Active Volcanoes of the Southwest Indian Ocean (eBook)

Preface 6
Contents 12
Part IPiton de la Fournaise Volcano 15
1 A Brief History of the Observation of the Central Area of Piton de la Fournaise 16
Abstract 16
1.1 Introduction 16
1.2 Early Observations at the Beginning of the Island's Colonization 17
1.3 Visits and Descriptions by Inhabitants and Naturalists During the 19th Century 20
1.4 Observations During the 20th Century 29
1.5 Modern Observations: Piton de La Fournaise Volcanological Observatory 30
Acknowledgments 33
References 33
2 Geodynamic Setting of La R00E9union 35
Abstract 35
2.1 Regional Tectonic Setting 35
2.2 La R00E9union and the Surrounding Lithosphere 37
2.2.1 Characteristics of the Oceanic Compartment of La R00E9union 37
2.2.1.1 Bathymetry Anomaly 37
2.2.1.2 Gravity and Magnetic Patterns 37
Gravity 37
Magnetics 39
2.2.1.3 Seamounts and Sediments of the Oceanic Plate 39
References 41
3 Construction of La R00E9union 43
Abstract 43
3.1 La R00E9union Edifice 44
3.2 Basement Geometry 45
3.3 Infrastructure of the Submarine Flanks 45
3.4 Internal Structures of the Volcanoes 48
3.4.1 Piton Des Neiges 48
3.4.2 Les Aliz00E9s Volcano 50
3.4.3 Piton de La Fournaise 51
3.5 Synthesis of the Construction of La R00E9union 53
Acknowledgements 54
References 54
4 Geology and Morphostructural Evolution of Piton de la Fournaise 57
Abstract 57
4.1 Introduction 58
4.2 Morphology 59
4.3 Volcano-Tectonic Structures 62
4.3.1 Collapse Structures 62
4.3.2 Rift Zones 64
4.4 Geological Evolution 65
4.4.1 The Ancient Piton de la Fournaise 65
4.4.2 The Recent Shield of Piton de la Fournaise 66
4.5 Synthesis 68
References 69
5 Groundwater Resources on Active Basaltic Volcanoes: Conceptual Models from La R00E9union Island and Grande Comore 72
Abstract 72
5.1 Introduction 72
5.2 Climatology of La R00E9union: The Case of Piton de la Fournaise 74
5.3 Groundwater Bodies: Typology, Geological, Hydrodynamical and Geochemical Aspects 75
5.3.1 Hydrogeological Analogy Between the Islands of Grande Comore and La R00E9union 75
5.3.2 The Coastal Area 75
5.3.3 The Inland Domain 75
5.3.4 Hydrochemical Aspects 77
5.3.5 Continuity Between Littoral Basal Groundwater and Deep Groundwater of High Elevation Zones 77
5.4 Hydrogeological Modelling of Piton de la Fournaise 78
5.5 Synthesis 79
References 80
6 Erosion and Volcaniclastic Sedimentation at Piton de la Fournaise: From Source to Deep Marine Environment 82
Abstract 82
6.1 Introduction 83
6.2 Geological and Climatic Settings 84
6.2.1 Geological Settings of La R00E9union Island 84
6.2.2 Climatic Settings of La R00E9union Island and Erosion Conditions 86
6.3 The Submarine Flanks of La R00E9union Volcanic Edifice 86
6.4 Onland Morphological Features of Piton de la Fournaise 87
6.5 Morphology of the Submarine Flank of Piton de la Fournaise 89
6.6 Onland Sediment Production and Transport from the High Relief to the Coastal Areas 92
6.6.1 Lava Flows Fragmentation 92
6.6.2 Landslides 93
6.6.3 Quantitative Approach of Erosional Processes 94
6.7 Sedimentary Deposits and Processes on the Submarine Flanks 95
6.7.1 Eastern Submarine Flank 95
6.7.2 Southern Submarine Flank 95
6.8 Source to Sink Interpretation 97
Acknowledgments 98
References 99
7 Magma Paths at Piton de la Fournaise Volcano 102
Abstract 102
7.1 Introduction 103
7.2 Review of the Intrusion Paths at Piton de la Fournaise 103
7.2.1 Magma Paths at the Edifice Scale 103
7.2.2 Magma Paths Centred on the Enclos Fouqu00E9 Caldera 105
7.3 Reappraisal of the Magma Paths 107
7.3.1 The Summit Plumbing System 109
7.3.2 The NW--SE Rift Zone, the South Volcanic Zone and the Deep Plumbing System 112
7.4 Comparison with Other Volcanoes 114
References 115
8 Pre-historic ( lessthan 5 kiloyear) Explosive Activity at Piton de la Fournaise Volcano 118
Abstract 118
8.1 Introduction 119
8.2 Wind Distribution Over La R00E9union Island and Microstratigraphic Drilling Strategy 120
8.3 Drilled Cores and Outcrop Description 122
8.3.1 The Partage Tephra 142
8.3.2 The Plaine des Sables Black Tephra 143
8.3.3 The ``Red Tephra'' 143
8.4 Frequency of PdF Explosive Activity During the Last 4000 Years 144
8.5 Concluding Discussion 146
Acknowledgments 148
References 148
9 Fifteen Years of Intense Eruptive Activity (1998--2013) at Piton de la Fournaise Volcano: A Review 150
Abstract 150
9.1 Introduction 150
9.2 OVPF Networks 152
9.3 Activity from 1998 to 2013 153
9.3.1 Eruption Activity: 1998--2006 153
9.3.1.1 The 1998 Eruptions 153
9.3.1.2 The 1999 Eruptions 158
9.3.1.3 The 2000 Eruptions 159
9.3.1.4 The 2001 Eruptions 160
9.3.1.5 The 2002 Eruptions 160
9.3.1.6 The 2003 Eruptions 161
9.3.1.7 The 2004 Eruptions 163
9.3.1.8 The 2005 Eruptions 164
9.3.1.9 The 2006 Eruptions 166
9.3.2 The 2007--2010 Activity 167
9.3.2.1 The 2007 Eruptions and Dolomieu Collapse 167
9.3.2.2 The 2008 Eruptions 168
9.3.2.3 The 2009 Eruptions 169
9.3.2.4 The 2010 Eruptions 170
9.3.3 Post 2011 Repose Period 171
9.3.4 Instability of the Eastern Flank 171
9.4 General Characteristics of Recent Eruptions at Piton de la Fournaise 172
9.4.1 Pre-eruptive, Eruptive and Post-eruptive Behavior 172
9.4.1.1 Characteristics of the Pre-eruptive Period 172
Seismicity 172
Ground Deformation 174
9.4.1.2 Eruptive and Post Eruptive Period 174
Seismicity 174
Ground Deformation 175
9.4.2 Characteristic of Eruptions 175
9.4.2.1 Location 175
9.4.2.2 Duration and Erupted Volume 175
9.4.2.3 Lava Areas 176
9.4.2.4 Lava Compositions 176
9.5 Discussion 177
9.5.1 Current View of the Shallow Magma Plumbing System 177
9.5.2 Conclusion: Recent Activity of Piton de la Fournaise 177
Acknowledgements 178
References 178
10 Petrological and Experimental Constraints on the Evolution of Piton de la Fournaise Magmas 182
Abstract 182
10.1 Piton de la Fournaise Magmas 182
10.1.1 Magma Types 182
10.1.2 Magma Components 186
10.2 Structure of the Magma Feeding System and Magmatic Conditions 189
10.2.1 Combined Geophysical and Petrological Constraints on the Structure of the Feeding System 189
10.2.2 Magma Temperature 189
10.2.3 Oxygen Fugacity 190
10.3 Experimental Constraints 191
10.3.1 General 191
10.3.2 Results 191
10.3.3 Application to Piton de la Fournaise Magmas 192
Acknowledgements 193
References 193
11 A Review of the Recent Geochemical Evolution of Piton de la Fournaise Volcano (1927--2010) 196
Abstract 196
11.1 Introduction 197
11.2 Eruptive History and Samples 197
11.3 Source Heterogeneity Versus Contamination Processes 199
11.4 Petrogenetic Processes 204
11.5 The Size and Shape of the Plumbing System 207
11.6 Brief Comparison with Kilauea Volcano 208
11.7 Synthesis 210
Acknowledgements 210
References 210
12 Magma Degassing at Piton de la Fournaise Volcano 213
Abstract 213
12.1 Introduction 214
12.2 Review of Volcanic Gas Analyses at Piton de la Fournaise 215
12.3 Compositions of Olivine and of Their Melt and Fluid Inclusions at Piton de la Fournaise 221
12.3.1 The Olivine Crystals 221
12.3.2 Experimental Olivine Geothermometry 222
12.3.3 Major Element Compositions of Melt Inclusions and Matrices 222
12.3.4 Volatile Content of ``Primary'' Melt Inclusions and Matrices 223
12.3.5 CO2-Rich Fluid Inclusions Trapped in Healed Fractures 225
12.4 Modelling Magma Degassing at Piton de la Fournaise 225
12.5 Conclusions 229
References 229
13 Seismic Monitoring at Piton de la Fournaise 233
Abstract 233
13.1 Seismic Monitoring Network 233
13.2 Overview of Piton de la Fournaise Seismicity 235
13.3 Compilation of the Piton de la Fournaise Activity Spanning the 1985--2010 Period 237
13.3.1 Types of Volcanic Events at Piton de la Fournaise 237
13.3.2 Eruptive Precursors at Piton de la Fournaise 238
13.3.3 Short-Term Precursors from the RER Broad-Band Seismic Station 239
13.3.4 Acceleration at the Very Broad-Band RER Station During Eruptions and Intrusions. Tools for Prediction 240
13.4 The March 1998 Pre-eruptive Earthquake Migration 241
13.5 The Caldera Collapse Episode of April 2007 at the Piton de la Fournaise Volcano Studied with the GEOSCOPE Broadband RER Station 243
13.5.1 Data Analysis of the Broadband Seismic RER Station 244
13.5.2 Collapse Events Before and After the Main Collapse at 20:48 GMT on April 5 245
13.6 Tremor Location and Lava Volume Quantification 245
13.7 Tracking Magma Movements Before Eruptions of Piton de la Fournaise Volcano with Seismic Methods 248
Acknowledgments 250
References 250
14 Static and Dynamic Seismic Imaging of Piton de la Fournaise 253
Abstract 253
14.1 Noise-Based Seismic Imaging and Monitoring of Piton de la Fournaise Volcano 253
14.1.1 Introduction 253
14.1.2 Noise-Based Seismic Imaging of Piton de la Fournaise Volcano 254
14.1.3 Noise-Based Seismic Monitoring of Velocity Changes at Piton de la Fournaise Volcano 255
14.2 P Wave Velocity Structure 257
Acknowledgments 259
References 259
15 Ground Deformation at Piton de la Fournaise, a Review From 20 Years of GNSS Monitoring 261
Abstract 261
15.1 Introduction 261
15.2 The Deformation Network at Piton de La Fournaise 263
15.3 The GNSS Network 263
15.4 Long-Term GNSS Variations 265
15.5 East Flank Movement 271
15.6 Short-Term GNSS Variations 272
15.6.1 February 17, 2005 Distal Eruption 272
15.6.2 October 4, 2005 Summit Eruption 272
15.6.3 July 20, 2006 Proximal Eruption 272
15.6.4 Dolomieu Crater Collapse 273
15.7 Inversion of GNSS Data---Imaging the Shallow Magma Plumbing System of Piton de La Fournaise 274
15.7.1 Long-Term Inflation Sources 275
15.7.2 Short-Term Dike Intrusions 275
15.8 Summary 276
Acknowledgments 277
References 277
16 The March--April 2007 Eruptions of Piton de la Fournaise as Recorded by Interferometric Data 280
Abstract 280
16.1 Introduction 281
16.2 Piton de la Fournaise Activity from 1998 to 2006 as Inferred from Insar Data 282
16.3 The March--April 2007 Eruptions 282
16.4 Data Processing and Results 283
16.4.1 Computation of the Interferograms 283
16.4.2 Computation of the Displacement 283
16.4.3 Co-eruptive Displacement 284
16.4.4 Post-eruptive Displacement 285
16.4.5 Displacements and Intrusive Activity 286
16.4.6 Displacement of the Central Cone 286
16.4.6.1 Post-eruptive Subsidence Decay 287
16.4.7 Displacement of the Grandes Pentes 288
16.4.7.1 Did the March 30 Dyke Intrusion Trigger the Detachment Slip? 289
16.4.7.2 An Intrusion Within the Central Eastern Flank 289
16.4.7.3 Sill Injection Promoting Detachment Slip 290
16.4.7.4 Post-eruptive Subsidence of the Sliding Sector 290
16.5 Main Lessons 291
Acknowledgements 292
References 292
17 Contribution of Tiltmeters and Extensometers to Monitor Piton de la Fournaise Activity 296
Abstract 296
17.1 Introduction 296
17.2 Volcano Setting 297
17.3 Tiltmeter and Extensometer Networks 299
17.4 Effects of External Parameters on the Signals 300
17.4.1 Seasonal Variations 301
17.4.2 Daily Variations 302
17.5 Signals Associated with Volcanic and Seismic Activity 302
17.5.1 Long-Term Eruptive Precursors 302
17.5.2 Short-Term Eruptive Precursors 304
17.5.3 Eruptive and Post-eruptive Summit Relaxation 307
17.5.4 Signals Associated with Pit Crater and Collapse Episodes 307
17.6 Perspectives 309
17.7 Conclusions 309
Acknowledgements 309
References 309
18 A Geographical Information System for Mapping Eruption Risk at Piton de la Fournaise 313
Abstract 313
18.1 Introduction 313
18.2 State-of-the-Art: The Use of GIS Technology in Volcanology 314
18.2.1 The Interest of GIS Technology for Volcanic Hazard Assessment 314
18.2.2 Some Approaches to Quantifying Volcanic Hazard Using GIS 315
18.3 Methodological Appraoch for the Design of a GIS for the Piton de la Fournaise 316
18.3.1 Volcanological Data 316
18.3.2 Architecture of the GIS 318
18.4 A Spatial Study of Eruptive Phenomena 318
18.4.1 Phenomenological Maps 319
18.4.2 Analysis Maps 319
18.5 Conclusion and Perspectives 322
References 322
19 Perception of Risk for Volcanic Hazard in Indian Ocean: La R00E9union Island Case Study 323
Abstract 323
19.1 Introduction 324
19.2 Methodology 324
19.2.1 The Survey 324
19.2.2 Distribution Procedures of Questionnaires 325
19.3 Results 326
19.3.1 Sample Grouping 326
19.3.2 Sample Characteristics 326
19.3.3 Hazard Salience 326
19.3.4 Risk Perception 327
19.3.5 Self-efficacy19.3.5 Self-efficacy19.3.5 Self-efficacy19.3.5 Self-efficacy19.3.5 Self-efficacy19.3.5 Self-efficacy19.3.5 Self-efficacy19.3.5 Self-efficacy19.3.5 Self-efficacy 329
19.3.6 Knowledge of Risk 329
19.3.7 Emergency Plan: Knowledge and Confidence 330
19.3.8 Confidence in the Authorities 330
19.3.9 Information on Volcanic Risk 331
19.3.10 Sense of Community 332
19.4 Synthesis 332
Acknowledgments 333
References 333
20 Volcanological Map of the Plaine des Sables, Piton de la Fournaise 335
References 337
Part IIKarthala Volcano 339
21 The Volcanism of the Comoros Archipelago Integrated at a Regional Scale 340
Abstract 340
21.1 Introduction 341
21.2 Volcanoes of the Comoros Archipelago 341
21.3 Hotspot and Rift-Related Interpretations of the Magmatism of the Comoros Archipelago 345
21.4 Discussion 346
21.4.1 Onset of the Volcanism of the Comoros Archipelago 346
21.4.2 Regional Distribution of the Volcanism 346
21.4.3 The Magmatism of the Comoros Archipelago Integrated in the Regional Geodynamics 347
21.5 Conclusion 349
References 349
22 Structure and Eruptive History of Karthala Volcano 352
Abstract 352
22.1 Introduction 353
22.2 The Tectonic Context of Grande Comore 354
22.3 Stratigraphy and Morphology of Karthala Volcano 357
22.4 Main Structural Features of Karthala Volcano 358
22.4.1 The Caldera Complex 359
22.4.2 Choungou-Chagnoumeni Pit-Crater 359
22.4.3 Choungou-Chahale Central Crater 361
22.4.4 Signs for the Probable Existence of an Older Caldera 362
22.4.5 Rift Zones and Links with La Grille Volcano 363
22.4.6 Flank Landslides 364
22.5 Recent Eruptive Activity 365
22.6 Summary 370
Aknowledgments 371
References 372
23 Geochemical and Petrological Aspects of Karthala Volcano 374
Abstract 374
23.1 Introduction 375
23.2 Petrography 376
23.2.1 General Aspects 376
23.2.2 Karthala Rock-Types 377
23.2.3 Main Distinctions with La Grille Lavas 379
23.2.4 Sandstones and Other Continental Rock Inclusions 379
23.3 Mineral Compositions 380
23.3.1 Olivine 380
23.3.2 Clinopyroxene 380
23.3.3 Plagioclases 381
23.3.4 Oxides 381
23.4 Geochemistry 382
23.4.1 Comorian Magmatic Suites 382
23.4.2 Major and Trace Element Variations 382
23.4.3 Mantle Source 385
23.4.4 Magma Generation 389
23.5 Summary 389
Acknowledgments 390
References 390
24 Groundwater Prospection in Grande Comore Island---Joint Contribution of Geophysical Methods, Hydrogeological Time-Series Analysis and Groundwater Modelling 392
Abstract 392
24.1 Introduction 393
24.2 Methodology 393
24.2.1 Geophysical Investigations 394
24.2.2 Time Series Analysis 394
24.2.3 Groundwater Modelling 394
24.3 General Settings of Grande Comore 395
24.3.1 Climate and Hydrology 395
24.3.2 Geology 395
24.3.3 Hydrogeology 395
24.3.3.1 Seawater Intrusion in Coastal Aquifers and Challenges of Prospecting and Managing the GroundwaterResources in Young Volcanic Islands 395
24.3.3.2 Current Status of Hydrogeological Knowledge and Gaps 396
24.3.3.3 Hydrogeological conceptual model---Analogy with La R00E9union Island 397
24.3.4 Water Uses 398
24.4 Results 399
24.4.1 Aquifers Structure from Geophysical Investigations 399
24.4.2 Hydrodynamics and Groundwater Time-Series 401
24.4.3 Theoretical Simulation of the 3D Impact of Volcanic Structures on Groundwater Flow and Saline Intrusion 402
24.4.4 Structure of the Perched Aquifers from Geophysical Investigations 403
24.4.5 Intermediate Staged Aquifers and Basal Aquifer of the Altitude Domain 404
24.5 Discussion 405
24.6 Conclusions and Recommendations for Groundwater Prospection and Management 406
Acknowledgments 407
References 407
25 Volcanic Risk and Crisis Management on Grande Comore Island 409
Abstract 409
25.1 Introduction 409
25.2 Grande Comore Island: The Entirety of the Territory Exposed to Volcanic Hazards 410
25.2.1 Hazards and Risks Associated with Magmatic Eruptions 411
25.2.2 Hazards and Risks Associated with Explosive Eruptions 413
25.2.3 Other Hazards and Risks 414
25.2.4 Risk Assessment and Mapping 414
25.2.5 Risk Mitigation Measures 415
25.3 Crisis Management at Karthala Over the Last Three Decades of Eruptions 416
25.3.1 Theoretical Volcanic Crisis Management Capacities at the Moment of the 2006 Eruption 416
25.3.1.1 Volcanic Crisis Monitoring and Forecasting 416
25.3.1.2 Crisis Planning 416
25.3.1.3 Launching Alerts 417
25.3.2 Conception and Growth of the Comorian Crisis Management System (1977--2005) 417
25.3.3 Feedback Analysis on the 2006 Eruption Management: Summary of Main Weaknesses 420
25.4 Is Grande Comore Ready to Face Future Volcanic Eruptions? 421
25.4.1 A Too Weak and Slow Evolution of the Crisis Management Capabilities? 421
25.4.1.1 A Weak Evolution from 2006 to 2014 421
25.4.1.2 Current Volcanic Crisis Management Capabilities on Grande Comore 425
25.5 Summary and Future Perspectives 425
25.5.1 Recommendations for More Efficient Risk and Crisis Management Capabilities 425
25.5.2 Future Prospects 426
Acknowledgments 426
References 426
Index 429