Scenario-Based Volcano Slope Stability Hazard Analysis: Case Study of Augustine Volcano, Alaska

Volcanoes worldwide have undergone cyclic destruction of their edifices, generating catastrophic volcanic debris avalanches. Augustine Volcano in Alaska, USA, has a history of debris avalanches, causing cyclic destruction of the edifice and cascading hazards. These collapses, together with eruption-related changes in the edifice structure, change the slope stability hazard of the volcano over time. This study aims to develop a current view of the slope stability hazard at Augustine Volcano by (a) characterizing collapse-prone source areas on the edifice under various scenarios typical of dynamic volcanic environments and (b) identifying the controlling factors that underlie the slope stability hazard. Scenario-based slope stability assessment was conducted using a quasi-3D limit equilibrium method to test for the effect of various factors that drive or resist failure, including topography, shallow edifice structure, strength of edifice-forming materials, pore fluid pressure distribution, and local and regional seismicity. Results show that in all scenarios assessed, the slopes of Augustine Volcano are stable with a factor of safety (FOS) greater than 1. The FOS, however, decreases with decreasing strength of edifice-forming materials, pore fluid pressurization, and earthquake loading. The location of the relatively less stable slope, changes to the southwestern flank when accounting for subsurface heterogeneities derived from geophysical observations. Subsurface heterogeneity is thus a key underlying factor, along with steep topography, in controlling where collapse-prone source areas occur, and it should be accounted for in volcanic slope stability hazard assessments.