1 Introduction.- The Sedimentary Record: Volcanic Contribution.- Chemical Composition of Tephra.- Types of Pyroclastic Accumulations.- 2 Volcanoes, Volcanic Rocks and Magma Chambers.- Tectonic Setting of Volcanoes.- Divergent Margins.- Convergent Margins.- Intraplate Volcanoes.- Form of Volcanoes.- Origin of Magmas and Classification of Volcanic Rocks.- Basaltic Magmas.- Basalts.- Andesite-Suite Magmas.- Andesites.- Differentiated Magmas.- Magma Chambers.- Volumes of Magma Chambers.- Zonation in Magma Chambers.- Large Calcalkalic Systems.- Small Highly Alkalic Systems.- Oceanic Rhyolite-Basalt Systems.- Very Small Mafic-Intermediate Magma Systems.- 3 Magmatic Volatiles and Rheology.- Volatiles.- Methods of Determining Volatiles.- Composition and Amount of Volatiles.- Water 38 - Carbon Dioxide 43 - Sulfur.- Volatile Distribution in Magma Columns.- Rheology.- Viscosity.- Vesiculation.- 4 Explosive Volcanic Eruptions.- Types of Volcanic Activity.- Types of Eruptions.- Pyroclastic Eruptive Systems.- Eruption Columns.- Plinian Eruptions and Eruption Columns.- Hawaiian and Strombolian Eruptions.- Observations 69 - Eruptive Mechanisms.- Hydroclastic Eruptive Processes.- Formation of Glassy Pyroclasts.- Granulation.- Inhibition of Vesiculation.- Transfer of Heat.- Steam Eruptions.- Magma-Water Mixing and Fuel-Coolant Interaction.- Phreatic and Phreatomagmatic (Vulcanian) Eruptions.- Volcanic Energy.- 5 Pyroclastic Fragments and Deposits.- General Components.- Vitric Particles and Pyrogenic Crystals.- Glass Shards.- Shards Formed by Vesiculation.- Pumice.- Pyrogenic Minerals.- Surface Textures of Minerals and Shards.- Structure.- Pyroclastic Bed or Stratum.- Graded Bedding.- Cross Bedding.- Massive Beds.- Alignment and Orientation Bedding.- Penecontemporaneous Deformation Structures.- Texture.- Grain Size and Size Distribution.- Distribution Curves.- Shape and Roundness.- Fabric.- 6 Subaerial Fallout Tephra.- Components of Subaerial Fallout.- Areal Distribution.- Distribution and Thickness.- Volume.- Structures.- Bedding.- Mantle Bedding.- Graded Bedding.- Fabric.- Size Parameters.- Maximum Size of Components.- Median Diameter.- Grain-Size Distribution (Sorting).- Eolian Fractionation.- 7 Submarine Fallout Tephra from Subaerial Eruptions.- Chemical Composition.- Structures of Submarine and Lacustrine Ash Layers.- Areal Thickness Distribution and Volume.- Grain Size and Sorting.- Regional Distribution and Tephrochronology.- Source.- Correlation and Age.- Pacific Region.- Atlantic Region.- 8 Pyroclastic Flow Deposits.- Historic Development of Concepts.- The Deposits.- Volume.- Relationship to Topography.- Flow Units and Cooling Units.- Components.- Primary Structures in Unwelded Deposits.- Internal Layering 198 - Gas-Escape Structures.- Emplacement Facies.- Texture.- Pyroclastic Flow Deposits 207 - Pyroclastic Surge Deposits 208 - Segregation of Crystals and Lithics.- Chemical Composition.- Temperature Effects.- Measured Temperatures 210 Inferred Temperatures 211 - Welding and Compaction 213 - Structures Related to Temperature and Viscosity.- Thermoremanent Magnetism.- Classification and Nomenclature.- The Flows.- Origin.- Transport and Mobility.- Tufolavas, Froth Flows, Foam Lavas and Globule Flows.- Ignimbrite Vents: Speculation.- 9 Deposits of Hydroclastic Eruptions.- Definition of Terms.- Components of Hydroclastic Deposits.- Grain Size Distribution.- Characteristics of Essential Components.- Accretionary Lapilli.- Accidental Clasts.- Maximum Size of Fragments Related to Energetics.- Ultramafic Xenoliths.- Structures.- Penecontemporaneous Soft Sediment Deformation.- Vesicles (Gas Bubbles).- Bedding Sags.- Mudcracks.- Base Surge Deposits.- Bed Forms from Base Surges.- Sandwave Beds 250 - Plane-Parallel Beds 254 - Massive Beds.- Bed Form Facies.- U-Shaped Channels.- Maar Volcanoes.- Classification.- Origin.- Dimensions.- Areal Extent and Geometry 260 - Volume.- Chemical Composition.- Littoral Cones.- Deposits.- Origin.- Peperites.- 10 Submarine Volcaniclastic Rocks.- Deep Water Stage.- Pillow Breccias.- Fine-grained Hyaloclastites.- Shoaling Submarine Volcano.- Transition Submarine - Subaerial.- Volcaniclastic Aprons.- Silicic Submarine Eruptions.- Subaqueous Pyroclastic Flows.- Terminology.- Nonwelded Deposits.- Environment of Deposition.- Components.- Grain Size, Sorting and Fabric.- Bedding and Grading.- The Massive Lower Division 289 - Upper Division.- Relationship to Eruptions and Eruptive Centers.- Welded Deposits.- Discussion.- 11 Lahars.- Debris Flows as Fluids.- Distribution and Thickness.- Surface of Lahars.- Basal Contact of Lahars.- Components of Lahars.- Grain-Size Distribution.- Vesicles.- Grading.- Fabric.- Comparison of Lahars with Other Kinds of Coarse-Grained Deposits.- Origin.- 12 Alteration of Volcanic Glass.- Diagenesis.- Alteration of Basaltic Glass.- Palagonite.- Physical Properties 315 - Textural Changes 315 - Mineralogical Changes 317 - Zeolites 318 - Chemical Changes.- Process of Palagonite Formation.- Rate of Palagonitization.- Alteration of Silicic Glass.- Hydration and Ion Exchange.- Advanced Stages of Alteration.- Saline Alkaline Lake Environment.- Marine Environment.- Bentonites and Tonsteins.- Burial Diagenesis and Metamorphism.- 13 Stratigraphic Problems of Pyroclastic Rocks.- Relation of Volcanic Activity to Rock Stratigraphy.- Volcanic Activity Units.- Eruption Unit.- Stratigraphic Problems in Young Volcanic Terranes.- Stratigraphic Nomenclature in Older Volcanic Terranes.- Tephrochronology.- Volcanic Facies.- Facies Based upon Position Relative to Source.- Near-Source Facies 358 - Intermediate-Source Facies 359 - Distant-Source Facies 359 - Caldera Facies.- Facies Based upon Environment of Deposition.- Facies Based upon Primary Composition.- Compositional Facies 362 - Petrofacies.- Diagenetic Rock Facies.- Stratigraphic Examples.- Oshima Volcano, Japan.- San Juan Volcanic Field, USA.- Archean Greenstone-Belt Volcanoes, Canada.- 14 Pyroclastic Rocks and Tectonic Environment.- Convergent Margins, Magmatic Arcs, and Sedimentation.- The Trench.- Fore-Arc and Back-Arc Basins.- The Cordilleran System.- Western North America: Paleozoic Rocks 392 - Southern South America: Upper Mesozoic Flysch 396 - Cenozoic Tectonism and Volcanism: Western North America.- Oceanic Island Arc Settings.- Volcaniclastic Rocks and Facies; Cenozoic 400 - Lau Basin and Tonga Arc 405 - Lesser Antilles Arc.- The Pre-Cambrian.- References.- Locality Index.