2025-10-03 ペンシルベニア州立大学 (PennState)
＜関連情報＞
- https://www.psu.edu/news/earth-and-mineral-sciences/story/new-tool-helps-forecast-volcano-slope-collapses-and-tsunamis
- https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2024JB030627
火山体傾斜、崩壊面形状、マグマ貫入深度が火山の側面不安定性の発達に与える影響 The Effect of Edifice Slope, Failure Surface Geometry, and Magma Intrusion Depth on the Development of Flank Instability at Volcanoes
J. Gonzalez-Santana, C. Wauthier, S. Tung, T. Masterlark
Journal of Geophysical Research: Solid Earth Published: 07 July 2025
DOI:https://doi.org/10.1029/2024JB030627
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.
Plain Language Summary
Rising magma is known to influence slip on the flanks of volcanoes, which can eventually cause collapses. To better understand how and where different volcano configurations create conditions that favor slip, we produce two dimensional models with variable edifice slope and dip of possible slip surfaces, using values for real volcanoes in nature. We apply a constant opening displacement at different depths in the model to represent the rising magma and obtain surface displacement predictions, to see how these differ from corresponding predictions from standard models that assume a flat surface. We also calculate fault stability changes inside the model volcano to show where sliding is more or less likely to be favored due to the imposed opening displacement. We find that slip is most favored on slip surfaces with shallow dips if opening happens within the volcano, regardless of the volcano steepness, or in volcanoes with steep sides when slip surfaces have steep dips and opening happens beneath the volcano. The steeper the slopes of the volcano, the greater the difference in surface displacements for the same source, particularly for horizontal displacements and shallower opening. Slope steepness also influences the stress changes, especially for magma rising through shallower openings.
Key Points
- We produce numerical models to assess how edifice slope, failure surface geometry, and dike depth influence magma-driven flank instability
- Shallow intrusions facilitate slip on shallow-dipping faults; deeper intrusions favor slip in steep edifices with steep-dipping faults
- Neglecting topography yields smaller amplitude surface displacements with longer wavelengths
