Understanding silicic volcanism [Elektronische Ressource] : constraints from elasticity and failure of vesicular magma / vorgelegt von Bettina Scheu

Bettina Scheu

Informations

• Publié par: ludwig-maximilians-universitat_munchen
• Publié le: 01 janvier 2005
• Nombre de lectures: 14
• Langue: English
• Poids de l'ouvrage: 8 Mo

Extrait

Understanding silicic volcanism: Constraints
from elasticity and failure of vesicular magma
Inaugural-Dissertation
zur Erlangung des Doktorgrades
der Fakultat¨ fur¨ Geowissenschaften der
Ludwig-Maximilians-Universitat¨ Munc¨ hen
vorgelegt von
Bettina Scheu
07. Juli 2005empty1. Berichterstatter: Prof. Dr. D.B. Dingwell
2. Prof. Dr. H. Igel
Tag der mundlichen¨ Prufung:¨ 21. Oktober 2005emptyContents
Table of Contents I
List of Figures IV
List of Tables VII
Preamble VIII
Zusammenfassung 1
1 Introduction 7
1.1 Silicic volcanism: explosive versus effusive . . . . . . . . . . . . . . 7
1.2 Fragmentation process . . . . . . . . . . . . . . . . . . . . . . . . . 8
1.3 Experimental volcanology . . . . . . . . . . . . . . . . . . . . . . . 12
1.4 Eruption history of Unzen Volcano . . . . . . . . . . . . . . . . . . . 14
1.5 history of Soufriere` Hills Volcano . . . . . . . . . . . . . . 16
2 Sample characterization 19
2.1 Petrology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
2.1.1 Unzen Volcano, Japan . . . . . . . . . . . . . . . . . . . . . 19
2.1.2 Soufriere` Hills Volcano, Montserrat . . . . . . . . . . . . . . 20
2.2 Density and porosity . . . . . . . . . . . . . . . . . . . . . . . . . . 22
2.2.1 Field measurements . . . . . . . . . . . . . . . . . . . . . . 24
2.2.2 Laboratory . . . . . . . . . . . . . . . . . . . 26
2.3 Surface area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
2.3.1 Methodology . . . . . . . . . . . . . . . . . . . . . . . . . . 28
2.3.2 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
III CONTENTS
2.4 Fracture toughness . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
2.4.1 Methodology . . . . . . . . . . . . . . . . . . . . . . . . . . 33
2.4.2 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
3 Elastic wave velocities 37
3.1 Sample description . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
3.2 Methodology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
3.3 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
3.3.1 Pressure effect . . . . . . . . . . . . . . . . . . . . . . . . . 40
3.3.2 Temperature effect . . . . . . . . . . . . . . . . . . . . . . . 41
3.4 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
3.5 Implications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
4 Fragmentation behavior 49
4.1 Sample description . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
4.2 Methodology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
4.3 Testing of setup and transducers . . . . . . . . . . . . . . . . . . . . 53
4.4 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
4.4.1 Unzen Volcano . . . . . . . . . . . . . . . . . . . . . . . . . 55
4.4.2 Montserrat . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
4.4.3 Influence of experimental temperature . . . . . . . . . . . . . 63
4.5 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
4.5.1 Restriction of the fragmentation speed . . . . . . . . . . . . . 64
4.5.2 Fragmentation energy and fragmentation mechanisms . . . . 66
5 Decompression history 73
5.1 Influence of permeability . . . . . . . . . . . . . . . . . . . . . . . . 73
5.2 Pressure profile along a sample at rapid decompression . . . . . . . . 78
5.2.1 Experimental setup . . . . . . . . . . . . . . . . . . . . . . . 78
5.2.2 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
5.3 Fragmentation profile along a sample at rapid
decompression . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87CONTENTS III
6 Implications for volcanic fragmentation 89
6.1 Porosity layering . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
6.2 Fragmentation behavior of a layered medium . . . . . . . . . . . . . 92
6.3 Dome collapse events . . . . . . . . . . . . . . . . . . . . . . . . . . 95
6.4 Vulcanian events . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
6.4.1 Vulcanian events at Unzen . . . . . . . . . . . . . . . . . . . 98
6.4.2 The 1997 Vulcanian eruptions at Montserrat . . . . . . . . . . 102
7 Conclusions 107
Bibliography 112
Acknowledgements 129
Appendices 131
A Photographs of samples 131
B Tables of experimental results 135
Curriculum Vitae 141IVList of Figures
1.1 The role of the glass transition for the response of magma to deformation 10
2.1 Thin section images of Unzen dacite . . . . . . . . . . . . . . . . . . 21
2.2 Thin section images of Montserrat andesite . . . . . . . . . . . . . . 23
2.3 Unzen Volcano: pyroclastic flow deposits of the 1990-1995 eruption
and locations for field density measurements . . . . . . . . . . . . . . 25
2.4 Unzen Volcano: field density data, and used samples . . . . . . . . . 27
2.5 Specific surface area of Unzen dacite . . . . . . . . . . . . . . . . . . 31
2.6 surface area of Montserrat andesite . . . . . . . . . . . . . . 32
2.7 Samples used for fracture toughness tests . . . . . . . . . . . . . . . 34
2.8 Fracture toughness results from Unzen dacites . . . . . . . . . . . . . 35
3.1 The cubic anvil press at the University of Kiel . . . . . . . . . . . . . 39
3.2 Pressure dependency of elastic wave velocities (MUZ 2000 A) . . . . 41
3.3 Temperature dependency of elastic wave velocities (MUZ 2000 A) . . 42
3.4 Mean Vp and Vs* values of all samples as a function of temperature . 43
3.5 Volumetric strain and bulk density . . . . . . . . . . . . . . . . . . . 44
3.6 Vesicles and groundmass of analyzed Unzen dacite . . . . . . . . . . 46
4.1 Fragmentation apparatus - technical drawing and photo . . . . . . . . 51
4.2 Setup for fragmentation speed experiments . . . . . . . . . . . . . . 52
4.3 Location of the pressure transducers at the autoclave . . . . . . . . . 52
4.4 Recorded pressure signals of Unzen dacite samples . . . . . . . . . . 57
4.5 Unzen: speed of fragmentation and fragmentation threshold . . . . . . 58
4.6 Recorded pressure signals of Montserrat pumice samples . . . . . . . 60
4.7 Montserrat: speed of fragmentation and fragmentation threshold . . . 62
VVI LIST OF FIGURES
4.8 Hot versus cold fragmentation threshold values . . . . . . . . . . . . 64
4.9 Removal speed of glass under rapid decompression . . . . . . . . . . 65
4.10 Unzen: speed of fragmentation in relation to energy density . . . . . . 67
4.11 Highly connected vesicles within porous Unzen dacite . . . . . . . . 67
4.12 Montserrat: speed of fragmentation in relation to energy density . . . 68
4.13 Fractured samples of the very dense sample set of Montserrat . . . . . 69
4.14 particles of the mid dense sample of . . . . . . . 69
4.15 Energy density and fragmentation speed - hint for different mechanisms? 72
5.1 Influence of permeability on fragmentation behavior . . . . . . . . . . 74
5.2 MUZ 2000 G: permeable flow curves of different samples . . . . . . 75
5.3 Permeability of volcanic rocks . . . . . . . . . . . . . . . . . . . . . 77
5.4 Setup to investigate the pressure profile within a sample . . . . . . . . 79
5.5 Pressure drop curves and related location along the sample . . . . . . 80
5.6 drop curves and reconstructed pressure profile . . . . . . . . 81
5.7 Pressure profiles of four samples from Unzen Volcano . . . . . . . . . 83
5.8 Numerically modelled pressure profiles . . . . . . . . . . . . . . . . 84
5.9 Best fit solutions and pressure profiles along an Unzen sample . . . . 85
5.10 Comparison of the measured and calculated pressure drop curves . . . 86
5.11 Fragmentation speed results at different sample length . . . . . . . . . 88
6.1 Porosity layering at the endogenous dome of Unzen Volcano . . . . . 90
6.2 variation within a layered block at Unzen Volcano . . . . . . 91
6.3 Porosity variation of the layered block and the assigned speed variation 92
6.4 ”Fragmentable” part of the 1990-1995 Unzen deposits . . . . . . . . 94
6.5 Dome collapse due to the fragmentation of a highly porous layer . . . 96
6.6 Dome scenario, amplified by a fragmentation event . . . . . 97
6.7 Dome collapse by a event, leading
to an explosive event . . . . . . . . . . . . . . . . . . . . . . . . . . 99
6.8 Implications for the Vulcanian events at Unzen, June 1991 . . . . . . 101
6.9 for the 1997 Vulcanian events at Montserrat . . . . . . . 105
A.1 Photographs of Unzen and Montserrat samples . . . . . . . . . . . . 132
A.2 Thinsections of Unzen dacite . . . . . . . . . . . . . . . . . . . . . . 133