Relationship between the Aspect Ratio of a Collapsed Caldera and the Regional Stress Field - Their Evaluations Using a Single Small Spherical Magma Chamber Model in an Anisotropic Stress Field

Kusumoto Shigekazu,Nagao Toshiyasu

doi:10.35840/2631-5033/1806

Abstract

We show a fundamental equation that yields a caldera morphology caused by a single magma chamber in an anisotropic homogeneous regional stress field, where the ratio between the maximum and minimum horizontal principal stresses is constant. The equation was obtained by evaluating the surface stress field due to the magma chamber's change in volume and the regional stress field using the Coulomb failure criteria.

Highlights

Collapsed calderas are well known as volcanic depressions on the kilometer scale caused by the collapse of the roofs of magma chambers under the Earth’s surface [1,2,3]
We evaluate the stress field made by superposition of a regional stress field and a surface stress field caused by a volume reduction, using the Coulomb failure criteria, and show the relationship between the regional stress field and the morphology of an elliptical caldera
We focused on how the regional stress field affects the morphology of a caldera, and derived a fundamental equation that yields the morphology of a caldera being formed under an arbitrary homogeneous regional stress field

Summary

Introduction

Collapsed calderas are well known as volcanic depressions on the kilometer scale caused by the collapse of the roofs of magma chambers under the Earth’s surface [1,2,3]. Holohan et al [23] conducted analogue experiments on the effect of the regional stress field, and found that ring faults and/or peripheral faults of the caldera will be elongated in the minimum compressional stress direction even if the shape of the magma chamber is not elliptical.

Results

Conclusion