xvi, 136 p. : ill. (some col.) A print copy of this thesis is available through the UO Libraries. Search the library catalog for the location and call number. / This dissertation discusses the contribution of deep-seated landslides and earthflows to the morphology, erosion, and evolution of mountainous landscapes, focusing on the northern California Coast Ranges. In active landscapes, channel incision is necessary to create relief but also increases stresses in adjacent hillslopes, ultimately leading to slope failure. While conceptually simple, the spatial relationships between channel incision and landsliding have not been well quantified. Along the South Fork Eel River, I mapped the distribution of deep-seated landslides using light detection and ranging (LiDAR) derived maps. Landslide density increases in regions subject to late Pleistocene-Holocene channel incision and particularly in response to lateral incision at the apex of meander bends. Wavelet analysis of channel sinuosity reveals hillslopes are most sensitive to meander wavelengths of 1.5 km. Argillaceous lithology generates abundant earthflow activity along the main stem Eel River, yet spatial and temporal patterns of earthflow movement are poorly understood. I undertook a detailed study of the Kekawaka Earthflow using LiDAR, meteoric 10 Be in soil, orthorectified historical aerial photographs, and field surveys. Inventories of 10 Be in soil pits increase systematically downslope, indicate an average movement rate of 2.1 ± 1.3 m/a over the past 150 years, and establish a minimum earthflow age of 1700 years. The Kekawaka earthflow has a systematic history of movement, both spatially, with greatest movement in the narrow transport zone, and temporally, as velocities peaked in the 1960's and have slowed since 1981. I used LiDAR and aerial photographs to map earthflow movement and calculate sediment flux across 226 km 2 of the main stem Eel River. From 1944-2006, 7.3% of the study area was active, and earthflows account for an erosion rate of 0.53 ± 0.04 mm/a, over half the regional average sediment yield. Velocity time series on 17 earthflows suggest temporal earthflow behavior is influenced by decadal-scale changes in precipitation, temperature, and river discharge, although local topographic factors can overwhelm this climatic signal. When active, earthflows erode an order of magnitude faster than surrounding terrain; however, source supply limitations appear to govern long- term earthflow evolution. This dissertation includes previously published coauthored material. / Committee in charge: Joshua Roering, Chairperson, Geological Sciences; Ilya Bindeman, Member, Geological Sciences; Dean Livelybrooks, Member, Physics; Ray Weldon, Member, Geological Sciences; W. Andrew Marcus, Outside Member, Geography

Master of Arts / Department of Geography / Richard A. Marston / The Black Vermillion River (watershed area = 1310 square kilometers) contributes runoff and sediment into Tuttle Creek Reservoir, a large federal reservoir (volume = 327 million cubic meters) northeast of Manhattan, Kansas. Tuttle Creek, completed in 1962, is filling with sediment faster than other federal reservoirs in the region. The Reservoir’s conservation pool is about 40 percent full of sediment and is predicted to fill by 2023. Debate rages over the relative contribution of sediment from upland sources (largely croplands and pasture) versus channel incision. In the Black Vermillion watershed, bedrock is overlain in most of the watershed by pre-Illinoian age easily erodible glacial till and loess. Row crop agriculture is the most common land use in the watershed and stream channels are incised and prone to frequent flooding and channel instability. This research focused on the spatial extent, timing, and causes of channel incision in the Black Vermillion watershed. I conducted a watershed-wide survey of channel cross-sections in 56 locations repeated at sites that had been surveyed 45 years ago by the Soil Conservation Service. Further, I collected channel cross sections in 2008 at a total of 51 more locations for a total of 107 study sites. Channel depths between 1963 and 2008 increased by a mean of 1.6 meters (maximum = 5.2 meters). Most channels throughout the watershed have incised, are actively incising, or incising and widening. Statistical testing between channel depths as measured in 1963 and 2008 showed that the amount of incision was related to land use/land cover, riparian buffer widths, upstream drainage area, and geology. As channels incise, they progress through six stages of channel evolution, which complicates the relationship between channelization and incision. Channel stage, as identified in the field, was statistically related to geology, occurrence and timing of channelization, land use/land cover, and upstream drainage area. Channelization has reduced channel length by a significant portion and was identified as one of the leading causes of incision. This finding suggests that planting buffers and/or expanding existing buffers along streams should be encouraged in the watershed to alleviate flooding and channel instability.