The movement characteristics of five landslides are compared and interpreted based on records of approximately 10-years duration. Condon landslide in the Oregon Coast Range has consistently exhibited brief (1 - 8 days) movement episodes in wet winter months, separated by long periods of no movement. The translatory movement is probably controlled by the orientation and structure of the underlying sedimentary rocks. From 1981 to 1990, annual movement averaged 109 mm, and individual events varied from 1 to 187 mm. All major movement events (> 10 mm in 4-10 days) were precipitation-induced. A non-linear relationship exists between movement rates and Antecedent Precipitation Index, which has a daily recession coefficient of 0.87. The API threshold for movement initiation was estimated to be 160 mm, based on 16 documented major events between 1984 and 1990. Groundwater level at the landslide responded to precipitation very quickly, with lag time usually less than 3 days. Movement started on days when the groundwater level rose above 2.5 m below ground surface, and a non-linear relationship exists between daily movement rate and groundwater level. Based on available data, there appears to be no change in movement characteristics of Condon landslide after two-third of it was clearcut in 1987. Wilhelm landslide, located near Condon landslide, has a similar movement pattern, but smaller movement magnitude (averaged 34 mm per year, 1985-1990). The Mid-Santiam and Jude Creek landslides in the volcanic terrane of the western Cascade Range move at much faster rates, averaging 3.8 and 7.8 m per year from 1982 to 1990, respectively. Unlike the Condon and Wilhelm landslides, where individual movement events correspond with individual storms, these two western Cascades landslides exhibit prolonged movement. The Mid-Santiam landslide moves all year, and annual movement shows little variation over the year. The other studied landslides all have large intra- and interannual variation in movement rates, and movement generally stops in the summer dry period. The Lookout Creek landslide (average annual movement = 79 mm, 1981-1990) has slowed in the past four years, and has exhibited movement patterns similar to the storm-dominated Coast Range slides. Geology and climatic patterns are the two most important factors contributing to the observed differences in timing and style of movement in the landslides studied. Climatic patterns trigger movement events, and geology influences movement patterns through control on geotechnical properties of landslide materials. These factors can be used to classify landslide movement patterns on a regional scale. / Graduation date: 1992

Timber management of coastal watersheds in southwest Oregon has been complicated by the need to protect anadromous fish habitat from accelerated stream sedimentation resulting from management activity. The rugged terrain of the Elk and Sixes River basins is underlain by the complex geological province of the Klamath Mountains, in which landslides are a common, natural, and important process of sediment production. A landslide investigation, using sequential aerial photographs which covered a time period of 37 years, was used to determine relationships between mass-wasting, geologic types, and timber harvest practices. Averaged over all rock types, harvested areas showed an increase in failure rate of 7 times, and roaded areas an increase of 48 times that of forested terrain. Terrane underlain by dioritic intrusions was the most sensitive to road-related activity, with an increase in failure rate of up to 108 times that of comparable unmanaged land. The complexity of lithologies and deformational history in the area strongly influence slope morphology, and produces characteristic soil types which experience predictable modes and rates of slope failure. Debris slides and torrents are the dominant form of mass-wasting in dioritic and Cretaceous sedimentary terrane. Areas underlain by more clay-rich metamorphic bedrock are prone to slumps and planar streambank failures. Stream morphology is profoundly influenced by both rock type and geologic structure. Within an area characterized by steep, deeply incised streams, several persistent low-gradient reaches were delineated. These low-gradient stream reaches occur where (1) large landslides have locally raised channel bed elevation and (2) valley-floor widening has occurred in sheared rocks along fault zones or in more readily eroded rock types upstream of rock types resistant to fluvial erosion. / Graduation date: 1987

A landslide inventory was conducted for the Redland and Estacada Quadrangles of western Oregon using LiDAR DEMs. Many of these landslides were field verified. In total, 957 landslides were mapped using LiDAR whereas previously, only 228 landslides were believed to exist in the study area based on SLIDO information. In Milo McIver State Park, 41 landslides were mapped using LiDAR. SLIDO indicated only three landslides present within the park. A sequence of seven terraces of the Clackamas River is mapped in Milo McIver State Park. Landslides in the park predominantly occur between these terraces. Soils studied from representative areas within landslide complexes and terrace surfaces help to formulate a soil chronosequence for the study area. The youngest soils, Entisols, develop in less than 1,600 years, Inceptisols between 1,600-10,000 years, and the oldest soils, Alfisols, develop in at least 10,000 years. Classifications of soil profiles netted ten Alfisols (mainly on upper terraces), 49 Inceptisols, and 20 Entisols (reactivated slides in the complexes). The soils are predominantly ML soils and have Loam and Silt Loam textures. Results of spectral analysis, carried out on the LiDAR DEMs, indicate that the spectral character of landslides changes with age. However, applying statistical tools such as the Kolmogorov-Smirnov test (K-S test) and cluster analysis suggest that it is not possible to use spectral analysis to determine the relative age of failed surfaces. The K-S test showed that the spectral character among landslides varies widely. Cluster analysis resulted groupings not based on age or terrain type. The result of the cluster analysis illustrates that it may not be realistic to use a single cutoff, which separates failed terrain from unfailed, in the spectral distributions to analyze an entire region. In all, the results of the spectral analysis were not conclusive. Individual landslides, not complexes, should be used in future studies, since complexes have slides that are continually reactivating. The landslides were also too young to display very much differentiation in age based on soils and spectral analysis. Essentially, a similar study should be conducted using individual landslides with a large age range for more conclusive results.

Landslide hazard assessment of densely forested, remote, and difficult to access areas can be rapidly accomplished with airborne light detection and ranging (lidar) data. An evaluation of geomorphic change by lidar-derived digital elevation models (DEMs) coupled with geotechnical soils analysis, aerial photographs, ground measurements, precipitation data, and numerical modeling can provide valuable insight to the reactivation process of unstable landslides. A landslide was selected based on previous work by Mickleson (2011) and Burns et al. (2010) that identified the Madrone Landslide with significant volumetric changes. This study expands on previous work though an evaluation of the timing and causation of slope failure of the Madrone Landslide. The purpose of this study was to evaluate landslide morphology, precipitation data, historical aerial photographs, ground crack measurements, geotechnical properties of soil, numerical modeling, and elevation data (with multi-temporal lidar data), to determine the conditions associated with failure of the Madrone Landslide. To evaluate the processes involved and timing of slope failure events, a deep seated potentially unstable landslide, situated near the contact of Eocene sedimentary and volcanic rocks, was selected for a detailed analysis. The Madrone Landslide (45.298383/-123.338796) is located in Yamhill County, about 12 kilometers west of Carlton, Oregon. Site elevation ranges from 206 meters (m) North American Vertical Datum (NAVD-88) near the head scarp to 152 m at the toe. The landslide is composed of two parts, an upper more recent rotational slump landslide and a lower much older earth flow landslide. The upper slide has an area of 2,700 m2 with a head scarp of 5-7 m and a volume of 15,700 m3. The lower earth flow has an area of 2300 m2, a head scarp of 15 m, and a volume of 287,500 m3. Analysis of aerial photographs indicates the lower slide probably originated between 1956 and 1963. The landslide is located at a geologic unit contact of Eocene deep marine sedimentary rock and intrusive volcanic rock. The landslide was instrumented with 20 crack monitors established across ground cracks and measured periodically. Field measurements did not detect ground crack displacement over a 15 month period. Soil samples indicate the soil is an MH soil with a unit weight of 12 kN/m3 and residual friction angle of 28φ'r which were both used as input for slope stability modeling. Differential DEMs from lidar data were calculated to generate a DEM of Difference (DoD) raster to identify and quantify elevation changes. Historical aerial photograph review, differential lidar analysis, and precipitation data suggest the upper portion of the landslide failed as a result of the December 2007 storm.

Landslides represent a serious hazard to people and property in the Pacific Northwest. Currently, the factors leading to sudden catastrophic failure vs. gradual slow creeping are not well understood. Utilizing high-resolution monitoring techniques at a sub-annual temporal scale can help researchers better understand the mechanics of mass wasting processes and possibly lead to better mitigation of their danger. This research used historical imagery analysis, precipitation data, aerial lidar analysis, Structure from Motion (SfM) photogrammetry, terrestrial laser scanning (TLS), and hydrologic measurements to monitor displacement of the Silt Creek Landslide in the western Cascade Mountain Range in Linn County, Oregon. This landslide complex is ~4 km long by ~400 m wide. The lower portion of the landslide reactivated following failure of an internal scarp in June 2014. Precipitation was measured on site and historical precipitation data was determined from a nearby SNOTEL site. Analysis of aerial lidar data found that the internal scarp failure deposited around 1.00x106 m3 of material over an area of 1.20x105 m2 at the uppermost portion of the reactivated slide. Aerial lidar analysis also found that displacement rates on the slide surface were as high as 3 m/yr during the 2015 water year, which was the year immediately following the failure. At the beginning of the 2016 water year, very low altitude aerial images were collected and used to produce point cloud data, via SfM, of a deformed gravel road which spans a portion of the reactivated slide. The SfM data were complimentary to the aerial and TLS scans. The SfM point cloud had an average point density of >7500 points per square meter. The resulting cloud was manipulated in 3D software to produce a model of the road prior to deformation. This was then compared to the original deformed model. Average displacement found in the deformed gravel road was 7.5 m over the 17 months between the scarp failure and the collection of the images, or ~3 m/yr. TLS point clouds were collected quarterly over the course of the 2016 water year at six locations along the eastern margin of the reactivated portion of the landslide. These 3D point cloud models of the landslide surface had an average density of 175 points per square meter. Scans were georeferenced to UTM coordinates and relative alignment of the scans was accomplished by first using the iterative closest point algorithm to align stable, off-slide terrain, and then applying the same rigid body translation to the entire scan. This was repeated for each scan at each location. Landmarks, such as tree trunks, were then manually selected at each location and their coordinates were recorded from the initial scan and each successive scan to measure displacement vectors. Average annual displacement for the 2016 water year ranged from a maximum of 0.92 m/yr in the uppermost studied area of the slide, to a low of 0.1 m/yr at the toe. Average standard deviation of the vectors of features on stable areas was 0.039 m, corresponding to a minimum detectable displacement of about ±4 cm. Displacement totals decreased with increasing distance downslope from the internal scarp failure. Additionally, displacement tended to increase with increasing distance laterally onto the slide body away from the right margin at all locations except the uppermost, where displacement rates were relatively uniform for all landmarks. Volumetric discharge measurements were collected for Silt Creek in 2016 using salt dilution gauging and found that discharge in the upslope portion of the study area was ~1 m3/s and increased to ~1.6 m3/s in the downslope portion. Landslide displacement rates were found to be much lower during the 2016 water year than during the 2015 water year, despite higher precipitation. This suggests that the over-all displacement trend was decoupled from precipitation values. Displacement rates at all locations on the slide decreased with each successive scan period with some portions of the landslide stopping by autumn of 2016, suggesting the study captured the slide as it returned to a state of stability. The spatial and temporal pattern of displacement is consistent with the interpretation that the landslide reactivation was a response to the undrained load applied by the internal scarp failure. This finding highlights the importance of detailed landslide monitoring to improve hazard estimation and quantification of landslide mechanics. This study provides new evidence that supports previous research showing that internal processes within landslide complexes can have feedback relationships, combines several existing 3D measurement tools to develop a detailed landslide monitoring methodology, uses a novel approach to landslide surface deformation measurements using SfM, and suggests that landslide initiation models which rely heavily on precipitation values may not account for other sources of landslide activation.

The West Tidewater earthflow, one of the largest in Oregon's history, occurred in December of 1994. The earthflow is located approximately 15 km north of Jewel, Oregon near the summit ofthe Northern Oregon Coast Range Mountains. The earthflow is 900 m long and 250 m wide, giving it a surface area of 9 ha, or 22 acres. Volume is 3.5 million m3. The earthflow occurred in low strength, well-bedded, tuffaceous, carbonaceous, micaceous, clay-rich mudstone, and very fine-grained, feldspathic, clay-rich siltstone of the lower Miocene age Northrup Creek Formation. The soil clay fractions contain up to 90% smectite with indications ofhalloysite. This earthflow is a reactivation ofa 650-year-old landslide (C-14 dating of uncovered buried trees). The failure mode is examined using a Janbu slope analysis and includes double wedge failure near the headscarp. High soil pore water pressure is one of the major causes of this slope failure. Rainfall levels for October, November, and December of 1994 were twice the previous five-year average. Present day groundwater level within the basin is less than one meter below ground surface. The earthflow is partially controlled by two faults of regional extent that dissect the basin near the headscarp in NW-SE and NE-SW directions. The Inceptisol soils in the basin remain moist below 20 cm year around. Soil in the basin may have been further weakened due to loss of root strength following timber harvest on the site in 1991. Soil liquid limits range from 42% to 95%, with PI values ranging from 2% to 77%. Soil clay content ranges between 18% and 30%. Direct shear tests on the mudstone and siltstone bedrock in both drained and undrained conditions produced internal friction angles of 14-18°, with cohesion values of 4 - 8 kPa. Back calculation of study area soil strength using the modified Bishop method results in a residual friction angle of 20.7°. The failure mode ofthe earthflow is from the headscarp downward and is modeled using Janbu methods. The study includes a detailed topographic map and a failure analysis of the earthflow basin.

LiDAR (Light Detection and Ranging) elevation data were collected in the Panther Creek Watershed, Yamhill County, Oregon in September and December, 2007, March, 2009 and March, 2010. LiDAR derived images from the March, 2009 dataset were used to map pre-historic, historic, and active landslides. Each mapped landslide was characterized as to type of movement, head scarp height, slope, failure depth, relative age, and direction. A total of 153 landslides were mapped and 81% were field checked in the study area. The majority of the landslide deposits (127 landslides) appear to have had movement in the past 150 years. Failures occur on slopes with a mean estimated pre-failure slope of 27° ± 8°. Depth to failure surfaces for shallow-seated landslides ranged from 0.75 m to 4.3 m, with an average of 2.9 m ± 0.8 m, and depth to failure surfaces for deep-seated landslides ranged from 5 m to 75m, with an average of 18 m ± 14 m. Earth flows are the most common slope process with 110 failures, comprising nearly three quarters (71%) of all mapped deposits. Elevation changes from two of the successive LiDAR data sets (December, 2007 and March, 2009) were examined to locate active landslides that occurred between the collections of the LiDAR imagery. The LiDAR-derived DEMs were subtracted from each other resulting in a differential dataset to examine changes in ground elevation. Areas with significant elevation changes were identified as potentially active landslides. Twenty-six landslides are considered active based upon differential LiDAR and field observations. Different models are used to estimate landslide susceptibility based upon landslide failure depth. Shallow-seated landslides are defined in this study as having a failure depth equal to less than 4.6 m (15 ft). Results of the shallow-seated susceptibility map show that the high susceptibility zone covers 35% and the moderate susceptibility zone covers 49% of the study area. Due to the high number of deep-seated landslides (58 landslides), a deep-seated susceptibility map was also created. Results of the deep-seated susceptibility map show that the high susceptibility zone covers 38% of the study area and the moderate susceptibility zone covers 43%. The results of this study include a detailed landslide inventory including pre-historic, historic, and active landslides and a set of susceptibility maps identifying areas of potential future landslides.

The Little North Santiam River Basin is a 111-square mile watershed located in the Cascade Range of western Oregon. The Little North Santiam River is a major tributary to the North Santiam River, which is the primary source of drinking water for Salem, Oregon and surrounding communities. Consequently, water quality conditions in the Little North Santiam River, such as high turbidity, affect treatment and delivery of the drinking water. Between 2001 and 2008, suspended-sediment loads from the Little North Santiam River accounted for 69% of the total suspended-sediment load that passed the treatment plant. Recent studies suggest that much of this sediment originates from landslide activity in the basin. Using airborne Light Detection and Ranging (LiDAR)-derived imagery, 401 landslides were mapped in the Little North Santiam River Basin. Landslide types vary by location, with deep-seated earth flows and earth slumps common in the lower half of the basin and channelized debris flows prominent in the upper basin. Over 37% of the lower basin shows evidence of landslide activity compared to just 4% of the upper basin. Instream turbidity monitoring and suspended-sediment load estimates during the winter of 2009-2010 demonstrate a similar distribution of sediment transport in the basin. During a 3-month study period, from December 2009 through February 2010, the lower basin supplied 2,990 tons, or 91% of the suspended-sediment load to the Little North Santiam River, whereas the upper basin supplied only 310 tons of sediment. One small 23-acre earth flow in the lower basin, the Evans Creek Landslide, supplied 28% of the total suspended-sediment load, even though it only comprises 0.0004% of the basin. The Evans Creek Landslide is an active earth flow that has been moving episodically since at least 1945, with surges occurring between 1945 and 1955, 1970 and 1977, in February 1996, and in January 2004. Recent erosion of the landslide toe by Evans Creek continues to destabilize the slope, supplying much of the sediment measured in the Little North Santiam River. Over the last 64 years, the average landslide movement rate has been between 5 and 12 feet per year.