HR: 14:55h
AN: H43H-06    [Abstracts]
TI: Progressive Landslides in Uplifted Volcanic Plateaus: Persistent Loci of Channel Perturbation
AU: * Safran, E B
EM: safran@lclark.edu
AF: Environmental Studies Program, Lewis & Clark College, Portland, OR 97219, United States
AU: Anderson, S W
EM: swa@lclark.edu
AF: Physics Department, Lewis & Clark College, Portland, OR 97219, United States
AU: Mills-Novoa, M
EM: meganm@lclark.edu
AF: Environmental Studies Program, Lewis & Clark College, Portland, OR 97219, United States
AU: Othus, S
EM: othuss@cwu.edu
AF: Department of Geological Sciences, Central Washington University, Ellensburg, WA 98926, United States
AU: Ely, L
EM: ely@cwu.edu
AF: Department of Geological Sciences, Central Washington University, Ellensburg, WA 98926, United States
AU: House, P K
EM: khouse@unr.edu
AF: Nevada Bureau of Mines and Geology, University of Nevada, Reno, NV 89557, United States
AU: O'Connor, J E
EM: oconnor@usgs.gov
AF: U. S. Geological Survey, Oregon Water Science Center, Portland, OR 97201, United States
AU: Grant, G
EM: gordon.grant@oregonstate.edu
AF: U. S. D. A. Forest Service, Pacific Northwest Station, Corvallis, OR 97331, United States
AU: Fenton, C
EM: crfenton@gfz-potsdam.de
AF: GeoForschungsZentrum Potsdam, Section 4.2, Telegrafenberg B123, Potsdam, 14473, Germany
AU: Beebee, R A
EM: robin.beebee@gmail.com
AF: U. S. D. A. Forest Service, Tongass National Forest, Sitka, AK 99835, United States
AB: The semi-arid uplifted volcanic plateaus of the southern interior Columbia River basin contain over 300 large landslides or landslide complexes, ranging in area from several tenths of a km² to several tens of km². The distribution of these landslides is dominated by the outcropping of key stratigraphic contacts between coherent, volcanic cap rock atop weak sedimentary or volcaniclastic units in areas of >100 m local relief. The morphologies of many of these landslide complexes suggest a progressive mode of mass movement, with rubble-capped failure slices arrayed downslope at intervals of 10s to 100s of meters and deep tension cracks separating incipient failure blocks from the intact headscarp. Field evidence from the Owyhee River in southeastern Oregon indicates that individual landslide complexes can persist for millions of years. In one reach, for example, remnants of a 1.9 million year old intracanyon lava flow are inset against ancient landslide blocks. In the same location, cosmogenic isotope dating of boulders on a likely dam-burst flood deposit reveal a channel-blocking mass movement that may be as young as Holocene in age. The persistence of these landslide complexes has important implications for channel evolution, as it suggests that, in some environments, sediment supply may be chronically elevated at point sources. On the basis of GIS-based mapping of regional landslides and on field study of individual landslide complexes, we hypothesize that: 1) this sediment supply becomes increasingly dominated by fine-grained material as channels progressively incise into the weak units underlying coherent lava caps; and 2) the mass movements that impinge on the channels become correspondingly more earthflow-like. Loci of persistent landsliding are also subject to episodic variations in channel width due to physical constrictions caused by impinging failure masses. The discrete localization of large landslide complexes by particular stratigraphic and topographic characteristics and the potential for long- term channel perturbation driven by such complexes requires re-consideration of continuous representations of discharge, sediment supply, channel bed erodibility, and channel width in fluvial incision models.
DE: 1815 Erosion
DE: 1817 Extreme events
DE: 1819 Geographic Information Systems (GIS)
DE: 1825 Geomorphology: fluvial (1625)
DE: 1826 Geomorphology: hillslope (1625)
SC: Hydrology [H]
MN: 2007 Fall Meeting