MAPPING ROCKFALL SUSCEPTIBILITY IN THE STEEP ROCKY SLOPES OF SKAGWAY, ALASKA
Loading...
Date
2024-08-07
Authors
Wachino, Ian
Journal Title
Journal ISSN
Volume Title
Publisher
University of Oregon
Abstract
Rockfall is a common occurrence in steep mountainous terrain which poses a hazard to nearby communities. It is useful to determine the likelihood of rockfall initiating from a given location, or rockfall susceptibility, which is largely controlled by discontinuities in the rock mass. Rockfall susceptibility can be evaluated by identifying unfavorably oriented discontinuities that intersect with the face of a rock slope, a technique called kinematic analysis. Modern kinematic analyses use Digital Elevation Models to identify common failure modes and rockfall susceptible slopes at the scale of entire valleys.The area of interest for this study is the rugged topography surrounding Skagway, a small town in southeast Alaska that has been threatened by rockfalls that initiate from its steep valley walls. The aim of this study is to identify areas with high rockfall susceptibility, and compare the results to mapped talus deposits which are a proxy for past rockfall activity. In the granodiorite bedrock, two steeply dipping orthogonal joint sets, and a third set of sheeting joints were identified. The most prominent joint set dips steeply to the southeast, which predisposes northwest-facing rock slopes to block toppling failure. Kinematic tests show block toppling failure is more common than planar slide failure in the study area, particularly on the eastern sides of Skagway valley and Nahku Bay that generally face northwest. These findings are consistent with the more abundant talus deposits on the eastern sides Skagway valley Nahku Bay. Three distinct areas with particularly high rockfall susceptibility, and known rockfall source areas, were identified for further investigation and mitigation.