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This is a parametric study that was carried out to investigate the signals generated by a hydrothermal system fed by a pulsating source of magmatic fluids. This study focuses on the effects that selected properties of the source have on the evolution of hydrothermal activity at Campi Flegrei, Italy. Numerical simulations are carried out to describe a multiphase and multicomponent hydrothermal system. Each simulation describes a short unrest phase, followed by a prolonged quiet period. During the unrest, specific properties of the fluid source (flow rate, fluid composition, source size, and unrest duration) are modified with respect to selected baseline values. The evolution of the system is tracked by looking at two parameters that can be monitored in active volcanic areas: the composition of fumarolic gases and gravity changes. The results describe the temporal evolution of these two observables and allow comparisons of the effects of different source properties. All of the simulated unrest events cause measurable changes in gas composition and gravity. For the geometry and system properties considered, these changes always last beyond the end of the unrest period, and can often persist for decades. Fluid flow rate is the source property that mostly affects the observable evolution. Gravity is more sensitive to source properties than gas composition, and it undergoes the largest and quickest changes. The results also highlight the major role that rock properties and initial conditions have in the evolution of these observable signals.

IN large eruptions, Vesuvius has generated catastrophic avalanches of tephra and hot gases, such as those that destroyed Pompei and Herculaneum in AD 79, and Torre del Greco and surrounding towns in 1631 1,12 . These avalanches (pyroclastic surges and flows) are produced from collapses of the eruptive column, and can travel at >100 m s -1 , with temperatures exceeding 800 °C. In 1944 Vesuvius ended its most recent cycle of activity, which had begun with the explosive eruption of 1631. Here we use numerical simulations to assess the hazards posed by the pyroclastic flows that are likely to accompany the onset of the next cycle of activity. We examine three different scales of eruption, and use vent conditions established by modelling magma ascent along the conduit 13,14 . Our results indicate that large- and medium-scale eruptions can produce complete destruction in the 7 km radius around the volcano (an area in which one million people live and work) in about 15 minutes or less, and that only small-scale eruptions can be arrested by the topographic relief of Monte Somma.

Strategies of risk mitigation become effective when citizens facing hazardous phenomena adopt rational behaviours that contribute to the lowering of the risk. This is more likely to occur when endangered communities share a widespread understanding of natural phenomena and their impacts. To reach this goal, educational and outreach materials are often organised around the descriptions of the natural process and its effects. Unfortunately, however, receiving correct information does not automatically grant the adoption of safe behaviours. Our teaching efforts may fail because of pre-existing biases, beliefs, and misconceptions. The identification of these biases is important to plan effective educational campaigns capable of providing the concepts that are needed to actually inform citizens' choices about natural hazards. In this work, we present the results of an unconventional workshop on volcanic risk that we proposed to primary and secondary schools (aged 6–13) in Italy. The workshop is meant to explore the mental models that kids and youngsters have about volcanic eruptions, and it takes the form of a creative exercise. We asked the pupils to write and illustrate a story in four frames, describing the onset and outcome of an imaginary eruption. All stories were then presented to the class and always provided useful hints to spark discussion about volcanic processes and hazards. As a whole, the collected stories provide a multifaceted description of volcanic eruptions and their potential impacts as imagined by the kids. A careful analysis of this material provided several insights useful to improve future outreach material and educational plans. The workshop is simple to reproduce, even remotely, and could easily be extended to different types of hazards. While very simple to organise, this approach grants the secure engagement of most participants and offers a very different perspective on pupils' understanding of natural phenomena.

Explosive events are commonly accompanied or followed by heavy rains. These eruption-induced storms together with the deposition of large amounts of ash contribute to destabilise the hydrological cycle in the areas affected by volcanic eruptions. Flooding of the region surrounding the active volcano can easily follow, increasing the complexity of the volcanic crisis and its management. This is particularly true in the case of Vesuvius, that is not only characterized by a dramatic volcanic hazard, but it is also located within an area that is normally prone to flood hazard. A complete assessment of the impact associated with explosive volcanic eruptions should involve a flood hazard assessment for the region. This work represents a first attempt to address the problem: a topographically based rainfall-runoff model was here applied to the Vesuvian area where two main sub-basins were analysed. The model was applied to evaluate the role of selected parameters on the total discharge at the basins' outlet. These parameters were chosen among those likely to be affected by an explosive event and were varied through a reasonable range. Results confirm that the deposition of large amounts of ash can affect the temporal evolution of the discharge and its maximum value, for a given precipitation event. The simulations presented outline the need for a detailed flood forecasting study for the Vesuvian area, that should be included within the hazard mitigation strategies.