Volcanic Plumes R. S. J. SPARKS University of Bristol, UK M. I. BURSIK State University of New York, USA S. N. CAREY University of Rhode Island, USA J. S. GILBERT Lancaster University, UK L. S. GLAZE NASA/Goddard Space Flight Center, USA H. SIGURDSSON University of Rhode Island, USA A. W. WOODS University of Bristol, UK JOHN WILEY & SONS Chichester New York Weinheim Brisbane Singapore Toronto
Contents Preface xiii Acknowledgements xv Chapter 1 Explosive Volcanism and the Generation of Volcanic Plumes 1 1.1 Introduction 1 1.2 Composition and volatile content of magma 2 1.3 Physical properties of magma 6 1.4 Causes of explosive volcanism 10 1.4.1 Degassing of juvenile volatiles 10 1.4.2 Interaction of magma with external water 13 1.5 Volcanic ejecta 17 1.6 Distribution of explosive volcanism 19 1.7 Styles of explosive volcanism and plume generation 22 1.7.1 Plinian eruptions - 24 1.7.2 Ignimbrite-forming eruptions 26 1.7.3 Strombolian eruptions 28 1.7.4 Vulcanian eruptions 29 1.7.5 Surtseyan eruptions '. 31 1.7.6 Hawaiian eruptions 31 1.7.7 Classification limitations 33 1.8 Magnitude and intensity of explosive volcanism 33 1.9 Frequency of explosive eruptions 34 1.10 Summary 35 Chapter 2 General Fluid Dynamical Principles 38 2.1 Introduction 39 2.2 Jets 41 2.3 Maintained buoyant plumes 42 2.4 Linearly mixing plumes 45 2.5 The uniform environment. 46 2.6 The stratified environment 49 2.7 Time-dependent buoyancy fluxes 52 2.8 Discrete thermals 53 2.9 Starting plumes 56
vi CONTENTS 2.10 Line sources 56 2.11 Negatively buoyant jets 57 2.12 Plumes with non-linear density mixing properties 58 2.13 Summary 61 Chapter 3 Source Conditions in Explosive Volcanic Eruptions 63 3.1 Introduction 64 3.2 Steady equilibrium ascent and eruption of magma 65 3.2.1 Dynamical model of conduit flow 67 3.2.2 Dynamic evolution of the flow 68 3.2.3 Conduit flow 70 3.2.4 Decompression into flared vents and craters 71 3.2.5 Pressure adjustment beyond the crater 74 3.3 Caveats and complications 77 3.3.1 Kinetic effects of gas exsolution 77 3.3.2 Fragmentation 77 3.3.3 Controls on initial plume temperature 78 3.3.4 Unsteady and heterogeneous conduit flow 79 3.3.5 Degassing during magma ascent: the lava problem 82 3.4 Transient Vulcanian-style eruptions 83 3.5 Summary 87 Chapter 4 Eruption Column Models 88 4.1 Introduction 89 4.2 Density variations in erupting mixtures 90 4.3 Fine-grained eruption columns 92 4.3.1 Gas thrust region 95 4.3.2 Convective region 96 4.3.3 The atmosphere 96 4.3.4 The motion of dry, dusty eruption columns 97 4.3.5 Fountain collapse 99 4.3.6 Column height 100 4.4 Particle fallout and thermal disequilibrium 101 4.5 Atmospheric controls on column behaviour 105 4.5.1 Variations in the environmental stratification 105 4.5.2 Wind-blown plumes 106 4.5.3 Moist convection in eruption columns 106 4.6 Short-lived eruptions 110 4.7 Starting plumes 112 4.8 Eruption columns associated with pyroclastic flows 112 4.9 Effects of particles on lower column dynamics 113 4.10 Multi-phase numerical models of eruption columns 114 4.11 Summary 116
CONTENTS vii Chapter 5 Observations and Interpretation of Volcanic Plumes 117 5.1 Introduction 117 5.2 Column height 118 5.3 Gas thrust region 122 5.4 Studies of starting plumes 124 5.4.1 Starting plume model 124 5.4.2 April 22, 1979 eruption of Soufriere, St Vincent 126 5.4.3 February 20, 1990 Lascar eruption 130 5.4.4 October 17, 1980 eruption of Mount St Helens 135 5.4.5 1947 Hekla Plinian eruption 137 5.5 Instantaneous explosions 138 5.6 Summary 139 Chapter 6 Pyroclastic Flows 141 6.1 Introduction 141 6.2 The nature of pyroclastic flows 142 6.2.1 Flows and surges 142 6.2.2 Observations 145 6.2.3 Range and aspect ratio of deposits 145 6.2.4 Constituents of pyroclastic flows 149 6.2.5 Dangers and hazards 149 6.3 Generation of pyroclastic flows by fountain collapse 149 6.3.1 Observations of eruptions 150 6.3.2 Experimental studies 155 6.3.3 Fluid dynamical models 158 6.3.4 Supercomputer models 166 6.3.5 Influence of flow inhomogeneities 168 6.3.6 Conclusions on fountain collapse, 171 6.4 Other forms of column instability and flow formation 171 6.4.1 Transitional behaviour 171 6.4.2 Collapse of column margins 173 6.4.3 Coarse ejecta fallout 175 6.4.4 Asymmetric collapse 176 6.4.5 Whole column collapse 176 6.4.6 Vent edge and decompression effects 177 6.4.7 Geological observations 177 6.5 Pyroclastic flows generated from lava domes 177 6.6 Summary 178 Chapter 7 Co-ignimbrite Plumes 180 7.1 Introduction 180 7.2 The nature of co-ignimbrite plumes 180 7.3 Mechanisms of plume formation 187 7.3.1 Flow-fed plumes: fluidization 187 7.3.2 Flow-fed plumes: boundary shear mixing 189
viii CONTENTS 7.3.3 Flow-fed plumes: non-linear mixing effects 189 7.3.4 Buoyant lift-off 192 7.3.5 Fountain-fed plumes 197 7.4 August 7, 1980 Mount St Helens flow: a case study 198 7.5 Theoretical models 201 7.5.1 A steady model 201 7.5.2 Comparison of steady model with observations 203 7.5.3 A thermal model 204 7.5.4 Comparisons of thermal model with observations 206 7.6 Summary 208 Chapter 8 Geothermal and Hydrovolcanic Plumes 209 8.1 Introduction 210 8.2 Geothermal systems 213 8.2.1 Steady venting 213 8.2.2 Geysers 215 8.3 Geothermal and fumarolic vapour plumes 217 8.3.1 Vapour plume model 218 8.3.2 Results of model calculations 219 8.4 Phreatic eruptions 224 8.5 Phreatomagmatic eruptions 225 8.5.1 Explosive energy and fragmentation 226 8.5.2 Properties of erupting water-magma mixtures 227 8.6 Submarine eruptions 230 8.7 Summary 232 Chapter 9 Hydrothermal Plumes 233 9.1 Introduction 234 9.2 Generation of hydrcsthermal plumes 234 9.3 Hydrothermal vents 237 9.3.1 Style of venting 237 9.3.2 Distribution of venting sites 239 9.4 Observations of sea-floor venting 241 9.4.1 Submersibles 241 9.4.2 Remote surveys of plume dispersal 241 9.4.3 Megaplumes 242 9.4.4 Bubble plumes 243 9.5 Particles in hydrothermal plumes 244 9.6 Dynamics and thermodynamics of hydrothermal plumes 244 9.6.1 Initial conditions 246 9.6.2 Plume models 247 9.6.3 Diffuse plumes 248 9.7 Properties of the plume and neutrally buoyant intrusion 251 9.7.1 Effects of abyssal cross-flows 252
CONTENTS ix 9.8 Fallout of particles from hydrothermal plumes 252 9.9 Summary 254 Chapter 10 Basaltic Eruptions and Fire Fountains 256 10.1 Introduction 257 10.2 Degassing phenomena in basaltic eruptions 258 10.2.1 Gas content 259 10.2.2 Viscosity 259 10.2.3 Vent geometry 260 10.3 Hawaiian fire fountains and Strombolian eruptions 260 10.3.1 Fire fountain activity 264 10.3.2 Height of rise of fire fountains 264 10.3.3 Variations in eruptive activity 266 10.3.4 Strombolian activity 266 10.4 The plumes above fire fountains 267 10.4.1 Height of rise for a line plume 268 10.4.2 A dynamical model of a Hawaiian plume 270 10.4.3 Comparison with observations 275 10.5 Basaltic Plinian and ignimbrite eruptions 276 10.6 Summary 276 Chapter 11 Atmospheric Dispersal 278 11.1 Introduction 279 11.2 Dynamics of umbrella clouds 280 11.2.1 Models of umbrella cloud growth 280 11.2.2 Entrainment 284 11.3 Plume-wind interaction 284 11.3.1 Strong plumes 285 11.3.2-^Weak plumes 288 11.3.3 Topographic effects 294 11.3.4 Regional and global transport 294 11.4 Comparison with observations 298 T 1.4.1 Umbrella clouds 298 11.4.2 Downwind spreading and plume dispersal patterns 300 11.4.3 Examples of hemispheric to global transport 302 11.5 Summary 306 Chapter 12 Remote Sensing of Volcanic Plumes 307 12.1 Introduction 307 12.2 Principles of electromagnetic theory 308 12.3 Electromagnetic remote sensing basics 311 12.3.1 Spectral region and resolution 312 12.3.2 Spatial resolution 314 12.3.3 Observation opportunities 314
x CONTENTS 12.4 Determination of plume properties 321 12.4.1 Plume height 321 12.4.2 Plume temperature 324 12.4.3 Output of SO 2 327 12.5 Satellite plume differentiation and eruption monitoring 331 12.5.1 Volcanic plume distinction 331 12.5.2 Plume dispersal observations from satellite 333 12.6 Monitoring of electric potential gradients and lightning generated by plumes 337 12.6.1 Background 337 12.6.2 Field measurements at volcanoes 339 12.7 Acoustic measurements of volcanic plumes 343 12.7.1 Principles 343 12.7.2 Measurements at Stromboli 344 12.8 Summary 345 Chapter 13 Tephra Fall Deposits 346 13.1 Introduction 346 13.2 Ejecta components 347 13.3 Petrology of ejecta 350 13.4 General description of fallout 353 13.5 Characteristics of fall deposits 356 13.5.1 Thickness 356 13.5.2 Volumes 365 13.5.3 Particle size 366 13.6 Classification of fall deposits 369 13.7 Co-ignimbrite fall deposits 372 13.8 Tephrochronology 373 13.8.1 Correlation and dating. 374 13.8.2 Archaeological applications 375 13.8.3 Marine tephrochronology ' 376 13.9 Summary 378 Chapter 14 Sedimentation from Volcanic Plumes 380 14.1 Introduction 381 14.2 Particle settling 382 14.2.1 The influence of particle shape 385 14.2.2 Variation of fall velocity with altitude 386 14.3 Ballistic particles 386 14.4 Sedimentation from turbulent suspensions 390 14.4.1 Basic principles 390 14.4.2 Radial gravity currents 391 14.4.3 Plumes and jets 391 14.4.4 Backflow 393 14.4.5 Re-entrainment 393
CONTENTS xi 14.4.6 Effects of wind 395 14.4.7 Atmospheric advection/diffusion models 396 14.5 Observations 397 14.5.1 Laboratory experiments 397 14.5.2 Volcanic deposits 398 14.5.3 Re-entrainment 403 14.6 Summary 403 Chapter 15 Quantitative Interpretation of Tephra Fall Deposits 404 15.1 Introduction 404 15.2 Maximum grain size data 405 15.2.1 Theoretical considerations 407 15.2.2 Maximum clast method 412 15.2.3 Evaluation of maximum clast method 416 15.2.4 Application to Plinian eruptions 418 15.3 Application of plume sedimentation models 422 15.3.1 Thickness variations 422 15.3.2 Particle size variations 426 15.3.3 Emplacement temperature and welding 428 15.4 Summary 431 Chapter 16 Particle Aggregation in Plumes 432 16.1 Introduction " 432 16.2 Geological observations 433 16.2.1 Anomalous deposit thicknesses 433 16.2.2 Particle size distributions 436 16.2.3 Aggregates 438 16.3 Aggregation mechanisms 444 16.3.1 Collision mechanisms 446 16.3.2 Binding mechanisms 448 16.4 Experiments and theory 449 16.4.1 Laboratory simulation 450 16.4.2 Theoretical models of aggregation 458 16.5 Summary 461 Chapter 17 Environmental Hazards 463 17.1 Introduction 463 17.2 Health hazards to humans 464 17.3 Hazards to animals 468 17.4 Effect on vegetation 471 17.5 Property damage 473 17.6 Disruption of community infrastructure ~ 476 17.7 Aviation hazards 480
xii CONTENTS 17.7.1 Disruptions of airport operations 480 17.7.2 Plume encounters in flight 481 17.7.3 Effect of ash and aerosols on aircraft 481 17.7.4 Mitigation 488 17.8 Summary and lessons learned 490 Chapter 18 Atmospheric Effects 493 18.1 Introduction 493 18.2 Early research 494 18.3 Physical principles 496 18.4 Sedimentation and dispersal of volcanic aerosols 499 18.5 The Pinatubo 1991 eruption 503 18.5.1 Sulphur dioxide emission 506 18.5.2 Sulphur dioxide decay and sulphate aerosol evolution 507 18.5.3 Stratospheric warming 516 18.5.4 Tropospheric and surface cooling 516 18.5.5 Ozone perturbation 518 18.5.6 Depletion of nitrogen dioxide 521 18.6 Volcanologic parameters 522 18.7 Summary 524 References 526 Index 560