Preface • Acknowledgements • Chapter 1 Introduction and key concepts Deposits of pyroclastic density currents • The role of ignimbrites in ideas about pyroclastic density currents • Key concepts • current steadiness and uniformity • Lower flow-boundary zones: sites of segregation and variable deposition • Ignimbrite architecture: a record of flow-boundary zone evolution through time and space • Chapter 2 The origin, nature and behaviour of pyroclastic density currents Origin and development of pyroclastic density currents Eruption styles • Current concentration and rheology • Deflation reappraised • The nature of pyroclastic density currents • The leading part of the current • Current velocity • Velocity profiles and turbulence intensity • Plug flow • Current stratification • Partitioning of mass flux in density-stratified currents • The behaviour of pyroclastic density currents • Inertia, buoyancy, runout distance and lofting • Internal waves, hydraulic jumps and granular jumps • Thalwegs (flow axes) and lateral migration • Effects of topography • A new twofold classification of pyroclastic density currents • Chapter 3 Mechanisms of particle support and segregation Significance of current heterogeneity and pyroclast diversity • Fluid turbulence • Support by fluid turbulence • Vertical segregation of clasts in the current during turbulent transport • Segregation at the flow-boundary zone due to turbulence • Support on an interface • Sustained support: rolling and sliding • Intermittent support: saltation • Overpassing: down current segregation at an interface • Granular temperature and dispersive pressure • Clast interactions and current mobility • Segregation in ganular flows • Fluidization • Fluidization and transport • Segregation by fluidization • Hindered settling, fluid escape and sedimentation-fluidization • Segregation by fluid escape and hindered settling • Clast buoyancy • Buoyancy and transport • Segregation by buoyancy • Acoustic mobilization • Acoustic mobilization and transport • Segregation by acoustic mobilization • Support by strength • Quasi-static grain contacts • Cohesion • Segregation associated with strength • Particle interlocking • Chapter 4 Conceptualizing deposition: a flow-boundary zone approach Deposition from steady currents • Direct fallout-dominated flow-boundary zone • Traction-dominated flow-boundary zone • Granular flow-dominated flow-boundary zone • Fluid escape-dominated flow-boundary zone • Gradational types of flow-boundary zone • Selective filtering: flow-boundary zone segregation and overpasing during deposition • Traction carpets • Deposition during unsteadiness • Fluctuating deposition • Sustained gradual changes • Rapid deposition • En masse deposition • Non-uniform deposition • Interpreting ignimbrite lobes and levees • Postdepositional remobilization • Effects of deposition on current behaviour • Chapter 5 Interpreting ignimbrite lithofacies A lithofacies scheme for ignimbrites • Massive lapilli-tuff lithofacies • Description • Interpretation • Origin of fabrics in massive lapilli-tuff lithofacies • Massive to stratified lithic breccia lithofacies • Description • Interpretation • Segregation of blocks from pumice and ask • Interpretation of stratified breccias and breccia lenses • Classifications of ignimbrite breccias • Massive agglomerate lithofacies • Description • Interpretation • Lithofacies with fines-poor (elutriation) pipes, sheets or pods • Description • Interpretation • Vertical grading patterns • Description • Interpretation • Diffuse-stratified and thin-bedded lithofacies • Description • Interpretation • Stratified and cross-stratified tuffs 7bull; Description • Interpretation • Pumice-rich layers, lenses and pods • Description • Interpretation • Massive and parallel-bedded lapilli deposits • Description • Interpretation • Parallel-bedded and parallel-laminated tuffs • Description • Interpretation 7bull; Eutaxitic, rheomorphic and lava-like lithofacies • Description • Interpretation • Origin of poor sorting in ignimbrites • Chapter 6 Ignimbrite architecture: constraints on current dynamics Conceptualizing architecture in a time-geometry framework • Longitudinal architectures • Transverse architecture • Interpreting longitudinal (proximal to distal) lithofacies variations • Longitudinal coarse-tail grading • Downcurrent lithofacies changes from stratified to massive • Distal lithofacies changes from massive to stratified • Interpreting vertical lithofacies variations • Gradational versus sharp lithofacies variations • Bedding and flow-unit boundaries • Repetitious and rhythmic lithofacies successions • Disordered lithofacies succession • Intercalated massive and stratified divisions • Complex longitudinal architecture • Interpreting lithofacies successions at bases of ignimbrites • Stratified bases • Basal pumice lenses • Fines-poor bases • Fine-grained layers at the base of ignimbrites • Some common successions of basal lithofacies • Sheared or loaded substrate • Interpreting lithofacies at the top of ignimbrites • Transverse lithofacies variations • Splay-and-fade stratification • Scour splay-and-fade stratification • Effects of current thalwegs and braiding • Gradations between massive valley-filling ignimbrite and stratified topographic veneers • Radially symmetrical ignimbriete distributions • Ignimbrite fans and asymmetric igimbrite distributions • Interpreting the shape of ignimbrites • A classification of ignimbrite shapes • Significance of aspect ratio • Top surfaces of ignimbrites • Chapter 7 Overview, key implications and future research Overview and key implications • Future research • Definitions of terms used • References • Index •