Caldera Volcanism (eBook)

Analysis, Modelling and Response

Joachim Gottsmann, Joan Marti (Herausgeber)

eBook Download: EPUB

2011 | 1. Auflage
516 Seiten
Elsevier Science (Verlag)
978-0-08-055897-4 (ISBN)

Infos

This volume aims at providing answers to some puzzling questions concerning the formation and the behavior of collapse calderas by exploring our current understanding of these complex geological processes. Addressed are problems such as:

- How do collapse calderas form?
- What are the conditions to create fractures and slip along them to initiate caldera collapse and when are these conditions fulfilled?
- How do these conditions relate to explosive volcanism?
- Most products of large caldera-forming eruptions show evidence for pre-eruptive reheating. Is this a pre-requisite to produce large volume eruptions and large calderas?
- What are the time-scales behind caldera processes?
- How long does it take magma to reach conditions ripe enough to generate a caldera-forming eruption?
- What is the mechanical behavior of magma chamber walls during caldera collapse? Elastic, viscoelastic, or rigid?
- Do calderas form by underpressure following a certain level of magma withdrawal from a reservoir, or by magma chamber loading due to deep doming (underplating), or both?
- How to interpret unrest signals in active caldera systems?
- How can we use information from caldera monitoring to forecast volcanic phenomena?

In the form of 14 contributions from various disciplines this book samples the state-of-the-art of caldera studies and identifies still unresolved key issues that need dedicated cross-boundary and multidisciplinary efforts in the years to come.

* International contributions from leading experts
* Updates and informs on all the latest developments
* Highlights hot topic areas and indentifies and analyses unresolved key issues

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This volume aims at providing answers to some puzzling questions concerning the formation and the behavior of collapse calderas by exploring our current understanding of these complex geological processes. Addressed are problems such as:- How do collapse calderas form? - What are the conditions to create fractures and slip along them to initiate caldera collapse and when are these conditions fulfilled? - How do these conditions relate to explosive volcanism?- Most products of large caldera-forming eruptions show evidence for pre-eruptive reheating. Is this a pre-requisite to produce large volume eruptions and large calderas?- What are the time-scales behind caldera processes? - How long does it take magma to reach conditions ripe enough to generate a caldera-forming eruption?- What is the mechanical behavior of magma chamber walls during caldera collapse? Elastic, viscoelastic, or rigid? - Do calderas form by underpressure following a certain level of magma withdrawal from a reservoir, or by magma chamber loading due to deep doming (underplating), or both?- How to interpret unrest signals in active caldera systems?- How can we use information from caldera monitoring to forecast volcanic phenomena?In the form of 14 contributions from various disciplines this book samples the state-of-the-art of caldera studies and identifies still unresolved key issues that need dedicated cross-boundary and multidisciplinary efforts in the years to come. - International contributions from leading experts- Updates and informs on all the latest developments- Highlights hot topic areas and identifies and analyzes unresolved key issues

Inhalt

Front cover 1
Caldera Volcanism: Analysis, Modelling and Response 4
Copyright page 5
Contents 6
Contributors 12
Preface 16
References 23
Chapter 1. Residence Times of Silicic Magmas Associated with Calderas 26
1. Introduction 27
2. Methods for Obtaining Time Constraints of Magmatic Processes 30
3. Residence Times of Magmas Associated with Selected Calderas 36
4. Interpretation of Residence Times and Integration with Thermal and Mechanical Constrains 60
5. Summary and Conclusions 70
Acknowledgments 72
References 72
Chapter 2. Sedimentology, Depositional Mechanisms and Pulsating Behaviour of Pyroclastic Density Currents 82
1. Introduction: What are Pyroclastic Density Currents? 83
2. Key Concepts 85
3. Sedimentology: Main Particle Support and Segregation Mechanisms in PDCs 88
4. Depositional Processes in PDCs 95
5. Field Evidences of Stepwise Aggradation in Pulsating PDCs 109
6. Conclusive Remarks and Future Perspectives 112
Acknowledgments 115
References 115
Chapter 3. The Use of Lithic Clast Distributions in Pyroclastic Deposits to Understand Pre- and Syn-Caldera Collapse Processes: A Case Study of the Abrigo Ignimbrite, Tenerife, Canary Islands 122
1. Introduction 123
2. Review of Lithic Component Studies and Inferred Caldera Processes 124
3. Case Study of the Abrigo Ignimbrite 131
4. Conclusions 160
Acknowledgments 161
References 161
Chapter 4. The Ignimbrite Flare-Up and Graben Calderas of the Sierra Madre Occidental, Mexico 168
1. Introduction 169
2. The Sierra Madre Occidental Volcanic Province 170
3. Regional Stratigraphy of the Sierra Madre Occidental 174
4. Graben Calderas of the Sierra Madre Occidental 178
5. Conclusions 198
Acknowledgments 198
References 199
Chapter 5. Characterisation of Archean Subaqueous Calderas in Canada: Physical Volcanology, Carbonate-Rich Hydrothermal Alteration and a New Exploration Model 206
1. Introduction 208
2. Abitibi Greenstone Belt Geology 208
3. Notion of Calderas 211
4. Hunter Mine Caldera 212
5. Normetal Caldera 227
6. Sturgeon Lake Caldera, Wabigoon Subprovince 236
7. The Link: Subaqueous Calderas with Chert-Iron Formation and Hydrothermal Carbonates 239
8. Discussion 245
9. Conclusions 250
Acknowledgements 251
References 252
Chapter 6. A Review on Collapse Caldera Modelling 258
1. Introduction 259
2. The Role of Experimental Models in Caldera Studies 260
3. Theoretical Models on Collapse Calderas Formation 269
4. Geophysical Imaging and Its Value for Caldera Studies 284
5. Discussion and Implications 298
6. Conclusions 302
Acknowledgements 302
References 303
Chapter 7. Structural Development of Calderas: a Synthesis from Analogue Experiments 310
1. Introduction 311
2. Analogue Modelling 312
3. Experimental Studies on Calderas 314
4. Discussion 324
5. Comparison to Nature: Guidelines 327
6. Towards a New Caldera Evolution Scheme 330
7. Conclusions 332
Acknowledgments 333
References 333
Chapter 8. Magma-Chamber Geometry, Fluid Transport, Local Stresses and Rock Behaviour During Collapse Caldera Formation 338
1. Introduction 339
2. Collapse Caldera Structures 342
3. Geometry of the Magma Chamber 349
4. Behaviour of Crustal Rocks 351
5. Magma-Chamber Rupture and Fluid Transport Along a Dyke 354
6. Stress Fields Triggering Ring-Fault Initiation 357
7. Discussion 365
8. Conclusions 369
Acknowledgments 370
References 370
Chapter 9. Facilitating Dike Intrusions into Ring-Faults 376
1. Introduction 377
2. Modeling Method 380
3. Results 381
4. Discussion 392
5. Conclusion 396
Acknowledgments 396
References 396
Chapter 10. A New Uplift Episode at Campi Flegrei Caldera (Southern Italy): Implications for Unrest Interpretation and Eruption Hazard Evaluation 400
1. Introduction 401
2. Recent Ground Deformation Data at Campi Flegrei Caldera 404
3. Displacement Shapes and Maximum Vertical to Horizontal Ratios 409
4. Discussion and Conclusion 413
Acknowledgments 415
References 415
Chapter 11. Hydrothermal Fluid Circulation and its Effect on Caldera Unrest 418
1. Introduction 419
2. The Hydrothermal Fluid Circulation 420
3. Modelling of Hydrothermal Fluid Circulation 422
4. Hydrothermal Systems and Volcano Monitoring 425
5. An Example of Assessing the Role of Hydrothermal Processes During Unrest: Solfatara (Phlegrean Fields Caldera, Italy) 429
6. Discussion and Conclusions 434
Acknowledgments 435
References 435
Chapter 12. Deciphering Causes of Unrest at Explosive Collapse Calderas: Recent Advances and Future Challenges of Joint Time-Lapse Gravimetric and Ground Deformation Studies 442
1. Introduction 443
2. The Subsurface Beneath Calderas: Hydrothermal Versus Magmatic Reservoirs 444
3. Joint Ground Deformation and Gravimetric Survey 445
4. Vertical Gravity-Height Gradients 448
5. Single and Distributed Sources 449
6. The Search for Causative Sources of Unrest: Recent Examples of Integrated Studies from the Long Valley, Campi Flegrei and Las Cañadas Calderas 452
7. The Problem of Aliasing of Time-Lapse Micro-Gravity Data 462
8. The Effect of Lateral Discontinuities on Ground Deformation and Residual Gravity Changes 462
9. Summary, Conclusions and Outlook 464
Acknowledgments 467
References 467
Chapter 13. The Failure Forecast Method: Review and Application for the Real-Time Detection of Precursory Patterns at Reawakening Volcanoes 472
1. Introduction 473
2. Theory of Precursors 474
3. The Theory of the Material Failure Forecast Method (FFM) 475
4. Techniques of Analysis 478
5. Viscoelastic Model 478
6. Seismicity as the Observable for FFM 479
7. FFM Applied to the Studies of Volcanoes 481
8. Conclusions 490
Acknowledgments 491
References 491
Chapter 14. Perspectives on the Application of the Geostatistical Approach to Volcano Forecasting at Different Time Scales 496
1. Introduction 497
2. The Probabilistic Approach 498
3. The Geostatistical Approach 499
4. Case Studies 502
5. Conclusions and Perspectives 509
Acknowledgments 510
References 510
Subject Index 514

Textauszug

Chapter 1 Residence Times of Silicic Magmas Associated with Calderas

Fidel Costa*,

CSIC, Institut de Ciències de la Terra ‘Jaume Almera’, Lluís Solé i Sabarís s/n, 08028 Barcelona, Spain.

* Corresponding author. Tel.: ++34-93-4095410; Fax: ++34-93-4110012

E-mail address: [e-mail]

Abstract

This paper reviews the times that silicic magmas related to major caldera systems spend in the crust prior to eruption. The significance of the time information is evaluated and combined with magma volumes and temperatures to quantify the mass and thermal fluxes associated to calderas. The data discussed includes the largest explosive eruptions on Earth: Taupo Volcanic Zone (New Zealand), the Youngest Toba Tuff (Indonesia), Yellowstone system (USA), Long Valley (USA), Carter Lake (USA), Valles-Toledo complex (USA), La Garita caldera (USA), La Pacana (Chile) and Kos (Greece). Magma residence times are calculated from the difference between the eruption age and the age obtained by radioactive clocks and minerals that are a closed system at high magmatic temperatures (e.g., U–Pb system in zircon).

Large ranges of residence times between different systems are found. The shortest residences (4–19 ky) are those of some magmas from the Taupo Volcanic Zone (Oruanui and Rotoiti) and Yellowstone (Dry Creek and Lava Creek). There is not a good correlation between magma volume and residence time, although most eruptions <10 km3 have residence times <100 ky, and those >100 km3 have longer residences, some up to 300–500 ky (Fish Canyon, La Pacana). The residence times of some small (<10 km3) pre- and post-caldera magmas indicate that they were extracted from the same reservoir as the caldera-forming magma (e.g., Long Valley, Taupo). However, the time information from most small-volume magmas seems to reflect the recycling of crystals from previous cycles of caldera-forming magmas (Yellowstone), from plutonic rocks of the same caldera cycle with or without erupted equivalents on the surface (Crater Lake, Taupo, Long Valley), or from a partially solidified magma reservoir (Taupo). These interpretations are in agreement with cooling rates and solidification times obtained from simple thermal models of magma reservoirs.

Magma production rates were calculated from the ratio of erupted volume and residence time, and they vary between <0.001 km3 y−1 for small deposits (<10 km3) and ca. 0.1 km3 y−1 for the Oruanui eruption (530 km3). Estimates for most eruptions >500 km3 are within 2±2×10−2 km3 y−1. These high magma production rates are probably transient and comparable to global eruptive fluxes of basalts (e.g., Hawaii). Magma cooling rates for deposits >100 km3 were calculated from the difference between the liquidus and pre-eruptive temperatures over their residence times, and they vary between 2×10−4 and 3×10−3 K y−1. Integration of the calculated residence times and magma fluxes with a simple rheological model of the crust is not possible and should be a main topic of research if we are to understand the mechanisms and rates which permit large amounts of silicic magma to be stored below calderas.

1 Introduction

Caldera-forming eruptions produce the most voluminous (up to 5,000 km3) explosive eruptions on Earth, and their activity appears to provide clues for understanding climatic and evolutionary biological changes (e.g., Lipman, 2000a; Francis and Oppenheimer, 2003). Collapse calderas are among the most investigated geological objects also because of their association with economic deposits and geothermal energy. The distinctive feature of caldera-related silica-rich volcanism is the topographical depressions left after the eruption. These are thought to be the result of either tremendous explosions that blew apart a pre-existing volcanic cone or due to subsidence of the roof of the reservoir after or during magma evacuation. High-level magma emplacement (typically <10 km depth) seems to be required for caldera formation, but when combined with the apparent large size of some reservoirs, questions arise as to the thermal and mechanical states of the crust and the magma, the rates and mechanisms of vapour- and silica-rich magma differentiation, and the timescales of transport and storage of huge quantities of eruptible silicic magma (e.g., Smith, 1979; Hildreth, 1981; Shaw 1985; Jellinek and DePaolo, 2003). These issues were addressed by Shaw (1985) who noted that “the interaction of magma generation rates, stress domains and injection rates leads to a spectrum of residence times which effectively determine the types of intrusive and volcanic suites seen at high crustal levels and at the surface.” Almost 25 years later, progress in analytical techniques have enabled the quantification of the time over which crystals and magma are stored before a caldera-forming eruption. This allows analysing the relations between the volumes, compositions, temperatures and depths of magma reservoirs below calderas from a new perspective. The purpose of this manuscript is to describe the approaches used to obtain the time scales of magmatic processes, to compile the data on residence times of major caldera-related complexes, and to use this information for deriving modes and rates of silica-rich magma production and storage in the Earth's crust.

1.1 What is the residence time of a magma?

It can be defined as the time elapsed since the magma was formed and its eruption. Uncertainties arise with the meaning of ‘when’ a magma is formed because what is finally erupted is a mixture of phases that might have very different origins in time and space (e.g., Bacon and Lowenstern, 2005). The most widespread use of residence time involves pinpointing when a given mineral started to crystallise, presumably during storage in a magma reservoir. This is different from the definition used in oceanic geochemistry or in highly active volcanic systems where it refers to the (mean) time that a given element or isotope spends in a reservoir before being removed (e.g., Holland, 1978; Albarède, 1993). In practice, one can calculate the residence time as the difference between the eruption age as obtained by K–Ar (or 40Ar/39Ar), (U, Th)/He and 14C methods (for prehistorical eruptions) and the age provided by other radioactive clocks, such as Rb–Sr, and U–Th–Pb. From this definition it is apparent that the residence time does not need to be a single value, and might depend on the phases and radioactive isotopes that are used. Multiple values of residence times may arise from different crystallisation ages of different minerals, but also from the fact that the very definition of an age requires knowledge of when the radioactive system became closed. This condition depends on several factors but strongly on the diffusion rate of the daughter isotope, and has been quantified with the use of a closure temperature (Dodson, 1973). This explains the a priori paradoxical situation that, for example, a sanidine might have two different ages and both could be correct: dated by the K–Ar system the mineral gives the eruption age but using Rb–Sr clock it may give a much older crystallisation age, simply because the K–Ar system becomes closed at much lower temperatures (e.g., on quenching of the magma upon eruption). Most of the age data used in this manuscript were obtained using zircon and the U–Th–Pb decay system and thus reflect the time since the beginning of zircon crystallisation and final eruption. It is worth mentioning that there might be a systematic bias between the radioactive clocks of the K–Ar and that of U–Pb systems, the latter giving slightly older ages (<1%; e.g., Renne et al., 1998; Min et al., 2000; Renne, 2000; Villeneuve et al., 2000; Schmitz and Bowring, 2001; Schoene et al., 2006). Since the issue is not resolved at the time of writing it has not been considered for calculating residence times. Recent reviews of the methods and time scales of magmatic processes can be found in Condomines et al. (2003), Reid (2003), Turner et al. (2003), Hawkesworth et al. (2004) and Peate and Hawkesworth (2005).

1.2 Magma production and cooling rates

Aside from compiling residence times and rates of processes, two other parameters were calculated. One is a ‘magma production rate,’ which is the ratio of the erupted volume over the residence time (e.g., Christensen and DePaolo, 1993; Davies et al., 1994). It is not sensu stricto a magma production rate because it only accounts for the erupted magma. It should be called ‘erupted magma production rate’ but this would be very cumbersome. These rates are different from the ‘average magma eruption rate’ (or output rate) calculated using the total erupted volume and time span of magmatic activity at a given volcanic system (Crisp, 1984; White et al., 2006). They are also different from the rates obtained from the erupted volume divided by the time interval between two subsequent eruptions (Bacon, 1982). A magma cooling rate has also been calculated for eruptions >100 km3. This is the difference between the magma temperature at pre-eruptive conditions and its liquidus calculated by MELTS (Ghiorso and Sack, 1995), over the residence time. The significance of such cooling...

Produkt-Details

• Erscheint lt. Verlag: 22.9.2011
• Sprache: englisch
• Themenwelt: Naturwissenschaften ► Geowissenschaften ► Geologie
• Themenwelt: Naturwissenschaften ► Geowissenschaften ► Geophysik
• Themenwelt: Naturwissenschaften ► Geowissenschaften ► Mineralogie / Paläontologie
• Themenwelt: Naturwissenschaften ► Physik / Astronomie
• Themenwelt: Technik ► Umwelttechnik / Biotechnologie
• ISBN-10: 0-08-055897-6 / 0080558976
• ISBN-13: 978-0-08-055897-4 / 9780080558974