El Misti is a 5822 m elevation symmetrical, andesitic stratovolcano located near the city of Arequipa in Peru. Numerous historic debris and avalanche deposits indicate that the volcano slopes could be unstable, and that seismic or volcanogenic activity might have the potential to trigger movement that could threaten Arequipa. To evaluate this potential, a cross-section was first developed along a transect from the summit southwest towards Arequipa based on available geologic information. The stability of the southwestern slope of El Misti approaching Arequipa was then investigated using 2D finite element homogenized continuum modeling. The shear strength reduction (SSR) method was used to find critical strength reduction factors (SRF) at which the slope is marginally stable (SRF ∼ 1) given a pseudo-static seismic loading based on the peak ground acceleration (PGA) for Arequipa. Possible mechanisms of slope failure for different assigned subsurface conditions were investigated.
El Misti is a 5820 m elevation composite stratovolcano with an extensive history of explosive eruptions, and lava and debris flows (Thouret et al., 2001). It is constructed of a composite of accumulated material from several sequences of eruptions and collapses. It lies to the northeast of the city of Arequipa, Peru. Arequipa has seen rapid growth in recent years, with a population of 1.38 million people per the 2017 national census, up from 700k in 1980 (CEIC, 2021).
Stratovolcanoes are built rapidly compared to non-volcanic mountains, leading to potentially unstable flanks and edifices (van Wyk de Vries and Francis, 1997). Collapse of these deposits can lead to large rock avalanches and debris flows with extensive runout lengths (Reid et al., 2000). Debris flow and collapse deposits can be seen in the historic geologic record of El Misti and pose a threat to the city of Arequipa and surrounding areas (Acocella, 2005; Thouret et al., 2001). Seismic activity, such as is common in the tectonic environment of Arequipa, or eruptions can trigger such massive collapses (Reid, 2004; Voight et al., 1983). Therefore, understanding the current stability of El Misti against seismic influences is vital to evaluating its long-term stability and the safety of residents of Arequipa.