Volcanic Plumes. JOHN WILEY & SONS Chichester New York Weinheim Brisbane Singapore Toronto

Transcription

1 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

2 Contents Preface xiii Acknowledgements xv Chapter 1 Explosive Volcanism and the Generation of Volcanic Plumes Introduction Composition and volatile content of magma Physical properties of magma Causes of explosive volcanism Degassing of juvenile volatiles Interaction of magma with external water Volcanic ejecta Distribution of explosive volcanism Styles of explosive volcanism and plume generation Plinian eruptions Ignimbrite-forming eruptions Strombolian eruptions Vulcanian eruptions Surtseyan eruptions ' Hawaiian eruptions Classification limitations Magnitude and intensity of explosive volcanism Frequency of explosive eruptions Summary 35 Chapter 2 General Fluid Dynamical Principles Introduction Jets Maintained buoyant plumes Linearly mixing plumes The uniform environment The stratified environment Time-dependent buoyancy fluxes Discrete thermals Starting plumes 56

3 vi CONTENTS 2.10 Line sources Negatively buoyant jets Plumes with non-linear density mixing properties Summary 61 Chapter 3 Source Conditions in Explosive Volcanic Eruptions Introduction Steady equilibrium ascent and eruption of magma Dynamical model of conduit flow Dynamic evolution of the flow Conduit flow Decompression into flared vents and craters Pressure adjustment beyond the crater Caveats and complications Kinetic effects of gas exsolution Fragmentation Controls on initial plume temperature Unsteady and heterogeneous conduit flow Degassing during magma ascent: the lava problem Transient Vulcanian-style eruptions Summary 87 Chapter 4 Eruption Column Models Introduction Density variations in erupting mixtures Fine-grained eruption columns Gas thrust region Convective region The atmosphere The motion of dry, dusty eruption columns Fountain collapse Column height Particle fallout and thermal disequilibrium Atmospheric controls on column behaviour Variations in the environmental stratification Wind-blown plumes Moist convection in eruption columns Short-lived eruptions Starting plumes Eruption columns associated with pyroclastic flows Effects of particles on lower column dynamics Multi-phase numerical models of eruption columns Summary 116

4 CONTENTS vii Chapter 5 Observations and Interpretation of Volcanic Plumes Introduction Column height Gas thrust region Studies of starting plumes Starting plume model April 22, 1979 eruption of Soufriere, St Vincent February 20, 1990 Lascar eruption October 17, 1980 eruption of Mount St Helens Hekla Plinian eruption Instantaneous explosions Summary 139 Chapter 6 Pyroclastic Flows Introduction The nature of pyroclastic flows Flows and surges Observations Range and aspect ratio of deposits Constituents of pyroclastic flows Dangers and hazards Generation of pyroclastic flows by fountain collapse Observations of eruptions Experimental studies Fluid dynamical models Supercomputer models Influence of flow inhomogeneities Conclusions on fountain collapse, Other forms of column instability and flow formation Transitional behaviour Collapse of column margins Coarse ejecta fallout Asymmetric collapse Whole column collapse Vent edge and decompression effects Geological observations Pyroclastic flows generated from lava domes Summary 178 Chapter 7 Co-ignimbrite Plumes Introduction The nature of co-ignimbrite plumes Mechanisms of plume formation Flow-fed plumes: fluidization Flow-fed plumes: boundary shear mixing 189

5 viii CONTENTS Flow-fed plumes: non-linear mixing effects Buoyant lift-off Fountain-fed plumes August 7, 1980 Mount St Helens flow: a case study Theoretical models A steady model Comparison of steady model with observations A thermal model Comparisons of thermal model with observations Summary 208 Chapter 8 Geothermal and Hydrovolcanic Plumes Introduction Geothermal systems Steady venting Geysers Geothermal and fumarolic vapour plumes Vapour plume model Results of model calculations Phreatic eruptions Phreatomagmatic eruptions Explosive energy and fragmentation Properties of erupting water-magma mixtures Submarine eruptions Summary 232 Chapter 9 Hydrothermal Plumes Introduction Generation of hydrcsthermal plumes Hydrothermal vents Style of venting Distribution of venting sites Observations of sea-floor venting Submersibles Remote surveys of plume dispersal Megaplumes Bubble plumes Particles in hydrothermal plumes Dynamics and thermodynamics of hydrothermal plumes Initial conditions Plume models Diffuse plumes Properties of the plume and neutrally buoyant intrusion Effects of abyssal cross-flows 252

6 CONTENTS ix 9.8 Fallout of particles from hydrothermal plumes Summary 254 Chapter 10 Basaltic Eruptions and Fire Fountains Introduction Degassing phenomena in basaltic eruptions Gas content Viscosity Vent geometry Hawaiian fire fountains and Strombolian eruptions Fire fountain activity Height of rise of fire fountains Variations in eruptive activity Strombolian activity The plumes above fire fountains Height of rise for a line plume A dynamical model of a Hawaiian plume Comparison with observations Basaltic Plinian and ignimbrite eruptions Summary 276 Chapter 11 Atmospheric Dispersal Introduction Dynamics of umbrella clouds Models of umbrella cloud growth Entrainment Plume-wind interaction Strong plumes ^Weak plumes Topographic effects Regional and global transport Comparison with observations 298 T Umbrella clouds Downwind spreading and plume dispersal patterns Examples of hemispheric to global transport Summary 306 Chapter 12 Remote Sensing of Volcanic Plumes Introduction Principles of electromagnetic theory Electromagnetic remote sensing basics Spectral region and resolution Spatial resolution Observation opportunities 314

7 x CONTENTS 12.4 Determination of plume properties Plume height Plume temperature Output of SO Satellite plume differentiation and eruption monitoring Volcanic plume distinction Plume dispersal observations from satellite Monitoring of electric potential gradients and lightning generated by plumes Background Field measurements at volcanoes Acoustic measurements of volcanic plumes Principles Measurements at Stromboli Summary 345 Chapter 13 Tephra Fall Deposits Introduction Ejecta components Petrology of ejecta General description of fallout Characteristics of fall deposits Thickness Volumes Particle size Classification of fall deposits Co-ignimbrite fall deposits Tephrochronology Correlation and dating Archaeological applications Marine tephrochronology ' Summary 378 Chapter 14 Sedimentation from Volcanic Plumes Introduction Particle settling The influence of particle shape Variation of fall velocity with altitude Ballistic particles Sedimentation from turbulent suspensions Basic principles Radial gravity currents Plumes and jets Backflow Re-entrainment 393

8 CONTENTS xi Effects of wind Atmospheric advection/diffusion models Observations Laboratory experiments Volcanic deposits Re-entrainment Summary 403 Chapter 15 Quantitative Interpretation of Tephra Fall Deposits Introduction Maximum grain size data Theoretical considerations Maximum clast method Evaluation of maximum clast method Application to Plinian eruptions Application of plume sedimentation models Thickness variations Particle size variations Emplacement temperature and welding Summary 431 Chapter 16 Particle Aggregation in Plumes Introduction " Geological observations Anomalous deposit thicknesses Particle size distributions Aggregates Aggregation mechanisms Collision mechanisms Binding mechanisms Experiments and theory Laboratory simulation Theoretical models of aggregation Summary 461 Chapter 17 Environmental Hazards Introduction Health hazards to humans Hazards to animals Effect on vegetation Property damage Disruption of community infrastructure ~ Aviation hazards 480

9 xii CONTENTS Disruptions of airport operations Plume encounters in flight Effect of ash and aerosols on aircraft Mitigation Summary and lessons learned 490 Chapter 18 Atmospheric Effects Introduction Early research Physical principles Sedimentation and dispersal of volcanic aerosols The Pinatubo 1991 eruption Sulphur dioxide emission Sulphur dioxide decay and sulphate aerosol evolution Stratospheric warming Tropospheric and surface cooling Ozone perturbation Depletion of nitrogen dioxide Volcanologic parameters Summary 524 References 526 Index 560