The Effect of Edifice Slope, Failure Surface Geometry, and Magma Intrusion Depth on the Development of Flank Instability at Volcanoes

Abstract

Magmatism is a known driver of flank instability at volcanoes where flank slip has been observed. Studies of instability at Kı̄lauea, Piton de la Fournaise, and Etna imply that long-term flank motion likely requires the presence of a layer accommodating the sliding, and a force, such as magma intrusion, that promotes slip. We present a parametric study using 2D Finite Element Models, to assess how edifice slope, failure surface geometry, edifice asymmetry, and intrusion depth affect the potential for development of flank instability at volcanoes. We quantify whether the tested conditions would favor flank slip based on the Coulomb Stress Changes (CSCs) associated with endmember scenarios and showcase the expected surface displacements for each scenario, to highlight their deviations from half-space models. Development of favored instability is more likely when dike intrusions span an edifice with shallower-dipping failure surfaces, or detachment faults, regardless of edifice steepness. Another favorable scenario occurs in steep edifices with steeply-dipping failure surfaces when the intrusion is beneath the edifice. The same is observed when introducing asymmetry on the opposing flank to simulate buttressing. We also find that neglecting topography yields smaller amplitude displacements with longer wavelengths, and these differences are greater the steeper the volcanic edifice. This topographical effect is more important when modeling horizontal displacements and stress changes induced by shallower intrusions.