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Insights into the 2020 instability crisis of Mt Merapi through numerical modeling

Michael Galarraga1, Luc Scholtes1, Karim Kelfoun1, Bastien Chevalier2

  • Affiliations: 1Laboratoire Magmas et Volcans, Université Clermont Auvergne, Clermont-Ferrand, France. 2Institut Pascal, Université Clermont Auvergne, Clermont-Ferrand, France

  • Presentation type: Poster

  • Presentation time: Tuesday 16:30 - 18:30, Room Poster Hall

  • Poster Board Number: 181

  • Programme No: 3.5.40

  • Theme 3 > Session 5

Abstract

The western flank of Mt Merapi (Indonesia), one of the most active volcanoes located in proximity to populated areas, became unstable in October 2020. Surveillance techniques such as Synthetic Aperture Radar (SAR) and Electronic Distance Measurements (EDM) give an idea of the displacement magnitude. However, these remote sensing methods are limited in providing information about subsurface processes and deformation mechanisms. This limitation is critical when assessing the potential for catastrophic flank failure (e.g., Mt. Saint Helens in 1980), which remains a significant concern. Observations show a correlation between this flank movement, a NW-SE fracture crossing the entire summit, and the presence of magma within this discontinuity. In order to better understand this instability, we developed numerical models in an attempt to relate the magma pressure to the slope deformation at Mt. Merapi. In particular, relying on its ability to describe progressive failure mechanisms in elasto-plastic media, we use the Discrete Element Method (DEM) to investigate the role of the NW-SE fracture pressurization on the deformation of Mt Merapi flanks. We show here the main results of sensibility analyses performed to study the influence of the rock mechanical properties, fracture length, and magma pressure magnitude on the flank stability, comparing the resulting deformation with the 2020 Merapi crisis displacements. Despite assumptions such as material homogeneity and hydrostatic pressurization, our modeling approach allows us to make predictions not only on the potential for collapse and its kinematics, but also on the mobilized volumes, all criticall for risk assessment.