Volcanoes can produce far-reaching hazards that extend distances of tens or hundreds of kilometres in large eruptions, or in certain conditions for smaller eruptions. About a tenth of the world's population lives within the potential footprint of volcanic hazards and lives are regularly lost through volcanic activity: volcanic fatalities were recorded in 18 of the last 20 years. This paper identifies the distance and distribution of fatalities around volcanoes and the activities of the victims at the time of impact, sourced from an extensive search of academic and grey literature, including media and official reports. We update and expand a volcano fatality database to include all data from 1500 AD to 2017. This database contains 635 records of 278,368 fatalities. Each record contains information on the number of fatalities, fatal cause, incident date and the fatality location in terms of distance from the volcano. Distance data were previously available in just 5% of fatal incidents: these data have been significantly increased to 72% (456/635) of fatal incidents, with fatalities recorded from inside the crater to more than 100 km from the summit. Local residents are the most frequently killed, but tourists, volcanologists and members of the media are also identified as common victims. These latter groups and residents of small islands dominate the proximal fatality record up to 5 km from the volcano. Though normally accounting for small numbers of fatalities, ballistics are the most common cause of fatal incidents at this distance. Pyroclastic density currents are the dominant fatal cause at 5 to 15 km. Lahars, tsunami and tephra dominate the record after about 15 km. The new location data are used to characterise volcanic threat with distance, as a function of eruption size and hazard type, and to understand how certain activities increase exposure and the likelihood of death. These findings support assessment of volcanic threat, population exposure and vulnerabilities related to occupation or activity.

Using ground deformation data from Soufrière Hills volcano (SHV), we present results from numerical modeling of the temperature‐ and time‐dependent stress evolution in a mechanically heterogeneous crust prior to reservoir failure and renewed eruptive activity. The best fit models do not allow us to discriminate between a magmatic plumbing system consisting of either a single vertically elongated reservoir or a series of stacked reservoirs. A prolate reservoir geometry with volumes between 50 and 100 km3, reservoir pressure changes between 4 and 7 MPa, and reservoir volume changes between 0.03 and 0.04 km3 with magma compressibility between 4 × 10−11 and 1 × 10−9 Pa−1 provide plausible thermomechanical model parameters to explain the deformation time series; around an order of magnitude less overpressure than is generally inferred from homogeneous, elastic crustal models. Reservoir failure is predicted to occur at the crest of the reservoir except for reservoirs with highly compressible magma (≳4×10−9 Pa) for which subhorizontal sill formation is predicted upon reservoir failure. Introducing a deep‐crustal hot zone modulates the partitioning of strains into the hotter underlying crust and results in a further reduction in overpressure estimates to values of around 1–2 MPa upon reservoir failure. Deduced volume fluxes are consistent with constraints from thermal modeling of active subvolcanic systems and imply dynamic failure of a compressible magma mush column feeding eruptions at SHV. Our interpretation of the results is that the combined thermomechanical effects of a deep‐crustal hot zone and hot encasing rocks around a midcrustal andesitic reservoir fundamentally alter the time‐dependent subsurface stress and strain partitioning upon reservoir priming. These effects substantially influence surface strains recorded by volcano geodetic monitoring.

On 11 February 2010, a partial dome collapse, the largest since 20 May 2006, occurred at Soufrière Hills Volcano (SHV), Montserrat. The collapse is also the largest generated on the northern flank of SHV since the eruption began in 1995. Approximately 50×106 m3 was removed from the dome, resulting in widespread pyroclastic density currents (PDCs). Mapping revealed a complex stratigraphy that varied widely across the northern and NE flanks, and reflected the complex evolution of the collapse. The deposits included a range of fine-grained ash-rich and pumice-rich units deposited by dilute PDCs, and several types of coarse-grained, blocky deposits from dense PDCs. Several previously unaffected areas, including Bugby Hole, Farm River Valley, the village of Harris and Trants, suffered significant damage to the natural and built environments. The collapse lasted 107 min but the bulk of the activity occurred in a 15 min period that included five of the six peaks in PDC generation and two Vulcanian explosions. Although powerful, the PDCs generated were not associated with a lateral blast. The likely cause was the piecemeal collapse of a series of large, unstable lobes that had been extruded on the northern flank of the pre-existing dome.

Volcanic water-sediment flows, commonly known as lahars, can often pose a higher threat to population and infrastructure than primary volcanic hazardous processes such as tephra fallout and Pyroclastic Density Currents (PDCs). Lahars are volcaniclastic flows of water, volcanic debris and entrained sediments that can travel long distances from their source, causing severe damage by impact and burial. Lahars are frequently triggered by intense or prolonged rainfall occurring after explosive eruptions, and their occurrence depends on numerous factors including the spatio-temporal rainfall characteristics, the spatial distribution and hydraulic properties of the tephra deposit, and the pre-and post-eruption topography. Modeling (and forecasting) such a complex system requires the quantification of aleatory variability in the lahar triggering and propagation. To fulfill this goal, we develop a novel framework for probabilistic hazard assessment of lahars within a multi-hazard environment, based on coupling a versatile probabilistic model for lahar triggering (a Bayesian Belief Network: Multihaz) with a dynamic physical model for lahar propagation (LaharFlow). Multihaz allows us to estimate the probability of lahars of different volumes occurring by merging varied information about regional rainfall, scientific knowledge on lahar triggering mechanisms and, crucially, probabilistic assessment of available pyroclastic material from tephra fallout and PDCs. LaharFlow propagates the aleatory variability modeled by Multihaz into hazard footprints of lahars. We apply our framework to Somma-Vesuvius (Italy) because: (1) the volcano is strongly lahar-prone based on its previous activity, (2) there are many possible source areas for lahars, and (3) there is high density of population nearby. Our results indicate that the size of the eruption preceding the lahar occurrence and the spatial distribution of tephra accumulation have a paramount role in the lahar initiation and potential impact. For instance, lahars with initiation volume ≥10 5 m 3 along the volcano flanks are almost 60% probable to occur after large-sized eruptions (∼VEI ≥ 5) but 40% after medium-sized eruptions (∼VEI4). Some simulated lahars can propagate for 15 km or reach combined flow depths of 2 m and speeds of 5-10 m/s, even over flat terrain. Probabilistic multi-hazard frameworks like the one presented here can be invaluable for volcanic hazard assessment worldwide.

Abstract. Scour (localised erosion) during flood events is one of the most significant threats to bridges over rivers and estuaries, and has been the cause of numerous bridge failures, with damaging consequences. Mitigation of the risk of bridges being damaged by scour is therefore important to many infrastructure owners, and is supported by industry guidance. Even after mitigation, some residual risk remains, though its extent is difficult to quantify because of the uncertainties inherent in the prediction of scour and the assessment of the scour risk. This paper summarises findings from an international expert workshop on bridge scour risk assessment that explores uncertainties about the vulnerability of bridges to scour. Two specialised structured elicitation methods were applied to explore the factors that experts in the field consider important when assessing scour risk and to derive pooled expert judgements of bridge failure probabilities that are conditional on a range of assumed scenarios describing flood event severity, bridge and watercourse types and risk mitigation protocols. The experts' judgements broadly align with industry good practice, but indicate significant uncertainty about quantitative estimates of bridge failure probabilities, reflecting the difficulty in assessing the residual risk of failure. The data and findings presented here could provide a useful context for the development of generic scour fragility models and their associated uncertainties.

Cycles of eruptive activity are generally interpreted as evidence of one or more mechanisms operating in equilibrium. Modulation of cycle characteristics thus reflects changes in the conditions affecting those mechanisms. This kind of semi-deterministic behaviour at the Soufrière Hills Volcano has occurred on multiple timescales and with a range of eruptive intensity. By documenting cyclic phenomena, it is possible to investigate the mechanisms that modulate the state of the eruption and examine conceptual models. Pattern recognition and model development allows some degree of short-term forecasting ability for volcanic activity. We report the cyclic eruptive phenomena that have occurred on Montserrat on scales of hours to centuries. We identify four dominant types of cyclicity: sub-daily variations in lava flux; sub-annual cycles in eruption intensity; multi-annual ‘on–off’ switching of lava extrusion; and multi-decadal recurrence of seismic crises. We exploit a wealth of multi-parameter datasets (including seismic, geodetic, thermal, archive and visual observations), and present the evidence and observations for each type of cyclicity, some of which are documented here for the first time. Wavelet time-series analysis is used to constrain cycle characteristics, where appropriate. We discuss the implications of these observations in understanding the eruptive mechanisms of the Soufrière Hills Volcano.Supplementary material:Details of all sub-daily cycles are listed in a supplementary table that is available at http://www.geolsoc.org.uk/SUP18700.

Vulcanian explosions generated at Soufrière Hills Volcano between 2008 and 2010 varied from simple events involving minimal pyroclastic density currents (PDCs) to complex events involving more than one explosion. Calculated volumes for the deposits of the PDCs formed by these explosions ranged up to 2.7×106 m3, with more than half the explosions having volumes greater than 1×106 m3. The deposits formed by the explosions varied in lithology, with some explosions generating pumice-rich PDCs (e.g. 29 July 2008 and 11 February 2010) showing development of sinuous lobes. These explosions are similar to those formed in 1997, with gas-rich, conduit-derived magma being the dominant driving mechanism. Other explosions were pumice-poor (c. 5 wt% pumice) and generated morphologically distinct PDC deposits. Many of the pumice-poor explosions were associated with lower tephra plumes of <8 km, but were some of the largest volume events in terms of PDC production and suggest a generation mechanism involving destruction of significant quantities of the lava dome. Analysis of video footage shows that PDC formation was pulsatory, probably related to destabilization of portions of the lava dome during the initial phases of the explosion.

Exogenous growth of Peléean lava domes occurs by addition of lava from a central summit vent and mass wasting on the flanks as rockfalls and pyroclastic flows, forming an apron of talus. We observed this process at the Soufrière Hills Volcano, Montserrat between 30 March and 10 April 2006 using a ground-based imaging mm-wave radar, AVTIS, to measure the shape of the dome surface. From a time series of range and intensity measurements at a distance of six kilometres we measured the topographic evolution of the lava dome. The locus of talus deposition moved to the southeast with time and the talus surface grew upwards on average at about 2 m/day. The AVTIS measurements show an acceleration in lava extrusion rate on 5 April, with a 2-day lag in the equivalent rockfall seismicity record. We account for the budget of lava addition and dispersal during the eleven days of measurements using: AVTIS range measurements to measure the talus growth (7.2 Mm 3 , 67%), AVTIS range and intensity measurements to measure the summit lava growth (1.7 Mm 3 , 16%), and rockfall seismicity and visual observations to measure the pyroclastic flow deposits (1.8 Mm 3 , 17%). This gives an overall dense rock equivalent extrusion rate of about 9.7 m 3 s -1 . These figures demonstrate how efficient non-explosive lava dome growth can be in generating large volumes of primary clastic deposits, and how this process could also reduce the propensity for large hazardous pyroclastic flows.