Secondary Lahars Impacting on Building Structures at Chimborazo Volcano: A Retrospective and Scenario-Based Modeling Approach

Abstract

The intense melting of glacial ice and permafrost can increase the presence of temporarily stored liquid water in dynamic high-alpine environments. A sudden release of this water, especially in volcanic settings, might trigger a process chain of severe consequences. During a period of increased periglacial degradation between 2015 and 2017, several large-volume (> 6.0 × 105 m³), outburst-related secondary lahars damaged local infrastructure on the populated southeastern slopes of Chimborazo volcano in Ecuador. The insufficient understanding of secondary lahars associated with the sudden outburst of water complicates the identification of initiating processes and hinders the ability to decipher the governing mechanisms involved during propagation. In this study, we present how we (1) identified initiation mechanisms of past secondary lahars at Chimborazo, (2) numerically back-calculated these events, (3) developed future lahar scenarios, and (4) quantified their impact on the local population. We performed a retrospective calibration approach to simulate a secondary lahar using the physics-based model RAMMS::Debris Flow. By introducing a novel two-stage outburst scenario development concept, we were able to predict potential future lahars. Finally, applying a standards-based verification of the structural components of residential development allowed us to evaluate the physical impact of potential lahars on infrastructure. We also assessed how increasing the wall thickness affects high- and low-risk areas. Our results show that the observed secondary lahars can be numerically reproduced with a set of frictional parameters of