Ash Fallout Research Articles

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.

Hydrothermal activity and subsoil complexity: implication for degassing processes at Solfatara crater, Campi Flegrei caldera

The Solfatara area and its fumaroles are the main surface expression of the vigorous hydrothermal activity within the active Campi Flegrei caldera system. At depth, a range of volcanic and structural processes dictate the actual state of the hydrothermal system below the crater. The presence of a large variety of volcanic products at shallow depth (including pyroclastic fallout ash beds, pyroclastic density current deposits, breccias, and lavas), and the existence of a maar-related fault system appears to exert major controls on the degassing and alteration behavior. Adding further to the complexity of this environment, variations in permeability and porosity, due to subsoil lithology and alteration effects, may further influence fluid flow towards the surface. Here, we report results from a field campaign conducted in July 2015 that was designed to characterize the in situ physical (temperature, humidity) and mechanical (permeability, strength, stiffness) properties of the Solfatara crater subsoil. The survey also included a mapping of the surficial hydrothermal features and their distributions. Finally, laboratory measurements (porosity, granulometry) of selected samples were performed. Our results enable the discrimination of four main subsoils around the crater: (1) the Fangaia domain located in a topographic low in the southwestern sector, (2) the silica flat domain on the western altered side, (3) the new crust domain in the central area, and (4) the crusted hummocks domain that dominates the north, east, and south parts. These domains are surrounded by encrusted areas, reworked material, and vegetated soil. The distribution of these heterogeneous subsoils suggests that their formation is mostly related to (i) the presence of the Fangaia domain within the crater and (ii) a system of ring faults bordering it. The subsoils show an alternation between very high and very low permeabilities, a fact which seems to affect both the temperature distribution and surficial degassing. A large range of surface temperatures (from 25 up to 95 degrees C) has been measured across these surfaces, with the hottest spot corresponding to the mud pools, the area of new crust formation, and the crusted hummocks. In the subsoil, the distribution of temperature is more complex and controlled by the presence of coarser, and more permeable, sandy/pebbly levels. These act as preferential pathways for hot hydrothermal fluid circulation. In contrast, low permeability, fine-grained levels act as thermal insulators that remain relatively cold and hinder fluid escape to the surface. Hot gases reach the surface predominantly along (vertical) fractures. When this occurs, mound-like structures can be formed by a cracking and healing process associated with significant degassing. It is anticipated that the results presented here may contribute to an improved understanding of the hazard potential associated with the ongoing hydrothermal activity within the Solfatara crater. At this site the permeability of the near-surface environment and its changes in space and time can affect the spatial and temporal distribution of gas and heat emission. Particularly, in areas where reduction in permeability occurs, it can produce pore pressure augmentation that may result in explosive events.

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.

A new approach to investigate an eruptive paroxysmal sequence using camera and strainmeter networks: Lessons from the 3–5 December 2015 activity at Etna volcano

Explosive sequences are quite common at basaltic and andesitic volcanoes worldwide. Studies aimed at short-term forecasting are usually based on seismic and ground deformation measurements, which can be used to constrain the source region and quantify the magma volume involved in the eruptive process. However, during single episodes of explosive sequences, integration of camera remote sensing and geophysical data are scant in literature, and the total volume of pyroclastic products is not determined. In this study, we calculate eruption parameters for four powerful lava fountains occurring at the main and oldest Mt. Etna summit crater, Voragine, between 3 and 5 December 2015. These episodes produced impressive eruptive columns and plume clouds, causing lapilli and ash fallout to more than 100 km away. We analyse these paroxysmal events by integrating the images recorded by a network of monitoring cameras and the signals from three high-precision borehole strainmeters. From the camera images we calculated the total erupted volume of fluids (gas plus pyroclastics), inferring amounts from 1.9×109 m3 (first event) to 0.86×109 m3 (third event). Strain changes recorded during the first and most powerful event were used to constrain the depth of the source. The ratios of strain changes recorded at two stations during the four lava fountains were used to constrain the pyroclastic fraction for each eruptive event. The results revealed that the explosive sequence was characterized by a decreasing trend of erupted pyroclastics with time, going from 41% (first event) to 13% (fourth event) of the total erupted pyroclastic volume. Moreover, the volume ratio fluid/pyroclastic decreased markedly in the fourth and last event. To the best of our knowledge, this is the first time ever that erupted volumes of both fluid and pyroclastics have been estimated for an explosive sequence from a monitoring system using permanent cameras and high precision strainmeters. During future explosive paroxysmal sequences this new approach might help in monitoring their evolution also to understand when/if they are going to finish. Knowledge of the total gas and pyroclastic fractions erupted during each lava fountain episode would improve our understanding of their processes and eruptive behaviour.

Ash aggregation enhanced by deposition and redistribution of salt on the surface of volcanic ash in eruption plumes

Interactions with volcanic gases in eruption plumes produce soluble salt deposits on the surface of volcanic ash. While it has been postulated that saturation-driven precipitation of salts following the dissolution of ash surfaces by condensed acidic liquids is a primary mechanism of salt formation during an eruption, it is only recently that this mechanism has been subjected to detailed study. Here we spray water and HCl droplets into a suspension of salt-doped synthetic glass or volcanic ash particles, and produce aggregates. Deposition of acidic liquid droplets on ash particles promotes dissolution of existing salts and leaches cations from the underlying material surface. The flow of liquid, due to capillary forces, will be directed to particle-particle contact points where subsequent precipitation of salts will cement the aggregate. Our data suggest that volcanically-relevant loads of surface salts can be produced by acid condensation in eruptive settings. Several minor and trace elements mobilised by surface dissolution are biologically relevant; geographic areas with aggregation-mediated ash fallout could be “hotspots” for the post-deposition release of these elements. The role of liquids in re-distributing surface salts and cementing ash aggregates also offers further insight into the mechanisms which preserve well-structured aggregates in some ash deposits.

Estimating the frequency of volcanic ash clouds over northern Europe

Fine ash produced during explosive volcanic eruptions can be dispersed over a vast area, where it poses a threat to aviation, human health and infrastructure. Here, we focus on northern Europe, which lies in the principal transport direction for volcanic ash from Iceland, one of the most active volcanic regions in the world. We interrogate existing and newly produced geological and written records of past ash fallout over northern Europe in the last 1000 years and estimate the mean return (repose) interval of a volcanic ash cloud over the region to be 44±7 years. We compare tephra records from mainland northern Europe, Great Britain, Ireland and the Faroe Islands, with records of proximal Icelandic volcanism and suggest that an Icelandic eruption with a Volcanic Explosivity Index rating (VEI) ≥ 4 and a silicic magma composition presents the greatest risk of producing volcanic ash that can reach northern Europe. None of the ash clouds in the European record which have a known source eruption are linked to a source eruption with VEI < 4. Our results suggest that ash clouds are more common over northern Europe than previously proposed and indicate the continued threat of ash deposition across northern Europe from eruptions of both Icelandic and North American volcanoes.

The 1909 Chinyero eruption on Tenerife (Canary Islands): insights from historical accounts, and tephrostratigraphic and geochemical data

The last eruption on Tenerife (Canary Islands, Spain) started on 18 November 1909 from the El Chinyero vent on the northwestern Santiago rift. This fissural eruption was well documented by scientists and eyewitnesses, but there is a lack of data on the high-energy phase that produced the most significant emissions of ash and lapilli at the onset of the eruption. Here, we review historical documents (e.g. newspapers, dispatches, telegrams); eyewitness accounts and scientific reports were reviewed from a volcanological perspective and integrated with data from the analysis of deposit features, allowing an accurate reconstruction of the eruption and its dynamics. The 1909 eruption of Chinyero was fed by a compositionally discrete magma batch that ascended rapidly within the crust, producing rather violent pulsating Strombolian explosive activity in the early phases of the eruption. This activity produced a ca. 80 m high scoria cone and heavy fallout of lapilli and ash over the entire northern sector of the island of Tenerife. The energy of explosive activity waned after 3 days, giving way to the weak Strombolian explosive activity that contributed to a lesser extent to the buildup of the pyroclastic pile. Eruptions such as those from the Chinyero vent in 1909 are representative of rift activity on Tenerife and constitute a volcanic hazard for present-day inhabitants.

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.

Smectites and zeolites in ash from the 2010 summit eruption of Eyjafjallajökull volcano, Iceland

Hydrothermal alteration minerals are often incorporated in volcanic ash from phreatic and phreatomagmatic activity. Here we assess the presence and abundance of such minerals in the ash materials produced during the April-May 2010 initial phreatomagmatic (phase I) and subsequent magmatic (phases II and III) eruptions of Eyjafjallajokull volcano, Iceland. The results of X-ray diffraction analyses reveal significant quantities of smectites (up to 4 wt%, mainly as saponite) and zeolites (up to 7 wt%) in ash from phase I. While a minor amount of smectites (<0.5 wt%) is present in ash from the subsequent weak explosive activity (phase II), both smectites and zeolites are absent in phase III ash. This material was generated following abrupt rejuvenation of explosive activity in the absence of magma-ice/water interaction. Smectites and zeolites in phase I ash result primarily from scouring of altered volcanic rocks in the subsurface, although some may derive also from water-rock interaction within the summit ice cauldrons through which fragmented magma was injected. We show that incorporation of smectites and zeolites in phase I ash can explain its anomalously high specific surface area. Further, the presence of these minerals in ash may enhance its ability to act as ice nuclei as well as favour particle aggregation processes in the volcanic plume/cloud. Finally, the Eyjafjallajokull eruption represents another case in which ash fallout acted as an exogenic source of 2:1-type clay minerals in volcanic soils.

Cinderella's helping pigeons of the microbial world: The potential of testate amoebae for identifying cryptotephra

Cryptotephra (particles <125μm) is a key record for monitoring past and current volcanic activity. However, its extraction from the host sediment and analysis is often long and difficult because of its small size. Finding a simple method to extract cryptotephra from environmental samples would therefore make its analysis much easier. We hypothesized that arcellinid testate amoebae may hold such a potential. These free-living shelled protists are among the earliest microorganisms to colonize volcanic tephra, and build their shell by agglutinating minerals from their environment. We analyzed by X-ray Spectrometry the mineral signature of tephra from the 2011 Puyehue-Cordon Caulle Volcanic Complex (Chile) eruption ash fallout and compared it to that of the shells of 51 individual testate amoebae (three individuals from each of 17 species) from 13 samples collected at different distances from the active vent. The mineral composition of particles within shells closely matched that of similar size class particles from their environment. The capacity of testate amoebae to randomly use mineral grains from their environment makes it possible to use their shells to assess the mineral composition of cryptotephra from soil, peat or sediment samples. Testate amoebae therefore represent the microbial world's version of Cinderella's helping pigeons.

Volcanic Deposits and Volcanic Hazard in Santo Domingo de Heredia, Costa Rica

The present research aims to investigate more precisely about the geology of the Eastern region of the Santo Domingo County. Santo Domingo is part of the structural plateau in the center of Costa Rica, which is located at the foot of the Cordillera Volcánica Central (CVF) [Central Volcanic Front] and is covered by volcanic deposits. On this plateau, called Central Valley, is the highest percentage of the population of the country and therefore, a large sector of the Costa Rican population is exposed to volcanic eruptions of the volcanoes in the CVF. For existing the national system for risk management and a law that demands actions to local authorities to prevent and mitigate disaster, it is necessary to identify the threats that exist in the cantons (counties) of Costa Rica. This will serve to take the prevention and mitigation actions necessary to reduce the impact of volcanic eruptions in the area of Santo Domingo.The research method consisted of review and analysis of previous works through literature research, data collection and analysis of boreholes from records of water-supply wells and open pits, and field work to better know the geology of the area. The results indicate that there are deposits of powerful volcanic eruptions of pyroclastic fall deposits (volcanic ash and lapilli) that mostly form clayey soils and lahars deposits that practically covers the entire territory. Underlying these deposits there is a pyroclastic flow deposit (ignimbrite), followed by lapilli tephra (a layer of pumice of at least 2 meters thick) that mark a change in the volcanic activity. Such pyroclastic flow is overlaid by an igneous presumably sub-volcanic activity of andesites interlayered with ancient tuffs, with a considerable thickness of over 350 meters according with borehole data and the exposure recognition on Pará river study sites. According to site locations (P1 to P23) of volcaniclastic deposits, there is evidence of an important environmental impact caused by the last eruptions of the CVF volcanoes. The real and current volcanic threat to the population of the County is the fall-out of ash emitted from the Turrialba and Irazú volcanoes. From local observations along the Virilla and Pará rivers sections, there is no evidence of younger pyroclastic flows overlying the volcanic sequence.

The eruptive chronology of the Ampato–Sabancaya volcanic complex (Southern Peru)

We have reconstructed the eruptive chronology of the Ampato–Sabancaya volcanic complex (Southern Peru) on the basis of extensive fieldwork, and a large dataset of geochronological (40K–40Ar, 14C and 3He) and geochemical (major and trace element) data. This volcanic complex is composed of two successive edifices that have experienced discontinuous volcanic activity from Middle Pleistocene to Holocene times. The Ampato compound volcano consists of a basal edifice constructed over at least two cone-building stages dated at 450–400ka and 230–200ka. After a period of quiescence, the Ampato Upper edifice was constructed firstly during an effusive stage (80–70ka), and then by the formation of three successive peaks: the Northern, Southern (40–20ka) and Central cones (20–10ka). The Southern peak, which is the biggest, experienced large explosive phases, resulting in deposits such as the Corinta plinian fallout. During the Holocene, eruptive activity migrated to the NE and constructed the mostly effusive Sabancaya edifice. This cone comprised many andesitic and dacitic blocky lava flows and a young terminal cone, mostly composed of pyroclastic material. Most samples from the Ampato–Sabancaya define a broad high-K magmatic trend composed of andesites and dacites with a mineral assemblage of plagioclase, amphibole, biotite, ortho- and clino-pyroxene, and Fe–Ti oxides. A secondary trend also exists, corresponding to rare dacitic explosive eruptions (i.e. Corinta fallout and flow deposits). Both magmatic trends are derived by fractional crystallisation involving an amphibole-rich cumulate with variable amounts of upper crustal assimilation.A marked change in the overall eruptive rate has been identified between Ampato (~0.1km3/ka) and Sabancaya (0.6–1.7km3/ka). This abrupt change demonstrates that eruptive rates have not been homogeneous throughout the volcano's history. Based on tephrochronologic studies, the Late Holocene Sabancaya activity is characterised by strong vulcanian events, although its erupted volume remained low and only produced a local impact through ash fallout. We have identified at least 6 eruptions during the last 4–5ka, including the historical AD 1750–1784 and 1987–1998 events. On the basis of this recurrent low-to-moderate explosive activity, Sabancaya must be considered active and a potentially threatening volcano.

Raman spectroscopy for the discrimination of tephras from the Hekla eruptions of AD 1510 and 1947

Tephrochronology (the dating of sedimentary sequences using volcanic ash layers) is an important tool for the dating and correlation of sedimentary sequences containing archives and proxies of past environmental change. In addition, tephra layers provide valuable information on the frequency and nature of ash fallout from volcanic activity. Successful tephrochronology is usually reliant on the correct geochemical identification of the tephra which has, until now, been based primarily on the analysis of major element oxide composition of glass shards using electron probe microanalysis (EPMA). However, it is often impossible to differentiate key tephra layers using EPMA alone. For example, the Hekla AD 1947 and 1510 tephras (which are found as visible layers in Iceland and also as ‘crypto-tephra’ microscopic layers in NW Europe) are currently indistinguishable using EPMA. Therefore, other stratigraphic or chronological information is needed for their reliable identification. Raman spectroscopy is commonly used in chemistry, since vibrational information is specific to the chemical bonds and symmetry of molecules, and can provide a fingerprint by which these can be identified. Here, we demonstrate how Raman spectroscopy can be used for the successful discrimination of mineral species in tephra through the analysis of individual glass shards. In this study, we obtained spectra from minerals within the glass shards – we analysed the microlites and intratelluric mineral phases that can definitely be attributed to the tephra shards and the glass itself. Phenocrysts were not analysed as they could be sourced locally from near-site erosion. Raman spectroscopy can therefore be considered a valuable tool for both proximal and distal tephrochronology because of its non-destructive nature and can be used to discriminate Hekla 1510 from Hekla 1947.

PM&amp;lt;sub&amp;gt;10&amp;lt;/sub&amp;gt; measurements in urban settlements after lava fountain episodes at Mt. Etna, Italy: pilot test to assess volcanic ash hazard to human health

Abstract. We have carried out a preliminary study on the potential risks caused by the sub-10 µm fraction of volcanic ash (particulate matter, PM10) after the basaltic explosive eruptions from Mt. Etna volcano (Italy), which have dramatically increased in frequency over the last 20 years. We present results deriving from the study of the ash concentration in the air following the lava fountain episode from the New Southeast Crater of Etna on 15 November 2011, which caused tephra fallout over the eastern slope of the volcano. Short-duration tests of PM10 measurements were carried out at three different sites using a TSI® DustTrakTM aerosol monitor a few hours after the end of the eruption, and readouts of the air quality were repeated at the same sites a month later without volcanic activity. Furthermore, ash samples were characterized by grain size, componentry and morphological and petrochemical analyses. By comparing PM10 levels measured a few hours after the 15 November lava fountain and on 15 December, we found that relatively low amounts (500–1500 g m−2) of tephra fallout cause high levels of PM10 in the air. This is because the coarse particles, particularly basaltic ash, are readily broken up by traffic and hence remobilized into the air. We believe the impact from ash fallout in the Etnean territory should receive greater attention, especially regarding potential health problems. Simple but effective actions can be implemented to reduce eventual risks, first and foremost the prompt removal of the ash deposits from the urbanized areas.

The Opala IV: An explosive caldera-generating super eruption, which was the largest in Kamchatka in the last 50000 years

It is shown that the youngest (~40000 14C years BP) caldera of the Opala caldera complex, the Opala IV, was formed by a catastrophic explosive supereruption, the largest in Kamchatka during the last 50000 years of the seven dated similar-type eruptions that occurred during the Late Pleistocene paroxysm of explosive volcanism. It is thought that the ejected volume was on the order of 250 km3 of pyroclastic material. A smaller part of it went to form pumice-rich pyroclastic flows, with the greater part being transported as tephra. The principal axis of the ash fallout was oriented NNE (azimuth ~30°) where the tephra thickness was 20–30 cm at a distance of 300–320 km from the eruptive center. The uncontaminated juvenile material is rhyolite, the concentration of SiO2 was 75–76%, the total alkali content 7.3–8.3%, and the K2O/Na2O ratio 0.83–0.96. It was concluded that no such eruption can occur in the Opala caldera complex in the future for hundreds or thousands of years.

Visualizing tephra deposits and sedimentary processes in the marine environment: The potential of X-ray microtomography.

Localized tephra deposition in marine sequences is the product of many complex primary and secondary depositional processes. These can significantly influence the potential applicability of tephra deposits as isochronous marker horizons and current techniques, used in isolation, may be insufficient to fully unravel these processes. Here we demonstrate the innovative application of X‐ray microtomography (µCT) to successfully identify tephra deposits preserved within marine sediments and use these parameters to reconstruct their internal three‐dimensional structure. Three‐dimensional visualizations and animations of tephra dispersal in the sediment permit a more thorough assessment of postdepositional processes revealing a number of complex microsedimentological features that are not revealed by conventional methods. These features include bioturbation burrows and horizontally discontinuous tephra packages, which have important ramifications for the stratigraphic placement of the isochron in a sedimentary sequence. Our results demonstrate the potential for utilizing rigorous two and three‐dimensional microsedimentological analysis of the ichnofabric to enhance and support the use of tephra deposits as isochronous marker horizons and to identify the stratigraphic position that best reflects the primary fallout of ash. The application also provides an exceptional insight into the style and rate of sedimentation processes and permits an assessment of the stratigraphic integrity of a tephra deposit. We discuss the possibility of applying these µCT methods to the identification of cryptotephras within various paleoclimatic sequences and to enhance our understanding of marine sedimentation processes.

Rising from the ashes: Changes in salmonid fish assemblages after 30 months of the Puyehue–Cordon Caulle volcanic eruption

Events such as volcanic eruptions may act as disturbance agents modifying the landscape spatial diversity and increasing environmental instability. On June 4, 2011 the Puyehue–Cordon Caulle volcanic complex located on Chile (2236m.a.s.l., 40° 02′ 24″ S- 70° 14′ 26″ W) experience a rift zone eruption ejecting during the first day 950millionmetrictons into the atmosphere. Due to the westerly winds predominance, ash fell differentially upon 24millionha of Patagonia Argentinean, been thicker deposits accumulated towards the West. In order to analyze changes on stream fish assemblages we studied seven streams 8, 19 and 30months after the eruption along the ash deposition gradient, and compare those data to pre eruption ones. Habitat features and structure of the benthic macroinvertebrate food base of fish was studied. After the eruption, substantial environmental changes were observed in association with the large amount of ash fallout. In western sites, habitat loss due to ash accumulation, changes in the riparian zone and morphology of the main channels were observed. Turbidity was the water quality variable which reflected the most changes throughout time, with NTU values decreasing sharply from West to East sites. In west sites, increased Chironomid densities were recorded 8months after the initial eruption as well as low EPT index values. These relationships were reversed in the less affected streams farther away from the volcano. Fish assemblages were greatly influenced both by habitat and macroinvertebrate changes. The eruption brought about an initial sharp decline in fish densities and the almost total loss of young of the year in the most western streams affecting recruitment. This effect diminished rapidly with distance from the emission center. Thirty months after the eruption, environmental changes are still occurring as a consequence of basin wide ash remobilization and transport.

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.

Vulkanismus und Kellwasser-Krise – Zirkon-Tephrostratigrafie, Identifizierung und Herkunft distaler Fallout-Aschenlagen (Oberdevon, Synklinorium von Dinant, Rheinisches Schiefergebirge, Harz)

Vulkanismus und Kellwasser-Krise – Zirkon-Tephrostratigrafie, Identifizierung und Herkunft distaler Fallout-Aschenlagen (Oberdevon, Synklinorium von Dinant, Rheinisches Schiefergebirge, Harz)

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.