Much of our understanding of explosive eruptions comes from detailed studies of the deposits they produce. Explosive activity produces fragments of solidified magma and debris from the volcano (both of these types of fragments are referred to as pyroclasts, from the Greek words for fire and broken). These pyroclasts are subsequently deposited around the volcano by a range of processes, including fallout from volcanic plumes that may reach tens of kilometers into the atmosphere, by simple ballistic ejection from a vent, and by mixtures of gases and pyroclasts that flow along the ground (often referred to as pyroclastic flows). The deposits of a given type of activity might be limited to within tens or hundreds of meters from a volcanic vent and have volumes of hundreds to thousands of cubic meters, as commonly produced by Strombolian activity, or they might extend hundreds of kilometers and comprise hundreds to thousands of cubic kilometers of volume, as produced by large caldera-forming eruptions.
Pyroclastic deposits are both sedimentary (produced by deposition of particles) and igneous (derived directly from magmatic processes). Like other sedimentary deposits, much about their emplacement can be learned by detailed studies of facies characteristics and variations, fabrics and textures, and grain size parameters. The properties of a given pyroclastic deposit depend both on the eruptive processes at the vent(s) and their variation with time, and on the complex range of transport and depositional processes that can occur in these energetic events. Similarly, as with igneous rocks, the material properties of the source magmas, such as viscosity and crystal and bubble content, also play a key role the final product. Field-based studies of pyroclastic deposits must be combined with experimental and theoretical studies in order to quantify their parent processes (see also Volcano fluid dynamics & modeling).
My interests in pyroclastic deposits range from improving our understanding of the controls on eruptive styles at small basaltic volcanoes such as scoria cones (see also Basaltic volcanism) to the mechanisms and fluid dynamics that result in large-volume pyroclastic flow deposits that cover wide areas such as in the western United States. In the latter case, much remains poorly known about how these flows are able to transport their pyroclastic load over such large distances. A research topic that I am pursuing over the next few years is aimed at improving our understanding of the initial conditions of pyroclastic flows in areas proximal to their sources (see also Volcano fluid dynamics & modeling) and what clues we can find in proximal deposits that might help us understand transport and emplacement in more distant areas.