Dynamic analysis of an extraordinarily mobile rock avalanche in the Northwest Territories, Canada

Abstract

The pre-historic rock avalanche at Avalanche Lake was a spectacularly mobile rock avalanche that resulted in the largest documented runup of any landslide on earth. The runout of the 200 Mm3 event was a complex and three-dimensional process that created three distinct depositional lobes. There is some controversy as to whether the presence of glacial ice played an important role in the dynamics of this event. To investigate this hypothesis an advanced, three-dimensional numerical landslide runout model was used to reconstruct the dynamics of this event. It was found that a conventional runout model is able to reproduce the bulk characteristics of this event, including its spectacular runup, without accounting for glacial ice. A sensitivity analysis was performed to determine the factors that control the mobility of this event. It was found that low strength in the source zone, as well as the presence of significant internal strength, is required to reproduce the 600 m runup. This has important implications for the hazard analysis of rock avalanches. It appears as though large-volume rock avalanches can move with a friction angle lower than that expected for dry fragmented rock, and the runout process can be strongly influenced by internal strength. These important factors must be accounted for when performing forward analyses of this type of natural disaster.

The role of initial coherence and path materials in the dynamics of three rock avalanche case histories

“…The best-fit friction angles are 10°and 26°, respectively. The low friction angle in the source zone likely corresponds to extreme polishing of the planar basal rupture surface due to shearing under high normal stress (Cruden & Krahn 1978;Aaron and Hungr, 2016a). The friction angle along the path corresponds closely to that expected for dry fragmented rock (~30°, Hsu (1975)).…”

“…Blasio & Crosta (2015) demonstrated that a steep path combined with isotropic fragmentation can increase centre of mass displacement; however, the effect disappears for slope angles typical of rock avalanche paths. Coe et al (2016) and Aaron & Hungr (2016a) both invoked low basal friction due to entrainment and overriding of saturated soil to explain the dynamics of the West Salt Creek rock avalanche and the Avalanche Lake rock avalanche, respectively. In both cases, this hypothesis was supported by field evidence of entrained path material at the base of the deposit.…”

Collapse of Granular Columns With Fractal Particle Size Distribution: Implications for Understanding the Role of Small Particles in Granular Flows

“…Dry rock avalanches usually happen in the mountainous regions. These granular flows are among the most dangerous natural disasters and can cause extensive damages to the engineering structures because of their powerful ability to move freely from their sources and destructive impact energy (Aaron & Hungr, 2016;Robinson et al, 2015). Various mechanisms have been proposed to explain the extremely large flow mobility that particle flows exhibit, such as entrapped air fluidization (Kent, 1966), air cushion theory (Shreve, 1968), dust dispersion fluidization (Hsü, 1975), fluidization caused by acoustic energy (Collins & Melosh, 2003;Melosh, 1979), lubrication by liquefied saturated soil (Hungr & Evans, 2004), size segregation (Iverson et al, 2010;Roche et al, 2011), self-lubrication by molten rock at the base (De Blasio & Elverhøi, 2008;Goren & Aharonov, 2007), and dynamic rock fragmentation (Davies et al, 2010;Langlois et al, 2015).…”

Finite element analysis for rockfall and debris flow mitigation works

“…During the calibration process, the internal friction angle (φ i ) of the debris flow material was adjusted so that the simulated cable forces and barrier deformations match the field measurements. This parameter was chosen because it dictates the shear strength and energy dissipation of the debris flow as well as the flow-structure interaction (Ng et al, 2018a;Aaron and Hungr, 2016;Mancarella and Hungr, 2010). However, this parameter cannot be readily determined in the field and has to be back-analyzed .…”