decrypting silicic magma plug fragmentation at azufral crater lake northern andes insights from fine to extremely fine ash morpho chemistry azufral sw colombia is a dangerous silicic volcano hosting a crater lake which serves as an excellent example of an incipient plug disruption through phreatomagmatism we studied the youngest succession of dilute pyroclastic density currents pdcs onlapping the north eastern crater rim scanning electron microscopy coupled with energy dispersive x ray spectroscopy was used to carry out an automated single particle analysis of fine to extremely fine ash we were able to obtain fast and accurate chemical analysis and imaging of 15 098 particles within the 250 63 m and the 63 32 m size ranges the 2d form and roughness parameters were determined for 4895 juvenile glassy particles and validated by 3d micro x ray computer tomography there are two end members of high group 1 and low group 2 roughness juvenile glassy particles group 1 comprises high roughness glass particles with solidity values as low as 0 34 in 2d and 0 33 in 3d and convexity values as low as 0 33 in 2d and 0 26 in 3d group 2 comprises low roughness glass particles with 2d solidity values 0 79 and 3d solidity values typically 0 58 in this group 2d convexity values are 0 68 and 3d convexity values are 0 71 both end members are mostly discriminated by the 2d concavity index 0 14 to 0 77 in group 1 vs 0 05 0 35 in group 2 the remaining group 3 comprises particles of intermediate roughness values in this study we show how an incipient plug developed over a short repose time might be subjected to only a few cycles of vesicle nucleation collapse and densification retaining the characteristics of juvenile glass each glassy juvenile ash type defined by a particular morphology roughness and microtexture can be linked to a density stratified conduit model in azufral the capping and conduit lining dense regions and the permeable zones of the incipient plug likely cracked the newly formed cracks could allow hydraulic forcing caused by external water and induce phreatomagmatic interaction this interaction favoured the fine fragmentation of the plug while enhancing ongoing magmatic processes finally the variations of bulk componentry provided clues on dilute pyroclastic density current transport and physical fractionation processes by secondary fragmentation elutriation and interaction with the crater rim

deep sea eruptions boosted by induced fuel coolant explosions the majority of earth s volcanic eruptions occur beneath the sea but the limited number of direct observations and samples limits our understanding of these unseen events subaerial eruptions lend some insight but direct extrapolation from the subaerial to the deep sea is precluded by the great differences in pressure thermal conditions density and rheology and the interplay among them here we present laboratory fragmentation experiments that mimic deep sea explosive eruptions and compare our laboratory observations with those from the kilometre deep submarine eruption of havre volcano kermadec arc new zealand in 2012 we find that the havre eruption involved explosive fragmentation of magma by a pressure insensitive interaction between cool water and hot magma termed an induced fuel coolant interaction the laboratory experiments show that this water magma interaction is initiated by the formation of cracks in cooling magma into which the water coolant can infiltrate driving explosive fragmentation explosive submarine eruptions have previously been considered unlikely because stabilization of a vapour film at the magma water contact was thought to be a key requirement but is suppressed at depths exceeding 100 m however here we demonstrate that these induced fuel coolant interactions between magma and water can occur in a range of wet environments regardless of pressure from the subaerial to the deep sea and may operate on different planets as well as apply to materials other than magma and water

understanding multi vent plinian eruptions at mt tongariro volcanic complex new zealand the andesitic tongariro volcanic complex in the central north island of new zealand comprises tens of vents along an actively extending graben past work has hypothesised that multiple vents may operate during a single explosive eruption episode providing an unprecedented hazard challenge for this region the stratigraphic record suggests an irregular clustering of eruption episodes over time including an unusual 200 year long period from 11 3 11 1 ka when several large explosive eruptions occurred we carried out new field mapping stratigraphy and sedimentology of the resulting pyroclastic deposits to identify seven episodes during this period locating the vent sites and calculating their climactic dynamic properties five of the episodes involved two or more vent locations that produced separate sub plinian plinian eruption columns eruption columns ranged between 16 and 24 km high and erupted volumes of 0 05 to 0 76 km3 indicating magnitudes of 4 to 5 each of these episodes show north to south unzipping of the tongariro graben with episodes beginning in northerly vents before being joined by vents south of these this included two scenarios northern edifice vents followed by central edifice ones or central edifice vents followed by southern ones in both cases the northerly vents generally display the greatest peak eruption magnitudes and the steadiest eruptions by contrast the southernmost vents formed along a fault controlled fissure like system these produced unsteady plumes and pyroclastic density currents the northward widening tectonic graben structure thus influences the pattern and style of these plinian style eruptions this study highlights a real possibility for an extreme hazard scenario involving successive large scale eruptions at volcanic systems in slowly rifting environments and sheds new light on the volcano tectonic interaction in such settings

a method for the calculation of the impact parameters of dilute pyroclastic density currents based on deposit particle characteristics 1 a new method for the reconstruction of the physical characteristics of dilute pyroclastic density currents is introduced the velocity density and particle volumetric concentration profiles of the stratified current are calculated together with the profile of dynamic pressure which is a useful parameter for checking resistance of buildings the model links turbulent boundary layer shear flow theory with particle coupling to gas turbulence the working procedure starts with the recognition in the field of the fining upward sequence of layers formed during the time integrated depositional history of an individual current distinct processes of particle transportation and deposition are associated with the different particle modes composing the bedset the system of equations for the solution of the fluid dynamic parameters is implemented in two alternative ways the first one uses data of particles coming from both the basal coarse layer and the overlying laminated layer of the bedset the second uses features of two distinct components of the laminated layer a statistical test is performed for checking model results against experimental data of actual particles model calculations give the average solution as well as solutions corresponding to a range of 68 of probability around the average value the maximum solution can be considered as a safety value for impact parameters the methodology is applied to deposits of recent eruptions of vesuvius and campi flegrei in italy and results are discussed in terms of hazard and expected damage

the analysis of the influence of pumice shape on its terminal velocity 1 pumice particles represent the basic ingredient of many large explosive eruptions and form as a result of magma fragmentation inside the conduit at the onset of eruption fragmental pumices are expelled at high velocity from the crater by the overpressure of gas liberated on explosion the resulting multiphase flow is forced through atmosphere by a variety of transportation mechanisms and pumices eventually decouple from the gas flow settling down to form pyroclastic deposits here we propose new experimental data of terminal velocity together with a quantitative shape analysis of a wide range of pumice particles the resulting model allows predicting the terminal velocity of pumice by means of easily measured particle characteristics with an average error of 12 which compares favourably with previous models

drivers of explosivity and elevated hazard in basaltic fissure eruptions the 1913 eruption of ambrym volcano vanuatu sw pacific abstract fissure eruptions along linear structures can extend for several tens of kilometres with distinct separate manifestations of volcanism along their length they typically involve low viscosity mafic magmas forming long lava flows and cinder cones eruptions in 1894 and 1913 on ambrym volcano vanuatu showed how these mildly explosive eruptions can rapidly transform into violent explosive events producing significant hazard and widespread volcanic ash clouds during the 1913 episode a fissure began in the central caldera and basaltic magmas broke out in a series of locations down the island s western flank in all sites over 100 m in elevation fissure outbreaks produced vigorous lava fountains and highly fluid lava flows that travelled rapidly to the shoreline when the outbreaks propagated along the island s axis into coastal plain areas a climactic series of explosive eruptions occurred producing a 1 2 km long by 600 m wide maar and tephra ring a further small tuff ring was formed later creating a temporary island 400 m offshore the onshore tephra ring destroyed a hospital and associated buildings its last evacuating occupants were close witnesses to the eruption processes deposits exposed in the lower portion of the tephra ring show that this part of the eruption began with a mild phreatomagmatic explosive eruption from a narrow vent followed by a magmatic scoria producing phase subsequently a complex sequence of highly explosive phreatomagmatic eruptions occurred producing pyroclastic surges along with repeated distinctive breccia horizons rich in coral and lava country rock these features tally with eye witness accounts to indicate that the main eruption phase was produced by a periodically shifting locus of phreatomagmatic fragmentation and eruption along a single e w fissure the glassy and vesicle poor pyroclasts produced during this eruption phase were dominantly fragmented in a brittle manner by magma water interaction low volatile content of the magma upon fragmentation is confirmed by ftir analysis showing

using fractal analysis to quantitatively characterize the shapes of volcanic particles 1 the shapes of volcanic particles reflect numerous eruptive parameters e g magma viscosity volatile content and degree of interaction with water and are useful for understanding fragmentation and transport processes associated with volcanic eruptions however quantitative analysis of volcanic particle shapes has proven difficult because of their morphological complexity and variability here a newly developed procedure for shape analysis based on fractal geometry is described and tested although volcanic particle shapes are not truly fractal their complexity can be effectively characterized in terms of fractal values pseudofractal dimensions reflecting morphological invariance over discrete ranges of scale using fractal data produced by dilation of a particle s two dimensional boundary a spectrum of fractal dimensions is calculated for each particle by taking the first derivative of the dilation data compared with fractal methods that express shape in terms of only one or two fractal dimensions typically derived from the slope of data on a richardson plot this technique results in better discrimination between samples in addition use of multiple fractal values allows incorporation of multivariate statistical analysis further strengthening the differentiating power of the technique this fractal spectrum technique yields promising results for samples of sideromelane shards from iceland and is likely to be effective at characterizing other kinds of volcanic particle shapes

fracture apertures from electrical borehole scans three dimensional finite element modeling was performed to investigate the response to fractures of the formation microscanner mark of schlumberger which records high resolution electrical scans of the borehole wall it is found that the equation w carmbrx0l describes over two orders of magnitude of resistivity contrasts between borehole mud and the formation the relationship between fracture width w in mm formation sensitivity rx0 mud resistivity rm and the additional current flow a caused by the presence of the fracture a is the additional current which can be injected into the formation divided by the voltage integrated along a line perpendicular across the fracture trace coefficient c and exponent b are obtained numerically from forward modeling tool standoffs of up to 2 5 mm and fracture dips in the range from 0 to 40 were found to have an insignificant effect on the above relation a three step approach to detect trace and quantify fractures is used potential fractures in formation

deep sea fragmentation style of havre revealed by dendrogrammatic analyses of particle morphometry in 2012 the eruption of deep sea volcano havre produced an abundance of fine ash at a depth of 1000 m below sea level in this study the 2d shapes of havre ash grains retrieved from the seafloor were compared quantitatively with those of particles generated in a suite of different fragmentation experiments which used remelted rhyolitic rock and pumice from the eruption site a new statistical data analysis technique denoted as dendrogrammatic analysis of particle morphology dapm is introduced it is designed to compare large numbers of morphometric data sets containing shape information for a set of ash particles to group them by morphological similarities and to visualize these clusters in a dendrogram further steps involve t tests and equivalence tests and reveal morphometric differences as well as matching features the dapm suggests that the majority of havre ash was thermohydraulically produced by induced fuel coolant interaction a subset of ash particles features an elongated tube morphology their morphometry matches that of particles that were experimentally produced by a combination of shearing and quenching and we infer that the natural particles were formed by synextrusive ash venting

3 d reconstruction of ash vesicularity insights into the origin of ash rich explosive eruptions abstract explosive volcanic eruptions are characterized by highly variable degrees of magma fragmentation even during a single eruptive event the increasing amount of fine pyroclasts is often uncritically related to explosive magma water interaction i e hydromagmatic fragmentation here we report examination of two examples of major explosive eruptions from the quaternary vulsini volcanic district central italy in which the fine grained nature of deposits even in near vent settings indicates negligible effect of transport and implies the eruption of highly fragmented magmas sem morphoscopy of the juvenile products rules out extensive ash production due to hydromagmatic fragmentation we apply a recently developed stereo scanning electron microscopy ssem technique proussevitch et al 2011 to determine vesicularity features e g bubble size distribution and bubble number density hereafter bsd and bnd respectively of ash particles ssem analysis provides new insights into magma vesiculation history and fragmentation mechanism leading to major ash rich eruptions we conclude that extensive ash production was related to essentially magmatic processes involving high degrees of decompression in shallow magma reservoirs

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

a parametric and comparative study of different tephra fallout models abstract we perform a parametric and comparative study on three different tephra dispersal models fall3d hazmap and tephra applied to two different scenarios expected for etna volcano these scenarios are similar to the recent 2002 03 and 1990 etna eruptions and correspond respectively to a weak and to a strong plume eruption for each model and scenario we perform a parametric study on several inputs in order to quantify how a variation on a given input parameter i e an uncertainty on the model input affects the results of the model the study considers topographic effects different description for the eruption column column height influence different fits for terminal velocities of particles the effect of particle shape and finally the variation of the modal grain size model differences are quantified by means of a normalized distance that indicates how close in average the results from two different simulations are we also compare predictions from different models to determine under which circumstances the use of a more elaborated model is justified results from our parametric study show that output of the models can be strongly sensitive to the uncertainties and assumptions on input parameters such as mainly mass eruption rate column height distribution of the mass along the column bulk grain size distribution this highlights that for optimal forecasts is urgent to improve the description of these parameters and of some important physical processes like fragmentation and eruption column dynamics further differences between models are often lower than those due to the uncertainties of input parameters although they become more high in simulating weak plumes thus the choice of the model mainly depends on the kind of application such as the need to simulate the evolution of volcanic clouds in the atmosphere finally the use of both a semi analytical hazmap and a fully computational fall3d model for inverting field data of the 2001 etna eruption showed that the best fit parameters are similar for both models and are consistent with values obtained using independent techniques

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

towards fast and routine analyses of volcanic ash morphometry for eruption surveillance applications the morphometry of volcanic ash produced by explosive eruptions yields ample information on fragmentation processes e g magmatic vs magma water interactions and on transport and sedimentation mechanisms most previous works on volcanic clast morphometry focused on the apparent 2d projected shape of ash grains here termed apash to infer processes and eruptive styles however textural analyses of ash grains has remained a long and tedious task that made such approaches inappropriate for eruption surveillance duties in this work we show that new technological advances on automated dispersion of granular materials imaged with a camera coupled microscope and enhanced computer capabilities enable fast and high resolution image acquisition of thousands of ash grains that resolve this limitation with a morpho grainsizer designed for such fast and routine measurements we perform a series of apash analyses on selected ash fractions of tephra deposits from known eruptive styles we record the size aspect ratio circularity and convexity of apash images and assess resolution reproducibility minimum population size and total analytical duration and offer recommendations for the reporting of apash data for inter laboratory comparisons to avoid fractal geometry concerns our analyses are carried out at constant size range 250 300 m and optical magnification 5 on 3000 grains per samples collected from homogenized samples results from the andesitic 1999 ongoing eruption of tungurahua volcano ecuador show that ash particles from the moderate 2001 phase are relatively equant and convex in shape while the stronger 2006 subplinian phase produced ash grains with more elongated less circular and less convex apash signatures ash grains from a basaltic scoria cone forming eruption show even more ragged apash characteristics overall our protocol allows obtaining accurate and reproducible morphometric measurements that reveal subtle variations of the morphological signature and the short duration 1 8 hours of the whole analytical process renders high resolution analyses of ash shape achievable for volcano surveillance applications this research ultimately aims to set up a morphometric database of apash results for well defined eruptive styles in order to interpret on a short term basis any apash data from active volcanoes for monitoring purposes

the statistical eigenvector analysis technique seat for dip data analysis abstract dip data acquired from image logs i e the dip azimuth of planar features are extensively used in the oil and gas industry to assist in interpreting subsurface geology gradual and or abrupt variations in dip data with depth may indicate different structural features e g faults folds etc or changes to sedimentary systems e g unconformity the statistical eigenvector analysis technique seat and accompanying computer application are useful in statistically calculating the orientation and geometry of subsurface structures from dip data poles to planes on a spherical projection over a given depth interval may reveal cluster or girdle distributions which can be interactively analyzed using statistical distribution functions on the unit sphere seat provides a mathematical solution for as few as two data points and has the potential to be applied to dip data at the meter scale the orientation and geometry of various subsurface geological features e g folds fault drag deformation etc can be interactively calculated over a chosen depth interval seat is applied to a dip dataset acquired from a modern 8 padded electronic borehole image log and a previously studied dipmeter data from the discovery well of the railroad gap field to illustrate its higher accuracy in determining the orientation and geometry of subsurface structures compared to older methods seat allows for a vastly improved interpretation of subsurface geological features when combined with high resolution borehole image logs and accurate dip data improved understanding of subsurface geometries may allow for better business decisions in future exploration and appraisal of existing assets

evolution and facies architecture of paleogene surtseyan volcanoes on chatham islands new zealand southwest pacific ocean abstract this paper reports for the first time phreatomagmatic deposits and preserved surtseyan tuff cones in the chatham islands new zealand fieldwork has located the relicts of at least six closely spaced paleogene surtseyan cones and associated volcaniclastic sediments within the red bluff tuff formation the complete stratigraphic section of the cones consists of two parts 1 the lower part represents volcanic aggradational processes that constructed tuff cones in a short period of time and is composed of a bedded interval of explosively fragmented vesicular glassy basaltic pyroclasts ash and lapilli sizes as well as feeder dykes pillow lavas and pillow sills and 2 the upper part represents the rapid denudation of these cones by shallow marine currents or gravity flows reflecting the instability of the tephra pile forming the cones and a much later marine faunal colonization stage e g corals brachiopods molluscs etc erosion could have occurred almost immediately after or even during the emplacement of the volcanic pile similar to what occurred at surtla vent a satellite submerged cone of the basaltic island volcano surtsey iceland the waiareka deborah volcanics bridge point aorere point and lookout bluff surtseyan cones otago new zealand and marion and prince edward islands southwest indian ocean amongst others by contrast the complete faunal colonization and stabilization of a diverse marine community could have taken hundreds or perhaps even thousands of years to reach their acme following the volcanic pulses the structural textural and compositional characteristics of the red bluff tuff formation support a phreatomagmatic mode of fragmentation similar to that at surtsey volcano iceland the red bluff tuff sequence represents one of the most complete marine tuff cones described in the geologic record

quantitative hazard assessment of phreatomagmatic eruptions at vulcano aeolian islands southern italy as obtained by combining stratigraphy event statistics and physical modelling abstract the detailed analysis of stratigraphy allowed the reconstruction of the complex volcanic history of la fossa di vulcano an eruptive activity mainly driven by superficial phreatomagmatic explosions emerged a statistical analysis of the pyroclastic successions led to the identification of dilute pyroclastic density currents base surges as the most recurrent events followed by fallout of dense ballistic blocks the scale of events is related to the amount of magma involved in each explosion events involving about 1 million cm 3 of magma occurred during recent eruptions they led to the formation of hundreds of meters thick dilute pyroclastic density currents moving down the volcano slope at velocities exceeding 50 m s the dispersion of density currents affected the whole vulcano porto area the vulcanello area they also overrode the fossa caldera s rim spreading over the piano area for the aim of hazard assessment deposits from la fossa cone and la fossa caldera were studied in detail to depict the eruptive scenarios at short term and at long term by means of physical models that make use of deposit particle features the impact parameters have been calculated they are dynamic pressure and particle volumetric concentration of density currents and impact energy of ballistic blocks a quantitative hazard map based on these impact parameters is presented it could be useful for territory planning and for the calculation of the expected damage

eruption dynamics and tephra dispersal from the 24 november 2006 paroxysm at south east crater mt etna italy abstract between 30 august and 15 december 2006 mt etna italy underwent both effusive and explosive activity which took place from the south east crater one of its summit craters several paroxysmal episodes followed in succession separated by a few days of minor activity and characterised by dissimilar explosive style and intensity here we report one of the most studied and powerful episodes which started early in the morning on 24 november 2006 and lasted about 13 h excellent weather conditions enabled reconstructing in detail the onset and evolution of the eruptive phenomena both by live camera recordings and direct observations the explosive activity consisted of powerful strombolian activity alternating with short periods of lava fountains a weak volcanic plume rose up to 2 km above the volcanic vent followed by tephra fallout which covered the se and s flanks of etna campaigns allowed collecting about 40 tephra samples and mapping the fallout deposit the clockwise shifting of the volcanic plume during the eruption caused the different timing of the fallout on the ground thus widening the dispersal area voronoi s method was used to evaluate i the total grain size distribution indicating that the fallout deposit peaked at 1 and for the first time at etna ii the total componentry distribution finding that most of the particles were lithics with a low proportion of juvenile vs lithics 34 65 the total erupted mass was estimated 1 9 108 kg corresponding to a mass eruption rate of 5 103 kg s 1 physical parameters and textural features of the erupted products suggest that the 24 november 2006 explosive event may be classified as small sized in the recent history of etna and that the eruptive dynamic was mainly governed by magma gas decoupling which produced relatively fine grained fallout deposits containing unusual elongated sideromelane ash particles

lithostratigraphy of the volcanic sequences at hole 917a leg 152 se greenland margin abstract an overall high recovery rate up to 52 and 450 m of continuous logging data of good quality at odp hole 917a leg 152 se greenland margin allow us to refine the petrological descriptions made onboard and to establish a precise lithostratigraphy of the palaeocene volcanic succession changes in the dips of the flow banding between the upper series and the middle and lower series coincide with the transition from continental magmatism to post breakup volcanism established by the geochemistry

characterization of shape and terminal velocity of tephra particles erupted during the 2002 eruption of etna volcano italy in this paper we present a complete morphological characterization of the ash particles erupted on 18 december 2002 from etna volcano italy the work is based on the acquisition and processing of bidimensional digital images carried out by scanning electron microscopy sem to obtain shape parameters by image analysis we measure aspect ratio ar form factor ff compactness cc and rectangularity rt of 2065 ash particles with size between 0 026 and 1 122 mm we evaluate the variation of these parameters as a function of the grain size ash particles with a diameter of 0 250 mm are subelongate we find that on average particles with a diameter of 0 50 mm are angular using this morphological analysis and an empirical relation between the drag coefficient cd and reynolds number re of wilson and huang earth planet sci lett 44 311 324 1979 we calculate the terminal settling velocities vwh the comparisons between these velocities and those calculated with the formula of kunii and levenspiel fluidization engineering wiley new york pp 97 1969 vkl which considers ash particles as spheres show that vkl are in average 1 28 greater than vwh hence we quantify the systematic error on the spatial distribution of the mass computed around the volcano carried out by tephra dispersal models when the particles are assumed to be spherical

explosive felsic volcanism on el hierro canary islands the canary islands consist of seven basaltic shield volcanoes whose submerged portion is much more voluminous than the subaerial part of each island like so many other volcanic oceanic islands the indicative deposits of explosive felsic volcanism are not a common feature on the canary archipelago hitherto they have only been documented from the central islands of gran canaria and tenerife which are the largest volcanic complexes of the islands on the other canary islands the presence of felsic rocks is mostly restricted to intrusions and a few lava flows generally within the succession in the oldest parts of individual islands in this paper we present a detailed stratigraphic lithological and sedimentological study of a significant felsic pumice deposit on the island of el hierro referred here as the malpaso member which represents the only explosive episode of felsic volcanism found on the canary islands outside of gran canaria and tenerife the products of the eruption indicate a single eruptive event and cover an area of about 15 km2 this work provides a detailed stratigraphic and chronological framework for el hierro and four subunits are identified within the member on the basis of lithological and granulometric characteristics the results of this study demonstrate the importance of an explosive eruption in a setting where the activity is typified by effusive basaltic events given the style and the spatial distribution of the malpaso eruption and its products a future event with similar characteristics could have a serious impact on the population infrastructure and economy of the island of el hierro

the role of bubbles in generating fine ash during hydromagmatic eruptions the abundant fine ash produced in the 2011 subglacial eruption of grimsvotn iceland highlights the fragmentation efficiency of mafic hydromagmatic eruptions which is considerably higher than for comparable dry eruptions ash from the 2011 eruption can be divided into three morphological components vesicular particles shards and dense fragments distinguished by the size and abundance of constituent vesicles we use the vesicle characteristics to define a new shape factor the concavity index which provides an unbiased way to classify individual ash particles as either bubbly vesicular particles and shards or dense the relative proportion of bubbly and dense particles varies systematically with grain size with the proportion of bubbly grains decreasing as the particle size approaches the modal bubble diameter measured bubble volume distributions are similar to those of rapidly quenched pyroclasts from hawaiian fountains and suggest a comparable degassing history during magma ascent yet concordance between the size distributions of ash and of bubbles in the grimsvotn samples stands in contrast to the size distributions in hawaiian fountains where pyroclasts are orders of magnitude larger than individual bubbles we propose that the grimsvotn ash formed by brittle disintegration of vesicular pyroclasts and that fragmentation efficiency was amplified by residual thermal stresses in glass quenched by glacial water the strong control of resulting particle sizes and morphologies by the size and spatial distribution of bubbles demonstrates that the bubble population cannot be ignored when modeling hydromagmatic fragmentation

fluxes of fast and epithermal neutrons from lunar prospector evidence for water ice at the lunar poles maps of epithermal and fast neutron fluxes measured by lunar prospector were used to search for deposits enriched in hydrogen at both lunar poles depressions in epithermal fluxes were observed close to permanently shaded areas at both poles the peak depression at the north pole is 4 6 percent below the average epithermal flux intensity at lower latitudes and that at the south pole is 3 0 percent below the low latitude average no measurable depression in fast neutrons is seen at either pole these data are consistent with deposits of hydrogen in the form of water ice that are covered by as much as 40 centimeters of desiccated regolith within permanently shaded craters near both poles

the clementine bistatic radar experiment during the clementine 1 mission a bistatic radar experiment measured the magnitude and polarization of the radar echo versus bistatic angle beta for selected lunar areas observations of the lunar south pole yield a same sense polarization enhancement around beta 0 analysis shows that the observed enhancement is localized to the permanently shadowed regions of the lunar south pole radar observations of periodically solar illuminated lunar surfaces including the north pole yielded no such enhancement a probable explanation for these differences is the presence of low loss volume scatterers such as water ice in the permanently shadowed region at the south pole

furthering the investigation of eruption styles through quantitative shape analyses of volcanic ash particles abstract volcanic ash morphology has been quantitatively investigated for various aims such as studying the settling velocity of ash for modelling purposes and understanding the fragmentation processes at the origin of explosive eruptions in an attempt to investigate the usefulness of ash morphometry for monitoring purposes we analyzed the shape of volcanic ash particles through a combination of 1 traditional shape descriptors such as solidity convexity axial ratio and form factor and 2 fractal analysis using the euclidean distance transform edt method we compare ash samples from the hydrothermal eruptions of iwodake japan in 2013 tangkuban perahu indonesia in 2013 and marapi sumatra indonesia in 2015 the dome explosions of merapi java indonesia in 2013 the vulcanian eruptions of merapi in 2010 and tavurvur rabaul papaua new guinea in 2014 and the plinian eruption of kelud indonesia in 2014 particle size and shape measurements were acquired from a particle size analyzer with a microscope camera attached to the instrument clear differences between dense blocky particles from hydrothermal or dome explosions and vesicular particles produced by the fragmentation of gas bearing molten magma are well highlighted by conventional shape descriptors and the fractal method in addition subtle differences between dense blocky particles produced by hydrothermal explosions dome explosions or quench granulation during phreatomagmatic eruptions can be evidenced with the fractal method the combination of shape descriptors and fractal analysis is therefore potentially able to distinguish between juvenile and non juvenile magma which is of importance for eruption monitoring

advances in borehole imaging technology and applications abstract borehole imaging devices are currently available for both wireline and logging while drilling lwd environments for use in both openhole and cased wells most wireline and all lwd devices provide indirect images that are derived from a high density grid of electrical or ultrasonic acoustic measurements optical techniques such as television and photography provide direct images of the borehole imaging devices consist of 1 a rotating sensor acoustic or electrical that scans the borehole with each revolution 2 multiple azimuthally placed sensors or 3 a downhole television or photographic camera advances in digital acquisition and processing permit real time display and evaluation of images of the open borehole or the inside of casing the resolution and borehole coverage of microelectrode devices has increased with newer designs that allow additional measurement sensors per pad additional pad segments on a four arm tool and the introduction of six arm imaging tools in nonconductive borehole fluids a four arm microinduction device can provide crude images macroelectrode imaging tools laterolog type wireline provide lower resolution electrical images from either an azimuthal arrangement of sensors around a mandrel wireline or from azimuthally sensitive sensors logging while drilling that scan the borehole during rotation of the bottomhole assembly in acoustic imaging recent devices incorporate design changes that provide improved image resolution and operate in a wider range of borehole conditions ultrasonic transducers now use lower transmitting frequencies and spherical focusing and these tools also offer surface selectable acquisition parameters acoustic and microresistivity imaging techniques measure different physical properties and these data are complementary one recently introduced wireline service combines microresistivity and acoustic imaging devices in a single tool for simultaneous single pass acquisition recent advances in cable and sonde design permit downhole video in a wider range of petroleum environments in flowing wells and in tubing openhole image interpretation involves qualitative visual identification and quantitative characterization of strike and dip on planar features lithology bedding fractures and vugs when core is available features identified on log derived images can be correlated or calibrated to it or when core is absent images may serve as a substitute borehole images are useful in formation evaluation when calibrated sedimentology stratigraphy and structural analysis current applications include core orientation reconstructing missing core identification and characterization of fractures and depositional features e g bedforms reservoir architecture bedding grain size porosity permeability net sand and net pay counts faults folds and fractures hydrocarbon water geothermal wells and in rock engineering evaluation of borehole stress borehole stability directional placement of wellbore for optimal drainage fractured reservoirs evaluation of fracture stimulations and perforation control cased hole applications include cement evaluation casing inspection detection of fluid entry identifying production blockages and assisting in fishing operations

adsorption and excess fission xe adsorption of xe on vacuum crushed minerals we report the results of xe adsorption studies at low partial pressures of xe 2 10 13 atm for a terrestrial labradorite and lunar anorthosite 15415 which were crushed under high vacuum the creation of fresh surfaces resulted in a distribution of surface adsorption potentials with the most energetic but least abundant fractions of the surface dominating adsorption behavior at lower temperatures atmospheric exposure tends to eliminate the most energetic surface fractions for sample 15415 surfaces with an adsorption potential as great as 13 7 kcal mole were created but these constituted only about 10 6 of the surface area observation of the adsorption behavior of this sample over a period of days revealed the gradual disappearance of the most energetic fractions of the surface probably because of site competition effects caused by sorption of active gases in our high vacuum manifold our results consist of values of the henry constants of xe adsorption at various temperatures we have used extrapolations based upon these data to evaluate the possible role of adsorption in the excess fission xe effect observed in lunar highland gas rich breccias for a model in which excess fission xe is concentrated by adsorption while diffusing through the regolith our experimental results and estimations of the sorptive properties of the in situ regolith based on the time scale of lunar surface rn emanations indicate that adsorption falls about five orders of magnitude short of accounting for the effect we also infer that the adsorption characteristics of our vacuum crushed lunar sample are reasonable analogs to those of in situ lunar soil so that the failure of adsorption to account for excess fission xe cannot be attributed to significant differences in sorptive behavior of these materials

stress induced borehole elongation a comparison between the four arm dipmeter and the borehole televiewer in the auburn geothermal well the nature and origin of borehole elongation recorded by the four arm dipmeter calipers is studied utilizing information obtained from hydraulic fracturing stress measurements and borehole televiewer data taken in a well located in auburn new york a preferred orientation n10 w s10 e 10 and a less prominant e w orientation of borehole elongation was observed on two runs of the dipmeter comparisons of borehole geometry determined using the televiewer and the dipmeter show that both tools give the same orientation of borehole elongtion provided that the zone of elongation is longer than 30 cm comparisons of dipmeter caliper data with orientation of in situ stress and natural fractures obtained from hydrofracturing tests and televiewer data show that the n10 w s10 e borehole elongations 1 are axisymmetric 2 are aligned with the minimum horizontal stress sh and 3 are not associated with natural fractures intersecting the well these elongations are interpreted as stress induced well bore breakouts the e w elongation direction is characterized by an asymmetric borehole cross section in thinly bedded rocks and is not caused by breakouts this asymmetric geometry can be discriminated from breakouts using the oriented electric measurements provided by the dipmeter this study demonstrates that the dipmeter can be used to determine the orientation of sh by mapping breakouts confirming the results of earlier less detailed studies and provides a firm basis for mapping regional stress patterns using existing dipmeter data

ice in the lunar polar regions revisited 1 the common wisdom that water ice may exist in lunar polar cold traps has become a significant factor in the selection of space research objectives the purpose of this paper is to address two topics that are missing from the discourse on lunar water the effect that the pristine cleanliness of the regolith has on water transport on the moon and the limits on water exposure implied by the extremely high adsorption potentials of the surfaces of soil grains water transport is characterized by chemisorption on soil grains and the mixing of wet grains into the regolith by meteoritic gardening ballistic lateral flow which is generally thought to be an efficient conduit for moving water to the poles is actually a secondary phenomenon that is facilitated by solar wind and micrometeor erosion but not by thermal desorption as is the case for the dominant lunar exospheric gases he and 40ar simulation results show that even under the most optimistic conditions less than 7 of the water accumulated in the regolith resides in the polar cold traps where water concentrations cannot be greater than 350 ppm more important when realistic transport parameters are used in the simulator the polar water concentration is reduced by almost 2 orders of magnitude in a word the concept of water ice at the lunar poles is insupportable

fragmentation versus transportation mechanisms in the pyroclastic sequence of monte pilato rocche rosse lipari italy abstract monte pilato is a rhyolitic pumice cone formed about 1400 years ago during the last volcanic activity which occurred at lipari its activity consisted of numerous explosive episodes ending with the extrusion of the rocche rosse obsidian lava flow we have identified nine different pyroclastic lithofacies of which four main lithofacies represent 90 of the erupted products they include 1 deposits consisting of decimeters to meters thick well sorted graded beds of pumice lapilli which are of fall origin 2 massive deposits consisting of decimeters thick beds of pumice lapilli in an ash matrix interpreted as being of pyroclastic flow origin 3 deposits of centimeters thick ash beds of surge origin 4 decimeter thick fine ash layers with scattered subcentimetric accretionary lapilli of turbulent flow origin the complex grain size distributions of the main lithofacies were distinguished using a multivariate statistic analysis r mode factor analysis variations of the grain size characteristics in relation to the distance from the vent area have been investigated in order to discriminate the roles played by fragmentation and transportation processes in the lithofacies 1 fall deposits the grain size distribution is always unimodal and varies from a rosin type distribution near the vent to a gaussian one in the distal outcrops this is caused by the transport process and the different particle trajectories in lithofacies 2 3 and 4 the grain size distributions are always polymodal the polymodality is not caused by preferential processes occurring during transportation but seems rather to be connected with the original fragmentation of the pyroclastic material the pumice lapilli present both in lithofacies 1 and 2 have mean vesicularity index values always in excess of 65 and the value is homogeneous throughout the sample these data suggest that for these two lithofacies the pumice lapilli originated from exsolution of magmatic gases in contrast the fine ash particles in lithofacies 2 and also the main mode of lithofacies 3 and 4 deposits show typical features of hydromagmatic fragmentation processes the grain size population is always centered at 4 5 0 032 0 064 mm and interestingly the same grain size has been obtained recently zimanowski et al 1991 for fragments produced by experimental magma water interaction field and laboratory data suggest that during monte pilato rocche rosse eruptions magmatic and hydromagmatic mechanisms were frequently operative at the same time

quantitative scanning electron microscope analysis of volcanic ash surfaces application to the 1982 1983 galunggung eruption indonesia qualitative analyses of volcanic ash are time consuming and subjective whereas quantitative analyses are methodical and automated not only volcanic ash particles but also many natural particles have been widely described and quantified by their outlines the qualitative data of volcanic ash surfaces need to be expressed quantitatively supported by supplementary methods such as statistical analysis and artificial intelligence well defined surface descriptors can be applied to volcanic ash particles in this study roughness and texture descriptors of pyroclastic material from the 1982 1983 eruption of galunggung java indonesia were used to describe the vesicle surfaces of the particles alteration intensity and or fine particle abundance these parameters are important for distinguishing the products of magmatic eruptions from those of phre atomagmatic eruptions further application of this method may allow these descriptors to be easily converted to alteration grade vesicularity index intensity of the fragmentation mechanism and relative proportions of the pyroclast types hence discrimination between products of different fragmentation mechanisms may permit forecasting of volcanic hazards

post eruptive sediment transport and surface processes on unvegetated volcanic hillslopes a case study of black tank scoria cone cima volcanic field california abstract conical volcanic edifices that are made up from lapilli to block bomb pyroclastic successions such as scoria cones are widespread in terrestrial and extraterrestrial settings eruptive processes responsible for establishing the final facies architecture of a scoria cone are not well linked to numerical simulations of their post eruptive sediment transport using sedimentological geomorphic and 2d fragment morphology data from a 15 ky old scoria cone from the cima volcanic field california this study provides field evidence of the various post eruptive sediment transport and degradation processes of scoria cones located in arid to semi arid environments this study has revealed that pyroclast morphologies vary downslope due to syn eruptive granular flows along with post eruptive modification by rolling bouncing and sliding of individual particles down a slope and overland flow processes the variability of sediment transport rates on hillslopes are not directly controlled by local slope angle variability and the flank length but rather by grain size and morphological characteristics of particles such as shape irregularity of pyroclast fragments and block lapilli ratio due to the abundance of hillslopes degrading in unvegetated regions such as those found in the southwestern usa granulometric influences should be accounted for in the formulation of sediment transport laws for geomorphic modification of volcanic terrains over long geologic time

fracture mapping with electrical core images naturally fractured reservoirs often contain a range of different fracture types and networks fractures that are relatively permeable and relatively impermeable unconnected and connected to the part of the fracture network that carries fluid flow and naturally occurring or drilling induced consequently in terms of their fluid connectivity fractures may be open or closed while individual fractures may be isolated or well connected we have adapted our approach to imaging sedimentary fabric in the laboratory where we related electrical core images to properties such as porosity permeability grain size and cementation to enable electrical imaging of fractures in core our approach uses similar principles to those employed in down hole electrical imaging the results demonstrate an ability to image conductive fractures in fully saturated low porosity water bearing core these fractures being electrically connected from the flat measurement surface through to the outer surface of the core published results for numerical modelling of down hole electrical imaging tools show the electrical response is related to fracture depth and fracture aperture our experimental results on fractured core in the laboratory support these numerical observations increased current flowing into the fracture as the aperture increases the finite size of the electrode however means that this technique cannot distinguish between a single fracture and smaller groups of fractures intersecting the electrode

migration calculations for water in the exosphere of the moon dusk dawn asymmetry heterogeneous trapping and d h fractionation water ice is trapped in permanently shadowed craters near the lunar poles where it is thought to have arrived from an exogenic or endogenic source via ballistic hops we use a model of the migration of water molecules in the lunar exosphere to investigate three problems 1 a strong continuous source would lead to an enhanced concentration of h2o at the morning terminator but not at the evening terminator hence spectral features observed at both terminators do not suggest that there is diurnal migration of volatiles 2 cold trapping after a comet impact leads to an unequal partitioning between the two hemispheres depending on the latitude of the impact but to nearly equal partitioning with respect to longitude 3 the d h fractionation as the water molecules migrate toward the poles is small hence the isotopic composition of ice deposits in the cold traps can be related to that of the source

grain shape of basaltic ash populations implications for fragmentation here we introduce a new quantitative method to produce grain shape data of bulk samples of volcanic ash and we correlate the bulk average grain shape with magma fragmentation mechanisms the method is based on automatic shape analysis of 2d projection ash grains in the size range 125 63 m loose bulk samples from the deposits of six different basaltic eruptions were analyzed and 20 000 shape measurements for each were obtained within 45 min using the particle insight dynamic shape analyzer pidsa we used principal component analysis on a reference grain dataset to show that circularity rectangularity form factor and elongation best discriminate between the grain shapes when combined the grain population data show that the studied eruptive environments produce nearly the same range of grain shapes although to different extents our new shape index the regularity index ri places an eruption on a spectrum between phreatomagmatic and dry magmatic fragmentation almost vesicle free surtseyan ash has an ri of 0 207 0 002 2 whereas vesiculated hawaiian ash has an ri of 0 134 0 001 2 these two samples define the end member ri while two subglacial one lacustrine and another submarine ash sample show intermediate ris of 0 168 0 002 2 0 175 0 002 2 0 187 0 002 2 and 0 191 0 002 2 respectively the systematic change in ri between wet and dry eruptions suggests that the ri can be used to assess the relative roles of magmatic vs phreatomagmatic fragmentation we infer that both magmatic and phreatomagmatic fragmentation processes played a role in the subglacial eruptions

relocating and orientating cores by the integration of electrical and optical images a case study from ocean drilling program hole 735b while the dip of structural features on recovered rotary drilled core can be accurately measured the azimuth of such features in a geographical reference frame is not known scribing techniques and analysis of magnetic signatures have been used in attempts to solve this problem but scribing has so far failed in deep sea drilling operations and magnetic signatures cannot always be easily resolved here we demonstrate a method for core reorientation and accurate location within a borehole using a comparison between borehole electrical images and whole core digital images odp hole 735b penetrates a 1500 m section of lower oceanic crustal gabbroic rocks with an average core recovery of 86 6 the absence of orientated core pieces severely restricts the interpretation of these data in this study the entire outer surface of individual core pieces was scanned using the dmt digital colour corescan system structural features on these unrolled digital images are correlated with images of the same features on formation microscanner logs obtained during the wireline logging programme using this approach it is possible to reorientate and accurately locate core pieces within the drilled section

the biancavilla montalto ingnimbrite etna sicily stratigraphic granulometric and sem grain texture studies have been carried out on pyroclastic deposits in the biancavilla and montalto areas on the lower sw flank of etna these studies support the interpretation that the deposits were emplaced as pyroclastic flows during the final stage of the ellittico eruptive activity 14 18 26 ka based on the high percentage of juvenile components and granulometric characteristics the deposits are classified as normal ignimbrite four separate flow units have been distinguished based on the presence of fine grained basal layers a multivariate g mode statistical analysis has been used to discriminate particle morphology populations between flow units and infer temporal changes in the nature of the eruptive processes the initial flow i was emplaced at a high temperature and involved a juvenile gas phase exolved from the magma subsequent flows ii iii iv exhibit evidence for the interaction of external water

the grain size dependency of vesicular particle shapes strongly affects the drag of particles first results from microtomography investigations of campi flegrei fallout deposits abstract acknowledging the grain size dependency of shape is important in volcanology in particular when dealing with tephra produced and emplaced during and after explosive volcanic eruptions a systematic measurement of the tridimensional shape of vesicular pyroclasts of campi flegrei fallout deposits agnano monte spina astroni 6 and averno 2 eruptions varying in size from 8 00 to 0 016 mm has been carried out by means of x ray microtomography data show that particle shape changes with size especially for juvenile vesicular clasts since it is dependent on the distribution and size of vesicles that contour the external clast outline two drag laws that include sphericity in the formula were used for estimating the dependency of settling velocity on shape results demonstrate that it is not appropriate to assume a size independent shape for vesicular particles in contrast with the approach commonly employed when simulating the ash dispersion in the atmosphere

the fractal and multifractal dimension of volcanic ash particles contour a test study on the utility and volcanological relevance abstract image processing analysis is used to check the ability of the fractal dimension for quantitatively describing the shape of volcanic ash particles digitized scanning electron microscopy images of fine pyroclasts from the eruptions of monte pilato rocche rosse lipari italy are investigated to test the efficiency of the fractal dimension to discriminate between particles of different eruptive processes multivariate analysis of multiple fractal components allows distinction between magmatic particles and phreatomagmatic particles which however is less significant than the discrimination obtained in previous studies by the use of simple adimensional shape parameters approximation of the actual particle boundary and the not rotation invariant nature of the fractal data frequently result in a significant scatter of data points in the mandelbrot richardson plot such behavior obscures in some cases the actual information of particle shape and renders the discriminating power of fractal analysis less effective than classical shape descriptors data less affected by scatter reveal that phreatomagmatic particles of the monte pilato rocche rosse eruptions are true mono fractals whereas magmatic particles are multifractals the textural small scale fractal of magmatic particles is similar to the fractal dimension value of phreatomagmatic particles and is attributed to the rheological behavior of melt upon brittle fragmentation the structural large scale fractal of magmatic particles refers to the walls of ruptured vesicles that lay on the particle outline the high difference between the values of the textural and structural fractals of magmatic particles of the monte pilato rocche rosse eruptions suggests two distinct and independent processes in the formation of such pyroclasts at the scales corresponding to the textural fractal the fragmentation process is independent of vesicles magmatic fragmentation is not simply related to growth expansion interference and explosion of vesicles but to a brittle cracking of the highly viscous melt likely related to rapid decompression

are the ashes from the latest eruptions 2010 2016 at turrialba volcano costa rica related to phreatic or phreatomagmatic events abstract the initial eruptive episodes of explosive eruptions are classified as phreatic if the amount of juvenile material scoria glass pumice is null and the amount of fresh accidental lithics and hydrothermally altered lithics is substantial phreatic eruptions have been in some cases recognized as precursory events preceding phreatomagmatic and magmatic eruptive phases usually the lithological features of tephra deposits are investigated and sampled in the field investigation of ash samples under binocular microscope or by back scattered electron bse microscope images of polished sections is usually considered sufficient to typify the fragmentation mechanism of the eruption the opening eruptive phases at turrialba volcano together with the formation of new intracraters i e 2010 2012 2014 and the enlargement of the western crater 29 october 2014 to present were classified in previous papers and internal reports as phreatic we studied a series of ash samples erupted from 2010 to 2016 with the aim of understanding the fragmentation processes characterizing the vent opening phases we used sem eds analyses in addition to field and microscopic investigation results showed a composition of accidental lithics of fresh to hydrothermally altered clasts and secondary minerals 82 98 besides juvenile andesite fragments 2 18 which leads us to revisit the classification of the initial eruptive phases of turrialba as phreatomagmatic our method allowed the detection of a juvenile component directly involved in an effective magma water interaction which was possible only by a scrutinous examination of the glass surface textures by sem in the range size between 3 and 3 5 phi we recommend such a type of investigation when the identification of fresh magma in a new eruption is crucial for the preparedness and hazard evaluation at active volcanoes

amplified hazard of small volume monogenetic eruptions due to environmental controls orakei basin auckland volcanic field new zealand orakei maar and tuff ring in the auckland volcanic field is an example of a basaltic volcano in which the style and impacts of the eruption of a small volume of magma were modulated by a fine balance between magma flux and groundwater availability these conditions were optimised by the pre 85 ka eruption being hosted in a zone of fractured and variably permeable plio pleistocene mudstones and sandstones orakei maar represents an end member in the spectrum of short lived basaltic volcanoes where substrate conditions rather than the magmatic volatile content was the dominant factor controlling explosivity and eruption styles the eruption excavated a crater 80 m deep that was subsequently filled by slumped crater wall material followed by lacustrine and marine sediments the explosion crater may have been less than 800 m in diameter but wall collapse and wave erosion has left a 1 000 m diameter roughly circular basin a tuff ring around part of the maar comprises dominantly base surge deposits along with subordinate fall units grain size texture and shape characteristics indicate a strong influence of magma water and magma mud interactions that controlled explosivity throughout the eruption but also an ongoing secondary role of magmatic gas driven expansion and fragmentation the tuff contains 70 of material recycled from the underlying plio pliestocene sediments which is strongly predominant in the 2 fraction the magmatic clasts are evolved alkali basalt consistent with the eruption of a very small batch of magma the environmental impact of this eruption was disproportionally large when considering the low volume of magma involved dre 0 003 km3 hence this eruption exemplifies one of the worst case scenarios for an eruption within the densely populated auckland city destroying an area of 3 km2 by crater formation and base surge impact an equivalent scenario for the same magma conditions without groundwater interaction would yield a scoria spatter cone with a diameter of 400 550 m destroying less than a tenth of the area affected by the orakei event

pyroclast characteristics of a subaqueous to emergent surtseyan eruption black point volcano california abstract we present the first ever quantitative analysis of pyroclast textures from subaqueous deposits of a surtseyan emergent volcano the volcano black point formed in mono lake s pleistocene precursor lake russell at 13 300 500 bp from an explosive basaltic eruption involving the interaction of shallow lake water 105 m with vesiculating magma the bulk of the edifice comprises unconsolidated tephra and represents submerged stages of eruption thin summit deposits formed during a final phase of emergent eruption and produced a group of low tuff rings lapillus clasts 16 mm to 32 mm and fine ash grains 4 0 0625 mm from the subaqueous deposits have textures that reveal a conduit history of bubble nucleation growth collapse intense microlite crystallisation and magma water interaction lapilli vesicularity ranges broadly to high values up to 89 while vesicle number densities 5 4 102 4 8 104 vesicles per mm3 are comparable to those published for strombolian and plinian basaltic eruptions 1 104 vesicles per mm3 vesicle size and volume distributions suggest continuous bubble nucleation but the suite of data as a whole indicates that a late stage nucleation event played a significant role in shaping the eruption ash grain morphology and surface features indicative of magma water interactions attest to water s role in fragmentation overall the pyroclast textures are consistent with water modification of a rather intense basaltic eruption which might have been of a violent strombolian or plinian style if the eruption had been dry and occurred subaerially

eifel maars quantitative shape characterization of juvenile ash particles eifel volcanic field germany abstract the eifel region in western central germany is the type locality for maar volcanism which is classically interpreted to be the result of explosive eruptions due to shallow interaction between magma and external water i e phreatomagmatic eruptions sedimentary structures deposit features and particle morphology found in many maar deposits of the west eifel volcanic field wevf in contrast to deposits in the east eifel volcanic field eevf lack the diagnostic criteria of typical phreatomagmatic deposits the aim of this study was to determine quantitatively the shape of wevf and eevf maar ash particles in order to infer the governing eruption style in eifel maar volcanoes the quantitative shape characterization was done by analyzing fractal dimensions of particle contours 125 250 m sieve fraction obtained from scanning electron microscopy sem and sem micro computed tomography sem micro ct images the fractal analysis dilation method and the fractal spectrum technique confirmed that the wevf and eevf maar particles have contrasting multifractal shapes whereas the low small scale dimensions of eevf particles eppelsberg green unit coincide with previously published values for phreatomagmatic particles the wevf particles meerfelder maar pulvermaar and ulmener maar have larger values indicating more complex small scale features which are characteristic for magmatic particles these quantitative results are strengthening the qualitative microscopic observations that the studied wevf maar eruptions are rather dominated by magmatic processes the different eruption styles in the two volcanic fields can be explained by the different geological and hydrological settings found in both regions and the different chemical compositions of the magmas

a comparison of fourier and fractal techniques in the analysis of closed forms abstract forty one samples of quartz sand grains derived from four different sources are analyzed using fourier grain shape and multi component fractal techniques the results from the two techniques are sufficiently similar to demonstrate clearly the potential usefulness of the fractal based technique in the analysis of sedimentary particles additionally the fact that the fractal technique is shown to extract information from shapes suitable for analysis via a radius expansion method lends credence to the expectation that it will yield comparable information when applied to more complex shapes not amenable to the radius expansion fourier technique

volcanic history of lipari aeolian islands italy during the last 10 000 years abstract examination of the volcanic stratigraphy of deposits younger than 10 000 years on lipari indicates four principal periods of volcanic activity related to specific centers the products from each different volcanic center are defined as volcano stratigraphic unit vsu from the oldest these are the canneto dentro gabellotto fiume bianco forgia vecchia and monte pilato rocche rosse vsus the study of textures and dispersal of the deposits permitted the vents to be localized and the recent volcanic history of lipari to be reconstructed the oldest event formed a small explosion breccia cone with a final obsidian lava in the canneto dentro area immediately afterward a complex series of explosions produced the widespread dry surge deposits of the gabellotto fiume bianco sequence this activity ended with the extrusion of a domical lava flow the renewal of activity occurred in the pirrera area with an explosive eruption that produced explosion breccia deposits the last eruptions from this vent were coeval with the first eruption of m pilato the rim of the explosion breccia cone was partially destroyed by the forgia vecchia lava flow m pilato cone grew in a very short period of time due to a continuous swarm of explosive events after a short repose time a series of more energetic and superficial explosions occurred through a vent slightly to the south the extrusion of the rocche rosse lava flow about 729 a d ended this cycle of activity all the volcanic centers follow a quite similar stochastic pattern starting with a fall or surge eruption and ending with effusion of viscous rhyolitic lavas the four centers are aligned along either nw se or ne sw fault systems according to the structural pattern of the island they can be placed into two groups the canneto dentro gabellotto centers and the forgia vecchia m pilato centers a long quiescence 3 500 years separates the activity of these two groups while inside of each the activities were nearly contemporaneous or in rapid succession

subsurface migration of h2o at lunar cold traps 1 permanently shaded areas near the poles of the moon and mercury may harbor water ice we develop a physical model for migration of water molecules in the regolith and discover two pathways that can lead to accumulation of h2o in the subsurface a small fraction of water molecules delivered either continuously or abruptly to permanently cold areas diffuses into the regolith and can remain there longer than on the surface higher temperatures lead to deeper burial at constant temperature this diffusive migration produces less than one molecular layer of volatile h2o on grains because it is driven by differences in surface concentrations the water is therefore expected to be in adsorbed form and the amount stored in this fashion could be at most a few hundred ppm of h2o a second pathway is pumping by diurnal temperature oscillations from a transient ice cover that may have formed during a large comet impact it can lead to high ground ice densities but the ground ice layer lasts not long beyond the disappearance of the ice cover both types of subsurface charging mechanism work best for temperatures typical of permanently shaded areas with sunlit surfaces in their field of view

comparative analyses of glass fragments from brittle fracture experiments and volcanic ash particles explosive volcanic eruptions are characterized by the rapid fragmentation of a magmatic melt into ash particles in order to describe the energy dissipation during fragmentation it is important to understand the mechanism of material failure a quantitative description of fragmentation is only possible under controlled laboratory conditions industrial silicate glasses have a high structural affinity with magmatic melts and have the advantage of being transparent which allows the study of the evolution of fractures by optical methods on a time scale relevant for explosive volcanism with this aim a series of low speed edge on hammer impact experiments on silicate glass targets has been conducted leading to the generation of fragments in the grain size spectra of volcanic ash in order to verify the general transferability of the experimentally generated fragmentation dynamics to volcanic processes the resulting products were compared by means of statistical particle shape analyses to particles produced by standardized magma fragmentation experiments and to natural ash particles coming from deposits of basaltic and rhyolitic compositions from the 2004 grimsvotn and the quaternary tepexitl tuff ring eruptions respectively natural ash particles from both grimsvotn and tepexitl show significant similarities with experimental fragments of thermally pre stressed float glasses indicating a dominant influence of preexisting stresses on particle shape and suggesting analogous fragmentation processes within the studied materials

particle size density relationships in pyroclastic deposits inferences for emplacement processes in moving pyroclastic systems particles are sorted as a function of their sizes densities and shapes the analysis of the distribution of these characteristics in particle populations of pyroclastic deposits is a major tool in evaluating properties and regimes of parent transport systems this paper reports a study of size density relationships of component subpopulations from selected quaternary pyroclastic deposits of the latera volcanic complex vulsini italy by means of integrated field and laboratory investigations including grain size and component analyses density measurements and sem crystal morphoscopy three kinds of particle size density relationships characterize the studied deposits as follows 1 a significant correlation of decreasing sizes with increasing component densities exists for direct suspension sedimentation products including plinian fall and pyroclastic surge deposits 2 a wide data dispersion with poor correlation normally occurs for the main zones of deposits from high concentration pyroclastic flows and 3 component subpopulations occur in a narrow size range irrespective of density in granular systems dominated by grain collisions such as traction zones beneath low concentration pyroclastic surges and sheared basal layers of pyroclastic flows the regression coefficients of size density relationships appear as a comparative measure of particle concentration in the parent systems consistent with that inferred from the degree of sorting and abrasion of crystal subpopulations from sequential fragmentation transport analysis of grain size data and quantitative morphoscopy the crystal component becomes less sorted and more abraded as the fit to the size density relationship decreases from plinian fall to pyroclastic surge to pyroclastic flow consistent with increasing particle concentration in the transporting current

surface area and volume measurements of volcanic ash particles using micro computed tomography micro ct a comparison with scanning electron microscope sem stereoscopic imaging and geometric considerations volcanic ash particles are important components of explosive eruptions and their surface textures are the subject of intense research characterization of ash surfaces is crucial for understanding the physics of volcanic plumes remote sensing measurements of ash and aerosols interfacial processes modelling transportation and deposition of tephra and characterizing eruptive styles a number of different methods have been used over the years to arrive at surface area estimates the more common methods include estimates based on geometric considerations geometric surface area and physisorption of gas molecules on the surface of interest physical surface area in this study micro computed tomography micro ct which is a non destructive method providing three dimensional data enabled the measurement of surface area and volume of individual ash particles results were compared with the values obtained from sem stereoscopic imaging and geometric considerations surface area estimates of micro ct and sem stereoscopic imaging are similar with surface area volume ratios sa v of 0 0368 and 0 0467 respectively ash particle surface textures show a large deviation from that of simple geometric forms and an approximation both to spheres and ellipsoids do not seem adequate for the representation of ash surface sem stereoscopic and or micro ct imaging are here suggested as good candidate techniques for the characterization of textures on macro pore regions of ash particles

processes controlling the shape of ash particles results of statistical ipa abstract ash particles have unique morphologies and shapes that are characteristic of certain fracture mechanisms and can be used to identify the type of fragmentation such as magmatic brittle or ductile fragmentation and phreatomagmatic molten fuel coolant interaction type fragmentation identifying these two different fragmentation processes is especially important in complex volcanic systems where both fragmentation processes can occur in this study image parameter analysis and statistical parameter analysis are used to compare ash particles from standardised magma fragmentation experiments with natural ash particles from the pleistocene lake purrumbete maar southeastern australia the pyroclastic lake purrumbete maar sequence containsvarious deposit types that show evidence for changing eruption conditions therefore it is of a main interest to determine the main fragmentation mechanism that formed these deposits a comparison with experimental ash particles revealed that lake purrumbete ash particles show significant differences from experimental samples of magmatic brittle type fragmentation whereas they show no significant differences from phreatomagmatic molten fuel coolant interaction type fragmentation samples indicating a predominance of phreatomagmatic fragmentation during the eruption of lake purrumbete the experiments further show that pre existing stresses also influence the particle shape and may be the reason for the absence of a significant similarity between most of the particle populations

granulometric characterization of paleosols in loess series by automated static image analysis abstract an automated image analysis method is proposed here to study the size and shape of siliciclastic sedimentary particles of paleosols of central european loess sequences several direct and indirect measurement techniques are available for grain size measurements of sedimentary mineral particles indirect techniques involve the use of some kind of physical laws however all requirements for calculations are in many cases not known even so the direct manual microscopic observation and measurement of large representative number of grains is time consuming and sometimes rather subjective therefore automated image analyses techniques provide a new and perspective way to analyse grain size and shape sedimentary particles here we test these indirect laser diffraction and direct automated static image analysis techniques and provide new granulometric size and shape data of paleosols our results demonstrate that grain size data of the mineral dust samples are strongly dependent on shape parameters of particles and shape heterogeneity was different between different size classes due to the irregular grain shape parameters uncertainties have arisen also for determination of grain sizes in this paper we present a possible correction procedure to reduce the differences among the results of the laser diffraction and image analysis methods by applying new correction factors results of the two approaches could become closer but the unknown thickness of particles remains a problem to solve the other presented correction procedure to assess the uncertain 3rd dimension of particles by their intensity size relationships makes us able to reduce further the deviations of the two sizing methods

space weathering effects on lunar cold trap deposits 1 both steady and episodic sources have been proposed as sources of hydrogen observed by lunar prospector in association with the regions of permanent shadow at the poles of the moon either source could supply significant quantities of water to the poles however space weathering processes affect the retention of water in the cold traps we investigate those effects by simulating the evolution of a column of regolith in the region of permanent shadow over time we determine the hydrogen concentration as a function of depth using a monte carlo model of discrete impacts and of delivery from the solar wind we treat the delivery sublimation sputtering and very small scale impacts as continual processes comparing the amount of water delivered to the poles to the amount remaining after space weathering we find a retention efficiency of 5 6 the retention efficiency of the polar cold traps is adequate for preserving volatile deposits over long periods of time the average hydrogen concentration in the regolith column is 4100 ppm in the top meter after 1 gyr this is a saturation level in the regolith increasing the amount of time deepens the enriched layer but does not lead to increased concentrations in 1 gyr about 1 6 m of the regolith is gardened therefore the top meter which is probed by the neutron spectroscopy technique has reached steady state in the simulations the 4100 ppm saturation level is about half of the amount of hydrogen inferred from the lunar prospector neutron data

exospheric transport restrictions on water ice in lunar polar traps there is little doubt that at least 1017 g of water has accreted on the moon as a result of the reduction of ferric iron at the regolith surface by solar wind protons the vaporization of chondrites and perhaps comet impacts lacking an efficient escape mechanism most of this water or its progeny is probably on the moon now if the water were to have migrated to permanently shaded cold traps near the lunar poles ice deposits with densities greater than 1000 g cm 2 would cover the traps providing accessible resources however exospheric transport considerations suggest that the actual amount of water ice in the cold traps is probably too small to be of practical interest the alternative is global assimilation of most of the water into the regolith a process that must account for about 30 micromoles of water per gram of soil

architecture of the volcanic layer from the costa rica rift constraints from core log integration 1 an understanding of the architecture of the ocean crust s volcanic layer is critical since this records the variations in volcanic activity during formation and subsequently controls the movement of hydrothermal fluids through this layer unfortunately core recovery in the majority of ocean drilling program odp deep sea drilling program basement holes is generally low and biased toward more massive lithologies consequently the identification and estimation of lithological diversity within the volcanic layer is only possible through the integration of core and wire line logging results wire line logging provides nearly continuous records of both physical and chemical properties of the borehole wall which can be used to identify the various volcanic sedimentary lithologies which then can be calibrated in regions of enhanced core recovery using this approach the architecture of the volcanics from odp hole 896a has been reconstructed this new model illustrates a hiatus in volcanism marked by a thick breccia horizon which probably marks the transition from axis to off axis volcanism

distinguishing styles of explosive eruptions at erebus redoubt and taupo volcanoes using multivariate analysis of ash morphometrics abstract the style and dynamics of volcanic eruptions control the level and type of hazards posed for local populations and can have a temporary long range impact on climate if eruptions are extremely energetic the purpose of this study is to provide a statistical approach to ash morphometrics in order to provide a means by which to evaluate diverse eruption styles and mechanisms of fragmentation the methodology presented can be applied to tephra deposits worldwide and may aid volcanic hazard mitigation by better defining a volcano s history of explosive behavior ash sized grains were collected from tephra deposits on mount erebus antarctica discriminant analysis of all parameters was found to be the best at differentiating the tephra deposits and allowing for interpretation of eruptive styles in conjunction with field observations a linear array of data forming a positive slope in factor space which explains 99 of the total data variance is interpreted to represent a continuum between fragmentations involving water magma interaction wet to grains that were formed predominately by magmatic dry fragmentation mechanisms the taupo hatepe ash which was deposited from a phreatoplinian eruption column has the highest factor values in the array which signifies in part more rectangular blocky morphologies with smooth grain edges factor values for the 2009 redoubt eruption events 2 4 are nearly as high as hatepe ash and based on this we suggest that it was produced in part by phreatomagmatic fragmentation this is supported by field observations that document melting and eruption through glacial ice during the early phases of the 2009 activity redoubt ash grains from later stages of the same eruption events 9 18 show a significant shift to lower values in factor space more irregular vesiculated grains and are interpreted to be a consequence of dryer conditions coarse ash data from mount erebus are completely separated from taupo and redoubt grains in factor space due primarily to the difference in mean gray value which is a proxy for vesicle density and size the vesicle characteristics larger and deeper are consistent with documented strombolian style activity and the scatter in grain shape data support fragmentation by a mixture of wet and dry processes as has previously been proposed based on deposit characteristics and resemblance to tephra produced by current activity

new occurrences of the white river ash east lobe in subarctic canada and utility for estimating freshwater reservoir effect in lake sediment archives abstract the freshwater reservoir effect fre in the canadian subarctic complicates development of high resolution age depth models based on radiocarbon dates from lake sediments volcanic ashfall layers tephras provide chronostratigraphic markers that can be used to estimate age offsets we describe the first recorded occurrence of a visible tephra in a lacustrine sequence in the central northwest territories the tephra observed in pocket lake near yellowknife is geochemically and stratigraphically attributed to the white river ash east lobe wrae 833 850 ce 1117 1100 cal bp which originated from an eruption of mount churchill alaska we also observed the wrae as a cryptotephra in bridge lake 130 km to the ne suggesting that records of this tephra are potentially widespread in cnt lakes the identification of this tephra presents opportunities for use of the wrae as a dating tool in the region and to quantify the magnitude of the fre in order to correct radiocarbon age depth models two well dated sediment cores from pocket lake containing a visible wrae record indicate a fre of 200 years at the time of the ash deposition which matches closely with the estimated fre of 245 years at the lake sediment water interface although additional results from other lakes in the region are required this finding implies that fre estimates for the late holocene in the region may be based either on down core wrae radiocarbon age model offsets or on radiocarbon dates obtained from the sediment water interface

particle interaction inside debris flows evidence through experimental data and quantitative clast shape analysis abstract results of analytical experiments related to the dynamic behavior of debris flows are presented particle interaction and the amount and type of fines content present in the matrix aspects that govern debris flow behavior are studied via the morphological evolution of constituent particles four different mixtures of water and sediment with compositions resembling debris flows were prepared and put into a rotating drum known as a los angeles standard abrasion machine and studied at different time intervals for each sampling time quantitative shape analysis was performed using three morphological coefficients mc 2 mc 3 8 and mc 30 34 coefficient mc 2 gives information about particle ellipticity mc 3 8 is related to basic irregularities at a macro scale such as roundness mc 30 34 is related to microscale irregularities like surface texture coefficient mc 3 8 was shown to be very sensitive to silt content in the matrix and coefficient mc 30 34 to the presence of clay all three coefficients point to the fact that changes in shape between granulometric classes are gradual and follow a power law coarse granulometric classes acquire more circular and smooth profiles while small particles maintain their irregular profiles this phenomenon is the result of clast interaction processes within mixtures clast collisions between particles produce comminution of the coarsest fractions while finer particles fracture along their entire surface the rate at which these changes occur is related to the type of fine sediment present in the matrix changes in particle shape are an important tool for revealing internal dynamics because they are related to clast interaction and affect sedimentation processes inside these flows this type of experiment although not on a real scale provides important physical information for understanding the phenomena that occur inside debris flows enabling the study of a variety of textural parameters and their changes at regular time intervals the experimental patterns observed offer new insights into clast clast interaction rounding and comminuting theory with important implications for understanding rheological behavior and kinematics of flows and related hazards

image processing analysis in reconstructing fragmentation and transportation mechanisms of pyroclastic deposits the case of monte pilato rocche rosse eruptions lipari aeolian islands italy abstract a quantitative study of particle morphology of samples from monte pilato rocche rosse deposits lipari aeolian islands italy shows a significant variability in particle structure and texture the study consisted of image processing techniques and multivariate statistical methods in analysis of the quantitative particle morphology data with the goal of identifying the genetic processes responsible for the formation of the deposits from these investigations we numerically define the form of the clasts thus avoiding subjectivity in the classification of clast morphology starting from this clast definition we then construct diagrams in which clasts due to different genetic processes i e magmatic vs hydromagmatic fragmentation are discriminated based on simple nondimensional parameters the application of the methods used seems to be of general interest in discriminating the fragmentation and transportation dynamics responsible for the formation of pyroclastic deposits