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Passive volcanic degassing often occurs at active but not actively erupting volcanoes. Gases are emitted by fumaroles and through diffuse soil degassing. This results in the emission of toxic gases such as H2S at quasi-steady rates over long periods of time (months to years). Whilst less apparent than gas emissions during more vigorous and violent paroxysms, the long duration of emission and the fact that such gases are dispersed at low altitude (i.e. along the flanks of the volcano, often at human height) means that even the typically low concentrations (e.g. tens of ppb H2S) pose a significant hazard to human health in nearby habitations.La Soufrière de Guadeloupe has been undergoing an unrest phase since 1992 and it has one of the highest gas emission rates of any volcano in the Lesser Antilles. Gas emissions here are principally from three fumarolic sites at the summit though the typically high winds and low gas temperatures result in a laterally dispersed plume within a few metres of the ground. In this study, gas dispersion from the volcano over the period 2016–2021 was modelled using a numerical code that takes into account wind direction and strength, atmospheric stability, local topography and gas flux measurements; we used information from local meteorological stations, ECMWF Climate Reanalysis data and the gas flux dataset acquired by MultiGas measurements during the mentioned period. We ran c.100 individual simulations of the most frequently observed wind and gas flux conditions using a Monte-Carlo scheme. From the ensemble of results, we calculated the mean (i.e. most probable gas concentration values at any given location) and found that the most exposed zones are the hamlet of Matouba and the upper parts of St. Claude. We also simulated particular dates with strong H2S odours reported by local inhabitants via online surveys and we compared the model results with the Gwad’air agency’s air quality station located at St Claude, the closest town to the volcano. This allowed us to establish the prevalence of gases coming from La Soufrière in nearby cities and the accuracy of our models. The resulting maps of the areas potentially long-term (>8 years) exposed by gas emissions can be used to evaluate health risks for all people living around the volcano. In these locations, our results suggest that there is a 20% and 5% probability, respectively, for these areas of exceeding H2S guidelines for long-term gas exposure (70 ppb).

Relating the mass eruption rate (MER) of explosive eruptions to column height in the atmosphere is key to reconstructing past eruptions and forecasting volcanic hazards. Using 134 eruptive events from the Independent Volcanic Eruption Source Parameter Archive (IVESPA v1.0), we explore the canonical MER-height relationship for four measures of column height: spreading level, sulfur dioxide height, and top height from both directly observed plumes and those reconstructed from deposits. These relationships show significant differences and should be chosen carefully for operational and research applications. The roles of atmospheric stratification, wind, and humidity remain challenging to assess across the large range of eruptive conditions in this database, ultimately resulting in empirical relationships outperforming analytical models that account for atmospheric conditions. This finding reveals the complexity of the height-MER relation that is difficult to constrain based on available heterogeneous observations, which reinforces the need for improved datasets to develop eruptive column models.

La surveillance par télédétection en champ rapproché (sol, drone …) partage de nombreux points communs avec la télédétection spatiale, traitée dans un autre chapitre. Mais elle offre aussi une gamme d'approches plus riche en raison de la plus grande facilité de mise en œuvre et d'expérimentation et elle permet d'atteindre des résolutions très fines. Ce chapitre fait le point sur les principales méthodes actuelles de la télédétection en champ proche.

International audience; The volcanic-hydrothermal geo-diversity of the Basse-Terre Island of Guadeloupe archipelago (Eastern Caribbean, France) is a major asset of the Caribbean bio-geoheritage. In this paper, we use Guadeloupe as a representative of many small island developing states (SIDS), to show that the volcanic-hydrothermal geodiversity is a major resource and strategic thread for resilience and sustainability. These latter are related to the specific richness of Guadeloupe’s volcanic-geothermal diversity, which is de facto inalienable even in the wake of climate change and natural risks that are responsible for this diversity, i.e., volcanic eruptions. We propose the interweaving the specificity of volcanic-geothermal diversity into planning initiatives for resilience and sustainability. Among these initiatives research and development programs focused on the knowledge of geodiversity, biodiversity and related resources and risks are central for the long-term management of the water resource, lato sensu. Such a management should include a comprehensive scientific observatory for the characterization, exploration, and sustainable exploitation of the volcanic-hydrothermal geodiversity alongside planning for and mitigating geophysical risks related to sudden volcanic-induced phenomena and long-term systemic drifts due to climate change. The results of this exercise for Guadeloupe could typify innovative paths for similar SIDS around their own volcanic-hydrothermal geodiversity.

Fumarolic gas composition and temperature record deep processes that generate and transfer heat and mass towards the surface. These processes are a result of the emplacement, degassing and cooling of magma and the overturning of the above hydrothermal system. A reasonable expectation, and too often an unproved assumption, is that fumarole temperatures and the deep heat sources vary on similar timescales. Yet signals from deep and shallow processes have vastly different temporal variations. This indicates that signals arising from deep activity may be masked or modified by intervening hydrothermal processes, such as fluid-groundrock reactions in which secondary minerals play a major role. Clearly, this complicates the interpretation of the signals such as the joint variation of fumarole vent temperature and geochemical ratios in terms of what is occurring at depth. So what do the differences between the timescales governing deep and shallow processes tell us about the intervening transport mechanisms?At the volcanic dome of La Soufrière de Guadeloupe, the Observatoire Volcanologique et Sismologique de la Guadeloupe has performed weekly-to-monthly in-situ vent gas sampling over many years. These analyses reliably track several geochemical species ratios over time, which provide important information about the evolution of deep processes. Vent temperature is measured as part of the in-situ sampling, giving a long time series of these measurements. Here, we look to exploit the temporal variations in these data to establish the common processes, and also to determine why these signals differ. By fitting sinusoids to the gas-ratio time series we find that several of the deep signals are strongly sinusoidal. For example, the He/CH4 and CO2/CH4 ratios, which involve conservative components and mark the injection of deep and hot magmatic fluids, oscillate on a timescale close to 3 years. We also analyse the frequency content of the temperature measurements since 2011 and find that such long signals are not seen. This may be due to internal buffering by the hydrothermal system, but other external forcings are also present. From these data we build up a more informed model of the heat-and-mass supply chain from depth to the surface. This will potentially allow us to predict future unrest (e.g. thermal crises, seismic swarms), and distinguish between sources of unrest.

Fumarolic gas survey of dormant volcanoes is fundamental because the compositional and flux changes in gas emissions are recognised signals of unrest and may even be precursors of eruptions on several dormant volcanoes in hydrothermal unrest [1-5].Here we report on the chemical compositions (CO2, H2S, SO2, H2) and mass fluxes of fumarolic gas emissions from the low-temperature (from 97° to 104°C) volcanic-hydrothermal system of La Soufrière de Guadeloupe (Lesser Antilles). This present study covers the period 2016 to present, encompassing the peak activity of April 2018. Long-term trends are acquired from both portable MultiGAS measurements (performed monthly) and two permanent MultiGAS stations (4 automated 20’ measurements per day). These MultiGAS data are discussed along with other geochemical and geophysical parameters monitored at OVSG, such as complete fumarole chemistry via Giggenbach bottles, fumarole temperatures, volcanic seismicity and deformation in order to track the deep-sourced magmatic signal contribution compared to the one of the hydrothermal system and detect potential signs of unrest [6].Dealing with MultiGAS data from a low-T fumarolic system in a tropical environment is not straightforward due to external forcing effect of meteoric water on gas composition. Hence, interpretation of the observed chemical changes must consider (i) the role of water-gas-rock interactions and gas scrubbing processes by the hydrothermal system and the perched volcanic pond [7], which particularly affect sulphur precipitation and remobilization and (ii) how these processes vary with rainfall and groundwater circulation (i.e. rainy vs non-rainy seasons, extreme events).[1] Giggenbach and Sheppard, 1989; [2] Symonds et al., 1994; [3] Hammouya et al., 1998; [4] De Moor et al., 2016; [5] Allard et al., 2014; [6] Moretti et al., submitted; [7] Symonds et al., 2001

In recent decades, reliable computational models have significantly advanced, and now represent a valuable tool to make quantitative and testable predictions, supporting gas dispersal forecasting and hazard assessments for public safety. In this study, we carried out a number of tests aimed to validate the modelling of gas dispersal at La Soufrière de Guadeloupe volcano (Lesser Antilles), which has shown quasi-permanent degassing of low-temperature hydrothermal nature since its last magmatic eruption in 1530 AD. In particular, we focused on the distribution of CO2 and H2S discharged from the three main present-day fumarolic sources at the summit, using the MultiGAS measurements of continuous gas concentrations collected during March-April 2017. We implemented the open-source Eulerian code DISGAS-2.0 for passive gas dispersion coupled with the mass consistent Diagnostic Wind Model (DWM), using wind measurements and atmospheric stability information from a local meteorological station and the ECMWF-ERA5 reanalysis data. We found that model outputs are highly dependent on the resolution of the topographic data, which affect mainly the reliability of DWM meteorological fields, especially on and around the steep dome. Our results satisfactory reproduce the observed data, indicating the potential usefulness of DISGAS-2.0 as a tool for quantifying gas hazard and reproducing the fumarolic degassing and at La Soufrière de Guadeloupe.

International audience; Eruptive columnmodels are powerful tools for investigating the transport of volcanic gas and ash, reconstructing past explosive eruptions, and simulating future hazards. However, the evaluation of these models is challenging as it requires independent estimates of themainmodel inputs (e.g.mass eruption rate) and outputs (e.g. column height). There exists no database of independently estimated eruption source parameters (ESPs) that is extensive, standardized, maintained, and consensus-based. This paper introduces the Independent Volcanic Eruption Source Parameter Archive (IVESPA, ivespa.co.uk), a community effort endorsed by the International Association of Volcanology and Chemistry of the Earth’s Interior (IAVCEI) Commission on Tephra HazardModelling.We compiled data for 134 explosive eruptive events, spanning the 1902-2016 period, with independent estimates of: i) total erupted mass of fall deposits; ii) duration; iii) eruption column height; and iv) atmospheric conditions. Crucially, we distinguish plume top versus umbrella spreading height, and the height of ash versus sulphur dioxide injection. All parameter values provided have been vetted independently by at least two experts. Uncertainties are quantified systematically, including flags to describe the degree of interpretation of the literature required for each estimate. IVESPA also includes a range of additional parameters such as total grain size distribution,eruption style, morphology of the plume (weak versus strong), and mass contribution from pyroclastic density currents, where available. We discuss the future developments and potential applications of IVESPA and make recommendations for reporting ESPs to maximize their usability across different applications. IVESPA covers an unprecedented range of ESPs and can therefore be used to evaluate and develop eruptive column models across a wide range of conditions using a standardized dataset.

International audience; Particularly in the presence of a hydrothermal system, many volcanoes output large quantities of heat through the transport of water from deep within the edifice to the surface. Thus, heat flux is a prime tool for evaluating volcanic activity and unrest. We review the volcanic unrest at La Soufrière de Guadeloupe (French West Indies) using an airborne thermal camera survey and in situ measurements of temperature and flow rate through temperature probes, Pitot-tube and MultiGAS measurements. We deduce mass and heat fluxes for the fumarolic, ground and thermal spring outputs and follow these over a period spanning 2000–2020. Our results are compared with published data and we performed a retrospective analysis of the temporal variations in heat flux over this period using the literature data. We find that the heat emitted by the volcano is 36.5 ± 7.9MW, of which the fumarolic heat flux is dominant at 28.3 ± 6.8 MW. Given a total heated area of 26 270 m2, this equates to a total heat flux density of 1366 ± 82 W/m2, which is amongst the highest established for worldwide volcanoes with hydrothermal systems, particularly for dome volcanoes. A major change at La Soufrière de Guadeloupe, however, is the development of a widespread region of ground heating at the summit where heat output has increased from 0.2 ± 1 MW in 2010 to 5.7 ± 0.9 MW in 2020. This change is concurrent with accelerating unrest at the volcano and the emergence of two new high-flux fumaroles in recent years. Our findings highlight the importance of continued and enhanced surveillance and research strategies at La Soufrière de Guadeloupe, the results of which can be used to better understand hydrothermal volcanic systems the world over.

Volcanic gas emissions from the main low-temperature fumaroles (around 100°C) of one of the most dangerous volcanoes in the Lesser Antilles, La Soufrière de Guadeloupe, are measured routinely using direct sampling with NaOH bottles (for H2O, CO2, H2Stot, H2, CH4, CO, N2, He, Ar, O2), with P2O5 bottles (for H2O, CO2, H2S, SO2, H2) and MULTIGAS (for H2O, CO2, H2S, SO2, H2). This allows us to perform a study about an intercomparison of volcanic gas monitoring methologies. The results show some good overlap and similar temporal evolution between the dataset of the different methologies, which is of utmost of importance for monitoring purposes. However, there is no good agreement between the three methodologies for the same chemical ratio. The differences could be explained by a timedependant diffusive phenomenon that affects the concentrations of sampled gases for two methods of the three (P2O5 bottles and MULTIGAS). P2O5-based analyses are affected because effusion on rapid decompression and fast sampling affects the gas volume in the pipeline connecting the vent outlet to the sampling. Although MULTIGAS is a continuous, flow-through, sampling method, results are likely affected because of the sampling architecture involving filter and pump. Moreover, sulphur reaction (precipitation of elemental S upon exit from the fumarole, conversion of H2S to SO2, chemical reaction with the P2O5 powder that release H2S) and water condensation can also explain some discrepancies.

In the last decade, probabilistic volcanic hazard assessment (PVHA) has become one of the most rapidly developing topics in volcanology. PVHA relies on a number of simulation tools, which have been catalogued within H2020 EUROVOLC project.Here we apply two of these tools that will concur to a probabilistic multi-hazard assessment for volcanic phenomena at La Soufrière de Guadeloupe, as reported in reference scenarios elaborated by OVSG-IPGP and communicated to the authorities. In the last 9 kyr the activity at La Soufrière is characterized by recurrent effusive to explosive activity, sector collapses and intense fumarolic emissions. Based on literature data, we focus particularly on the most likely explosive (phreatic or hydrothermal) scenario and explore the hazard posed by gas dispersal and ballistics impact, which have never been the focus of PVHA. We also set up a preliminary spatial map for phreatic vent opening, a baseline for the PVHA here presented.

Eruptive column models are crucial for managing volcanic crises, forecasting future events, and reconstructing past eruptions. Given their central role in volcanology and the large uncertainties weakening their predictions, the evaluation and improvement of these models is critical. Such evaluation is challenging as it requires independent estimates of the main model inputs (e.g. mass eruption rate) and outputs (e.g. column height). Despite recent efforts to extend datasets of independently estimated eruption source parameters (ESP) (e.g. Mastin 2014, Aubry et al. 2017), there is no standardized, maintained, and community-based ESP database devoted to the evaluation of eruptive column models.Here we present a new ESP database designed to respond to the needs of the plume modelling community, and which will also be valuable to observatories, field volcanologists, and volcanic ash advisory centers. We compiled data for over 130 eruptive events with independent estimates of: i) the mass eruption rate; ii) the height reached by the column; and iii) atmospheric conditions during the eruption. In contrast with previous ESP datasets, we distinguish estimates of column height that relate to different phases (ash and SO2) and parts of the column (plume top or umbrella). We additionally provide the total grain size distribution, uncertainties in eruption parameters, and multiple sources for atmospheric profiles for events where these parameters are available. The database also includes a wealth of additional information which will enable modelers to distinguish between different eruptions when evaluating or calibrating models. This includes the type of eruption, the morphology of the plume (weak/transitional/strong), and the occurrence and mass entrained within pyroclastic density currents.We will apply the new database to revisit empirical scaling relationships between the mass eruption rate and “plume height”. In particular, we will show how such relationships depend on the type of height (e.g. SO2 height vs. ash top height) and eruption (e.g. magmatic vs. phreatomagmatic) considered. We will also discuss the difficulties and limitations of compiling ESP estimates from the literature as well as characterizing fundamentally unsteady volcanic events by a single value for each ESP.

After 25 years of gradual increase, volcanic unrest at La Soufriere of Guadeloupe reached its highest seismic energy level on 27 April 2018, with the largest felt volcano-tectonic (VT) earthquake (M-L 4.1 or M-W 3.7) recorded since the 1976-1977 phreatic eruptive crisis. This event marked the onset of a seismic swarm (180 events, 2 felt) occurring after three previous swarms on 3-6 January (70 events), 1 st February (30 events, 1 felt) and 16-17 April (140 events, 1 felt). Many events were hybrid VI's with long-period codas, located 2-4 km below the volcano summit and clustered within 2 km along a regional NW-SE fault cross-cutting La Soufriere. Elastic energy release increased with each swarm whereas inter-event time shortened. At the same time, summit fractures continued to open and thermal anomalies to extend. Summit fumarolic activity increased significantly until 20 April, with a maximum temperature of 111.4 degrees C and gas exit velocity of 80 m/s, before declining to similar to 95 degrees C and similar to 33 m/s on 25 April. Gas compositions revealed increasing C/S and CO2/CH4 ratios and indicate hydrothermal P-T conditions that reached the critical point of pure water. Repeated MultiGAS analysis of fumarolic plumes showed increased CO2/H2S ratios and SO2 contents associated with the reactivation of degassing fractures (T = 93 degrees C, H2S/SO2 approximate to 1). While no direct evidence of upward magma migration was detected, we attribute the above phenomena to an increased supply of deep magmatic fluids that heated and pressurized the La Soufriere hydrothermal system, triggering seismogenic hydro-fracturing, and probable changes in deep hydraulic properties (permeability) and drainage pathways, which ultimately allowed the fumarolic fluxes to lower. Although this magmatic fluid injection was modulated by the hydrothermal system, the unprecedented seismic energy release and the critical point conditions of hydrothermal fluids suggest that the 2018 sequence of events can be regarded as a failed phreatic eruption. Should a similar sequence repeat, we warn that phreatic explosive activity could result from disruption of the shallow hydrothermal system that is currently responsible for 3-9 mm/y of nearly radial horizontal displacements within 1 km from the dome. Another potential hazard is partial collapse of the dome's SW flank, already affected by basal spreading above a detachment surface inherited from past collapses. Finally, the increased magmatic fluid supply evidenced by geochemical indicators in 2018 is compatible with magma replenishment of the 6-7 km deep crustal reservoir feeding La Soufriere and, therefore, with a potential evolution of the volcano's activity towards magmatic conditions.

Co-auteur étranger; International audience; Vulcano Fossa's fumarole field (Italy) has been active for more than a century and has become a well-studied benchmark for fumarolic degassing, often being considered the "model" hydrothermal system. Satellite thermal monitoring is increasingly being used to monitor such systems, so we here use Vulcano to test a new method for assessing heat flux at such systems. Our methodology involves converting ground-based vent temperature measurements to heat fluxes emitted by the fumaroles, with the diffuse heat flux obtained from satellite-sensor (in our case Advanced Spaceborne Thermal Emission and Reflection Radiometer) data. While diffuse heat losses were typically 9 MW, vent heat losses were 1 MW. The average total flux of 10 MW over the 19-year period of study places Vulcano in the top 20 most active hydrothermal systems globally. This work highlights the value of high spatial resolution infrared satellite data in building thermal inventories for persistently active hydrothermal systems. Plain Language Summary Hydrothermal systems are the most ubiquitous and strongest emitters of heat by volcanoes worldwide. But these emissions are very poorly constrained; indeed, they are very difficult to measure so that we have data for only a few of the many active systems worldwide. We here present a method to obtain this value for all global hydrothermal systems. By way of case study, we apply the method to the Vulcano Fossa hydrothermal system in Italy so as to obtain an inventory over the last 20 years (with the last data point coming from May 2019) at this frequently visited tourist site. Our approach represents a globally applicable heat flux model that can be used to track the thermal evolution of hazardous volcanic systems on a time scales of tens of years.

Speed of movement is fundamental to the outcome of many human actions. A variety of techniques can be implemented in order to maximise movement speed depending on the goal of the movement, constraints, and the time available. Knowing maximum movement velocities is therefore useful for developing movement strategies but also as input into muscle models. The aim of this study was to determine maximum flexion and extension velocities about the major joints in upper and lower limbs. Seven university to international level male competitors performed flexion/extension at each of the major joints in the upper and lower limbs under three conditions: isolated; isolated with a countermovement; involvement of proximal segments. 500 Hz planar high speed video was used to calculate velocities. The highest angular velocities in the upper and lower limb were 50.0 rad·s-1 and 28.4 rad·s-1, at the wrist and knee, respectively. As was true for most joints, these were achieved with the involvement of proximal segments, however, ANOVA analysis showed few significant differences (p

Indirect measurement of disc hydration can be obtained through measures of spinal height using stadiometry. However, specialised stadiometers for this are often custom-built and expensive. Generic wall-mounted stadiometers alternatively are common in clinics and laboratories. This study examined the reliability of a custom set-up utilising a wall-mounted stadiometer for measurement of spinal height using custom built wall mounted postural rods. Twelve participants with non-specific chronic low back pain (CLBP; females n = 5, males n = 7) underwent measurement of spinal height on three separate consecutive days at the same time of day where 10 measurements were taken at 20 s intervals. Comparisons were made using repeated measures analysis of variance for 'trial' and 'gender'. There were no significant effects by trial or interaction effects of trial x gender. Intra-individual absolute standard error of measurement (SEM) was calculated for spinal height using the first of the 10 measures, the average of 10 measures, the total shrinkage, and the rate of shrinkage across the 10 measures examined as the slope of the curve when a linear regression was fitted. SEMs were 3.1 mm, 2.8 mm, 2.6 mm and 0.212, respectively. Absence of significant differences between trials and the reported SEMs suggests this custom set-up for measuring spinal height changes is suitable use as an outcome measure in either research or clinical practice in participants with CLBP.

International audience; Volcanic plumes are turbulent mixtures of particles and gas which are injected into the atmosphere during avolcanic eruption. Depending on the intensity of the eruption, plumes can rise from a few tens of metres upto many tens of kilometres above the vent and thus, present a major hazard for the surrounding population.Currently, however, few if any algorithms are available for automated plume tracking and assessment. Here,we present a new image processing algorithm for segmentation, tracking and parameters extraction of convectiveplume recorded with thermal cameras. We used thermal video of two volcanic eruptions and twoplumes simulated in laboratory to develop and test an efficient technique for analysis of volcanic plumes.We validated our method by two different approaches. First, we compare our segmentation method to previouslypublished algorithms. Next, we computed plume parameters, such as height, width and spreadingangle at regular intervals of time. These parameters allowed us to calculate an entrainment coefficient andobtain information about the entrainment efficiency in Strombolian eruptions. Our proposed algorithm israpid, automated while producing better visual outlines compared to the other segmentation algorithms,and provides output that is at least as accurate as manual measurements of plumes.

Fluidisation is the process by which the weight of a bed of particles is supported by a gas flow passing through it from below. When fluidised materials flow down an incline, the dynamics of the motion differs from their non-fluidised counterparts because the granular agitation is no longer required to support the weight of the flowing layer. Instead, the weight is borne by the imposed gas flow and this leads to a greatly increased flow mobility. In this paper, a framework is developed to model this two-phase motion by incorporating a kinetic theory description for the particulate stresses generated by the flow. In addition to calculating numerical solutions for fully developed flows, it is shown that for sufficiently thick flows there is often a local balance between the production and dissipation of the granular temperature. This phenomenon permits an asymptotic reduction of the full governing equations and the identification of a simple state in which the volume fraction of the flow is uniform. The results of the model are compared with new experimental measurements of the internal velocity profiles of steady granular flows down slopes. The distance covered with time by unsteady granular flows down slopes and along horizontal surfaces and their shapes are also measured and compared with theoretical predictions developed for flows that are thin relative to their streamwise extent. For the horizontal flows, it was found that resistance from the sidewalls was required in addition to basal resistance to capture accurately the unsteady evolution of the front position and the depth of the current and for situations in which sidewall drag dominates, similarity solutions are found for the experimentally measured motion.

Objective. Loss of disc height is commonly associated with chronic low back pain (CLBP). Isolated lumbar extension (ILEX) exercise for the lumbar extensors is recommended to treat CLBP and is suggested such exercise might promote disc healing and regeneration. This study examined a 12-week ILEX intervention on indirect determination of disc height and shrinkage through seated stadiometry, strength, pain, and disability. Design. A quasi-experimental wait-list controlled design was used. Nine participants underwent pretesting (T1), a 12-week control period, retesting (T2), a 12-week intervention period, and finally posttesting (T3). Seated stadiometry, ILEX strength, pain, and disability were measured at each time point. Results. No significant repeated-measures effects for any seated stadiometry variables occurred. Significant improvement across the intervention period (T2 to T3) was found for strength ( P

International audience; Turbulent volcanic jets are produced by highly-energetic explosive eruptions and may form buoyant plumes that rise many tens of kilometres into the atmosphere to form umbrella clouds or collapse to generate ground-hugging pyroclastic flows. Ash injected into the atmosphere can be transported for many hundreds of kilometres with the potential to affect climate, disrupt global air travel and cause respiratory health problems. Pyroclastic flows, by contrast, are potentially catastrophic to populations and infrastructure close to the volcano. Key to which of these two behaviours will occur is the extent to which the mechanical entrainment and mixing of ambient air into the jet by large (entraining) eddies forming the jet edge changes the density of the air–ash mixture: low entrainment rates lead to pyroclastic flows and high entrainment rates give rise to buoyant plumes. Recent experiments on particle-laden (multi-phase) volcanic jets from flared and straight-sided circular openings suggest that the likelihood for buoyant plumes will depend strongly on the shape and internal geometry of the vent region. This newly recognised sensitivity of the fate of volcanic jets to the structure of the vent is a consequence of a complex dynamic coupling between the jet and entrained solid particles, an effect that has generally been overlooked in previous studies. Building on this work, here we use an extensive series of experiments on multi-phase turbulent jets from analogue linear fissures and annular ring fractures to explore whether the restrictive vent geometry during cataclysmic caldera-forming (CCF) eruptions will ultimately lead a relatively greater frequency of pyroclastic flows than eruptions from circular vents on stratovolcanoes. Our results, understood through scaling analyses and a one-dimensional theoretical model, show that entrainment is enhanced where particle motions contribute angular momentum to entraining eddies. However, because the size of the entraining eddies scales approximately with vent width, the extent of entrainment is reduced as the vent width becomes small in comparison to its length. Consequently, our work shows that for specified mass eruption rates, the high length-to-width ratio vents typical of CCF events are more likely to produce pyroclastic flows. We suggest that the enigmatic trend in the geological record for the largest CCF eruptions to produce pyroclastic flows is an expected consequence of their being erupted through continuous or piece-wise continuous caldera ring fractures.

International audience; Pumice flows are potentially destructive volcanic events that derive from eruption column collapse and whose dynamics are poorly understood. The challenges in studying these flows include the lack of constraints on the dynamics, kinematics and initial conditions that control their emplacement. We present a morphological study of the distal deposits (lobes) of the pumice flows resulting from the 1993 eruption at Lascar, Chile. The surface geometry of the lobes was measured in detail using a LiDAR device, which allowed for detailed characterisation of their morphology, consisting of central channel and lateral levees, and terminal frontal snout. In particular we find that the ratio of channel/levee height as a function of the ratio of the distance between levees/total width of the lobe has a characteristic curve for these pumice flow lobes. Our analysis of several of the Lascar pumice lobe deposits (south east sector) identified several dimensionless groups of the available parameters which, when compared against published results from both experimental and numerical investigations, allowed us to constrain crucial kinematic and dynamic information on the terminal phase of the pumice flows. Notably, we estimate the velocity of the terminal phase of pumice flows to be 5-10 m/s. Froude numbers of 1.5-2 are comparable with values found for experimental granular flows. Height-width aspect ratios for the levee-channel section of the pumice lobes are similar to those for experimental flows although these same aspect ratios for the snout are much larger for the natural deposits than their small-scale analogues. Finally, we discuss the possible emplacement dynamics of the terminal Lascar 1993 pumice flows. A pseudo-Reynolds number based on the velocity estimation is found to be up to 100 times larger for the pumice flows than experimental-scale flows. This suggests that the flow-retarding frictional forces for large-scale flows are relatively unimportant compared to flows at smaller scales. Mechanical effects such as fluidisation, mobilisation of material lying on the slopes over which they propagate and lubrication due to polydispersivity could provide an explanation for their ability to propagate on shallow slopes (6-11°).

Study Design. Randomized controlled trial.Objective. To compare the effects of full range of motion (ROM) and limited ROM isolated lumbar extension exercise upon full ROM lumbar extension strength, ROM, perceived pain, and disability.Summary of Background Data. Limited ROM is common in chronic low back pain as is lumbar extensor deconditioning. Limited ROM exercise is a common prescription but is yet to be empirically tested.Methods. Males (n = 21) and females (n = 17) with nonspecific chronic low back pain were initially recruited. Participants were randomized to either a full ROM (FullROM) or limited ROM (LimROM) training group or a control group. A total of 24 participants (males: n = 14, females: n = 10) completed the study and were included in analysis. The intervention lasted 12 weeks. FullROM and LimROM groups completed isolated lumbar extension resistance training once per week, performing one set of exercise at 80% of their maximal tested functional torque to failure. FullROM group trained through a full ROM. LimROM group trained through the mid 50% of their full ROM.Full ROM isolated lumbar extension strength, lumbar and standing ROM (Schobers test), perceived pain (visual analogue scale), and disability (Revised Oswestry Disability Index) were measured pre- and postintervention.Results. FullROM and LimROM significantly improved in full ROM lumbar extension strength, perceived pain, and disability compared with the control group. No changes occurred in lumbar or standing ROM. No significant differences were found between either FullROM or LimROM for any outcome measure. Changes in perceived pain and disability met minimal clinically important change values for FullROM (visual analogue scale, −30.3 + 25.76 mm and Oswestry Disability Index, −18.2 + 6.63 patients) and LimROM (visual analogue scale, −16.29 + 10.97 mm and Oswestry Disability Index, −12 + 5.16 patients).Conclusion. The results suggest that both FullROM and LimROM are equally effective in increasing full ROM lumbar extension strength and producing clinically meaningful improvement in perceived pain and disability.Level of Evidence: 2

BACKGROUND:Chronic low back pain (CLBP) is a multifactorial condition with a variety of symptoms, one of which is abnormal gait. The lumbar spine and its musculature are important in controlling gait, and in CLBP the lumbar extensors are often deconditioned. Because of this specific isolated lumbar extension, exercise often is recommended. It was therefore of interest to examine its effects of upon gait variability.OBJECTIVE:To examine the effects of isolated lumbar extension resistance training on lumbar kinematic variability during gait in participants with CLBP.DESIGN:Randomized controlled trial.SETTING:University Health, Exercise and Sport Science Laboratory.PARTICIPANTS:Twenty-four participants with nonspecific CLBP.INTERVENTIONS:Participants were randomly allocated to a 12-week isolated lumbar extension exercise intervention (1×/week performing a single set to momentary muscular failure using a load equal to 80% max tested torque) or nontraining control period.MAIN OUTCOME MEASUREMENTS:Lumbar kinematics during gait, including angular displacement, kinematic waveform pattern (CVp), and offset (CVo) variability, were examined via 3-dimensional analyses.RESULTS:No significant changes in displacement or CVo were found as a result of the intervention; however, a small but significant reduction in sagittal plane CVp (-20.90 ± 3.53%, effect size = 0.48, P = .044) occurred, indicating improved motor pattern replication through this movement plane.CONCLUSIONS:Considering the role of the lumbar extensors in gait, and their common deconditioning in CLBP, an isolated lumbar extension resistance exercise intervention may reduce gait variability. These results suggest isolated lumbar extension exercise may specifically reduce sagittal plane variability, indicating improved motor pattern replication through this movement plane, perhaps attributable to the plane of movement used during the exercise.

BackgroundChronic low back pain is a multifactorial condition with many dysfunctions including gait variability. The lumbar spine and its musculature are involved during gait and in chronic low back pain the lumbar extensors are often deconditioned. It was therefore of interest to examine relationships between lumbar kinematic variability during gait, with pain, disability and isolated lumbar extension strength in participants with chronic low back pain.MethodsTwenty four participants with chronic low back pain were assessed for lumbar kinematics during gait, isolated lumbar extension strength, pain, and disability. Angular displacement and kinematic waveform pattern and offset variability were examined.FindingsAngular displacement and kinematic waveform pattern and offset variability differed across movement planes; displacement was highest and similar in frontal and transverse planes, and pattern variability and offset variability higher in the sagittal plane compared to frontal and transverse planes which were similar. Spearman's correlations showed significant correlations between transverse plane pattern variability and isolated lumbar extension strength (r = −.411) and disability (r = .401). However, pain was not correlated with pattern variability in any plane. The r2 values suggested 80.5% to 86.3% of variance was accounted for by other variables.InterpretationConsidering the lumbar extensors role in gait, the relationship between both isolated lumbar extension strength and disability with transverse plane pattern variability suggests that gait variability may result in consequence of lumbar extensor deconditioning or disability accompanying chronic low back pain. However, further study should examine the temporality of these relationships and other variables might account for the unexplained variance.

International audience; Efficient turbulent entrainment causes otherwise dense volcanic jets to rise high into the atmosphere as buoyant plumes. Classical models suggest that the inflow of air is 10–15% of the axial velocity, giving predictions for the height of the plume and, in turn, the composition and structure of the resulting umbrella clouds. Crucially, entrainment is assumed independent of source geometry and mechanically unaffected by the pyroclastic mixture properties. We show that particle inertia and vent geometry act to modify the shape of the largest eddies defining the jet's edge and thus entrainment of the ambient. Whereas particle-free flows are essentially unaffected by vent shape, entrainment into particle-laden flows is enhanced for flared vents and reduced for cylindrical vents. Our results predict that vent erosion during an explosive eruption reduces the height of volcanic jets, alters the structure and sedimentation regime of the umbrella cloud, and the resulting deposit.

Despite manufacturer claims that athletic socks attenuate force during exercise, no device exists to assess this. Therefore, this study outlines the development of a custom built impact testing device for assessing the cushioning properties of socks. The device utilised a gravity driven impact striker (8.5 kg), released from 0.05 m, which impacted a no sock, sock or a basic shoe/sock condition in the vertical axis. A load cell (10000 Hz) assessed peak impact force, time to peak impact force and loading rate. Reliability was investigated between day, between trial and within trial. Excellent reliability (coefficient of variation5% adjusted for 95% confidence limits) was reported for peak impact force in all conditions, with no evidence of systematic bias. Good reliability (coefficient of variation10% adjusted for 68% confidence limits) was reported for time to peak impact force and loading rate with some evidence of systematic bias. It was concluded that the custom built impact testing device was reliable and sensitive for the measurement of peak impact force on socks.

Background One of the aims of the sock/shoe unit is to reduce the severity of impact forces on the lower extremity although the injury prevention potential of the sock through the attenuation of impact force has yet to be established. This study aims to determine the effect of athletic socks and a sock/shoe unit on peak impact force, time to peak impact force and loading rate using an impact testing methodology. Methods An impact testing system with a gravity driven vertical impact striker (8.5 kg) fitted with a load cell (10,000 Hz) which was released from 0.05 m to impact the specimen on the vertical axis (impact velocity = 0.99 m·s− 1) was used throughout the study. Findings All socks reduced peak impact force by between 6% and 20% when compared to a no sock control condition. Furthermore, large significant correlation coefficients (r = .62 to .72) were observed between thickness and peak impact force, time to peak impact force and loading rate in the sock only condition. Interpretation Athletic socks demonstrate cushioning properties under impact testing conditions.

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International audience; Currents of particles have been quite successfully modelled using techniques developed for fluid gravity currents. These models require the rheology of the currents to be specified, which is determined by the interaction between particles. For relatively small slow currents, this is determined primarily through friction, which can be controlled and reduced by fluidizing the particles, which then become much more mobile. Recent results cannot be predicted using many of the proposed models, and may be defined by the interaction between the particles and the fluid through which they are passing. However, in addition, particles that are only initially fluidized also form currents that are also mobile, but otherwise are different from continuously fluidized currents. The mobility of these currents appears not to be connected to the time taken for them to degas. This suggests that defining the continuous stresses on the particle current may not be sufficient to understand its motion and that a challenge for the future is to understand the structure of these flows and how this affects their motion.

(1976). The colonial stock act of 1900: A symptom of the new imperialism? The Journal of Imperial and Commonwealth History: Vol. 4, No. 2, pp. 154-163.

International audience; The motion of fluidised granular currents over horizontal surfaces is investigated experimentally and by mathematical modelling of solid and fluid phases. Analytical solutions for the bulk motion were tested by experiments involving material being introduced at a constant volume flux, and a reasonable agreement found between theoretical predictions and laboratory measurements.

Despite manufacturer claims that athletic socks attenuate force during exercise, no device exists to assess this. Therefore, this study outlines the development of a custom-built impact-testing device for assessing the cushioning properties of socks. The device used a gravity-driven impact striker (8.5 kg), released from 0.05 m, which impacted a no-sock, sock or a basic shoe/sock condition in the vertical axis. A load cell (10,000 Hz) assessed peak impact force, time to peak impact force and loading rate. Reliability was investigated between day, between trial and within trial. Excellent reliability (coefficient of variation < 5% adjusted for 95% confidence limits) was reported for peak impact force in all conditions, with no evidence of systematic bias. Good reliability (coefficient of variation < 10% adjusted for 68% confidence limits) was reported for time to peak impact force and loading rate with some evidence of systematic bias. It was concluded that the custom-built impact-testing device was reliable and sensitive for the measurement of peak impact force on socks.

Co-auteur étranger; International audience; Volcanic gas dispersal can be a serious threat to people living near active volcanoes since it can have short- and long-term effects on human health, and severely damage crops and agricultural land. In recent decades, reliable computational models have significantly advanced, and now they may represent a valuable tool to make quantitative and testable predictions, supporting gas dispersal forecasting and hazard assessments for public safety. Before applying a specific modelling tool into hazard quantification, its calibration and its sensitivity to initial and boundary conditions should be carefully tested against available data, in order to produce unbiased hazard quantifications. In this study, we provided a number of prototypical tests aimed to validate the modelling of gas dispersal from a hazard perspective. The tests were carried out at La Soufrière de Guadeloupe volcano, one of the most active gas emitters in the Lesser Antilles. La Soufrière de Guadeloupe has shown quasi-permanent degassing of a low-temperature hydrothermal nature since its last magmatic eruption in 1530 CE, when the current dome was emplaced.We focused on the distribution of CO2 and H2S discharged fromthe threemain present-day fumarolic sources at the summit, using the measurements of continuous gas concentrations collected in the period March–April 2017. We developed a new probabilistic implementation of the Eulerian code DISGAS-2.0 for passive gas dispersion coupled with the mass-consistent DiagnosticWindModel, using local wind measurements and atmospheric stability information froma local meteorological station and ERA5 reanalysis data.We found that model outputswere not significantly affected by the type of wind data but rather upon the relative positions of fumaroles and measurement stations. Our results reproduced the statistical variability in daily averages of observed data over the investigated period within acceptable ranges, indicating the potential usefulness of DISGAS-2.0 as a tool for reproducing the observed fumarolic degassing and for quantifying gas hazard at La Soufrière. The adopted testing procedure allows for anaware application of simu ation tools for quantifying the hazard, and thus we think that this kind of testing should actually be the first logical step to be taken when applying a simulator to assess (gas) hazard in any other volcanic contexts.