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Volcanic ash and gas is, like sulphur dioxide (SO2), a major risk for air traffic. To mitigate this risk and to improve situational awareness for air traffic management (ATM), we describe a new service using the SWIM (System Wide Information System Management) Yellow Profile – see https://www.eurocontrol.int/publication/eurocontrol-specifications-system-wide-information-management-swim – and aligned with the ATM Information Reference Model (AIRM) as required.This new service provides early warnings of volcanic SO2 layer height (SO2LH) retrievals from 3 satellite instruments (TROPOMI on board S5P, and IASI-A&-B on board MetOp-A&B). The implementation of this service is enveloped in the framework of OPAS – Operational alert Products for ATM via SWIM – project, a KTN (Knowledge Transfer Network) Engage Catalyst funded project (Thematic Challenge 3; https://engagektn.com) of SESAR JU (Single European Sky ATM Research Joint Undertaking; https://www.sesarju.eu).We present the TROPOMI SO2LH algorithm and the uses of inverse modelling and external observations from satellites and ground-based DOAS-FLAME instruments to validate TROPOMI SO2LH products for recent eruptions (i.e. Etna in Dec. 2018, Raikoke in June 2019, Ubinas in July 2019, Taal in January 2020). Cross-comparison with the satellite instruments CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization), IASI (Infrared Atmospheric Sounder Interferometer) and with GNSS (Global Navigation Satellite System) radio-occultations, is shown. This study will describe the specification of our SWIM service and highlight the point of view of an engine constructor (Rolls-Royce) directly in relation with airlines and ATM, with regard to the objectives of the APOS project. Note that due to engine susceptibility to aerosols, the avoidance of flights through volcanic plumes and SO2 clouds is critical.The development of our new SO2LH products from TROPOMI contributes to an existing early warning system, so called SACS (Support to Aviation Control Service; http://sacs.aeronomie.be). This system is dedicated to support aviation and ATM, and was recently upgraded in the frame of EUNADICS-AV project (European Natural Airborne Disaster Information and Coordination System for Aviation; http://www.eunadics.eu), with many other alert products related to natural airborne hazard affecting air traffic (e.g. volcanic ash column and layer height, smoke from forest fires and desert dust).

Uncertainty in the physicochemical and optical properties of volcanic ash particles creates errors in the detection and modeling of volcanic ash clouds and in quantification of their potential impacts. In this study, we provide a dataset that describes the physicochemical and optical properties of a representative selection of volcanic ash samples from nine different volcanic eruptions covering a wide range of silica contents (50 - 80 wt. % SiO2). We measured and calculated parameters describing the physical (size distribution, complex shape, and dense-rock equivalent mass density), chemical (bulk and surface composition) and optical (complex refractive index from ultra-violet to near-infrared wavelengths) properties of the volcanic ash and classified the samples according to their SiO2 and total alkali contents into the common igneous rock types Basalt to Rhyolite. We found that the mass density ranges between ρ = 2.49 and 2.98 g/cm3 for rhyolitic to basaltic ash types, and that the particle shape varies with changing particle size (d < 100 μm). The complex refractive indices in the wavelength range between λ = 300 nm and 1500 nm depends systematically on the composition of the samples. The real part values vary from n = 1.38 to 1.66 depending on ash type and wavelength and the imaginary part values from k = 0.00027 to 0.00268. We place our results into the context of existing data, and thus provide a comprehensive dataset that can be used for future and historic eruptions, when only basic information about the magma type producing the ash is known.

This paper describes the motivation, procedures, and results of archaeological and geological field survey of the Ndutu Unit, Olduvai Gorge, conducted in June and July of 2013. Survey focused upon the area of Olduvai Gorge between the second fault and the Obalbal depression, although selective survey occurred in other areas in and around the Gorge. Over 72 archaeological find-spots were recorded, and hundreds of Middle Stone Age (MSA) artifacts were recovered, as was a small sample of fauna. Geological observations provisionally suggest that the Ndutu was formed, in part, from a series of pyroclastic density flow and ash fallout events from neighbouring volcanoes; this contrasts slightly with previous interpretations of the deposits in that at least some of the beds are thought to be in primary stratigraphic context. Our initial field findings are conducive to discussions of a number of issues directly relevant to the MSA in East Africa, and overall we conclude that there is strong potential for Olduvai's Ndutu Unit to shed light on the behavior, adaptations, and evolution of Homo sapiens prior to, during, and just after its physical emergence.

Particle aggregation governs the sedimentation of small volcanic tephra particles from ash clouds generated by explosive volcanic eruptions. Particle aggregates have larger sizes, lower densities, and higher terminal fall velocities than individual ash particles. Critically, this process reduces the atmospheric lifetime of volcanic ash clouds. Aggregation increases sedimentation rates in proximal regions and correspondingly decreases airborne ash mass loadings in distal regions. Aggregation processes and products vary with distance from a volcano. Proximal aggregates are larger (up to centimeter size), may have concentric internal structures, may be strongly bound (cemented and/or frozen), and can be associated with pyroclastic density currents. Distal aggregates are smaller (submillimeter), less well structured, weakly bound, and are deposited exclusively from the base of ash clouds. Bonding forces for individual ash particles include hydrostatic bonds (liquid and ice water) and electrostatic forces, and the availability of liquid determines the aggregate morphology. Gravitational convective instabilities observed in recent eruption clouds influence aggregation rates. Recently, much progress has been made in documenting and understanding aggregation through field studies, laboratory experiments, and numerical modeling. However, there remains uncertainty over the roles of eruption source parameters (eg, particle size distribution, erupted mass, eruption column height, cloud liquid content, and temperature), the eruption plume temperature lapse rate, and environmental parameters in determining the nature and distribution of aggregates. This chapter will provide an overview of aggregates observed falling out of recent volcanic clouds, aggregates found in deposits, and key formation mechanisms.

The May 2008 eruption of Chaitén volcano, Chile, provided a rare opportunity to measure the long-range transport of volcanic emissions and characteristics of a widely-dispersed terrestrial ash deposit. Airborne ash mass, quantified using thermal infrared satellite remote sensing, ranged between 0.2 and 0.4. Tg during the period 3-7 May 2008. A high level of spatiotemporal correspondence was observed between cloud trajectories and changes in surface reflectivity, which was inferred to indicate ash deposition. The evolution of the deposit was mapped for the first time using satellite-based observations of surface reflectivity.The distal (>80. km) ash deposit was poorly sorted and fine grained, and mean particle size varied very little beyond a distance >300. km. There were three particle size subpopulations in fallout at distances >300. km which mirror those identified in fallout from the 18 May 1980 eruption of Mount St. Helens, known to have a high propensity for aggregation. Discrete temporal sampling and characterisation of fallout demonstrated contributions from specific eruptive phases. Samples collected at the time of deposition were compared to bulk samples collected months after deposition and provided some evidence for winnowing.Experimentally-derived ash leachates had near-neutral pH values and charge balance which indicates minimal quantities of adsorbed acids. X-ray Photoelectron Spectroscopy (XPS) analyses revealed surface enrichments in Ca, Na and Fe and the presence of coatings of mixed Ca-, Na- and Fe-rich salts on ash particles prior to deposition. Low S:Cl ratios in leachates indicate that the eruption had a low S content, and high Cl:F ratios imply gas-ash interaction within a Cl-rich environment. We estimate that ash fallout had potential to scavenge ~42% of total S released into the atmosphere prior to deposition. XPS analyses also revealed ash particle surfaces were strongly enriched in Fe (in contrast to the results from bulk leachate analyses), which suggests that Chaitén ash fallout over oceans had potential to influence productivity in high-nutrient, low-chlorophyl regions of the oceans. Therefore ash particle surface geochemical analysis should be applied to quantify Fe-modulated biologically-forced CO 2 draw-down potential of volcanic ash fallout over oceans. Fil: Durant, Adam J.. Norwegian Institute for Air Research; Noruega. Michigan Technological University; Estados Unidos. University of Cambridge; Estados Unidos Fil: Villarosa, Gustavo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; Argentina Fil: Rose, William I.. Michigan Technological University; Estados Unidos Fil: Delmelle, Pierre. University of York; Reino Unido Fil: Prata, Alfred J.. Norwegian Institute for Air Research; Noruega Fil: Viramonte, Jose German. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Salta. Instituto de Investigaciones en Energía no Convencional. Universidad Nacional de Salta. Facultad de Ciencias Exactas. Departamento de Física. Instituto de Investigaciones en Energía no Convencional; Argentina

On average, about 45 per cent of global annual anthropogenic carbon dioxide (CO 2 ) emissions remain in the atmosphere, while the remainder are taken up by carbon reservoirs on land and in the oceans—the CO 2 ‘sinks’. As sink size and dynamics are highly variable in space and time, cross-verification of reported anthropogenic CO 2 emissions with atmospheric CO 2 measurements is challenging. Highly variable CO 2 sinks also limit the capability to detect anomolous changes in natural carbon reservoirs. This paper argues that significant uncertainty reduction in annual estimates of the global carbon balance could be achieved rapidly through coordinated up-scaling of existing methods, and that this uncertainty reduction would provide incentive for accurate reporting of CO 2 emissions at the country level. We estimate that if 5 per cent of global CO 2 emissions go unreported and undetected, the associated marginal economic impacts could reach approximately US$20 billion each year by 2050. The net present day value of these impacts aggregated until 2200, and discounted back to the present would have a mean value exceeding US$10 trillion. The costs of potential impacts of unreported emissions far outweigh the costs of enhancement of measurement infrastructure to reduce uncertainty in the global carbon balance.

This paper presents the motivation, procedures, and results of an experiment that examines short episodes of animal trampling in dry and water saturated substrates in South India. While horizontal artifact displacement was similar to that modeled by other trampling experiments, vertical artifact displacement in water saturated substrates was greater than any reported experiment to date. The toolstone used in this experiment, a silicious limestone, exhibited minimal damage after trampling. Artifact inclination patterning appeared to be a potentially diagnostic middle-range marker of trampling in water saturated substrates. Given the abundant number of Paleolithic sites that are located on flat, open surfaces near water-bodies, or experience monsoonal climatic regimes, we propose that future excavations should measure artifact inclination on a regular basis.

Water is a dominant component of volcanic clouds and has fundamental control on very fine particle deposition. Particle size characteristics of distal tephra-fall (100s km from source volcano) have a higher proportion of very fine particles compared to predictions based on single particle settling rates. In this study, sedimentological analyses of fallout from for the 18 August and 16–17 September 1992 eruptions of Crater Peak, Alaska, are combined with satellite observations, and cloud trajectory and microphysics modeling to investigate meteorological influences on particle sedimentation. Total grain size distributions of tephra fallout were reconstructed for both Crater Peak eruptions and indicate a predominance of fine particles − 2 g m − 3 (based on an estimated cloud thickness of ~ 1000 m from trajectory modeling). Hydrometeor formation on particles in the volcanic cloud and subsequent sublimation may induce a cloud base instability that leads to rapid bulk ( en masse ) sedimentation of very fine particles through a mammatus-like mechanism.

During volcanic eruptions, volcanic ash transport and dispersion models (VATDs) are used to forecast the location and movement of ash clouds over hours to days in order to define hazards to aircraft and to communities downwind. Those models use input parameters, called “eruption source parameters”, such as plume height H, mass eruption rate Ṁ, duration D, and the mass fraction m63 of erupted debris finer than about 4ϕ or 63 μm, which can remain in the cloud for many hours or days. Observational constraints on the value of such parameters are frequently unavailable in the first minutes or hours after an eruption is detected. Moreover, observed plume height may change during an eruption, requiring rapid assignment of new parameters. This paper reports on a group effort to improve the accuracy of source parameters used by VATDs in the early hours of an eruption. We do so by first compiling a list of eruptions for which these parameters are well constrained, and then using these data to review and update previously studied parameter relationships. We find that the existing scatter in plots of H versus Ṁ yields an uncertainty within the 50% confidence interval of plus or minus a factor of four in eruption rate for a given plume height. This scatter is not clearly attributable to biases in measurement techniques or to well-recognized processes such as elutriation from pyroclastic flows. Sparse data on total grain-size distribution suggest that the mass fraction of fine debris m63 could vary by nearly two orders of magnitude between small basaltic eruptions (∼ 0.01) and large silicic ones (> 0.5). We classify eleven eruption types; four types each for different sizes of silicic and mafic eruptions; submarine eruptions; “brief” or Vulcanian eruptions; and eruptions that generate co-ignimbrite or co-pyroclastic flow plumes. For each eruption type we assign source parameters. We then assign a characteristic eruption type to each of the world's ∼ 1500 Holocene volcanoes. These eruption types and associated parameters can be used for ash-cloud modeling in the event of an eruption, when no observational constraints on these parameters are available.

In explosive eruptions, the mass proportion of ash that is aerodynamically fine enough to cause problems with jet aircraft or human lungs ( 50%).

This retrospective study focuses on the fine silicate particles (

International audience; The 18 May 1980 eruption of Mount St. Helens started with a lateral blast that fed a pyroclastic surge, which then uplifted to form a co-blast plume. Thirty minutes later, Plinian activity started at the vent and fluctuated in intensity for ~9 h. The resulting fallout deposit, documented to > 600 km from vent, presents some striking features: (1) displacement of the overall deposit to the north of the vent, (2) a secondary thickness and mass maximum at ~300 km from vent, (3) a total grain size distribution dominated by fine ash (62 wt % of the deposit < 63 μm), and (4) individual grain size distributions that vary dramatically in the crosswind direction from strongly bimodal in the south to skewed unimodal in the north. Results from a new deconvolution of the individual grain size distributions show that they are a combination of a coarse subpopulation that decreases in size with distance from vent and a constant fine subpopulation with a mean of ∼15 μm. Relative proportions of each subpopulation vary asymmetrically in the crosswind directions, with the fine subpopulation preponderant toward the north and the coarse one dominating the south of the deposit, both reach their absolute maxima in mass on the deposit axis. Componentry analyses of selected samples show that blast-derived material is greatly enriched toward the north of the deposit. These results indicate that the co-blast plume dispersed fine-grained material over great distances and dominated the fine subpopulation. Comparison with reanalysis data of atmospheric wind fields and satellite images of the spreading ash cloud suggests contrasting ash transport and depositional processes for the (early) co-blast plume and the (later) vent-derived Plinian plumes. The co-blast plume is displaced to the north; it had a high overshoot height, and eastward dispersion via strong winds low in the stratosphere (~10-15 km). The Plinian plumes were lower and dispersed most of the material to the southeast as the direction of high-velocity winds shifted just before the late climactic Plinian eruptive phase. Fine ash (fine subpopulation) was deposited continuously throughout the deposit, with an increase of sedimentation rate ~300 km from the vent where there is a secondary maximum in the deposit mass and thickness. Fine ash probably settled by a combination of enhanced sedimentation mechanisms, including not only aggregation but also gravitational convective instabilities of cloud base, hydrometeor formation and destruction, and entrainment of small particles by larger ones. Finally, we show that half of the deposit (by mass) in the medial area was deposited by the co-blast plume, and that a significant proportion of the Mount St. Helens fallout deposit is nonjuvenile, which has implications for the magmatic budget of this eruption.

Mammatus clouds are an intriguing enigma of atmospheric fluid dynamics and cloud physics. Most commonly observed on the underside of cumulonimbus anvils, mammatus also occur on the underside of cirrus, cirrocumulus, altocumulus, altostratus, and stratocumulus, as well as in contrails from jet aircraft and pyrocumulus ash clouds from volcanic eruptions. Despite their aesthetic appearance, mammatus have been the subject of few quantitative research studies. Observations of mammatus have been obtained largely through serendipitous opportunities with a single observing system (e.g., aircraft penetrations, visual observations, lidar, radar) or tangential observations from field programs with other objectives. Theories describing mammatus remain untested, as adequate measurements for validation do not exist because of the small distance scales and short time scales of mammatus. Modeling studies of mammatus are virtually nonexistent. As a result, relatively little is known about the environment, formation mechanisms, properties, microphysics, and dynamics of mammatus. This paper presents a review of mammatus clouds that addresses these mysteries. Previous observations of mammatus and proposed formation mechanisms are discussed. These hypothesized mechanisms are anvil subsidence, subcloud evaporation/sublimation, melting, hydrometeor fallout, cloud-base detrainment instability, radiative effects, gravity waves, Kelvin–Helmholtz instability, Rayleigh–Taylor instability, and Rayleigh–Bénard-like convection. Other issues addressed in this paper include whether mammatus are composed of ice or liquid water hydrometeors, why mammatus are smooth, what controls the temporal and spatial scales and organization of individual mammatus lobes, and what are the properties of volcanic ash clouds that produce mammatus? The similarities and differences between mammatus, virga, stalactites, and reticular clouds are also discussed. Finally, because much still remains to be learned, research opportunities are described for using mammatus as a window into the microphysical, turbulent, and dynamical processes occurring on the underside of clouds.

We report laboratory observations of higher freezing temperatures when an ice-forming nucleus is near the surface of an undercooled water drop than when the nucleus is immersed in the drop. The nucleation rate at the water surface is a factor of 10(10) greater than in bulk water, thereby complementing and providing evidence for homogeneous surface crystallization, which has been hypothesized recently. Interpretation of the data via classical nucleation theory shows that the free energy of formation of a critical ice germ is decreased by a factor of approximately 2 when the substrate is near the air-water interface. Furthermore, the analysis suggests that the jump frequency of molecules from the liquid to the solid may be greatly enhanced at the interface.

A technique for estimating a whole object surface area and volume of a micro-scale three-dimensional model with a partially visible surface includes receiving a single-view stereoscopic image of an object of interest and an unconstrained three-dimensional point cloud of the object, generating a constrained three-dimensional point cloud using the image, the unconstrained three-dimensional point cloud, and a digital elevation model (DEM) of the object generated from the image, generating, using the constrained three-dimensional point cloud, a three-dimensional mesh representing an estimate of the surface of the object, calculating a partial surface area and/or partial volume of the object using the three-dimensional mesh, estimating an extent of a visible surface of the object, and calculating a whole surface area and/or a whole volume of the object based on the partial surface area of the object and the estimated extent of the visible surface of the object.

Modeling the transport of volcanic ash and gases released during volcanic eruptions is crucially dependent on knowledge of the source term of the eruption, that is, the source strength as a function of altitude and time. For the first time, an inversion method is used to estimate the source terms of both volcanic sulfur dioxide (SO2) and ash. It was applied to the explosive volcanic eruption of Grimsvotn, Iceland, in May 2011. The method uses input from the particle dispersion model, FLEXPART (flexible particle dispersion model), a priori source estimates, and satellite observations of SO2 or ash total columns from Infrared Atmospheric Sounding Interferometer to separately obtain the source terms for volcanic SO2 and fine ash. The estimated source terms show that SO2 was emitted mostly to high altitudes (5 to 13 km) during about 18 h (22 May, 00-18 UTC) while fine ash was emitted mostly to low altitudes (below 4 km) during roughly 24 h (22 May 06 UTC to 23 May 06 UTC). FLEXPART simulations using the estimated source terms show a clear separation of SO2 (transported mostly northwestward) and the fine ash (transported mostly southeastward). This corresponds well with independent satellite observations and measured aerosol mass concentrations and lidar measurements at surface stations in Scandinavia. Aircraft measurements above Iceland and Germany confirmed that the ash was located in the lower atmosphere. This demonstrates that the inversion method, in this case, is able to distinguish between emission heights of SO2 and ash and can capture resulting differences in transport patterns. Key Points Ash and SO2 source terms estimated using inverse techniques and satellite data The transport and separation of ash and SO2 are modeled Model simulations correspond well with a range of independent observations ©2014. The Authors.

Ash cloud detection and forecasting became a research priority and societal concern ([Bonadonna et al., 2014][1]) after the 2010 Eyjafjallajokull (Iceland) eruptions caused widespread flight cancellations and an estimated U.S.$5.0 billion impact on global gross domestic product (GDP) (5 day period

The 2008 Chaitén Volcano eruption began on 2 May 2008 with an explosive phase that injected large amounts of tephra into the atmosphere. During the first week of the eruption, volcanic ash clouds were transported for hundreds of kilometres over Argentina by the prevailing westerly winds. Tephra deposition extended to the Atlantic Ocean and severely affected the Argentinean Patagonia. Impacts included air and water quality degradation, disruption of ground transportation systems and cancellation of flights at airports more than 1,500 km apart. We use the FALL3D tephra transport model coupled with the Weather Research and Forecasting-Advanced Research Weather (WRF-ARW) meteorological model to simulate tephra fall from the 2-9 May 2008 eruptive period. Our hindcast results are in good agreement with satellite imagery and reproduce ground deposit observations. Key aspects of our analysis, not considered during syn-eruptive forecasts, are the re-initialization of each simulation with actualized meteorological forecast cycles and better constrained model inputs including column heights (inferred from reanalysis of GOES-10 imagery and nearby atmospheric soundings) and granulometric data obtained from field campaigns. This study shows the potential of coupling WRF/ARW and FALL3D models for short-term forecast of volcanic ash clouds. Our results highlight that, in order to improve forecasting of ash cloud dispersion and tephra deposition, it is essential to implement an operational observation system to measure temporal variations of column height and granulometric characteristics of tephra particles in nearly real-time, at proximal as well as distal locations. La erupción del volcán Chaitén se inició el 2 de Mayo de 2008 con una fase explosiva que inyectó grandes cantidades de tefra a la atmósfera. Durante la primera semana de erupción, se dispersaron nubes volcánicas por cientos de kilómetros sobre Argentina, siguiendo los vientos dominantes del oeste. El depósito de tefra se extendió hasta el océano Atlántico y afectó severamente a la Patagonia. Los impactos incluyen degradación de la calidad del aire y el agua, interrupción del sistema de transporte terrestre y la cancelación de vuelos incluso en aeropuertos a 1.500 km del volcán. Aquí se usó el modelo FALL3D de transporte y depósito de tefra con el modelo meteorológico Weather Research and Forecasting-Advanced Research Weather (WRF-ARW) para simular el período eruptivo del 2 al 9 de mayo de 2008. Los resultados obtenidos del pronóstico retrospectivo tienen una buena concordancia con las imágenes satelitales y reprodujeron las observaciones de depósito en superficie. Los aspectos claves de este análisis, no considerado durante los pronósticos contemporáneos, son la reinicialización de cada simulación con ciclos de pronósticos actualizados y condiciones iniciales del modelo más ajustadas, incluyendo alturas de columna eruptiva (inferidas a través del análisis de imágenes satelitales GOES-10 y radiosondeos cercanos) y datos granulométricos obtenidos a partir de campañas de campo. Este estudio muestra el gran potencial que tiene el acoplar el modelo WRF/ARW con el FALL3D para generar pronósticos a corto plazo de la nube volcánica. Los resultados presentados revelan que, para mejorar los pronósticos de dispersión y depósito de tefra, es esencial implementar un sistema de observación operativo con el fin de medir las variaciones temporales de la altura de columna y las características granulométricas de las partículas de tefra casi en tiempo real, tanto en lugares próximos como lejanos al volcán. Fil: Osores, María Soledad. Ministerio de Defensa. Armada Argentina. Servicio de Hidrografía Naval; Argentina. Ministerio de Defensa. Secretaria de Planeamiento. Servicio Meteorológico Nacional; Argentina. Comision Nacional de Actividades Espaciales; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Folch Duran, Arnau. Barcelona Supercomputing Center - Centro Nacional de Supercomputacion; España Fil: Collini, Estela Angela. Ministerio de Defensa. Armada Argentina. Servicio de Hidrografía Naval; Argentina. Ministerio de Defensa. Secretaria de Planeamiento. Servicio Meteorológico Nacional; Argentina Fil: Villarosa, Gustavo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones En Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Reg.universidad Bariloche. Instituto de Investigaciones En Biodiversidad y Medioambiente; Argentina Fil: Durant, Adam. Norwegian Institute for Air Research; Noruega. Michigan Technological University; Estados Unidos. University of Cambridge; Reino Unido Fil: Pujol, Gloria. Ministerio de Defensa. Secretaria de Planeamiento. Servicio Meteorológico Nacional; Argentina Fil: Viramonte, Jose German. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Salta. Instituto de Investigaciones en Energia No Convencional. Universidad Nacional de Salta. Facultad de Ciencias Exactas. Departamento de Física. Instituto de Investigaciones en Energia No Convencional; Argentina

] Explosive volcanic eruptions emit large proportions ofvery fine ash (

Voluminous rhyolitic eruptions from Toba, Indonesia, and Taupo Volcanic Zone (TVZ), New Zealand have dispersed volcanic ash over vast areas in the late Quaternary. The ~74 ka Youngest Toba Tuff (YTT) eruption deposited ash over the Bay of Bengal and the Indian subcontinent to the west. The ~340 ka Whakamaru eruption (TVZ) deposited the widespread Rangitawa Tephra, dominantly to the southeast (in addition to occurrences northwest of vent), extending across the landmass of New Zealand, and the South Pacific Ocean and Tasman Sea with distal terrestrial exposures on the Chatham Islands. These super-eruptions involved ~2500 km 3 and ~1500 km 3 of magma (dense-rock equivalent; DRE), respectively.Ultra-distal terrestrial exposures of YTT at two localities in India, Middle Son Valley, Madhya Pradesh, and Jurreru River Valley, Andhra Pradesh, at distances of >2000 km from the source caldera, show a basal 'primary' ashfall unit ~4 cm thick, although deposits containing reworked ash are up to ~3 m in total thickness. Exposures of Rangitawa Tephra on the Chatham Islands, >900 km from the source caldera, are ~15-30 cm thick. At more proximal localities (~200 km from source), Rangitawa Tephra is ~55-70 cm thick and characterized by a crystal-rich basal layer and normal grading. Both distal tephra deposits are characterized by very-fine ash (with high PM 10 fractions) and are crystal-poor.Glass chemistry, stratigraphy and grain-size data for these distal tephra deposits are presented with comparisons of their correlation, dispersal and preservation. Using field observations, ash transport and deposition were modeled for both eruptions using a semi-analytical model (HAZMAP), with assumptions concerning average wind direction and strength during eruption, column shape and vent size. Model outputs provide new insights into eruption dynamics and better estimates of eruption volumes associated with tephra fallout. Modeling based on observed YTT distal tephra thicknesses indicate a relatively low (

Most volcanic ash particles with diameters

International audience; Investigation of the climatic and environmental impacts of the Youngest Toba Tuff (YTT, ∼74 ka BP) eruption of Toba volcano, Sumatra, is crucial for understanding the consequences of the eruption for contemporaneous human populations. The Middle Son Valley, in India, was the first locality on the Indian subcontinent where the YTT was reported. The ash bed forms a discontinuous layer stretching for over 30 km along the river. Here we report on the stratigraphic contexts of YTT ash layers in alluvial deposits of the Middle Son Valley, in order to reconstruct the taphonomy of the ash deposits and the dynamic of their deposition. Although the distal ash has been studied since the 1980s, its stratigraphic integrity and the mechanisms and pathways involved in its transport and deposition have bit previously been assessed. We find that the YTT occurrences in the Middle Son Valley may not be reliable chronostratigraphical markers for millennial scale palaeoenvironmental reconstruction.

The April-May, 2010 volcanic eruptions of Eyjafjallajokull, Iceland caused significant economic and social disruption in Europe whilst state of the art measurements and ash dispersion forecasts were heavily criticized by the aviation industry. Here we demonstrate for the first time that large improvements can be made in quantitative predictions of the fate of volcanic ash emissions, by using an inversion scheme that couples a priori source information and the output of a Lagrangian dispersion model with satellite data to estimate the volcanic ash source strength as a function of altitude and time. From the inversion, we obtain a total fine ash emission of the eruption of 8.3 +/- 4.2 Tg for particles in the size range of 2.8-28 mu m diameter. We evaluate the results of our model results with a posteriori ash emissions using independent ground-based, airborne and space-borne measurements both in case studies and statistically. Subsequently, we estimate the area over Europe affected by volcanic ash above certain concentration thresholds relevant for the aviation industry. We find that during three episodes in April and May, volcanic ash concentrations at some altitude in the atmosphere exceeded the limits for the "Normal" flying zone in up to 14% (6-16%), 2% (1-3%) and 7% (4-11%), respectively, of the European area. For a limit of 2 mg m(-3) only two episodes with fractions of 1.5% (0.2-2.8%) and 0.9% (0.1-1.6%) occurred, while the current "No-Fly" zone criterion of 4 mg m(-3) was rarely exceeded. Our results have important ramifications for determining air space closures and for real-time quantitative estimations of ash concentrations. Furthermore, the general nature of our method yields better constraints on the distribution and fate of volcanic ash in the Earth system., SCOPUS: ar.j, info:eu-repo/semantics/published

Volcanic emissions consist of a mixture of gases, aerosol, and silicate particles, which collectively span seven orders of magnitude in size. Airborne ash and sulfate aerosol in the lower atmosphere has short-lived atmospheric and climatic effects. Volcanic aerosol injected high into the stratosphere impacts atmospheric chemical cycles and the solar and terrestrial radiation budgets, and may influence climate over longer time-scales than aerosol particles in the lower atmosphere. Once at the surface, the impacts on local environments can be substantial through transport of halogens, trace metals, and metalloids, and subsequent leaching in aqueous solutions. Volcanic emissions may cause disruption to travel and aviation, and may damage surface infrastructure, potentially causing large economic losses.

[1] Uncertainty remains on the origin of distal mass deposition maxima observed in many recent tephra fall deposits. In this study the link between ash aggregation and the formation of distal mass deposition maxima is investigated through reanalysis of tephra fallout from the Mount St. Helens 18 May 1980 (MSH80) eruption. In addition, we collate all the data needed to model distal ash sedimentation from the MSH80 eruption cloud. Four particle size subpopulations were present in distal fallout with modes at 2.2 Φ, 4.2 Φ, 5.9 Φ, and 8.3 Φ. Settling rates of the coarsest subpopulation closely matched predicted single-particle terminal fall velocities. Sedimentation of particles

[1] Textural characteristics of recently emplaced volcanic materials provide information on the degassing history, volatile content, and future explosive activity of volcanoes. Thermal infrared (TIR) remote sensing has been used to derive the micron-scale roughness (i.e., surface vesicularity) of lavas using a two-component (glass plus blackbody) spectral deconvolution model. We apply and test this approach on TIR data of pyroclastic flow (PF) deposits for the first time. Samples from two PF deposits (January 2005: block-rich and March 2000: ash-rich) were collected at Bezymianny Volcano (Russia) and analyzed using (1) TIR emission spectroscopy, (2) scanning electron microscope (SEM)-derived roughness (profiling), (3) SEM-derived surface vesicularity (imaging), and (4) thin section observations. Results from SEM roughness (0.9–2.8 μm) and SEM vesicularity (18–26%) showed a positive correlation. These were compared to the deconvolution results from the laboratory and spaceborne spectra, as well as to field-derived percentages of the block and ash. The spaceborne results were within 5% of the laboratory results and showed a positive correlation. However, a negative correlation between the SEM and spectral results was observed and was likely due to a combination of factors; an incorrect glass end-member, particle size effects, and subsequent weathering/reworking of the PF deposits. Despite these differences, this work shows that microscopic textural heterogeneities on PF deposits can be detected with TIR remote sensing using a technique similar to that used for lavas, but the results must be carefully interpreted. If applied correctly, it could be an important tool to map recent PF deposits and infer the causative eruption style/mechanism.

Airborne dust affects the Earth's energy balance — an impact that is measured in terms of the implied change in net radiation (or radiative forcing, in W m-2) at the top of the atmosphere. There remains considerable uncertainty in the magnitude and sign of direct forcing by airborne dust under current climate. Much of this uncertainty stems from simplified assumptions about mineral dust-particle size, composition and shape, which are applied in remote sensing retrievals of dust characteristics and dust-cycle models. Improved estimates of direct radiative forcing by dust will require improved characterization of the spatial variability in particle characteristics to provide reliable information dust optical properties. This includes constraints on: (1) particle-size distribution, including discrimination of particle subpopulations and quantification of the amount of dust in the sub-10 µm to

[1] Water is the dominant component of volcanic gas emissions, and water phase transformations, including the formation of ice, can be significant in the dynamics of volcanic clouds. The effectiveness of volcanic ash particles as ice-forming nuclei (IN) is poorly understood and the sparse data that exist for volcanic ash IN have been interpreted in the context of meteorological, rather than volcanic clouds. In this study, single-particle freezing experiments were carried out to investigate the effect of ash particle composition and surface area on water drop freezing temperature. Measured freezing temperatures show only weak correlations with ash IN composition and surface area. Our measurements, together with a review of previous volcanic ash IN measurements, suggest that fine-ash particles (equivalent diameters between approximately 1 and 1000 μm) from the majority of volcanoes will exhibit an onset of freezing between ∼250–260 K. In the context of explosive eruptions where super-micron particles are plentiful, this result implies that volcanic clouds are IN-rich relative to meteorological clouds, which typically are IN-limited, and therefore should exhibit distinct microphysics. We can expect that such “overseeded” volcanic clouds will exhibit enhanced ice crystal concentrations and smaller average ice crystal size, relative to dynamically similar meteorological clouds, and that glaciation will tend to occur over a relatively narrow altitude range.

Doswell has proposed a mechanism for mammatus called double-diffusive convection, the mechanism responsible for salt fingers in the ocean. The physics of salt fingers and mammatus are different. Unlike the ocean where the diffusivity is related to molecular motions within solution, the hydrometeors in clouds are affected by inertial and gravitational forces. Doswell misinterprets the vertical temperature profiles through mammatus and fails to understand the role of settling in volcanic ash clouds. Furthermore, given that mixing is a much more effective means of transferring heat in the atmosphere and given idealized numerical model simulations of mammatus showing that the destabilizing effect of subcloud sublimation is an effective mechanism for mammatus, this reply argues that double-diffusive convection is unlikely to explain mammatus, either in cumulonimbus anvils or in volcanic ash clouds.

[1] Ice formation in atmospheric clouds is crucial to our understanding of precipitation and cloud radiative properties. In recent work it was shown that heterogeneous ice nucleation rates can be strongly enhanced by a form of surface crystallization (Shaw et al., 2005). Here we present new laboratory data and consider the implications for contact nucleation and its relevance to ice nucleation in atmospheric clouds. Our observations contradict three leading hypotheses for contact nucleation and suggest, instead, that the notion of contact nucleation should be generalized to include surface crystallization from particles contacting a supercooled drop from the inside out, as well as from the outside in. Our findings lead to the hypothesis that the freezing temperature of an evaporating drop will suddenly become higher once the drop surface contacts an immersed ice nucleus. This mechanism for evaporation freezing is therefore a plausible explanation for the abundant observations of high ice concentrations associated with cloud dilution and droplet evaporation.

While suspended in Earth's atmosphere, fine ash influences radiative transfer, weather, and climate (e.g., [Newhall and Self, 1982][1]). Sulfate aerosol, also in volcanic ash clouds, dominates atmospheric effects, having stratospheric residence times of months to years ([Robock, 2000][2]), so large

Connecting graduate students with experts in a given discipline is vital to their success but has often been challenging because of logistics, costs, and scheduling. However, advances in Internet video conferencing now allow multiple parties to meet simultaneously and engage in real-time discussion.

Erratum to ‘A multidisciplinary effort to assign realistic source parameters to models of volcanic ash-cloud transport and dispersion during eruptions’ by Mastin et al. [J. Volcanol. Geotherm. Res. 188(2009)1–21] L.G. Mastin ⁎, M. Guffanti , R. Servranckx , P. Webley , S. Barsotti , K. Dean , A. Durant , J.W. Ewert , A. Neri , W.I. Rose , D. Schneider , L. Siebert , B. Stunder , G. Swanson , A. Tupper , A. Volentik , C.F. Waythomas h

Volcanic ash (VA) clouds in flight corridors present a significant threat to aircraft operations as VA particles can cause damage to gas turbine engine components that lead to a reduction of engine performance and compromise flight safety. In the last decade, research has mainly focused on processes such as erosion of compressor blades and static components caused by impinging ash particles as well as clogging and/or corrosion effects of soft or molten ash particles on hot section turbine airfoils and components. However, there is a lack of information on how the fan separates ingested VA particles from the core stream flow into the bypass flow and therefore influences the mass concentration inside the engine core section, which is most vulnerable and critical for safety. In this numerical simulation study, we investigated the VA particle–fan interactions and resulting reductions in particle mass concentrations entering the engine core section as a function of particle size, fan rotation rate, and for two different flight altitudes. For this, we used a high-bypass gas-turbine engine design, with representative intake, fan, spinner, and splitter geometries for numerical computational fluid dynamics (CFD) simulations including a Lagrangian particle-tracking algorithm. Our results reveal that particle–fan interactions redirect particles from the core stream flow into the bypass stream tube, which leads to a significant particle mass concentration reduction inside the engine core section. The results also show that the particle–fan interactions increase with increasing fan rotation rates and VA particle size. Depending on ingested VA size distributions, the particle mass inside the engine core flow can be up to 30% reduced compared to the incoming particle mass flow. The presented results enable future calculations of effective core flow exposure or dosages based on simulated or observed atmospheric VA particle size distribution, which is required to quantify engine failure mechanisms after exposure to VA. As an example, we applied our methodology to a recent aircraft encounter during the Mt. Kelud 2014 eruption. Based on ambient VA concentrations simulated with an atmospheric particle dispersion model (FLEXPART), we calculated the effective particle mass concentration inside the core stream flow along the actual flight track and compared it with the whole engine exposure.

Volcanic eruptions can produce ash particles with a range of sizes and morphologies. Here we morphologically distinguish two textural types: Simple (generally smaller) ash particles, where the observable surface displays a single measureable bubble because there is at most one vesicle imprint preserved on each facet of the particle; and complex ash particles, which display multiple vesicle imprints on their surfaces for measurement and may contain complete, unfragmented vesicles in their interiors. Digital elevation models from stereo-scanning electron microscopic images of complex ash particles from the 14 October 1974 sub-Plinian eruption of Volcan Fuego, Guatemala and the 18 May 1980 Plinian eruption of Mount St. Helens, Washington, U.S.A. reveal size distributions of bubbles that burst during magma fragmentation. Results were compared between these two well-characterized eruptions of different explosivities and magma compositions and indicate that bubble size distributions (BSDs) are bimodal, suggesting a minimum of two nucleation events during both eruptions. The larger size mode has a much lower bubble number density (BND) than the smaller size mode, yet these few larger bubbles represent the bulk of the total bubble volume. We infer that the larger bubbles reflect an earlier nucleation event (at depth within the conduit) with subsequent diffusive and decompressive bubble growth and possible coalescence during magma ascent, while the smaller bubbles reflect a relatively later nucleation event occurring closer in time to the point of fragmentation. Bubbles in the Mount St. Helens complex ash particles are generally smaller, but have a total number density roughly one order of magnitude higher, compared to the Fuego samples. Results demonstrate that because ash from explosive eruptions preserves the size of bubbles that nucleated in the magma, grew, and then burst during fragmentation, the analysis of the ash-sized component of tephra can provide insights into the spatial distribution of bubbles in the magma prior to fragmentation, enabling better parameterization of numerical eruption models and improved understanding of ash transport phenomena that result in pyroclastic volcanic hazards. Additionally, the fact that the ash-sized component of tephra preserves BSDs and BNDs consistent with those preserved in larger pyroclasts indicates that these values can be obtained in cases where only distal ash samples from particular eruptions are obtainable.