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Title:
Analyzing the Spatial Pattern of Deep-Seated Landsliding Evidence for Base Level Control, South Fork Eel River, California
Authors:
Mackey, B. H.; Roering, J. J.; McKean, J.; Dietrich, W. E.
Affiliation:
AA(Department of Geological Sciences, 1272 University of Oregon, Eugene, OR 97403 United States ; ), AB(Department of Geological Sciences, 1272 University of Oregon, Eugene, OR 97403 United States ; ), AC(USDA Forest Service, Rocky Mountain Research Station 322 E. Front St., Suite 401, Boise, ID 83702 United States ; ), AD(Department of Earth and Planetary Science, University of California, Berkeley, CA 94720 United States ; )
Publication:
American Geophysical Union, Fall Meeting 2006, abstract #H53B-0619
Publication Date:
12/2006
Origin:
AGU
AGU Keywords:
1815 Erosion, 1826 Geomorphology: hillslope (1625)
Abstract Copyright:
(c) 2006: American Geophysical Union
Bibliographic Code:
2006AGUFM.H53B0619M

Abstract

Deep-seated landsliding is considered a major source of sediment in the rapidly uplifting Coast Ranges of Northern California, yet the geomorphic setting and consequences of landslides remain poorly understood. While the immediate triggers of deep slides are well-known, questions remain regarding long-term controls on slide location and activity. Hillslope base level changes and climate are often cited causal mechanisms for deep seated landsliding, yet unraveling their respective roles can prove challenging with Pleistocene and early Holocene landslides, many of which are effectively dormant under present environmental conditions. Here we document the spatial pattern of deep-seated landsliding in the headwaters of the South Fork Eel River in northern California, utilizing an extensive 230 km2 lidar dataset (1 m2 resolution). We find a high degree of coupling between the channel and adjacent hillslopes the spatial distribution of instability suggests that baselevel has a primary role in both initiating and partially reactivating deep seated landslides. We are able to distinguish two different spatial patterns of landsliding which we attribute to base level operating on different scales. In steep, low-order catchments, landsliding correlates strongly with knickpoints and local variations in the river long profile, suggesting vertical channel incision is a primary control on slope stability. Lithology modulates this pattern, as landslides in weak, argillaceous rocks impinge on the channel illustrating a tight channel-hillslope coupling, whereas more competent sandstone units preserve a transient inner gorge A different pattern of slope instability is evident along the main stem South Fork Eel River. The terrain at the inside edge of river bends is characterized by stable, classic ridge and valley topography, whereas slopes adjoining the outer edge of river bends exhibit abundant deep seated landsliding. This suggests that lateral planation of the river drives landsliding in the high-order sections of the South Fork, in contrast to the vertical pattern of incision observed in smaller catchments. The transition between the two processes appears to be controlled by slope and drainage area as well as zones of high terrace preservation. Accentuating the recent role of base level, some of the larger landslides contain newer slides nested within them, which are distinguishable from the host slide as they present a rougher surface and a characteristic internal headscarp. These inset slides can be attributed to a fall in base level, as the recent instability is proximate to the channel and the upper bench regions of the older slide remain largely unaffected. Both changes in climate and base level are likely to generate landsliding, and although their respective effects can prove difficult to distinguish, we see a strong signal of base level in the recent evolution of this landscape.
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