delimiting oceanographic provinces to determine drivers of mesoscale patterns in benthic megafauna a case study in the barents sea abstract communities of benthic megafauna in the deep waters of continental shelves 100 m are important components of marine ecosystems in high latitude ecosystems this fauna is increasingly impacted by human activities and climate variability in this study we provide baseline knowledge on the oceanographic conditions affecting its distribution in the barents sea in the vicinity of the polar front an oceanic front occurring at the transition zone between the atlantic and arctic water masses we used fields of temperature and currents from an ocean circulation model regional ocean modelling system roms to derive variables divided into 3 groups relevant to bottom fauna temperature water column structure and bottom currents expressing either mean conditions or temporal variability over 10 years 2001 2010 benthic megafauna was surveyed in summer 2011 at 139 sites to analyze the relationship between spatial variability in the composition of benthic megafauna i e diversity and oceanographic conditions we 1 used generalized dissimilarity modelling gdm and 2 delimited oceanographic provinces i e regions of similar conditions for each group of variables using principal component analysis pca followed by cluster analysis turnover in benthic megafauna was explained by 7 oceanographic variables temperature 4 water column structure 2 bottom currents 1 depth and geographic distance 56 7 of total deviance explained concurrently patterns in oceanographic provinces among the 3 groups of variables coincided with results from the gdm where provinces derived from temperature were sharply delimited relative to the other groups we concluded that the spatial structure of the environment is important in the relationship between spatial variability of benthic megafauna and oceanographic conditions in shelf deep waters ocean models are powerful tools to study this relationship but the way in which their inherent uncertainty affects the conclusions of ecological models should be assessed more thoroughly

multiphase petrography of volcanic rocks using element maps a method applied to mount st helens 1980 2005 quantitative textural analyses including crystal size distributions csds provide insights into crystallisation kinetics of magmatic systems investigations of volcanic crystal textures often rely on greyscale variations on backscattered electron images to identify crystal phases which must then be thresholded and or traced manually a laborious task and investigations are typically restricted to a single crystal phase a method is presented that uses energy dispersive x ray element maps to generate textural data each pixel is identified as a crystal phase glass or vesicle according to relative chemical composition enabling concurrent acquisition of multiphase csd crystallinity and mineral mode data data processing is less time intensive for the operator but considerable instrument time is required to generate element maps the method is applied to 17 dacite samples from the 1980 1986 and 3 from the 2004 2005 eruptive periods of mount st helens volcano usa to provide quantitative insights into multiphase textural evolution all of the csds are curved and concave up in the standard csd plot with curvature increasing with plagioclase content to facilitate comparisons with previous studies csds for microlites 50 m length crystals are approximated as straight lines the line intercepts and slopes provide information on n 0 nucleation density and characteristic length or g the product of growth rate g and residence time respectively these parameters as well as the total groundmass crystallinity show distinct differences between explosive deposits from summer 1980 and post summer 1980 domes post summer 1980 microlite n 0 values are mostly at the lower end of the range of those measured for summer 1980 samples total groundmass crystallinities during summer 1980 are between 10 and 30 vol whereas post summer 1980 crystallinity increases to between 39 and 51 vol the range of n 0 values is similar to those previously published for mount st helens but g is consistently higher g of a may 1985 sample analysed in this study is approximately 2 m higher compared with previously published data for the same sample when processed using similar methodologies groundmass crystallinity data show similar trends to those previously published for the 1980 to 1986 eruption increasing sharply after summer 1980 then increasing more gradually during the dome building phase of the eruption the effects of varying l the apparent crystal size and crystal aspect ratio on resultant csds are also investigated whilst relative temporal variations in csds for a given dataset can be investigated absolute values from different studies cannot be compared unless methods of data acquisition and processing are exactly the same

on estimating crystal shape for crystal size distribution analysis abstract the accurate determination of three dimensional crystal habit long intermediate short axis is a requirement to enable correct stereological conversion of 2d crystal size measurements to true 3d crystal size distributions csds in this contribution we introduce a database and spreadsheet program which provides an objective estimate of true crystal habit from raw 2d measurements the database compares the sample s 2d measurements with 2d shape curves for random sections through 703 different habits the output gives the five best match curves and corresponding crystal habits based on a least squares fit between sample and database the minimum sample size required to give good shape estimates from 2d data is tested using random runs of sections through known shapes with different population densities at minimum 75 crystal sections are required to robustly determine crystal habit for csd measurements if crystals are tabular in shape with more acicular shapes requiring a minimum of 250 sections suggesting a sample size of 250 sections to be used for shape determination in natural examples where the true 3d shape is unknown the crystal habit of the best match shape can then be used to provide a more robust csd analysis which in turn can be used to investigate magmatic processes with more certainty

the cooling kinetics of plagioclase feldspar as revealed by electron microprobe mapping in this study we have used electron microprobe mapping to investigate plagioclase compositional evolution due to cooling kinetics we re analyzed five run products from a prior study iezzi et al 2011 crystallized by cooling a natural andesitic melt from 1300 to 800 c at 25 12 5 3 0 5 and 0 125 c min under atmospheric pressure and air redox state as the cooling rate decreases the texture of large plagioclases changes from skeletal to hollow to nearly equant in this study we use x ray map data to obtain a database of 12 275 quantitative chemical analyses the frequency of an rich plagioclases showing disequilibrium compositions substantially increases with increasing cooling rate at 25 and 12 5 c min the distribution is single mode and narrow at 0 5 and 0 125 c min is single mode but very broad whereas at the intermediate cooling rate of 3 c min two distinct plagioclase populations are present this intermediate cooling rate is fast enough to cause departure from equilibrium for the crystallization of the an rich population but also sufficiently slow that an poor plagioclases nucleate from the residual melt we interpret our findings in the context of time temperature transformation ttt diagrams and infer the crystallization kinetics of plagioclase in the experiments compositional trends and our inferences regarding ttt systematics are consistent with two discrete nucleation events that produced separate populations of plagioclase i e an rich and an poor populations at 3 c min using plagioclase melt pairs as input data for the thermometric reaction between an and ab components we find that plagioclase mirrors very high near liquidus crystallization temperatures with increasing cooling rate these results have important implications for the estimate of post eruptive solidification conditions lava flows and intrusive bodies from centimeters to a few meters thick are characterized by a short solidification time and a significant thermal diffusion under such circumstances it is possible to crystallize plagioclases with variable and disequilibrium chemical compositions simply by cooling a homogeneous andesitic melt x ray element maps enrich the study of plagioclase compositional variations generated under conditions of rapid cooling

multiple levels of magma storage during the 1980 summer eruptions of mount st helens wa transitions in eruptive style explosive to effusive sustained to pulsatory are a common aspect of volcanic activity and present a major challenge to volcano monitoring efforts a classic example of such transitions is provided by the activity of mount st helens wa during 1980 where a climactic plinian event on may 18 was followed by subplinian and vulcanian eruptions that became increasing pulsatory with time throughout the summer finally progressing to episodic growth of a lava dome here we use variations in the textures glass compositions and volatile contents of melt inclusions preserved in pyroclasts produced by the summer 1980 eruptions to determine conditions of magma ascent and storage that may have led to observed changes in eruptive activity five different pyroclast types identified in pyroclastic flow and fall deposits produced by eruptions in june 12 july 22 and august 7 1980 provide evidence for multiple levels of magma storage prior to each event highly vesicular clasts have h2o rich 4 5 5 5 wt melt inclusions and lack groundmass microlites or hornblende reaction rims characteristics that require magma storage at p 160 mpa until shortly prior to eruption all other clast types have groundmass microlites ph20 estimated from both h2o bearing melt inclusions and textural constraints provided by decompression experiments suggest pre eruptive storage pressures of 75 40 and 10 mpa the distribution of pyroclast types within and between eruptive deposits can be used to place important constraints on eruption mechanisms fall and flow deposits from june 12 1980 lack highly vesicular microlite free pyroclasts this eruption was also preceded by a shallow intrusion on june 3 as evidenced by a seismic crisis and enhanced so2 emissions our constraints suggest that magma intruded to a depth of 4 km beneath the crater floor fed the june eruption in contrast eruptions of july and august although shorter in duration and smaller in volume erupted deep volatile rich magma if modeled as a simple cylinder these data require a step wise decrease in effective conduit diameter from 40 50 m in may and june to 8 12 m in july and august the abundance of vesicular intermediate to deep clast types in july and august further suggests that this change was effected by narrowing the shallower part of the conduit perhaps in response to solidification of intruded magma remaining in the shallow system after the june eruption eruptions from july to october were distinctly pulsatory transitioning between subplinian and vulcanian in character as originally suggested by scandone and malone 1985 a growing mismatch between the rate of magma ascent and magma disruption explains the increasingly pulsatory nature of the eruptions through time recent fragmentation experiments spieler et al 2004 suggest this mismatch may have been aided by the multiple levels at which magma was stored and degassed prior to these events

on the role of the mesoscale circulation on an idealized coastal upwelling ecosystem 1 an idealized circulation model of coastal upwelling coupled to an ecosystem model has been built to address the impact of features such as eddies and filaments emerging from mesoscale dynamics on a marine ecosystem the model mimics coastal upwelling along an infinite straight coast with north south cyclic boundary conditions thanks to the parametrization of the geostrophic onshore flow in the thermocline the circulation captures the typical characteristics of a coastal upwelling region an equatorward coastal jet a poleward undercurrent along the continental slope and mesoscale eddies and filaments this eddying three dimensional simulation is compared to a two dimensional simulation using the averaged velocity field of the first simulation as velocity field this approach allows us to compare simulations having similar upwelling and nutrient input but differing in the nature of the flow an offshore spreading of the phytoplankton bloom is found in the eddying simulation the width of the productive coastal band is increased from 80 km to 200 km by the mesoscale activity a biogeochemical budget carried out in a 300 km wide coastal band provides evidence that mesoscale activity decreases the total phytoplankton content mainly by exporting a significant part of the surface phytoplankton below the euphotic layer in presence of mesoscale activity the downward and offshore export of phytoplankton zooplankton and detritus significantly contributes to total export of organic matter out of the surface coastal ocean whereas their contribution to export is weak in the two dimensional case

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

wind and buoyancy induced transport of the norwegian coastal current in the barents sea 1 the focus of this study is on the fluxes and forcing of the norwegian coastal current ncc at the entrance to the barents sea the structure and dynamics of the ncc which consists of a slope branch and an offshore branch are investigated using 1 a recent 1 year full depth current meter record in the core of the slope region 2 repeated hydrographic data at an inshore monitoring station 3 broader regional hydrographic surveys and 4 atmospheric reanalysis data the total fluxes are estimated to 1 8 sv for volume and 26 msv for freshwater relative to a reference salinity of 34 8 with the largest contributions from baroclinic offshore branch the heat flux calculated for the slope branch only is 34 tw these estimates are higher compared to earlier estimates but are based on more comprehensive data the major mode of variability in the slope branch is consistent with a continental shelf wave on time scales in the range of 3 16 days forced by the along coast component of the wind stress maximum along slope currents during fall winter corresponding to the stronger wind forcing during these seasons suggest that the observed seasonality in the ncc can be attributed to a similar mechanism

volcanic drumbeat seismicity caused by stick slip motion and magmatic frictional melting during volcanic eruptions solidifying magma ascends through the volcanic conduit often accompanied by repetitive drum beat seismicity laboratory experiments on magma samples from soufriere hills volcano montserrat and mount st helens volcano usa show that viscous melt formed at the surface between the rising magma and conduit walls can temporarily halt magma ascent accentuating the cyclical seismicity

selective melting processes as inferred from experimentally generated pseudotachylytes abstract high speed friction experiments have been conducted on gabbros and granites to better constrain the process of frictional melting during seismogenic fault motion experiments were done on cylindrical specimens of 25 mm in diameter under a normal stress of 1 0 1 5 mpa and at slip rates up to 2 m s using a rotary shear high speed frictional testing machine the experimentally generated pseudotachylytes consist of a fused glassy matrix with abundant vesicles and angular or sub angular to rounded fragments these locally occur as injected network veins in the fractured rock x ray diffraction analysis has revealed the presence of as much as 40 70 wt glass the mineral contents of clasts in the experimental pseudotachylyte in granite as determined by x ray diffraction analysis indicate that quartz is the most resistant to melting biotite the least and feldspar is intermediate thus the sio2 depletion in natural pseudotachylyte glass is likely to be due to the selective melting of constituent materials during frictional melting

groundmass crystallization of mount st helens dacite 1980 1986 a tool for interpreting shallow magmatic processes the 1980 1986 eruption of mount st helens volcano provides an unprecedented opportunity to observe the evolution of a silicic magma system over a short time scale groundmass plagioclase size measurements are coupled with measured changes in matrix glass plagioclase and fe ti oxide chemistry to document increasing groundmass crystallinity and thus to better constrain proposed physical models of the post may 18 1980 magmatic reservoir measurements of plagioclase microlite and microphenocryst sizes demonstrate that relatively rapid growth approximately 10 9 cm s of groundmass plagioclase occurred immediately subsequent to may 18 relatively rapid plagioclase growth continued through the end of 1980 at an average rate of 3x10 11 cm s plagioclase growth rates then decreased to 1x10 11 cm s through 1986 changes in groundmass crystallinity are reflected in changes in both matrix glass and plagioclase microphenocryst rim chemistry although the matrix glass composition appears to have remained approximately constant from 1981 1986 after a rapid compositional change from may 18 until the end of 1980 plagioclase microphenocrysts show increasingly more complex zoning patterns with time microphenocryst core compositions are commonly positively correlated with crystal size both of these observations indicate continuous groundmass plagioclase growth through 1986 magmatic temperatures estimated from fe ti oxide pairs are approximately constant through 1981 at eruption temperatures of 930 c and at log fo2 of 10 8 by 1985 1986 oxide temperatures decreased to 870 c chemical and textural changes can be explained by 1 rapid degassing and crystallization in response to the intrusion of magma into a shallow 4 5 km reservoir toward the end of the may 18 1980 eruption 2 continued crystallization at a much reduced rate through 1986 due to slow cooling of the shallow magma reservoir growth rates and consequent chemical changes appear to decrease at the end of 1980 this is coincident with the change in eruption style from explosive eruptions sometimes followed by dome growth to solely extrusive dome building events and can be explained by the expected viscosity increase of both degassing and increasing crystallinity the model of twostage crystallization of magma in a shallow reservoir is consistent with conclusions from gas studies casadevall et al 1983 gerlach and casadevall 1986 a b patterns of crater deformation chadwkck et al 1988 and post 1980 seismicity endo et al 1990 although it does not explain the experimental data of hill and rutherford 1989 on the growth rate of amphibole reaction rims textural measurements on mount st helens dacite can also be used to evaluate crystallization kinetics in silicic magmas systems for which experimental data is almost non existent plagioclase growth rates are 5 10 times slower than estimated plagioclase growth rates in basaltic systems a result consistent with the higher viscosity of a more silicic melt furthermore patterns of textural change both average crystal size and number density are similar to those observed during the 1984 mauna loa eruption by lipman and banks 1987 suggesting that the only modification to the crystallization behavior of plagioclase required in extrapolation from basaltic systems is a moderate decrease in rates such that the rate of crystallization scales with the melt viscosity

magma ascent rates from amphibole breakdown an experimental study applied to the 1980 1986 mount st helens eruptions recent 1980 1986 mount st helens dacites contain the phenocryst assemblage plagioclase amphibole low ca pyroxene magnetite ilmenite and rare high ca pyroxene which indicates that they all originated from an 8 km deep reservoir at 900 20 c with xh2o 0 67 in fluid according to experimental data iron titanium oxide phenocryst compositions indicate that all post may 18 dacitic magmas erupted at 900 20 c except for the final lava extrusion in october 1986 the magma reservoir may have cooled to 866 c by october 1986 amphiboles in the post may 18 1980 magma contain one or more amphibole populations characterized by reaction rims of different thicknesses the development of the amphibole reaction rims in these rocks is a response to water loss from the coexisting melt during an approximately adiabatic ascent from a deep reservoir constant p and t and isothermal decompression experiments show that during a 900 c constant rate decompression from 8 km to the surface no reaction rim develops on amphibole in 4 days a 10 m rim develops in 10 days and a 35 m rim develops in 20 days these experimental data and histograms of rim widths in 1980 1986 mount st helens dacites show that post may 18 eruptions are composed in large part of magma represented by a population of thin rimmed amphiboles magma which ascended from the deep 8 km reservoir in 6 to 10 days the remainder of each sample consists of magma containing amphiboles with reaction rims ranging from 14 to 60 m magma which apparently spent from 8 to 25 days along the conduit margins before being mixed thoroughly millimeter scale into the erupting magma the mixing in a viscous slowly ascending dacite may be enhanced by its flow through partially crystallized magma emplaced earlier and by the evolution and loss of a large vesicle population the experimental calibration of amphibole reaction rim width versus decompression time yields average ascent velocities for post may 18 dacites of about 15 30 m h for magma represented by the thick rimmed amphiboles and from 35 to 50 m hr for magma represented by the thin rimmed crystals an ascent rate of 66 m h is indicated for the may 18 1980 eruption which contains amphiboles with no reaction rims the volume of endogenous dome growth which preceded extrusion of magma newly derived from the deep source region suggests that the effective conduit volume beneath mount st helens in 1981 1982 was equivalent to a cylinder 8 km long and 8 9 m in radius

mnd microlite number density water exsolution rate meter abstract microlites in effusive or pyroclastic rocks are possible indicators of water exsolution in particular the microlite number density mnd is considered to be a function of the rate of water exsolution from melt in this paper we have constructed a mnd water exsolution rate meter based on the recent results of theory experiments and the natural observation of crystallization kinetics the mnd method accounts for the effects of melt composition and water content on the diffusivity of crytallizing components in melt by using this meter we can estimate the water exsolution rate at the microlite nucleation depth from a mnd value provided the crystal phase plagioclase or clinopyroxene is known we applied the meter to the case of the 1991 1995 dome eruption at unzen and the 1986b subplinian eruption at izu oshima we obtained the water exsolution rates in the range of 6 1 10 6 to 2 8 10 5 wt s approximately at 70 mpa for unzen plagioclase mnd 1014 to 1015 m 3 and 1 1 10 3 to 1 1 10 1 wt s for izu oshima pyroxene mnd 1015 to 1017 m3 under the assumption of equilibrium vesiculation and steady state flow the corresponding decompression rate and ascent velocity are calculated in the range of 240 to 1100 pa s and 0 014 to 0 068 m s for unzen and 1 2 104 to 1 3 106 pa s and 1 3 to 133 m s for izu oshima this contrast in the ascent velocity at the microlite nucleation depth is closely related to the reason why unzen and izu oshima revealed the different eruption styles namely dome growth and explosive eruption respectively

fuzzy clustering for seafloor classification in order to develop quantitative seafloor sediment classification techniques it is important to acknowledge that by nature the boundaries between soft sediments are characterized by transition zones and therefore are indeterminate and gradual a fuzzy clustering method fuzzy c means fcm was used to identify these transition zones within a subset of the data used to generate the australian seascapes classification model the overlapping classes and gradual boundaries resulting from the fuzzy c means algorithm provided estimates of sediment boundaries that are a closer model of reality than sharp boundaries fcm output is given in the form of membership layers for each class hard classes for each grid cell based on the maximum membership value and a confusion index layer quantifying uncertainty in class attribution the confusion index layer provided a spatial representation of transition zones and overlap between seafloor classes and highlighted areas of greatest uncertainty we extended the standard fcm algorithm by applying the new fmle fuzzy clustering algorithm that takes into account spatial relationships in the data in addition we implemented and applied new cluster validity techniques pcaes pbmf and xb to determine the optimal number of clusters in the data which is a novel pattern recognition application for seabed mapping the 5 class fcm classification provided the most reliable result the results of this research were tested and validated on a simulated dataset and then the clustering and validation algorithms were applied to marine sediment data to identify seascapes the new results were compared with previously published seascapes classes identified with hard isodata clustering techniques from geoscience australia s seascapes classification result with the increasing use of physical surrogates to explain marine biodiversity this research plays a crucial role in the development of techniques to identify habitat zones on the seabed

evolution of crystal sizes in the series of dissolution and precipitation events in open magma systems article i nfo we propose a model that describes the evolution of crystal sizes and crystal size distributions csd of igneous phenocrysts in a sequence of dissolution and crystallization events this model is based on the assumption that crystal dissolution is rate limited by diffusion in melt while crystal growth is controlled by the slower kinetic of new nucleation and growth as a result the dissolution rate is inversely proportional to crystal size coming into effect through the curvature of the crystal s surface but the growth rate does not depend on the crystal size closed form analytical solution of equation for csd is obtained we apply results of modeling to quartz and zircon two prime minerals in silicic igneous systems that are widely used in geochemical and isotopic investigations the time series of multiple solution reprecipitation episodes generate concave downward csds and this result fits well with experimental and natural observations on the abundant concave down csd in silicic igneous rocks we suggest that maturation of crystal populations with sizes above several micrometers can not be caused by a size effect on the solubility of the crystals ostwald ripening but is rather driven by thermal oscillations in experiments and in nature the model predicts that mean crystal size increases with time proportionally to t 0 20 which is very close to the published experimental results for quartz maturation with the exponent of 0 19 0 22 our proposed model gives an opportunity to use natural csds for interpretation of pre eruptive magma history when solubilities and diffusion data are available for constituent elements of the dissolving mineral in particular we present time estimates for maturing zircon populations in large volume ignimbrites and estimate that it takes 100 1000 yrs to mature an initially exponential csd to a lognormal csd

crystallization of mount st helens 1980 1986 dacite a quantitative textural approach quantitative measurements of crystal size distributions csds have been used to obtain kinetic information on crystallization of industrial compounds randolph and larson 1971 and more recently on hawaiian basalts cashman and marsh 1988 the technique is based on a population balance resulting in a differential equation relating the population densityn of crystals to crystal sizel i e at steady staten no exp l itg whereno is nucleation density g is the average crystal growth rate is the average growth time and the nucleation ratej nog csd inn vsl plots of plagioclase phenocrysts in 12 samples of mount st helens blast dacite and 14 samples of dacite from the 1980 1986 mount st helens dome are similar and averageg 9 6 1 1 10 3 cm andno 1 2 106 cm 4 reproducibility of the measurements was tested by measuring csds of 12 sections cut from a single sample in three mutually perpendicular directions precision of the size distributions is good in terms of relative but not necessarily absolute values 10 growth and nucleation rates for plagioclase have been calculated from these measurements using time brackets of 30 150 years growth ratesg are 3 10 10 12cm s and nucleation ratesj are 5 21 10 6 cm3 s g andj for fe ti oxides calculated from csd data areg 2 13 10 13 cm sec andj 7 33 10 5 cm3 s respectively the higher nucleation rate and lower growth rate of oxides resulted in a smaller average crystal size than for plagioclase sizes of plagioclase microlites 0 01 mm in the blast dacite groundmass have been measured from backscatter sem photographs nucleation of these microlites was probably triggered by intrusion of material into the cone of mount st helens in spring 1980 this residence time of 52 days gives minimum crystallization estimates ofg 1 3 10 11 cm s andj 9 16 1o3 cm3 s the skeletal form of the microlites provides evidence for nucleation and growth at high values of undercooling t relative to the phenocrysts a comparison of nucleation and growth rates for the two crystal populations phenocrysts vs microlites suggests that while growth rate seems to be only slightly affected by changes in t nucleation rate is a very strong function of undercooling a comparison of plagioclase nucleation and growth rates measured in the mount st helens dacite and in basalt from makaopuhi lava lake in hawaii suggests that plagioclase nucleation rates are not as dependent on composition groundmass textures suggest that plagioclase microphenocrysts crystallized at depth rather than in the conduit in the dome or after extrusion onto the surface most of this crystallization appears to be in the form of crystal growth coarsening of groundmass microphenocrysts at small degrees of undercooling rather than extensive nucleation of new crystals this continuous crystallization in a shallow magmatic reservoir may provide the overpressurization needed to drive the continuing periodic domebuilding extrusions which have been the pattern of activity at mount st helens since december 1980

tof sims and electron microprobe investigations of zoned magmatic orthopyroxenes first results of trace and minor element analysis with implications for diffusion modeling zoned phenocrysts in volcanic rocks potentially provide an archive of magmatic processes as a crystal grows and comes into contact with different melt batches the chemical and textural signature of this journey is recorded within its crystal lattice the timescale of some magmatic processes can be investigated through the relaxation of chemical gradients across crystal growth zones through the application of diffusion modeling techniques one of the current limitations to diffusion modeling is the spatial and analytical resolution of the chemical profile that conventional techniques such as electron probe microanalyzer epma dynamic secondary ion mass spectrometry sims and laser ablation inductively coupled plasma mass spectrometry la icpms can achieve here for the first time we present time of flight tof sims tof sims data for zoning of orthopyroxene crystals from the may 1982 eruption of mount st helens volcano u s a and cross calibrate these data between backscattered electron images and epma tof sims has the advantage of being able to achieve micrometer to nanoscale spatial resolution of major elements as well as analyses of light elements such as li and trace and minor elements na k and ni at concentrations that cannot be achieved by epma provided that convolution overlap effects and polyatomic mass inferences are carefully considered with tof sims analyses we identified zoning of li on a spatial scale ca 5 10 m that would be inaccessible to most other conventional analytical techniques preliminary results indicate that li a fast diffusing element may be introduced to the crystals in the minutes hours or days prior to eruption and may provide insights into pre eruptive magmatic processes thus tof sims has the potential to be a powerful tool for obtaining minor and trace element profiles across compositional interfaces within crystals at high spatial resolution

fault rheology beyond frictional melting during earthquakes comminution and frictional heating both contribute to the dissipation of stored energy with sufficient dissipative heating melting processes can ensue yielding the production of frictional melts or pseudotachylytes it is commonly assumed that the newtonian viscosities of such melts control subsequent fault slip resistance rock melts however are viscoelastic bodies and at high strain rates they exhibit evidence of a glass transition here we present the results of high velocity friction experiments on a well characterized melt that demonstrate how slip in melt bearing faults can be governed by brittle fragmentation phenomena encountered at the glass transition slip analysis using models that incorporate viscoelastic responses indicates that even in the presence of melt slip persists in the solid state until sufficient heat is generated to reduce the viscosity and allow remobilization in the liquid state where a rock is present next to the melt we note that wear of the crystalline wall rock by liquid fragmentation and agglutination also contributes to the brittle component of these experimentally generated pseudotachylytes we conclude that in the case of pseudotachylyte generation during an earthquake slip even beyond the onset of frictional melting is not controlled merely by viscosity but rather by an interplay of viscoelastic forces around the glass transition which involves a response in the brittle solid regime of these rock melts we warn of the inadequacy of simple newtonian viscous analyses and call for the application of more realistic rheological interpretation of pseudotachylyte bearing fault systems in the evaluation and prediction of their slip dynamics

crystallization and textural evolution of a closed system magma chamber insights from a crystal size distribution study of the lilloise layered intrusion east greenland the recognition that postcumulus processes significantly modify primary textures in layered mafic intrusions has thrown into question many early observations on which classical crystallization theories are based petrographic observations combined with quantitative textural analysis of samples from various stratigraphic levels of the lilloise intrusion east greenland demonstrate that postcumulus textural modification of cumulates formed during the solidification of a closed system magma chamber may be detected crystal size distribution csd measurements of lilloise cumulates and the resulting csd profiles are compared to predicted theoretical closed system csd profiles similarities between the measured csd profiles and published predicted csd profiles support lilloise magma evolving in a closed system chamber and indicate that primary crystallization processes can be distinguished using quantitative textural techniques textural coarsening driven by syn magmatic deformation is suggested to be the dominant postcumulus process affecting csd plot morphology csd slope values and profiles plot shapes remain relatively constant for a given liquidus mineral particularly olivine and clinopyroxene so that the number of phases on the liquidus at any one time affects mineral modal abundances as a result csds generally exhibit overall smaller grainsizes and progressively lower nucleation densities at higher levels in the intrusion

combining csd and isotopic microanalysis magma supply and mixing processes at stromboli volcano aeolian islands italy integrating isotopic microanalysis with other analytical techniques creates powerful new methodologies for understanding the evolution of rock samples at the sub grain scale here we present crystal size distribution csd data for a 26 000 year old sample from stromboli volcano and accompanying isotopic microanalysis of the phenocrysts a technique called the icsd plot is introduced which given stated assumptions allows the integration of both sets of data to generate timelines of isotopic evolution through the volcanic system the combined approach is powerful allowing investigation of the magma supply mixing crystallisation and contamination processes prior to eruption of a volcanic sample for stromboli volcano the combined analysis suggests that the change in magma type following a cone collapse took roughly five years to complete similar to the timescale of changes seen in recent decades

experimental constraints on plagioclase crystallization during h2o and h2o co2 saturated magma decompression experiments simulating magma decompression allow the textures of volcanic rocks to be calibrated against known eruptive conditions interpretation of natural samples may be complicated however by both the decompression path and the composition of exsolving volatiles which affect the time evolution of crystal textures here we present the results of decompression experiments at elevated temperature and pressure designed to assess the effects of degassing path on crystallization of mount st helens rhyodacite three families of experiments were employed to simulate varied ph2o t trajectories single step h2o saturated decompression ssd continuous h2o saturated decompression cd continuous h2o co2 saturated decompression quantitative textural data crystal abundance number density and size are used to calculate plagioclase nucleation and growth rates and assess deviations from equilibrium in run products these are the first experiments to quantify feldspar nucleation and growth rates during h2o co2 saturated decompression we find that reducing the initial melt water content through addition of co2 increases nucleation rates relative to the pure water case an effect most pronounced at low dp dt moreover these early formed textural distinctions persist at the lowest pressures examined suggesting that deep h2o co2 fluids could leave a lasting textural fingerprint on erupted magmas crystals formed prior to decompression during the annealing process also modulate sample textures and growth on pre existing crystals contributes significantly to added crystallinity at a wide range of experimental conditions the phase assemblage itself is a dynamic variable that can be used in conjunction with textural data to infer conditions of magma ascent and eruption finally quantitative textural data from experimental samples are compared with those of natural pyroclasts erupted during the summer 1980 explosive effusive transition at mount st helens this comparison supports a model of magma ejected from multiple storage regions present in the upper crust following the may 18 plinian eruption such that subsequent eruptions tapped magmas that experienced varied decompression and degassing histories

linking benthic hydrodynamics and cold water coral occurrences a high resolution model study at three cold water coral provinces in the ne atlantic observations from numerous cold water coral locations in the ne atlantic show energetic near bottom flow dynamics along the european continental margin at individual coral mounds and mound clusters dynamics are largely controlled by tide topography interaction generating and enhancing periodic motions such as trapped waves freely propagating internal tides and internal hydraulic jumps in this study linkages between key abiotic parameters and cold water coral occurrences are explored across entire cold water coral mound provinces using an integrated modelling and observational approach the 3 d ocean circulation model roms agrif was applied to simulate near bottom hydrodynamic conditions at three provinces in the ne atlantic logachev mounds arc mounds and belgica mounds adopting a nested model setup with a central grid resolution of 250 m simulations were carried out with a focus on accurate high resolution topography and tidal forcing the central model bathymetry was taken from high resolution inss irish national seabed survey seafloor mapping data the model was integrated over a full one year reference period starting from the 1st january 2010 interannual variability was not considered tidal forcing was obtained from a global solution of the oregon state university osu inverse tidal model modelled fields of benthic currents were validated against available independent in situ observations coral assemblage patterns presence and absence locations were obtained from benthic surveys of the eu fp7 coralfish programme and supplemented by data from additional field surveys modelled near bottom currents temperature and salinity were analysed for a 1 month subset 15th april to 15th may 2010 corresponding to the main coralfish survey period the model results show intensified near bottom currents in areas where living corals are observed by contrast with coral absence and random background locations instantaneous and time mean current speeds at mound clusters in the logachev province exceeded typical values in non coral areas by up to a factor of three currents at cold water coral locations in the arc and belgica mound provinces were less energetic but still elevated compared to non coral locations an analysis of dynamical processes associated with oscillatory flow interacting with topography suggests that these motions are locally important food supply mechanisms to cold water corals by promoting large amplitude local vertical mixing and organic matter fluxes it is shown that their presence varies considerably between provinces based on the interplay of topographic slope flow magnitude and ambient stratification

quantifying the influence of atlantic heat on barents sea ice variability and retreat abstractthe recent arctic winter sea ice retreat is most pronounced in the barents sea using available observations of the atlantic inflow to the barents sea and results from a regional ice ocean model the authors assess and quantify the role of inflowing heat anomalies on sea ice variability the interannual variability and longer term decrease in sea ice area reflect the variability of the atlantic inflow both in observations and model simulations during the last decade 1998 2008 the reduction in annual july june sea ice area was 218 103 km2 or close to 50 this reduction has occurred concurrent with an increase in observed atlantic heat transport due to both strengthening and warming of the inflow modeled interannual variations in sea ice area between 1948 and 2007 are associated with anomalous heat transport r 0 63 with a 70 103 km2 decrease per 10 tw input of heat based on the simulated ocean heat budget it is found that the heat transport into the western barents sea sets the bou

subvolcanic plumbing systems imaged through crystal size distributions the configuration of subvolcanic magma storage regions exercises a fundamental control on eruptive style and hazard such regions can be imaged remotely using seismic geodetic or magnetotelluric methods although these are far from routine and rarely unambiguous the textures of erupted volcanic rocks as quantified through crystal size distributions csd provide space and time integrated information on subvolcanic plumbing systems although these data cannot be used readily for reconstruction of key parameters such as conduit geometry or magma chamber depth here we develop a numerical approach to interpretation of csd in products of steady eruptions based on crystallization kinetics and hydrodynamic flow simulation to image subvolcanic plumbing systems the method requires knowledge of magma properties crystal growth kinetics measured experimentally and discharge rate measured observationally the method is applicable to steady state eruptive regimes distributions of pressure temperature crystal content and conduit cross section area with depth are obtained from a csd from a sample erupted from mount st helens volcano usa values of average conduit diameter 30 m and magma chamber depth 14 km below the summit are in good agreement with independent estimates

multiple plagioclase crystal populations identified by crystal size distribution and in situ chemical data implications for timescales of magma chamber processes associated with the 1915 eruption of lassen peak ca products of the 1915 lassen peak eruption reveal evidence for a magma recharge magma mixing event that may have catalyzed the eruption and from which four compositional members were identified light dacite black dacite andesitic inclusion and dark andesite crystal size distribution textural and in situ chemical major and trace element and sr isotope data for plagioclase from these compositional products define three crystal populations that have distinct origins phenocrysts long axis40 5 mm that typically have core an contents between 34 and 36 mol microphenocrysts long axis between 0 1 and 0 5 mm that have core an contents of 66 69 and microlites long axis50 1mm with variable an core contents from 64 to 52 phenocrysts are interpreted to form in an isolated dacitic magma chamber that experienced slow cooling based on textural compositional and isotopic data for the magma represented by the dacitic component magma recharge was not an important process until just prior to the 1915 eruption average residence times for phenocrysts are in the range of centuries to millennia microphenocrysts formed in a hybrid layer that resulted from mixing between endmember reservoir dacite and recharge magma of basaltic andesite composition high thermal contrast between the two end member magmas led to relatively high degrees of undercooling which resulted in faster crystal growth rates and acicular and swallowtail crystal habits some plagioclase phenocrysts from the dacitic chamber were incorporated into the hybrid layer and underwent dissolution precipitation seen in both crystal textures and rim compositions average microphenocryst residence times are of the order of months microlites may have formed in response to decompression and or syn eruptive degassing as magma ascended from the chamber through the volcanic conduit chemical distinctions in plagioclase microlite an contents reveal that melt of the dark andesite was more mafic than the melt of the other three compositions we suggest that mixing of an intruding basaltic andesite and reservoir dacite before magma began ascending in the conduit allowed formation of a compositionally distinct microlite population melt in the other three products was more evolved because it had undergone differentiation during the months following initial mixing as a consequence melt and microlites among these three products have similar compositions the results of this study highlight the integrated use of crystal size distribution textural and in situ chemical data in identifying distinct crystal populations and linking these populations to the thermal and chemical characteristics of complex magma bodies

verification of ideal semi logarithmic lognormal or fractal crystal size distributions from 2d datasets crystal size distributions can follow any function provided the total crystal content is less than 100 however many theories suggest that they approximate a number of ideal distribution models the most widely adopted model for igneous rocks produces a straight line on a classic csd diagram of ln population density versus size lognormal by size distributions have been proposed for igneous and metamorphic rocks and materials that crystallise at low temperatures lognormal models are difficult to prove with simple linear frequency histograms or on a classic csd diagram instead it is better to use a normalized cumulative distribution function diagram which gives a straight line for lognormal distributions similarly fractal size distributions can best be verified simply by using a bi logarithmic diagram statistical measures can be used to invalidate a null hypothesis but with much caution for real data especially those derived from two dimensional measurements and with a limited range in sizes these methods are applied to csds of plagioclase in three igneous rock samples to illustrate the pitfalls of model fitting a simple nomenclature is proposed for ideal csd shapes

the arctic front in the greenland sea during february 1989 hydrographic and biological observations high resolution hydrographic and biological observations in the arctic frontal regime were made in february 1989 along 74 45 n the frontal zone was found to contain four individual frontal interfaces these fronts were a result of the large scale convergence of the currents around the greenland sea gyre bringing together arctic and polar surface waters and two modes of atlantic surface water the distribution of arctic and atlantic copepod species as well as the composition of their developmental stages showed a strong correlation with the distribution of water masses whereby the frontal interfaces acted as biogeographic boundaries whereas the fronts bounding the polar water reached only to a depth of about 100 m the fronts bordering the atlantic water masses could be observed to depths of 600 m at subsurface levels a core of atlantic intermediate water from the jan mayen current was observed the properties of this water type can be explained quantitatively from double diffusive exchange with the overlying water the mixing across the fronts was found to be dominated by fluxes of heat salt and copepods toward the central greenland sea gyre

rapid remobilization of magmatic crystals kept in cold storage we lack thermal histories for magma reservoirs but here the magma under mount hood oregon usa is shown to have been too cold to mobilize for most of the time it has been stored which implies that magma mobilizes at which point it can be imaged geophysically very quickly prior to eruption this paper presents a novel approach to constraining the thermal history of the subsurface magma bodies that feed eruptions by combining temporal information from a variety of sources kari cooper and adam kent combine timescales derived from uranium series disequilibria textural information and trace element zoning in crystals they show that at mount hood oregon only a small fraction of the total storage duration has been spent at temperatures above the critical crystallinity the point at which magma is easily mobilized they conclude that largely liquid bodies that could be imaged geophysically will be ephemeral features and therefore their detection could indicate imminent eruption the processes involved in the formation and storage of magma within the earth s upper crust are of fundamental importance to volcanology many volcanic eruptions including some of the largest result from the eruption of components stored for tens to hundreds of thousands of years before eruption1 2 3 although the physical conditions of magma storage and remobilization are of paramount importance for understanding volcanic processes they remain relatively poorly known4 5 eruptions of crystal rich magma are often suggested to require the mobilization of magma stored at near solidus conditions6 7 8 however accumulation of significant eruptible magma volumes has also been argued to require extended storage of magma at higher temperatures7 8 9 what has been lacking in this debate is clear observational evidence linking the thermal and therefore physical conditions within a magma reservoir to timescales of storage that is thermal histories here we present a method of constraining such thermal histories by combining timescales derived from uranium series disequilibria crystal sizes and trace element zoning in crystals at mount hood oregon usa only a small fraction of the total magma storage duration at most 12 per cent and probably much less than 1 per cent has been spent at temperatures above the critical crystallinity 40 50 per cent at which magma is easily mobilized partial data sets for other volcanoes also suggest that similar conditions of magma storage are widespread and therefore that rapid mobilization of magmas stored at near solidus temperatures is common magma storage at low temperatures indicates that although thermobarometry calculations based on mineral compositions may record the conditions of crystallization they are unlikely to reflect the conditions of most of the time that the magma is stored our results also suggest that largely liquid magma bodies that can be imaged geophysically will be ephemeral features and therefore their detection could indicate imminent eruption

effects of magma storage and ascent on the kinetics of crystal growth the size distributions of crystals of olivine plagioclase and oxides of the 1991 93 eruption at mt etna italy are analyzed the simultaneous collection of this information for different minerals gives precious insight into the cooling history of lavas three distinct episodes are detectable a storage of the magma in a deep reservoir characterized by nearly constant and low nucleation and growth rates near to equilibrium an ascent phase with an ever increasing nucleation rate related to volatile exsolution and finally a quenching phase in addition to geochemical and geophysical evidence the similarity of the crystal size distributions of the present eruption with those of previous ones of this century makes it possible to exclude that crystal size distributions of etnean lavas are due to mixing of different populations this strongly suggests that the main features of the volcano feeding system have not changed despite observed variations in the magma output rates

rheological controls on the eruption potential and style of an andesite volcano a case study from mt ruapehu new zealand abstract the evolving magma rheology of three recent ruapehu eruptions 1969 1977 and 1995 is estimated using a combination of thermodynamic models and rheological calculations supported by textural observations of the erupted scoria we use a well established thermodynamic model to determine the composition of these representative ruapehu magmas from 300mpa to 30mpa the outputs of the model provide the changing crystal and bubble content in a closed system assuming no gas loss as well as the fractionating melt compositions we calculate the melt viscosity and the effect of bubbles and crystals to quantify the rheology of the magma during ascent under assumed equilibrium conditions the moderately high phenocryst content of ruapehu scoria 30 means that only a small amount of additional microlite crystallisation 5 would result in a yield strength which may lead the magma to stall however if the strain rates are high enough more crystallisation would be possible without developing a yield stress this suggests that microlite rich magmas are almost certain to stall unless they encounter significant fluid addition from a source such as a hydrothermal system groundwater or surface water i e ruapehu s crater lake ruapehu magmas are initially h 2 o undersaturated and as a consequence crystallisation and bubble growth were suppressed until the magma achieved saturation at 100 to 50 mpa from this analysis we suggest that ruapehu magmas are more likely to erupt compared to magmas of a similar composition that are h 2 o saturated this partly explains the regular albeit small volume eruptions at ruapehu and the propensity for phreatomagmatic eruptions when the magma water ratio is low

an origin for harrisitic and granular olivine in the rum layered suite nw scotland a crystal size distribution study dendritic crystal morphologies occur in a number of igneous rocks and are thought to originate from the rapid growth of crystals yet many examples of dendritic morphologies are found in plutonic igneous rocks where cooling rates should be low results from crystal size distribution csd measurements on harrisitic olivines from rum scotland combined with estimated olivine growth rates suggest that the characteristic skeletal hopper and branching olivines of harrisitic cumulates that are up to centimetres long may have exceptionally short crystal growth times several hours to several hundreds of days this together with very low calculated nucleation densities for harrisitic olivine supports the interpretation of harrisite being a disequilibrium texture developed in response to supersaturation of the magma in olivine we propose that this supersaturation arose through undercooling of thin picrite sheets emplaced along the rum magma chamber floor beneath cooler resident magma it is envisaged that the picrite sheets were largely free of suspended olivine crystals coupled with the olivine enriched composition of the melt and the increasing cooling rate this allowed homogeneous nucleation of olivine to set in at deeper undercooling and greater olivine supersaturation than if there had been plentiful suspended olivines to act as heterogeneous nuclei the enhanced supersaturation caused rapid growth of olivine once nucleation began with skeletal and dendritic shapes it is suggested that the observed interlayered sequences of harrisite and cumulus peridotite found throughout the rum layered suite are a result of multiple episodes of harrisite crystallization resulting from picrite emplacement that alternated with periods of crystal growth and accumulation in the main body of magma at lesser degrees of undercooling

crystal size distribution csd in rocks and the kinetics and dynamics of crystallization ii makaopuhi lava lake crystal size distribution csd theory has been applied to drill core samples from makaopuhi lava lake kilauea volcano hawaii plagioclase and fe ti oxide size distribution spectra were measured and population densities n were calculated and analyzed using a steady state crystal population balance equation n n0 exp l g slopes on ln n versus crystal size l plots determine the parameter g a product of average crystal growth rate g and average crystal growth time the intercept is j g where j is nucleation rate known temperature depth distributions for the lava lake provide an estimate of effective growth time allowing nucleation and growth rates to be determined that are independent of any kinetic model plagioclase growth rates decrease with increasing crystallinity 9 9 5 4 10 11 cm s as do plagioclase nucleation rates 33 9 1 6 10 3 cm3 s ilmenite growth and nucleation rates also decrease with increasing crystallinity 4 9 3 4 10 10 cm s and 15 2 2 10 3 cm3 s respectively magnetite growth and nucleation rates are also estimated from the one sample collected below the magnetite liquidus g 2 9 10 10 cm s j 7 6 10 2 cm3 s moments of the population density function were used to examine the change in crystallization rates with time preliminary results suggest that total crystal volume increases approximately linearly with time after 50 crystallization a more complete set of samples is needed for material with 50 crystals to define the entire crystallization history comparisons of calculated crystallization rates with experimental data suggests that crystallization in the lava lake occurred at very small values of undercooling this interpretation is consistent with proposed thermal models of magmatic cooling where heat loss is balanced by latent heat production to maintain equilibrium cooling

viscosity measurements of subliquidus magmas alkali olivine basalt from the higashi matsuura district southwest japan abstract we carried out viscosity measurements and sampling of a crystal suspension derived from alkali olivine basalt from the matsuura district sw japan at subliquidus temperatures from 1230 c to 1140 c under 1 atm with nno oxygen buffered conditions viscosity increased from 31 to 1235 pa s with a decrease in temperature from 1230 to 1140 c on cooling olivine first appeared at 1210 c followed by plagioclase at 1170 c the crystal content of the sample attained 31 vol at 1140 c plagioclase 22 olivine 9 non newtonian behaviors including thixotropy and shear thinning were pronounced in the presence of tabular plagioclase crystals the cause of such behavior is discussed in relation to shear induced changes in melt crystal textures relative viscosities r s m where s and m are the viscosities of the suspension and the melt respectively were obtained by calculating melt viscosities from the melt composition and temperature at 1 atm using the equation proposed by giordano and dingwell giordano d dingwell d b 2003 non arrhenian multicomponent melt viscosity a model earth and planetary science letters 208 337 349 the obtained relative viscosities are generally consistent with the einstein roscoe relation which represents r for suspensions that contain equant and equigranular crystals even though the crystal suspension analyzed in the present experiments contained tabular plagioclase and granular olivine of various grain sizes this consistency is attributed to the fact that the effect of crystal shape was counterbalanced by the effect of the dispersion of crystal size the applicability of the einstein roscoe equation with respect to crystal shape is discussed on the basis of the present experimental results our experiments and those of sato sato h 2005 viscosity measurement of subliquidus magmas 1707 basalt of fuji volcano journal of mineralogical and petrological sciences 100 133 142 show that the relationship between relative viscosity and crystal fraction is consistent with the einstein roscoe relationship for axial ratios that are smaller than the critical value of 4 6 5 but discrepancies occur for higher ratios

objective automated classification technique for marine landscape mapping in submarine canyons abstract this study proposes a fully automated and objective technique to map marine landscapes in submarine canyons the method is suitable for broad and regional scale mapping derived from sonar data using multivariate statistical analysis the method is divided into two main parts the terrain analysis and the multivariate statistical analysis the first part aims to optimise the sonar data and comprises three steps 1 data resampling 2 determination of length scale and 3 multiple scale analysis the second part covers the actual marine landscape classification and consists of 1 principal component analysis pca 2 k means clustering and 3 cluster determination in addition a confidence map is presented based on cluster membership derived from cluster distance in attribute space the technique was applied in the lisbon setubal and cascais canyons offshore portugal the area was classified into 6 marine landscapes that represent the geomorphological features present in submarine canyons the main findings from the study are 1 the transferability of a tool from geomorphometric analysis estimation of scale parameter esp to detect the length scale of potential patterns in bathymetric grids 2 multiple scale terrain analysis allows an appropriate discrimination of local and broad scale geomorphic features in marine landscape mapping 3 the method not only delineates geomorphic seafloor features but also points out properties that might influence biodiversity in a complex terrain

the role of oxides in the shallow vesiculation of ascending magmas abstract despite their generally low volume fraction fe ti oxides have the potential to greatly influence the eruptive style because they lower the supersaturation pressure for heterogeneous bubble nucleation once nucleated bubbles respond fast to pressure changes fostering rapid expansion and explosive behavior yet oxide microlite quantifications are often absent from data of explosive products we used new re analyzed and published data to build a compilation of oxide number densities onds and vesicle number densities vnds of trachytic and calc alkaline products four eruptive styles were selected 1 vulcanian explosions from soufriere hills volcano montserrat lascar volcano chile and kilian volcano france 2 blasts from mt pelee volcano lesser antilles mount st helens usa and merapi volcano indonesia 3 a sub plinian explosion from merapi volcano and 4 lava dome effusions with intermittent collapse from soufriere hills and mt pelee volcanoes natural samples were separated into two groups according to the dominant texture of the products of each event 1 vesicular pumice clasts from explosions with a strong vertical component and 2 dense clasts with diktytaxitic textures from dome collapse event and lateral blast group 1 samples are either distributed alongside the 1 1 trend between vnd and ond that spans from 1015 to 1017 m 3 or have a constant vnd of 1016 16 5 m 3 regardless of ond a large proportion of oxides 55 100 touch vesicles a more variable proportion of vesicles 16 72 are in contact with oxides because of syn explosive growth and coalescence group 2 samples have onds in the same broad range as group 1 samples we also used new and published data to build a compilation of onds and vnds of five series of experimental decompression of rhyolitic and phonolitic melts in samples with ond vnd most bubbles are in contact with more than one oxide and 64 88 of the oxides are in contact with bubbles such high levels of connectivity suggest that the role of oxides in controlling bubble nucleation has been underestimated when vnd ond nucleation densities of experimental vesicles can be reproduced by heterogeneous nucleation models which we used to calculate syn explosive decompression rates from vnds at merapi soufriere hills and kilian these rates and textural evidence suggest that the decompression front accompanying these vulcanian and sub plinian explosions is responsible for syn explosive bubble nucleation we calculated the average pre explosive ascent rates necessary to yield the observed onds at soufriere hills and merapi volcanoes the resulting rates 0 005 20 m s overlap considerably with the range of critical ascent rate inferred for the effusive explosive transition supporting the hypothesis that this transition is primarily controlled by oxide microlites in the conduit because oxides are a primer for explosive behavior when present in sufficiently high number densities focusing on the older eruption of kilian for which no observation is available we infer that pre explosive ascent rates of 7 10 3 m s were necessary for explosive behavior to occur

textural studies of vesicles in volcanic rocks an integrated methodology abstract vesicles in volcanic rocks are frozen records of degassing processes in magmas for this reason their sizes spatial arrangements numbers and shapes can be linked to physical processes that drive magma ascent and eruption although numerous techniques have been derived to describe vesicle textures there is no standard approach for collecting analyzing and interpreting vesicular samples here we describe a methodology for techniques that encompass the entire data acquisition process from sample collection to quantitative analysis of vesicle size and number carefully chosen samples from the lower mean and higher density vesicularity endmembers are characterized using image nesting strategies we show that the texture of even microvesicular samples can be fully described using less than 20 images acquired at several magnifications to cover efficiently the range of existing vesicle sizes a new program foams was designed to perform the quantification stage from vesicle measurement to distribution plots altogether this approach allows substantial reduction of image acquisition and processing time while preserving enough user control to ensure the validity of obtained results we present three cameo investigations on basaltic lava flows scoria deposits and pumice layers to show that this methodology can be used to quantify a wide range of vesicle textures which preserve information on a wide range of eruptive conditions

quantifying the building blocks of igneous rocks are clustered crystal frameworks the foundation most phenocryst populations in volcanic rocks and those preserved in shallow level igneous intrusions are clustered variously referred to as clots clumps or glomerocrysts these clusters of crystals are the building blocks that accumulate to form the high porosity touching crystal frameworks from which igneous cumulates form examination of touching crystal frameworks in olivine komatiite cumulates and experimental charges and plagioclase dominant crystal populations holyoke flood basalt connecticut usa reveal complex high porosity clustered crystal arrangements olivine touching frameworks in komatiite flows are interpreted to form in hundreds of days plagioclase frameworks are calculated to have formed in less than 17 years for a crystal growth rate of 1 x 10 10 mm s to less than 3 years for a growth rate of 5 x 10 10 mm s based on crystal size distributions the origin of crystal clusters is likely to involve either or a combination of heterogeneous nucleation remobilization of cumulate mushes or crystals sticking together during settling and or flow the spatial distribution pattern of clustered crystal frameworks from both natural and experimental examples constrains fields on spatial packing diagrams that allow the identification of touching and non touching crystal populations and further improve our understanding of crystal packing arrangements and cluster size distributions

ascent driven crystallisation of dacite magmas at mount st helens 1980 1986 we introduce a novel scheme that enables natural silicic glasses to be projected into the synthetic system qz ab or h2o in order to relate variations in volcanic glass chemistry to changing pressure p and temperature t conditions in the sub volcanic magma system by this means an important distinction can be made between ascent driven and cooling driven crystallisation under water saturated or undersaturated conditions in samples containing feldspar and a silica phase quartz or tridymite quantitative p t estimates of the conditions of last equilibrium between crystals and melt can be made formation of highly silicic melts i e 77 wt sio2 is a simple consequence of the contraction of the silica phase volume with decreasing pressure such that high silica glasses can only form by crystallisation at low pressure resorption of quartz crystals appears to be a further diagnostic feature of decompression crystallisation groundmass and inclusion glasses in dacites from the 1980 1986 eruption of mount st helens volcano wa span a wide range in sio2 68 80 wt anhydrous the compositions of the least evolved sio2 poor inclusions in amphibole phenocrysts record entrapment of silicic liquids with 5 4 wt water corresponding to a water saturation pressure of 200 mpa at 900 c the compositions of more evolved higher sio2 plagioclase hosted inclusions and groundmass glasses are consistent with extensive ascent driven fractional crystallisation of plagioclase oxide and orthopyroxene phenocrysts and microlites to low pressures during this polybaric crystallisation plagioclase phenocrysts trapped melts with a wide range of dissolved water contents 3 5 5 7 wt magmas erupted during the plinian phase of the 18 may 1980 eruption were derived from a large reservoir at depths of 6 km subsequent magmas ascended to varying depths within the sub volcanic system prior to extraction from glass chemistry and groundmass texture two arrest levels have been identified at depths of 0 5 1 and 2 4 km a single dome sample from february 1983 contains groundmass plagioclase tridymite and quartz testifying to temperatures of at least 885 c at 11 mpa these shallow storage conditions are comparable to those in the cryptodome formed during spring 1980 the corresponding thermal gradient 0 2 c mpa 1 is consistent with near adiabatic magma ascent from 8 km we argue that the crystallisation history of mount st helens dacite magma was largely a consequence of decompression crystallisation of hot magma beyond the point of water saturation this challenges the conventional view that phenocryst crystallisation occurred by cooling in a large magma chamber prior to the 1980 1986 eruption because the crystallisation process is both polybaric and fractional it cannot be simulated directly using isobaric equilibrium crystallisation experiments however calculation of the phase proportions in water saturated 910 15 c experiments by rutherford et al 1985 over the pressure range 220 125 mpa reproduces the crystallisation sequence and phenocryst modes of mount st helens dacites from 18 may 1980 by allowing for the effects of fractional versus equilibrium crystallisation entrained residual source material and small temperature differences between nature and experiment phase compositions can also be matched to the natural samples we conclude that decompression of water saturated magma may be the dominant driving force for crystallisation at many other silicic volcanic centres

crystal size distribution of plagioclase and amphibole from soufriere hills volcano montserrat evidence for dynamic crystallization textural coarsening cycles the crystal size distributions csds of plagioclase and amphibole were determined from andesites of the soufriere hills volcano montserrat plagioclase occurs as separate crystals and as chadocrysts in large amphibole oikocrysts the chadocrysts represent an earlier stage of textural development preserved by growth of the oikocryst seventeen rock and eight chadocryst plagioclase csds are considered together as a series of samples of textural development all are curved concave up and coincident differing only in their maximum crystal size three amphibole csds have a similar shape and behaviour but at a different position from the plagioclase csds a dynamic model is proposed for the origin of textures in these rocks crystallization of plagioclase started following emplacement of andesite magma at a depth of at least 5km a steep straight csd developed by nucleation and growth this process was interrupted by the injection of mafic magma into the chamber or convective overturn of hotter magma the magma temperature rose until it was buffered initially by plagioclase solution and later by crystallization during this period textural coarsening ostwald ripening of plagioclase and amphibole occurred small crystals dissolved simultaneously with the growth of large crystals the csd became less steep and extended to larger crystal sizes early stages of this process are preserved in coarsened amphibole oikocrysts repetitions of this cycle generated the observed family of csds textural coarsening followed the communicating neighbours model hence each crystal has its own unique growth solution history without appealing to mixing of magmas that crystallized in different environments

viscosity determinations of some frictionally generated silicate melts implications for fault zone rheology at high strain rates analytical scanning electron microscopy has been used to determine the major element compositions of some natural and artificial silicate glasses and their microcrystalline equivalents derived by the frictional melting of intermediate to acid protoliths the data show that the matrices of the friction melts which cool to form pseudotachylytes are relatively basic and hydrous even when their protoliths are intermediate to acid this is because frictional fusion involves the selective comminution and nonequilibrium melting of minerals based on their individual mechanical properties and melting points not the formation of minimum melts through equilibrium mineral interaction this means that hydrous ferromagnesian minerals e g micas and amphiboles melt preferentially to form the liquid matrix while feldspars and especially quartz more readily survive as clasts pseudotachylytes generated by frictional melting are therefore not bulk melts and as clast melt suspensions they cannot be considered as simple newtonian fluids the calculated viscosities of the friction melts are low for example at 1200 c most friction melts possess zero shear suspension viscosities of 102 104 dpa s 1 dpa s 1 p this is equivalent to the viscosities of tholeiitic and alkaline basaltic magmas at the same temperature these viscosities are maximum determinations because as clast melt suspensions friction melts may undergo shear thinning and exhibit pseudoplasticity at high shear rates i e during slip on a fault surface contrary to earlier suggestions where the bulk melting of intermediate to acid protoliths was believed to result in the generation of viscous friction melts that could act to inhibit continued sliding this work shows that most pseudotachylytes are partial melts possessing low viscosities the formation of highly fluid suspensions during slip may have profound effects on the dissipation of stored strain energy in the rocks surrounding a fault interface lubrication could facilitate an increase in the slip rate and the rate of energy dissipation this would be manifest as an increase in high frequency seismic wave radiation and vibrational

crystallization kinetics in continuous decompression experiments implications for interpreting natural magma ascent processes decompression experiments were performed to study the kinetics of plagioclase crystallization during ascent of hydrous rhyodacite magma these experiments differ from previous studies in that they employ a continuous rather than stepwise pressure time trajectory four series of experiments were performed at rates of 0 5 10mpa h corresponding to ascent rates of 0 007 0 14 m s experiments quenched along each decompression path allow snapshot style monitoring of progressive crystallization as expected rates of plagioclase nucleation and growth depend strongly on decompression rate regardless of decompression rate approximately equal volumes of feldspar crystallize during a given decompression interval even when the observed crystallinity is lower than the equilibrium crystallinity apparently a constant degree of solidification is maintained by a crystallization mechanism striking a shifting balance between nuclei formation and growth of existing crystals other key results pertain to the efficacy with which experimental results allow interpretation of the decompression histories of natural rocks feldspar microlites do not maintain chemical equilibrium with melt they are more anorthite rich than equilibrium plagioclase suggesting that interpretations of magma ascent processes in nature require comparisons with dynamic rather than static phase equilibrium experiments although decompression rate is an important element controlling final textures in volcanic rocks no single compositional or textural parameter uniquely records this rate of the criteria examined microlite number density and morphology are the best indicators of magma decompression rate based on a small number of comparisons between continuous and multi step decompression style at the same time integrated decompression rate 1mpa h decompression path evidently influences crystal texture with stepwise decompression yielding textures correlative with faster decompression than indicated by the time integrated decompression rate thus consideration of magma ascent style in addition to rate will undoubtedly strengthen the interpretive power of experimental studies for constraining natural magma ascent processes

textural constraints on the kinetics of crystallization of igneous rocks natural systems provide time controlled experiments on scales unreachable in the laboratory and with complexities unapproachable by computer experiments since temperature undercooling cannot be directly scaled with time in situ crystallization experiments provide information unavailable by other means the kinetics of crystallization in simple silicate systems have been studied extensively for glass ceramic systems e g uhlmann 1982 james 1982 but predictive models for nucleation behavior in particular remain inadequate part of the problem in creating models of nucleation lies in the difficulty of experimentally isolating the nucleation process crystal growth measurements are more accessible experimentally and for this reason crystal growth is better understood e g dowty 1980 kirkpatrick 1981 james 1982 baronnet 1984 however predictive models of crystal growth e g lasaga 1982 require accurate models for the temperature and compositional dependence of both the thermodynamic and kinetic driving forces for crystallization information that is currently limited the cse parameterization of the position of ymax as a function of t tl and t suggested by dearnley 1983 provides a potentially useful model that requires further testing similarly application of the adiabatic nucleation model of meyer 1986 to simple systems suggests that the position of tmax relative to tl has an approximately constant value of 0 55 0 60 exceptions are low dsf minerals such as albite and quartz additionally while experimental crystallization rate data is a necessary link between processes in natural melts and numerical models experimental growth rate data is confined to simple systems and conditions of moderately large undercooling while growth rate estimates in complex natural systems suggest that under most conditions undercoolings remain very small quantitative textural studies of dikes suggest a pronounced dependence of growth rate on total crystallization time e g ikeda 1977 which is in turn related to effective undercooling a function of both total dike width and distance from the dike margin by analogy minimum crystallization rates may be estimated from programmed cooling experiments if a temperature interval of crystallization is assumed growth rates determined in this way show the same relationship between growth rate and total crystallization time seen in the dike studies reflecting a systematic relationship between growth rate and cooling rate effective undercooling for plagioclase in basaltic systems while the data are not available for other mineral systems there is no reason to believe that similar patterns would not exist for other silicate minerals i e the similarity in dendritic olivine growth rates estimated by fowler et al 1989 using fractal analysis to the growth rates of plagioclase under conditions of rapid cooling estimated from programmed cooling rate experiments analysis of measured crystal size frequencies provides a means of extracting effective bulk kinetic information from geologic systems that can help to constrain the dynamic feedback between physical models of magmatic systems and rates of chemical change