Volcanic Ash Fallout Research Articles

Impact of ash fallout of the 2023 Shiveluch volcano eruption (Kamchatka) on forest vegetation

The ash fallout of Shiveluch volcano (April 11, 2023, Kamchatka) is the most intensive volcanic ash fallout of the last 60 years. We present the results of the reconnaissance fi eld investigations supplemented with analyses of satellite images of the area for estimations of deposits distribution and area aff ected by the ash fallout. We also estimated the properties of fi ne grained ash of andesitic composition and its infl uence on the forest vegetation composed by Picea yezoensis (Siebold et Zucc.) Carrière, Larix cajanderi Mayr и Betula ermanii Cham. As a result of moderate- scale ash fallout in the forest (thickness of freshly deposited ash is 5–8 cm), the negative impact on vegetation was minimal because the ash was fi ne-grained and was deposited on a thick snowpack, and the leaves were not formed yet. The forest vegetation on lower elevations was not damaged at all but strong changes occurred in grass and bush vegetation. We have observed the diminished density of plant coverage, decreased size of grass vegetation and a decreased number of plant species. Calamagrostis purpurea (Trin.) Link. s. l., a broadly represented dominant species among grass vegetation, became less common, but Chamerion angustifolium (L.) Holub became more widespread. The possibility of small plants to grow through the ash layer turned out to be strongly reduced. Mosses and lichens in the forest have been buried under the ash, the recovery could take several decades. We have found a notable impact on plants by ash remobilized by strong wind, this impact is the strongest in the open areas and on forest edges. This process can continue for many years due to the large volume of the deposited ash covering the open spaces of the volcano foot.

Godzilla mineral dust and La Soufrière volcanic ash fallout immediately stimulate marine microbial phosphate uptake

During the “Godzilla” dust storm of June 2020, unusually high fluxes of mineral dust traveled across the Atlantic from the Sahara Desert, reaching the Caribbean Basin, Gulf Coast, and southeastern United States. Additionally, an eruption of the La Soufrière volcano on St. Vincent in April 2021 generated substantial ashfall in the southeastern Caribbean. While many studies have analyzed mineral dust’s ability to relieve nutrient limitation of phosphorus (P) in the P-stressed North Atlantic, less is known about the impact of extreme events and other natural aerosols on fluxes of P into seawater and from seawater into marine microbial cells. We quantified P and iron (Fe) content in mineral dust from the Godzilla dust storm and volcanic ash from the La Soufrière eruption collected at Ragged Point, Barbados. We also performed seawater incubations to assess the marine microbial response to aerosol deposition. Using environmentally-relevant concentrations of atmospheric particles for within the ocean’s mixed layer allowed us to draw realistic conclusions about how these deposition events impacted P cycling in situ. Volcanic ash has lower P content than mineral dust, and P in volcanic ash is far less soluble (~1%) than assumed in current atmospheric deposition models. Adding mineral dust and the volcanic ash leachate in concentrations representing different deposition scenarios increased soluble reactive phosphorus (SRP) concentrations in coastal seawater by ~7-32 nM. Phosphate uptake rate was stimulated in coastal seawater after either mineral dust or volcanic ash deposition at aerosol concentrations relevant to the Godzilla dust event, with ash eliciting the fastest uptake rate. Furthermore, high concentrations of both the mineral dust and volcanic ash led to slightly elevated alkaline phosphatase activity (APA) compared to the relevant controls, indicating higher potential for use of dissolved organic phosphorus (DOP) as a P source. Quantifying these aerosols’ impacts on P cycling is a significant step towards achieving a better understanding of their potential roles in relieving nutrient limitation and fueling the biological carbon pump.

Characterization of a Vision-Based Tool for the Investigation of Geometric Characteristics of Ground-Deposited Volcanic Ash

With the support of public authorities and research institutions, volcanic ash fallout and its impact on the safety of people, infrastructure and services are addressed with the aim of defining protocols and instruments for the reliable and effective handling of related emergencies. Most of the solutions proposed in the literature on ash fallout monitoring suffer from high cost and are demanding in terms of installation and maintenance. The approach suggested in this work is based on the use of a low-cost vision embedded system and a dedicated algorithm which automatically processes acquired frames of ground-deposited volcanic ash in order to estimate the main geometric properties of each particle identified in the work area. A complete characterization of the system is presented, along with a robustness analysis of particle shapes, their orientation and their position in the inspected frame. An accuracy of ±40.2 µm (with a 3σ limit) and a resolution of 32.9 µm (in the worst case), over a framed area of 130 mm by 100 mm, were estimated; these values would fulfill the objectives of the application.

Forecasting and communicating the dispersion and fallout of ash during volcanic eruptions: lessons from the September 20, 2020 eruptive pulse at Sangay volcano, Ecuador

Volcanic ash is a hazard to human health and activities. Accurate and timely forecasts coupled with effective communication about the dispersion and fallout of volcanic ash during explosive events are essential to reduce impacts on local communities and limit economic losses. In this study, we present the first detailed description of an eruptive pulse at Sangay volcano and its eruption source parameters. The eruptive pulse on September 20, 2020, started at about 9:20 UTC and lasted between 90 and 100 min, producing an eruptive column that rapidly separated into (1) a higher (15.2 km above sea level, asl), gas-rich cloud moving east-southeast and (2) a lower (12.2 km asl), ash-rich cloud moving west and causing ash fallout up to 280 km from the volcano. Field data collected immediately after the event allow estimating the volume of bulk tephra to be between 1.5 and 5.0 × 106 m3, corresponding to a volcanic explosivity index of 2. The eruptive pulse, identified as violent Strombolian, emitted andesitic ash that was more mafic than products ejected by Sangay volcano in recent decades. Component analysis and glass chemistry of juvenile particles support the hypothesis that this event excavated deeper into the upper conduit compared to typical Strombolian activity at Sangay volcano, while grain-size analysis allows reconstruction of the total grain-size distribution of the fallout deposit. The discrepancies between the ash fallout simulations performed with the Ash3D online tool and the actual deposit are mainly the result of inaccurate pre- and syn-eruptive configurations and highlight the importance of additional processes such as aggregation. Communication products issued during the event included (1) several standard short reports, (2) volcano observatory notices for aviation, (3) social media posts, and (4) a special report providing the results of the ash fallout simulation. Although communication was effective with the authorities and the connected population, an effort must be made to reach the most vulnerable isolated communities for future events. This study shows that forecasting ash dispersion and fallout during volcanic eruptions can guide early warnings and trigger humanitarian actions, and should become a standard in volcano observatories worldwide.

A report on radon emission from bauxitic material in Perth, Manchester, Jamaica

Bauxitic soils in Jamaica are enriched with rare earth elements and other heavy minerals/elements by up to two orders of magnitude relative to bedrock. Geochemical evidence supports the origin of Jamaican bauxite as volcanic ash fall-out from Central America and windblown dust from West Africa. Jamaican bauxite, by virtue of its possible igneous origins, is suspected of being a source of radioactive material. The potential concentration and mobility of radon gas from bauxite waste is an environmental health and safety risk. Therefore, this paper investigates the theoretical radon concentrations and exposure rates in the bauxite mining community in Perth, Manchester. Results from the study show that the exposure rates in the Perth community are all below the recommended 1 WLM/yr. Therefore, radon from the bauxite waste is not a concern for radiation exposure and could be a potential recycled material for brick and other low-income housing materials in Jamaica.

Removal of ammonium from wastewater by zeolite synthetized from volcanic ash: Batch and column tests

Volcanic ash (VA) fallout during explosive activity of Mt. Etna (Sicily, Italy) negatively impacts the economy of local municipalities due to the management and disposal costs. In order to investigate an alternative use of VA in the civil and environmental engineering field, zeolites synthetized from VA were employed to remove ammonium from various aqueous solutions. Specifically, batch adsorption experiments were conducted to assess the effect of different synthesis conditions (e.g., incubation temperature, use of seawater or distilled water, VA particle size) on the adsorption capacity of ammonium on the produced zeolites. Adsorption isotherms were well fitted by Freundlich model and showed that zeolite synthetized at 70 °C using distilled water (C1H70) exhibited the highest adsorption capacity (~18.4 mg g−1). The observed ammonium adsorption capacity is higher or comparable to other natural or synthetized zeolites reported in literature. C1H70 was used in column experiments under different operational conditions, including initial ammonium concentration (10 and 40 mg L−1), empty bed contact time (EBCT, 4 and 8 min) and water quality (deionized water vs. secondary effluent wastewater). The Dose-Response model showed the best fitting in describing the breakthrough curves. Obtained results showed a good removal of ammonium even though the adsorption capacity decreased in presence of competing ions (e.g., calcium) and when tap water or wastewater was used. Moreover, the adsorption capacity of C1H70 regenerated through NaCl solution was found similar to the fresh C1H70. However, the regenerated zeolite was characterized by a slower mass transfer process. Overall, synthetized zeolites from VA can be used to remove ammonium from wastewater, reducing both the landfilling of VA and the extraction of natural zeolite under the circular economy perspective.

Probabilistic Hazard Maps of Volcanic Ash Dispersion and Fallout from Lascar Volcano: Implications for Argentine Territory and Surroundings Areas

Probabilistic Hazard Maps of Volcanic Ash Dispersion and Fallout from Lascar Volcano: Implications for Argentine Territory and Surroundings Areas

A Vision-Based Approach for the Analysis of Core Characteristics of Volcanic Ash.

Volcanic ash fall-out represents a serious hazard for air and road traffic. The forecasting models used to predict its time–space evolution require information about the core characteristics of volcanic particles, such as their granulometry. Typically, such information is gained by the spot direct observation of the ash collected at the ground or by using expensive instrumentation. In this paper, a vision-based methodology aimed at the estimation of ash granulometry is presented. A dedicated image processing paradigm was developed and implemented in LabVIEW™. The methodology was validated experimentally using digital reference images resembling different operating conditions. The outcome of the assessment procedure was very encouraging, showing an accuracy of the image processing algorithm of 1.76%.

Eruptive style controls the formation of silicon hexafluoride salts on volcanic ash: The case of the 2010 eruption of Eyjafjallajökull volcano, Iceland

The presence of fluoride (F−)-bearing compounds in volcanic ash fallout is recognised to pose significant environmental and health hazards. Nevertheless, understanding of the formation and composition of these compounds remains limited, or even inconsistent. This hampers full comprehension of the risks and impacts elicited by fluorine-rich ash emissions after an explosive eruption. The 2010 activity of Eyjafjallajökull volcano in Iceland was characterised by contrasted eruptive styles - phreatomagmatic and magmatic - which produced ash deposits with distinct soluble F− contents. Based on X-ray photoelectron spectroscopy and leachate analyses of Eyjafjallajökull ash materials, we infer the existence of silicon hexafluoride salts, particularly Na2SiF6, dominantly if not exclusively on the magmatic ash, and suggest a reaction mechanism for their formation. The presence of Na2SiF6 explains the much greater F− concentration and higher acidity measured in leachates of the magmatic ash compared to those of the phreatomagmatic ash. River waters affected by ash deposition during the magmatic activity showed a temporary increase in F− and decrease in dissolved silicon isotope values (δ30Si). We contend that the formation of silicon hexafluoride salts on ash leads to a surface enrichment of the ash's silicate glass and mineral components in 28Si, with the release of this light Si from the magmatic ash during the early stage of weathering causing a depression in the riverine δ30Si. This supports existing evidence of silicate dissolution processes being influenced by the presence of fluorine. Our study also points to the likely important role of Na2SiF6 in modulating the environmental and health effects of ash emissions from fluorine-rich magmatic eruptions.

Genesis of end-Guadalupian bauxite and pyrite deposits in the Youjiang Basin (South China): Insights into the causative link between magmatic events and mass extinction

Mass extinction was commonly considered as the response to interaction between geosystems, and volcanism can be viewed as a vital link between the surface systems and deep geodynamic processes. This causative link between end-Guadalupian mass extinction and volcanism has been clarified, based on the research of bauxite and pyrite deposits in the Youjiang Basin, South China Block (SCB). Geochronological and geochemical evidences show that the source materials of bauxite-pyrite deposits were mainly derived from the Emeishan large igneous province (LIP) to the northwest and the continental arc along the SW margin of SCB associated with the subduction of the Paleo-Tethys Ocean underneath the Indochina block. Volcanic ash fallout by atmospheric dispersal driven by the easterly trade winds could best account for the spatial variation of both bauxite and pyrite deposits given their relative paleogeographic positions with respect to the two flanking sources. Massive volcanic tephra from arc volcanism fell on exposed carbonate platforms, underwent intensive chemical weathering and transformed into bauxites under the warm and humid tropical climate in Tethys, which could be also favored by acid precipitation caused by volcanic degassing. Extensive SO2 released from Emeishan LIP emission could be the major source of pyrite ores, probably with minor contribution from arc volcanism. This indicates that the prolonged and extensive continental arc volcanism induced environmental stress in the poorly-ventilated Paleo-Tethys Ocean, while the coincidental eruption of the large igneous provinces was the final straw, leading to the dramatic biotic crises during the Middle-Late Permian interval.

Absolute dating of the L-chondrite parent body breakup with high-precision U–Pb zircon geochronology from Ordovician limestone

The breakup of the L-chondrite parent body (LCPB) in the mid-Ordovician is the largest documented asteroid breakup event during the past 3 Gyr. It affected Earth by a dramatic increase in the flux of L-chondritic material and left prominent traces in both meteorite and sedimentary records. A precise constraint on the timing of the LCPB breakup is important when evaluating the terrestrial biotic and climatic effects of the event, as well as for global stratigraphic correlations. Direct dating using heavily shocked L chondrites is hampered by both incomplete initial K-Ar degassing and isotopic resetting by later impact events. In order to better constrain the absolute age of this event we carried out high-precision U–Pb dating of zircons from three limestone beds recording discrete volcanic ash fallouts within mid-Ordovician strata in southern Sweden. These strata are rich in fossilized L-chondritic meteorites (1-20 cm large) that arrived on Earth shortly after the breakup event. Zircons from the ash-bearing layers provide stratigraphically consistent depositional ages that range from 464.22 ± 0.37 Ma to 465.01 ± 0.26 Ma. Combined with recently published 3He profiles that pinpoint the arrival on Earth of the first dust from the breakup, and sedimentation rates constrained by cosmogenic 21Ne in the fossil meteorites, the LCPB breakup is estimated to have occurred at 465.76 ± 0.30 Ma. This provides the presently most precise absolute dating of the LCPB breakup, enabling a robust global stratigraphic correlation of bounding strata. Based on our new U–Pb data for the ash-bearing beds, the absolute ages for the boundaries of biozones and Dapingian–Floian stages overlap within error with those given by the 2012 Geological Timescale and require no modification.

Volcanism and geochemistry of soil and vegetation cover of Kamchatka. Communication 3. Elemental composition of vegetation of volcanic ecosystems

The link of the chemical composition of the plant with the active volcanism of Kamchatka, is determined by the stable occurrence into the composition of the priority chemical elements for plants, volcanic ashes and soils: Ca, Mg, Mn, P, Cu, Zn and Sr. An elevated geochemical background of Kamchatka plants relative to the bulk chemical composition of the peninsula’s soils was established. The contents of Br, Hg, Hf, Sb, Ga, W, K relative to the clarks for living matter in the plants of the region are exceeded by 3–5 times. Against the background of small variations in the contents of chemical elements in plants of different regions, the relatively rich biogeochemical background of the Western region of the southern province (the western coast of Kamchatka) is determined, where most ancient near-surface volcanic ashes for Kamchatka are transformed into humus-accumulative horizons. On the territory of young volcanic ash fallout in the immediate vicinity of volcanoes, the relative richness of vegetation with chemical elements and the poverty of soils by mobile forms of elements have been established. On the contrary, at a distance from the volcanoes in the zone of far transfer fallout ashes, there is a marked relative poverty of plants and soil richness of available chemical elements.

Surface crusting of volcanic ash deposits under simulated rainfall

Explosive volcanic eruptions can have severe impacts on watershed hydrology. Among them, surface crusting of volcanic ash fallout following rainfall has been shown to favour runoff, erosion and lahar initiation. It may also hamper seed emergence and depress plant growth. However, ash crust formation is poorly understood. Reconstructed ash deposits were subjected to simulated rainfall to investigate the microscale morphological modifications of the ash deposit surface in response to raindrop impact. Ash samples from three volcanic eruptions (Mt. Merapi, MER, Indonesia; Eyjafjallajokull, EYJA, Iceland; and San Cristobal, SC, Nicaragua) with different particle size distributions and soluble salt contents were used in the experiment. Microcraters and micropeaks formed on the surface of all ash deposits after rainfall initiation. This was accompanied by fine material (also referred to as micromass) accumulation in the form of one or several layers, a few tens to hundreds of micrometres thick. Such morphological changes point to structural crust formation. The crusts consisted of a thin layer of tightly packed clay and silt-size ash particles (SC), overlain by loose coarser materials in micro-craters (MER) or by an almost continuous coarse-grained layer (EYJA). In all cases, the surface crust had a reduced porosity compared with the bulk material. Depending on ash particle size, crusting was governed by splash, compaction and vertical sorting (MER), vertical particle sorting (EYJA) or compaction (SC). No samples showed evidence of particle cementation through secondary salt precipitation. Our results shed new light on the mechanisms responsible for post-depositional crusting of a natural ash deposit.

Mineralogy and geochemistry of various colored boles from the Deccan volcanic province: Implications for paleoweathering and paleoenvironmental conditions

Boles are markers of hiatus in successive eruptions of the Deccan flood volcanism (DFV) emplaced at the Cretaceous-Paleogene boundary that are interpreted to retain paleoenvironmental information from their subaerial exposure. To evaluate paleoenvironment during these hiatuses, mineralogy and geochemistry of three different colors of boles, i.e., red (dark = 10R-3/6 and light = 10R-4/8), brown (5YR-4/4) and green (5G-6/2) were examined. The plagioclase index of alteration (PIA) (loss of Ca and Na relative to Al) was between 76 and 81 for all the boles, indicating moderate chemical weathering that is probably due to their short subaerial exposures. Mass balance calculations show significant enrichments of K, Si, Mg and Rb in green and brown boles suggesting an allochthonous input that is interpreted as volcanic ash fallout. Mineralogically, the red bole is dominated by montmorillonite and hematite, the brown bole of ferruginous smectite and montmorillonite, and the green bole of celadonite and nontronite.Montmorillonite and hematite genesis in red boles indicates leaching in an oxidative environment at near neutral pH (~5.5 to 8) conditions. Further, heating of the altered basalt from emplacement of upper lava flows under subaerial-dry conditions could have also promoted the formation of hematite in red boles. The hydrothermal alteration of K and Mg enriched volcanic ash admixed with the altered lower flow basalt under slightly reducing oxidation potential led to the genesis of nontronite and celadonite in the green bole. The aluminous Fe-smectite in brown bole occurred from hydrothermal alteration of aluminous clays (e.g., montmorillonite). The different colored boles, therefore, suggest a range of weathering processes including chemical leaching to hydrothermal alteration in oxidative to reducing environmental conditions throughout DFV emplacement that could reflect changing surficial conditions associated with volcanically forced changes to the environment.

Spatial distribution of volcanic ash deposits of 2011 Puyehue-Cordón Caulle eruption in Patagonia as measured by a perturbation in NDVI temporal dynamics

Volcanic ash fallout is a recurrent environmental disturbance in forests, arid and semi-arid rangelands of Patagonia, South America. The ash deposits over large areas are responsible for several impacts on ecological processes, agricultural production and health of local communities. Public policy decision making needs monitoring information of the affected areas by ash fallout, in order to better orient social, economic and productive aids. The aim of this study was to analyze the spatial distribution of volcanic ash deposits from the eruption of Puyehue-Cordón Caulle in 2011, by identifying a sudden change in the Normalized Difference Vegetation Index (NDVI) temporal dynamics, defined as a perturbation located in the time series. We applied a sparse-wavelet transform using the Basis Pursuit algorithm to NDVI time series obtained from the Moderate Resolution Image Spectroradiometer (MODIS) sensor, to identify perturbations at a pixel level. The spatial distribution of the perturbation promoted by ash deposits in Patagonia was successfully identified and characterized by means of a perturbation in NDVI temporal dynamics. Results are encouraging for the future development of a new platform, in combination with data from forecasting models and tracking of ash cloud trajectories and dispersion, to inform stakeholders to mitigate impact of volcanic ash on agricultural production and to orient public intervention strategies after a volcanic eruption followed by ash fallout over a wide region.

Cost-benefit analysis of rehabilitation and opening new cultivation land for tangerine cv Madu impacted by volcanic ash fallout of Mount Sinabung, North Sumatra, Indonesia

Mufidah L, Sugiyatno A, Ratule MT. 2017. Short Communication: Cost-benefit analysis of rehabilitation and opening new cultivation land for tangerine cv Madu impacted by volcanic ash fallout of Mount Sinabung, North Sumatra, Indonesia. Nusantara Bioscience 9: 339-345. Indonesian tangerine plants which have diverse varieties possess the adaptability from lowlands to highlands in the tropical region. Some of the tangerine production centers in Indonesia, such as Karo, Mandailing Natal, Dairi, Malang, Batu, and Bali are located in the volcano path which is prone to eruption. The eruption of Mount Sinabung in 2013 and 2014 had caused damage to the local tangerine cv Madu cultivation which was estimated to reach more than 476 billion rupiahs. The eruption affected a cultivation area of 7.202,89 ha and has been predicted to be one of the factors that caused the decline of North Sumatra’s contribution to tangerine production. Therefore, this paper has tried: (i) to analyze the financial feasibility of rehabilitating tangerine cv Madu cultivation located in between 7-10 km radius of the eruption center (zone 1) and in between 5-7 km radius of the eruption center (zone 2), and (ii) to consider the option of opening up a new tangerine cultivation land.The results showed that the BCR for the immediate rehabilitation of zones 1 and 2 were 3.33 and 2, respectively. Thus, the rehabilitation scheme was feasible to be implemented and can reduce the damage and losses suffered by farmers. On the other hand, the opening of new land still takes approximately three years to be productive. The BCRof the option of opening new land within that period of time was 0.47, which is lower compared with that of the rehabilitation of zones 1 and 2 (2.61 and 2.57, respectively).This study was intended as an initial guidance for making decisions and determining the potential benefit to be gained and the losses that can be avoided. This study also gave an overview of the budget that should be prepared. In conclusion, we recommended the farmers to carry out the rehabilitation over opening up new cultivation land.

Relationship between volcanic ash fallouts and seismic tremor: quantitative assessment of the 2015 eruptive period at Cotopaxi volcano, Ecuador

Understanding the relationships between geophysical signals and volcanic products is critical to improving real-time volcanic hazard assessment. Thanks to high-frequency sampling campaigns of ash fallouts (15 campaigns, 461 samples), the 2015 Cotopaxi eruption is an outstanding candidate for quantitatively comparing the amplitude of seismic tremor with the amount of ash emitted. This eruption emitted a total of ~1.2E + 9 kg of ash (~8.6E + 5 m3) during four distinct phases, with masses ranging from 3.5E + 7 to 7.7E + 8 kg of ash. We compare the ash fallout mass and the corresponding cumulative quadratic median amplitude of the seismic tremor and find excellent correlations when the dataset is divided by eruptive phase. We use scaling factors based on the individual correlations to reconstruct the eruptive process and to extract synthetic Eruption Source Parameters (daily mass of ash, mass eruption rate, and column height) from the seismic records. We hypothesize that the change in scaling factor through time, associated with a decrease in seismic amplitudes compared to ash emissions, is the result of a more efficient fragmentation and transport process. These results open the possibility of feeding numerical models with continuous geophysical data, after adequate calibration, in order to better characterize volcanic hazards during explosive eruptions.

First discovery of Holocene cryptotephra in Amazonia.

The use of volcanic ash layers for dating and correlation (tephrochronology) is widely applied in the study of past environmental changes. We describe the first cryptotephra (non-visible volcanic ash horizon) to be identified in the Amazon basin, which is tentatively attributed to a source in the Ecuadorian Eastern Cordillera (0–1°S, 78-79°W), some 500-600 km away from our field site in the Peruvian Amazon. Our discovery 1) indicates that the Amazon basin has been subject to volcanic ash fallout during the recent past; 2) highlights the opportunities for using cryptotephras to date palaeoenvironmental records in the Amazon basin and 3) indicates that cryptotephra layers are preserved in a dynamic Amazonian peatland, suggesting that similar layers are likely to be present in other peat sequences that are important for palaeoenvironmental reconstruction. The discovery of cryptotephra in an Amazonian peatland provides a baseline for further investigation of Amazonian tephrochronology and the potential impacts of volcanism on vegetation.

Hail formation triggers rapid ash aggregation in volcanic plumes.

During explosive eruptions, airborne particles collide and stick together, accelerating the fallout of volcanic ash and climate-forcing aerosols. This aggregation process remains a major source of uncertainty both in ash dispersal forecasting and interpretation of eruptions from the geological record. Here we illuminate the mechanisms and timescales of particle aggregation from a well-characterized ‘wet' eruption. The 2009 eruption of Redoubt Volcano, Alaska, incorporated water from the surface (in this case, a glacier), which is a common occurrence during explosive volcanism worldwide. Observations from C-band weather radar, fall deposits and numerical modelling demonstrate that hail-forming processes in the eruption plume triggered aggregation of ∼95% of the fine ash and stripped much of the erupted mass out of the atmosphere within 30 min. Based on these findings, we propose a mechanism of hail-like ash aggregation that contributes to the anomalously rapid fallout of fine ash and occurrence of concentrically layered aggregates in volcanic deposits.

A GIS-based tool for the management of industrial accidents triggered by volcanic ash fallouts

In this last decade, worldwide attention has been focused on the hazards derived from the interaction between extreme natural phenomena and critical infrastructures and/or chemical and process industry (natural–technological hazards or Na-Tech). Due to the recent occurrence of significant events, great attention has also been given to Na-Tech hazards triggered by volcanic eruptions; in particular, the eruption of the Icelandic volcano alarmed the European community due to the ash fallout over the continent, which caused significant problems for the population, road, rail and air traffic and production activities. This study aims at defining a procedure for the representation of the vulnerability of industrial facilities to potential volcanic ash fallouts. Its implementation on a Geographical Information System has also been executed and a semi-automatic procedure for the vulnerability mapping has been constructed.