| Abstrakt: |
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. Plain Language Summary: Several active volcanoes worldwide have slope failures where large parts of their structure collapse, generating destructive mass flows called volcanic debris avalanches. These flows travel long distances and sometimes have cascading hazards like eruptions and tsunamis. Subsequently, the volcano's structure rebuilds with new material ejected during eruptions. Augustine Volcano in Alaska has a history of these cycles of slope failures and reconstruction. This study aims to understand the volcano's current slope stability hazard considering factors such as inherent topographic structure and several conditions that can occur in active volcanic environments (e.g., changes in the volcano's structure and strength of rocks, earthquakes, and pore pressure conditions). In all scenarios assessed in this study, the volcano's slopes remain stable, with the relatively least stable slope occurring in the southwestern parts of the volcano. Overall, the steep landscape and structure underneath the volcano are vital in determining where relatively less stable areas exist. Factors such as weakening of the rocks, pressure from water in cracks and voids in the rock, and ground shaking due to earthquakes can make such slopes susceptible to sliding. Key Points: Augustine Volcano's edifice is stable under the slope‐stability scenarios assessedTopography and subsurface heterogeneity are key underlying factors controlling where collapse‐prone source areas occurPore fluid pressurization and earthquake loading reduce the relative stability of the volcano's edifice [ABSTRACT FROM AUTHOR] |
Plný text