The effect of edifice slope, detachment fault geometry, and magmatic
triggers on the development of volcanic flank instability
Abstract
Magmatism is a known driver of flank instability at volcanoes where
flank slip has been observed. Studies of instability at Kīlauea, 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 (FEMs), to assess how edifice
aspect ratio, detachment fault geometry, asymmetric buttressing, and
intrusion depth affect the potential for development of magma-driven
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 instability is more likely when
flank slip is along a shallower-dipping receiver fault and the dike
intrusion spans the edifice, regardless of edifice steepness. Another
favorable scenario occurs in steep edifices with a steeply-dipping
receiver fault when the dike is beneath the edifice. Buttressing
slightly enlarges the region with conducive CSCs on shallow-dipping
faults when the dike is within the edifice but shrinks the region with
conducive CSCs in the steep edifice case with steeply-dipping faults. We
also find that neglecting topography yields different magnitudes and
extents of surface deformation, especially for steeper volcanic
edifices. This topographical effect is more important when modeling
horizontal displacements and stress fields induced by shallower
intrusions.