widespread Landsliding with High Resolution Airborne Laser Swath Mapping (ALSM) Data, South Fork Eel River, Northern California.
AU: * Mackey, B H
EM: bmackey@darkwing.uoregon.edu
AF: University of Oregon, Department of Geological Sciences 1272 University of Oregon, Eugene, OR 97403-1272 United States
AU: Roering, J J
EM: jroering@uoregon.edu
AF: University of Oregon, Department of Geological Sciences 1272 University of Oregon, Eugene, OR 97403-1272 United States
AU: Dietrich, W E
EM: bill@geomorph.berkeley.edu
AF: University of California, Berkeley, Earth and Planetary Science University of California, Berkeley 307 McCone Hall , Berkeley, CA 94720-4767 United States
AB: Long-term average uplift rates in Northern California are as high as 1-5mm/yr, yet in many areas the relief remains modest due to pervasive slope instability. Here, we analyze deep-seated hillslope instability using an extensive ALSM dataset covering 230 km2 of the South Fork Eel River in Northern California. Through a combination of geomorphic mapping and statistical terrain analysis, we identify ubiquitous deep-seated landslide and earthflow features, whose locations are strongly correlated with underlying Franciscan m‚lange lithology, large-scale structural features, and connectivity to channels. In contrast to the well-ordered ridge-valley topography of unfailed hillslopes, deep-seated landslides present a rough or hummocky surface due to movement and internal deformation of the sliding mass. Such landslides are therefore ideally suited to recognition by various techniques that statistically measure small-scale variations in topographic roughness. To objectively identify and characterize landslide features using a process-based framework, we employed surface roughness algorithms and hillslope hydraulic models. Our techniques are clearly able to identify and delineate the extent and surface features of landslide prone terrain. We find a high correlation between slope instability and low values of drainage area per unit contour width (a/b). Active landslides have a marked impact on the hillslope hydrology by retarding the ability of the channels to incise and establish a drainage network, thus promoting large areas with significantly low a/b values compared to surrounding unfailed terrain. The landslides and earthflows are a major geomorphic process in the study area, as greater than 50 percent of the landscape is affected. Flows with a rougher surface, which we interpret to be more active than flows with smoother surfaces, are proximate to active stream channels suggesting undercutting of the toe is a primary control on the rate of slide movement. By analyzing stream profiles, we observe the signature of hillslope instability in the wake of knickpoints that appear to migrate upstream. This study illustrates the potential of ALSM in objectively analyzing large-scale hillslope instability with techniques that go beyond interpreting high-resolution shaded relief maps. ALSM will help underpin a process-based understanding of landslide behavior and mechanics.
DE: 1810 Debris flow and landslides
DE: 1826 Geomorphology: hillslope (1625)
SC: Hydrology [H]
MN: Fall Meeting 2005