HR: 14:40h
AN: H43H-05    [Abstracts]
TI: A Hot Knife Through Ice-Cream: Earthflow Response to Channel Incision (Or Channel Response to Earthflows?), Eel River Canyon, California
AU: * Mackey, B H
EM: bmackey@uoregon.edu
AF: Department of Geological Sciences, 1272 University of Oregon, Eugene, OR 97403, United States
AU: Roering, J J
EM: jroering@uoregon.edu
AF: Department of Geological Sciences, 1272 University of Oregon, Eugene, OR 97403, United States
AU: McKean, J A
EM: jmckean@fs.fed.us
AF: USDA Forest Service, Rocky Mountain Research Station 322 E. Front St., Suite 401, Boise, ID USA, United States
AB: Abundant glacier-like earthflow features are recognized as a primary erosional process in the highly erodable Franciscan Melange of the Eel River Basin, CA. Despite their prominence in this "melting ice-cream" topography, many questions regarding their effects on the long term sediment flux from this rapidly eroding basin remain unresolved. For example, does an earthflow's basal shear zone propagate vertically downwards with vertical river incision? What controls the upslope and lateral extent of individual earthflows? How does the erosive power of a river influence the rate of earthflow movement, or conversely do earthflow toe deposits regulate the rate of river incision? Here we present preliminary findings derived from study of 200km2 of lidar data (1m resolution) covering hillslopes adjacent to 30km of the Eel River. Lidar allows detailed analysis of the interaction between earthflows and the drainage network, and we document how inferred changes in local base level are propagated throughout adjacent hillslopes via earthflow movement. The most active earthflows (determined by field surveying and analysis of aerial photos rectified using lidar- generated digital topography) coincide with locally steep sections of channel, while downstream of the most active flows we frequently observe less-active or dormant earthflows. This observation supports the idea that the locations of the most active earthflows coincide with headward propagating knickpoints in the channel. The rate of earthflow movement appears to slow when an earthflow exhausts the upslope area of easily mobilized sediment. Earthflow toes can protrude directly into the channel, causing the channel to narrow and steepen, and even undercut the opposite bank. Large resistant boulders (>2m diameter) transported by the earthflow accumulate in the streambed and appear to both act as a check on further channel incision and earthflow movement. In contrast, areas adjacent to active earthflows exhibit smooth hillslopes, which show little or no evidence for recent instability. Such unfailed hillslopes preferentially occur near ridges or adjacent to strath terraces, and appear to be largely isolated from the effects of channel incision.
DE: 1625 Geomorphology and weathering (0790, 1824, 1825, 1826, 1886)
DE: 1640 Remote sensing (1855)
DE: 1810 Debris flow and landslides
SC: Hydrology [H]
MN: 2007 Fall Meeting