laboratory experiments of forced plumes in a density stratified crossflow and implications for volcanic plumes the mass eruption rate feeding a volcanic plume is commonly estimated from its maximum height winds are known to affect the column dynamics causing bending and hence reducing the maximum plume height for a given mass eruption rate however the quantitative predictions including wind effects on mass eruption rate estimates are not well constrained to fill this gap we present a series of new laboratory experiments on forced plumes rising in a density stratified crossflow we identify three dynamical regimes corresponding to increasing effect of wind on the plume rise the transition from one regime to another is governed by two dimensionless velocity scales defined as a function of source and environmental parameters the results are found consistent with the conditions of historical eruptions and provide new empirical relationships to estimate mass eruption rate from plume height in windy conditions leading to valuable tools for eruption risk assessment

variations in column height and magma discharge during the may 18 1980 eruption of mount st helens abstract peak eruption column heights for the b1 b2 b3 and b4 units of the may 18 1980 fall deposit from mount st helens have been determined from pumice and lithic clast sizes and models of tephra dispersal column heights determined from the fall deposit agree well with those determined by radar measurements b1 and b2 units were derived from plinian activity between 0900 and about 1215 hrs b3 was formed by fallout of tephra from plumes that rose off pyroclastic flows from about 1215 to 1630 hrs a brief return to plinian activity between 1630 and 1715 hrs was marked by a maximum in column height 19 km during deposition of b4 variations in magma discharge during the eruption have been reconstructed from modelling of column height during plinian discharge and mass balance calculations based on the volume of pyroclastic flows and coignimbrite ash peak magma discharge occurred during the period 1215 1630 hrs when pyroclastic flows were generated by collapse of low fountains through the crater breach pyroclastic flow deposits and the widely dispersed co ignimbrite ash account for 77 of the total erupted mass with only 23 derived from plinian discharge a shift in eruptive style at noon on may 18 may have been associated with increase in magma discharge and the eruption of silicic andesite mingled with the dominant mafic dacite increasing abundance of the silicic andesite during the period of highest magma discharge is consistent with the draw up and tapping of deeper levels in the magma reservoir as predicted by theoretical models of magma withdrawal return to plinian activity late in the afternoon when magma discharge decreased is consistent with theoretical predictions of eruption column behavior the dominant generation of pyroclastic flows during the may 18 eruption can be attributed to the low bulk volatile content of the magma and the increasing magma discharge that resulted in the transition from a stable convective eruption column to a collapsing one

hydrometeor enhanced tephra sedimentation constraints from the 18 may 1980 eruption of mount st helens 1 uncertainty remains on the origin of distal mass deposition maxima observed in many recent tephra fall deposits in this study the link between ash aggregation and the formation of distal mass deposition maxima is investigated through reanalysis of tephra fallout from the mount st helens 18 may 1980 msh80 eruption in addition we collate all the data needed to model distal ash sedimentation from the msh80 eruption cloud four particle size subpopulations were present in distal fallout with modes at 2 2 4 2 5 9 and 8 3 settling rates of the coarsest subpopulation closely matched predicted single particle terminal fall velocities sedimentation of particles 100 m was greatly enhanced predominantly through aggregation of a particle subpopulation with modal diameter 5 9 0 2 19 3 m mammatus on the msh80 cloud provided a mechanism to transport very fine ash particles with predicted atmospheric lifetimes of days to weeks from the upper troposphere to the surface in a matter of hours in this mechanism ash particles initiate ice hydrometeor formation high in the troposphere subsequently the volcanic cloud rapidly subsides as mammatus develop from increased particle loading and cloud base sublimation rapid fallout occurs as the cloud passes through the melting level in a process analogous to snowflake aggregation aggregates sediment en masse and form the distal mass deposition maxima observed in many recent volcanic ash fall deposits this work provides a data resource that will facilitate tephra sedimentation modeling and allow model intercomparisons

impact of the lateral blast on the spatial pattern and grain size characteristics of the 18 may 1980 mount st helens fallout deposit the 18 may 1980 eruption of mount st helens started with a lateral blast that fed a pyroclastic surge which then uplifted to form a co blast plume thirty minutes later plinian activity started at the vent and fluctuated in intensity for 9 h the resulting fallout deposit documented to 600 km from vent presents some striking features 1 displacement of the overall deposit to the north of the vent 2 a secondary thickness and mass maximum at 300 km from vent 3 a total grain size distribution dominated by fine ash 62 wt of the deposit 63 m and 4 individual grain size distributions that vary dramatically in the crosswind direction from strongly bimodal in the south to skewed unimodal in the north results from a new deconvolution of the individual grain size distributions show that they are a combination of a coarse subpopulation that decreases in size with distance from vent and a constant fine subpopulation with a mean of 15 m relative proportions of each subpopulation vary asymmetrically in the crosswind directions with the fine subpopulation preponderant toward the north and the coarse one dominating the south of the deposit both reach their absolute maxima in mass on the deposit axis componentry analyses of selected samples show that blast derived material is greatly enriched toward the north of the deposit these results indicate that the co blast plume dispersed fine grained material over great distances and dominated the fine subpopulation comparison with reanalysis data of atmospheric wind fields and satellite images of the spreading ash cloud suggests contrasting ash transport and depositional processes for the early co blast plume and the later vent derived plinian plumes the co blast plume is displaced to the north it had a high overshoot height and eastward dispersion via strong winds low in the stratosphere 10 15 km the plinian plumes were lower and dispersed most of the material to the southeast as the direction of high velocity winds shifted just before the late climactic plinian eruptive phase fine ash fine subpopulation was deposited continuously throughout the deposit with an increase of sedimentation rate 300 km from the vent where there is a secondary maximum in the deposit mass and thickness fine ash probably settled by a combination of enhanced sedimentation mechanisms including not only aggregation but also gravitational convective instabilities of cloud base hydrometeor formation and destruction and entrainment of small particles by larger ones finally we show that half of the deposit by mass in the medial area was deposited by the co blast plume and that a significant proportion of the mount st helens fallout deposit is nonjuvenile which has implications for the magmatic budget of this eruption

the importance of double diffusion to the settling of suspended material the vertical fingering motions which can occur when warm salty water overlies colder fresher water are important to the vertical flux of salt in the ocean an analogous and not uncommon situation is that where turbid water overlies clearer and denser water for the case of an originally sharp horizontal interface between the two water layers associated as an example with an interflow due to a warm muddy river entering a stratified lake the resulting downward sediment flux is compared with that occurring by way of gravitational settling rules are proposed to ascertain when the fingering effect could be important to sedimentation for example it seems that fingering could be of consequence in the situation where the sediment has a diameter of 2 m and the upper layer is about 1 c warmer than the clear lower layer when the upper layer concentration is 1 ppm the effect of fingering on the residence time of a gravitationally stable turbid layer is calculated such layers may be more short lived than commonly thought

settling driven gravitational instabilities associated with volcanic clouds new insights from experimental investigations downward propagating instabilities are often observed at the bottom of volcanic plumes and clouds these instabilities generate fingers that enhance the sedimentation of fine ash despite their potential influence on tephra dispersal and deposition their dynamics is not entirely understood undermining the accuracy of volcanic ash transport and dispersal models here we present new laboratory experiments that investigate the effects of particle size composition and concentration on finger generation and dynamics the experimental set up consists of a plexiglas tank equipped with a removable plastic sheet that separates two different layers the lower layer is a solution of water and sugar initially denser than the upper layer which consists of water and particles particles in the experiments include glass beads as well as andesitic rhyolitic and basaltic volcanic ash during the experiments we removed the horizontal plastic sheet separating the two fluids particles were illuminated with a laser and filmed with a hd camera particle image velocimetry piv is used to analyse finger dynamics results show that both the number and the downward advance speed of fingers increase with particle concentration in the upper layer while finger speed increases with particle size but is independent of particle composition an increase in particle concentration and turbulence is estimated to take place inside the fingers which could promote aggregation in subaerial fallout events finally finger number finger speed and particle concentration were observed to decrease with time after the formation of fingers a similar pattern could occur in volcanic clouds when the mass supply from the eruptive vent is reduced observed evolution of the experiments through time also indicates that there must be a threshold of fine ash concentration and mass eruption rate below which fingers do not form this is also confirmed by field observations

comparison of lake and land tephra records from the 2015 eruption of calbuco volcano chile tephra layers in lake sediment cores are regularly used for tephrostratigraphy as isochronous features for dating and recording eruption frequencies however their value for determining volcanic eruption size and style may be complicated by processes occurring in the lake that modify the thickness and grain size distributions of the deposit to assess the reliability of data from lake cores we compare tephra deposited on land during the 2015 eruption of calbuco volcano in chile to records in sediment cores from three lakes of different sizes that are known to have received primary fall deposits in general the thickness and granulometry of the deposit in lake cores and nearby terrestrial sections are very similar as anticipated however cores sampled close to here within 300 m of fluvial inflows were affected by sediment deposition from the lake s catchment they differed from primary deposits not only in their greater thickness and organic content but also in poor sorting and lack of grading cores 850 m away from the inlet were not affected we consider our results in the context of the particle settling regime as well as each lake s location bathymetry and catchment area we find that the particle settling regime is important in more distal settings where the ash particles are small and particle settling occurs in density plumes rather than as individual particles we conclude that lake cores can be useful for physical volcanology providing consideration is given to eruption parameters such as particle size and mass flux as well as lake features such as bathymetry and catchment area

characteristics of two phreatoplinian ashes and their water flushed origin abstract the whole deposit grain size populations have been determined for two phreatoplinian ashes of the rhyolitic taupo volcano new zealand one is much finer than plinian pumice deposits studied from the same volcano and the other differs in having a lower content of coarse pumice the poor sorting of the two ashes is attributed mainly to water scavenging of the ash cloud the very limited fractionation with distance from source combined with the very regular exponential thickness decrease indicates that the scavenging water was an integral part of the ash cloud and was derived from lake taupo at times when the proportion of erupted water to magma became particularly high erosion of the underlying deposits took place and to this is attributed the striking gullying of the surface which separates the two ashes

the influence of diffusive convection on sedimentation from buoyant plumes abstract diffusive convection driven by the differential diffusion of density altering fluid properties may enhance the scavenging of particles from natural buoyant plumes for single phase fluid solute heat systems this phenomenon has been extensively studied because salt fingering generated at the oceanic thermocline is a major mechanism of salt transport in the oceans however the influence of this process on particle laden plumes for example fluvial plumes in lakes and estuaries volcanic clouds and seafloor hydrothermal plumes is largely unknown in this paper we present direct experimental measurements of the interfacial particle flux at the plume base which can be applied to predict particle scavenging from natural buoyant plumes particle flux is measured using a light attenuation technique employing a chain of photodiodes which average concentration over a large number of fingers the results are in good general agreement with earlier studies based on finger velocity flux measurements cover a wide range of conditions from those where diffusive convection dominates to those where settling and diffusive convection are of a similar magnitude for very small particles double diffusive salt finger theory is applicable to two component particulate systems as suggested by earlier studies green t 1987 the importance of double diffusion to the settling of suspended material sedimentology 34 319 331 two component diffusive convection theory is extended to three components in order to predict particle scavenging from marine fluvial plumes which involve the diffusion of sediment salt and heat for larger particles which settle significantly the flux can be approximated by adding the double diffusive and settling fluxes a theory to predict particle transport through the lower layer and sedimentation at the bed is developed based on the observation of strong convection below the plume application of our theory and experimental results indicates that while double diffusion may significantly influence the longitudinal distribution and vertical sorting of deposits from lacustrine plumes the diffusive convection process is generally insignificant in marine plumes observational evidence for lacustrine double diffusion based on water column measurements is presented

settling driven convection a mechanism of sedimentation from stratified fluids convection driven by sediment particles may play an important role in sedimentation from the base of buoyant hypopycnal plumes for example fluvial plumes in stratified estuaries and lakes black smokers on the ocean floor volcanic clouds and coastal currents in addition to the well known double diffusive convection mechanism another mode of convective instability development is by settling across the density interface we performed laboratory experiments to investigate this fingering convective instability mechanism and its effect on particle distribution in the water column and deposition at the bed a simple theoretical model of finger formation at a fluid density interface is developed based on an analogy with thermal plume formation at a flat heated plate this model which involves a thickening interface layer that becomes gravitationally unstable relative to the ambient fluid is in good agreement with measurements of finger size and instability wavelength from visualization experiments since fingering at the density interface drives larger scale convection in the fluid below a mass balance model of the lower layer assuming strong mixing i e uniform sediment concentration is successfully applied to predict sediment concentration in the water column and deposition at the bed strong mixing can be assumed since convective velocities are usually much greater than the particle fall velocities as convection proceeds the sediment concentrations in the two layers approach each other and convection will die out using the model equations we develop analytical expressions for the time when convection ceases and the portion of sediment remaining in the water column

particle sedimentation and diffusive convection in volcanic ash clouds 1 understanding the longevity of volcanic ash clouds generated by powerful explosive eruptions is a long standing problem for assessing volcanic hazards and the nature and time scale of volcanic forcings on climate change it is well known that the lateral spreading and longevity of these clouds is influenced by stratospheric winds particle settling and turbulent diffusion observations of the recent 2010 eyjafjallajokull and 2011 grimsvotn umbrella clouds as well as the structure of atmospheric aerosol clouds from the 1991 mt pinatubo event suggest that an additional key process governing the cloud dynamics is the production of internal layering here we use analog experiments on turbulent particle laden umbrella clouds to show that this layering occurs where natural convection driven by particle sedimentation and the differential diffusion of primarily heat and fine particles give rise to a large scale instability where umbrella clouds are particularly enriched in fine ash this particle diffusive convection strongly influences the cloud longevity more generally cloud residence time will depend on fluxes due to both individual settling and diffusive convection we develop a new sedimentation model that includes both sedimentation processes and which is found to capture real time measurements of the rate of change of particle concentration in the 1982 el chichon 1991 mt pinatubo and 1992 mt spurr ash clouds a key result is that these combined sedimentation processes enhance the fallout of fine particles relative to expectations from individual settling suggesting that particle aggregation is not the only mechanism required to explain volcanic umbrella longevity

a laboratory study of explosive volcanic eruptions this paper describes a series of laboratory experiments in which buoyant mixtures of methanol and ethylene glycol meg are injected as a downward propagating jet into a tank of fresh water as the meg mixes with water it becomes denser than the water if the meg mixes with sufficient water before its initial momentum is exhausted the jet fluid may become dense and continue downward into the tank as a convecting plume if the jet does not have sufficient initial momentum then a collapsing fountain develops and the material in the jet rises back toward the top of the tank and spreads laterally as a gravity current subsequent mixing can cause some of the material in the gravity current to become dense separate from the current and sink into the tank although the direction of gravity is reversed these experiments simulate many of the important dynamical features of eruption columns which can develop during explosive volcanic eruptions in the volcanic situation a hot dense and dusty mixture of gas ash and clasts is erupted from a vent at high speed if sufficient ambient air is entrained into the jet then the mixture may become buoyant through heating and expansion of the air it therefore continues rising high into the atmosphere otherwise the material collapses back to the ground these experiments allow one to investigate systematically the different styles of behavior of the erupted material as the eruption conditions change four different styles of behavior have been identified with transitions from one style to the next as the initial momentum flux of the jet is decreased 1 plinian style convecting columns 2 the periodic release of discrete convecting clouds originating close to the vent from a collapsed fountain 3 coignimbrite eruption columns centered some distance from the vent which are generated when a fraction of a pyroclastic flow becomes buoyant and 4 pyroclastic flows in which the majority of the material remains relatively dense and therefore spreads laterally from the vent using a simple theoretical model of the laboratory experiments an analytical expression describing the conditions necessary for collapse of the analogue laboratory columns has been derived this is successfully compared with the laboratory experiments the simple analysis predicts that column collapse may be induced by 1 increasing the density of the erupted material 2 decreasing the maximum buoyancy the mixture can attain on mixing with ambient 3 increasing the erupted mass flux for a given momentum flux or 4 decreasing the initial momentum flux for a given mass flux as may occur if the vent is eroded these results are consistent with earlier studies wilson et al 1980 wilson and walker 1987 bursik and woods 1991 although the analogue experimental system is somewhat simplified the observations of the periodic release of convecting thermals just after column collapse suggest a mechanism for the complex grading which is commonly found just below the collapse horizons in fall deposits for example the fogo a deposit walker and croasdale 1970 and the vesuvius a d 79 deposit carey and sigurdsson 1987 in conjunction with partial column collapse this periodicity also suggests a means by which flow deposits may become interspersed with fall deposits this feature has been observed in a number of cases including the taupo deposit wilson and walker 1985

nanomechanical characterization of organic matter in the bakken formation by microscopy based method abstract organic rich shales are highly heterogeneous due to the presence of a variety of constituent components among them organic matter is poorly known in terms of mechanical properties due to the lack of high resolution analytical equipment to isolate organic matter in situ for mechanical testing in this study we proposed a new method to link morphology and geochemical properties of organic matter to its mechanical characteristics at the nanoscale kerogen type and thermal maturity along with mineralogy were evaluated by rock eval 6 pyrolysis total organic carbon toc analysis and x ray diffraction xrd analysis then the atomic force microscopy peakforce quantitative nano mechanical mapping afm peakforce qnm mode was employed and coupled with optical and electron microscopy to first visualize and then quantify the elastic properties of organic components in three different samples from the bakken formation hebamorphinite matrix bituminite and solid bitumen were identified as the main organic constituent along with oil prone marine kerogen type ii alginite and acritarch and also a bacterial derived granular micrinite like maceral based on tmax and vitrinite ro values or vro eq from bitumen ro thermal maturity of the samples ranged from immature to mature past peak oil window the average value of young s modulus for organic matter was measured in the range of 2 91 11 77 gpa it was also found that organic matter becomes stiffer with increased thermal maturity this study exhibits a great potential as a novel method for in situ analysis of mechanical properties of organic matter in shale reservoirs at a fine scale

effects of particle mixtures and nozzle geometry on entrainment into volcanic jets efficient turbulent entrainment causes otherwise dense volcanic jets to rise high into the atmosphere as buoyant plumes classical models suggest that the inflow of air is 10 15 of the axial velocity giving predictions for the height of the plume and in turn the composition and structure of the resulting umbrella clouds crucially entrainment is assumed independent of source geometry and mechanically unaffected by the pyroclastic mixture properties we show that particle inertia and vent geometry act to modify the shape of the largest eddies defining the jet s edge and thus entrainment of the ambient whereas particle free flows are essentially unaffected by vent shape entrainment into particle laden flows is enhanced for flared vents and reduced for cylindrical vents our results predict that vent erosion during an explosive eruption reduces the height of volcanic jets alters the structure and sedimentation regime of the umbrella cloud and the resulting deposit

petrographic and geochemical characterization of organic rich mississippian black shales in the north of spain vegamian formation cantabrian zone abstract black shales 1 60 m thick with minor cherts radiolarites and phosphate nodules of mississippian age middle upper tournaisian vegamian formation occur in the fold and thrust belt of the cantabrian zone n spain at the base of the carboniferous succession which is infilling the variscan foreland basin the vegamian formation was accumulated in a similar sedimentary and paleogeographic context to the upper devonian carboniferous black shales of the appalachian arkoma fort worth western canada and antler foreland basins north america and to the variscan foreland basin in belgium and germany five stratigraphic sections were investigated in the southern branch of the cantabrian zone corresponding to the shallower sectors of the passive margin of the variscan foreland basin in n spain where this stratigraphic unit reaches a thickness of generally the organic matter is dominated by bitumen found either as diffuse masses or concentrated in spaces and cavities often parallel to the bedding planes or filling voids within calcite veins and fractures generally the bitumen masses are homogeneous without secondary porosity but occasionally they show mosaic optical texture indicating thermal transformation anastomosing structures likely related to bituminite are also common and exhibit a large range of reflectances autochthonous organic matter algae bacteria is seen as scarce tasmanites and liptodetrinite whereas allochthonous components vitrinite inertinite are also scarce except in the olleros section the range of reflectances of vitrinite like particles is similar to that of bitumen but the identification is uncertain and therefore the reflectance of bitumen brr has been used for thermal maturity assessment a gaussian like distribution of bitumen reflectances was found for la brana section brr 0 70 whereas a bimodal distribution was observed in olleros brr 0 70 and vegamian sections brr 0 95 and large scatter of readings in millaro brr 1 55 the vitrinite reflectance equivalent estimated from aromatic compounds indicates that most of the existing correlations between vitrinite and bitumen reflectances underestimate the maturity of the lowest reflecting sections and overestimate it in the highest reflecting one ts toc ratios the geochemistry of organic matter and spectral gamma ray measurements suggest a normal marine to dysoxic environment of deposition with only local anoxia at the base of the vegamian formation

water column anoxia enhanced productivity and concomitant changes in δ13c and δ34s across the frasnian famennian boundary kowala holy cross mountains poland the investigation of the trace element and organic geochemistry of the frasnian famennian boundary section at kowala holy cross mountains poland shows that the lower water column was oxygen deficient during late frasnian and early famennian times the abundance and carbon isotopic composition of diaryl isoprenoids biomarkers indicative for green sulfur bacteria prove that euxinic waters reached into the photic zone at least episodically total organic carbon toc contents show two maxima that are time equivalent to the kellwasser horizons deposited in shallower water settings enhanced toc concentrations are explained by a higher primary productivity presumably as a consequence of an enhanced nutrient supply from the continent the increase in the abundance of hopanes and bituminite suggests that the bacterial contribution to toc increased at the frasnian famennian transition the sulfur isotopic composition of pyritic and organically bound sulfur shows a 27 excursion across the boundary the observation that the 34s values of organic bound sulfur closely resemble that of pyrite sulfur indicates a common sulfur source likely early diagenetic sulfide a change in the 13c of total dissolved inorganic carbon as a consequence of an enhanced burial of 12c enriched organic carbon is indicated by a 3 excursion measured for toc as well as for individual n alkanes and isoprenoids the burial of large amounts of organic carbon is expected to result in a decrease in pco2 and should affect the photosynthetic carbon isotope fractionation ep the fact that we observe no change in ep can be explained by the circumstance that ep was most probably at maximum values as a consequence of high atmospheric and oceanic dissolved co2 concentrations during the devonian

ash sedimentation by fingering and sediment thermals from wind affected volcanic plumes ash fallout and volcanic plume dispersion represent critical hazards for local and global human populations for minutes to years after the onset of an eruption understanding the key processes governing the sedimentation of ash particles is a major challenge in modern volcanology from modeling and risk management perspectives recent experiments predict that sedimentation from eruption clouds rich in fine grained ash can be driven by convective phenomena in the form of 100 m to km scale ash fingers related to the intermittent formation and detaching of ash rich particle boundary layer remote sensing observations of mammatus and cloud veils from numerous eruptions over recent years as well as field observations of spatially discontinuous ash deposits are consistent with this prediction indeed this mode of ash sedimentation is predicted to be the predominant mechanism of fine ash removal for a significant fraction of eruptions in the geological records here we use a novel combination of 3 millimeter wavelength doppler radar observations and time series of optical disdrometer data to characterize for the first time in real time the time varying structure and sedimentation properties of volcanic ash plumes under steady wind conditions as a case study we apply this new method to weak short lived plumes from stromboli volcano 96 of the disdrometer proximal sedimentation data highlight pulsatory phases of increased sedimentation rate that are 20 60 s apart and characterized by particle size distribution variation with bulk concentrations up to 681 mg m3 radar data also record intermittent periods of higher reflectivity i e a factor of 3 in mass concentration inside the ash sedimentation interspersed by 30 to 50 s and interpreted as ash fingers crossing the radar beam from time series of radar signals and ground based disdrometer measurements together with simple analog experiments we develop a conceptual model for intermittent sedimentation from wind affected ash plumes in particular we show that when wind speeds are comparable to or greater than ash settling velocities the dynamics of wind driven rolls in ash clouds can govern the production of gravitational instabilities and the occurrence and timing of ash fingers that form descending sediment thermals in turn this study suggests that ambient wind should affect the maximum size and minimum concentration of ash particles needed to form fingers but also control where and when fingers form at the base of wind drifted ash plumes these novel predictions highlight the need for future work aimed at refining our understanding of ash finger formation under windy conditions from the perspectives of in situ characterization numerical modeling and risk assessment of fine ash dispersal from the most frequent style of eruptions on earth

a role for organic petrology in integrated studies of mudrocks examples from devonian black shales of the eastern us abstract over the years the study of mudrocks has lagged far behind that of other lithologies a circumstance that is in part due to their fine grained nature and in part due to economic realities yet within petroleum systems mudstones are usually the main source of hydrocarbons and typically are also important as hydrocarbon seals recent work on late devonian mudstones from the eastern us shows that much progress can be made through an integration of outcrop study macro and micropaleontology ichnofossils gamma ray spectroscopy microscopic examination of thin sections in transmitted and reflected light electron microscopy sem bse electron microprobe carbon and sulfur isotopes and organic geochemistry erosion surfaces within this black shale succession have been traced over large distances and provide the foundation for a sequence stratigraphic re interpretation of these rocks evidence of storm wave reworking of the seabed as well as the realization that benthic colonization was much more widespread than previously believed suggest that anoxic conditions in the water column were not a controlling factor in the accumulation of the large quantities of organic matter found in these shales these distal devonian shales accumulated slowly and allowed accumulation of large proportions of organic matter in modern settings of abundant organic matter accumulation the original material is broken down by bacteria within a matter of months into a mass of largely unidentifiable organic particles and extracellular bacterial slime although one can still find identifiable material within this mass slime and amorphous material strongly dominate after burial and maturation this material turns into the various organic macerals that organic petrologists are accustomed to describe one might wonder in this context how much information about the origin of a given mudstone unit can we hope to extract through organic petrology in order to illustrate how organic petrology of mudrocks can contribute to their better understanding late devonian black shales of the eastern us will be examined from a sedimentological perspective combining sedimentologic and geochemical data with basic observations on organic petrology illustrates how the latter can contribute to more realistic scenarios of black shale genesis

application of confocal laser scanning microscopy clsm to autofluorescent organic and mineral matter in peat coals and siliciclastic sedimentary rocks a qualitative approach abstract organic matter occurring in the form of macerals and natural solid bitumens in peats coals and siliciclastic sediments of various stratigraphic ages and locations was studied by means of conventional incident light microscopy and clsm classical optical microscopic investigations are restricted by conventional 2 d imaging and are often hindered by the associated out of focus blur effects the qualitative application of clsm overcomes these limitations permitting to reveal precisely 3 d morphology and detailed microstructure of autofluorescent organic matter the in depth examinations along z axis in xy xz or yz scanning modes at increments of 250 nm are capable to reconstruct 3 d internal configuration and arrangement occurring in autofluorescent macerals the non invasive and non destructive laser raster technique is applied to characterize in situ autofluorescent organic particles at micron to sub micron scale resolution in polished whole rock pellets in this study we demonstrate that clsm is suitable to i detect fine scale microstructure of autofluorescent organic matter iii reconstruct 3 d morphology at cellular and tissue level iii analyze maceral composition in terms of its relicts and fragments beyond the classical optical assignment limits iv detect and examine inorganic components enclosed in the embedding mineral bituminous groundmass and v differentiate mineral constituents from the remaining organic matter clsm as an optical microscopic technique was applied to generate high resolution 2 d and 3 d images projections as well as 3 d reconstructions of autofluorescent objects excited with aid of laser induced light operating at variable visible wavelengths clsm is applicable to support microscopic studies of thermally immature and mature organic matter within the oil and early gas windows enclosed either within siliciclastic and carbonate sediments or in peat and low to medium rank coals the application of this technique will be of great interest to a wide range of geology related disciplines such as petroleum geology biostratigraphy marine geology peat petrography and archeology

crystal capture sorting and retention in convecting magma the mystery of producing strong compositional diversity among suites of comagmatic igneous rocks is investigated by considering the dynamic evolution of basaltic magma in a sheet like chamber a central conclusion is that inward progressing crystallization produces strong viscosity and temperature gradients that promote convection only near the leading edge of the upper thermal boundary layer convection is apparently confined to an essentially isoviscous isothermal region that hugs the downward growing roof zone strong changes in viscosity with crystallization divide the upper and lower thermal boundary layers into regions of decreasing viscosity and crystallinity n called rigid crust n 0 5 mush 0 5 n 0 25 and suspension n 0 25 the strong increase in viscosity near the mush suspension interface acts as a capture front that overtakes and traps slowly settling crystals initial phenocrysts mostly escape capture but crystals nucleated and grown in the suspension zone can escape only if the capture front slows to a critical rate attainable only in bodies thicker than about 100 m escaping crystals are redistributed and sorted by convection driven by the advance of the capture front itself crystal laden plumes traverse the central hot core of the body and deposit partially resorbed and sorted crystals within the lower suspension zone convection is never vigorous but is part of an overall intimate balance between roofward heat loss rigid crust growth crystallization kinetics and transport and sorting of sinking escaped crystals there is a strong similarity between these processes and those producing both varves and saline pan deposits it is clear that lavas lava lakes and sills are indeed examples of true magma chambers strongly exhibiting certain aspects of this over all process these aspects commonly also characterize the large mafic magmatic bodies because strong compositional changes in the residual melt occur largely outward that is at lower temperatures and higher crystallinities of the capture front which is immobile and mostly within rigid crust the possible range in comagmatic compositions available for eruption anywhere within the active magma is very limited this is in broad agreement with the compositional range observed in basaltic lava lakes sills and plutons like skaergaard the tuning of convection crystallization kinetics and phase equilibria in chambers of this type can produce a variety of textures and layering but not a diversity of compositions

the role of gravitational instabilities in deposition of volcanic ash volcanic ash is a significant hazard for areas close to volcanoes and for aviation gravitational instabilities forming at the bottom of spreading volcanic clouds have been observed in many explosive eruptions here we present the first quantitative description of the dynamics of such instabilities and correlate this with the characteristics of the fall deposit from observations of the 4 may 2010 eyjafjallajokull iceland eruption gravitational instabilities initially took the form of downward propagating fingers that formed continuously at the base of the cloud and appeared to be advected passively at the crosswind speed measurements of finger propagation are consistent with initial conditions inferred from previous studies of ash cloud dynamics dedicated laboratory analogue experiments confirmed that finger downward propagation significantly exceeded the settling speed of individual particles demonstrating that gravitational instabilities provide a possible mechanism for enhanced sedimentation of fine ash our observations challenge the view that aggregation is the primary explanation of proximal fine ash sedimentation and give direct support for the role of gravitational instabilities in providing regions of high particle concentration that can promote aggregation

the remarkable longevity of submarine plumes implications for the hydrothermal input of iron to the deep ocean the longevity of submarine plumes generated at sea floor hydrothermal systems constrains the hydrothermal input of chemical species into the deep ocean decades of observations of episodic event plumes suggest that a key process governing the dynamics of an hydrothermal cloud spreading out laterally from a buoyant rising plume is the production of internal layering here we use analog experiments on turbulent hot particle laden plumes and clouds to show that this layering occurs where particle diffusive convection driven by the differential diffusion of heat and small mineral precipitates gives rise to a large scale double diffusive instability where hydrothermal clouds are enriched in fine minerals this particle diffusive convection can extend the longevity of an event plume to 2 yr after its emplacement the very long residence time imposed by diffusive convective effects enables complete dissolution of fine sulfide and sulfate minerals we develop a new theoretical model that includes both sedimentation and dissolution processes to quantify the potential amount of iron produced by the dissolution of iron sulfide minerals settling through the cloud by diffusive convection a key prediction is that the concentration of dissolved iron in hydrothermal clouds can reach up to 19 3 nm19 3 nm which represents about 5 of the global hydrothermal discharge if these results are representative of all hydrothermal vent fields hydrothermal systems could provide 75 of the global budget of dissolved iron in the deep ocean regionally this flux is expected to scale in magnitude with mid ocean ridge heat flow consistent with observations and global ocean models

flow of buoyant granular materials along a free surface we study experimentally the flow of light granular material along the free surface of a liquid of greater density despite a rich set of related geophysical and environmental phenomena such as the spreading of calved ice volcanic ash debris and industrial wastes there are few previous studies on this topic we conduct a series of lock release experiments of buoyant spherical beads into a rectangular tank initially filled with either fresh or salt water and record the time evolution of the interface shape and the front location of the current of beads we find that following the release of the lock the front location obeys a power law behaviour during an intermediate time period before the nose of beads reaches a maximum runout distance within a finite time we investigate the dependence of the scaling exponent and runout distance on the total amount of beads the initial lock length and the properties of the liquid that fills the tank in the experiments scaling arguments are provided to collapse the experimental data into universal curves which can be used to describe the front dynamics of buoyant granular flows with different size and buoyancy effects and initial lock aspect ratios

organic petrology and rockeval analysis of the lower carboniferous emma fiord formation in sverdrup basin canadian arctic archipelago abstract samples of the lower carboniferous emma fiord formation from two localities in the sverdrup basin of arctic canada were examined using reflected white and fluorescent light the samples from kleybolte peninsula on ellesmere island show a relatively high level of thermal maturity in contrast those from grinnell peninsula on devon island are immature to marginally mature and include subbituminous coals and oil shales two types of oil shales are distinguished on the basis of liptinite content mineral matrix rockeval pyrolysis analysis and concentration of boron one is characterized by a liptinite rich clay carbonate matrix with a relatively high hydrogen index and boron content and the other by a liptinite poor carbonate matrix with a relatively low hydrogen index and boron content hydrogen rich components of these shales consist of alginite matrix bituminite and minor amounts of exsudatinite and sporinite kerogen types iii and iv comprise only minor components of the organic matter thermal maturity of the grinnell peninsula oil shales increases with depth matrix bituminite in these oil shales has seeped into cavities and microfractures in the kerogen types iii and iv forming exsudatinite the distribution and character of the organic constituents and also the concentration of boron in these samples indicate a fresh to brackish water environment

the 1989 1990 eruption of redoubt volcano alaska impacts on aircraft operations abstract the december 1989 june 1990 eruption of redoubt volcano affected commercial and military air operations in the vicinity of anchorage alaska these effects were due to the direct impact of volcanic ash on jet aircraft as well as to the rerouting and cancellations of flight operations owing to eruptive activity between december and february five commercial jetliners were damaged from ash encounters the most serious incident took place on december 15 1989 when a boeing 747 400 aircraft temporarily lost power of all four engines after encountering an ash cloud as the airplane descended for a landing in anchorage while there were no injuries to passengers the damage to engines avionics and aircraft structure from this encounter is estimated at 80 million four additional encounters between jet aircraft and redoubt ash clouds occurred in the anchorage area on december 15 and 16 1989 and february 21 1990 none resulted in engine failure two additional encounters took place on december 17 1989 when jet airliners encountered the redoubt cloud over west texas at the time of these encounters the cloud was up to 55 hours old and had traveled in excess of 2 900 nautical miles 5 300 km following the december 15 encounters anchorage international airport remained open however most airline companies canceled operations for up to several days as communications between federal agencies and airlines improved and as a better understanding of the nature and behavior of ash rich eruption clouds was achieved most airlines resumed normal service by early january 1990 the resulting loss of revenue at anchorage international airport during several months following the eruption is estimated to total 2 6 million the impact on general aviation and military operations consisted mostly of cancellation and rerouting of flights

erosion of a stable density gradient by sedimentation driven convection stable density gradients are common in the world s oceans and lakes and play a crucial part in their physical chemical and biological evolution it has recently been suggested1 that turbidity currents provide an indirect mechanism for eroding this stratification in these currents light ambient fluid that has been mixed by cyclones with dense suspended sediment is transported to greater depths where it convectively erodes the gradient as the sediment settles here i present experimental results which show that in these circumstances the density gradient is eroded in a number of cycles of decreasing intensity and increasing duration in each cycle some of the sediment settles to the base of a stagnant region of unimpeded sedimentation while the rest is mixed into an overlying region that is vigorously convecting my experimental observations agree with a simple physical model that predicts the rate and extent of vertical mixing as well as the variation of particle sizes in the resulting turbidite

insights into the formation and dynamics of coignimbrite plumes from one dimensional models coignimbrite plumes provide a common and effective mechanism by which large volumes of fine grained ash are injected into the atmosphere nevertheless controls on formation of these plumes as a function of eruptive conditions are still poorly constrained herein two 1 d axysymmetric steady state models were coupled the first describing the parent pyroclastic density current and the second describing plume rise global sensitivity analysis is applied to investigate controls on coignimbrite plume formation and describe coignimbrite source and the maximum plume height attained for a range of initial mass flow rates between 108 and 1010 kg s modeled liftoff distance the distance at which neutral buoyancy is attained assuming radial supercritical flow is controlled by the initial flow radius gas mass fraction flow thickness and temperature the predicted decrease in median grain size between flow initiation and plume liftoff is negligible calculated initial plume vertical velocities assuming uniform liftoff velocity over the pyroclastic density current invasion area are much greater several tens of m s than those previously used in modeling coignimbrite plumes 1 m s such velocities are inconsistent with the fine grain size of particles lofted into coignimbrite plumes highlighting an unavailability of large clasts possibly due to particle segregation within the flow prior to plume formation source radius and initial vertical velocity have the largest effect on maximum plume height closely followed by initial temperature modeled plume heights are between 25 and 47 km comparable with plinian eruption columns highlighting the potential of such events for distributing fine grained ash over significant areas

sources and preservation of organic matter in the cretaceous toolebuc formation eastern australia abstract the organic matter rich toolebuc formation of eastern australia was deposited in a lower cretaceous epicontinental sea parameters from biological marker studies indicate that the organic matter is immature to marginally mature for hydrocarbon generation the occurrence of abundant coccoliths and the distribution of alkane biomarkers suggest that the organic matter type ii is largely of planktonic origin and only in the southeastern part of the depositional area can a terrestrial influence be discerned variations in kerogen composition can be attributed to the extent of the oxidation of the source materials and the degree of incorporation of sulphur the atomic h c ratios c 1 1 are remarkably constant for most of the toolebuc formation atomic o c ratios vary from 0 1 and 0 4 and can be related both to depth and paleogeographic position kerogen sulphur contents range up to 7 and the highest values occur in the most carbonate rich sediments total sulphur inorganic organic to carbon ratios in the sediments vary from 1 to

impact of geohydrology and neotectonic activity on radon concentration in groundwater of intermontane doon valley outer himalaya india radon concentration was measured in 133 water samples from tubewells handpumps dug wells and springs of the doon valley outer himalaya india the observed radon values were found to vary from 10 to 154 bq l whereas radium in selected water samples varied from 0 11 to 0 75 bq l three different clusters of high radon values were observed in the north western central and south eastern parts of the doon valley these clusters were found to be associated with tectonics thrust fault and associated uranium mineralization in the area in general radon concentration in groundwater was found to be positively correlated with the depth of the wells whereas no significant correlation was observed between radon concentration in groundwater and the water temperature ph value conductivity and altitude of the water samples an attempt has also been made to determine the nature and extent of aquifers in the doon valley on radon concentration in groundwater the variation in radon concentration within the groundwater of the study area was found to be controlled by the neotectonic activity and geohydrological processes that occur in the area the impact of these activities on radon concentration in groundwater are discussed

addressing complexity in laboratory experiments the scaling of dilute multiphase flows in magmatic systems the kinematic and dynamic scaling of dilute multiphase mixtures in magmatic systems is the only guarantee for the geological verisimilitude of laboratory experiments we present scaling relations that can provide a more complete framework to scale dilute magmatic systems because they explicitly take into account the complexity caused by the feedback between particles crystal bubble or pyroclast and the continuous phase liquid or gas we consider three canonical igneous systems magma chambers volcanic plumes and pyroclastic surges and we provide estimates of the proposed scaling relations for published experiments on those systems dilute magmatic mixtures can display a range of distinct dynamical regimes that we characterize with a combination of average eulerian properties and instantaneous lagrangian variables the eulerian properties of the mixtures yield the reynolds number re which indicates the level of unsteadiness in the continuous phase the lagrangian acceleration of particles is a function of the viscous drag and gravity forces and from these two forces are derived the stokes number st and the stability number rt two dimensionless numbers that describe the dynamic behavior of the particles within the mixture the compilation of 17 experimental studies relevant for pyroclastic surges and volcanic plumes indicates that there is a need for experiments above the mixing transition ren10 4 and for scaling st and rt among the particle dynamic regimes present in surges and plumes some deserve special attention such as the role of mesoscale structures on transport and sedimentary processes or the consequences of the transition to turbulence on particle gathering and dispersal the compilation of seven experimental studies relevant to magma bodies indicates that in the laminar regime crystals mostly follow the motion of the melt and thus the physical state of the system can be approximated as single phase in the transition to turbulence magmas can feature spatially heterogeneous distributions of laminar regions and important velocity gradients this heterogeneity has a strong potential for crystals sorting in conclusion the re st rt framework demonstrates

contemporaneous convective and collapsing eruptive dynamics the transitional regime of explosive eruptions 1 two contrasting eruptive regimes have been classically postulated to describe the behavior of explosive eruptions convective and collapsing early studies have recognized that many eruptions evolve from the first to the second regime and have assumed the existence of a sharp boundary between them consequently the dynamics of such transition has never been investigated in detail here we present results of integrated deposit analyses and numerical simulations which demonstrate univocally that both dynamics can and often do coexist for hours in a new intermediate transitional regime of explosive eruptions the study elucidates the features of the new regime in terms of mass partitioning pyroclastic current dynamics and interplay among convective and collapsing styles

experimental constraints on the distinct effects of ash lapilli and larger pyroclasts on entrainment and mixing in volcanic plumes the rate at which atmosphere is entrained and mixed into relatively dense explosive volcanic jets of gas and pyroclasts ash lapilli determines whether they rise into the atmosphere as buoyant plumes or collapse to form pyroclastic flows here we use analog experiments on grid stirred turbulence to isolate particle inertial effects related to the motions of ash and lapilli on the quantitative dynamical conditions for the onset of turbulent entrainment and mixing from energetic considerations we estimate the distinct effects of ash and lapilli on the entrainment rate we find that whereas large ash and lapilli sized pyroclasts contribute angular momentum to entraining eddies and may enhance entrainment into volcanic jets by 37 compared to expectations without inertial particles ash is dissipative and may reduce entrainment by 14 we also show that the internal turbulent mixing properties are largely insensitive to particle inertial effects our results predict that highly explosive events involving water or ice should for example feed plumes that rise higher than eruption columns that are enriched in larger pyroclasts although these events are also more likely to produce pyroclastic flows

sedimentation from turbulent jets and plumes theoretical models are developed for the sedimentation from the margins of a particle laden axisymmetric turbulent buoyant plume in a still environment and for an axisymmetric turbulent momentum jet the models assume that the mass of each individual size fraction of sediment carried in a parcel of fluid decreases exponentially with time for relatively coarse particles the fallout models predict that the sediment deposition beyond a distance r on the ground expressed in log units should decay linearly with distance away from the vent for the momentum jet and should decrease with r1 3 for the buoyant plume the exponential decay constant j is proportional to the terminal fall velocity vt of the particles in both cases and inversely proportional to the square root of the initial momentum flux m0 for the jet fallout jj vtmo 1 2 and to the third power of the initial buoyancy flux fo for the plume fallout jp vtfo 1 3 smaller particles are affected by reentrainment caused by the turbulent eddies sweeping ambient fluid back into the plume or jet and thus reincorporating some particles that were released from the flow at greater heights this is taken into account by introducing a reentrainment coefficient into the theoretical models with the assumption that the coefficient has a constant value for a plume of given strength in new experiments fallout occurs from the margins of particle laden fresh water buoyant jets and plumes in a tank of salty water and sedimentation is measured on the tank floor two experiments were weakly affected by reentrainment and show excellent agreement with the simple theory for smaller particles and increasingly buoyant plumes and strong jets particle reentrainment is important the experimental data are fitted by the new reentrainment theory confirming that values of the reentrainment coefficient are approximately constant for a given flow a settling number is defined as the ratio of the characteristic velocity of the jet or plume to the particle settling velocity for 1 reentrainment seems to reach an equilibrium state for which the reentrainment coefficient is a constant of value 0 1 for jets and 0 4 for plumes irrespective of flow strength or particle size the plume experiments indicate that the value of the reentrainment coefficient is strongly dependent on plume strength and particle size for slightly less than 1 the general principles of sedimentation from turbulent plumes and jets are applied to the fallout of pumice from volcanic eruption columns and of metalliferous particles from black smokers on the ocean floor for volcanic eruptions the results provide an explanation for the near vent overthickening of tephra fall deposits and imply that lithic and pumice fragments from small lapilli up to at least 1 m diameter blocks are efficiently reentrained into eruption columns the size of particles reentrained in hydrothermal plumes is predicted to vary from less than 100 m in weakly buoyant plumes up to over 1000 m in megaplumes

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

sedimentation of long lasting wind affected volcanic plumes the example of the 2011 rhyolitic cordon caulle eruption chile sedimentation processes and fragmentation mechanisms during explosive volcanic eruptions can be constrained based on detailed analysis of grain size variations of tephra deposits with distance from vent and total grain size distribution tgsd grain size studies strongly rely on deposit exposure and in case of long lasting eruptions can be complicated by the intricate interplay between eruptive style atmospheric conditions particle accumulation and deposit erosion the 2011 cordon caulle eruption chile represents an ideals laboratory for the study of long lasting eruptions thanks to the good deposit accessibility in medial to distal area all layers analyzed are mostly characterized by bimodal grain size distributions with both the modes and the fraction of the coarse subpopulation decreasing rapidly with distance from vent and those of the fine subpopulation being mostly stable due to gradually changing wind direction the two subpopulations characterizing the deposit of the first 2 days of the eruption are asymmetrically distributed with respect to the dispersal axis the tgsd of the climactic phase is also bimodal with the coarse subpopulation representing 90 wt of the whole distribution polymodality of individual samples is related to size selective sedimentation processes while polymodality of the tgsd is mostly related to the complex internal texture e g size and shape of vesicles of the most abundant juvenile clasts the most representative tgsd could be derived based on a combination of the voronoi tessellation with a detailed analysis of the thinning trend of individual size categories finally preferential breakage of coarse pumices on ground impact was inferred from the study of particle terminal velocity

the contribution of experimental volcanology to the study of the physics of eruptive processes and related scaling issues a review abstract the experimental approach has become a major tool increasingly used by volcanologists in recent decades to investigate the physics of eruptive processes in complement to field and theoretical works researchers have developed various methodologies to study volcanic phenomena at reduced length scale the works involve natural or analogue materials and their types range from first order tests to identify fundamental processes and make qualitative comparison with field observations to more sophisticated experiments in which precise data obtained in a controlled environment can be used to validate outputs of theoretical models scaling is a central issue to ensure dynamic similarity between the small scale experiments and the large scale volcanic phenomena when natural conditions cannot be simulated due to inherent length scale difference and or technical limitations in this respect dimensionless numbers are used to map physical regimes and to define scaling laws which allow experimental results to be extrapolated to natural scale this review presents the variety of experimental studies conducted to investigate subterraneous and aerial volcanic phenomena involving in particular fluid particle mixtures we focus on the major scaling issues and the physical regimes investigated and we also highlight in a historical perspective some of the major advances achieved through experimental studies finally we conclude on some perspectives for future works

sem petrography of eastern mediterranean sapropels analogue data for assessing organic matter in oil and gas shales abstract examination of organic matter hosted pore systems in unconventional reservoir rocks has drawn attention to the appearance of sedimentary organic matter om as seen in high resolution sem images field emission sem imaging of eastern mediterranean sapropels pliocene pleistocene age from ocean drilling program drill sites was performed on samples prepared by ar ion cross section polishing the immaturity of marine kerogen in these rocks allows inspection of petrographic textures without overprints related to thermal maturation hydrocarbon generation kerogen in these samples includes discrete particles that in some cases contain primary intragranular pores the most abundant organic matter is in the form of microns thick flaky or stringy material largely nonporous and internally amorphous and lacking the well defined shapes of discrete particles this dominant om has behaved in a highly ductile manner in compaction and is now highly pervaded into intergranular spaces between silt and clay size grains a portion of the larger mineral hosted pores remain open unfilled by ductile om minor nanometer scale pores of uncertain origin occur in the dominant om silt and clay size mineral crystals are distributed in organic matter of most types and it is difficult to fully ascertain if the om mineral mixing has occurred during compaction versus during aggregation during gravity settling marine snow sedimentation or through sediment accumulation in om rich microbial mats results indicate that sediments rich in marine kerogen are subject to substantial compactional porosity loss in early burial these observations of marine detrital organic matter in its early diagenetic state provide a useful baseline for interpretation of petrographic features in more mature om rich mudrocks it is clear that petrographic discrimination of diagenetically generated organic matter bitumen and related om types from ductile dispersed amorphous detrital om kerogen using sem data will be challenging in the absence of compositional information

volcan reventador s unusual umbrella 1 photographs of a volcanic column in a recent eruption of reventador show a prominently scalloped umbrella that is unlike any umbrella previously documented on a volcanic column we propose that the scallops in this umbrella are the result of a turbulent rayleigh taylor rt instability a type of fluid instability with no precedents in volcanology negative buoyancy drives this instability and we ascribe the unusual negative buoyancy of the reventador umbrella to the fact that the reventador column fed on a cool co ignimbrite cloud from the wavelength of the scallops we estimate a value for the eddy viscosity of the umbrella d 4 000 m2 s the first such value to be inferred directly from an observation in the field collapse of the umbrella back to the ground could result in a previously unrecognized hazardous flow we hope this work will elicit new reports on scalloped umbrellas and further study of the characteristics and evolution of such umbrellas

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

correlation between highly abundant oil prone leiosphaerid acritarchs and hydrocarbon source rocks from the triassic yanchang formation eastern gansu province northwestern china abstract an abundance of acritarchs dominated by leiosphaeridia was extracted from the middle and upper triassic cores of ordos basin northwestern china by means of palynological maceration phycomata of leiosphaeridia occurred in clusters bunches and single vesicular forms occasionally with connecting macroalgal branches indicating their in situ preservation apart from proterozoic and early paleozoic marine leiosphaeridia the highly abundant leiosphaerids from the yanchang formation in northwestern china likely came from a lacustrine environment and the assemblage includes both phytoplanktonic green algae and spores of muticellular algae toc and 13 corg in the middle and upper triassic sediments of the basin show a correlation with the abundance of leiosphaerids this correlation suggests that leiosphaerids were important biological precursors for the generation of petroleum in the main chang 7 3 hydrocarbon source rocks

on the rise of turbulent plumes quantitative effects of variable entrainment for submarine hydrothermal vents terrestrial and extra terrestrial explosive volcanism 1 the maximum height reached by a turbulent plume rising in a stratified environment is a key tool to estimate the flux released at its source particularly for large scale flows because flux can often be very hard to measure directly this height is known to be mainly controlled by the stratification of the ambient fluid source buoyancy flux and the efficiency of turbulent mixing between the plume and the external fluid the latter effect has been only superficially explored in spite of its fundamental control on the dynamics here we show that commonly used one dimensional models incorporating a constant entrainment coefficient do not provide satisfying predictions we propose a new model allowing for variable entrainment which gives excellent predictions of maximum heights reached by laboratory plumes in stratified environments we then apply our formalism to natural plumes produced by explosive volcanic eruptions under terrestrial paleo martian and venusian conditions and by submarine hydrothermal activity at mid ocean ridges source mass discharge rates deduced from maximum volcanic column heights for terrestrial eruptions are found to be greater than those estimated with the commonly used constant entrainment parameterization by a factor of 2 in the paleo martian atmosphere existing models overestimate plume heights by 14 27 in the current atmosphere of venus the maximum height reached by a volcanic plume is also found to be smaller than previously estimated for large eruption rates the source heat flux released by the tag field atlantic ocean deduced from several submarine hydrothermal plumes is found greater by a factor 3 with our model

a model for the numerical simulation of tephra fall deposits abstract a simple semianalytical model to simulate ash dispersion and deposition produced by sustained plinian and sub plinian eruption columns based on the 2d advection dispersion equation was applied the eruption column acts as a vertical line source with a given mass distribution and neglects the complex dynamics within the eruption column thus the use of the model is limited to areas far from the vent where the dynamics of the eruption column play a minor role vertical wind and diffusion components are considered negligible with respect to the horizontal ones the dispersion and deposition of particles in the model is only governed by gravitational settling horizontal eddy diffusion and wind advection the model accounts for different types and size classes of a user defined number of particle classes and changing settling velocity with altitude in as much as wind profiles are considered constant on the entire domain the model validity is limited to medium range distances about 30 200 km away from the source the model was used to reconstruct the tephra fall deposit from the documented plinian eruption of mt vesuvius italy in 79 a d in this case the model was able to broadly reproduce the characteristic medium range tephra deposit the results support the validity of the model which has the advantage of being simple and fast to compute it has the potential to serve as a simple tool for predicting the distribution of ash fall of hypothetical or real eruptions of a given magnitude and a given wind profile using a statistical set of frequent wind profiles it also was used to construct air fall hazard maps of the most likely affected areas around active volcanoes where a large eruption is expected to occur

a new view of the dynamics stability and longevity of volcanic clouds abstract powerful explosive volcanic eruptions inject ash high into the atmosphere which spreads to form umbrella clouds identifying key physical processes governing the dynamics stability and longevity of umbrella clouds is central to assessing volcanic hazards as well as the nature of volcanic forcings on climate here we present a series of laboratory experiments producing turbulent particle laden jets and subsequent axisymmetric intrusive gravity currents into a stratified environment our experiments reproduce many of the main dynamical regimes observed during the formation of an explosive volcanic column and highlight new dynamics for the umbrella cloud theoretical predictions of column collapse from a simple model of a turbulent jet are in good agreement with experimental observations as well as previous studies depending on the flow intensity the strength of the initial environmental density stratification and the particle concentration at the source resulting umbrella clouds can however evolve through a series of new regimes as a result of the dynamics of particle sedimentation within these flows as well as from their bases using scaling theory we show that during cloud spreading internal sedimentation drives the growth and intermittent overturn of thin gravitationally unstable particle boundary layers pbls as particle rich plumes this pbl driven convection can have remarkable effects ranging from progressive dilution of clouds to their catastrophic overturn and collapse in natural eruptions whether the dynamics of pbls play a major role in particle sedimentation depends on the grain size distribution inside the cloud and on eruption column height in general particles larger than 60 m 1 mm are expected to settle individually whereas finer particles will accumulate pbls resulting in the formation of armless mammatus clouds or dangerous gravity currents at much larger distances from the volcanic vent than ever considered before such dynamics is apparent in observations of numerous modern eruptions and is inferred from the deposits of historic and prehistoric eruptions for where there exist appropriate data consideration of the consequences of these phenomena for problems such as volcanic hazards to humans and climate change may thus be very important in the assessment of future eruptions

model for transgressive black shales many black shales in thick epicontinental basinal successions formed beneath an oxygen restricted puddle of deep water other black shales formed during rapid transgression when basinal deposition expanded to cover basin margin areas normally characterized by shallow water deposition an expanding puddle model is developed from the early jurassic of england wherein rapid sea level rise leads to marine sediment starvation due to sediment entrapment in flooded river valleys subsidence sea level rise and decreased sediment supply during early transgression are suggested to lead to rapid deepening and therefore the expansion of the are of the puddle such that in previously shallow water areas black shales rest on condensed basal transgressive lags or unconformities that in turn rest on shallow water facies reestablishment of sediment influx and aggradation in excess of any continued sea level rise cause shallowing throughout the basin and the cessation of black shale formation

particle recycling and oscillations of volcanic eruption columns we study the dynamics of sedimentation and reentrainment of particles from the umbrella cloud above an axisymmetric turbulent particle laden buoyant plume we develop a model to show that the reentrainment of particulate material into the uprising plume will cause the particle flux to increase by a factor of e between the plume source and the umbrella cloud a buoyant plume rising in an environment of uniform density may thereby become negatively buoyant if its particle loading becomes sufficiently high we compare the predictions of the model to a series of laboratory experiments and show that at high particle loadings the plume undergoes an oscillatory collapse this periodic collapse generates dense gravity flows down the flanks of the plume in the context of volcanic eruptions such an instability associated with particle recycling may lead to the formation of interleaved fall and flow deposits such as have been observed near the collapse horizon in a number of pyroclastic deposits

enhanced sedimentation beneath particle laden flows in lakes and the ocean due to double diffusive convection the transport rate of particles beneath sediment laden overflows and interflows in lakes and in the ocean can be enhanced by double diffusive and settling driven convection in previous experiments with sediment laden fluid overlaying a saline layer visual measurements could only be made in the optically clear lower layer hence there was difficulty distinguishing the two processes hindering predictions of when enhanced sedimentation occurs we used an acoustic doppler velocimeter adv to measure velocities and turbulence above and below the initial sediment salt interface the velocity of the sediment fingers in the lower layer were always larger than the stokes settling velocity of the particles leading to an asymmetry in the flow field of the two convective layers sediment fingers only dominated when there were marginal density differences between the two layers we conclude that double diffusive sediment fingers control sedimentation beneath interflows in most lakes whereas settling driven convection is dominant in most oceanic overflows

the mysteries of mammatus clouds observations and formation mechanisms mammatus clouds are an intriguing enigma of atmospheric fluid dynamics and cloud physics most commonly observed on the underside of cumulonimbus anvils mammatus also occur on the underside of cirrus cirrocumulus altocumulus altostratus and stratocumulus as well as in contrails from jet aircraft and pyrocumulus ash clouds from volcanic eruptions despite their aesthetic appearance mammatus have been the subject of few quantitative research studies observations of mammatus have been obtained largely through serendipitous opportunities with a single observing system e g aircraft penetrations visual observations lidar radar or tangential observations from field programs with other objectives theories describing mammatus remain untested as adequate measurements for validation do not exist because of the small distance scales and short time scales of mammatus modeling studies of mammatus are virtually nonexistent as a result relatively little is known about the environment formation mechanisms properties microphysics and dynamics of mammatus this paper presents a review of mammatus clouds that addresses these mysteries previous observations of mammatus and proposed formation mechanisms are discussed these hypothesized mechanisms are anvil subsidence subcloud evaporation sublimation melting hydrometeor fallout cloud base detrainment instability radiative effects gravity waves kelvin helmholtz instability rayleigh taylor instability and rayleigh benard like convection other issues addressed in this paper include whether mammatus are composed of ice or liquid water hydrometeors why mammatus are smooth what controls the temporal and spatial scales and organization of individual mammatus lobes and what are the properties of volcanic ash clouds that produce mammatus the similarities and differences between mammatus virga stalactites and reticular clouds are also discussed finally because much still remains to be learned research opportunities are described for using mammatus as a window into the microphysical turbulent and dynamical processes occurring on the underside of clouds

evaluating the structure and magnitude of the ash plume during the initial phase of the 2010 eyjafjallajokull eruption using lidar observations and name simulations 1 the eyjafjallajokull volcano in iceland erupted explosively on 14 april 2010 emitting a plume of ash into the atmosphere the ash was transported from iceland toward europe where mostly cloud free skies allowed ground based lidars at chilbolton in england and leipzig in germany to estimate the mass concentration in the ash cloud as it passed overhead the uk met office s numerical atmospheric dispersion modeling environment name has been used to simulate the evolution of the ash cloud from the eyjafjallajokull volcano during the initial phase of the ash emissions 14 16 april 2010 name captures the timing and sloped structure of the ash layer observed over leipzig close to the central axis of the ash cloud relatively small errors in the ash cloud position probably caused by the cumulative effect of errors in the driving meteorology en route result in a timing error at distances far from the central axis of the ash cloud taking the timing error into account name is able to capture the sloped ash layer over the uk comparison of the lidar observations and name simulations has allowed an estimation of the plume height time series to be made it is necessary to include in the model input the large variations in plume height in order to accurately predict the ash cloud structure at long range quantitative comparison with the mass concentrations at leipzig and chilbolton suggest that around 3 of the total emitted mass is transported as far as these sites by small 100 m diameter ash particles

influence of particle aggregation on deposition of distal tephra from the may 18 1980 eruption of mount st helens volcano the may 18 1980 eruption of mount st helens msh produced an extensive ashfall deposit in washington idaho and montana with a minumum volume of 0 55 km3 tephra an unusual feature of the deposit is the occurrence of a second thickness maximum 325 km ene of msh near ritzville washington grain size and component abundance analysis of samples along the main dispersal axis indicates that ash in this region is very fine grained mean size 22 m poorly sorted polymodal and rich in glass shards and pumice fragments a computer simulation of ash fallout from an atmospherically dispersed eruption plume was developed to evaluate various hypotheses for the origin of the distal ash characteristics particularly the thickness versus distance relationship the model was constrained by observations of the eruption column height elevation of major ash transport lateral spreading of the eruption plume and atmospheric wind structure in the vicinity of msh results of different simulations indicate that the second thickness maximum cannot be attributed to either decreased wind velocities over central washington or injection of fine ash above the horizontal wind velocity maximum near the tropopause for the model to fit the observed characteristics of the deposit significant particle aggregation of ash finer than 63 m must be invoked the best fit occurs when ash less than 63 m is aggregated into particles several hundred microns in diameter with a settling velocity of 0 35 m s support for this process comes from the observation and collection of fragile ash clusters of similar size which fell at pullman washington during the may 18 eruption sorem 1982 the premature fallout of fine ash as particle aggregates is a fundamental process in the origin of the grain size characteristics variations in component abundances and thickness versus distance relationship of the may 18 msh ash fall deposit

satellite observations and interpretation of the 1991 mount pinatubo eruption plumes we demonstrate the use of hourly geostationary meteorological satellite gms and noaa polar orbiting advanced very high resolution radiometer avhrr satellite images of the june 1991 mount pinatubo volcanic eruption plumes in providing details of the timing changing eruptive style and umbrella plume movement and dynamics a chronology of explosive events which culminated in a 9 hour long climactic phase on june 15 has been determined from satellite data and favorably compared to ground based and other ancillary information maximum eruption column altitudes of 40 km and column top undercooling in excess of 55 c below the ambient atmosphere occurred during the climactic phase phases dominated by plinian versus coignimbrite eruptive plumes can be distinguished on the images analysis of the spreading umbrella plume during the climactic phase suggests that over the first 4 5 hours the plume spread laterally as a gravitational intrusion before becoming advected in the ambient winds we compare the rate of plume growth to a model of a radially symmetric continuously fed intrusion to describe the motion the rate of plume growth shows good agreement with this simple model for the first 4 5 hours from column top heights we determine eruption rates and obtain an independent estimate of the total volume of magma erupted from june 12 16 of 5 5 km3 dense rock equivalent dre in good agreement with an independent estimate of the total eruptive volume made from deposits on land and submarine ash fall of up to 5 3 km3 dre we also show that secondary explosions in the pinatubo ignimbrite deposits produced ash plumes reaching altitudes as high as 19 km in september 1991 this study indicates that realistic interpretation and monitoring of major eruption plumes can be accomplished by analysis of high temporal resolution satellite data

algal bloom episodes and the formation of bituminite and micrinite in hydrocarbon source rocks evidence from the devonian and mississippian northern williston basin canada organic petrology incident light microscopy of middle devonian inter reef laminates and devonian mississippian epicontinental black shales williston basin canada indicates that algal bloom episodes and consequential bacterial activity played a significant role in the accumulation of amorphous bituminite iii rich organic microfacies corpohuminite like algal akinete cells produced by filamentous algae during algal bloom periods are persistent maceral inclusions within the potential hydrocarbon source rock intervals these cells ro mean range 0 24 0 90 are regarded as positive indicators of stressful palaeoenvironmental conditions unicellular tasmanites and leiosphaeridia marine alginite and variably degraded alginite remnants ghosts within the amorphous kerogen may be products of cell lysis photo oxidation and microbial alteration these processes are characteristic of algal bloom periods minute ca 1 m spheroidal and coccoidal bacteria like macerals are dispersed throughout the bituminite iii network attesting to the importance of microbial activity within the water column and sediment during and after organic matter accumulation dispersed granules laminations and replacement textures of micrinite like macerals within bituminite iii are interpreted as remnants of microbial alteration rather than a residual product of thermal maturation and hydrocarbon generation

are eruptions from linear fissures and caldera ring dykes more likely to produce pyroclastic flows turbulent volcanic jets are produced by highly energetic explosive eruptions and may form buoyant plumes that rise many tens of kilometres into the atmosphere to form umbrella clouds or collapse to generate ground hugging pyroclastic flows ash injected into the atmosphere can be transported for many hundreds of kilometres with the potential to affect climate disrupt global air travel and cause respiratory health problems pyroclastic flows by contrast are potentially catastrophic to populations and infrastructure close to the volcano key to which of these two behaviours will occur is the extent to which the mechanical entrainment and mixing of ambient air into the jet by large entraining eddies forming the jet edge changes the density of the air ash mixture low entrainment rates lead to pyroclastic flows and high entrainment rates give rise to buoyant plumes recent experiments on particle laden multi phase volcanic jets from flared and straight sided circular openings suggest that the likelihood for buoyant plumes will depend strongly on the shape and internal geometry of the vent region this newly recognised sensitivity of the fate of volcanic jets to the structure of the vent is a consequence of a complex dynamic coupling between the jet and entrained solid particles an effect that has generally been overlooked in previous studies building on this work here we use an extensive series of experiments on multi phase turbulent jets from analogue linear fissures and annular ring fractures to explore whether the restrictive vent geometry during cataclysmic caldera forming ccf eruptions will ultimately lead a relatively greater frequency of pyroclastic flows than eruptions from circular vents on stratovolcanoes our results understood through scaling analyses and a one dimensional theoretical model show that entrainment is enhanced where particle motions contribute angular momentum to entraining eddies however because the size of the entraining eddies scales approximately with vent width the extent of entrainment is reduced as the vent width becomes small in comparison to its length consequently our work shows that for specified mass eruption rates the high length to width ratio vents typical of ccf events are more likely to produce pyroclastic flows we suggest that the enigmatic trend in the geological record for the largest ccf eruptions to produce pyroclastic flows is an expected consequence of their being erupted through continuous or piece wise continuous caldera ring fractures

distal enhanced sedimentation from volcanic plumes insights from the secondary mass maxima in the 1992 mount spurr fallout deposits some tephra fallout deposits show an increase of mass and thickness at distances from the source 100 km areas of secondary mass maximum asmm which demonstrates distal enhanced sedimentation from volcanic plumes we explore development of the asmms during the 1992 august and september mount spurr eruptions usa by combining eld data on the spatial distribution of mass and grain size with 1 simulations of individual particle settling through a homogeneous and horizontally strati ed atmosphere and 2 mesoscale models of the three dimensional wind eld that include the effect of the underlying topography the crosswind and downwind variations of deposit characteristics indicate that the increase of sedimentation at the asmms is not formed solely because of preferential settling of small ash particles 125 m as commonly assumed in aggregation models instead asmm grain sizes correspond to the ne modes of the bimodal total grain size distributions there also appears to be a link between the asmm and the topography the mass local minima occur across the windward ank of 2 km high mountain ranges while the asmms spread on the leeward ank mesoscale models of the three dimensional wind eld show vertical oscillations in the wind over mountainous regions which may enhance mechanisms of en masse sedimentation aggregation hydrometeor formation and particle boundary layers as well as strong spatial variations of the horizontal wind eld in the lower troposphere our study demonstrates the importance of using grain size as well as mass data to constrain the complex processes responsible for particle sedimentation from volcanic plumes

solid bitumen bituminite and thermal maturity of the upper jurassic lower cretaceous chia gara formation kirkuk oil field zagros fold belt kurdistan iraq abstract the upper jurassic lower cretaceous chia gara formation a proven marine source rock characterised by predominance of amorphous organic matter aom is known from few outcrops in ne iraq and a number of exploration wells in the zagros fold belt this study presents comprehensive organic petrographic and mineralogical investigations of the dispersed organic matter and rock forming minerals of the tithonian berriasian chia gara formation intersected by the kirkuk well k 109 drilled in the giant kirkuk oil field ne iraq the organic petrographic analyses including incident light microscopy and confocal laser scanning microscopy clsm were applied to carbonate source rocks with low to moderate organic carbon contents our data demonstrate the predominance of bituminite and solid bitumen among the examined dispersed organic matter followed by oil exudates and oil globule inclusions as well as the presence of minor contributions of alginite i e tasmanites and leiospheridia liptodetrinite and vitrinite based on optical characteristics and clsm spectral fluorescence measurements examinations of bituminite point towards the presence of bituminite type iii the bituminite type iii encloses dark orange fluorescent amorphous components suggesting a genetic relationship either with liptodetrinite and or with solid bitumen the qualitative assessment of solid bitumen reveals several dissimilar forms identified in the analysed samples the photometric and spectral fluorescence measurements point to distinct reflectance values ranging between 0 19 and 0 43 sbrr and lambda max values extending from 515 nm to 590 nm respectively the corresponding results of the solid bitumen exhibit 1 a lack of a relationship with depth and 2 suggest its poor property as a reliable maturity indicator for the examined samples the presence of oil exudates oil globule inclusions and their association with solid bitumen suggests a genetic relation with the examined residues of liquid hydrocarbon phase the performed thermal maturities assessments of dispersed organic matter point towards early mature to peak mature oil window with vitrinite reflectance values ranging between 0 52 vrr at 2801 m to 0 83 vrr at 3089 m depth mineralogical analyses revealed the predominance of calcite over dolomite in the examined limestone to marl lithofacies e g clear rimmed dolomite with localised intensive dolomitisation in the phyllosilicate rich matrix predominance of calcite and siderite is observed followed by zinc blende and pyrite the composition of organic matter in the examined chia gara formation with predominance of bituminite and solid bitumen makes the major marine source rock of iraq s cretaceous petroleum systems distinctive in terms of hydrocarbon generation and migration at an oil window stage as it provides suitable explanations for its generally low hydrogen index hi with only minor terrestrial input in addition the results presented herein can be helpful for future evaluation of thermal maturities and characterisation of optical appearances of dispersed organic matter in carbonates by incident light microscopy and especially by clsm during hydrocarbon prospecting

bituminite a tem view abstract an illinois coal high volatile bituminous b of carboniferous age containing typical bituminite has been examined by transmission electron microscopy tem to supplement observations with the light microscope with tem the bituminite has a fine fairly regular structure including voids of a characteristic shape this structure is almost certainly inherited from a botanical precursor and is thought to represent much altered remains of former colonies of algae probably green algae the present remains contain abundant lipid rich globules and probably also include matter of algal and bacterial origin which cannot be resolved even at tem resolutions

an improved quantitative measure of the tendency for volcanic ash plumes to form in water implications for the deposition of marine ash beds laboratory experiments and numerical simulations have shown that volcanic ash particles immersed in water can either settle slowly and individually or rapidly and collectively as particle laden plumes the ratio of timescales for individual and collective settling in the form of analytical expressions provides a dimensionless quantitative measure of the tendency for such plumes to grow and persist which has important implications for determining particle residence times and deposition rates however existing measures in the literature assume that collective settling obeys stokes law and is therefore controlled by the balance between gravitational forces and viscous drag despite plume development actually being controlled by the balance between gravitational forces and inertial drag even in the absence of turbulence during early times this paper presents a new measure for plume onset which takes into account the inertial drag controlled rather than viscous drag controlled nature of plume growth and descent a parameter study comprising a set of numerical simulations of small scale volcanic ash particle settling experiments highlights the effectiveness of the new measure and by comparison with an existing measure in the literature also demonstrates that the timescale of collective settling is grossly under estimated when assuming that plume development is slowed by viscous drag furthermore the formulation of the new measure means that the tendency for plumes to form can be estimated from the thickness and concentration of the final deposit the magnitude and duration of particle flux across the water s surface do not need to be known the measure therefore permits the residence times of particles in a large body of water to be more accurately and practically determined and allows the improved interpretation of layers of volcaniclastic material deposited at the seabed

a numerical study of turbulent mixing in eruption clouds using a three dimensional fluid dynamics model 1 the dynamics of eruption clouds in explosive volcanic eruptions are governed by entrainment of ambient air into eruption clouds by turbulent mixing we develop a new numerical pseudo gas model of an eruption cloud by employing three dimensional coordinates a third order accuracy scheme and a fine grid size in order to investigate the behavior of entrainment due to turbulent mixing the quantitative features of entrainment are measured by a proportionality constant relating the inflow velocity at the edge of the flow to the average vertical velocity i e the entrainment coefficient our model has successfully reproduced the quantitative features of entrainment observed in the laboratory experiments as well as fundamental features of the dynamics of eruption clouds such as the generation of eruption columns and or pyroclastic flows the value of the entrainment coefficient for eruption clouds is estimated from the column height and critical condition for column collapse by comparing results of our model with those of previous one dimensional models it is suggested that the value of the entrainment coefficient for an eruption cloud is approximately constant although the value estimated from the critical condition for column collapse k 0 07 is slightly smaller than that based on the column height k 0 1 this difference reflects the vertical change of flow structure in the eruption cloud the eruption cloud in the upper region exhibits a meandering instability which leads to efficient mixing whereas the cloud near the vent maintains a concentric structure with an inner dense core surrounded by an outer shear region our model is consistent with previous one dimensional models for steady eruption clouds supported by the laboratory experiments and it is also applicable to unsteady and transient features of actual eruption clouds

sedimentation of tephra by volcanic plumes i theory and its comparison with a study of the fogo a plinian deposit sao miguel azores sedimentation of ejecta from volcanic plumes has been studied as a function of distance from the source in the fogo a plinian deposit sao miguel azores the fogo a trachytic pumice deposit is reversely graded and can be divided into two parts on the basis of pumice colour abundance of syenite accessory lithic clasts and distribution the lower syenite poor part was dispersed to the south and was clearly influenced by wind the upper syenite rich part is coarsegrained and has a nearly symmetrical distribution around the vent elongation of isopachs to the east indicate a weak wind influence the grain size variations of lithic and crystal components in the upper coarse part were studied total accumulation and accumulation per unit area expressed in kg m2 show good fits to a gaussian function at distances greater than 7 km for grain diameters less than 2 cm these results agree with a theoretical model for a radially spreading turbulent current moving over a quiescent fluid the gaussian coefficient is shown to be a function of grain size and the flow rate of material into the umbrella region of the eruption column the coefficient is therefore also a function of column height the column height deduced from these data is 21 km which is in broad agrrement with the column height of 27 km deduced from maximum clast dispersal using the method of carey and sparks 1986 the accumulation of clasts larger than 2 cm agrees with a theory for the fallout of clasts from the margins of the ascending eruption column which treats the plume as a succession of large eddies that decrease their mass of particles as an exponential function of time calculations are also presented for the influence of the radial inflow of surrounding air into the column on the deposition of clasts these calculations constrain the wind speed during the later part of the fogo a eruption to be at most a few metres per second the study has allowed four different dynamic categories of clast behaviour to be recognised in eruption columns

sedimentation from gravity currents generated by turbulent plumes sedimentation from radially spreading gravity currents generated at the top of ascending sediment laden plumes is described by a model which assumes that sediment is dispersed homogeneously by turbulence in the gravity current resulting in an exponential decrease in the concentration of sediment with time as particles settle out of the lower boundary of the current for radial spreading this model predicts a gaussian distribution of sediment accumulation away from the source with an exponential constant b which depends on flow rate q and particle settling velocity v b nv q in the experiments described sedimentation occurs from gravity currents generated by ascent of buoyant particle laden plumes of fresh water in a tank of salty water the sediment accumulation shows close agreement with the theoretical model and the gaussian decay constant b can be determined from a maximum in the accumulated mass of sediment per unit distance and from the slope of the line in s s0 br2 where r is the radial distance s is the sediment mass flux per unit area and s0 is the value of s at r 0 data from the dispersal of volcanic ejecta from a large c 24 km high plinian eruption column in the azores also show good agreement with the theory confirming that it is general and independent of scale and the nature of the fluid the experimental data also show a change in sedimentation behaviour at distances from the source corresponding to the corner of the plume where it diverts into a lateral gravity current and there is an abrupt decrease in vertical velocity sedimentation of coarse grain sizes between the source and the corner occurs from the inclined plume margins and does not behave as predicted by the theoretical model

impact of wind on the condition for column collapse of volcanic plumes the collapse of volcanic plumes has significant implications for eruption dynamics and associated hazards we show how eruptive columns can collapse and generate pyroclastic density currents as a result of not only the source conditions but also of the atmospheric environment the ratio of the potential energy and the kinetic energy at the source quantified by the richardson number and the entrainment efficiency quantified by the radial entrainment coefficient have already been identified as key parameters in controlling the transition between a buoyant and collapsing plume here we quantify how this transition is affected by wind using scaling arguments in combination with a one dimensional plume model air entrainment due to wind causes a volcanic plume to lower its density at a faster rate and therefore to favor buoyancy we identify the conditions when wind entrainment becomes dominant over radial entrainment and quantify the effect of wind on column collapse these findings are framed into a generalized regime diagram that also describes previous regime diagrams for the specific case of choked flows many observations confirm how bent over plumes typically do not generate significant collapses a quantitative comparison with the 1996 ruapehu and the 2010 eyjafjallajokull eruptions shows that the likelihood of collapse is reduced even at moderate wind speeds relative to the exit velocity at the vent

a case of no wind plinian fallout at pululagua caldera ecuador implications for models of clast dispersal the caldera of pululagua is an eruptive centre of the northern volcanic zone of the south american volcanic arc located about 15 km north of quito ecuador activity leading to formation of the caldera occurred about 2450 b p as a series of volcanic episodes during which an estimated 5 6 km3 dre of hornblende bearing dacitic magma was erupted a basal pumice fall deposit covers more than 2 2x104 km2 with a volume of about 1 1 km3 and represents the principal and best preserved plinian layer circular patterns of isopachs and pumice lithic and md isopleths of the basal fallout bf around the caldera indicate emplacement in wind free conditions absence of wind is confirmed by an ubiquitous normally graded thin ash bed at the top of the lapilli layer which originated from slow settling of fines after cessation of the plinian column co plinian ash the unusual atmospheric conditions during deposition make the bf deposit particularly suitable for the application and evaluation of pyroclast dispersal models application of the carey and sparks 1986 model shows that whereas the 3 2 1 6 and 0 8 cm lithic isopleths predict a model column height of about 36 km the 6 4 cm isopleth yields and estimate of only 21 km the 4 9 and 6 4 cm isopleths yield a column height of 28 km using the model of wilson and walker 1987 the two models give the same mass discharge rate of 2x108 kg s 1 a simple exponential decrease of thickness with distance as proposed by pyle 1989 for plinian falls fits well with the bf exponential decrease of size with distance is followed by clasts less than about 3 cm suggesting in agreement with wilson and walker 1987 that only a small proportion of large clasts reach the top of the column variations with distance in clast distribution patterns imply that in order to obtain column heights by clast dispersal models the distribution should be known from both proximal and distal zones knowledge of only a few isopleths irrespective of their distance from the vent is not sufficient as seemed justified by the method of pyle 1989

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

wind entrainment in jets with reversing buoyancy implications for volcanic plumes explosive volcanic eruptions commonly undergo a transition from stable plume to collapsing fountain with associated destructive pyroclastic density currents a major goal in physical volcanology is to predict quantitatively the limit between the flow regimes as a function of the source and environmental conditions atmospheric winds influence the dynamics and stability of the column causing bending and enhancing turbulent air entrainment however the predictions made with 1 d models of volcanic plumes accounting for the presence of wind strongly depend on the wind entrainment coefficient a parameter whose value varies in the literature here we present a new theoretical model to identify an analytical criterion for column collapse in windy conditions we then present new laboratory experiments on turbulent jets with reversing buoyancy rising in a crossflow in order to better constrain our results show that a single value of 0 5 can be used to describe the behavior of laboratory jets with arbitrary buoyancy the results allow us to parameterize our 1 d model of volcanic plumes ppm and to show the crucial importance of wind gradient and profile on volcanic column dynamics through the use of the 1991 mt hudson eruption as a case study finally we propose a new transition diagram between the stable plume and collapsing fountain regimes as a function of wind speed and mass discharge rate only which can be used for the rapid assessment of major hazards during an explosive eruption

cannel coals implications for classification and terminology abstract cannel coals are tough massive coals with a dull luster that break with an even compact grain and conchoidal cross fractures historically cannel coals were of significant economic and social importance during the early industrialization of the usa they were the source for a sophisticated petrochemical industry and a fuel source for heating gas making coke making and oil generation petrographic data proximate analysis and ultimate analysis data were obtained for 68 cannel coals from kentucky to decide how well the cannel coals fit the generally accepted definitions of a cannel coal four maceral assemblages were found sporinite with abundant medium grained vitrinite and inertinite sporinite with abundant fine grained vitrinite and inertinite of which micrinite is abundant bituminite may be present alginite with abundant fine grained vitrinite and inertinite and alginite and bituminite with minor vitrinite and inertinite volatile matter and h c ratios are highest for those samples with abundant liptinite with a sample from breckenridge having the highest value of each five samples were analyzed by the rock eval method the s2 and hi indices show that the coals would make excellent source rocks discrepancies between the values for the five samples are related to maceral composition and there may be a good correlation between source rock potential and importance as a feedstock for synthetic crude oil production in the 1800s the maceral composition of the microlithotypes is related to the environment of deposition coal composed of assemblage i formed in humic peat swamps in which unusually large numbers of spores were introduced possibly because of unusual climatically controlled reproductive cycles coals composed of assemblages ii to iv formed as sapropelic coals in lakes at some stage of peat swamp development

organic microfacies and basinal tectonic control on source rock accumulation a microscopic approach with examples from an intracratonic and extensional basin abstract relationships among organic petrographic maceral assemblages and hydrocarbon source rock depositional environments distinguish broad marine terrestrial and mixed kerogen accumulation settings organic microfacies from paleozoic and mesozoic source rock intervals in the intracratonic williston basin and the extensional sverdrup basin have been studied using incident white and fluorescent light microscopy distinct anoxic organic microfacies are defined in upper ordovician bighorn group subtidal platformal kukersites and middle devonian upper elk point group carbonate lithologies that preserve a progression of depositional environments from platformal to starved basinal paleozoic carbonate platform microfacies are characterized by well preserved cyanophyceae alginite stromatolitic mats displaying upper surface textural features such as pustules pinnacles endolithic algal borings and interlaminated vertical and horizontal alginite resulting from phototactic growth potential source intervals in middle and upper triassic shelf shales from the sverdrup basin and middle devonian carbonate platform marginal mudstones in the williston basin are both characterized by high concentrations of sapropelic bituminite kerogen hosting unicellular marine alginite similar bituminite rich organic microfacies occur in middle devonian basinal settings associated with larger more abundant alginite and significant amounts of dasycladacean calcareous algae the main controls on source rock accumulation are water depth and chemistry as controlled by depositional setting and basin restriction