Plume Processes Research Articles

Volcanic controls on ash iron solubility: New insights from high-temperature gas–ash interaction modeling

Recent studies strongly suggest that volcanic ash can fertilize the surface ocean by releasing soluble iron. However, the volcanic and atmospheric processes that solubilize ash iron during its transport from the volcano to the ocean are poorly understood. Using thermodynamic equilibrium calculations, we investigate the influence of gas–ash interaction within the hot core (T>600°C) of the volcanic plume and the consequences of this for ash iron solubility. Simulations are performed by considering the plume hot core as a box model in which 1000°C magmatic gas, ash and 25°C ambient air are mixed together. We show that mixing and the resulting cooling of the gas–ash–air mixture affect the mineralogy and oxidation state of iron in the ash surface rim. Iron mineralogy in the ash surface layer after high-temperature plume processing is primarily governed by the ratio of the H2 and H2S content of the magmatic gas to the amount of entrained O2 into the hot plume (Xmix). The model results indicate that most of the iron in the ash surface layer is oxidized to ferric iron (Fe(III)) when log Xmix drops below −3.5 in the hot core. Such conditions may be encountered at convergent plate volcanoes, which release H2O-rich magmatic gases. In contrast, high temperature gas–ash interaction at divergent plate and hot spot volcanoes, which tend to be associated with CO2-rich and SO2-rich magmatic gases, respectively, may produce ash surfaces where iron mostly occurs as ferrous (Fe(II)). These volcanoes seem to be more favorable for iron fertilization because log Xmix does not fall below −3.5 and >80% of the iron in the ash surface remains ferrous (Fe(II)), which is more soluble in water than Fe(III).

A comparison of satellite‐ and ground‐based measurements of SO2 emissions from Tungurahua volcano, Ecuador

AbstractSatellite‐measured SO2 mass loadings and ground‐based measurements of SO2 emission rate are not directly comparable, with ∼40% differences between mean emissions reported by each technique from Tungurahua volcano, Ecuador, during late 2007. Numerical simulations of postemission processing and dispersal of Tungurahua's SO2 emissions enable more effective comparison of ground‐ and satellite‐based SO2 data sets, reducing the difference between them and constraining the impact of plume processing on satellite SO2 observations. Ground‐based measurements of SO2 emission rate are used as the model input, and simulated SO2 mass loadings are compared to those measured by the Ozone Monitoring Instrument (OMI). The changing extent of SO2 processing has a significant impact on daily variation in SO2 mass loading for a fixed volcanic emission rate. However, variations in emission rate at Tungurahua are large, suggesting that overall volcanic source strength and not subsequent processing is more likely to be the dominant control on atmospheric mass loading. SO2 emission rate estimates are derived directly from the OMI observations using modeled SO2 lifetime. Good agreement is achieved between both observed and simulated mass loadings (∼21%) and satellite‐derived and ground‐measured SO2 emission rates (∼18%), with a factor of 2 improvement over the differences found by simple direct comparison. While the balance of emission source strength and postemission processing will differ between volcanoes and regions, under good observation conditions and where SO2 lifetime is ∼24 hours, satellite‐based sensors like OMI may provide daily observations of SO2 mass loading which are a good proxy for volcanic source strength.

Basin and Range volcanism as a passive response to extensional tectonics

A long-standing issue in Cordilleran geology involves the nature of Basin and Range (western USA) volcanism, and whether such magmatism provides a trigger for extensional deformation, or if volcanic activity is a passive response to extension. We use space-time-composition patterns across the central and southern Basin and Range, and where appropriate, reconstructed latitudes and longitudes of volcanic rocks, to show that volcanism is fundamentally a passive process. Our analysis suggests that Basin and Range volcanism is initiated by the transition from a subduction to a transform boundary (now manifest as the San Andreas fault), which causes a slab window to open, as the subducting Farallon plate falls away. Accordingly, volcanic activity follows the northward-migrating Mendocino Triple Junction (MTJ). In the wake of the MTJ, continental mantle lithosphere is heated over a time scale of 10–12 Ma; it then rapidly degrades (or is removed) 17–20 Ma after MTJ arrival at any given latitude, and is replaced by asthenosphere. In the central Basin and Range, MTJ migration triggers the well-documented structural migration of the Sierra Nevada away from the Colorado Plateau. Not only is volcanism triggered by the tectonic transition, but in the central Basin and Range volcanism also migrates west, following the initiation of upper crustal extensional faulting; the lag between the onset of extension and initiation of volcanism is a remarkably consistent 2 Ma. Within this framework, the initial stage of eastward-concentrated volcanism is dominated by felsic magmatism, which then gradually degrades to a more mafic composition. This pattern, and temporal relations indicate that once lithospheric extension begins, between 2 and 5 Ma are needed to develop conduits through which nonviscous magmas can transit the crust, and that especially high amounts of extensional strain favor the eruption of K 2 O-rich, low-degree partial melts. Our observations indicate that it is unlikely that mantle plume processes initiated Basin and Range volcanism within the study area, and that decreases in SiO 2 and increases in incompatible element abundances to the east within the Cordillera are best explained by continental mantle lithosphere that thickens to the east, which reduces average melt fractions.

Evaluation of the Physical and Chemical Properties of Eyjafjallajökull Volcanic Plume Using a Cloud-Resolving Model

The Eyjafjallajokull volcanic eruption, which occurred on April 14, 2010, caused many environmental, air traffic and health problems. An attempt has been made to demonstrate for the first time that certain improvements could be made in the quantitative prediction of the volcanic ash parameters, and in the accounting of the processes in the immediate vicinity of the volcano, using a cloud-resolving model. This type of explicit modeling by treatment of volcanic ash and sulfate chemistry parameterization, with input of a number parameters describing the volcanic source, is the way forward for understanding the complex processes in plumes and in the future plume dispersion modeling. Results imply that the most significant microphysical processes are those related to accretion of cloud water, cloud ice and rainwater by snow, and accretion of rain and snow by hail. The dominant chemical conversion rates that give a great contribution to the sulfate budget are nucleation and dynamic scavenging and oxidation processes. A three-dimensional numerical experiment has shown a very realistic simulation of volcanic ash and other chemical compounds evolution, with a sloping structure strongly influenced by the meteorological conditions. In-cloud oxidation by H2O2 is the dominant pathway for SO2 oxidation and allows sulfate to be produced within the SO2 source region. The averaged cloud water pH of about 5.8 and rainwater pH of 4.5 over simulation time show quantitatively how the oxidation may strongly influence the sulfate budget and acidity of volcanic cloud. Compared to observations, model results are close in many aspects. Information on the near field volcanic plume behavior is essential for early preparedness and evacuation. This approach demonstrates a potential improvement in quantitative predictions regarding the volcanic plume distribution at different altitudes. It could be a useful tool for modeling volcanic plumes for better emergency measures planning.

The offshore export of sand during exceptional discharge from California rivers

Littoral cells along active tectonic margins receive large inputs of sand and gravel from coastal watersheds and commonly lose this sediment to submarine canyons. One hypothesis is that the majority of coarse (sand and gravel) river sediment discharge will be emplaced within and immediately “resupply” local littoral cells. A competing hypothesis is that the infrequent, large floods that supply the majority of littoral sediment may discharge water-sediment mixtures within negatively buoyant hyperpycnal plumes that transport sediment offshore of the littoral cell. Here we summarize pre- and post-flood surveys of two wave-dominated California (United States) river deltas during record to near-record floods to help evaluate these hypotheses: the 1982–1983 delta at the San Lorenzo River mouth and the 2005 delta at the Santa Clara River mouth. Flood sedimentation at both deltas resulted in several meters of aggradation and hundreds of meters of offshore displacement of isobaths. One substantial difference between these deltas was the thick (>2 m) aggradation of sand on the inner shelf of the Santa Clara River delta that contained substantial amounts (∼50%) of littoral-grade sediment. Once deposited on the inner shelf, only a fraction (∼20%) of this river sand was observed to migrate toward the beach over the following 5 yr. Furthermore, simple hypopycnal plume behavior could not explain deposition of this sand on the inner shelf. Thus, during an exceptional flood a substantial amount of littoral-grade sand was exported offshore of the littoral system at the Santa Clara River mouth—likely from hyperpycnal plume processes—and was deposited on the inner shelf.

The metatranscriptome of a deep-sea hydrothermal plume is dominated by water column methanotrophs and lithotrophs

Microorganisms mediate geochemical processes in deep-sea hydrothermal vent plumes, which are a conduit for transfer of elements and energy from the subsurface to the oceans. Despite this important microbial influence on marine geochemistry, the ecology and activity of microbial communities in hydrothermal plumes is largely unexplored. Here, we use a coordinated metagenomic and metatranscriptomic approach to compare microbial communities in Guaymas Basin hydrothermal plumes to background waters above the plume and in the adjacent Carmen Basin. Despite marked increases in plume total RNA concentrations (3-4 times) and microbially mediated manganese oxidation rates (15-125 times), plume and background metatranscriptomes were dominated by the same groups of methanotrophs and chemolithoautotrophs. Abundant community members of Guaymas Basin seafloor environments (hydrothermal sediments and chimneys) were not prevalent in the plume metatranscriptome. De novo metagenomic assembly was used to reconstruct genomes of abundant populations, including Marine Group I archaea, Methylococcaceae, SAR324 Deltaproteobacteria and SUP05 Gammaproteobacteria. Mapping transcripts to these genomes revealed abundant expression of genes involved in the chemolithotrophic oxidation of ammonia (amo), methane (pmo) and sulfur (sox). Whereas amo and pmo gene transcripts were abundant in both plume and background, transcripts of sox genes for sulfur oxidation from SUP05 groups displayed a 10-20-fold increase in plumes. We conclude that the biogeochemistry of Guaymas Basin hydrothermal plumes is mediated by microorganisms that are derived from seawater rather than from seafloor hydrothermal environments such as chimneys or sediments, and that hydrothermal inputs serve as important electron donors for primary production in the deep Gulf of California.

Size fractionation of trace metals in the Edmond hydrothermal plume, Central Indian Ocean

The investigation of the distribution of trace elements between the dissolved, colloidal and particulate phases within a hydrothermal plume is key to understanding plume processes. Particulate and colloidal size fractions of four trace elements (iron, manganese, copper and phosphorus) along with the dissolved size fraction of iron, manganese and copper have been determined in the hydrothermal plume overlying the Edmond vent-site in the Central Indian Ocean. Dissolved iron and manganese are the most heavily enriched metals in hydrothermal fluids emerging from vents and iron plays a significant role in subsequent dissolved-particulate interactions within hydrothermal plumes. Copper and phosphorus are each representative members of discrete groups of tracers (chalcophile elements and oxyanions, respectively) that are known to exhibit distinct patterns of behaviour, relative to iron, within hydrothermal plumes. Here we show that iron is present in all three hydrothermal plume fractions (dissolved, colloidal and particulate), being least abundant in dissolved form. Manganese resides predominantly in the dissolved fraction, copper resides primarily in the particulate phase and phosphorus is abundant in both the colloidal and coarser particulate phases, but not the dissolved fraction. The correlation of phosphorus to iron in the Edmond hydrothermal plume is both (i) constant across the colloidal and coarser particulate phases and (ii) matches well to broader inter-ocean trends reported previously from the Atlantic and Pacific Oceans. These results demonstrate a mechanism whereby plume-height P:Fe ratios are established during the very earliest stages of dissolved Fe(II) oxidation, followed by aggregation into coarser hydrothermal plume particles. This provides a strong argument for the study of P:Fe ratios in hydrothermal sediments as potential paleotracers of deep-water dissolved phosphate distributions and, hence, past deep-ocean circulation patterns.

Laser Ablation Transient Plasma Structures Expansion in Vacuum

The dynamics of transient plasmas generated by high-fluence nanosecond laser ablation has been investigated by means of a fast intensified charge-coupled device imaging system. The recorded pictures reveal a specific splitting process of the plasma plume into fast and slow components.

Review of effective emissions modeling and computation

Abstract. An important issue in the evaluation of the environmental impact of emissions from concentrated sources such as transport modes, is to understand how processes occurring at the scales of exhaust plumes can influence the physical and chemical state of the atmosphere at regional and global scales. Indeed, three-dimensional global circulation models or chemistry transport models generally assume that emissions are instantaneously diluted into large-scale grid boxes, which may lead, for example, to overpredict the efficiency of NOx to produce ozone. In recent times, various methods have been developed to incorporate parameterizations of plume processes into global models that are based e.g. on correcting the original emission indexes or on introducing "subgrid" reaction rates in the models. This paper provides a review of the techniques proposed so far in the literature to account for local conversion of emissions in the plume, as well as the implementation of these techniques into atmospheric codes.

Toxicological evaluation of realistic emission source aerosols (TERESA): summary and conclusions

The toxicological evaluation of realistic emissions of source aerosols (TERESA) study seeks to delineate health effects of aerosols formed from emissions of particulate matter sources. This series of papers reports the findings of experiments using coal-fired power plants as the source of emissions and this paper summarizes the findings and knowledge acquired from these studies. Emissions were drawn directly from the stacks of three coal-fired power plants in the US, and photochemically aged in a mobile laboratory to simulate downwind power plant plume processing. The power plants used different sources of coal and had different emission controls. Exposure scenarios included primary particles, secondary particles and mixtures of these with common atmospheric constituents (α-pinene and ammonia). Extensive exposure characterization was carried out, and toxicological outcomes were evaluated in Sprague-Dawley rats exposed to different emission scenarios. Breathing pattern, pulmonary inflammatory responses, in vivo pulmonary and cardiac chemiluminescence and cardiac response in a model of acute myocardial infarction were assessed. The results showed no response or relatively mild responses to the inhaled aerosols studied; complex scenarios which included oxidized emissions and α-pinene to simulate biogenic secondary organic aerosol tended to induce more statistically significant responses than scenarios of oxidized and non-oxidized emissions alone. Relating adverse effects to specific components did not consistently identify a toxic constituent. These findings are consistent with most of the previously published studies using pure compounds to model secondary power plant emissions, but importantly add substantial complexity and thus have considerable merit in defining toxicological responses.

Toxicological Evaluation of Realistic Emission Source Aerosols (TERESA): Introduction and overview

Determining the health impacts of sources and components of fine particulate matter (PM2.5) is an important scientific goal. PM2.5 is a complex mixture of inorganic and organic constituents that are likely to differ in their potential to cause adverse health outcomes. The Toxicological Evaluation of Realistic Emissions of Source Aerosols (TERESA) study focused on two PM sources—coal-fired power plants and mobile sources—and sought to investigate the toxicological effects of exposure to emissions from these sources. The set of papers published here document the power plant experiments. TERESA attempted to delineate health effects of primary particles, secondary (aged) particles, and mixtures of these with common atmospheric constituents. TERESA involved withdrawal of emissions from the stacks of three coal-fired power plants in the United States. The emissions were aged and atmospherically transformed in a mobile laboratory simulating downwind power plant plume processing. Toxicological evaluations were carried out in laboratory rats exposed to different emission scenarios with extensive exposure characterization. The approach employed in TERESA was ambitious and innovative. Technical challenges included the development of stack sampling technology that prevented condensation of water vapor from the power plant exhaust during sampling and transfer, while minimizing losses of primary particles; development and optimization of a photochemical chamber to provide an aged aerosol for animal exposures; development and evaluation of a denuder system to remove excess gaseous components; and development of a mobile toxicology laboratory. This paper provides an overview of the conceptual framework, design, and methods employed in the study.

Active multibeam sonar-derived bubble plume fluxes and dynamics.

By their nature, seeps are spatially and temporally variable and episodic; thus, effective emissions’ quantification presents significant challenges because local measurements likely are unrepresentative. A multibeam sonar system was developed to observe ebullition spatially and used to study water column bubble plume processes, as well as subsurface migration processes for seepage from the Coal Oil Point seep field and the East Siberian Arctic Sea is presented. The system is designed for deep-sea application related to hydrates as part of a benthic observatory.

Photochemical processing of organic aerosol at nearby continental sites: contrast between urban plumes and regional aerosol

Abstract. As part of the BAQS-Met 2007 field campaign, Aerodyne time-of-flight aerosol mass spectrometers (ToF-AMS) were deployed at two sites in southwestern Ontario from 17 June to 11 July 2007. One instrument was located at Harrow, ON, a rural, agriculture-dominated area approximately 40 km southeast of the Detroit/Windsor/Windsor urban area and 5 km north of Lake Erie. The second instrument was located at Bear Creek, ON, a rural site approximately 70 km northeast of the Harrow site and 50 km east of Detroit/Windsor. Positive matrix factorization analysis of the combined organic mass spectral dataset yields factors related to secondary organic aerosol (SOA), direct emissions, and a factor tentatively attributed to the reactive uptake of isoprene and/or condensation of its early generation reaction products. This is the first application of PMF to simultaneous AMS measurements at different sites, an approach which allows for self-consistent, direct comparison of the datasets. Case studies are utilized to investigate processing of SOA from (1) fresh emissions from Detroit/Windsor and (2) regional aerosol during periods of inter-site flow. A strong correlation is observed between SOA/excess CO and photochemical age as represented by the NOx/NOy ratio for Detroit/Windsor outflow. Although this correlation is not evident for more aged air, measurements at the two sites during inter-site transport nevertheless show evidence of continued atmospheric processing by SOA production. However, the rate of SOA production decreases with airmass age from an initial value of ~10.1 μg m−3 ppmvCO−1 h−1 for the first ~10 h of plume processing to near-zero in an aged airmass (i.e. after several days). The initial SOA production rate is comparable to the observed rate in Mexico City over similar timescales.

Sulfur isotope fractionation during the May 2003 eruption of Anatahan volcano, Mariana Islands: Implications for sulfur sources and plume processes

Sulfur isotope compositions of pumice and adsorbed volatiles on ash from the first historical eruption of Anatahan volcano (Mariana arc) are presented in order to constrain the sources of sulfur erupted during the period 10–21 May, 2003. The isotopic composition of S extracted from erupted pumice has a narrow range, from δ 34S V-CDT +2.6‰ to +3.2‰, while the composition of sulfur adsorbed onto ash has a larger range (+2.8‰ to +5.3‰). Fractionation modeling for closed and open system scenarios suggests that degassing of SO 2 raised the δ 34S V-CDT value of S dissolved in the melt from an initial composition of between +1.6‰ and +2.6‰ for closed-system degassing, or between −0.5‰ and +1.5‰ for open-system degassing, however closed-system degassing is the preferred model. The calculated values for the initial composition of the magma represent a MORB-like (δ 34S V-CDT ∼ 0‰) mantle source with limited contamination by subducted seawater sulfate (δ 34S V-CDT +21‰). Modeling also suggests that the δ 34S V-CDT value of SO 2 gas in closed-system equilibrium with the degassed magma was between +0.9‰ and +2.5‰. The δ 34S V-CDT value of sulfate adsorbed onto ash in the eruption plume (+2.8‰ to +5.1‰) is consistent with sulfate formation by oxidation of magmatic SO 2 in the eruption column. The sulfur isotope composition of sulfate adsorbed to ash changes from lower δ 34S values for ash erupted early in the eruption to higher δ 34S values for ash erupted later in the eruption. We interpret the temporal/stratigraphic change in sulfate isotopic composition to primarily reflect a change in the isotopic composition of magmatic SO 2 released from the progressively degassing magma and is attributed to the expulsion of an accumulated gas phase at the beginning of the eruption. More efficient oxidation of magmatic SO 2 gas to sulfate in the early water-rich eruption plume probably contributed to the change in S isotope compositions observed in the ash leachates.

Research Spotlight: Ridge versus plume: A closer look at the seafloor south of Iceland

Site of many volcanoes, Iceland is generally thought to be fueled by a plume of hot mantle rising from the core‐mantle boundary. It also sits atop the Mid‐ Atlantic Ridge, the plate boundary where the North American plate is spreading away from the Eurasian plate. Because of the possible interaction of these complex deep and shallow geodynamic processes, the degree to which ridge processes may influence plume processes and vice versa is a subject of much debate.

Straining and advection contributions to the mixing process of the Patos Lagoon coastal plume, Brazil

The Southern Brazilian Shelf is a region influenced by freshwater, and the evolution of stratification can present important ecological consequences in this area. The aim of this paper was to investigate the importance of straining and advection processes that affect the stratification and destratification of the water column along the Southern Brazilian inner shelf, a region that is influenced by the Patos Lagoon coastal plume. The study was carried out through 3‐D numerical modeling experiments and the results were analyzed using the potential energy anomaly equation and wavelet analysis. Results showed that the potential energy anomaly showed strong variability over a time scale of several days and followed the wind pattern over the study region, and was accompanied by the monthly modulation of river discharge and remote effects associated with variability in oceanic circulation. However, the most important events in synoptic time scales occurred in periods shorter than 20 days and were coincident with the passage of meteorological systems over the study region. Straining and advection were the most important mechanisms for the evolution of stratification in the adjacent coastal region. Nonlinearities and dispersion terms were as important as modulation effects, mainly during periods of high fluvial discharge. Close to the Patos Lagoon mouth, vertical advection explained most of the stratification evolution, due to the morphological characteristics in this region. In the frontal region and far field of the plume, the following two regions must be considered: the northeast part, which is characterized by the convergence of the coastal currents and ebb flows associated with the freshwater discharge that promote the domination of the cross‐shore straining and advection, and the southwest part, which is controlled by the coastal currents that result in the domination by alongshore straining and advection and cross‐shore advection terms. Close to the mouth of the Patos Lagoon, the occurrence of downward velocities generated downward displacement of the isopycnals, which decreases the potential energy anomalies, and vice versa. Near the frontal region, the anomalies were dependent on the intensity of the fluvial discharge. During moderate to high discharge events, the northeastward currents intensified mixing along shore, which decreased the potential energy anomalies. In the same way, the southwestward currents intensified the spreading of freshwater and increased the stratification and the potential energy anomalies.

Eruption chronologies, plume heights and eruption styles at Tungurahua Volcano: Integrating remote sensing techniques and infrasound

Satellite remote sensing allows volcanic ash plumes to be detected and tracked and routinely aids in hazard mitigation, especially to the aviation community. Although satellite imagery provides valuable information about volcanic plume processes (i.e. plume heights, plume composition and plume transport), it has its limitations. In addition to the observational gaps produced by meteorological clouds as well as temporal and spatial resolution restrictions, large volcanic clouds often obscure the vent during an eruption. Therefore, some key information about eruption dynamics and processes are impossible to obtain from satellite images. In this paper we investigate four eruptions at Tungurahua Volcano, Ecuador during the 2006–2008 time period. We integrate satellite-derived eruption chronologies, plume heights and plume aspect ratios with infrasound data, primarily acoustic power and hand-held thermal imagery when available. Integrating these datasets allows us to identify accurate eruption onsets, durations and cessations as well as define different types of eruption styles ranging from plinian to weak vulcanian. Transitions between the different eruption styles were also documented. Results show that there is a positive correlation between plume height and acoustic power. We conclude that combining the two datasets allows better constraints on eruption processes and source parameters. Using these methods in real-time monitoring will allow more accurate eruption monitoring and ash hazard mitigation.

Volcanic and geochemical evolution of the Teno massif, Tenerife, Canary Islands: Some repercussions of giant landslides on ocean island magmatism

Large‐scale, catastrophic mass wasting is a major process contributing to the dismantling of oceanic intraplate volcanoes. Recent studies, however, have highlighted a possible feedback relationship between flank collapse, or incipient instability, and subsequent episodes of structural rearrangement and/or renewed volcano growth. The Teno massif, located in northwestern Tenerife (Canary Islands), is a deeply eroded Miocene shield volcano that was built in four major eruptive phases punctuated by two lateral collapses, each removing >20–25 km3 of the volcano's north flank. In this paper, we use detailed field observations and petrological and geochemical data to evaluate possible links between large‐scale landslides and subsequent volcanism/magmatism during Teno's evolution. Inspection of key stratigraphic sequences reveals that steep angular unconformities, relics of paleolandslide scars, are marked by polymict breccias. Near their base, these deposits typically include abundant juvenile pyroclastic material, otherwise scarce in the region. While some of Teno's most evolved, low‐density magmas were produced just before flank collapses, early postlandslide lava sequences are characterized by anomalously high proportions of dense ankaramite flows, extremely rich in clinopyroxene and olivine crystals. A detailed sampling profile shows transitions from low‐Mg # lavas relatively rich in SiO2 to lavas with low silica content and comparatively high Mg # after both landslides. Long‐term variations in Zr/Nb, normative nepheline, and La/Lu are coupled but do not show a systematic correlation with stratigraphic boundaries. We propose that whereas loading of the growing precollapse volcano promoted magma stagnation and differentiation, the successive giant landslides modified the shallow volcano‐tectonic stress field at Teno, resulting in widespread pyroclastic eruptions and shallow magma reservoir drainage. This rapid unloading of several tens of km3 of near‐surface rocks appears to have upset magma differentiation processes, while facilitating the remobilization and tapping of denser ankaramite magmas that were stored in the uppermost mantle. Degrees of mantle melting coincidently reached a maximum in the short time interval between the two landslides and declined shortly after, probably reflecting intrinsic plume processes rather than a collapse‐induced influence on mantle melting. Our study of Teno volcano bears implications for other oceanic volcanoes where short‐term compositional variations may also directly relate to major flank collapse events.

Interaction of a plasma plume induced by a pulsed plasma thruster with an incident flow of rarefied magnetized plasma

A three-dimensional computational model and the results of the calculation for the dynamics of a plasma plume induced by a pulsed plasma thruster (PPT) in a magnetized flow of the ambient plasma are presented. A nonstationary expansion process of a PPT-induced plasma plume is studied in the ionospheric plasma over 100 µs after the start of a 6-microsecond plasma pulse. The parameters of the plasma plume in the PPT outlet section simulate the performance characteristics of a pulsed thruster PPT-4 (Pulsed Plasma Thruster 4 [3]) utilizing solid Teflon propellant. The magnetohydrodynamic (MHD) model of the process is based on the approximation of the ideal magnetic gas dynamics and makes it possible to predict the dynamics of a plasma bunch after the pulse termination during its interaction with the ambient medium and the magnetic field as well as the induced electric fields and currents in the vicinity of the expanding plasma

Natural Attenuation Processes in Landfill Leachate Plumes at Three Danish Sites

This article provides an overview of comprehensive core and fringe field studies at three Danish landfill sites. The goal of the research activities is to provide a holistic description of core and fringe attenuation processes for xenobiotic organic compounds in landfill leachate plumes. The approach used is cross-disciplinary, encompassing integration of field-scale observations at different scales, field injection experiments, laboratory experiments, and reactive solute transport modeling. This is illustrated in examples from the most recently investigated site-the Sjoelund Landfill. The research performed serves as good case studies to conceptualize natural attenuation processes in landfill leachate plumes and also supports the notion that monitored natural attenuation (MNA) may be a possible remediation strategy at landfills. However, landfill leachate plumes challenge traditional approaches and tools used in the application of MNA. In particular, the use of in situ indicators to document mass removal in landfill leachate plumes is emphasized. In this article, we advocate the application of conceptual and numerical models as tools for the integration of data and testing of hypotheses.