The rock slope stability of high granitic-granodiorite domes has become of increasing concern over recent decades. As tourism increases in popularity the risk posed by rockfall from these domes has also increased. Using the 417 m high Stawamus Chief, in Squamish, BC, Canada as a case study, we describe the use of multi-sensor remote sensing in understanding the failure mechanisms and the factors controlling instability. The Grand Wall and the North Wall of Stawamus Chief experienced significant rockfalls in 2021. Remote sensing using LiDAR and thermal imaging has added to our understanding of rockfall at Stawamus Chief. The application of these methods is discussed through detailed characterization of the rock slopes. Evidence shows that potential causal failure processes include root jacking, freeze-thaw effects, heavy precipitation, and expansion of joints due to extreme heat.
Rockfalls are well documented in high granitic-granodiorite domes worldwide (e.g., Stock et al. 2013). Despite this hazard, these terrains form some of the most popular recreation areas in the world, Yosemite National Park, U.S.A, being the most famous example. Increased participation in outdoor recreational activities such as hiking, and rock climbing has heightened the risk posed to the public by these rockfalls. Stawamus Chief Provincial Park in Squamish, British Columbia, is no exception with BC Parks noting a province-wide increase in visitors of 26.5% between 2019 and 2022 (BC Gov. News, 2022). The 417m high granodiorite cliffs of Stawamus Chief dominate the landscape of the park and have produced numerous rockfall events in the past decade.
Stawamus Chief Provincial Park is located 60 km north of Vancouver, BC (Fig. 1). The Chief, as it is known locally, is a granodiorite pluton thought to have crystallized roughly 100 million years ago (Mathews and Monger 2005) and exhumed by tectonic processes involved in the formation of the Coast Mountain Range. During the last glaciation, ice was up to 2 km thick in the area, covering the Chief in ∼1300 m of ice (Turner et al. 2010). Tectonic and glacial unloading are thought to have led to the distinctive exfoliation joints observed at the Chief and other granitic domes (Hencher et al. 2011). The cliff faces consist predominantly of massive, unaltered rock with fresh to slightly weathered discontinuities. A rock mass assessment carried out on the Chief determined the rock mass quality as excellent, with GSI values between 80 and 90 (Tuckey 2012). A distinctive feature on the Grand Wall is the "Black Dyke", an intrusive mafic body steeply dipping at 80° and which has an estimated GSI value between 70 and 80 (Tuckey 2012).
