Page 338 - Caldera Volcanism Analysis, Modelling and Response

CHA P T E R 8

Magma-Chamber Geometry, Fluid

Transport, Local Stresses and Rock
Behaviour During Collapse Caldera

Formation

Agust Gudmundsson

Contents

1. Introduction 314
2. Collapse Caldera Structures 317
3. Geometry of the Magma Chamber 324
4. Behaviour of Crustal Rocks 326
5. Magma-Chamber Rupture and Fluid Transport Along a Dyke 329
6. Stress Fields Triggering Ring-Fault Initiation 332
7. Discussion 340
7.1. The underpressure model 341
7.2. Ring-fault structure and slip 343
8. Conclusions 344
Acknowledgements 345
References 346

Abstract
Collapse calderas are common on Earth and some other solid planetary bodies,
particularly on Io (a satellite of Jupiter), Mars and Venus. Caldera structures are
generally similar on all these bodies but the sizes vary considerably. Here I present
numerical models of caldera-fault formation in volcanoes with shallow, spherical or
sill-like magma chambers. In all the anisotropic models, the crustal segment (including
the volcano) above the shallow chamber is composed of 30 comparatively thin layers
with stiffnesses (Young’s moduli) alternating between 1 and 100 GPa. The chamber itself

Corresponding author. Tel.: 44 (0) 1784-443581; Fax: 44 (0) 1784-471780
E-mail address: a.gudmundsson@gl.rhul.ac.uk
Department of Structural Geology and Geodynamics, GZG, University of Go ¨ttingen, Germany; Department of Earth Sciences,
Royal Holloway, University of London, Queens Building, Egham, Surrey, TW20 0EX, UK
Developments in Volcanology, Volume 10 r 2008 Elsevier B.V.
ISSN 1871-644X, DOI 10.1016/S1871-644X(07)00008-3 All rights reserved.
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