evidence for microbes in early neoproterozoic stromatolites abstract the biogenesis of stromatolites has long been discussed since many lack convincing evidence of their biological origin this has particularly been the case with older precambrian examples where widespread diagenetic and metamorphic processes have commonly destroyed microbial relics in some cases however evidence has been preserved through very early mineralisation precambrian stromatolites are relatively abundant but it is extremely rare that they contain calcified or dolomitized cyanobacteria and biofilms this study provides evidence from early neoproterozoic columnar stromatolites in the jiuliqiao formation from the southeastern margin of the north china platform for fossilized extracellular polymeric substances eps and cyanobacteria along with nanospheres which may represent permineralised viruses or viral like particles a similar chemical composition and colour along with their embedded and cross cutting relationships with the matrix suggest they are syn depositional products and not modern artefacts or the result of sample preparation the interweaving of cyanobacterial filaments with detrital grains such as quartz and intraclasts indicates trapping baffling and binding processes the presence of virus like particles and mineralized eps with anhedral fine grained calcite suggests they may have provided initial nucleation sites for subsequent carbonate precipitation this study demonstrates the use of a high definition scanning electron microscope to detect fossilized calcified filamentous and spheroidal bacteriomorphs within ancient stromatolites in order to confirm their biogenesis

microbial carbonates the geological record of the calcified bacterial algal mats and biofilms summary deposits produced by microbial growth and metabolism have been important components of carbonate sediments since the archaean geologically best known in seas and lakes microbial carbonates are also important at the present day in fluviatile spring cave and soil environments the principal organisms involved are bacteria particularly cyanobacteria small algae and fungi that participate in the growth of microbial biofilms and mats grain trapping is locally important but the key process is precipitation producing reefal accumulations of calcified microbes and enhancing mat accretion and preservation various metabolic processes such as photosynthetic uptake of co2 and or hco3 by cyanobacteria and ammonification denitrification and sulphate reduction by other bacteria can increase alkalinity and stimulate carbonate precipitation extracellular polymeric substances widely produced by microbes for attachment and protection are important in providing nucleation sites and facilitating sediment trapping microbial carbonate microfabrics are heterogeneous they commonly incorporate trapped particles and in situ algae and invertebrates and crystals form around bacterial cells but the main component is dense clotted or peloidal micrite resulting from calcification of bacterial cells sheaths and biofilm and from phytoplankton stimulated whiting nucleation interpretation of these texturally convergent and often inscrutable fabrics is a challenge conspicuous accumulations are large domes and columns with laminated stromatolite clotted thrombolite and other macrofabrics which may be either agglutinated or mainly composed of calcified or spar encrusted microbes stromatolite lamination appears to be primary but clotted thrombolite fabrics can be primary or secondary microbial precipitation also contributes to hot spring travertine cold spring mound calcrete cave crust and coated grain deposits as well as influencing carbonate cementation recrystallization and replacement microbial carbonate is biologically stimulated but also requires favourable saturation state in ambient water and thus relies uniquely on a combination of biotic and abiotic factors this overriding environmental control is seen at the present day by the localization of microbial carbonates in calcareous streams and springs and in shallow tropical seas and in the past by temporal variation in abundance of marine microbial carbonates patterns of cyanobacterial calcification and microbial dome formation through time appear to reflect fluctuations in seawater chemistry stromatolites appeared at 3450 ma and were generally diverse and abundant from 2800 to 1000 ma inception of a proterozoic decline variously identified at 2000 1000 and 675 ma has been attributed to eukaryote competition and or reduced lithification thrombolites and dendrolites mainly formed by calcified cyanobacteria became important early in the palaeozoic and reappeared in the late devonian microbial carbonates retained importance through much of the mesozoic became scarcer in marine environments in the cenozoic but locally re emerged as large agglutinated domes possibly reflecting increased algal involvement and thick micritic reef crusts in the late neogene famous modern examples at shark bay and lee stocking island are composite coarse agglutinated domes and columns with complex bacterial algal mats occurring in environments that are both stressed and current swept products of mat evolution ecological refugia sites of enhanced early lithification or all three

utilization of seismically recorded infrasonic acoustic signals to monitor volcanic explosions the el chichon sequence 1982 a case study infrasonic acoustic signals from five explosive eruptions of el chichon volcano during march 29 through april 4 1982 were recorded by a microbarograph array and seismic research observatory sro seismograph collocated near mckinney texas analyses of these signals for frequencies from 0 0033 to 0 025 h have demonstrated functional relationships of amplitude to frequency consistent with 1 for microbarometric data 2 for vertical mode seismic data and 3 for radial mode seismic data these observed slopes are in agreement with those theoretically predicted by sorrells 1971 estimations of kinetic energy releases by the explosions of el chichon are presented and range from 4 9 1022 ergs to 2 0 1023 for the largest eruption on april 4 1982 to 4 2 1021 to 6 1 1021 ergs for the smallest eruption on april 3 1982 the method of posey and pierce 1971 to estimate the explosivity from long period infrasonic signals is not likely to be applicable strictly speaking to the shorter period data thus it is believed that the energy release for the smallest eruption is overestimated by possibly an order of magnitude comparable estimations of volcanic explosivity from sro radial seismic data and microbarometric array data strongly recommend using sro and international deployment accelerometers network data for far field analyses of volcanic explosions and construction of a rigorous volcanic explosivity scale

microbe mineral interactions early carbonate precipitation in a hypersaline lake eleuthera island bahamas microbialites benthic microbial carbonate deposits were discovered in a hypersaline alkaline lake on eleuthera island bahamas from the edge towards the centre of the lake four main zones of precipitation could be distinguished 1 millimetre sized clumps of mg calcite on a thin microbial mat 2 thicker and continuous carbonate crusts with columnar morphologies 3 isolated patches of carbonate crust separated by a dark non calcified gelatinous mat and 4 a dark microbial mat without precipitation in thin section the precipitate displayed a micropeloidal structure characterized by micritic micropeloids strong autofluorescence surrounded by microspar and spar cement no fluorescence observations using scanning electron microscopy sem equipped with a cryotransfer system indicate that micrite nucleation is initiated within a polymer biofilm that embeds microbial communities these extracellular polymeric substances eps are progressively replaced with high mg calcite discontinuous eps calcification generates a micropeloidal structure of the micrite possibly resulting from the presence of clusters of coccoid or remnants of filamentous bacteria at high magnification the microstructure of the initial precipitate consists of 200 500 nm spheres no precipitation is observed in or on the sheaths of cyanobacteria and only a negligible amount of precipitation is directly associated with the well organized and active filamentous cyanobacteria in deeper layers of the mat indicating that carbonate precipitation is not associated with co2 uptake during photosynthesis instead the precipitation occurs at the uppermost layer of the mat which is composed of eps empty filamentous bacteria and coccoids gloeocapsa spp two dimensional mapping of sulphate reduction shows high activity in close association with the carbonate precipitate at the top of the microbial mat in combination these findings suggest that net precipitation of calcium carbonate results from a temporal and spatial decoupling of the various microbial metabolic processes responsible for caco3 precipitation and dissolution theoretically partial degradation of eps by aerobic heterotrophs or uv fuels sulphate reducing activity which increases alkalinity in microdomains inducing caco3 precipitation this degradation could also be responsible for eps decarboxylation which eliminates ca 2 binding capacity of the eps and releases ca 2 ions that were originally bound by carboxyl groups at the end of these processes the eps biofilm is calcified and exhibits a micritic micropeloidal structure the eps free precipitate subsequently serves as a substrate for physico chemical precipitation of spar cement from the alkaline water of the lake the micropeloidal structure has an intimate mixture of

exceptionally preserved microbially induced sedimentary structures from the ediacaran post glacial successions in the kimberley region northwestern australia abstract a set of exceptionally preserved microbially induced sedimentary structures miss is described from the post glacial yurabi formation of late ediacaran age in the kimberley region northwestern australia these miss comprise oriented grains bamboo leaf like cracks polygonal cracks worm like cracks sinuous cracks gas domes pyrite concentrated laminae and micrite laminae most of the yurabi miss are morphologically comparable with their ancient and modern counterparts micrometre or nannometre scale bacteria or biofilm like inorganic objects are detected from most miss and are interpreted as bacterial bodies or remains that have been replaced with inorganic minerals upon fossilization oriented grains indirectly support microbial control on their accumulation both pyrite conformable laminae and micrite laminae suggest degradation and decay of original microbial mats upon diagenesis sinuous cracks were likely generated in a soft sediment deformation process whereas other sand cracks bamboo leaf like cracks worm like cracks polygonal cracks could have formed from sediment surface layer microbial organics shrinkage upon desiccation gas domes may have formed as the result of anoxic redox reactions and being filled with gases and sediments transported from below two proxies bedding plane coverage percentage and accumulative thickness of single miss bearing beds are developed to semi quantitatively evaluate miss abundance on bedding plane and vertical outcrop respectively the yurabi miss have substratum preference to fine sandstone facies and intertidal settings the yurabi formation yields the most abundant and diverse post glacial miss assemblages during the late ediacaran worldwide both kimberley and global fossil records indicate that miss may have proliferated in shallow marine ecosystems soon after the retreat of ediacaran gaskiers glaciation during late neoproterozoic

evidence for explosive silicic volcanism on the moon from the extended distribution of thorium near the compton belkovich volcanic complex we reconstruct the abundance of thorium near the compton belkovich volcanic complex on the moon using data from the lunar prospector gamma ray spectrometer we enhance the resolution via a pixon image reconstruction technique and find that the thorium is distributed over a larger 40km 75 km area than the 25km 35 km high albedo region normally associated with compton belkovich our reconstructions show that inside this region the thorium concentration is 14 26ppm we also find additional thorium spread up to 300km eastward of the complex at 2 ppm the thorium must have been deposited during the formation of the volcanic complex because subsequent lateral transport mechanisms such as small impacts are unable to move sufficient material the morphology of the feature is consistent with pyroclastic dispersal and we conclude that the present distribution of thorium was likely created by the explosive eruption of silicic magma

pyrite framboids interpreted as microbial colonies within the permian zoophycos spreiten from southeastern australia two types of pyrite framboids pf probably sulphate reducing bacteria have been found within the zoophycos spreiten hosted in the guadalupian middle permian glaciomarine greywacke of the westley park sandstone member within the broughton formation from the southern sydney basin of southeastern australia they are composed of non sheathed pf1 and sheathed pf2 sub micron balls respectively chemically the sub micron balls consist of iron sulphur carbon and oxygen both pf1 and pf2 occur in rhythmic alternation within the thick light grey and thin dark grey minor lamellae of zoophycos spreiten the framboids from the minor lamellae are highly abundant and occur in an orderly arrangement of equal density and in a good state of preservation within zoophycos spreiten no homogeneous filling fecal pellets or any sign of re exploitation of the minor lamellae have been recognized no similar framboids have been observed outside zoophycos spreiten therefore the framboids are interpreted as the pyritized remains of microbial colonies within zoophycos spreiten the trace zoophycos would be a multifunctional garden that may have been carefully constructed by the zoophycos maker where different microbial colonies were orderly and carefully planted and cultured within different minor lamellae further it is proposed that the zoophycos maker had a symbiotic relationship with microbial colonies on the mutual basis of food supply and redox conditions the fact that the overlying spreiten cut the underlying ones indicates that the zoophycos from the study area is of an upward construction the rhythmic alternation of both the thick light grey and thin dark grey minor lamellae within zoophycos spreiten may be suggestive of a gardening manner of the zoophycos maker responding to the warm and cold changes food supply in pulses and variations of sedimentation rate for planting and culturing microbial colonies under the conditions of a glaciomarine environment at the high latitudes

the evolution of volcanic plume morphology in short lived eruptions the details of volcanic plume source conditions or internal structure cannot readily be revealed by simple visual images or other existing remote imaging techniques for example one predominant observable quantity the spreading rate in steady or quasi steady volcanic plumes is independent of source buoyancy flux however observable morphological features of short duration unsteady plumes appear to be strongly controlled by volcanic source conditions as inferred from our recent work here we present a new technique for using simple morphological evolution to extract the temporal evolution of source conditions of short lived unsteady eruptions in particular using examples from stromboli italy and santiaguito guatemala volcanoes we illustrate simple morphologic indicators of 1 increasing injection rate during the early phase of an eruption 2 onset of source injection decline and 3 the timing of source injection cessation combined these observations indicate changes in eruption discharge rate and injection duration and may assist in estimating total mass erupted for a given event in addition we show how morphology may provide clues about the vertical mass distribution in these plumes which may be important for predicting ash dispersal patterns

probabilistic modeling of tephra dispersal hazard assessment of a multiphase rhyolitic eruption at tarawera new zealand 1 the tarawera volcanic complex comprises 11 rhyolite domes formed during five major eruptions between 17 000 b c and a d 1886 the first four of which were predominantly rhyolitic the only historical event erupted about 2 km3 of basaltic tephra fall a d 1886 the youngest rhyolitic event erupted a tephra fall volume more than 2 times larger and covered a wider area northwest and southeast of the volcano a d 1315 kaharoa eruption we have used the kaharoa scenario to assess the tephra fall hazard from a future rhyolitic eruption at tarawera of a similar scale the plinian phase of this eruption consisted of 11 discrete episodes of vei 4 we have developed an advection diffusion model tephra that allows for grain size dependent diffusion and particle density a stratified atmosphere particle diffusion time within the rising plume and settling velocities that include reynolds number variations along the particle fall simulations are run in parallel on multiple processors to allow a significant implementation of the physical model and a fully probabilistic analysis of inputs and outputs tephra is an example of a class of numerical models that take advantage of new computational tools to forecast hazards as conditional probabilities far in advance of future eruptions three different scenarios were investigated for a comprehensive tephra fall hazard assessment upper limit scenario eruption range scenario and multiple eruption scenario hazard curves and probability maps show that the area east and northeast of tarawera would be the most affected by a kaharoa type eruption

estimation and propagation of volcanic source parameter uncertainty in an ash transport and dispersal model application to the eyjafjallajokull plume of 14 16 april 2010 data on source conditions for the 14 april 2010 paroxysmal phase of the eyjafjallajokull eruption iceland have been used as inputs to a trajectory based eruption column model bent this model has in turn been adapted to generate output suitable as input to the volcanic ash transport and dispersal model puff which was used to propagate the paroxysmal ash cloud toward and over europe over the following days some of the source param eters specifically vent radius vent source velocity mean grain size of ejecta and standard deviation of ejecta grain size have been assigned probability distributions based on our lack of knowledge of exact conditions at the source these probability distributions for the input variables have been sampled in a monte carlo fashion using a technique that yields what we herein call the polynomial chaos quad rature weighted estimate pcqwe of output parameters from the ash transport and dispersal model the advantage of pcqwe over monte carlo is that since it intelligently samples the input parameter space fewer model runs are needed to yield estimates of moments and probabilities for the output variables at each of these sample points for the input variables a model run is performed output moments and probabilities are then computed by properly summing the weighted values of the output parameters of interest use

a three dimensional eulerian model for transport and deposition of volcanic ashes abstract volcanic ash fallout represents a serious threat to people living near active volcanoes because it can produce several undesirable effects such as collapse of roofs by ash loading respiratory sickness air traffic disruption or damage to agriculture the assessment of such volcanic risk is therefore an issue of vital importance for public safety and its mitigation often requires to evaluate the temporal evolution of the phenomenon through reliable computational models we develop an eulerian model named fall3d for the transport and deposition of volcanic ashes the model is based on the advection diffusion sedimentation equation with a turbulent diffusion given by the gradient transport theory a wind field obtained from a meteorological limited area model lam and the source term derived from by buoyant plume theory it can be used to forecast either ash concentration in the atmosphere or ash loading on the ground model inputs are topography meteorological data given by a lam mass eruption rate and a particle settling velocity distribution a test application to the july 2001 etna eruption is presented

velocities in the plume of the 2010 eyjafjallajokull eruption 1 the eruption of the icelandic volcano eyjafjallajokull in the spring of 2010 lasted for 39 days with an explosive phase 14 18 april an effusive phase 18 april to 4 may and a phase with renewed explosive activity 5 17 may images every 5 s from a camera mounted 34 km from the volcano are available for most of the eruption applying the maximum cross correlation method mcc on these images the velocity structure of the eruption cloud has been mapped in detail for four time intervals covering the three phases of the eruption the results show that on average there are updrafts in one part of the cloud and lateral motion or downdrafts in another even within the updraft part there are alternating motions of strong updrafts weak updrafts and downward motion these results show a highly variable plume driven by intermittent explosions the results are discussed in the context of integral plume models and in terms of elementary parcel theory

stromatolite reef from the early archaean era of australia the 3 430 million year old strelley pool chert spc pilbara craton australia is a sedimentary rock formation containing laminated structures of probable biological origin stromatolites determining the biogenicity of such ancient fossils is the subject of ongoing debate however many obstacles to interpretation of the fossils are overcome in the spc because of the broad extent excellent preservation and morphological variety of its stromatolitic outcrops which provide comprehensive palaeontological information on a scale exceeding other rocks of such age here we present a multi kilometre scale palaeontological and palaeoenvironmental study of the spc in which we identify seven stromatolite morphotypes many previously undiscovered in different parts of a peritidal carbonate platform we undertake the first morphotype specific analysis of the structures within their palaeoenvironment and refute contemporary abiogenic hypotheses for their formation finally we argue that the diversity complexity and environmental associations of the stromatolites describe patterns that in similar settings throughout earth s history reflect the presence of organisms

the dynamics and thermodynamics of volcanic clouds theory and observations from the april 15 and april 21 1990 eruptions of redoubt volcano alaska on april 15 1990 and april 21 1990 two relatively small explosive eruptions occurred at redoubt volcano alaska lasting about 4 and 8 minutes respectively on both occasions the erupted material travelled as a pyroclastic flow down an ice canyon on the north flank of the volcano using slow scan television recordings of the eruption and the seismic record in both the near and far field we deduce that after a few minutes the upper parts of these pyroclastic flows became buoyant and a large and hot ash cloud ascended off the flow these thermals rose to a height of about 12 km at which point they began to spread laterally as umbrella clouds using a simple thermodynamic model we estimate that the clouds had a temperature in the approximate range 600 700 k as they rose buoyantly from the flow after entraining and heating air and melting and vaporizing ice we also estimate that in each eruption approximately 109 kg of fine ash was injected into the atmosphere during the april 15 eruption a slow scan television camera recorded the ascent of the cloud these observations are described analysed and compared with the predictions of a new model for the dynamics governing the ascent of such clouds in accord with the observations our model predicts that the cloud initially ascended rather sluggishly since it is only just buoyant on rising from the pyroclastic flow as it ascends it entrains and heats up more air and hence generates more buoyancy therefore it accelerates upwards only much higher in the cloud does the velocity decrease again as the thermal energy of the cloud becomes exhausted the model also predicts that the height of rise of such coignimbrite thermals is a function of the initial mass and temperature of the cloud but is almost independent of the initial velocity during the april 21 eruption a sequence of photographs recorded the lateral spreading of the umbrella cloud during an interval of about 10 minutes after the eruption these photographs are analysed and successfully compared with a simple model for the spreading of the umbrella cloud as a gravity current in a stratified environment using an avhrr satellite image of the air fall deposit from the april 15 eruption combined with a simple model we suggest that the primary mechanism of ash dispersal was transport by the ambient wind

microbial primary dolomite from a norian carbonate platform northern calabria southern italy the origin of fine grained dolomite in peritidal rocks has been the subject of much debate recently and evidence is presented here for a microbial origin of this dolomite type in the norian dolomia principale of northern calabria southern italy microbial carbonates there consist of stromatolites thrombolites and aphanitic dolomites high relief thrombolites and stromatolites characterize sub tidal facies and low relief and planar stromatolites with local oncoids typify the inter supratidal facies skeletal remains are very rare in the latter whereas a relatively rich biota of skeletal cyanophycea red algae and foraminifera is present in the sub tidal facies some 75 of the succession consists of fabric preserving dolomite especially within the microbial facies whereas the rest is composed of coarse dolomite with little fabric preservation three end members of dolomite replacement fabric are distinguished type 1 and type 2 fabric retentive with crystal size 5 and 5 60 m respectively and type 3 fabric destructive with larger crystals from 60 to several hundred microns in addition there are dolomite cements precipitated in the central parts of primary cavities during later diagenesis microbialite textures in stromatolites are generally composed of thin dark micritic laminae of type 1 dolomite alternating with thicker lighter coloured laminae of the coarser type 2 dolomite thrombolites are composed of dark micritic clotted fabrics with peloids composed of type 1 dolomite surrounded by coarser type 2 dolomite marine fibrous cement crusts are also present now composed of type 2 dolomite scanning electron microscope observations of the organic rich micritic laminae and clots of the inter supratidal microbialites reveal the presence of spherical structures which are interpreted as mineralized bacterial remains these probably derived from the fossilization of micron sized coccoid bacteria and spheroidal ovoidal nanometre scale dwarf type bacterial forms furthermore there are traces of degraded organic matter probably also of bacterial origin the microbial dolomites were precipitated in a hypersaline environment most likely through evaporative dolomitization as suggested by the excess ca in the dolomites the small crystal size and the positive 18o values the occurrence of fossilized bacteria and organic matter in the fabric preserving dolomite of the microbialites could indicate an involvement of bacteria and organic matter degradation in the precipitation of syn sedimentary dolomite

uncertainty analysis of a model of wind blown volcanic plumes mathematical models of natural processes can be used as inversion tools to predict unobserved properties from measured quantities uncertainty in observations and model formulation impact on the efficacy of inverse modelling we present a general methodology history matching that can be used to investigate the effect of observational and model uncertainty on inverse modelling studies we demonstrate history matching on an integral model of volcanic plumes that is used to estimate source conditions from observations of the rise height of plumes during the eruptions of eyjafjallajokull iceland in 2010 and grimsvotn iceland in 2011 sources of uncertainty are identified and quantified and propagated through the integral plume model a preliminary sensitivity analysis is performed to identify the uncertain model parameters that strongly influence model predictions model predictions are assessed against observations through an implausibility measure that rules out model inputs that are considered implausible given the quantified uncertainty we demonstrate that the source mass flux at the volcano can be estimated from plume height observations but the magmatic temperature exit velocity and exsolved gas mass fraction cannot be accurately determined uncertainty in plume height observations and entrainment coefficients results in a large range of plausible values of the source mass flux our analysis shows that better constraints on entrainment coefficients for volcanic plumes and more precise observations of plume height are required to obtain tightly constrained estimates of the source mass flux

aerobic microbial dolomite at the nanometer scale implications for the geologic record microbial experiments are the only proven approach to produce experimental dolomite under earth s surface conditions although microbial metabolisms are known to induce dolomite precipitation by favoring dolomite growth kinetics the involvement of microbes in the dolomite nucleation process is poorly understood in particular the nucleation of microbially mediated dolomite remains a matter for investigation because the metabolic diversity involved in this process has not been fully explored herein we demonstrate that halomonas meridiana and virgibacillus marismortui two moderately halophilic aerobic bacteria mediate primary precipitation of dolomite at low temperatures 25 35 c this report emphasizes the biomineralogical implications for dolomite formation at the nanometer scale we describe nucleation of dolomite on nanoglobules in intimate association with the bacterial cell surface a combination of both laboratory culture experiments and natural samples reveals that these nanoglobule structures may be 1 the initial step for dolomite nucleation 2 preserved in the geologic record and 3 used as microbial tracers through time and or as a proxy for ancient microbial dolomite as well as other carbonate minerals

kinematic features of isolated volcanic clouds revealed by video records 1 ascent processes of small volcanic clouds are analyzed using video records obtained for some eruptive events at asama and miyakejima volcanoes japan in this analysis each segment of the volcanic cloud is treated as an isolated thermal i e a spherical body ascending independently by its buoyancy our kinematic analysis reveals simple relationships among the ascent velocity radius and height of volcanic clouds the applicability of the entrainment hypothesis and the relation that was obtained from a dimensional analysis by scorer is examined for natural volcanic clouds the empirical dimensionless constants characterizing the entrainment hypothesis and the scorer s relation are more or less scattered and their mean values are about 0 36 and 0 6 respectively these empirical relations can be used to evaluate kinematic features of volcanic clouds approximately without thermodynamic consideration

mineralogical variation of sr nd isotopic and elemental compositions in loess and desert sand from the central loess plateau in china as a provenance tracer of wet and dry deposition in the northwestern pacific we determined sr and nd isotopic compositions and major trace and rare earth element ree compositions of evaporite and detrital minerals in loess and desert sand from the central loess plateau clp where 80 of the loess deposits in china are found the loess exhibited a narrow range of variation in 87sr 86sr 0 715 0 001 a sequential extraction experiment on the loess however showed that water and acetic acid hoac soluble minerals mainly halite and calcite hydrochloric acid hcl soluble minerals chlorite and phosphate and hcl insoluble minerals illite kaolinite smectite vermiculite feldspar and quartz have distinct 87sr 86sr ratios approximately 0 7111 0 0004 0 7141 0 0004 and 0 7195 0 0010 respectively the water and hoac soluble ratios were regionally uniform and were close to the 87sr 86sr value of river water from the huanghe yellow river and the maximum 87sr 86sr value of spring rainwater in japan suggesting selective solution of eolian halite and calcite into the chinese river water and into the japanese rainwater the mineralogical elemental and sr nd isotopic compositions of hcl soluble and insoluble minerals in the clp loess were different from those of the northern desert sand but were indistinguishable from those of its fine grained fraction supporting the view that the loess is composed of the fine grained fraction of desert sand that was transported to the southeast in the atmosphere the 87sr 86sr end and gd yb values of hcl insoluble minerals in the clp loess were almost identical to those of airborne dust soil minerals and deep sea sediments in the northwestern pacific considered to be of eolian origin suggesting dissolution of the loess evaporite minerals during atmospheric transportation these relationships demonstrate the usefulness of sr isotopes of water and hoac soluble minerals and sr and nd isotope ratios and ree compositions of acid insoluble minerals in loess as provenance markers for wet and dry deposition respectively

evaporitic subtidal stromatolites produced by in situ precipitation textures facies associations and temporal significance abstract the transition between carbonate platforms or isolated carbonate buildups and overlying evaporites commonly is marked by assemblages of stromatolites and interlaminated carbonates and evaporites stromatolites display lamination textures that vary from peloidal and discontinuous on a scale of a millimeter to a few centimeters to isopachous and continuously laminated on a scale of a centimeter to a few meters the isopachous lamination texture may be composed of either 1 micritic or radial fibrous calcite or 2 dolomite isopachous stromatolitic laminae are remarkably uniform varying little in thickness over a given lateral distance in contrast to stromatolites formed of peloidal laminae which show marked variation in thickness over an equivalent lateral distance these isopachous textures are uncommon on most open marine carbonate platforms and apparently developed in transitional carbonate to evaporite settings because of increasing temperature salinity and anoxia related to water stratification which would have created ecologic restriction and an opportunity for stromatolite growth stromatolites with isopachous lamination are here interpreted to have formed as a result of in situ precipitation of sea floor encrusting calcite and possibly dolomite whereas the stromatolites composed of peloidal discontinuous lamination are inferred to have formed by trapping and binding of loose carbonate sediment in microbial mats while the presence of microbes in almost all near surface environments nullifies use of the term abiotic to describe most precipitated minerals we interpret growth of the isopachous stromatolites to have been dominated by chemogenic precipitation in the absence of microbial mats and the growth of peloidal stromatolites to have been controlled by sedimentation in the presence of microbial mats these transitional stromatolite facies are best developed atop proterozoic and paleozoic carbonate platforms that underlie major evaporite successions however inspection of jurassic and younger evaporite basins such as the messinian of the mediterranean region shows that stromatolites with thin isopachous lamination and radial fibrous textures though present are rare instead these facies may have been replaced by stromatolites with peloidal clastic textures and by low diversity diatomaceous and coccolith mudstones accumulation of the mudstones would have imposed two important effects 1 production of coccoliths would have helped extract calcium carbonate from seawater thus lowering the growth potential for precipitation of sea floor encrusting stromatolites 2 settling of both coccoliths and diatoms would have created a sediment flux to the sea floor which would have served to impede growth of precipitated stromatolites because of smothering of growing crystals

correlations between eruption magnitude so2 yield and surface cooling about the book humans have long marvelled at and feared the odorous and colourful manifestations of volcanic emissions and in some cases have harnessed them for their economic value the degassing process responsible for these phenomena is now understood to be one of the key factors influencing the timing and nature of volcanic eruptions moreover the surface emissions of these volatiles can have profound effects on the atmospheric and terrestrial environment and climate even more fundamental are the relationships between the history of planetary outgassing differentiation of the earth s interior chemistry of the atmosphere and hydrosphere and the origin and evolution of life this book provides a compilation of 23 papers that investigate the behaviour of volatiles in magma the feedbacks between degassing and magma dynamics and the composition flux and environmental atmospheric and climatic impacts of volcanic gas emissions

spatial and temporal evolution of kimberlite magma at a154n diavik northwest territories canada abstract the a154n kimberlite pipe is part of the diavik kimberlite cluster in the northwest territories canada the pipe is filled by deposits that record a sequence of eruptive and intrusive events for which we have established relative times and modes of emplacement as such this sequence of kimberlite deposits provides a unique opportunity to explore the connections between magma properties pipe or conduit geometry and eruption style deposits within the a154n pipe represent four discrete volcanic events including 1 an array of pre cursor dykes of coherent kimberlite that intrude the adjoining country rock ck 1 2 pyroclastic deposits recording the explosive eruption of a154n pk 1 3 late dykes of coherent kimberlite intruding the main infill of the pipe ck 2 and 4 a sequence of water laid pyroclastic deposits that sourced from another kimberlite volcano pk 2 we use observations on polished slabs and thin sections to characterize the magma that erupted to produce each deposit image analysis techniques are used to quantify olivine content abundance and size distributions and abundances of vesicles within deposits and within individual juvenile pyroclasts our analysis shows that during the eruption cycle ck 1 to pk 1 to ck 2 olivine content increased and volatile content decreased lastly we estimate physical properties for the magmas that produced each deposit the magma properties are combined with 3 d models for the geometry of the conduit at the time of eruption to constrain the mass flux and duration of each eruptive event steady state assumptions for velocity and magma flux yield total eruption durations of minutes to hours the diversity of textures and compositions recorded in pyroclastic kimberlite pk 1 and dykes of coherent kimberlite ck 1 and ck 2 are a possible manifestation of separated three phase flow involving kimberlite melt and crystals and an ever increasing proportion of exsolved co 2 h 2 o fluid specifically we suggest that the early dykes ck 1 pyroclastic kimberlite pk 1 and late stage dykes ck 2 are representative of three separate regimes of kimberlite magma created by the ascent of a vigorously degassing magma we envisage this being composed of a the gas charged front of the magma created by decoupling the more buoyant gas phase from the silicate melt b a transient gas rich body of magma in which later stage exsolved fluids gases are essentially coupled to the melt and c a fluid depleted tail of magma which remains buoyant within the lithosphere but ascends more slowly than the fluid and exsolving gas phases

evolution of volcanic eruption columns 1 the classical steady state model for plinian eruption columns is extended to allow the source conditions at the volcanic vent to change in time it is shown that when the source conditions change rapidly over time scales typically less than approximately 3 4 min this new time dependent volcano model becomes appropriate differences between changes in source velocity and source temperature are also considered qualitatively similar structures are formed when either the source velocity or source temperature is reduced a transient region is formed characterized by a narrowing of the top hat eruption column radius a first attempt to a model a plinian eruption column from its dynamic initiation in a volcanic eruption is made it is shown that the velocity at the front of the eruption column is significantly slower than the velocity at the same height in an established eruption column

release of iron from chlorite weathering and links to magnetic enhancement in chinese loess deposits abstract chlorite weathering is potentially useful as an indicator of in situ weathering related to the strength of the east asian summer monsoon in chinese loess deposits the chlorite ratio the integral area ratio of chlorite diffraction peaks at 0 47 nm and 0 7 nm is a new proxy for evaluating the release of free iron from chlorite weathering this ratio was measured using x ray diffraction xrd on the

biostratigraphic and chemostratigraphic constraints on the age of early neoproterozoic carbonate successions in north china abstract thick carbonate successions of proterozoic age were deposited in the huaibei and huainan regions along the southern margin of the north china block these successions including the huaibei group in the huaibei region and the huainan and feishui groups in the huainan region have been correlated with the qingbaikou group which outcrops in the jixian area of north china and is the eponymous succession of the qingbaikouan system traditionally regarded as 1000 800 ma recently it has been shown that lower qingbaikouan strata in the jixian area may be as old as 1300 1400 ma by correlation the huaibei huainan and feishui groups may include mesoproterozoic strata but these units have also been interpreted as tonian or cryogenian ediacaran cambrian in age these contradictory age interpretations hamper our ability to explore the rich paleontological and sedimentary records preserved in these rocks and to assess paleogeographic reconstructions in this report we describe new microfossils and stable isotope data 13ccarb 18ocarb 34scas from the huaibei huainan and feishui groups possible vase shaped microfossils from the jiayuan formation of the lower huaibei group and characteristic early neoproterozoic acritarchs particularly trachyhystrichosphaera aimika from the gouhou and liulaobei formations are consistent with a tonian age for the huaibei and huainan groups similarly carbon isotope trends in the huaibei huainan and feishui groups are comparable with tonian 13ccarb patterns in south australia and laurentia with a plateau of moderately positive 1 5 values followed by pronounced negative 13ccarb excursion in the gouhou formation which may be equivalent to the bitter springs anomaly in south australia 34scas values of the huaibei group are mostly 25 40 similar to values from the stratigraphically equivalent jingeryu formation in the jixian area overall the combination of biostratigraphic chemostratigraphic and available radiometric data suggests that the huaibei huainan and feishui groups are early neoproterozoic tonian in age

the possible role of nannobacteria dwarf bacteria in clay mineral diagenesis and the importance of careful sample preparation in high magnification sem study abstract bacterial textures are present on clay minerals in oligocene frio formation sandstones from the subsurface of the corpus christi area texas in shallower samples beads 0 05 0 1 m in diameter rim the clay flakes at greater depths these beads become more abundant and eventually are perched on the ends of clay filaments of the same diameter we believe that the beads are nannobacteria dwarf forms that have precipitated or transformed the clay minerals during burial of the sediments rosettes of chlorite also contain after hcl etching rows of 0 1 m bodies in contrast kaolinite shows no evidence of bacterial precipitation we review other examples of bacterially precipitated clay minerals a danger present in interpretation of our earlier work and much work of other is the development of nannobacteria looking artifacts caused by gold coating times in excess of one minute we strongly recommend a 30 second coating time bacterial growth of clay minerals may be a very important process both in the surface and subsurface

soufriere volcano st vincent observations of its 1979 eruption from the ground aircraft and satellites rapid response by earth atmospheric and space scientists made possible diverse observations during the explosive phase of the 1979 eruption of soufriere volcano the 11 reports that follow indicate that with the availability of appropriate personnel equipment and logistical support a significant body of geophysical data can be gathered on short notice at erupting volcanoes in remote parts of the world

confort 15 model of conduit dynamics applications to pantelleria green tuff and etna 122 bc eruptions numerical simulations are useful tools to illustrate how flow parameters and physical processes may affect eruption dynamics of volcanoes in this paper we present an updated version of the conflow model an open source numerical model for flow in eruptive conduits during steady state pyroclastic eruptions mastin and ghiorso in a numerical program for steady state flow of magma gas mixtures through vertical eruptive conduits u s geological survey open file report 00 209 2000 in the modified version called confort 15 the rheological constraints are improved incorporating the most recent constitutive equations of both the liquid viscosity and crystal bearing rheology this allows all natural magma compositions including the peralkaline melts excluded in the original version to be investigated the crystal bearing rheology is improved by computing the effect of strain rate and crystal shape on the rheology of natural magmatic suspensions and expanding the crystal content range in which rheology can be modeled compared to the original version conflow is applicable to magmatic mixtures with up to 30 vol crystal content moreover volcanological studies of the juvenile products crystal and vesicle size distribution of the investigated eruption are directly incorporated into the modeling procedure vesicle number densities derived from textural analyses are used to calculate through toramaru equations maximum decompression rates experienced during ascent finally both degassing under equilibrium and disequilibrium conditions are considered this allows considerations on the effect of different fragmentation criteria on the conduit flow analyses the maximum volume fraction criterion porosity criterion the brittle fragmentation criterion and the overpressure fragmentation criterion simulations of the pantelleritic and trachytic phases of the green tuff pantelleria and of the plinian etna 122 bc eruptions are performed to test the upgrades in the confort 15 modeling conflow and confort 15 numerical results are compared analyzing the effect of viscosity decompression rate temperature fragmentation criteria critical strain rate porosity and overpressure criteria and equilibrium versus disequilibrium degassing in the magma flow along volcanic conduits the equilibrium simulation results indicate that an increase in viscosity a faster decompression rate a decrease in temperature or the application of the porosity criterion in place of the strain rate one produces a deepening in fragmentation depth initial velocity and mass flux of the mixture are directly correlated with each other inversely proportional to an increase in viscosity except for the case in which a faster decompression rate is assumed taking into account up to date viscosity parameterization or input faster decompression rate a much larger decrease in the average pressure along the conduit compared to previous studies is recorded enhancing water exsolution and degassing disequilibrium degassing initiates only at very shallow conditions near the surface brittle fragmentation i e depending on the strain rate criterion in the pantelleritic green tuff eruption simulations is mainly a function of the initial temperature in the case of the etna 122 bc plinian eruption the viscosity strongly affects the magma ascent dynamics along the conduit using confort 15 and therefore incorporating the most recent constitutive rheological parameterizations we could calculate the mixture viscosity increase due to the presence of microlites results show that these seemingly low viscosity magmas can explosively fragment in a brittle manner mass fluxes resulting from simulations which better represent the natural case i e microlite bearing are consistent with values found in the literature for plinian eruptions 106 kg s the disequilibrium simulations both for green tuff and etna 122 bc eruptions indicate that overpressure sufficient for fragmentation if present occurs only at very shallow conditions near the surface

response of silicate weathering to monsoon changes on the chinese loess plateau abstract eolian deposits of loess on the chinese loess plateau are investigated to decipher the influence of sequentially changed monsoon climate on silicate weathering process detailed hydrochloric acid dissolution experiments are applied to establish a sensitive proxy for silicate weathering combined elemental and mineralogical studies show that the minerals which are susceptible to incipient chemical weathering can be totally dissolved in hot hydrochloric acid 80 c 3mol l after 4h while other stable minerals are nearly unaffected thus the hydrochloric acid dissolvable fractions adf of loess and paleosol are more sensitive than bulk samples in the weathering reaction since mg is tend to be leached out from the adf while al is conserved during the incongruent weathering mg al ratio of the adf mg al adf could indicate the weathering intensities of the mg bearing minerals mainly chlorite the mg al adf of the modern soils on the chinese loess plateau is closely correlated to the local precipitation amounts suggests that the intensity of summer monsoon is a key factor in the weathering of mg silicate the silicate weathering intensity of the loess paleosol deposits of past 130kyrs shows strong procession cycle of 23kyrs coupled by glacial interglacial variation the 23krys cycles are coherent to the variations of the intensity of summer monsoon while the 100kyrs glacial interglacial variation may relates to the changes in winter monsoon phased intensification of east asian summer monsoon and thus enhanced silicate weathering and atmosphere co 2 drawdown in response to the uplift of tibetan plateau may be another mechanism relating the late cenozoic tectonics to global cooling

dynamics of strombolian ash plumes from thermal video motion morphology and air entrainment 1 imaging volcanic plumes is essential to provide an observational basis for understanding and modeling plume dynamics during june july 2004 150 strombolian ash plumes were imaged at stromboli volcano italy with a forward looking infrared radiometer flir thermal video camera 30 hz of these 25 80 plumes were suited for different levels of quantitative analyses in this study some simple analyses are applied to constrain basic parameters for the dynamics of strombolian plumes during their initial ascent 130 m plume rise rates covered both gas thrust 15 m s 1 and buoyant regimes 15 m s 1 which in turn controlled lateral spreading rates and air entrainment rates the half angle of lateral spreading of the plume front averaged 7 3 1 6 for gas thrust regimes and 13 5 1 6 for buoyant regimes equating to mean air entrainment coefficients of 0 06 0 12 for gas thrust regimes and 0 22 0 03 for buoyant regimes these factors were also linked to plume morphologies which included jets starting plumes and thermals a rooted thermal form was observed and presumed as an intermediary between starting plumes and discrete thermals plume rise could be approximated by a power law dependence with time rooted thermals spread and entrained air at rates approaching those of a discrete thermal but rose at a rate similar to that of a starting plume phenomena including helical motion and sedimentation were visible in the flir imagery these results demonstrate that emergent plume behavior is progressive and highly transient furthermore this study offers empirical reinforcement that entrainment dynamics are intrinsically different in 1 gas thrust versus buoyantly driven regimes and 2 plume fronts versus steady plumes

mechanism of the 1979 explosive eruption of soufriere volcano st vincent abstract the vulcanian explosive phase of the soufriere of st vincent in 1979 occurred when magma penetrated the water logged 1971 1972 lava island in the center of the crater lake the 13 day period of explosive and volcanoseismic activity ceased when the crater lake had dried up and subsequent activity was restricted to quiet lava extrusion the explosive phase produced 15 5 105m3 dense rock equivalent d r e of new magma and 22 106m3 d r e of lithic material from the 1971 1972 island whereas the following extrusive phase produced a dome of volume 47 106m6 considerations of the energetics of the explosive eruption indicate that the available heat content of the new magma 5 8 1016j was not sufficient to account for the observed phenomena including evaporation of the 25 106m3 crater lake and that additional 8 1016 j of heat remaining in the 1971 1972 lava mass are required to drive the eruption plumes field relations the high proportion of lithic material and the energy relations of the eruption are consistent with a phreato magmatic eruption mechanism involving a three way interaction of the 1971 1972 lava mass crater lake water and magma as a consequence of net veining and thermally induced hydraulic fracturing of the water logged 1971 1972 lava island by new magma in 1979

eruption mass estimation using infrasound waveform inversion and ash and gas measurements evaluation at sakurajima volcano japan abstract eruption mass and mass flow rate are critical parameters for determining the aerial extent and hazard of volcanic emissions infrasound waveform inversion is a promising technique to quantify volcanic emissions although topography may substantially alter the infrasound waveform as it propagates advances in wave propagation modeling and station coverage permit robust inversion of infrasound data from volcanic explosions the inversion can estimate eruption mass flow rate and total eruption mass if the flow density is known however infrasound based eruption flow rates and mass estimates have yet to be validated against independent measurements and numerical modeling has only recently been applied to the inversion technique here we present a robust full waveform acoustic inversion method and use it to calculate eruption flow rates and masses from 49 explosions from sakurajima volcano japan six infrasound stations deployed from 12 20 february 2015 recorded the explosions we compute numerical green s functions using 3 d finite difference time domain modeling and a high resolution digital elevation model the inversion assuming a simple acoustic monopole source provides realistic eruption masses and excellent fit to the data for the majority of the explosions the inversion results are compared to independent eruption masses derived from ground based ash collection and volcanic gas measurements assuming realistic flow densities our infrasound derived eruption masses for ash rich eruptions compare favorably to the ground based estimates with agreement ranging from within a factor of two to one order of magnitude uncertainties in the time dependent flow density and acoustic propagation likely contribute to the mismatch between the methods our results suggest that realistic and accurate infrasound based eruption mass and mass flow rate estimates can be computed using the method employed here if accurate volcanic flow parameters are known application of this technique could be broadly applied to enable near real time calculation of eruption mass flow rates and total masses these critical input parameters for volcanic eruption modeling and monitoring are not currently available

the 1982 eruptions of el chichon volcano mexico 2 observations and numerical modelling of tephra fall distribution tephra fallout from the a 1 march 29 0532 ut b april 4 0135 ut and c april 4 1122 ut 1982 explosive eruptions of el chichon produced three tephra fall deposits over southeastern mexico bidirectional spreading of eruption plumes as documented by satellite images was due to a combination of tropospheric and stratospheric transport with heaviest deposition of tephra from the ene tropospheric lobes maximum column heights for the eruptions of 27 32 and 29 km respectively have been determined by comparing maximum lithic clast dispersal in the deposits with predicted lithic isopleths based on a theoretical model of pyroclast fallout from eruption columns these column heights suggest peak mass eruption rates of 1 1 108 1 9 108 and 1 3 108 kg s maximum column heights and mass eruption rates occured early in each event based on the normal size grading of the fall deposits sequential satellite images of plume transport and the production of a large stratospheric aerosol plume indicate that the eruption columns were sustained at stratospheric altitudes for a significant portion of their duration new estimates of tephra fall volume based on integration of isopach area and thickness yield a total volume of 2 19 km3 1 09 km3 dre dense rock equivalent or roughly twice the amount of the deposit mapped on the ground up to one half of the erupted mass was therefore deposited elsewhere as highly dispersed tephra

cristobalite pyroxene in an l6 chondrite implications for metamorphism crispy is a cristobalite pyroxene assemblage in the l6 chondrite alha 76003 it was formed by reaction of a very siliceous inclusion with the surrounding olivine rich rock oxygen isotopes show that the inclusion was derived from a source with non chondritic isotopic composition the isotopes also show that the oxygen of the pyroxene reaction product was derived by simple mixing of oxygen from the inclusion and its immediately adjacent surroundings with exchange with the bulk meteorite limited to a distance of about a millimeter the persistence of cristobalite in close proximity to olivine and the lack of isotopic equilibration show that the metamorphic processes that form petrographic grade 6 chondrites involve transport of major elements over distances only on the order of millimeters

controls on development and diversity of early archean stromatolites the 3 450 million year old strelley pool formation in western australia contains a reef like assembly of laminated sedimentary accretion structures stromatolites that have macroscale characteristics suggestive of biological influence however direct microscale evidence of biology namely organic microbial remains or biosedimentary fabrics has to date eluded discovery in the extensively recrystallized rocks recently identified outcrops with relatively good textural preservation record microscale evidence of primary sedimentary processes including some that indicate probable microbial mat formation furthermore we find relict fabrics and organic layers that covary with stromatolite morphology linking morphologic diversity to changes in sedimentation seafloor mineral precipitation and inferred microbial mat development thus the most direct and compelling signatures of life in the strelley pool formation are those observed at the microscopic scale by examining spatiotemporal changes in microscale characteristics it is possible not only to recognize the presence of probable microbial mats during stromatolite development but also to infer aspects of the biological inputs to stromatolite morphogenesis the persistence of an inferred biological signal through changing environmental circumstances and stromatolite types indicates that benthic microbial populations adapted to shifting environmental conditions in early oceans

laboratory simulations of sustained volcanic eruptions many violent eruptions are driven by rapid exsolution of dissolved volatiles within liquid magma the accelerating two phase mixture emerges at the vent as a sustained quasi steady discharge lasting for periods from hours to days refs 1 2 the initial growthin discharge rate commonly observed subsequent fluctuations and discrete pulses and shocks remain largely unexplained we have simulated volcanic conduit flows by producing sustained quasi steady explosions in a liquid undergoing rapid exsolution of a gas this was done by rapidly decompressing large volumes of co 2 saturated water the results reveal fluctuations in discharge rate that reflect heterogeneities in the two phase mixture that form spontaneously as a consequence of the size and geometry of the experimental system an initial transient with a growing discharge rate is observed in experiments in which material is erupted from a spherical flask up a narrow neck that mimics the magma chamber conduit assembly of volcanic systems the fragmentation region propagates down the neck during the initial transient until it reaches a stable position at the top of the flask at which point a quasi steady discharge ensues

explosive volcanic eruptions viii the role of magma recycling in controlling the behaviour of hawaiian style lava fountains explosive eruptions of mafic magmas produce lava fountains whose heights are a function of the exsolved volatile content of the magma its erupted mass flux and the geometry of the vent which may be an elongate fissure or a localized near circular conduit the geometry of the initial vent and the eruptive behaviour can be distinctly modified by lava drainback and accumulating ejecta hot pyroclasts landing near the vent may coalesce to form rootless flows some of which may drain back into the vent to be recycled into the eruption products rootless flows may be at least partially confined by pre existing topographic features or by spatter or cinder ramparts being built up by the eruption itself so that they accumulate into a lava pond over and around the vent the erupting jet of magmatic gas and pyroclasts must force its way through such a pond and will entrain some of the pond lava as it does so the energy expended in entraining and accelerating previously erupted materials will reduce the eruption velocity and the lava fountain height by an amount which can be calculated as a function of the eruption conditions and the lava pond depth or lava drainback rate the results of such calculations are presented and are used to assess the influence of this process on attempts to infer magma volatile contents from field observations of lava fountain heights

volcanic plume heights on mars limits of validity for convective models 1 previous studies have overestimated volcanic plume heights on mars in this work we demonstrate that volcanic plume rise models as currently formulated have only limited validity in any environment these limits are easily violated in the current mars environment and may also be violated for terrestrial and early mars conditions we indicate some of the shortcomings of the model with emphasis on the limited applicability to current mars conditions specifically basic model assumptions are violated when 1 vertical velocities exceed the speed of sound 2 radial expansion rates exceed the speed of sound 3 radial expansion rates approach or exceed the vertical velocity or 4 plume radius grossly exceeds plume height all of these criteria are violated for the typical mars example given here solutions imply that the convective rise model is only valid to a height of 10 km the reason for the model breakdown is that the current mars atmosphere is not of sufficient density to satisfy the conservation equations it is likely that diffusion and other effects governed by higher order differential equations are important within the first few kilometers of rise when the same criteria are applied to eruptions into a higher density early mars atmosphere we find that eruption rates higher than 1 4 109 kg s also violate model assumptions this implies a maximum extent of 65 km for convective plumes on early mars the estimated plume heights for both current and early mars are significantly lower than those previously predicted in the literature therefore global scale distribution of ash seems implausible

dispersal and characteristics of pyroclastic fall deposits from mt misery volcano west indies mt misery volcano near the northern end of the lesser antilles island arc produced late quaternary airfall layers that have different dispersal patterns these are controlled by a the style of explosive activity which determined the heights of the eruption columns and b a layered atmospheric system with contrasted bipolar wind directions at different altitudes isopach and isopleth maps are given for 10 eruptions belonging to the mansion series 41 730 1 750 yrs b p basaltic strombolian type scoria fall deposits were dispersed mainly by surface lower tropospheric winds to the nw and w in contrast green and brown andesitic sub plinian and plinian falls with higher eruption columns were dispersed to the se and e by upper tropospheric winds thinly laminated phreatomagmatic ashes within the mansion series are again dispersed to the nw and controlled by surface winds

fall out and deposition of volcanic ash during the 1979 explosive eruption of the soufriere of st vincent abstract the 1979 explosive activity of soufriere volcano st vincent commenced on april 13th and continued for two weeks producing eleven eruption columns the activity produced air fall ash with abundant accretionary lapilli plus minor pyroclastic flows and base surge deposits the dispersal of the columns was observed by an sms 1 geostationary satellite all but two of the plumes were dispersed entirely to the east the last event on april 26th formed a minor lobe to the east and a major lobe to the south southeast the april 26th column was observed to rise to 8 km within five minutes and ascended to a maximum of 14 km in the next hour the magma discharge rate was greater than 3000 m3 s the plume expanded at a rate of 4000 km2 hr and was dispersed at a mean velocity of 15 m s the ash deposits show bimodal grain size distribution with 95 of the ash collected being sub 1 mm diameter modelling of the ash fall out has allowed interpretation of grainsize parameters in a quantitative manner the fall velocities of ash particles appear to have been reduced by turbulence and downwind ascent of the plume which is attributed to fallout of ash reducing the plume density the coarse population of the april 26th deposit displayed a systematic change in md and away from source the fine mode displays uniform md and everywhere and is interpreted as having been deposited in the form of accretionary lapilli

explosive volcanic eruptions v observations of plume dynamics during the 1979 soufriere eruption st vincent summary during the 1979 eruption of the soufritre of st vincent west indies a 14min period of explosive activity occurred on april 22 the first three minutes of this activity were filmed five individual explosions formed distinct plumes which fed an eruption column which eventually ascended to a height of over 18 km the ascent velocities of the fronts of these plumes ranged from 8 5 to 61 7m s the half angle of spreading of the plume fronts ranged from 21 5 to 24 one of the plumes was observed to 8 km height and decelerated steadily from 5 1 5 to 23 m s l the main column fed by individual explosions was however observed to accelerate from 8 5 to 58 m s l in the same height interval a theoretical treatment of volcanic plume motion is presented measurements of dimensions velocities and spreading rates from the film are used to estimate plume parameters such as temperature particle content and volume discharge rate of magma from the theoretical relationships these calculations show that the individual plumes became hotter and richer in juvenile ash with time the acceleration of the main eruption column was the result of being fed by increasingly hotter and more ash rich explosions an average volume discharge rate of 12600m3s is estimated from the analysis of the plume motions this value agrees closely with an estimate of discharge rate based on the heat flux required to form an 18 km high column this agreement suggests that theories of convective motions in plumes can be successfully adapted to the volcanic case as long as the effect of hot entrained ash particles is considered

bacterial fossils and microbial dolomite in triassic stromatolites triassic stromatolitic dolomite from italy preserves mineralized bacterial remains one of the first unequivocal identifications of such structures in the geological record they consist of empty spheroids 1 0 m diameter resembling coccoid bacteria and smaller 150 400 nm objects interpreted as dwarf bacterial forms occurring within and between syn sedimentary dolomite crystals moreover gently folded sheets 100 200 nm thick and several micrometers long form a sub polygonal network reminiscent of eps extracellular polymeric substance their granular textured surfaces suggest bacterial degradation of original organic matter these features confirm a biological origin for the stromatolites as in modern microbial mats and the preserved original geochemical signatures indicate early precipitation of mg carbonates induced through microbial sulfate reducing metabolic activities

experimental studies of particle laden plumes experiments are described in which buoyant plumes of fresh water and solid particles are generated in a tank of salt water dependence of the behavior of the plumes on particle concentration and grain size was studied at low concentrations behavior was similar to single component plumes and the principal effect of the particles was to reduce the buoyancy flux measurements of particle concentration across the plumes demonstrated that there were substantial amounts of particle reentrainment from an outer sedimenting veil reentrainment caused the plume margins to become denser than the ambient fluid total particle flux in the plumes increased with height and can be several times greater than the flux at the plume source plumes with high particle concentration exhibit several kinds of convective instability which generated gravity currents and rapid sedimentation gravity currents were generated at the margins of concentrated plumes these flows are attributed to reentrainment causing the flow margins to have excess density when the plume density was close to but less than the density of the ambient fluid a fountain forms high in the plumes which collapsed asymmetrically to generate a gravity current on one side of the plume when the density of the particle laden flow was greater than the ambient fluid a symmetrical fountain formed and gravity currents moved across the tank floor depositing sediment at a well defined distance from the source buoyant fluid ascended from the flow fronts to form a ring of plumes around the central fountain these plumes coalesced to form a broad buoyant cloud the plumes are generated by the sedimentation from the gravity currents which resulted in the fresh water and some entrained particles being released all the experimental plumes ascended to the top of the tank and spread out as gravity currents beneath the upper surface particles often fall from this layer in discrete parcels of particle rich fluid with shapes similar to thermals the fall velocities were much greater than the terminal velocities of individual particles and the sedimenting region is inhomogeneous these observations indicate that sedimentation is enhanced by convective instabilities when particle rich fluid is emplaced above particle free fluid the experiments indicate that there may be several different mechanisms of generating pyroclastic flows and surges from the collapse of volcanic eruptions columns the experiments also demonstrate that the sedimentation of particles from a plume has an important influence on dynamical behavior

reducing discrepancies in ground and satellite observed eruption heights abstract the plume height represents a crucial piece of evidence about an eruption feeding later assessment of its size character and potential impact and feeding real time warnings for aviation and ground based populations there have been many observed discrepancies between different observations of maximum plume height for the same eruption a comparison of maximum daily height estimates of volcanic clouds over indonesia and papua new guinea during 1982 2005 shows marked differences between ground and satellite estimates and a general tendency towards lower height estimates from the ground without improvements in the quality of these estimates reconciled among all available methods warning systems will be less effective than they should be and the world s record of global volcanism will remain hard to quantify examination of particular cases suggests many possible reasons for the discrepancies consideration of the satellite and radar cloud observations for the 1991 pinatubo eruptions shows that marked differences can exist even with apparently good observations the problem can be understood largely as a sampling issue as the most widely reported parameter the maximum cloud height is highly sensitive to the frequency of observation satellite and radar cloud heights also show a pronounced clumping near the height of the tropopause and relative lack of eruptions reaching only the mid troposphere reinforcing the importance of the tropopause in determining the eruption height in convectively unstable environments to reduce the discrepancies between ground and satellite estimates a number of formal collaboration measures between vulcanological meteorological and aviation agencies are suggested

characterisation of the 1997 vulcanian explosions of soufriere hills volcano montserrat by video analysis the activity of convention at montserrat soufriere hills volcano montserrat during the period 1995 1999 included numerous violent explosions two major cycles of vulcanian explosions occurred in 1997 a first of 13 explosions between 4 and 12 august and a second of 75 between 22 september and 21 october the explosions were short lived events lasting a few tens of seconds during which partial fountain collapse generated pyroclastic surges and pyroclastic flows and buoyant plumes ascended 3 15 km into the atmosphere each explosion discharged on average 3 105 m3 dense rock equivalent dre of magma draining the conduit to depths of 1 2 km the paper focuses on the first few seconds of three explosions of the 75 that occurred in september october 1997 6 october 1997 at 17 50 7 october 1997 at 16 02 and 9 october 1997 at 12 32 physical parameters such as exit velocities magmatic water contents and magma pressures at fragmentation are estimated by following and modelling the ascent of individual momentum dominated finger jets visible on videos during the initial stages of each explosion the model treats each finger jet as an incompressible flow sustained by a steady flux of gas and particles during the few seconds of ascent and produces results that compare favourably with those using a multiphase compressible code run using similar eruptive parameters each explosion reveals a progressive increase in eruptive intensity with time jet exit velocities increasing from 40 m s 1 at the beginning of the explosion up to 140 m s 1 after a few seconds modelling suggests that the first magma to exit was largely degassed whereas that discharged after a few seconds contained up to 2 wt water magma overpressures up to 10 mpa are estimated to have existed in the conduit immediately prior to each explosion progressive increases in jet exit velocity with time over the first few seconds of each explosion provide direct evidence for strong pre eruptive gradients in water content and magma pressure in the upper reaches probably 100 500 m of the conduit fountain collapse occurred during the first 10 20 s of each explosion because the discharging jets had bulk densities up to 100 times that of the atmosphere and were unable to entrain enough air to become buoyant such high eruptive densities were due to the presence of partially degassed magma in the conduit

carbonate and silicate biomineralization in a hypersaline microbial mat mesaieed sabkha qatar roles of bacteria extracellular polymeric substances and viruses in a modern peritidal microbial mat from qatar both biomediated carbonates and mg rich clay minerals palygorskite were identified the mat ca 5 cm thick shows a clear lamination reflecting different microbial communities the initial precipitates within the top millimetres of the mat are composed of ca mg si al s amorphous nanoparticles few tens of nanometres that replace the ultrastructure of extracellular polymeric substances the extracellular polymeric substances are enriched in the same cations and act as a substrate for mineral nucleation successively crystallites of palygorskite fibres associated with carbonate nanocrystals develop commonly surrounding bacterial bodies micron sized crystals of low mg calcite are the most common precipitates together with subordinate aragonite very high mg calcite dolomite and ankerite pyrite nanocrystals and framboids are present in the deeper layers of the mat calcite crystallites form conical structures circular to triangular hexagonal in cross section evolving to crystals with rhombohedral terminations some crystallite bundles develop into dumb bell and stellate forms spheroidal organo mineral structures are also common within the mat nanospheres a few tens of nanometres in diameter occur attached to coccoid bacteria and within their cells these are interpreted as permineralized viruses and could be significant as nuclei for crystallite crystal precipitation microspheres 1 to 10 m in diameter result from intracellular permineralization within bacteria or the mineralization of the bacteria themselves carbonates and clay minerals are commonly aggregated to form peloids tens of microns in size surrounded by residual organic matter magnesium silicate and carbonate precipitation are likely to have been driven by ph saturation index redox changes within the mat related to microenvironmental chemical changes induced by the microbes extracellular polymeric substances viruses and their degradation

the impact of the atmosphere on the eyjafjallajokull 2010 eruption plume 1 the eruption of eyjafjallajokull volcano in 2010 lasted 39 days 14 april 23 may the eruption had two explosive phases separated by a phase with lava formation and reduced explosive activity during the explosive phases there were episodes of strong winds that advected ash to the south and southeast leading to widespread disruptions in air traffic the height of the eruption plume was monitored with a weather radar and with web cameras mounted with a view of the volcano three different types of the impact of the ambient atmosphere on the eruption plume are described first the weather situation throughout the eruption has been analyzed the frequency of northerly wind component is found to be unusually high or 71 in comparison to 49 on average in spring secondly during the effusive phase of the eruption diurnal variation was observed in the plume altitude and there is evidence that suggest that nocturnal inversions may have played a role limiting the rise of the weak plume thirdly images from a web camera were analyzed and the rise of individual cloud heads associated with explosions at the volcano vent mapped the velocity profiles obtained largely agree with conceptual models of volcanic plumes

stromatolites in precambrian carbonates evolutionary mileposts or environmental dipsticks stromatolites are attached lithified sedimentary growth structures accretionary away from a point or limited surface of initiation though the accretion process is commonly regarded to result from the sediment trapping or precipitation inducing activities of microbial mats little evidence of this process is preserved in most precambrian stromatolites the successful study and interpretation of stromatolites requires a process based approach oriented toward deconvolving the replacement textures of ancient stromatolites the effects of diagenetic recrystallization first must be accounted for followed by analysis of lamination textures and deduction of possible accretion mechanisms accretion hypotheses can be tested using numerical simulations based on modern stromatolite growth processes application of this approach has shown that stromatolites were originally formed largely through in situ precipitation of laminae during archean and older proterozoic times but that younger proterozoic stromatolites grew largely through the accretion of carbonate sediments most likely through the physical process of microbial trapping and binding this trend most likely reflects long term evolution of the earth s environment rather than microbial communities

estimation of exit velocity of volcanic plume from analysis of vortex structures abstract we propose a simple method for estimating the exit velocities of volcanic eruptions from the observation of volcanic plumes for this purpose we used a model of a vortex ring of an experimental jet which was developed in the engineering field to validate the model for the vortex structures of volcanic plumes we applied it to plumes generated in 3 d numerical simulations in 11 cases where exit velocity 66 8 200 5 m s is given as a boundary condition we successfully estimated it with 7 underestimation by analyzing the size and motion of the leading vortex ring that forms at the plume front using the same procedure we could also estimate the exit velocity by analyzing the trailing vortices that develop behind the vortex ring 14 underestimation from these results we conclude that i the model of the vortex ring proposed by the jet engineering studies is appropriate for the vortex ring at the front of simulated volcanic plumes and ii the model is also applicable to the trailing vortices of the plumes these conclusions indicate that we can estimate the time evolution of the exit velocity for a series of eruptions from observations of the vortex structures of the actual volcanic plumes by applying that method to an eruption of sakurajima volcano on february 15 2011 we found that following an increase during the first 10 s of the eruption the exit velocity remained constant at 40 m s up to 80 s after the onset of the eruption our method will be useful in understanding the time evolution of eruptive events such as the transitional behavior from stable column to column collapse from observations of volcanic plumes

transport of so2 by explosive volcanism on venus observations by the pioneer venus orbiter and many different types of analyses have suggested the possibility of contemporary explosive volcanism on venus the rise of volcanic eruption plumes on venus is reexamined using recent improvements in buoyant plume modeling the first order model applied to venus by previous authors features nonphysical discontinuous solutions for all of the model parameters and lacks internal consistency in the formulation of the governing equations this makes it difficult to assess the validity of the venus applications and conclusions derived from these models the model used here contains several improvements including two corrections to the formulation and a change in the criterion for the transition of the plume from the jet region to the buoyancy driven region the model used in earlier works assumed a discontinuous transition between these two regions resulting in an overestimate of the transition height as well as the maximum plume height the effect of the transition criterion is magnified on venus where the continuous solution appears to have very little dependence on initial vent size in contrast the discontinuous solution shows a very strong dependence on initial vent size the continuous solution used here indicates that plumes on venus become dominated by buoyancy effects almost immediately above the vent use of the discontinuous solution however suggests that jets up to 10 km above the vent are possible for the boundary conditions considered the combined effect of using the older model for conditions on venus is a 5 8 overestimate of the maximum plume height for vent radii ranging from 20 to 250 m the influence of latitude and elevation are also explored for large eruptions on venus plumes rising in the northern highlands would rise much higher than plumes with identical boundary conditions erupted in the equatorial lowlands this is due to the greater stability of the upper atmosphere at higher latitudes and the sharp decrease in atmospheric pressure as a function of altitude to examine the net effect of all the model assumptions and ambient influences eruptions are simulated for a range of conditions at maat mons and compared with results in the literature these simulations indicate that for small mass fluxes the new model predicts smaller plumes than the older model for larger mass fluxes however the new model predicts larger plumes than the older model because the maat mons summit elevation is already more than 9 km above the mean planetary radius the reduced atmospheric pressure results in a plume with enough buoyancy to more than compensate for all of the model effects these results continue to support the possibility that explosive eruptions on venus may be capable of producing plumes that rise buoyantly to heights detected by the pioneer venus orbiter

macroscopic worm like body fossils from the upper precambrian 900 700 ma huainan district anhui china and their stratigraphic and evolutionary significance abstract abundant and varied macroscopic worm like body fossils from the late precambrian liulaobei formation huainan group and the jiuliqiao formation feishui group in the huainan district northern anhui province china are further investigated through this progress report after the initial discovery by zheng wenwu and a recent study by wang guixiang sinosabellidites zheng in the liulaobei formation is a worm like organism of questionable metazoan origin it has merely a superficial resemblance with the tubes of late vendian early cambrian true sabelliditida but has much in common with the accompanying macroscopic algal remains of tawuia hofmann both pararenicola wang and protoarenicola wang are representatives of primitive worm like animals in the jiuliqiao formation their macroscopic size elongate cylindrical body anterior aperture and apparatus prominent and elastic annulations are characteristic for their metazoan origin although they lack sufficient evidence for their definite relationship with any known kind of living worms the liulaobei formation and the jiuliqiao formation are dated at about 850 ma and 740 ma respectively regional geology and stratigraphic correlation and the occurrence of the distinctive chuaria tawuia assemblage suggest a time range between less than 900 ma and over 700 ma for the whole shallow water marine sedimentary sequence of the huainan and feishui groups this latter group is disconformably covered by the drop stone facies diamictites and tillites of the late precambrian luoquan glaciation apart from the enigmatic sinosabellidites both pararenicola and protoarenicola are claimed to be the oldest multicellular animals so far discovered in the world and the first reliable evidence for the pre ediacarian evolutionary history of manifest metazoan life

explosive volcanism on hecates tholus mars investigation of eruption conditions evidence is presented supporting the identification of a discrete well preserved air fall deposit generated by explosive volcanism on mars the deposit is located immediately to the west of the summit caldera of hecates tholus 32on 209ow the northernmost of the three volcanic constructs in the elysium planitia region the absence of superposed impact craters larger than the resolution limit of the viking images 40 m per pixel indicates a very young age for this eruption which evidently postdates even the most recent collapse episode of the olympus mons caldera 300 m y b p neukum and hiller 1981 from the distribution of craters smaller than 2 km in diameter it appears that the air fall material mantles an area about 50 x 75 km in extent to an estimated thickness of about 100 m by adapting numerical models for terrestrial volcanic eruptions to the martian environment these dimensions imply an eruption cloud height of about 70 km in order to attain such an altitude the mass eruption rate must have been 107 kg s and the volatile content either 1 wt for h20 or 2 wt for co2 although it is not possible to distinguish between silicic and basaltic volcanism on hecates were the volatile species co2 the depth of most recent storage prior to eruption of the magma would have to be 50 100 km due to the solubility of co2 in the melt if h20 were the driving volatile a minimum depth of storage would be 0 2 4 km thereby permitting the possibility of ground water assimilation by the magma

the effect of total grain size distribution on the dynamics of turbulent volcanic plumes abstract the impact of explosive volcanic plumes on climate and on air traffic strongly depends on the concentration and grain size distribution gsd of pyroclastic fragments injected into the atmosphere accurate and robust modelling of the evolution of gsd during pyroclast transport from the vent to the ash cloud is therefore crucial for the assessment of major volcanic hazards analysis of field deposits from various recent plinian eruptions shows that their total gsd is well described by a power law as expected from the physics of magma fragmentation with an exponent d ranging from 3 0 to 3 9 by incorporating these measured gsd into the initial conditions of a steady state 1d model of explosive eruption columns we show that they have a first order impact on the dynamical behaviour of explosive eruption columns starting from an initial value of d the model tracks the evolution of gsd in the column and calculates the dynamical consequences of particle sedimentation the maximum height reached by the column one of the first order results relevant to aircraft safety changes by 30 for mass fluxes of 10 7 kg s 1 or larger and by 45 85 for mass fluxes between 105 and 10 7 kg s 1 depending on exponent d we compare our predictions to a specially assembled set of geologic field data and remote sensing observations from 10 plinian eruptions for which maximum column height and mass flux are known independently the incorporation of realistic power law gsd in the model greatly improves the predictions which opens new perspectives for estimation of ash load and gsd in volcanic clouds from near real time measurements available from satellite payloads our results also contribute to the improvement of volcanic source term characterization that is required input for meteorological dispersion models

particle segregation of an eruption plume as revealed by a comprehensive analysis of tephra dispersal theory and application abstract a new way to deduce particle segregation in an uprising eruption column is developed this method subdivides an eruption column into horizontal slices and particle dispersal from each column slice is calculated using an advection diffusion model named tephra2 a grid search is employed to obtain the particle segregation from each column slice and other unknown parameters vent position diffusion coefficient and particle density the initial conditions for the calculation were mass loading data collected on the ground wind profile and minimum empirical parameters this method is applied to the 1986b eruption of izu oshima volcano japan which was a sub plinian eruption with a vertically uprising column of 10 km high a previous study of this eruption employed a gravity current model which assumes that most of the tephra segregation took place at the column umbrella transition and at the base of the umbrella cloud the gravity current model was used to calculate the base height of the umbrella cloud from the mass loading distribution on the ground and the calculated base height 7 9 km is consistent with the observed column height however the present study shows that most of the particles segregated from the lower parts of the column 1 3 km high and no significant fallout from the upper part of the column was observed even though the segregation pattern is different between the present and past studies the total mass and total grain size distribution are similar this coincidence is attributed to the use of the same decay function of mass loading in both models both assume the exponential decay of mass loading as a function of the area enclosed by the isopleth although the physical meaning of the decay rate is different in the two models this conclusion also implies that the shape of the decay function itself cannot be used to determine which model is appropriate in describing the source column however the applicability of the gravity current model should be justified when the decay rate is low and when an unreasonably high diffusion coefficient is obtained by inversion techniques that use advection diffusion models the new approach of this study also enables the calculation of the total mass and total grain size distribution without hand drawn isopleth maps and uses all of the point data with error evaluations for each point data the calculation results e g the erupted mass are shown with associated errors

gpr investigation of tephra fallout cerro negro volcano nicaragua a method for constraining parameters used in tephra sedimentation models most tephra fallout models rely on the advection diffusion equation to forecast sedimentation and hence volcanic hazards here we test the application of the advection diffusion equation to tephra sedimentation using data collected on the proximal 350 to 1 200 m from the vent to medial greater than 1 200 m from the vent tephra blanket of a basaltic cinder cone cerro negro volcano located in nicaragua our understanding of tephra depositional processes at this volcano is significantly improved by combination of sample pit data in the medial zone and high resolution ground penetrating radar gpr data collected in the near vent and proximal zones if the advection diffusion equation applies then the thickness of individual tephra deposits should have gaussian crosswind profiles and exponential decay with distance away from the vent at cerro negro steady trade winds coupled with brief eruptions of relatively low energy vei 2 3 create relatively simple deposits gpr data were collected along three crosswind profiles at distances of 700 1 600 m from the vent sample pits were used to estimate thickness of the 1992 tephra deposit up to 13 km from the vent horizons identified in proximal gpr profiles exhibit gaussian distributions with a high degree of statistical confidence with diffusion coefficients of 500 m2 s 1 estimated for the deposits confirming that the advection diffusion equation is capable of modeling sedimentation in the proximal zone the thinning trend downwind of the vent decreases exponentially from the cone base 350 m to 1 200 m from the vent beyond this distance deposit overthickening occurs identified in both gpr and sample pit datasets the combined data reveal three depositional regimes 1 a near vent region on the cone itself where fallout remobilizes in granular flows upon deposition 2 a proximal zone in which particles fall from a height of less than 2 km and 3 a medial zone in which particles fall from 4 to 7 km and the deposit is thicker than expected based on thinning trends observed in the proximal zone of the deposit this overthickening of the tephra blanket defining the transition from proximal to medial depositional facies is indicative of transition from sedimentation dominated by fallout from plume margins to that dominated by fallout from the buoyant eruption cloud a feature of deposits previously identified in larger volume eruptions we interpret this change to represent a change in diffusion law occurring at total particle fall times the fall time threshold of numerical models of 400 s thus the detailed gpr profiles and pit data collected at cerro negro help to validate current numerical models of tephra sedimentation

microbial signatures in peritidal siliciclastic sediments a catalogue a catalogue of microbial structural signatures is presented based upon the coupling of fundamental biogeochemical microbial processes and local morphogenetic determinants it summarizes a collection of sedimentary structures obtained from two modern siliciclastic peritidal environments in different climatic zones temperate humid mellum island southern north sea subtropical arid coast of southern tunisia textural geometries reveal a high structural diversity but their determinants are primarily based upon six major parameters 1 intrinsic biofactors structural diversification of sedimentary microbial films and mats inherent in the organisms i e their construction morphology growth taxis and behaviour and local abundance of specific morphotypes most prominent are the ensheathed filamentous cyanobacteria microcoleus chthonoplastes and lyngbya aestuarii and the sheathless filamentous cyanobacterium oscillatoria limosa 2 biological response to physical disturbances sediment supply erosion and fracturing of surface layers resulting from desiccation cause growth responses of biofilms and microbial mats 3 trapping binding effects physicobiological processes give rise to grain orientations and wavy to lenticular lamina lamina specific grain arrangements and sucrose calcium carbonate accumulations 4 secondary physical deformation of biogenic build ups mechanical stresses acting upon sediments overgrown and biostabilized by biofilms and mats produce erosional and overthrust structures 5 post burial processes textural fabrics that evolve from mechanical effects of gas formation from decaying mats and features related to the formation of authigenic minerals calcium carbonates calcium sulphates pyrite 6 bioturbation and grazing post depositional structures such as skolithos type dwellings traces of burrowing insects gastropod grazing traces and faecal pellets in synopsis the catalogue firstly comprises a sound set of ubiquitous signatures this uniformity in architectural characteristics is attributed to the presence and local dominance of certain microbes throughout the different settings the catalogue secondly documents signatures that are extremely sensitive to tidal position hydrodynamic regime and overall climatic conditions these kinds of signature indicate narrow facies zones which often coincide with the activity or dominance zones of certain organisms an overview of structures of microbial origin from the fossil record underlines the potential of many of the signatures included in this catalogue to become fossilized and provide strong indicators of former siliciclastic tidal settings

alternative origins for nannobacteria like objects in calcite more than 40 calcite precipitation experiments were performed under sterile conditions in order to investigate the origins of 25 300 nm spherical rod and ovoid shaped objects that have been widely interpreted as evidence of nanometer scale life i e nannobacteria individual experiments included the addition of soluble organic compounds common species of eubacteria or phage induced eubacterial lysates these experiments indicate that many of the nanometer scale objects have inorganic or nonnannobacterial origins in the precipitation experiments calcite formed euhedral crystals 50 800 nm in diameter and smaller 50 nm anhedral or rounded particles or protocrystals the small anhedral or rounded solids resembled nannobacteria the relative amount of anhedral or rounded calcite was greatest in experiments with a dissolved organic component these controlled experiments are in accord with observations that rounded nanometer scale objects are more common in minerals formed in organic rich environments bacterial fragments occur as rounded to irregularly shaped particles that included cell wall fragments expulsed cytoplasm and relict capsules that also closely resembled nannobacteria acid etching of the large euhedral crystals produced in the precipitation experiments also resulted in the formation of nanometer scale features that resembled nannobacteria in natural carbonates the shapes of the etching artifacts vary as a function of the strength of the acid and the duration of etching much caution is advisable in interpreting the origin of rounded features 50 nm

on lava dome growth with application to the 1979 lava extrusion of the soufriere of st vincent abstract a theoretical analysis is presented for the spread of a viscous liquid flowing under its own hydrostatic pressure on a horizontal surface in order to model lava dome formation two situations are considered in detail the spreading of a constant volume of liquid and the case where the amount of liquid is continually increased experiments with silicone liquids show close agreement with theory the formation of a basaltic andesite lava extrusion in 1979 on the crater floor of the soufriere of st vincent west indies provided the motivation for and an application of the model the extrusion reached a diameter of 868 m and a height of 133 m over a period of 150 days over the first 90 days the growth relationships were consistent with those predicted by theory application of the theory to the soufriere dome suggests an effective viscosity of 2 x 10 12 poise for the basaltic andesite lava the large effective viscosity calculated for the lava may be attributed to the dominant influence of a high viscosity skin which forms at the margins of the flow as it cools after 70 days the rate of growth of the extrusion markedly decreased because a substantial collar of rubble accumulated at the flow front due to this collar the growth of the extrusion ceased after 150 days from approximately two weeks after the initiation of the extrusion the discharge rate of lava decreased approximately linearly with increasing dome height this observation suggests that the lava ascended under a decreasing hydrostatic driving pressure and that extrusion ceased when the lava column reached hydrostatic equilibrium

volcanoes the stratosphere and climate abstract a list of volcanic eruption plumes observed to ascend into or near the stratosphere since 1883 shows that the volcanoes divide readily into two groups one at low and one at higher latitudes a model for the rise of a buoyant volcanic plume rise as applied to volcanic eruptions is corrected for realistic temperature profiles and for the finite vertical extent of the resultant debris clouds the utility of the model can be questioned however owing to the highly uncertain and variable nature of the efficiency of use of heat energy of buoyant rise the observed correlation of stratospheric plumes with climatic effects indicates that those plumes nearer the equator have the largest impact on surface temperatures analysis of the observations also suggests that injection of debris into the stratosphere is more important in determining the effect on climate than either the total volcanic explosivity of the eruption or the actual height reached within the stratosphere

the emplacement dynamics of pumice lobes ascertained from morphology and granulometry examples from the 1993 deposits at lascar volcano chile abstract the work presented here focuses on lobe shapes and clast populations within lobate termini of the 1993 pumice flow deposits at lascar volcano chile a new method to analyze a coarse tail grain size population with field photographs is presented using this method 33 000 0 5 cm clasts from the pumice lobes of the 1993 pumice flow deposits were measured at 36 sites and the resultant grain size distributions were then related to lobe morphology lobe margins i e levees clefts and snouts were found to contain significantly larger pumice clasts and be more poorly sorted than lobe central channels i e locations away from the margins previous laboratory experiments suggest lobe margins form by the floatation and deflection of larger clasts to the margins of an advancing flow lobe results here indicate that the same sorting process efficiently segregates clasts into two flow regimes 1 a mobile central channel depleted in coarse clasts and 2 friction dominated margins enriched in clasts 15 cm the lobe margins 60 enriched in larger particles with matrix

fluid dynamics in volcanology wager prize lecture fluid motions are important in virtually all volcanic processes attempts to understand the mechanism of volcanic activity or the origin of magmas generally require knowledge of fluid dynamics the use of fluid dynamics is illustrated by considering the reynolds numbers of some volcanic fluid flow systems the physics of high reynolds number buoyant plumes is found to be important in situations ranging from the rise of eruption columns in the atmosphere to the replenishment of basaltic magma chambers application of theoretical and experimental work on plumes enables eruption rates to be deduced from eruption column heights and new hypotheses on the origin of some magmatic ores to be put forward the influence of reynolds number on the behaviour of lava is also discussed with application to the origin of archaean komatiite lavas komatiite lavas are argued to have flowed in a turbulent manner whereas modern basalt lavas nearly always flow by laminar shear the turbulent character of komatiites seems to provide an explanation for the origin of associated nickel sulfide mineralization in komaiites by melting and assimilation of sulfide rich sediment this hypothesis depends on komatiite flow having had a high reynolds number

sedimentation from strong volcanic plumes 1 we develop descriptions of the key processes influencing tephra dispersal from strong volcanic plumes these are characterized by the development of a subvertical eruption column in the atmosphere that forms a spreading current at a level of neutral buoyancy we describe the propagation of the spreading current due to both gravity and wind advection using scaling arguments and a simplified geometry to model particle sedimentation in a windy as well as a wind free environment new parameterizations are used to describe the wind field below the spreading current particle aggregation and particle density variations we conducted a broad study to investigate the effects of these processes and made comparisons with field observations the greatest variations resulted from wind advection below the spreading current which shifts the plume corner mass accumulation and the position of transitions in fallout regimes downwind particle aggregation strongly depends on the initial grain size distribution and significantly affects deposit thinning depending on the aggregate size and density and on the relative amount of aggregating particles small aggregates can reproduce secondary maxima of mass accumulation when sedimenting in a wind field variation of particle density also affects the resulting thinning trend the model provides acceptable reproduction of observations of the propagation of the spreading current tested with the plinian phase of the 18 may 1980 eruption of mount st helens and of observed thinning of tephra fallout deposits tested with deposits from mount st helens 1980 askja d 1875 quizapu 1932 minoan eruption 3 6 ka b p novarupta a 1912 and hudson 1991

transport of atmospheric water vapor by volcanic eruption columns contrary to assumptions often made in the literature explosive volcanic eruptions are capable of transporting significant amounts of water into the stratosphere in addition to the magmatic water component atmospheric water vapor is entrained by the column at lower levels a theoretical model for the conservation of mass momentum and thermal energy of four separate components dry air water vapor liquid condensates and solid particles is used to determine the extent of atmospheric water redistribution we examine the effects of water vapor condensation on dynamical characteristics and ambient water vapor transport a simple technique is presented for deriving canonical forms for the complex system of ordinary differential equations governing the column components solutions of this model are presented that show the influence of different volcanic boundary conditions and a range of ambient water vapor distributions on transport of the buoyant column we show that the water component vapor liquid of small eruption columns rising through a wet atmosphere is dominated by entrained water whereas larger columns are dominated by the magmatic water this is due in part to the proportionately smaller entrainment surface area in relation to the control volume for the larger columns we also show that a maintained column with an initial mass flux of 2 7 108 kg s 1 erupted into a wet atmosphere would inject 96 mt of water vapor into the stratosphere over 24 hours comparable to the annual input from methane oxidation or 100 midlatitude thunderstorms this increase may accelerate the conversion of simultaneously erupted volcanic so2 into sulfuric acid

sensitivity of the dynamics of volcanic eruption columns to their shape this paper presents a one dimensional steady state model to investigate the sensitivity of the dynamics of sustained eruption columns to radius variations with height due to thermal expansion of the entrained air and decreases in atmospheric pressure with height in contrast to a number of previous models using an equation known as the entrainment assumption the new model is based on similarity arguments to derive an equation set equivalent to the model proposed by woods bull volcanol 50 169 193 1988 this approach allows investigation of the effect of gas compressibility on the entrainment rate of ambient air which has been little examined for a system in which a decrease in pressure significantly affects the density stratification of a compressible fluid the new model provides results that include two end members one in which the volume change within the eruption columns affects only the radial expansion without changing the vertical motion and the other is the converse the woods bull volcanol 50 169 193 1988 model can be regarded as being between those two end members the range of uncertainty arises because the extremely high temperature of discharged materials from a volcanic vent and the exceptional terminal height of the eruption columns allow significant expansion of the gas component in the eruption columns making them behave differently from common turbulent plumes this study indicates that the maximum height of the eruption columns is affected considerably by this uncertainty particularly when the eruption columns extend above a height of 10 km at which the pressure is about one fourth the pressure at the ground surface column collapse may also be suppressed in wider parameter ranges than previously estimated however the uncertainty can be reduced by measuring column radii through a vertical profile during actual volcanic eruptions accordingly this paper suggests that appropriate observation of eruption column shapes is essential for improving our understanding of the dynamics of eruption columns

nannobacteria and the precipitation of carbonate in unusual environments abstract nannobacteria are abundant not only in normal marine limestones but also in other environments such as continental caliches fresh water streams springs water pipes caves etc cells are typically 50 to 200 nm in diameter