phreatomagmatic to strombolian eruptive activity of basaltic cinder cones montana los erales tenerife canary islands abstract phreatomagmatic activity results from the interaction of magma and external water during a volcanic eruption and is a frequent eruptive phenomenon worldwide such fuel coolant reactions change the eruptive dynamics thus generating particles that reflect the degree of explosivity different eruptive phases may thus be identified from deposits allowing us to reconstruct conditions that prevailed in the past and use these to predict the level of explosivity in a given geological setting in the future a detailed study of the deposits from montana los erales a 70 m high quaternary cinder cone belonging to a rift related chain of vents in the bandas del sur region in southeast tenerife was undertaken field observations on excavated sections and sem analysis of tephra suggest that the eruption style changed progressively from an initial phreatomagmatic phase through a transitional stage to one that was entirely strombolian to investigate the causes and the nature of these changes in eruptive style products from each major unit were analysed for their morphology using hand specimen observations secondary electron microscopy backscatter electron microscopy and reflected light microscopy to examine fragment size variation fragment morphologies vesicularity and the level of secondary hydrous alteration e g palagonitisation and zeolitisation study results demonstrate that the initial phase of activity was largely driven by magma water interaction where magma may have interacted with a lens of fresh ground or surface water with proceeding eruptive activity the water became exhausted giving rise to an entirely strombolian eruptive style examples of phreatomagmatic activity that occur on typical rift related basaltic vent alignments are not infrequent in the canary islands these vent systems usually erupt in strombolian fashion producing scoria and lava flows that do not generally extend far beyond the vent area however aligned feeders may intersect different strata structural features and different hydrological situations thus giving rise to activity that is less predictable in setting intensity and duration the occurrence of phreatomagmatism in an otherwise low explosivity basaltic eruptive environment increases the need for awareness of the geo hydrological situation in volcanically active areas studying the past eruptive history is therefore essential to derive realistic scenarios for future vulnerability evaluation and risk assessment especially in densely populated areas like the canary islands

contrasting styles of welding observed in the proximal askja 1875 eruption deposits i regional welding abstract as an alternative to classical welding models of fall deposits due to the progressive accumulation of hot tephra which then weld we describe here welded deposits on the northern 1875 caldera rim of askja volcano that have welded due to the influence of hot discrete spatter bombs impacting into and supplying heat to a halo of surrounding tephra this style of welding we term local welding in contrast to regional welding which is described elsewhere carey r j houghton b f thordarson t 2008 contrasting styles of welding observed in the proximal askja 1875 eruption deposits i regional welding j volcanol geotherm res 171 1 19 doi 10 1016 j jvolgeores 2007 11 020 locally welded deposits are associated with the rhyolitic plinian phase of the 1875 eruption of askja volcano two distinct welding units w1 and w2 are interbedded with plinian fall on the northern caldera rim and grade outwards to weakly dispersed non welded fall spatter bombs are found in both welding units but vary in their characteristic sizes and internal features in the w1 unit simple bombs with homogeneous internal characteristics up to 60 cm in diameter are found in the w2 unit large discrete spatter bombs with complex internal features range up to 9 m in diameter we describe here two case studies showing the effects of a single small spatter bombs b multiple small spatter bombs and c large discrete spatter bombs varying in size vertical and lateral profiles through welding zones reveal that the primary controls on local welding are the availability of supplied or added heat and the loading capacity of the spatter bomb local welding grades are much higher than that of regional welding as the combined effects of heat compaction and insulation can provide suitable conditions which lead to dense welding and proximal to the spatter bomb rheomorphic flowage if heating and loading exceed the critical requirement for welding porosity loss via matrix welding and vesicle collapse occurs to a point where further strain must be accommodated as shearing and ductile flowage the spatter bombs are found only within the weakly dispersed welding units and are the final erupted products of each fountaining phase their low viscosities are evident by their deformation on impact and fluidal forms and hold some important clues to eruption dynamics in the shallow conduit and vent regions

constraints on magma wall rock thermal interaction during explosive eruptions from textural analysis of cored bombs abstract cored bombs a kind of pyroclast consisting of a lithic core surrounded by a chilled shell of juvenile material record the thermal interaction of magma with wall rocks we performed textural analysis of cored bombs solid melt heat transfer theoretical modelling and high temperature coating experiments to put temporal and intensity constraints on the thermal interaction of potassic magma feeder systems with carbonate wall rocks during explosive eruptions in the quaternary colli albani volcanic district roman province it appears that the degree of thermal alteration of lithic cores records the duration of magma core heat transfer whereas the core shell size ratio records the initial entrainment temperature of the lithic fragment both parameters appear to vary significantly with the eruptive style magnitude and vent location specifically small scale 0 1 1 km 3 dre hydromagmatic eruptions show magma core heat transfer durations of 0 1 10 s and entrainment temperatures in the range of 100 300 c in the case of a monogenetic maar located in the colli albani peripheral area while entrainment temperature is as high as to 800 c for a polygenetic maar in a high enthalpy geothermal system at the margins of the main colli albani magma chamber a large scale 30 km 3 dre caldera forming explosive event shows magma core heat transfer duration in the order of 10 2 10 3 s and temperature of 100 500 c at the initial magma wall rock contact on these grounds we derived the cooling rate of magmas as a function of the initial temperature mass and size distribution of lithic clasts entrained magma cooling by lithic entrainment may have occurred on the same time scale as that of eruptive pulses seconds to hours implying that lithic entrainment may effect changes in magma physico chemical properties on a short time scale and consequently affect eruptive conduit dynamics

hydrogeochemical processes and quality assessment of groundwater in dumka and jamtara districts jharkhand india the hydrogeochemical study of groundwater in dumka and jamtara districts has been carried out to assess the major ion chemistry hydrogeochemical processes and groundwater quality for domestic and irrigation uses thirty groundwater samples were collected and analyzed for ph electrical conductivity total dissolved solids tds total hardness anions f cl no3 hco3 so42 and cations ca2 mg2 na k the analytical results show the faintly alkaline nature of water and dominance of mg2 and ca2 in cationic and hco3 and cl in anionic abundance the concentrations of alkaline earth metals ca2 mg2 exceed the alkali metals na k and hco3 dominates over so42 cl concentrations in the majority of the groundwater samples ca mg hco3 is the dominant hydrogeochemical facies in 60 of the groundwater samples while 33 samples occur as a mixed chemical character of ca mg cl hydrogeochemical facies the water chemistry is largely controlled by rock weathering and ion exchange processes with secondary contribution from anthropogenic sources the inter elemental correlations and factor and cluster analysis of hydro geochemical database suggest combined influence of carbonate and silicate weathering on solute acquisition processes for quality assessment analyzed parameter values were compared with indian and who water quality standards in majority of the samples the analyzed parameters are well within the desirable limits and water is potable for drinking purposes total hardness and concentrations of tds cl no3 ca2 and mg2 exceed the desirable limits at a few sites however except no3 all these values were below the highest permissible limits the calculated parameters such as sodium adsorption ratio percent sodium na and residual sodium carbonate revealed excellent to good quality of groundwater for agricultural purposes except at few sites where salinity and magnesium hazard mh values exceeds the prescribed limits and demands special management

the role of partial melting in the 15 ma geochemical evolution of gran canaria a blob model for the canary hotspot the subaerial portion of gran canada canary islands was built by three cycles of volcanism a miocene cycle 8 5 15 ma a pliocene cycle 1 8 60 ma and a quaternary cycle 1 8 0 ma only the pliocene cycle is completely exposed on gran canaria the early stages of the miocene cycle are submarine and the quaternary cycle is still in its initial stages during the miocene sio2 saturation of the mafic volcanics decreased systematically from tholeiite to nephelinite for the pliocene cycle sio2 saturation increased and then decreased with decreasing age from nephelinite to tholeiite to nephelinite sio2 saturation increased from nephelinite to basanite and alkali basalt during the quaternary in each of these cycles increasing melt production rates sio2 saturation and concentrations of compatible elements and decreasing concentrations of some incompatible elements are consistent with increasing degrees of partial melting in the sequence melilite nephelinite to tholeiite the mafic volcanics from all three cycles were derived from co2 rich garnet lherzolite sources phlogopite ilmenite sulfide and a phase with high partition coefficients for the light rare earth elements lree u th pb nb and zr possibly zircon were residual during melting to form the miocene nephelinites through tholeiites phlogopite ilmenite and sulfide were residual in the source of the pliocene quaternary nephelinites through alkali basalts highly incompatible element ratios e g nb u pb ce k u nb pb ba rb zr hf la nb ba th rb nb k nb zr nb th nb th la and ba la exhibit extreme variations in many cases larger than those reported for all other ocean island basalts but these ratios correlate well with degree of melting survival of residual phases at higher degrees of melting during the miocene cycle and differences between major and trace element concentrations and melt production rates between the miocene and pliocene tholeiites suggest that the miocene source was more fertile than the pliocene quaternary source s we propose a blob model to explain the multi cycle evolution of canary volcanoes and the temporal variations in chemistry and melt production within cycles each cycle of volcanism represents decompression melting of a discrete blob of plume material small degree nephelinitic and basanitic melts are derived from the cooler margins of the blobs whereas the larger degree tholeiitic and alkali basaltic melts are derived from the hotter centers of the blobs the symmetrical sequence of mafic volcanism for a cycle from highly undersaturated to saturated to highly undersaturated compositions reflects melting of the blob during its ascent beneath an island in the sequence upper margin corelower margin volcanic hiatuses between cycles and within cycles represent periods when residual blob or cooler entrained shallow mantle material fill the melting zone beneath an island

intra cone plumbing system and eruptive dynamics of small volume basaltic volcanoes a case study in the calatrava volcanic field abstract the manoteras volcano tortonian to pleistocene calatrava volcanic field spain is composed of a scoria and spatter cone surrounded by a field of pahoehoe lava the volcanic cone is made essentially of vitreous lapilli tuffs with intercalations of vitreous tuffs and spatter deposits without any intercalations of lava flows erosion has uncovered an intra cone plumbing system formed by coherent dykes and pyroclastic dykes mixed type dykes this dyke swarm reflects processes of intrusion at the end of the eruption or even post eruption all the volcanic products are nephelinitic in composition the main dyke is up to 3 4 m thick and has an exposed length of 1000 m it is composed mostly of coherent nephelinite with some pyroclastic sections at its northern extremity this dyke is regarded as a feeder dyke of the volcano although the upper parts of the dike have been eroded which prevents the observation of the characteristics and nature of the possible overlying vent s mixed type dykes could also have acted as small linear vents and indicate that the magma fragmentation level during final waning stages of the eruption was located inside the volcanic cone the pyroclastic deposits that make up the volcanic cone at the current exposure level were probably developed during a major phase of violent strombolian style that formed the scoria cone followed by a hawaiian phase that formed the summital intracrater spatter deposit three central type vents have been identified one at the highest point of the remnant volcanic cone summital vent from where the earlier explosive eruptions took place and the other two at the fringe of the cone base from where emissions were only effusive the lava flows were emitted from these boccas through the scoria cone feeding the lava field the results obtained based on careful field observations add substantial complexity to the proposed eruptive models for small volume basaltic volcanoes as it appears evident that there may exist and evolution through time from central conduit settings to fissure eruptions moreover it is shown that intracone plumbing systems can integrate coherent and clastic dykes of variable thicknesses which in some cases could represent feeder dykes

criteria for interpreting kimberlite as coherent insights from the muskox and jericho kimberlites nunavut canada the jurassic muskox and jericho kimberlites northern slave province nunavut canada contain a variety of facies exhibiting different geometries contact relationships internal organisation country rock abundance and olivine shapes although many have similar matrix groundmass mineralogies and textures five facies are examined that either have characteristics consistent with coherent rocks in general i e intrusive and extrusive non fragmental rocks or are mineralogically and texturally similar to kimberlite described as coherent or apparent coherent three facies are interpreted as coherent on the basis of 1 geological setting 2 apparent porphyritic texture 3 sharp contacts with fragmental kimberlite 4 relative abundance of elongate and unbroken olivine crystals and 5 paucity of country rock xenoliths while the remaining two facies are interpreted as fragmental on the basis of 1 the gradational contacts with demonstrably fragmental kimberlite 2 relative abundance and range of sizes of country rock lithic clasts and 3 numerous broken olivine crystals comparisons are made with coherent and apparent coherent kimberlite from the literature our three coherent facies are similar to literature reported coherent kimberlite dykes hosted in country rock ckd in terms of internal organisation low abundance of country rock xenoliths and apparent porphyritic texture conversely our two fragmental facies share attributes with previously described pipe filling coherent and apparent coherent kimberlite ckpf in terms of geometry internal organisation and abundance of country rock xenoliths we conclude that ckd and most ckpf although similar in matrix groundmass mineralogy and texture can be distinguished on the basis of internal organisation country rock lithic clast abundance texture e g apparent porphyritic texture and possibly olivine crystal shapes and suggest that fragmental kimberlite is more common than reported

coupled textural and compositional characterization of basaltic scoria insights into the transition from strombolian to fire fountain activity at mount etna italy strombolian and fire fountain activities represent a common expression of explosive basaltic eruptions however the transition between these two eruptive styles and their source mechanisms are still debated we use textural and compositional studies to characterize pyroclastic material from both the strombolian and hawaiian style fire fountain phases of the january june 2000 etna activity we find that basaltic scoria presents distinctive textural and compositional features that reflect different modes of magma vesiculation and crystallization in the two eruptive regimes overall magma that forms strombolian scoria is far more crystallized less vesicular and more evolved indicating strong volatile depletion and longer residence time before being erupted fire fountain scoria indicates a fast rising magma with evidence of moderate syneruptive volatile exsolution the new textural and compositional data set is integrated with previous volcanological and geophysical investigations to provide further insights into the dynamics of fire fountains and to frame the transition from strombolian explosions to fire fountain activity into a model that may apply to future eruptions at mount etna as well as other active basaltic volcanoes

volcanic ash clusters tephra rafts and scavengers abstract much of the volcanic ash deposited in the vicinity of pullman washington from the may 18th eruption of mt st helens in 1980 fell in the form of composite ash clusters 0 25 to 0 5 mm in diameter particles in the clusters ranged from sub micron to more than 40 microns in size the porous clusters rafted large ash particles great distances and scavenged particles of all sizes as the wind blew them eastward the result is poorly sorted ash deposits as far as 644 km east missoula within individual clusters textural relationships suggest that both mechanical interlocking and electrostatic attraction played a role in cluster formation the clusters are very fragile and may never be preserved in the stratigraphic record but it is suggested that this kind of ash transport may well have occurred in the geologic past documentation of this ash cluster fall will promote a better understanding of the physical aspects of the downwind distribution of fine grained volcanic ash the poor size sorting in some ancient ash deposits may thus be explained

fitting data but poor predictions reverberation prediction uncertainty when seabed parameters are derived from reverberation measurements for many decades researchers have been developing inverse techniques for estimating seabed parameters from reverberation data notably scattering strength generally the angular dependence of the scattering kernel is unknown and is either solved for or assumed fixed in either case agreement is typically quite good between the measured reverberation and that modeled by fitting scattering parameters however what are the resulting uncertainties in a reverberation prediction if the ocean or geometry changes the main results of the paper are that 1 these prediction uncertainties are surprisingly large of order 10 db at 10 km and thus 2 traditional current methods for reverberation inversion should be augmented mitigating the large prediction uncertainties by an additional measurement several options for additional measurements are discussed

thermohydraulic explosions in phreatomagmatic eruptions as evidenced by the comparison between pyroclasts and products from molten fuel coolant interaction experiments 1 thermohydraulic explosions were produced by molten fuel coolant interaction mfci experiments using remelted shoshonitic rocks from vulcano italy the fragmentation history and energy release were recorded the resulting products were recovered and analyzed with the scanning electron microscope fine particles from experiments show shape and surface features that result from melt fragmentation in brittle mode these clasts relate to the thermohydraulic phase of the mfci where most of the mechanical energy is released they are here called active particles the total surface area of such particles is proportional to the energy of the respective explosions other particles from experiments show shape and surface features that result from melt fragmentation in a ductile regime these fragments called passive particles form after the thermohydraulic phase during the expansion phase of the mfci in order to verify thermohydraulic explosions in volcanic eruptions we compared experimental products with samples from phreatomagmatic base surge deposits of vulcano ash particles from the experiments show features similar to those from the deposits suggesting that the experiments reproduced the same fragmentation dynamics to achieve discrimination between active and passive particles we calculated shape parameters from image analysis the mass of active particles in base surge deposits was calculated as the material properties for the natural samples are identical to the experimental ones the energy measurements and calculations of the experiments can be applied for a single phreatomagmatic eruption at vulcano a maximum mechanical energy release of 2 75 1013 j was calculated representing a tnt analogue of 6 5 kt

inheritance an influence on the particle size of pyroclastic deposits the size distribution of particles in pyroclastic fall deposits has been interpreted as a strong indication of efficiency of the fragmentation process during the parent explosions fall deposits however contain two distinct populations of pyroclasts juvenile i e magmatic clasts fragmented from the magma and wall rock particles derived from walls of the vent and volcanic conduit while sizes and shapes of the former are always sensitive indicators of eruptive processes properties of the wall rock population may reflect various external influences here we describe how the wall rock component of a powerful historical eruption largely inherited its size distribution from properties of the host rocks and how this in turn strongly biases the entire deposit grain size distribution of the near vent deposits the use of wall rock particles to infer style of fragmentation and eruption must always be coupled with other independent lines of evidence 2010 geological society of america

estimating seabed scattering mechanisms via bayesian model selection a quantitative inversion procedure is developed and applied to determine the dominant scattering mechanism surface roughness and or volume scattering from seabed scattering strength data the classification system is based on trans dimensional bayesian inversion with the deviance information criterion used to select the dominant scattering mechanism scattering is modeled using first order perturbation theory as due to one of three mechanisms interface scattering from a rough seafloor volume scattering from a heterogeneous sediment layer or mixed scattering combining both interface and volume scattering the classification system is applied to six simulated test cases where it correctly identifies the true dominant scattering mechanism as having greater support from the data in five cases the remaining case is indecisive the approach is also applied to measured backscatter strength data where volume scattering is determined as the dominant scattering mechanism comparison of inversion results with core data indicates the method yields both a reasonable volume heterogeneity size distribution and a good estimate of the sub bottom depths at which scatterers occur

hydrochemical characterisation of water quality in the sarcheshmeh copper complex se iran hydrochemical investigations were conducted to identify variations in surface water chemistry in different parts of the sarcheshmeh copper complex twenty three water samples from mine drainage stream water processing water of the concentrator plant and tailings dam water were collected to understand processes that control the elements mobility changes in trace metal concentrations and variation of major ions show two distinct water types a neutral mine drainage nmd associated with the sarcheshmeh mine waters containing lower trace metal so42 concentrations and neutral ph values and b acid mine drainage amd with waters from tailings impoundments and waste rock dumps corresponding to higher trace metals fe cu zn mo and major anions so42 and cl than the first type with typically acidic ph contents as a result of cu mo sulphides flotation process under alkaline conditions high ph values high mo concentration and low contamination loads of al mn fe cu and cd were observed in reject waters from the concentrator plant sulphide oxidation especially pyrite dissolution precipitation of the secondary minerals and discharge of the reject waters from concentrator plant were some of the most important factors that influence water quality at the tailings impoundments the results of phreeqc speciation and solubility modelling indicated supersaturation of the waters in the tailings impoundments with respect to hydronium jarosite schwertmannite and gypsum

mechanisms of hydrovolcanic pyroclast formation grain size scanning electron microscopy and experimental studies pyroclasts produced by explosive magma water interactions are of various sizes and shapes data from analysis of over 200 samples of hydrovolcanic ash are interpreted by comparison with experimentally produced ash grain size and scanning electron microscopy sem reveal information on the formation of hydrovolcanic pyroclasts strombolian explosions result from limited water interaction with magma and the pyroclasts produced are dominantly centimeter sized with increasing water interaction hydrovolcanism increases in explosivity to surtseyan and vulcanian activity these eruptions produce millimeter to micron sized pyroclasts the abundance of fine ash 63 m diameter increases from 5 to over 30 percent as water interaction reaches an explosive maximum this maximum occurs with interactions of virtually equal volumes of melt and water five dominant pyroclast shape types determined by sem result from hydrovolcanic fragmentation 1 blocky and equant 2 vesicular and irregular with smooth surfaces 3 moss like and convoluted 4 spherical or drop like and 5 plate like types 1 and 2 dominate pyroclasts greater than 100 m in diameter types 3 and 4 are typical of fine ash type 5 pyroclasts characterize ash less than 100 m in diameter resulting from hydrovolcanic fragmentation after strong vesiculation fragmentation mechanisms observed in experimental melt water interactions result from vapor film generation expansion and collapse fragments of congealed melt are products of several alternative mechanisms including stress wave cavitation detonation waves and fluid instability mixing all result in rapid heat transfer these mechanisms can explain the five observed pyroclast shapes stress wave fracturing cavitation of the melt results from high pressure and temperature gradients at the melt water interface simultaneous brittle fracture and quenching produces type 1 pyroclasts type 2 develops smooth fused surfaces due to turbulent mixing with water after fracture and before quenching fluid instabilities promote turbulent mixing of melt and water and produce fine ash this kind of fragmentation occurs during high energy explosions the increased melt surface area due to fine fragmentation promotes high efficiency heat exchange between the melt and water shapes of resulting pyroclasts are determined by maximum surface area type 3 and surface tension effects type 4 type 5 pyroclasts result from nearly simultaneous vesicle burst and melt water fragmentation

composition resolved size distributions of volcanic aerosols in the mt etna plumes 1 particle size distributions for soluble and insoluble species in mt etna s summit plumes were measured across an extended size range 10 nm d 100 m using a combination of techniques automated scanning electron microscopy qemscan was used to chemically analyze many thousands of insoluble particles collected on pumped filters allowing the relationships between particle size shape and composition to be investigated the size distribution of fine silicate particles d 10 m was found to be lognormal consistent with formation by bursting of gas bubbles at the surface of the magma the compositions of fine silicate particles were found to vary between magmatic and nearly pure silica this is consistent with depletion of metal ions by reactions in the acidic environment of the gas plume and vent measurements of the size shape and composition of fine silicate particles may potentially offer insights into preemission synemission and postemission processes the mass flux of fine silicate particles from mt etna released during noneruptive volcanic degassing in 2004 and 2005 was estimated to be 7000 kg d 1 analysis of particles in the range 0 1 d m 100 by ion chromatography shows that there are persistent differences in the size distributions of sulfate aerosols between the two main summit plumes analysis of particles in the range 0 01 m d 0 1 m by scanning transmission electron microscopy stem shows that there are significant levels of nanoparticles in the mt etna plumes although their compositions remain uncertain

world wide delivery of river sediment to the oceans new data and new estimates from old data show that rivers with large sediment loads annual discharges greater than about 15 times 10 6 tons contribute about 7 times 10 9 tons of suspended sediment to the ocean yearly extrapolating available data for all drainage basins the total suspended sediment delivered by all rivers to the oceans is about 13 5 times 10 9 tons annually bedload and flood discharges may account for an additional 1 2 times 10 9 tons about 70 of this total is derived from southern asia and the larger islands in the pacific and indian oceans where sediment yields are much greater than for other drainage basins

source levels of shallow explosive charges experimental measurements are reported in this article for the source levels of 0 82 kg signals underwater sound sus charges detonated at nominal depths of 18 3 91 and 183 m the data were recorded in the farfield using a high resolution digital data acquisition system that provided good reproduction of both the high and low frequency components of the signal from the explosion the results are presented in 1 3 octave bands from 5 630 hz and represent the mean values of samples of at least 30 charges for each depth group the standard deviations were within 1 db for most frequency bands analysis of the distribution of explosion depths indicated that the average detonation depths were consistently deeper than the nominal depths this result was attributed to the effect of the relatively cold water temperatures at the experimental site in addition to the measured source levels estimates for 0 82 kg sus charges at 244 m were scaled from the experimental data using a method suggested by hughes r hu

major ion chemistry of the ganga brahmaputra river system weathering processes and fluxes to the bay of bengal the ganga brahmaputra one of the world s largest river systems is first in terms of sediment transport and fourth in terms of water discharge a detailed and systematic study of the major ion chemistry of these rivers and their tributaries as well as the clay mineral composition of the bed sediments has been conducted the chemistry of the highland rivers upper reaches of the ganga the yamuna the brahmaputra the gandak and the ghaghra are all dominated by carbonate weathering ca mg and hco3 account for about 80 of the cations and anions in the lowland rivers the chambal the betwa and the ken hco3 excess over ca mg and a relatively high contribution of na k to the total cations indicate that silicate weathering and or contributions from alkaline saline soils and groundwaters could be important sources of major ions to these waters the chemistry of the ganga and the yamuna in the lower reaches is by and large dictated by the chemistry of their tributaries and their mixing proportions illite is the dominant clay mineral about 80 in the bedload sediments of the highland rivers kaolinite and chlorite together constitute the remaining 20 of the clays in the chambal betwa and ken smectite accounts for about 80 of the clays this difference in the clay mineral composition of the bed sediments is a reflection of the differences in the geology of their drainage basins the highland rivers weather acidic rocks whereas the others flow initially through basic effusives the ganga brahmaputra river system transports about 130 million tons of dissolved salts to the bay of bengal which is nearly 3 of the global river flux to the oceans the chemical denudation rates for the ganga and the brahmaputra basins are about 72 and 105 tons km yr 1 respectively which are factors of 2 to 3 higher than the global average the high denudation rate particularly in the brahmaputra is attributable to high relief and heavy rainfall

high resolution swath sonar investigation of sand ridge dune and ribbon morphology in the offshore environment of the new jersey margin abstract sand ridges on the northeast us atlantic shelf form in the near shore environment most likely in response to storm driven flows as the holocene transgression has continued the ridges have been transferred to an offshore hydrodynamic regime where currents are not constrained by the coast and storms do not influence bottom currents as frequently or as strongly here we qualitatively and quantitatively investigate the morphology of offshore sand ridges and smaller scale features in an effort to place constraints on bedform development in these deeper waters a recent high resolution swath sonar survey mapped a portion of the new jersey shelf from 20 m water depth to the shelf break 120 m imaging both sand ridges and smaller scaled dunes and ribbons in far greater detail than has been previously possible using a robust statistical analysis we find that the gross morphology of ridges height width length does not change with depth beyond 20 m water depth and changes in ridge orientation generally mirror changes in regional contour orientation hence ridges have not continued to grow since transgression has brought them into the offshore hydrodynamic regime however on the inner shelf 20 m water depth to the mid shelf shore we do find evidence in the ridge shape which has an asymmetry opposite to that seen near shore and in the complex backscatter response that some important modifications to ridges are taking place at these water depths in contrast on the mid shelf from the mid shelf shore to the franklin shore ridges tend to have higher backscatter at the crests implying that these are largely winnowed relict features lineated smaller scale 100 500 m wavelength

the structure and composition of microspheres from the kilauea volcano hawaii microspheres from the plume of the kilauea volcano hawaii display previously unrecognized structural and compositional features indicating that the spheres are concentrically differentiated and at least partially crystalline the surfaces of some spheres display evenly spaced hexagonal sub micrometer grains whose compositions suggest that they may be spinels distinctive prismatic and dendritic structures on the surfaces of the microspheres are remarkably consistent through the population and indicate that the spheres have crystalline outer shells indications of chemical etching are present probably from exposure to hf in the volcanic plume the structures and compositions of the microspheres suggest that they differentiated and then solidified during rapid cooling as they passed through the gradients of temperature chemical composition and redox conditions established in the plume as air diluted the gaseous species evolved from magma

preliminary studies on the geochemistry of the mahanadi river basin india water and suspended and bed sediments were collected during 1986 1987 for the two seasons and analysed to study the geochemistry of the mahanadi river basin which is one of the eight major drainage systems in india the water chemistry reflects the control exercised on weathering by the most abundant lithology namely the carbonates in the basin water composition is in equilibrium with dolomite kaolinite and chlorite xrd studies in suspended and bed sediments show the presence of dolomite kaolinite chlorite and minor quantities of montmorillonite the mahanadi annually delivers 15 74 106t of sediments to the bay of bengal which is high compared to its basin size the dissolved load dominates over physical load by a factor of 4 with 95 of the transport taking place in the monsoon season the basin is characterised by an erosion rate of 138 24 t km 2 yr 1 with a lowering rate of 0 31 mm yr 1 textural studies indicate that the bed sediments are relatively coarser grained than the suspended sediments due to reworking the sediments are finer downstream fe mn cu zn and pb concentrations in the sediments are higher compared to the other peninsular indian rivers eventhough mahanadi transports annually to the bay of bengal 10 of the total load by other indian rivers and its weathering in a complex geological terrain with rich mineral deposits controls to a larger extent the chemistry of the sediments in the bay of bengal

the transition of spatter to lava like body in lava fountain deposits features and examples from the cabezo segura volcano calatrava spain abstract the cabezo segura ii volcanic cone calatrava volcanic province iberian microplate comprises proximal wall deposits with a well defined crater wall unconformity and crater fill deposits the complex volcanic succession that shows evidence of several eruptive episodes was built by magmatic and hydrovolcanic explosions of different styles strombolian hawaiian sub plinian and phreato strombolian generated from a multiple feeder ultrabasic dyke intra crater rock units at the volcano summit include spatter deposits together with up to 10 m thick and more than 200 m long lava like bodies geological logs for the main lava like bodies define a characteristic facies model that involves a central lava like mass which grades vertically into a transition zone of apparently coherent spatter then dense spatter and finally into vuggy spatter deposits these units are inferred to have formed during pulsating lava fountain type explosive eruptions the depicted facies distribution being the result of progressive increase in welding grade and densification of the spatter in response to variations in the accumulation rate their field features may be used as a guide for the precise identification of vent sites in deposits of hawaiian eruptions also structures like those here recognised that might have survived in lava like flows could be of help to identify when lava producing eruptions represented an explosive hawaiian event lava fountains and not a purely effusive event

environmental geochemistry and quality assessment of mine water of jharia coalfield india a long mining history and unscientific exploitation of jharia coalfield caused many environmental problems including water resource depletion and contamination a geochemical study of mine water in the jharia coalfield has been undertaken to assess its quality and suitability for domestic industrial and irrigation uses for this purpose 92 mine water samples collected from different mining areas of jharia coalfield were analysed for ph electrical conductivity ec major cations ca2 mg2 na k anions f cl hco3 so4 2 no3 dissolved silica h4sio4 and trace metals the ph of the analysed mine water samples varied from 6 2 to 8 6 indicating mildly acidic to alkaline nature concentration of tds varied from 437 to 1 593 mg l 1 and spatial differences in tds values reflect the variation in lithology surface activities and hydrological regime prevailing in the region so4 2 and hco3 are dominant in the anion and mg2 and ca2 in the cation chemistry of mine water high concentrations of so4 2 in the mine water of the area are attributed to the oxidative weathering of pyrites ca mg so4 and ca mg hco3 are the dominant hydrochemical facies the drinking water quality assessment indicates that number of mine water samples have high tds total hardness and so4 2 concentrations and needs treatment before its utilization concentrations of some trace metals fe mn ni pb were also found to be above the desirable levels recommended for drinking water the mine water is good to permissible quality and suitable for irrigation in most cases however higher salinity residual sodium carbonate and mg ratio restrict its suitability for irrigation at some sites

features of crustal structure under the canary islands abstract the data and interpretation of a seismic refraction project carried out in the canary islands in 1977 and 1979 are presented the moho is reached at about 15 km under fuerteventura gran canaria and tenerife whereas under lanzarote a value of 11 km has been found the velocity at the surface varies even within one island from 2 8 to 4 4 km s there are variations in the velocity of the main crustal layer under the volcanic deposits a continuous velocity depth function seems to be more appropriate for the island of tenerife contrary to fuerteventura lanzarote and gran canaria which seem to have a layered structure there is evidence for pronounced structural differences between lanzarote and fuerteventura the mantle velocity has a value of about 8 0 km s under the western islands whereas a very low value of 7 4 km s has been found under lanzarote and fuerteventura despite the clear structural differences between the islands our results leave little doubt about the oceanic character of all the islands the differences between the eastern and western group may be due to the islands being situated close to the african continental margin the seismic velocities under the volcanic deposits do not support the idea of a common basement for all the islands they rather suggest independent volcanic edifices finally a comparison of the structure of the crust under the canary islands with that under other volcanic islands reveals remarkable similarities

a model data comparison for low frequency bottom backscatter this article describes a model for bottom backscattering strength applicable over the frequency range 100 1000 hz the model includes backscatter due to both a rough water sediment interface and internal sediment inhomogeneities i e sediment volume scattering within an upward refracting sediment the net result is predictions for bottom backscattering strength that depend on the following frequency sound speed of the water near the water sediment interface density ratio sound absorption within the sediment near surface sound speed gradient within the sediment two interfacial roughness parameters and a parameter proportional to the scattering cross section of a unit volume of sediment the sediment sound speed profile is specified in terms of near surface values for the sound speed ratio and gradient salient features of the modeled backscatter strength include marked departures from lambert s law for sediments with sound speed ratios greater than 1 1 5 db oscillations as a function of grazing an

solute geochemistry and its sources of the groundwaters in the qinghai lake catchment nw china major ion compositions were analyzed in 65 groundwater samples to decipher water quality solute geochemistry and sources of groundwater within the qinghai lake catchment ne tibetan plateau groundwaters were slightly alkaline with ph varying from 7 2 to 8 7 the total dissolved solids tds varied over two orders of magnitude from fresh 88 to brackish 12 with a mean value of 672 mg l higher than river waters within the qinghai lake catchment and river waters draining the himalayas and the southeastern tibetan plateau most of the samples approximately 80 were the ca 2 mg 2 hco 3 type and suitable for drinking and irrigation some of the lakeside the buha and the qinghai lake water were cl type and not suitable for drinking and irrigation water quality of hargai and shaliu samples was better than the others rock weathering ion exchange and precipitation are the major geochemical processes responsible for the solutes in the groundwater within the qinghai lake catchment anthropogenic input to the groundwater is minor the forward models on the input of groundwaters from various sources showed that the contributions were 40 1 for carbonate weathering 29 0 for evaporite dissolution 16 8 for atmospheric input and 14 1 for silicate weathering of the total dissolved cations for the whole catchment evaporite dissolution was dominating in the lakeside the buha and the daotang samples contributing 15 3 45 9 20 4 61 1 and 21 3 63 9 of the total dissolved cations respectively carbonate weathering was dominated in the shaliu and the hargai samples contributing 23 9 71 7 and 31 8 95 4 of the total dissolved cations respectively the result also demonstrated that carbonate weathering had higher contribution to the groundwaters than silicate weathering

geochronology and stratigraphy of the roque nublo cycle gran canaria canary islands the roque nublo cycle of pliocene age is the second main cycle of subaerial volcanic activity in gran canaria during this cycle a stratovolcano at least 2500 m high developed in the central part of the island its volcanic products covered an area of about 540 km 2 the detailed stratigraphy of the roque nublo cycle together with a magnetostratigraphic study and six new k ar dates which complement 22 previously published ones have led to the reconstruction of the volcanic history of this cycle in which six main stages have been distinguished the revised chronology of the roque nublo cycle implies an overlap in age with the earliest rocks of the third cycle of subaerial activity in gran canaria no volcanic hiatus occurred between the second and third cycles as was previously thought to be the case

pele s hairs and tears natural probe of volcanic plume we present a detailed petrographic study of pele s hairs and tears sampled from masaya volcano nicaragua this study provides new observations of these little known pyroclastic objects using both secondary electron images sei and back scattering electron images bsei our work shows that pele s tears can be associated with pele s hairs after their formation tears can be trapped on the walls and or in the cavities of pele s hairs moreover chemical investigations of the pele s hairs and tears highlight the presence of a chemical zonation the edge of these tears and hairs show a siliceous enrichment allowing us to quantify the interaction time of the silicate glass with acid gases in the volcanic plume this study confirms the syneruptive and post eruptive volatile exsolution from pele s hairs and tears

physical parameters governing the formation of pele s hair and tears the physical parameters that affect the formation of pele s hair and pele s tears during lava fountaining are discussed experiments on ink jets produced from a nozzle under different weber number we and reynolds number re show the following results if re is relatively large compared with we an ink droplet is produced however if re is relatively small and we is large the spurting ink becomes thread like i define the pele number pe as we re which is expressed as v 0 where v is the spuring velocity from an erupting vent and are viscosity and interfacial tension of the erupting magma and and 0 are density of air and magma the experimental results from ink jets suggest that pele s hair will be produced for larger pe while pele s tears are very likely produced for relatively small pe i conclude that pele s hair could be produced when the spurting velocity of erupting magmas is high and pele s tears when it is relatively low as an additional point of interest the similarity of sem photographs of the characteristic shape of pele s hair to those of the failed products of commercial glass fibre are shown

acoustic scattering from mud volcanoes and carbonate mounds submarine mud volcanoes occur in many parts of the world s oceans and form an aperture for gas and fluidized mud emission from within the earth s crust their characteristics are of considerable interest to the geology geophysics geochemistry and underwater acoustics communities for the latter mud volcanoes are of interest in part because they pose a potential source of clutter for active sonar close range single interaction scattering measurements from a mud volcano in the straits of sicily show scattering 10 15db above the background three hypotheses were examined concerning the scattering mechanism 1 gas entrained in sediment at near mud volcano 2 gas bubbles and or particulates emitted in the water column 3 the carbonate bio construction covering the mud volcano edifice the experimental evidence including visual acoustic and nonacoustic sensors rules out the second hypothesis at least during the observation time and suggests that for this particular mud volcano the dominant

geochemical and environmental risk assessment of hazardous elements in river sediment the peninsular river damodar is the life line of eastern india facing critical pollution problems due to sewage industrial waste disposal as well as coal mining along the river valley sediment samples were collected and analyzed for various geochemical phases of hazardous elements and associated environmental risks were evaluated this paper provides chemical fractionation of nine cd mn zn ni cu pb co cr fe elements from river sediment by using tessier five step sequential extraction method the study was aimed 1 to understand dynamics and mobility of elements in different geochemical fractions 2 to evaluate bioavailability and ecological risk of these elements by rac and 3 to identify contaminated and uncontaminated sites by using cluster analysis the result of the study revealed maximum bioavailable fraction was that of cd bioavailable elements in studied sediment followed the order cd 23 76 mn 14 19 zn 13 54 ni 12 82 cu 7 12 pb 7 05 co 6 09 fe 4 98 cr 2 03 maximum of the reducible fraction was found for fe 14 38 while in organic fraction cu 11 25 was maximum residual fraction dominates in all elements with a maximum percentage of 83 85 for co risk assessment by rac reveals that the river was under medium risk due to cd mn zn and ni while at low risk for rest of the elements cluster analysis shows that three sampling sites were highly contaminated three were moderately contaminated and six were contaminated while only one site was uncontaminated

a new approach to kimberlite facies terminology using a revised general approach to the nomenclature of all volcanic rocks and deposits descriptive to genetic although kimberlite pipes bodies are usually the remains of volcanic vents in vent deposits and subvolcanic intrusions the terminology used for kimberlite rocks has largely developed independently of that used in mainstream volcanology existing kimberlite terminology is not descriptive and includes terms that are rarely used used differently and even not used at all in mainstream volcanology in addition kimberlite bodies are altered to varying degrees making application of genetic terminology difficult because original components and depositional textures are commonly masked by alteration this paper recommends an approach to the terminology for kimberlite rocks that is consistent with usage for other volcanic successions in modern terrains the eruption and emplacement origins of deposits can often be readily deduced but this is often not the case for old variably altered and deformed rock successions a staged approach is required whereby descriptive terminology is developed first followed by application of genetic terminology once all features including the effects of alteration on original texture and depositional features together with contact relationships and setting have been evaluated because many volcanic successions consist of both primary volcanic deposits as well as volcanic sediments terminology must account for both possibilities

sequence and eruptive style of the 1783 eruption of asama volcano central japan a case study of an andesitic explosive eruption generating fountain fed lava flow pumice fall scoria flow and forming a cone the 3 month long eruption of asama volcano in 1783 produced andesitic pumice falls pyroclastic flows lava flows and constructed a cone it is divided into six episodes on the basis of waxing and waning inferred from records made during the eruption episodes 1 to 4 were intermittent vulcanian or plinian eruptions which generated several pumice fall deposits the frequency and intensity of the eruption increased dramatically in episode 5 which started on 2 august and culminated in a final phase that began on the night of 4 august lasting for 15 h this climactic phase is further divided into two subphases the first subphase is characterized by generation of a pumice fall whereas the second one is characterized by abundant pyroclastic flows stratigraphic relationships suggest that rapid growth of a cone and the generation of lava flows occurred simultaneously with the generation of both pumice falls and pyroclastic flows the volumes of the ejecta during the first and second subphases are 0 21 km3 dre and 0 27 km3 dre respectively the proportions of the different eruptive products are lava cone pumice fall 84 11 5 in the first subphase and lava cone pyroclastic flow 42 2 56 in the second subphase the lava flows in this eruption consist of three flow units l1 l2 and l3 and they characteristically possess abundant broken phenocrysts and show extensive welding texture these features as well as ghost pyroclastic textures on the surface indicate that the lava was a fountain fed clastogenic lava a high discharge rate for the lava flow up to 106 kg s may also suggest that the lava was initially explosively ejected from the conduit the petrology of the juvenile materials indicates binary mixing of an andesitic magma and a crystal rich dacitic magma the mixing ratio changed with time the dacitic component is dominant in the pyroclasts of the first subphase of the climactic phase while the proportion of the andesitic component increases in the pyroclasts of the second subphase the compositions of the lava flows vary from one flow unit to another l1 and l3 have almost identical compositions to those of pyroclasts of the first and second subphases respectively while l2 has an intermediate composition suggesting that the pyroclasts of the first and second subphases were the source of the lava flows and were partly homogenized during flow the complex features of this eruption can be explained by rapid deposition of coarse pyroclasts near the vent and the subsequent flowage of clastogenic lavas which were accompanied by a high eruption plume generating pumice falls and or pyroclastic flows

discrimination between discrete and continuum scattering from the sub seafloor there is growing evidence that seabed scattering is often dominated by heterogeneities within the sediment volume as opposed to seafloor roughness from a theoretical viewpoint sediment volume heterogeneities can be described either by a fluctuation continuum or by discrete particles in at sea experiments heterogeneity characteristics generally are not known a priori thus an uninformed model selection is generally made i e the researcher must arbitrarily select either a discrete or continuum model it is shown here that it is possible to acoustically discriminate between continuum and discrete heterogeneities in some instances for example when the spectral exponent 3 4 the volume scattering cannot be described by discrete particles conversely when 3 2 the heterogeneities likely arise from discrete particles furthermore in the range 2 3 4 it is sometimes possible to discriminate via physical bounds on the parameter values the ability to so discriminate is important because there are few tools for measuring small scale o 10 2 to 10 1 m sediment heterogeneities over large areas therefore discriminating discrete vs continuum heterogeneities via acoustic remote sensing may lead to improved observations and concomitant increased understanding of the marine benthic environment

a plinian treatment of fallout from hawaiian lava fountains a new model is presented which simulates the dispersal and deposition of material from a hawaiian eruption column the model treats the hawaiian column as a coarse grained plinian column and uses a modified version of the wilson and walker wilson l walker g p l 1987 explosive volcanic eruptions vi ejecta dispersal in plinian eruptions the control of eruption conditions and atmospheric properties geophys j r astron soc 89 657 679 plinian pyroclast dispersal model to simulate the fall out of material during a hawaiian eruption the model results are found to be in good agreement with independent estimates of various parameters made for the 1959 kilauea iki eruption of kilauea volcano the close agreement between the model results and these independent estimates shows that dynamically hawaiian eruptions are indistinguishable from plinian eruptions the major differences in the styles and deposits of these two types of eruptions are accounted for by differences in the mass fluxes and gas contents of the erupting magmas and most fundamentally by differences in the grainsize distribution of the erupted clasts plume heights predicted by the model are greater than those found for previous models of hawaiian eruptions this is because previous models did not allow for the progressive fall out of particles from the plume and more importantly made no correction for the velocity disequilibrium between gas and clasts when the grainsize distribution is coarse

chemical and isotopic characteristics of the euphrates river water syria factors controlling its geochemistry hydrochemical parameters and stable isotope 18o and 2h ratios were monitored at 10 stations along the euphrates river er within the syrian reach during 2004 2006 the average concentrations of major ions in the er were comparable to those of semi arid and arid zone rivers temporal variations of major ion concentrations were small at the first two upper sites and more pronounced at the lower downstream stations temporal fluctuations of stable isotope ratios at the first two upper sites were identical and have a distinct opposite evolution trend to those of the remaining downstream stations with depleted values during summer autumn and enriched values during february may salinity and stable isotope values of the er systemically increase with the distance downstream with sharp enrichments in stable isotope values at al assad lake primarily because of evaporation from the lake the chemical and isotopic properties of the er water suggest negligible role of precipitation and local runoff compared with evaporation cluster analysis in q mode resulted in classifying the major ions into the most predominant species so42 hco3 cl ca2 and na liberated as a result of rock water interactions or dissolution of soluble evaporate salts and the less abundant ions mg2 k no3 and sio2 partially imported from different sources rainfall silicate weathering and anthropogenic pollution factor analysis suggests that the geochemistry of the er water is mainly controlled by four factors rock weathering or salt dissolution dissolved co2 partial pressure water temperature t and evaporation these factors explain more than 80 of the total variance in the data matrix

the cerro chopo basaltic cone costa rica an unusual completely reversed graded pyroclastic cone with abundant low vesiculated cannonball juvenile fragments cerro chopo is a partially dissected asymmetric isolated pleistocene pyroclastic cone located in front of the cordillera de guanacaste in northern costa rica the cone consists of similar to 0 09 km 3 of basaltic tephra as well as similar to 0 14 km 3 of lateral lava flows tephras are tholeiitic high alumina olivine basalts and represent minor degrees 5 of crystal fractionation major and trace element compositions are consistent with minor fractionation from a mixture of e morb and oib magmas the cone walls consist of alternating coarser and finer grained well sorted beds containing continuous spectra from breadcrust to smooth surface cannonball bombs but also less frequent cylindric fragments and broken clasts cerro chopo is unique compared to other typical scoria cones because it contains ubiquitous reversely graded layers scarcity of scorias and instead a wide range of dense 1 54 2 49 g cm 3 poorly vesicular 5 40 vol juvenile clast morphologies including abundant cannonball juvenile bombs and lapilli these are bombs with concentric layers surrounding vesiculated dense and lapillistone cores and are interpreted to have repeatedly recycled through the vent the cannonball bombs and lapilli have been described in a few scoria cones but are much less abundant than in chopo the reverse graded sequences are interpreted to have resulted from decreasing explosivity at the vent in addition to local failure of tephra on slopes as the consequence of grain flows elsewhere on the earth most of the poorly vesiculated spherical bombs particularly cannonball accretionary composite and core bombs and its equivalent lapilli size pelletal spinning droplets and ellipsoidal lapilli are all related to mafic to ultramafic low viscosity magmas c 2010 elsevier b v all rights reserved

complex bombs of phreatomagmatic eruptions role of agglomeration and welding in vents of the 1886 rotomahana eruption tarawera new zealand 1 basaltic bombs ejected from a rotomahana crater during the 1886 tarawera eruption in new zealand are of two fundamental types cored bombs which have single large fragments generally of rhyolite wall rock material as their cores and loaded bombs which contain abundant small fragments dispersed through the bombs similar lithic bearing bombs are common products of other phreatomagmatic eruptions worldwide cored bombs originate when a large wall rock fragment is entrained in basaltic melt and then ejected with an adhering skin of basalt in contrast loaded bombs are constructed by agglomeration of multiple fragments of basalt among which smaller rhyolitic wall rock fragments are dispersed different styles and rates of bomb loading are reflected in the bombs textures and compositions these textures provide insight into the nature of fragmentation during the eruption the processes of recycling that produce multiply ejected clasts versus recapitulated ones those where early formed clasts were reingested in magma and then formed the cores of new bombs the degree and timescale of interaction of magma with vent walls and the timescales over which lithic material from the vent walls is incorporated into complex bombs prior to their ejection because fragments of rhyolitic pumice are readily refused their condition constrains estimates of the timing of fragmentation and agglomeration the presence of nonfused rhyolite pumice within many loaded bombs implies that the processes forming and quenching the bombs cannot have exceeded several seconds in contrast other bombs contain patches of compositionally modified basalt with isolated rhyolite derived feldspar xenocrysts that indicate complete fusing melting and assimilation of entrained rhyolitic debris the bomb population overall indicates that conditions within this rotomahana vent were thermally and physically heterogeneous and that recycling of debris was ubiquitous both as recycling of large individual clasts and by fallback and aggregation of material which was reingested in magma before being reejected as new bombs

premixing of magma and water in mfci experiments experimental studies have been performed to evaluate pre explosive water melt mixes with respect to explosive volcanic molten fuel coolant interaction mfci i e phreatomagmatic explosion remolten ultrabasic volcanic rock was used as a magma simulant measurement of the explosion intensity was used to determine optimal premixing conditions a well defined optimal range was found for the hydrodynamic mixing energy differential flow speed of 4 2 m s as well as for the water melt mass ratio 0 03 to 0 04 under experimental conditions the mass flux of water had a minor influence on the explosion intensity additionally transparent mixing experiments with silicon oil and inked water were carried out they indicate a direct dependence of the pre explosive water melt interface area on the explosion intensity the experimental results show that the contact conditions of water and melt required for explosive mfci may easily be established in natural volcanic systems thus explosive mfci is a probable mechanism of explosive volcanism

hydrochemistry of reservoirs of damodar river basin india weathering processes and water quality assessment water samples collected from the six reservoirs of damodar river basin in pre and post monsoon have been analysed to study the major ion chemistry and the weathering and geochemical processes controlling the water composition ca na and hco3 dominate the chemical composition of the reservoir water the seasonal data shows a minimum concentration of most of the ions in post monsoon and a maximum concentration in pre monsoon seasons reflecting the concentrating effects due to elevated temperature and increased evaporation during the low water level period of the pre monsoon season water chemistry of the reservoirs strongly reflects the dominance of continental weathering aided by atmospheric and anthropogenic activities in the catchment area higher concentration of so4 and tds in panchet durgapur and tenughat reservoirs indicate mining and anthropogenic impact on water quality the high contribution of ca mg to the total cations high concentration of dissolved silica relatively high na k tz ratio 0 3 and low equivalent ratio of ca mg na k suggests combined influence of carbonate and silicate weathering kaolinite is the possible mineral that is in equilibrium with the water implying that the chemistry of reservoir water favours kaolinite formation the calculated values of sar rsc and sodium percentage indicate the excellent to good quality of water for irrigation uses

major ion geochemistry and nutrient behaviour in the mixing zone of the changjiang yangtze river and its tributaries in the three gorges reservoir inorganic ions and nutrients were measured at different depths of the xiangxi and daninghe rivers to explore the mixing processes of representative bays in the three gorges reservoir tgr hco 3 and ca 2 are the dominant ions carbonate weathering is the most important mechanism controlling the ion water chemistry however important differences exist between the main channel and its tributaries major ion levels in the tgr bays depend on hydrological mixing results show that the major ions of ca 2 mg 2 na k sr 2 so 4 2 and cl show chemically conservative behaviour during transit through the bays of the tgr this means the ions can be used as tracers in the same way that salinity is used in estuaries to explore behaviour of other non conservative elements and to indicate specific source waters in contrast nutrients are not conserved in the mixing zone the mixing of the main channel and tributaries and biological utilization in backwater reaches were the key factor controlling nutrient distributions in xiangxi and daninghe bays copyright 2010 john wiley sons ltd

pele s tears and spheres examples from kilauea iki abstract pele s tears are a well known curiosity commonly associated with low viscosity basaltic explosive eruptions however detailed studies of these pyroclasts are rare and thus there is no full explanation for their formation these intriguing pyroclasts have smooth glassy surfaces vesiculated interiors 30 and fluidal morphologies trending towards teardrops and then spheres as they decrease in size to

maar diatreme phreatomagmatism at hopi buttes navajo nation arizona usa remnants of an extensive maar diatreme volcanic field are magnificently exposed at various depths of erosion in the hopi buttes volcanic field of northeastern arizona field and petrographic studies of both the maar and diatreme elements of a selection of volcanoes within the field show that 1 lower sections of the maar rim sequences are typically rich in sandy mudrock derived from the pre eruptive mio pliocene bidahochi formation and the muddy bidahochi sediment was soft and wet at the time of maar eruptions 2 beds higher within the rims contain generally increased proportions of sandstone clasts from the triassic wingate formation in the diatremes late emplaced breccia has deeper seated lithics than more marginal breccia emplaced earlier and 3 many vents are topped by megacryst enriched scoria and spatter and deep seated xenoliths are known only from upper diatreme and craterfilling tephra these observations show that 1 eruptions at hopi buttes involved interaction of magma with unconsolidated mudrock at shallow levels and the phreatomagmatic processes that provided the bulk of the energy involved in the violent eruptions were driven by the interaction of magma and wet sediment 2 the locus of explosive activity migrated downward as eruptions progressed and 3 the closing stage of many eruptions was characterized by rapid magma rise and relative depletion of water

a rare occurrence of a crater filling clastogenic extrusive coherent kimberlite victor northwest ontario canada kimberlite pipes can contain significant proportions of dark and dense kimberlite that have mostly been interpreted as intrusive coherent hypabyssal in origin this study reports a well documented occurrence of a fresh intra crater clastogenic extrusive coherent kimberlite that is concluded to have formed as a result of lava fountaining this paper focuses on a dark dense competent generally crystal rich massive kimberlite unit within the victor northwest kimberlite pipe ontario canada using a comprehensive volcanological and petrographic analysis of all available drill cores it is shown that this unit has a fresh well crystallised coherent groundmass and is extrusive and pyroclastic in origin the proposed clastogenic coherent extrusive origin is based on deposit morphology gradational contacts to enveloping pyroclastic units as well as the presence of remnant pyroclast outlines and angular broken olivines this paper and an increasing number of other studies suggest that fragmental extrusive coherent kimberlite in intra crater settings may be more common than previously thought the emplacement history and volcanology of these pipes need to be reconsidered based on the emerging importance of this particular kimberlite facies

comment on development of spheroid composite bombs by welding of juvenile spinning and isotropic droplets inside a mafic eruption column by carracedo sanchez et al 2009 abstract pelletal and spinning lapilli as well as concentric shelled lapilli bombs are present in ultra alkaline rocks worldwide there are well established models for generation of those pyroclasts in diatreme conduit leading to the formation of subvolcanic pyroclastic rocks i e tuffisites by diatremic fluidisation in contrast carracedo sanchez et al 2009 introduced a completely different model for all the above pyroclasts and composite concentric shelled bombs in particular in the strombolian deposits of cabezo segura ii cs ii calatrava spain in their model the pyroclasts are formed in a strombolian eruptive column on the basis of our observations and physical chemical constraints we contend that this model is not feasible the authors aa model requires agglutination accretion by sintering in the eruption column keeping the particles in a partially molten state we find that composite bombs from cs ii show evidence for very rapid quenching of the melt preventing sintering which in any case is impossible in a convective region where the temperature will be reduced below the solidus of the melt analysis of terminal velocity indicates that it would be possible to transport pelletal lapilli in a strombolian thrust region but dense between 2 25 and 2 85 g cm 3 lapilli and bombs cannot reach a convective region stage 3 of the aa s model which in any case is unlikely to exist at cs ii by contrast pelletal spinning and concentric shelled lapilli and composite bombs can be erupted but their formation does not depend on the surficial extrusion mechanism the presence of carbonatite at cs ii indicates juvenile co 2 to be fundamental and indicative of diatremic fluidisation concentric shelled bombs composed of agglutinated pelletal and spinning lapilli are interpreted as a development in the upper diatreme

transgressive and highstand systems tracts and post glacial transgression the east china sea abstract the late pleistocene holocene depositional sequence on the shelf in the east china sea ecs is interpreted on the basis of the analyses of four sediment cores and high resolution seismic reflection sub bottom profiler records along a ne sw across shelf transect sedimentary strata deposited above a lowermost planar erosional surface that was formed during sea level fall of the last glacial are divided into two units along a ne sw across shelf transect changjiang okinawa the lower unit is characterized by seaward dipping tangential clinoforms with a thickness of 30 40 m at mid shelf depths and less than 30 m beneath the outer shelf prograding clinoforms are more obvious in mid shelf environments the upper unit is characterized by an upper transparent layer that is formed into ridge and swale topography the boundary between the upper and lower units is sharp and erosional surficial sediments taken by cores from the central ecs shelf are also divided into two facies a sandy facies consisting of sand or sandy gravel with moderately abundant molluscan shell fragments and a muddy facies comprising mud intercalated with thin sand layers the sandy facies is widely distributed on the middle to outer shelf seafloor and has a measured thickness of 30 cm up to several metres radiocarbon ages of molluscan shells in this sediment are less than approximately 10 ka bp except for ages from basal shell lag deposits which are 10 40 ka bp the muddy facies underlies the sandy facies and has radiocarbon ages of 2 7 2 9 ka bp previous work and 20 38 ka bp this study and tl ages of 27 50 ka bp previous work the boundary between these lithologic units is an erosional sharp contact the sandy and muddy facies are correlated with the upper and lower seismic units respectively the lower unit is characterized by prograding clinoforms and is interpreted to represent deltaic or nearshore tidal ridge sediments of the paleo changjiang river that were deposited during the last glacial lowstand of sea level as a lowstand systems tract the underlying erosional surface is interpreted to be a sequence boundary formed as a regressive marine erosional surface during the fall of sea level the erosional boundary between the lower and upper units is interpreted as a transgressive surface of erosion formed during the subsequent rise of sea level the upper unit has a modern sand ridge topography and is interpreted to represent offshore shelf sand ridges of the transgressive to highstand systems tract

geochemical factors controlling the chemical nature of water and sediments in the gomti river india r mode factor analysis of the recently acquired data on water and sediment chemistry has been performed basic chemical parameters have been merged together which aid in interpreting a few empirical geochemical factors controlling the chemical nature of water and sediments of the gomti river a major himalayan tributary of the ganges drainage basin water chemistry seems to be controlled by three factors bicarbonate rainfall and silicate and phosphate factors sediment chemistry is largely controlled by the following four factors clay adsorption desorption fe mn hydroxide and mercury factors these factors show spatial and temporal variability in terms of their r scores

mechanism of formation of volcanic bombs insights from a pilot study of anisotropy of magnetic susceptibility and preliminary assessment of analytical models volcanic bombs and achneliths are a special type of pyroclastic fragments formed by mildly explosive volcanic eruptions models explaining the general shapes of those particles can be divided in two broad categories the most popular envisages the acquisition of shapes of volcanic bombs as the result of the rush of air acting on a fluid clot during flight and it includes many variants the less commonly quoted model envisages their shapes as the result of forces acting at the moment of ejection of liquid from the magma pool in the conduit experiencing an almost negligible modification through its travel through air quantitative evidence supporting either of those two models is limited in this work i explore the extent to which the anisotropy of magnetic susceptibility ams might be useful in the study of mechanisms of formation of volcanic bombs by comparing measurements made on two spindle and two bread crusted bombs the results of this pilot study reveal that the degree of anisotropy of spindle bombs is larger and their principal susceptibility axes are better clustered than on bread crusted bombs also the orientation of the principal susceptibility axes is consistent with two specific models one of the in flight variants and the general ejection model consequently the reported ams measurements albeit limited in number indicate that it is reasonable to focus attention on only two specific models to explain the acquisition of the shapes of volcanic bombs based on a parallel theoretical assessment of analytical models a third alternative is outlined envisaging volcanic bomb formation as a two stage process that involves the bursting of large m gas bubbles on the surface of a magma pond the new model advanced here is also consistent with the reported ams results and constitutes a working hypothesis that should be tested by future studies richer in data fortunately since this work also establishes that ams can be used to determine magnetic fabric in small size samples the possibility to expand this study to a larger collection of bombs is granted

cryptoachneliths hidden glassy ash in composite spheroidal lapilli abstract cryptoachneliths perceptible by means of electron microscopy but unresolved under the optical microscope occur unnoticed inside spheroidal lapilli of ultrabasic composition of the cabezo segura volcano calatrava volcanic province spain the cryptoachneliths are glassy spherical particles that have compositions of al rich silicate with minor amounts of fe ca and other elements the smallest cryptoachneliths of 1 m microachneliths and homogeneous less regular masses of similar composition nano and microachneliths welded each other or to other types of volcanic particles crystals crystal fragments spinning droplets cognate lithic clasts etc to form spheroidal lapilli and even bomb size clasts within proximal fall deposits of the cabezo segura volcano the welding processes took place inside the eruptive column previous to the fall of the spheroidal lapilli on top of the volcanic cone the presence of the cryptoachneliths implies that lapilli and even bomb size tephra within deposits formed during explosive eruptions of low viscosity basic to ultrabasic magmas should be carefully examined in order to establish key parameters of eruption dynamics like size amount and distribution of juvenile fine particles

on the welding of pyroclasts from very low viscosity magmas examples from kimberlite volcanoes abstract lithofacies in kimberlite pipes in southern africa exhibit features consistent with welded pyroclastic rocks these include flared conduit filling geometries abundant lithic clasts lithic clast layers subhorizontal clast fabrics gradational contacts with volcaniclastic rocks and sintered and coalesced globular ash and lapilli and melt coated particles the welding dynamics of kimberlite pyroclasts differ from those of glassy vesiculated pyroclasts in silicic volcanic systems low melt viscosity 0 1 pa s results in the efficient separation of volatiles and melt and the breakup of magma into nonvesicular spherical droplets the glassy state is difficult to form in silica deficient magmas because the crystallization kinetics are fast in low viscosity melts three pyroclastic lithofacies are recognized that primarily relate to the state of the initial melt phase in the pyroclasts on deposition 1 densely welded kimberlite forms where the initial melt phase in pyroclasts remains as pure mel

the influence of conduit processes on changes in style of basaltic plinian eruptions tarawera 1886 and etna 122 bc basaltic volcanism is most typically thought to produce effusion of lava with the most explosive manifestations ranging from mild strombolian activity to more energetic fire fountain eruptions however some basaltic eruptions are now recognized as extremely violent i e generating widespread phreatomagmatic subplinian and plinian fall deposits we focus here on the influence of conduit processes especially partial open system degassing in triggering abrupt changes in style and intensity that occurred during two examples of basaltic plinian volcanism we use the 1886 eruption of tarawera new zealand the youngest known basaltic plinian eruption and the only one for which there are detailed written eyewitness accounts and the well documented 122 bc eruption of mount etna italy and present new grain size and vesicularity data from the proximal deposits these data show that even during extremely powerful basaltic eruptions conduit processes play a critical role in modifying the form of the eruptions even with very high discharge and presumably ascent rates partial open system behaviour of basaltic melts becomes a critical factor that leads to development of domains of largely stagnant and outgassed melt that restricts the effective radius of the conduit the exact path taken in the waning stages of the eruptions varied in response to factors which included conduit geometry efficiency and extent of outgassing and availability of ground water but a relatively abrupt cessation to sustained high intensity discharge was an inevitable consequence of the degassing processes

linking variable explosion style and magma textures during 2002 at stromboli volcano italy microtextural characteristics of fresh ejecta from stromboli volcano were examined from three periods of differing eruption style and intensity in 2002 activity shifted from relatively weak and infrequent ash charged explosions during january through may into two broad cycles of waxing activity in june through late september and late september through december followed by the onset on 28 december of the 2002 2003 effusive eruption analyzed sets of lapilli from may september october and 28 december show contrasts in the physical properties of magma resident in the shallow conduit during this range of activity three distinct textures are observed among the analyzed pyroclasts low density ld with an abundance of subspherical bubbles the presence of large irregularly shaped bubbles and a light to transparent glass matrix transitional texture tt with an intermediate number of subspherical bubbles a high frequency of large irregularly shaped bubbles and a honey colored glass matrix and high density hd with sparse relatively small bubbles conspicuous large irregular bubbles and a dark glass matrix observational and quantitative data density vesicle size indicate that these textures are linked through variable residence time in stromboli s shallow conduit with an ongoing evolution from ld to hd magma calculations suggest that residual ld magma will evolve to hd texture in a period of hours to days contrasting amounts of the ld tt and hd magmas are present in each sample with the most tt in may the most ld in september october and the most hd in december this implies that the shallow magma had a different rheology at each collection period the viscosity of ld and hd magmas are calculated to be in the range of 2 000 to 2 600 and 3 000 to 5 000 pa s respectively which with their changing proportions must have implications for rates of bubble slug ascent and processes of fragmentation this study suggests that an increasing maturity of magma in stromboli s shallow conduit with resultant increase in viscosity feeds back to reduce the intensity of explosions whereas a steady flux of ld magma favors more powerful explosions

trace elements in the particulate phase of the plume of masaya volcano nicaragua masaya volcano nicaragua has been passively degassing since 1993 this gas crisis provides a unique opportunity for investigating the degassing of magmatic volatiles here we studied the chemical composition of the volcanic particulate phase collected directly from the plume the objective was to gain new insights into the volatilities and emission rates of trace elements the results indicate enrichments in the aerosol phase of all analyzed trace elements including not only those known to be volatile such as cu and te but also elements considered as refractory such as rare earth elements rees and th rees were fractionated with a significant enrichment of light rare earth elements lrees over heavy rare earth elements hrees this pattern suggests degassing of lrees as chlorides in general the emission of most trace elements in volcanic plumes is governed by the primary degassing of chloride compounds however sem eds data and chemical analysis of aerosol filters allow us to state that trace elements can also be released as sulphate and chloro sulphate compounds the trace element emission rates at masaya are significant and place this volcano as a major gas emitter however for some elements like cu masaya s contribution to the global volcanic flux seems disproportionate probably pointing to the poor dataset available for other degassing volcanoes

sedimentation and welding processes of dilute pyroclastic density currents and fallout during a large scale silicic eruption kikai caldera japan abstract sedimentation and welding processes of the high temperature dilute pyroclastic density currents and fallout erupted at 7 3 ka from the kikai caldera are discussed based on the stratigraphy texture lithofacies characteristics and components of the resulting deposits the welded eruptive deposits unit b were produced during the column collapse phase following a large plinian eruption and preceding an ignimbrite eruption and can be divided into two subunits units b l and b u unit b l is primarily deposited in topographic depressions on proximal islands and consists of multiple thin u shows densely welded stratified facies composed of alternating lithic rich and pumice rich layers the layers mantle lower units and are sometimes viscously deformed by ballistics the sedimentary characteristics of unit b l such as welded stratified or cross stratified facies indicate that high temperature dilute pyroclastic density currents were repeatedly generated from limited magma water interactions it is thought that dense brittle particles were segregated in a turbulent current and were immediately buried by deposition of hot lighter pumice rich particles and that this process repeated many times it is also suggested that the depositional temperature of eruptive materials was high and the eruptive style changed from a normal plinian eruption through surge generating explosions unit b l into an agglutinate dominated fallout eruption unit b u on the basis of field data welded pyroclastic surge deposits could be produced only under specific conditions such as 1 rapid accumulation of pyroclastic particles sufficiently hot to weld instantaneously upon deposition and 2 elastic particles interactions with substrate deformation these physical conditions may be achieved within high temperature and highly energetic pyroclastic density currents produced by large scale explosive eruptions

seabed roughness parameters from joint backscatter and reflection inversion at the malta plateau this paper presents estimates of seabed roughness and geoacoustic parameters and uncertainties on the malta plateau mediterranean sea by joint bayesian inversion of mono static backscatter and spherical wave reflection coefficient data the data are modeled using homogeneous fluid sediment layers overlying an elastic basement the scattering model assumes a randomly rough water sediment interface with a von karman roughness power spectrum scattering and reflection data are inverted simultaneously using a population of interacting markov chains to sample roughness and geoacoustic parameters as well as residual error parameters trans dimensional sampling is applied to treat the number of sediment layers and the order zeroth or first of an autoregressive error model to represent potential residual correlation as unknowns results are considered in terms of marginal posterior probability profiles and distributions which quantify the effective data information content to resolve scattering geoacoustic structure results indicate well defined scattering roughness parameters in good agreement with existing measurements and a multi layer sediment profile over a high speed elastic basement consistent with independent knowledge of sand layers over limestone

silicate microspherules intercepted in the plume of etna volcano a possible volcanic origin has been suggested for the micrometre sized spherules that have been discovered in polar snows or ice cores1 5 and in the stratosphere6 7 however although such particles especially when black and magnetic have been identified among the tephra deposits of some volcanoes3 8 12 their volcanic emission has never been directly observed here we describe micro spherules intercepted in the plume of mount etna sicily during moderate recurring volcanic activity their study using analytical transmission and scanning electron microscopy atem and asem demonstrates the simultaneous presence in the plume of glassy silicate microspherules of various chemical compositions 47 98 sio2

mfci experiments on the influence of nacl saturated water on phreatomagmatic explosions abstract molten fuel coolant interaction mfci experiments were performed using remelted foiditic rock samples from the west eifel volcanic field germany two experimental series were carried out with one magmatic melt and two water compositions bi distilled water was used in the first series dw 1 to dw 5 in the second series sw 1 to sw 5 the bi distilled water was saturated 350 g l 1 with sodium chloride nacl for both experimental series the fragmentation history and the energy release were recorded and compared the smallest particles 125 m were studied using scanning electron microscopy sem most mfci experiments with bi distilled water reached higher explosion intensities than the experiments with the saline water this was accompanied by higher particle ejection velocities as well as the formation of more fine grained and more interactive particles of angular shape additionally the smallest artificial pyroclasts were examined by evolved gas analyses ega the particles from the mfci experiments with salt solutions are found to contain more sodium hydroxide naoh these observations can be explained by thermodynamic arguments in contrast to the mfci experiments with pure water an additional reaction occurs with saline water that results in evolution of hydrogen chloride hcl gas and leaves a residue of sodium hydroxide the mfci process with saline water consumes more enthalpy and gibbs free energy so that less energy is available for the explosion with other sodium halides dissolved in the water naf nabr or nai the additional reaction can be predicted to have greater or lesser effects on phreatomagmatic explosions

the indus river system india pakistan major ion chemistry uranium and strontium isotopes the indus river is one of the large river systems draining the himalaya we report in this paper the major ion chemistry sr and u isotope systematics of the indus system particularly its headwaters the results show that 1 on an average about a third of the cations in the waters can be from silicate weathering however most of the ca mg is likely to be from the weathering of carbonates and evaporites 2 the 87sr86sr of the waters ranges between 0 7085 and 0 7595 the higher values 0 72 are typical of the tributaries draining the precambrian granite gneissic terrains the 87sr86sr of the indus main channel throughout its entire stretch shows only minor variations 0 7104 0 7116 the indus transports 8 8 106 mol sr to the arabian sea annually with a 87sr86sr of 0 7111 if our results of sr concentration and 87sr86sr measured at thatta can be considered typical of the indus throughout the year and 3 the u concentration in the indus and its tributaries is generally high 0 37 10 3 g 1 1 the source for the high uranium can be the weathering of granites zones of uranium mineralisation and black shales the indus results when compared with our earlier data on the ganga brahmaputra show that in all these three river systems carbonate weathering is the dominant source of ca mg and hco3 and that u concentrations are high in the case of 87sr86sr the indus waters are less radiogenic however its tributaries draining the precambrian granites gneisses have 87sr86sr in excess of 0 72 similar to that in the rivers of the ganga system the low 87sr86sr of the indus 0 7111 suggests that its contribution to the sr isotope evolution of oceans since the cenozoic is less significant than that of the ganga brahmaputra

evaluation of hydrogeochemical processes and groundwater quality in the jhansi district of bundelkhand region india a base line study involving analysis of groundwater samples from the jhansi district were carried out to determine the major and trace element chemistry and to assess the hydrogeochemical processes and water quality for domestic and irrigation uses study results show that groundwater is mildly acidic to alkaline in nature and hco3 cl ca2 na and mg2 are the major contributing ions for the dissolved loads the data plotted on the gibbs and piper diagrams reveal that the groundwater chemistry is mainly controlled by rock weathering with secondary contribution from anthropogenic sources in a majority of the groundwater samples alkaline earth metals exceed alkalies and weak acid dominate over strong acids ca mg hco3 is the dominant hydrogeochemical facies in the majority of the groundwater samples the computed saturation indices demonstrate that groundwater is oversaturated with respect to dolomite and calcite kaolinite is the possible mineral that is in equilibrium with the water implying that the groundwater chemistry favors kaolinite formation a comparison of groundwater quality parameters in relation to specified limits for drinking water shows that the concentrations of tds f no3 total hardness and fe are exceeding the desirable limits in many water samples quality assessment for irrigation uses reveal that the groundwater is of good to suitable category higher salinity and residual sodium carbonate values at some sites restrict the suitability of groundwater and need an adequate drainage and water management plan for the area

development of spheroidal composite bombs by welding of juvenile spinning and isotropic droplets inside a mafic eruption column abstract it is generally assumed that spheroidal volcanic bombs are formed during cooling of molten clots pulled up into spheres by the surface tension of the magma also volcanic bombs are regarded as non fragmental structures i e made of coherent material we describe non coherent spheroidal bombs of mafic composition from the tuff cinder cone of the cabezo segura volcano calatrava volcanic province spain that exhibit features consistent with welding of essentially non vesicular juvenile spherical droplets it is assumed that the eruption of a low viscosity magma containing suspended phenocrysts mantle clasts and cognate lithic clasts resulted in the efficient separation of volatiles and melt and the explosive fragmentation of the magma into different types of pyroclasts the finest magma fragments would yield melt blobs achneliths or lava spray ca 1 5 m small droplets largely made up also of melt and isolated solid clasts phenocryst microphenocryst and lithic the largest lava fragments incorporated phenocrysts microphenocrysts and lithic clasts all these types of clasts would be erupted in a rapid gas thrust that prevented rapid collision among particles massive aggregation and premature collapse by defluidization the rotation of the largest magma droplets during ascent in a fluidized system produced spinning droplets similar to pelletal lapilli the collision and aggregation of the fluidal clasts might start as soon as the pyroclasts gas mixture was thrust out and progressively decelerated a model is proposed for the formation of spheroidal composite bombs assuming fluidal clasts sintering either by coalescence or agglutination and welding of constituent pyroclasts inside the eruption column prior to bomb accumulation on the field

root zone processes in the phreatomagmatic pipe emplacement model and consequences for the evolution of maar diatreme volcanoes abstract the understanding of processes within the root zone of maar diatreme volcanoes is important for the interpretation of the geology volcanology and even hazard assessment of these volcanoes in the phreatomagmatic model of pipe formation the irregularly shaped root zone is the site of the phreatomagmatic explosions and thus functions as the engine for pipe formation in this model the root zone grows over a period of time in a series of many single thermohydraulic i e phreatomagmatic explosions the explosions initially occur close to the surface and with ongoing explosive activity penetrate towards deeper levels the ejection of country rock clasts from the root zone results in a mass deficiency in the root zone that causes the overlying tephra and the adjacent country rocks to subside passively in a sinkhole like fashion into the root zone many phreatomagmatic eruptions consequently result in the formation of a cone shaped diatreme thus with ongoing eruptions the cone shaped diatreme has to grow systematically both in depth and diameter during its growth processes in the lower diatreme levels successively destroy the upper levels of the evolving root zone at the surface the maar crater in turn reacts to the underlying subsidence processes and also grows both in depth and diameter thermohydraulic explosions which fragment both magma and the surrounding country rocks mostly occur within the bottom part of the root zone violent explosions in small pipes may clear the overlying diatreme for a short period of time before tephra fall and collapse of the walls of the new crater refill the small initial diatreme in larger pipes via expansion of the mixture of highly pressurized water vapor juvenile gas phases and explosively produced tephra the confined and expanding eruption cloud has to pierce through the diatreme fill in a feeder conduit in order to erupt diatreme clearing events in large pipes are difficult or impossible to maintain since the explosive force in the root zone is only in exceptional instances strong enough to lift or entrain the entire diatreme tephra knowledge of the genetic relationships between root zones and diatremes is critical to understand pipe growth processes the combination of such processes can lead to substantial variation in volcanic behavior and thus produce fundamentally different volcano and rock types it is the purpose of this paper to outline important features of root zones and suggest their significance for the genesis and evolution of maar diatreme and related volcanoes

origin of accretionary lapilli within ground hugging density currents evidence from pyroclastic couplets on tenerife aggregation of airborne particles is an important way in which the atmosphere is cleansed of fine dust particles such as following explosive eruptions and meteorite impacts we identify successive stages in the growth history of particle aggregates based upon well preserved ash aggregate bearing pyroclastic layers on tenerife the layers are persistently organized into couplets made up of a lower ignimbrite layer and an upper widespread coignimbrite ash fall layer the upper part of each ignimbrite contains whole and fragmented concentric laminated accretionary lapilli whereas the overlying coignimbrite ash fall layer lacks accretionary lapilli and is composed of framework supported smaller and nonlaminated ash pellets sometimes slightly deformed or partly disaggregated the pellets resemble the cores of the larger accretionary lapilli in the underlying ignimbrite layer these field relations are repeated numerous times in several different successions and they indicate that ash pellets not accretionary lapilli form within the coignimbrite ash plumes some pellets fell directly to the ground producing coignimbrite ash fall layers but others settled into pyroclastic density currents where they accreted successive concentric laminations of fine ash as they circulated through the variously turbulent levels of the stratified current and heat of the lower part of the current dried and partly lithified them into brittle accretionary lapilli the fully formed whole and broken accretionary lapilli were then deposited from the current along with ash and pumice lapilli numerous ignimbrite veneers on tenerife have the form of ash layers a few centimeters thick that drape topography and locally contain matrix supported accretionary lapilli most volcanoes lack laterally continuous field exposure and such accretionary lapilli bearing layers might be mistaken for ash fall deposits we highlight the value of careful distinction between different types of ash aggregate facies when interpreting the origin of pyroclastic deposits for example during hazard assessments

correlative and comparative characterization of main ion concentrations in laterite groundwater in semi arid northern burkina faso about 24 samples from hand dug wells and boreholes were used to characterize concentrations of the main inorganic ions in a laterite environment under semi arid climatic conditions in tikare northern burkina faso it was found that the most represented groundwater anion in groundwater was hco3 with average levels of 49 1 mg l in the dry season and 33 5 mg l in the rainy season the most represented cation was ca2 with mean concentrations of 13 7 and 9 5 mg l respectively the main processes which influence the concentrations of these ions are evaporation dry season local enrichment of recharge water in some elements ion exchange and fixation by clay minerals in case of k the best correlations were found between ca2 and mg2 r 0 95 cl and na r 0 95 hco3 and mg2 r 0 89 hco3 and ca2 r 0 89 and between hco3 and na r 0 80 in general the quality of the groundwater from the different wells sampled for this study was good enough to serve as drinking water however there were situations where the quality of water was polluted because of anthropogenic contaminants mainly no3 k cl from septic tanks and manure pits located in the vicinity of some sampled wells in addition application of fertilizers also represents a potential anthropogenic contamination source with regard to so4 2 ca2 k na and mg2 considering the high concentrations of so4 2 mg2 na and ca2 found in one borehole the deeper fractured aquifers were also likely to be enriched in these elements in contrast the shallow aquifers are likely to be contaminated with cl no3 and k cl and k seem to be locally present in recharge water as shown by their relative higher mean concentrations in the rainy season samples

environmental geochemistry and quality assessment of surface and subsurface water of mahi river basin western india the hydrogeochemical study of surface and subsurface water of mahi river basin was undertaken to assess the major ion chemistry solute acquisition processes and water quality in relation to domestic and irrigation uses the analytical results show the mildly acidic to alkaline nature of water and dominance of na and ca2 in cationic and hco3 and cl in anionic composition in general alkaline earth elements ca2 mg2 exceed alkalis na k and weak acids hco3 dominate over strong acids so42 cl in majority of the surface and groundwater samples ca2 mg2 hco3 is the dominant hydrochemical facies both in surface and groundwater of the area the weathering of rock forming minerals mainly controlled the solute acquisition process with secondary contribution from marine and anthropogenic sources the higher concentration of sodium and dissolved silica high equivalent ratios of na k tz na k cl and low ratio of ca2 mg2 na k suggest that the chemical composition of the water is largely controlled by silicate weathering with limited contribution from carbonate weathering and marine and anthropogenic sources kaolinite is the possible mineral that is in equilibrium with the water implying that the chemistry of river water favors kaolinite formation assessment of water samples for drinking purposes suggests that the majority of the water samples are suitable for drinking at some sites concentrations of tds th f no3 and fe are exceeding the desirable limit of drinking however these parameters are well within the maximum permissible limit except for some cases to assess the suitability for irrigation parameters like sar rsc and na were calculated in general both surface and groundwater is of good to suitable category for irrigation uses except at some sites where high values of salinity na and rsc restrict its uses

silicate glass micro and nanospherules generated in explosive eruptions of ultrabasic magmas implications for the origin of pelletal lapilli abstract the genesis of spherical ash to lapilli sized clasts with a central phenocryst or lithic fragment mantled by a rim of fine grained juvenile material that includes abundant concentrically arranged prismatic crystals is interpreted as either i the result of the spinning of a magma bleb with a crystalline kernel in a fluidized system or ii the accretion of small melt droplets to a previously crystallized nucleus in a gas jet we demonstrate that the rims of pelletal lapilli within tephras of the cabezo segura volcano calatrava spain are clastic and were formed by the progressive welding of juvenile crystals and silicate glass droplets and to a lesser extent filaments both melt in origin around a large crystalline nucleus our results support the accretion hypothesis and offer explicit and new images of the melt droplets that were so far considered hypothetical particles these results indicate also that nanometre scale juvenile pyroclasts melt droplets and crystals can be generated in explosive eruptions of ultrabasic magmas those pyroclasts can be subsequently welded together inside a dense gas jet generating pelletal lapilli and ash

formation of clastogenic lava flows during fissure eruption and scoria cone collapse the 1986 eruption of izu oshima volcano eastern japan the 1986 eruption of b fissure at izu oshima volcano japan produced among other products one andesite and two basaltic andesite lava flows locally the three flows resemble vent effused holocrystalline blocky or aa lava however remnant clast outlines can be identified at most localities indicating that the flows were spatter fed or clastogenic the basaltic andesite flows are interpreted to have formed by two main processes a reconstitution of fountain generated spatter around vent areas by syn depositional agglutination and coalescence followed by extensional non particulate flow and b syn eruptive collapse of a rapidly built spatter and scoria cone by rotational slip and extensional sliding these processes produced two morphologically distinct lobes in both flows by a earlier non particulate flow of agglutinate and coalesced spatter which formed a thin lobe of rubbly aa lava ca 5 m thick with characteristic open extension cracks revealing a homogeneous holocrystalline interior and b later scoria cone collapse which created a larger lobe of irregular thickness 20 m made of large detached blocks of scoria cone interpreted to have been rafted along on a flow of coalesced spatter the source regions of these lava flows are characterized by horseshoe shaped scarps 30 m high with meso blocks ca 30 m in diameter of bedded scoria at the base one lava flow has a secondary lateral collapse zone with lower ca 7 m scarps backward tilted meso blocks are interpreted to be the product of rotational slip and forward tilted blocks the result of simple toppling squeeze ups of coalesced spatter along the leading edge of the meso blocks indicate that coalescence occurred in the basal part of the scoria cone this low viscosity coalesced spatter acted as a lubricating layer along which basal failure of the scoria cone occurred rotational sliding gave way to extensional translational sliding as the slide mass spread out onto the present caldera floor squeeze ups concentrated at the distal margin indicate that the extensional regime changed to one of compression probably as a result of cooling of the flow front sliding material piled up behind the slowing flow front and coalesced spatter was squeezed up from the interior of the flow through fractures and between rafted blocks the andesite flow although morphologically similar to the other two flows has a slightly different chemical composition which corresponds to the earliest stage of the eruption it is a much smaller lava flow emitted from the base of the scoria cone 2 days after the eruption had ceased this lava is interpreted to have been formed by post depositional coalescence of spatter under the influence of the in situ cooling rate and load pressure of the deposit extrusion occurred through the lower part of the scoria cone and subsequent non particulate flow of coalesced material produced a blocky and aa lava flow the mechanisms of formation of the lava flows described may be more common during explosive eruptions of mafic magma than previously envisaged

sub surface dynamics and eruptive styles of maars in the colli albani volcanic district central italy protezione civile italy 2004 2006 agreement with istituto nazionale di geofisica e vulcanologia ingv project v3 1

geology of a complex kimberlite pipe k2 pipe venetia mine south africa insights into conduit processes during explosive ultrabasic eruptions k2 is a steep sided kimberlite pipe with a complex internal geology geological mapping logging of drillcore and petrographic studies indicate that it comprises layered breccias and pyroclastic rocks of various grain sizes lithic contents and internal structures the pipe comprises two geologically distinct parts k2 west is a layered sequence of juvenile and lithic rich breccias which dip 20 45 inwards and k2 east consists of a steep sided pipe like body filled with massive volcaniclastic kimberlite nested within the k2 pipe the layered sequence in k2 west is present to 900 m below present surface and is interpreted as a sequence of pyroclastic rocks generated by explosive eruptions and mass wasting breccias generated by rock fall and sector collapse of the pipe walls both processes occurred in tandem during the infill of the pipe several breccia lobes extend across the pipe and are truncated by the steep contact with k2 east dense pyroclastic rocks within the layered sequence are interpreted as welded deposits k2 east represents a conduit that was blasted through the layered breccia sequence at a late stage in the eruption this phase may have involved fluidisation of trapped pyroclasts with loss of fine particles and comminution of coarse clasts we conclude that the k2 kimberlite pipe was emplaced in several distinct stages that consisted of an initial explosive enlargement followed by alternating phases of accumulation and ejection

formation of composite pyroclasts by welding inside a lithic rich mafic eruption column los marteles caldera canary islands abstract the tuff ring of the los marteles phreatomagmatic maar gran canaria canary islands includes a particular unit that comprises abundant composite spheroidal clasts however these clasts differ from cored clasts elsewhere that consist of erupted lithic pyroclasts with an adhering rim of coherent chilled magma the composite clasts here studied range from lapilli to bombs and are cored or concentrically banded among the welded components several types of primary clasts are discerned that include i juvenile clasts resultant of the magma inertial fragmentation and ii cognate or accessory lithic clasts juvenile clasts include glass spheres nano and microachneliths and crystals lithic clasts include lava fragments scoriae and olivine xenocrysts primary clasts are interpreted to have been produced by the explosion of a partially crystallized mafic sio 2 50 55 magma that erupted into a maar filled up with scoriae plus lava fragments the explosion would have originated as a dense and turbulent gas thrust into which the repeated collisions of melt droplets with solid clasts generated droplet coated crystals lithic clasts and single glass spheres we interpret the cored and concentrically banded pyroclasts to be made of coalesced and or agglutinated particles coated with a melt rim to the rest of the components these composite clasts developed spheroidal shapes during transport within a violent strombolian eruption column due to spin effect and finally landed in solid state

on the volcanology of the gibeon kimberlite field namibia kimberlite volcanism in the upper cretaceous gibeon kimberlite field southern namibia consisting of at least 42 diatremes and a number of associated dykes is closely related to carbonatitic and ultrabasic volcanic and intrusive activity which occurred at the margin of the field the volcanology of the diatremes and dykes as well as their structural setting is reported here because of the paleohydrogeological setting and since juvenile kimberlite occurring in dykes intrusive plugs and spherical lapilli is devoid of vesicles a phreatomagmatic eruption mechanism is proposed for the genesis of the kimberlite diatremes karoo dolerite basalt and sediment xenoliths in the diatremes provide evidence for the former extent of karoo strata at the time of eruption

the formation of high grade ignimbrites i experiments on high and low concentration transport systems containing sticky particles high grade ignimbrites are thought to be deposited by pyroclastic flows at temperatures exceeding minimum welding temperature or even solidus temperature corresponding pyroclastic flow particles range from plastic to partially liquid and are able to aggregate or coalesce this contrasts with particles in pyroclastic flows producing unwelded ignimbrite which are capable of elastic grain interactions the low aspect ratio and great areal extent of high grade ignimbrites requires transport in a particulate state either by a high concentration mass flow facilitated by fluidizing gas reducing internal friction or by b expanded turbulent flow of low but downward increasing concentration this paper presents experiments designed to investigate the effects of plastic to liquid particles on these two contrasting transport mechanisms gas fluidization experiments using polyethyleneglycole peg powders heated above minimum sintering tms and melting tm temperatures cover a wide range of fluidization velocities umf ua 0 6 ut but are always in the bubbly fluidization regime similar to fluidized ignimbrite ash where particle volume concentration outside the bubbles is high 10 1 when the powders reach a critical temperature tm t tms defluidization by catastrophic particle aggregation immediately commences in both stationary and laterally moving fluidized beds as well as in experiments using mixtures of high and low tm 30 wt peg powders when t tms of the lower tm powder this indicates that extended particulate transport at t tms is not possible at such high particle concentrations in the turbulent flow experiments liquid sprays of molten peg or water vertically injected into a high re 104 horizontal air flow form a low concentration 10 5 to 10 4 turbulent suspension current proximal formation of partially coalesced aggregates which settle faster than individual particles causes the measured downstream decay of sedimentation rate to be steeper than predicted by theory of single solid particle sedimentation from turbulent suspensions as particles become finer downstream and coalescence efficiency decreases in response to cooling more distally formed aggregates become too small and rare to modify sedimentation rate decay from that of suspension flows containing solid particles the key difference between the two transport systems is particle concentration c since particle collision rate rcoll c2 collision rates in fluidized beds are so high that all particles immediately aggregate when coalescence efficiency 1 ecoal 0 is larger than 10 3 low concentration suspensions on the other hand require much higher values of ecoal for significant aggregation to occur dilute pyroclastic flows will have higher particle volume fractions 10 3 than the experimental currents but then viscous pyroclasts should have lower coalescence efficiencies than peg droplets experimental results thus support an expanded turbulent transport mechanism of pyroclastic flows generating extensive high grade ignimbrite sheets

evolution of the quaternary melitite nephelinite herchenberg volcano east eifel the quaternary herchenberg composite tephra cone east eifel fr germany with an original bulk volume of 1 17 107 m3 dre of 8 2 106 m3 and dimensions of ca 900 600 90 m length width height erupted in three main stages a initial eruptions along a nw trending 500 m long fissure were dominantly vulcanian in the northwest and strombolian in the southeast removal of the unstable underlying 20 m thick tertiary clays resulted in major collapse and repeated lateral caving of the crater the northwestern lower cone 1 lc1 was constructed by alternating vulcanian and strombolian eruptions b cone building mainly strombolian eruptions resulted in two major scoria cones beginning initially in the northwest cone 1 and terminating in the southeast cones 2 and 3 following a period of simultaneous activity of cones 1 and 2 lapilli deposits are subdivided by thin phreatomagmatic marker beds rich in tertiary clays in the early stages and devonian clasts in the later stages three dikes intruded radially into the flanks of cone 1 c the eruption and deposition of fine grained uppermost layers phreatomagmatic tuffs accretionary lapilli and strombolian fallout lapilli presumably from the northwestern center cone 1 terminated the activity of herchenberg volcano the herchenberg volcano is distinguished from most strombolian scoria cones in the eifel by 1 small volume of agglutinates in central craters 2 scarcity of scoria bomb breccias 3 well bedded tephra deposits even in the proximal facies 4 moderate fragmentation of tephra small proportions of both ash and coarse lapilli bomb size fraction 5 abundance of dense ellipsoidal juvenile lapilli and 6 characteristic depositional cycles in the early eruptive stages beginning with laterally emplaced fine grained xenolith rich tephra and ending with fallout scoria lapilli herchenberg tephra is distinguished from maar deposits by 1 paucity of xenoliths 2 higher depositional temperatures 3 coarser grain size and thicker bedding 4 absence of glassy quenched clasts except in the initial stages and late phreatomagmatic marker beds and 5 predominance of strombolian cone building activity the characteristics of herchenberg deposits are interpreted as due to a high proportion of magmatic volatiles dominantly co2 relative to low viscosity magma during most of the eruptive activity

the al du aythah volcanic cones al madinah city implications for volcanic hazards in northern harrat rahat kingdom of saudi arabia the basaltic al du aythah volcanic cones lie in the northern part of the extensive lava field of harrat rahat and only 13 km from the centre of al madinah city in the kingdom of saudi arabia historical records indicate they may have erupted in ad 641 the four cones are formed by deposits that record a transition from phreatomagmatic to magmatic explosions followed by minor lava effusion three cones display elongated tuff rings at the base and two produced late stage lava flows the cones themselves are symmetrical and constructed mostly by the accumulation of ballistically ejected pyroclasts spherical bombs and lapilli cannonball bombs lapilli occasionally with country rock fragments inside both cored and loaded bombs lapilli are common within the tuff ring deposits lidar data show a total volume of 1 664 10 6 km3 for the four cones 418 10 6 km3 dre whole rock chemical analyses indicate alkali basalt compositions sio2 44 7 45 9 wt with little compositional variation and no relationship between chemistry and eruptive styles small differences in composition may reflect variations in fractional crystallisation of clinopyroxene and olivine a magnetotelluric 2d cross section shows that the cones are located adjacent to a buried sediment filled alluvial channel along a nnw sse fault dipping to the east the al du aythah eruption was related to the ascent of magma through this structure with the first phase of the eruption triggered by the interaction of the magma with water from the northern harrat rahat aquifer that exists in the al madinah basin this initial water source was rapidly exhausted while the eruption progressed roughly from north to south and from west to east the latter motion probably along the fault controlled feeding dyke our work draws attention to the existence of recent explosive phreatomagmatic eruptions in the al madinah basin which despite the hyperarid climate of the area must be considered a potential future eruption hazard

evidence for a common scale o 0 1 m that controls seabed scattering and reverberation in shallow water analysis of the spectral content of long range reverberation yields two observations first there is a remarkably similar scale o 0 1 m between three diverse continental shelf regions this is surprising given the complexity and diversity of geologic processes second there is strong evidence that the scale is associated with heterogeneities within the sediment thus sediment volume scattering not interface scattering controls long range reverberation from a few hundred hertz to several kilohertz this is also unexpected given that at long ranges the vertical grazing angles are less than the critical angle and hence the penetration of the acoustic field into the sub bottom is expected to be modest the consistency of the scale o 0 1 m suggests an underlying feature or mechanism that is consistent across many ostensibly diverse geological settings neither the feature nor mechanism is known at this time