Introduction and key concepts
Pyroclastic density currents are inhomogeneous mixtures of volcanic particles and gas that flow according to their density relative to the surrounding fluid (generally the atmosphere) and due to Earth's gravity. They can originate by fountain-like collapse of parts of an eruption column following explosive disintegration of magma and rock in a volcanic conduit, or from laterally inclined blasts, or from hot avalanches derived from lava domes. They can transport large volumes of hot debris rapidly for many kilometres across the ground and they constitute a lethal and destructive volcanic hazard. Ground-hugging pyroclastic density currents produce a buoyant counterpart, known as a phoenix cloud or co-ignimbrite ash plume, which can carry ash and aerosols into the stratosphere and so cause significant climatic perturbation. Most processes within pyroclastic density currents are impossible to observe and so are commonly inferred from the associated deposits.
Figures & Tables
Pyroclastic Density Currents and the Sedimentation of Ignimbrites
Pyoclastic density currents are awesome volcanic phenomena that can wreak destruction on a regional scale and can impact global climate. They deposit ignimbrites, which include vast impact lansdscape-modifying sheets with volumes exceeding 1000 km3.This book takes stock of our understanding of pyroclastic density currents and presents a new conceptual framework for investigating how ignimbrites are deposited. It integrates the results of field-based studies, laboratory experiments and numerical modelling, including work on clastic sedimentologym and industrial particle transport. Topics covered include the behaviour or particulate currents, mechanisms of clast support and segregation, interpreting ignimbrite lithofacies and architectures, and future research directions. The new approach focuses on processes and conditions within the lower flow-boundary zone of currents. Superb diagrams explain many new concepts, while the 95 photographs make an explanatiry atlas of deposit types. This is essential reading for workers investigating volcanic hazards, and for anyone wishing to interpret modern or ancient ignimbrites, as well as other catastrophically emplaced sediments.
“Given the depth of scholarship that they have brought to the subject, the power of their arguments, and the degree of synthesis with other fields, this would seemto qualify as a seminal work… I think that this will be the paper on the topic that others will have to contend with for many years to come.” Marcus Bursik, State University of New York