## 3 Results
### Study Site A  
Study Site A is a 90 m section of steeply inclined (>60 degrees) road cut located along the Glenn Highway near milepost 85.5 (Figure 7). The exposed cliff is approximately 8 m in height, but ranges from 4-10 m in height. The southern portion of Alaska is located within an active subduction zone, and the geology of the state is largely a product of ongoing terrain accretion [55]. The Glenn Highway generally follows a glacially cut valley through the Matanuska and Chickaloon Formations, which consist of sedimentary materials of continental origin that were eroded during uplift of local mountain ranges and subsequently despotized in the region [56]. Rock at Site A consists of fine- to medium-grained, moderately weathered grey and tan hard sandstone of the Chickaloon formation. The rock mass includes three approximately orthogonal discontinuity sets that produce well-defined \(\sim\)10 to \(\sim\)30 cm rock blocks. Seepage was not observed during the fieldwork. Mass wasting at the site occurs through release of these blocks, leading to numerous small rockfalls. Figure 8: Results from an approximately 35 m section of exposed rock at Site A (0.05 m cell size surface model from 2013). Figure 7: Photograph of rock slope study Site A showing three well-defined discontinuity sets. Figure 8 shows a sample triangulated shaded relief surface model with all holes filled for Site A. This model was generated with a 0.05 m cell size and adequately preserves the blocky rock mass features present across the slope. Analysis indicated that 13% (2014) to 15% (2013 data) of rock slope surface area was comprised of filled holes. Figure 9 shows the rockfall clustering results with resolutions ranging from 0.01-0.50 m without hole filling. As expected, the size of the change clusters increases for the coarser resolution models. Figure 9: Rockfall clustering results between 2013 and 2014 with varying model resolution including (**A**) 0.01 m; (**B**), 0.05 m; (**C**) 0.10 m; (**D**) 0.20 m; and (**E**) 0.50 m for Site A (90 m). The grey indicates portions of the cliff that did not experience significant erosional change. (Note that these sections may have experienced accretion). Larger white sections indicate holes or spacing between centroid points. Other colors represent a rock cluster where material has dislodged from the cliff. Each cluster is given an ID and colored based on that ID with a repeating pattern so that they can be distinguished from one another. For simplicity of rendering, the point cloud was used rather than the surface model. Figure 10 presents cumulative magnitude-frequency relationships derived from the clustering analysis of both the filled and unfilled models. The form of the magnitude-frequency relationships are similar to those derived for other rock slopes (e.g., [57,58]), and include characteristic \"rollover\" for small volumes as well as linearity in log-log space across several orders of magnitude of volume. The rollover phenomenon in landslide magnitude-frequency relationships has been attributed to data ensuring that occurs when survey resolutions are approached [59]. The deviation from log-log linearity for large volumes has been noted by others (e.g., [57,58]) and attributed to the temporal ensuring that occurs over relatively short monitoring time periods. Figure 11a shows the estimated erosion volume calculated at different resolutions for models with and without hole filling. Note that for this analysis, hole filling window sizes varied with resolution and were selected such that small holes were filled, but larger holes that required excessive interpolation were not filled. The differences between erosion volumes calculated using models with holes filled _versus_ those without hole filling generally increase as cell size decreases, and reach a maximum when the cell size equals ~0.025 m (the maximum feasible modeling resolution given the acquisition sampling of this dataset).