Fine Ash Particles Research Articles

Discrete model for simulation of char particle gasification with structure evolution

Based on percolation theory, the discrete model of char particle gasification with structure evolution under various distinct regimes was developed. Initial structure of individual char particle was modeled as a simple cubic lattice consisting of a large number of small sites. Sites arranged in the char lattice were randomly classified as either carbon, ash, or macropore, depending upon the proximate analysis data and the porosity of coal char. Suggested model was used to study the effects of structure parameter and reaction condition on the gasification reactivity and the evolution of char structure. Simulation results showed that under external diffusion controlled regime, the gasification rate decreased as reaction advanced for char particles with lower porosity (porosity<0.15), and the gasification rate vs. conversion curves exhibited maxima for large char particles with higher porosity (porosity>0.15). Besides, the particle sizes of coal char decreased slowly in the early stage of gasification, and then they decreased slightly fast. The gasification reaction of fine coal chars under the external diffusion controlled region could inhibit the particle fragmentation and reduce the formation of fine ash particles to a certain degree.

Effect of particle size of fly ash on the properties of lightweight insulation materials

The paper reports the effects of fly ash particle size on the properties of the lightweight insulation materials. The microstructure and mechanical properties of lightweight insulation materials are separately investigated by SEM (scanning electron micrograph) and tabulate thermal conductivity apparatus methods. In addition, the effects of particle size distribution of fly ash on the properties of lightweight insulation materials is studied by grey incidence analysis. The results show that when the ball milling time increases, the particle size of fly ash decreases and the distribution becomes narrow. At the same time, the polymerization state of fly ash would be depolymerize from high poly structure to low polymeric structure. Moreover, the linear shrinkage, bulk density, compressive strength, acid resistance and thermal conductivity of lightweight insulation materials have also increased, but the apparent porosity decreases. And the studies highlight that when the content of fine fly ash particles increases, the nucleation and growth of mullite is accelerated and the sintering driving force is improved at high temperature, which have a positive effect on improving the physicochemical properties of materials. The particles ranging from 20 to 30μm has a great influence on the linear shrinkage, bulk density, compressive strength, acid resistance rate and thermal conductivity of lightweight insulation materials.

The mineralogy, morphology and sintering characteristics of ash deposits on a probe at different temperatures during combustion of blends of Zhundong lignite and a bituminous coal in a drop tube furnace

Ash deposits formed on an air-cooled probe at different temperatures during combustion of coal blends of a Zhundong lignite (ZL) and an Australian bituminous (AB) were studied in the present work. The blends with various AB ratios were combusted in a drop tube furnace in air at 1400°C, and the ash deposits formed on the probe top surface maintained at 500°C, 600°C, 700°C, and 750°C, were collected and characterised using XRD and SEM-EDS for their mineralogy, morphology and elemental composition. The size distributions and sintering temperatures of the ash deposits were also determined. At the probe temperature of 500°C, the ZL ash deposit was dominated by fluxing minerals where significant amounts of fine particles (<10μm) and their aggregates existed, leading to low ash sintering temperatures. As the AB ratio increased to 20wt% and above, the amount of the fluxing minerals in the deposits decreased while the amount of refractory quartz and mullite minerals increased. Morphologically, the refractory ash particles from AB coal diluted the Na-bearing mineral phases and the contacts between fine ash particles, leading to the absence of nepheline and, correspondingly, an increase in the ash sintering temperature. In addition, as the probe temperature increased, mineral interactions and ash sintering were facilitated when the AB ratio was less than 20wt%, leading to the formation of new mineral phases and an increase in ash particle sizes. However, no significant mineralogical and morphological changes were observed when the AB ratio was higher than 40wt%, indicating that these ash deposits were more refractory and resistant to the temperature change.

Engineering Systems of Heat Supply and Working on Coal as Sources of Air Pollution by Finely Dispersed Dust

The article contains important issues about functioning of technical means and engineering systems of cities as sources of the human impact on the surrounding ecosystem, namely, the study of the functioning of boiler plants as sources of the human impact on a condition of the atmospheric air located near urbanized areas. So, we solved the problem of improving standardization systems, licensing, certification, environmental safety requirements, design and research activities in the building and operation of municipal services, in particular, improving methods of forecasting air pollution by solid particles contained in emissions released from the production of heat and electricity by burning coal. We made studies and mathematical treatment of the dispersed composition of dust emitted from the organized (boilers) and unorganized (ash dumps) boiler emissions sources, we established that solid particles are entered in the atmospheric air and most of them has a size up to 20μm. We got expressions for determining the sedimentation rate of fine particles of ash and slag.

Wettability of ash conditions splash erosion and runoff rates in the post-fire

Although the impact of ash on the hydrological and erosive response of burned soils has been studied in the last years, the effect of ash wettability on particle detachment by splash erosion has been rarely studied. In this research, we have studied the effect of wettable and water-repellent ash on the intensity of splash erosion after a prescribed burn in a Mediterranean shrubland. Runoff rates from wettable and water-repellent ash layers were also studied by rainfall simulation experiments (6mmmin−1 during 10min) at plot scale. Splash erosion experiments showed that the intensity of ash water repellency strongly conditioned the detachment and mobilization of ash and soil particles due to raindrop impacts in the post-fire. Although the intensity of water repellency and the amount of ash decreased through the experimental period, it was observed that splash erosion in originally water-repellent ash areas was about three times higher than in wettable ash areas. Plot-scale rainfall simulation experiments showed that runoff rates were much higher in water-repellent ash areas, where runoff rates increase with decreasing depth of the ash layer. In water-repellent ash areas, thick ash layers store a significant proportion of water that does not infiltrate soil, but contributes to relatively low runoff rates. In contrast, thin water-repellent ash layers are rapidly redistributed by rainfall, and the burned mineral soil surface is exposed. Pore clogging with fine water-repellent ash particles enhances runoff rates. During low or moderate intensity storms, patches of wettable/water-repellent ash arrange in a pattern that produces water infiltration/runoff generation areas, reducing the connectivity of water and sediments through the slope.

Experimental investigation of aerodynamic agglomeration of fine ash particles from a 330 MW PC-fired boiler

This paper reports the experimental investigation of fine particle agglomeration through an in-situ trial on aerodynamic agglomerators installed in front of the electrostatic precipitator (ESP) of a 330MW PC-fired (i.e. pulverized-coal-fired) boiler. It is demonstrated that the agglomerators greatly reduce the fine particles entering the ESP. In particular, for the present case, the fine particles of the aerodynamic diameter ⩽2.5μm (PM2.5) and those ⩽10μm (PM10) are found to decrease 56.2% and 50.6%, hence reducing the overall particle concentration by 26.3mg/Nm3 at the outlet of the ESP. Also, the mercury concentration of 891.08ng/g obtained in the ash from hoppers of the ESP with the agglomerators is 26.4% higher than that of the ESP without agglomerator. Therefore, the application of aerodynamic agglomerators is believed to reduce both emissions of fine particles and mercury from the flue gas of PC-fired boilers. In addition, the reason for the above observations is also explored in the paper.

Desirability based multiobjective optimisation of abrasive wear and frictional behaviour of aluminium (Al/3.25Cu/8.5Si)/fly ash composites

Aluminium alloy (Al/3.25Cu/8.5Si) composites reinforced with fly ash particles of three different size ranges (53–75 μm, 75–103 μm and 103–125 μm) in 3, 6 and 9 wt-% were fabricated using liquid metallurgy technique. Pin on disc abrasive wear tests were carried against the disc surface fixed with SiC emery paper (120 grades). A mathematical model was developed to predict the abrasive wear and coefficient of friction of the composites. Analysis of variance technique was used to check the validity of the developed model. Composites reinforced with coarse fly ash particles exhibited better abrasive wear resistance than those reinforced with fine fly ash particles. Abrasive wear in composites with fine fly ash particles is a combination of adhesive wear and abrasive wear. Larger fly ash particles present in composites gets fractured into fine particles and entrapped between the composite pin and the disc, thereby decreasing the wear rate. Worn surfaces of the pins were then analysed using scanning electron microscopy to study the wear mechanisms of the composites. The abrasive wear was optimised using desirability based multiobjective optimisation technique.

Full-Scale Plant Study of the Innovative Spray-Drying-Based Sludge Incineration (SDSI) Process: Behavior of Heavy Metals

Large-scale applications of sludge incineration, particularly with fluidized-bed incinerators, are extremely restricted in China at present by their high investment and operating costs. An innovative spray-drying-based sludge incineration (SDSI) process was proposed in our recent study, which has been applied in a full-scale sludge incineration plant with a capacity of 1200 tonnes/day (80% moisture). In the present research, behavior of selected heavy metals (Cu, Zn, Pb, Cd, As, Hg, Cr, and Ni) in this plant was investigated, aiming to provide further evidence about the SDSI performance. The results showed that concentrations of Cu, Zn, and Ni in the slag were higher than those in the fly ash after combustion. Nevertheless, concentrations of Pb, Cd, Hg, and As in the fly ash, particularly in the fine ash particles, were significantly higher than those in the slag. Unlike other heavy metals, the concentration of Cr in the slag was higher than that in coarse ash particles but roughly equal to that in fine a...

Geochemistry of tin (Sn) in Chinese coals.

Based on 1625 data collected from the published literature, the geochemistry of tin (Sn) in Chinese coals, including the abundance, distribution, modes of occurrence, genetic types and combustion behavior, was discussed to make a better understanding. Our statistic showed the average Sn of Chinese coal was 3.38mg/kg, almost two times higher than the world. Among all the samples collected, Guangxi coals occupied an extremely high Sn enrichment (10.46mg/kg), making sharp contrast to Xinjiang coals (0.49mg/kg). Two modes of occurrence of Sn in Chinese coals were found, including sulfide-bounded Sn and clay-bounded Sn. In some coalfields, such as Liupanshui, Huayingshan and Haerwusu, a response between REEs distribution and Sn content was found which may caused by the transportation of Sn including clay minerals between coal seams. According to the responses reflecting on REEs patterns of each coalfield, several genetic types of Sn in coalfields were discussed. The enrichment of Sn in Guangxi coals probably caused by Sn-rich source rocks and multiple-stage hydrothermal fluids. The enriched Sn in western Guizhou coals was probably caused by volcanic ashes and sulfide-fixing mechanism. The depletion of Sn in Shengli coalfield, Inner Mongolia, may attribute to hardly terrigenous input and fluids erosion. As a relative easily volatilized element, the Sn-containing combustion by-products tended to be absorbed on the fine particles of fly ash. In 2012, the emission flux of Sn by Chinese coal combustion was estimated to be 0.90×10(9)g.

Volcanic plume characteristics determined using an infrared imaging camera

Measurements of volcanic emissions (ash and SO2) from small-sized eruptions at three geographically dispersed volcanoes are presented from a novel, multichannel, uncooled imaging infrared camera. Infrared instruments and cameras have been used previously at volcanoes to study lava bodies and to assess plume dynamics using high temperature sources. Here we use spectrally resolved narrowband (~0.5–1μm bandwidth) imagery to retrieve SO2 and ash slant column densities (gm−2) and emission rates or fluxes from infrared thermal imagery at close to ambient atmospheric temperatures. The relatively fast sampling (0.1–0.5Hz) of the multispectral imagery and the fast sampling (~1Hz) of single channel temperature data permit analysis of some aspects of plume dynamics. Estimations of SO2 and ash mass fluxes, and total slant column densities of SO2 and fine ash in individual small explosions from Stromboli (Italy) and Karymsky (Russia), and total SO2 slant column densities and fluxes from Láscar (Chile) volcanoes, are provided. We evaluate the temporal evolution of fine ash particle sizes in ash-rich explosions at Stromboli and Karymsky and use these observations to infer the presence of at least two distinct fine ash modes, with mean radii of <10μm and >10μm. The camera and techniques detailed here provide a tool to quickly and remotely estimate fluxes of fine ash and SO2 gas and characterize eruption size.

Condensation Characteristics of Flue Gas/Steam Mixtures with Fine Lignite and Ash Particles along Horizontal Finned Tube Bundles

The condensation behavior for a gas/steam mixture with fine lignite particles and lignite ash particles is experimentally investigated as the particles flow over horizontal finned tube bundles. The effects of the gas velocity, inlet temperature of cooling water, excess air coefficient, and particle dimension are discussed. The total mass flow rate of the condensate and the condensation heat transfer coefficient for flue gas including particles are higher than those of flue gas excluding particles when Reynolds number is higher than 2,300. The area covered by ash depositions tends to grow from the leeward toward the windward side with increasing particle diameter.

Perils in distinguishing phreatic from phreatomagmatic ash; insights into the eruption mechanisms of the 6 August 2012 Mt. Tongariro eruption, New Zealand

The weak geophysical precursors of the 6 August 2012 Te Maari eruption of Mt. Tongariro and a lack of obvious juvenile components in its proximal ballistic deposits imply that the eruption was caused by the sudden decompression of a sealed, hot hydrothermal system. Strong magmatic signals in pre- and post-eruption gas emissions indicate that fresh magma had intruded to shallow levels shortly before this eruption. Here we examine the volcanic ash produced during the August eruption with the aim of determining whether juvenile magma was erupted or not. The widely applied criteria for identifying fresh juvenile pyroclasts provided inconclusive results. The Te Maari ash sorting and trend towards a unimodal grain-size distribution increase with distance along the dispersal axis. Proximal to intermediate sites showing polymodal grain-size distributions can be related to the re-fragmentation of different pre-existing lithologies, overlapped erupted pulses and transport mechanisms, and to particle aggregation. Between 69 and 100vol.% of particles coarser than 3 ϕ and 45–75vol.% of grains finer than 3 ϕ were sourced from the pre-existing, commonly hydrothermally altered, vent-area lavas and pyroclasts. Free crystals (pyroxene>plagioclase>magnetite>pyrite) make up 0–23vol.% of particles coarser than 3 ϕ, and 22–41vol.% of grains finer than 3 ϕ. Brown to black fragments of fresh glass are a small (1–15vol.%), but notable, component. Under SEM, these blocky, glassy particles are poorly vesicular, and irregularly shaped, some with fluidal or bubble-wall surfaces, and others with fragmented stepped surfaces and fine adhering ash. In thin section, they contain variable amounts of microlites within an isotropic groundmass. The range in silica content of the microprobe-analysed glass is very wide (56–77wt.%) and cannot be correlated to any specific particle textural type. These chemically and texturally diverse glassy fragments are identical to mechanically broken pieces of country rock lavas and pyroclasts; both their diversity, and their match with vent country rocks, argue strongly against a “juvenile” origin for the glassy fragments. We conclude that rising magma provided only heat and gas into the overlying, sealed vapour-dominated hydrothermal system. A landslide from this area led to a rapid decompression and ash was produced by top-down hydrothermal explosions. Careful attention must be paid to the combination of compositions and textures of fine ash particles in such situations, as well as to the context of their source vent, in order to be confident that new magma has reached the surface.

Dual polarisation C-band weather radar imagery of the 6 August 2012 Te Maari Eruption, Mount Tongariro, New Zealand

The 6 August 2012 eruption of Mt. Tongariro from Upper Te Maari Crater in the central North Island of New Zealand was the first volcanic eruption observed by an operational weather radar in New Zealand, and is believed to be one of only a small number of eruptions observed by a dual-polarisation radar worldwide. The eruption was also observed by a GeoNet webcam, and detailed ash deposit studies have permitted analysis of the plume characteristics. A combination of radar and webcam imagery show 5 pulses within the first 13min of the eruption, and also the subsequent ash transport downwind. Comparison with ash samples show the radar was likely detecting ash particles down to about 0.5mm diameter. The maximum plume height estimated by the radar is 7.8±1.0km above mean sea level (amsl), although it is possible this may be a slight under estimation if very small ash particles not detected by the radar rose higher and comprised the very top of the plume. The correlation coefficient and differential reflectivity fields that are additionally measured by the dual polarisation radar provide extra information about the structure and composition of the eruption column and ash cloud. The correlation coefficient easily discriminates between the eruption column and the ash plume, and provides some information about the diversity of ash particle size within both the ash plume and the subsequent detached ash cloud drifting downwind. The differential reflectivity shows that the larger ash particles are falling with a horizontal orientation, and indicates that ice nucleation and aggregation of fine ash particles was probably occurring at high altitudes within 20–25min of the eruption.

Fine coal beneficiation by column flotation

The amenability of beneficiating a fine hard coal from Hwa-Sun coal mine using column flotation has been studied using a CoalPro flotation column developed by Canadian Process Technologies (CPT). After initial testwork using a batch flotation cell to determine the optimal flotation conditions, tests were carried out to compare its performance with the column. The results showed that the performance of the column was far superior to that of the conventional cell owing to the large fines content present in the coal. It was established that a stable froth column of 40cm in height and a suitable balance between froth and collection zone could be maintained at 1.0cm/s superficial gas rate. A suitable reagent scheme and the optimal operating conditions that minimized adverse effects generally encountered in treating fine coal, such as gangue entrainment, have been identified. An increase in water recovery significantly decreased ash rejection implying entrainment of fine ash particles. Column flotation is capable of producing an acceptable clean coal concentrate of 85% combustible recovery with 81% ash rejection at a maximum separation efficiency of 62%, compared to conventional flotation which has 70% recovery with 70% ash rejection at an efficiency of 42%.

Modeling volcanic ash resuspension – application to the 14–18 October 2011 outbreak episode in central Patagonia, Argentina

Abstract. Volcanic fallout deposits from the June 2011 Cordón Caulle eruption on central Patagonia were remobilized in several occasions months after their emplacement. In particular, during 14–18 October 2011, an intense outbreak episode generated widespread volcanic clouds that were dispersed across Argentina, causing multiple impacts in the environment, affecting the air quality and disrupting airports. Fine ash particles in volcanic fallout deposits can be resuspended under favorable meteorological conditions, particularly during strong wind episodes in arid environments with low soil moisture and poor vegetation coverage. As opposed to eruption-formed ash clouds, modeling of resuspension-formed ash clouds has received little attention. In consequence, there are no emission schemes specially developed and calibrated for resuspended volcanic ash, and few operational products exists to model and forecast the formation and dispersal of resuspension ash clouds. Here we implement three dust emission schemes of increasing complexity in the FALL3D tephra dispersal model and use the 14–18 October 2011 outbreak episode as a model test case. We calibrate the emission schemes and validate the results of the coupled WRF–ARW (Weather Research and Forecasting – Advanced Research WRF)/FALL3D modeling system using satellite imagery and measurements of visibility (a quantity related to total suspended particle concentration at the surface) and particulate matter (PM10) concentration at several meteorological and air quality stations located at Argentina and Uruguay. Our final goal is to test the capability of the modeling system to become, in the near future, an operational forecast product for volcanic ash resuspension events.

Estimation of Trace Elements in Fly Ash Released from Coal Combustion

Qingshan Thermoelectric Plant located in Wuhan City, Hubei Province, China, and it uses coal as a fuel. Coal combustion generates not only gaseous pollutants like SO2 and NOx but also toxic and heavy metals to the atmosphere. From the environmental point of view, the determination and speciation of trace toxic and heavy metals released from coal combustion are very important. In this work, the atomic spectroscopic methods for determination of some trace elements were first established. Graphite furnace atomic absorption spectrometry (GFAAS) method was used to determine the trace Pb in standard reference material SRM 8322 (fly ash from combustion of pulverized coal). The hydride generation atomic absorption spectrometry coupled with flow injection analysis (HGAAS-FIA) was used to analyze the concentration of As in SRM 8322 and the ICP-AES for determination of trace elements Co, Ni, Cu, Cr, etc. For the laboratory research work, all the coal samples were digested with a mixture of acids (HNO3-HF-HCLO4) after burned at 650℃ for one hour. Based on the establishment of atomic spectroscopic determination methods Tessier sequential speciation and separation methods were used in the studies of speciation distribution of some heavy metals in fine particles released from coal combustion of Qingshan Thermoelectric Plant. The transition elements in two samples from Qingshan Thermoelectric Plant (with different combustion condition) were extracted into five fractions by sequential extraction. In each fraction a suitable reagents with an optimum pH and time were used. Centrifugate separation of liquid part from the solid part was used after each fraction, the liquid part is taken for analysis and the solid part was extracted with a suitable reagents for the next fraction and the reaction continued for certain time. This procedure was done for the five fractions (exchangeable, carbonate bounded, Fe-Mn oxide bounded, organic matter bounded and residual). The experiment of the stimulant acid rain reacted with coal ash were also done in order to evaluate the transformation of these trace elements into water system after the fine particles of coal ash act with acid rain. The results showed that most parts of the metal in particles are stable. In order to study the distribution tendency of trace elements in coal, the separation of different coal particles were done using organic solvent extraction and gravity settlement method. The results showed that different trace elements had different distribution tendency in coal.

An experimental investigation into the characteristics and deposition mechanism of high-viscosity coal ash

Coal-fired boilers often develop massive fouling and slagging deposits on heat transfer surfaces in areas where coal ash particles have relatively high viscosities (⩾106Pas). In order to investigate the characteristics and mechanism of the problems, experiments were performed in a drop tube furnace and by use of a slagging probe in this study. The results showed that fouling deposits developed on the probe in the first stage, and then transformed into partially or fully fused slagging deposits. The deposition of high-viscosity coal ash was closely related to both the experimental conditions and the chemical composition of the ash. A low temperature on the probe surface and a high impact velocity of ash particles significantly inhibited ash deposition for the high-viscosity ash. The relative deposition ratio of high-viscosity ash, defined as the ratio of the mass of the deposit on the probe to the total mass of ash fed into the DTF, increased along with time initially and then diminished after reaching the maximum. Fine ash particles had higher deposition tendency compared to coarse particles, probably due to local eddies between the fingers on the front of the probe. The chemical compositions of coal ashes had an observable effect on the deposition behavior of high-viscosity ash. The findings of this work are significant for understanding the mechanism of high-viscosity ash deposition and determining the effect of key operating conditions relevant to deposition of high-viscosity ash.

Effect of Particle Size on Tribological Behavior of Rice Husk Ash–Reinforced Aluminum Alloy (AlSi10Mg) Matrix Composites

Rice husk ash of three different particle size ranges (50–75, 75–100 and 100–150 μm) a 3, 6, 9, and 12% by weight is reinforced with an aluminum alloy (AlSi10Mg) using the liquid metallurgy method. The dry sliding wear behavior of the composites in the cast conditions is examined using the pin-on-disc tribotesting machine for three different loads (20, 30, and 40 N) with three different sliding velocities (2, 3, and 4 m/s). The results reveal that the composite reinforced with the coarse rice husk ash particles exhibits superior wear resistance compared to the fine rice husk ash particles. The wear rate of the composite decreased with an increase in the weight percentage of rice husk ash particles for all size ranges. Finally, the wear mechanism was investigated with the worn surface using a scanning electron microscope.

High-flying diatoms: Widespread dispersal of microorganisms in an explosive volcanic eruption

Research Article| November 01, 2013 High-flying diatoms: Widespread dispersal of microorganisms in an explosive volcanic eruption Alexa R. Van Eaton; Alexa R. Van Eaton School of Geography, Environment and Earth Sciences, Victoria University of Wellington, PO Box 600, Wellington 6140, New Zealand *Current address: U.S. Geological Survey, Cascades Volcano Observatory, 1300 SE Cardinal Court, Suite 100, Vancouver, Washington 98683, USA; E-mail: avaneaton@usgs.gov. Search for other works by this author on: GSW Google Scholar Margaret A. Harper; Margaret A. Harper School of Geography, Environment and Earth Sciences, Victoria University of Wellington, PO Box 600, Wellington 6140, New Zealand Search for other works by this author on: GSW Google Scholar Colin J.N. Wilson Colin J.N. Wilson School of Geography, Environment and Earth Sciences, Victoria University of Wellington, PO Box 600, Wellington 6140, New Zealand Search for other works by this author on: GSW Google Scholar Author and Article Information Alexa R. Van Eaton *Current address: U.S. Geological Survey, Cascades Volcano Observatory, 1300 SE Cardinal Court, Suite 100, Vancouver, Washington 98683, USA; E-mail: avaneaton@usgs.gov. School of Geography, Environment and Earth Sciences, Victoria University of Wellington, PO Box 600, Wellington 6140, New Zealand Margaret A. Harper School of Geography, Environment and Earth Sciences, Victoria University of Wellington, PO Box 600, Wellington 6140, New Zealand Colin J.N. Wilson School of Geography, Environment and Earth Sciences, Victoria University of Wellington, PO Box 600, Wellington 6140, New Zealand Publisher: Geological Society of America Received: 10 Jun 2013 Revision Received: 07 Aug 2013 Accepted: 12 Aug 2013 First Online: 09 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 © 2013 Geological Society of America Geology (2013) 41 (11): 1187–1190. https://doi.org/10.1130/G34829.1 Article history Received: 10 Jun 2013 Revision Received: 07 Aug 2013 Accepted: 12 Aug 2013 First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Alexa R. Van Eaton, Margaret A. Harper, Colin J.N. Wilson; High-flying diatoms: Widespread dispersal of microorganisms in an explosive volcanic eruption. Geology 2013;; 41 (11): 1187–1190. doi: https://doi.org/10.1130/G34829.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Explosive eruptions create a transient bridge between the solid Earth and atmosphere, frequently injecting volcanic aerosols to stratospheric levels. Although known to disrupt terrestrial and aquatic ecosystems at the surface, the role of explosive volcanism in airborne transport of microscopic organisms has never been characterized. This study documents abundant freshwater diatoms (microskeletons of siliceous algae) in widespread tephra from the 25.4 ka Oruanui eruption of Taupo volcano, New Zealand. By matching the tephra-hosted species assemblages to those in coerupted clasts of lacustrine sediment, we demonstrate that ∼0.6 km3 of diatom remains were incorporated during magma-water interaction with a lake system overlying the vents, and were dispersed along with fine ash particles hundreds of kilometers downwind. One of the dominant species, Cyclostephanos novaezeelandiae, is endemic to New Zealand’s North Island and serves as a unique identifier of the eruptive source region. Our results suggest that dispersal of microorganisms may be an overlooked feature of a number of ancient and modern eruptions, and indicate a novel pathway of microbe transport in airborne volcanic plumes. We conclude that the biogenic signatures contained within distal tephras have potential application in the characterization of eruption dynamics, location, and environmental settings of volcanic source areas. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Subaqueous basaltic magmatic explosions trigger phreatomagmatism: A case study from Askja, Iceland

Sequences of basaltic pillow lavas that transition upward with systematic gradation from pillow fragment breccias to fluidal bomb-bearing breccias to bomb-bearing lapilli tuffs are common at Askja volcano, Iceland. Based on the detailed textural investigation of three of these sequences, we argue that they record temporally continuous transitions from effusive to explosive products that were erupted from, and deposited at or near a single subaqueous vent. The recognition of such sequences is important as they provide evidence for controls on the onset of explosive activity in subaqueous environments. Such investigations are complicated by the interplay of magmatic gas expansion, and phreatomagmatic and mechanical granulation fragmentation mechanisms in the subaqueous eruptive environment.All of the sequences studied at Askja have textural, componentry and sedimentological characteristics suggestive of a close genetic and spatial relationship between the pillow lavas and all of the overlying glassy clastic deposits. The identification of magma fragmentation signatures in pyroclasts was accomplished through detailed textural studies of pyroclasts within the full range of grain sizes of a given deposit i.e. bomb/blocks, lapilli and fine ash. These textural characteristics were compared and evaluated as discriminators of fragmentation in pyroclastic deposits. The presence of angular vitric clasts within the breccia and lapilli tuff displaying fragile glassy projections indicates little or no post-depositional textural modification. A shift in vesicle and clast textures between the pillow lavas and the large concentration of fluidal bombs in the breccia indicates that the phreatomagmatic explosions were initially triggered by magmatic vesiculation. The initial magmatic gas expansion may have been triggered by depressurization caused by the drainage of the ice-confined lake surrounding Askja. The fuel coolant interactions (FCIs) of the more efficient phreatomagmatic explosions were enabled by the increase in the surface area to volume ratio of the fluidal bombs in the water, producing a premix of magma and water. The onset and increasing influence of phreatomagmatic fragmentation is preserved in the presence of very fine blocky ash particles and diminished presence of larger particles such as fluidal bombs. The textural, sedimentological and environmental characteristics of these deposits suggest that phreatomagmatic explosions can be triggered by initial magmatic gas expansion, but that it is likely one of many mechanisms for triggering such explosions.