Abstract Volcanoes produce probably the most spectacular geological phenomena on Earth. Any of their eruptions can have a strong consequence on the surrounding environment, often captured in great detail in the sedimentary records of volcanically active regions. In addition, flank landslides and background erosive processes affecting volcanic sequences release volcanic particles that circulate within sedimentary environments up to billions of years after their generation. Therefore, exploring volcanically influenced sedimentary environments is an exciting and challenging scientific exercise requiring insights across multiple geological disciplines, drawing upon an increasing varied range of expertise and analytical approaches from across the geoscientific community. This book aims to provide an updated collection of works that illustrate the state-of-the-art in this topic, and to define the future directions of the geological sciences in utilizing and interpreting sedimentary records of volcanism.

Abstract Subaerial volcaniclastic deposits are produced principally by volcanic debris avalanches, pyroclastic density currents, lahars, and tephra falls. Those deposits have widely ranging geomorphic and sedimentologic characteristics; they can mantle, modify, or create new topography, and their emplacement and subsequent reworking can have an outsized impact on the geomorphic and sedimentologic responses of watersheds surrounding, and channels draining, volcanoes. Volcaniclastic deposits provide a wealth of information about eruptive histories, volcanic processes, and landscape responses to eruptions. The volcanic processes that produce these deposits, and consequently the character and sedimentary structures of the deposits themselves, are influenced by initiation mechanism. Deposit preservation is affected by deposit magnitude, texture, and composition, depositional environment, and climate regime. Innovative analyses of deposits from several modern eruptions and advancements in physical and numerical modelling have vastly improved our understanding of volcanic processes, interpretations of eruptive histories, and recognition of the hazards posed by volcanic eruptions. This contribution highlights and summarizes major advances that have occurred in the past few decades in understanding of volcaniclastic deposits and linkages with volcanic processes.

Abstract Bedforms that develop at the interface between a fluid flow and a loose sediment bed are among some of the most fundamental morphodynamic processes, perhaps among the greatest examples of canonical autogenic adjustments between flow and sediments. Because different types of bedforms develop under specific combinations of flow and sediment properties, these sedimentary features have commonly been used to aid interpretations of flow conditions and infer the nature of depositional environments. While subaerial (river) bedforms are relatively well understood, their counterparts in deep water (i.e., related to gravity underflows, namely, density or turbidity currents) remain somewhat elusive, largely due to the difficulty of direct observation in their natural setting, due to the limited number of experimental studies, and due to their inherent process complexity. Although widely practiced, extrapolation of equilibrium regime diagrams developed for subaerial bedforms to the deep-water realm remains questionable, particularly in light of recent experimental and field observations that suggest some departures from the subaerial counterpart. Herewe present results from an experimental program aimed at investigating equilibrium bedforms resulting from saline density currents under bypass conditions. Saline density currents have been typically treated as the surrogate of muddy turbidity currents for which sediments never settle. More than 500 separate experiments were run, comprising currents that spanned a wide range of the densimetric Froude number including all flow regimes (supercritical, critical, subcritical: Fr d = 0.6 to 2.8). Results confirm some similarities between subaerial and gravity flow bedforms both in process and product but also reveal some interesting differences. For example, ripples form under both subcritical and supercritical density currents, while supercritical currents yield dunes and both small-wavelength, downstream-migrating, and long-wavelength, upstream-migrating antidunes, where the latter may transition to cyclic steps. Supercriticality of the flow, the proportion of bedload to suspended load (when looking at the sediment composing the bed), and the bed characteristic sediment size are the major controls on the prevailing bedform observed. To investigate the flow and morphodynamic mechanisms related to some of the observed bedforms (e.g., supercritical dunes), detailed analyses of flow structure over the bed features were performed using particle image velocimetry techniques. Outcrop examples are presented to demonstrate that the gravity flow bedforms we observed experimentally might have counterparts at the field scale. Our findings underscore the rich spectrum of potential bed states produced by dense underflows and their deviation from bed behavior in open-channel flows. As a result, we argue that inversion of gravity flow bed features based on known subaerial bedform regimes might be potentially misleading.

The field of volcanology has greatly changed during the last half century. The profession is now much more diverse and interdisciplinary, even including collaborating researchers from the social and medical sciences. This new mode of cooperation and working has been more successful in mitigating volcanic hazards and risks. There are fewer of the strong-willed lone rangers of the past and more of those who work with teams to more effectively understand how volcanoes work to protect those living on or near active or potentially active volcanoes. Moreover, there are more university departments with volcanology in their curricula and more international symposia and workshops focusing on mitigation of risk posed by volcano-related hazards. We all have respected colleagues and volcano observatories in many countries. The importance of understanding explosive volcanic eruptions and tracking of eruption plumes involves volcanologists, atmospheric physicists, and air-traffic controllers and is of great interest to the aviation industry. We now have the links in place between great science and practical applications.