introduction to the special issue the formation and evolution of ceres occator crater abstract ceres the largest body in the asteroid belt was explored from orbit for the first time by the dawn mission the 92 km diameter occator crater contains bright regions or faculae which are one of the most remarkable discoveries of dawn s exploration of ceres a pit within the center of the crater contains both the cerealia facula and a central dome the vinalia faculae are located in the eastern crater floor occator s faculae are composed mostly of sodium carbonate and their single scattering albedo is the highest of any material on ceres surface the faculae do not occur in other impact craters on ceres and occator s extensive interior lobate materials are unusual understanding the driving forces behind the formation of occator crater and its faculae has the potential to lead us to a new understanding of the processes and conditions in ceres past and to possibly provide constraints about the present day internal state in this special issue we present a variety of investigations which use dawn data theoretical modeling and laboratory experiments to investigate occator crater and its faculae the results of these investigations are summarized and synthesized in the final paper of this collection herein we introduce ceres and the dawn mission and summarize the geophysical geological mineralogical and geochemical properties of ceres as derived from dawn data we also discuss the regional setting of occator crater and introduce occator crater itself

mineralogical analysis of the ac h 6 haulani quadrangle of the dwarf planet ceres abstract ac h 6 haulani is one of five quadrangles that cover the equatorial region of the dwarf planet ceres this quadrangle is notable for the broad spectrally distinct ejecta that originate from the crater haulani which gives the name to the quadrangle these ejecta exhibit one of the most negative bluest visible to near infrared spectral slope observed across the entire body and have distinct color properties as seen in multispectral composite images besides haulani here we investigate a broader area that includes other surface features of interest with an emphasis on mineralogy as inferred from data obtained by dawn s visible infrared mapping spectrometer vir combined with multispectral image products from the dawn framing camera fc so as to enable a clear correlation with specific geologic features our analysis shows that crater haulani stands out compared to other surface features of the quadrangle albedo maps obtained in the near infrared range at 1 2 m and 1 9 m reveal that the floor and ejecta of haulani are indeed a patchwork of bright and dark material units visible to near infrared spectral slopes display negative values in crater haulani s floor and ejecta highlighting bluish younger terrains diagnostic spectral features centered at 2 7 m and 3 1 m respectively indicate a substantial decrease in the abundances of magnesium bearing phyllosilicates and ammoniated phyllosilicates in crater haulani s floor and bright ejecta similar but less prominent spectral behavior is observed in other geologic features of this quadrangle while the general trend in quadrangle ac h 6 for these two mineral species is to increase from the northwest to the southeast however it is worth noting that the correlation between the 2 7 m and 3 1 m spectral parameters is generally strong in the haulani crater s area but much weaker elsewhere which indicates a variable degree of mixing between these two major mineral phases in moving away from the crater finally the region of crater haulani displays a distinct thermal signature and a local enhancement in calcium and possibly sodium carbonate minerals which is hardly found in the rest of the quadrangle and is likely the result of intense hydrothermal processes following the impact event these evidences all together confirm the young age of crater haulani as they have not been erased or made elusive by space weathering processes

very shallow earthquakes and brittle deformation in active volcanic areas the eatnean region as an example abstract some aspects of the stress field acting in active volcanic areas were investigated by studying the relationship between surficial seismicity h 1 2 km and the brittle deformation pattern of the etna volcano the magmatic composition and structural character of mt etna are described together with its geodynamic regional context after a discussion of the problem of the state of stress in active volcanoes and a definition of very shallow seismicity the high level of surficial seismicity the morphology of the sedimentary basement and the kinematic behaviour of the faults suggest that the eastern flank of mt etna is a shallow seismotectonic domain structurally decoupled from the rest of the volcanic body this flank shows a tendency to slide in an eastern direction and is bound to the north by a left lateral oblique slip normal fault trending e w and in the south by an arcuate fault system with right lateral features right lateral oblique slip normal faults

dynamics and energetics of bubble growth in magmas analytical formulation and numerical modeling we have developed a model of diffusive and decompressive growth of a bubble in a finite region of melt which accounts for the energetics of volatile degassing and melt deformation as well as the interactions between magmatic system parameters such as viscosity volatile concentration and diffusivity on the basis of our formulation we constructed a numerical model of bubble growth in volcanic systems we conducted a parametric study in which a saturated magma is instantaneously decompressed to one bar and the sensitivity of the system to variations in various parameters is examined variations of each of seven parameters over practical ranges of magmatic conditions can change bubble growth rates by 2 4 orders of magnitude our numerical formulation allows determination of the relative importance of each parameter controlling bubble growth for a given or evolving set of magmatic conditions an analysis of the modeling results reveals that the commonly invoked parabolic law for bubble growth dynamics r t1 2 is not applicable to magma degassing at low pressures or high water oversaturation but that a logarithmic relationship r log t is more appropriate during active bubble growth under certain conditions a second aspect of our study involved a constant decompression bubble growth model in which an initially saturated magma was subjected to a constant rate of decompression model results for degassing of initially water saturated rhyolitic magma with a constant decompression rate show that oversaturation at the vent depends on the initial depth of magma ascent on the basis of decompression history explosive eruptions of silicic magmas are expected for magmas rising from chambers deeper than 2 km for ascent rates 1 5 m s 1

a model for predicting the volumes of vesicles in submarine basalts the total volume percentage of vesicles in submarine pillow basalt rinds can be modelled by the exsolution of h o and co vapor using available solubility determinations for these components in basalt in accordance with observations on natural samples co is predicted to be the major vapor component in vesicles at eruption depths 1 2 km only small initial contents of co 0 1 0 2 wt are consistent with the vesicle volumes observed in most deep sea pillow lavas h o is important only at shallow depths crystallization of pillow interiors can lead to more extensive vesiculation inside of pillow lavas than in the vesicle poor outer rinds

ceres ezinu quadrangle a heavily cratered region with evidence for localized subsurface water ice and the context of occator crater abstract dawn is the first spacecraft to visit and orbit ceres the largest object in the asteroid belt and the only dwarf planet in the inner solar system the dawn science team undertook a systematic geologic mapping campaign of ceres entire surface here we present our contribution to this mapping campaign a geologic map and geologic history of the ezinu quadrangle located in the northern mid latitudes from 21 66 n and 180 270 e from our map we reconstruct the geologic history of ezinu quadrangle which is dominated by impact cratering large impact craters that formed a few hundreds to tens of millions of years ago such as datan messor ninsar and occator are surrounded by ejecta and contain the products of mass wasting hummocky crater floor material and talus material and crater wall collapse terrace material two of these large impact craters are the sources of lobate flows which we interpret as melt flows emplaced after the ballistically deposited ejecta morphological evidence suggests these lobate flows are rich in water ice bearing material that was excavated during the formation of the impact craters there are only a few localized occurrences of lobate flows suggesting that the water ice bearing source materials have restricted extents and or are deeply buried within ceres subsurface the quadrangle also contains a variety of linear features secondary crater chains are formed by the impact of locally and globally sourced material and pit chains and grooves are formed by the collapse of surficial materials into sub surface fractures the ezinu quadrangle contains the northern portion of occator crater which is the host crater of prominent bright regions called faculae our geologic analysis therefore also provides context for the future investigation of occator and its intriguing faculae

dissolution crystallization kinetics recorded in the 2002 2003 lavas of stromboli italy on 28 december 2002 new vents opened on the flanks of stromboli just below the summit craters interrupting the persistent activity of the volcano with a 7 month long effusive eruption we here report on the plagioclase size distribution plgsd in lava samples collected following the chronology of the 2002 2003 eruption data reveal a linear plgsd similar to that found in samples of normal stromboli activity indicating that the switch from strombolian explosive to effusive activity is not associated with changes in texture nevertheless the crystal size distribution slopes and intercepts exhibit slight sinusoidal temporal variations that are here ascribed to a magma supply mechanism able to induce resonance in the crystal size distribution with an amplitude that depends on the supply rate

hydrographic section aeross the kuroshio near 35 n 143 e a closely spaced conductivity temperature depth hydrographic section was conducted off the east coast of japan in july 1992 the southeastward section crossed the japan trench and the kuroshio in the vicinity of the kashima 1 seamount vertical sections of temperature salinity density oxygen and nutrients are discussed in conjunction with the movement and interleaving of water masses complicated vertical and horizontal mixings of water masses are inferred from the temperature and salinity relationships mixing processes are patchy and not continuous beneath the front warm salty water found beneath the kuroshio may result from upward mixing of water from intermediate depths the main axis of the kuroshio indicated by the 14 c isotherm at 200 m is at 35 7 n 142 6 e about 20 km from the north wall surface thermal front geostrophic speeds exceed 170 cm s 1 at the surface volume transport through the section is 81 106 m3 s 1

petrology and sr nd isotope geochemistry of recent lavas from mt etna bearing on the volcano feeding system abstract the volcanic activity of mt etna during the period 1971 1987 has been investigated based on new volcanological petrographic geochemical and isotopic data the magma output rate since 1971 is much higher than that of the last 200 years marking a significant change in the feeding regime of mt etna the highest output rate has been observed for the 1981 eruption sub aphyric lavas emitted during the excentric activity of 1974 are the most primitive of those studied mg 57 55 the major and trace element chemistry of the lavas indicates limited differentiation by crystal fractionation mainly involving mafic phases nevertheless the observed variability of some ratios between highly incompatible elements suggests possible source heterogeneities the sr nd isotopic compositions range between 0 70362 0 70377 and 0 512829 0 512892 respectively with the lowest and highest 87sr 86sr ratios measured in the 1981 and 1974 lavas the observed isotopic variability is not due to late contamination processes but probably to the mantle source variations in sr and nd isotopic composition could indicate the lack of large magma chambers at any level in mt etna feeding system suggesting a model in which magma reaches the surface through a network of dikes where complete homogenization of different batches cannot be attained

magma dynamics beneath kameni volcano thera greece as revealed by crystal size and shape measurements size distributions of plagioclase crystals in series of recent porphyritic dacite lavas from kameni volcano greece can be modelled by mixing two populations of crystals each with overlapping linear crystal size distributions csd termed microlites and megacrysts the magmas bearing the microlites and megacrysts started to crystallise 6 13 and 24 96 years respectively before each eruption the dates of initiation of crystallisation of the megacrysts indicate that they are left overs of earlier injections of new magma into a shallow chamber some magma remains after each eruption and continues to crystallise new magma with few or no crystals is then introduced and the microlites crystallise from the mixed magma eruption followed 6 13 years after mixing such a model would suggest that some porphyritic magmas are products of a shallow magma chamber that is never completely emptied just topped up from time to time

exploring the moon s surface for remnants of the lunar mantle 1 dunite xenoliths in mare basalts a crustal or mantle origin remotely sensed observations from recent missions e g grail kaguya chandrayaan 1 have been interpreted as indicating that the deep crust and upper mantle are close to or at the lunar surface in many large impact basins e g crisium apollo moscoviense if this is correct the capability of either impact or volcanic processes to transport mantle lithologies to the lunar surface should be enhanced in these regions somewhat problematic to these observations and interpretations is that examples of mantle lithologies in the lunar sample collection apollo program luna program lunar meteorites are at best ambiguous dunite xenoliths in high ti mare basalt 74275 are one of these ambiguous examples in this high ti mare basalt olivine occurs in three generations olivine associated with dunite xenoliths olivine megacrysts and olivine microphenocrysts the dunite xenoliths are anhedral in shape and are generally greater than 800 m in diameter the interior of the xenoliths are fairly homogeneous with regard to many divalent cations for example the mg mg mg fe 100 ranges from 82 to 83 in their interiors and decreases from 82 to 68 over the 10 30 m wide outer rim titanium and phosphorus x ray maps of the xenolith illustrate that these slow diffusing elements preserve primary cumulate zoning textures these textures indicate that the xenoliths consist of many individual olivine grains approximately 150 200 m in diameter with low ti al and p cores these highly incompatible elements are enriched in the outer fe rich rims of the xenoliths and slightly enriched in the rims of the individual olivine grains highly compatible elements in olivine such as ni exhibit a decrease in the rim surrounding the xenolith an increase in the incompatible element depleted cores of the individual olivine grains and a slight decrease in the interior rims of the individual olivine grains inferred melt composition liquid lines of descent and zoning profiles enable the reconstruction of the petrogenesis of the dunite xenoliths preservation of primary magmatic zoning ti p al and lack of textures similar to high pressure mineral assemblages exhibited by the mg suite shearer et al 2015 indicate that these xenoliths do not represent deep crustal or shallow mantle lithologies further they are chemically and mineralogically distinct from mg suite dunites identified from the apollo 17 site more likely they represent olivine cumulates that crystallized from a low ti mare basalt at intermediate to shallow crustal levels the parent basalt to the dunite xenolith lithology was more primitive than low ti basalts thus far returned from the moon furthermore this parental magma and its more evolved daughter magmas are not represented in the basalt sample suite returned from the taurus littrow valley by the apollo 17 mission the dunite xenolith records several episodes of crystallization and re equilibration during the last episode of re equilibration the dunite cumulate was sampled by the 74275 high ti basalt and transported over a period of 30 70 days to the lunar surface

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

crystal size distributions of plagioclase in lavas from the july august 2001 mount etna eruption during the 2001 eruption of mount etna two independent vent systems simultaneously erupted two different lavas the upper vents system uv opened between 3100 and 2650 m a s l emitted products that are markedly porphyritic and rich in plagioclase while the lower vents system lv opened at 2100 and 2550 m a s l emitted products that are sparsely porphyritic with scarce plagioclase in this study the crystal size distributions csds of plagioclase were measured for a series of 14 samples collected from all the main flows of the 2001 eruption the coefficient of r 2 determination was used to evaluate the goodness of fit of linear models to the csds and the results are represented as a grid of r 2 values by using a numerical code developed ad hoc r 2 diagrams suggest that the 2001 products can be separated into two main groups with slightly different characteristics plagioclase csds from the uvs can be modeled by three straight lines with different slopes while the plagioclase csds from the lvs are largely concave we have interpreted the csds of the uvs as representing three different populations of plagioclases i the large phenocrysts type i which started to crystallize at lower cooling rate in a deep reservoir from 13 to 8 months before eruption onset ii the phenocrysts type ii which crystallized largely during continuous degassing in a shallow reservoir and iii the microlites which crystallized during magma ascent immediately prior to the eruption the plagioclase csd curves for the lvs lava are interpreted to reflect strong and rapid changes in undercooling induced by strong and sudden degassing

mt etna a model for the 1989 eruption abstract during the 1989 eruption of mt etna one of the most important in the last 20 years in terms of effusion rate a pair of fractures formed on the slopes of the southeast crater cone and propagated in a few days trending ca northeast and southeast with large quantities of magma being drained from the northern fracture in contrast the southern fracture after a short initial eruptive phase grew by 5 km in five days without eruptive or seismic activity when the fracture system crossed the southern scarp of the valle del bove wall some 6 km se of the active crater an intense seismic swarm started in the same area this lasted about four days and consisted of several hundred events clustering in a small focal volume although such a sequence of failure events contains elements of compatibility with a shallow dyke intrusion it did not lead to the expected flank eruption which would have threatened settlements just a few kilometres from the distal end of the fracture the question arises therefore whether or not the fracture system was dyke related and if so to what extent we attempt here to answer such a question by integration and interpretation of the available field observation and geophysical data indeed field observation constraints on the southern fracture system and the typical depth 2 km of the swarm do not contain evidence for shallow dyke emplacement beneath the lowermost part of the sse fracture conversely the inferred direction and shape of the tremor source the location and extent of a gravity anomaly observed a few months before the eruption the near horizontal migration of the seismic focii during the swarm and the change with time of related focal mechanisms lead us to hypothesize that the extreme development of the fracture system at its south was due to a deeper intrusion beneath the southern slope of the volcano

ceres impact craters relationships between surface composition and geology abstract impact craters of different geological ages sizes and morphologies are not only the most obvious surface features on ceres surface the investigation of their spectral properties in combination with ceres geology and topography reveals not only lateral compositional variations in ceres surface material but also possible stratigraphic differences within ceres crust spectral properties of impact craters with different ages do show distinct trends implying variations with increasing exposure duration of the impact material onto ceres surface local concentrations of h2o ice and carbonates are associated with the youngest either recently emplaced or excavated surface deposits on the contrary regionally higher amounts of ammoniated phyllosilicates originate from deeper regions of ceres crust and strengthen the theory of ammonia being a primordial constituent of ceres the blue spectral slope clearly associated with relatively weak absorptions of oh bearing and or ammoniated phyllosilicates is limited to fresh impact material either the blue spectral slope diminishes slowly with increasing geologic age due to space weathering processes or shortly as a result of gravitation induced slumping forming a fine and loosely consolidated regolith

the surface composition of ceres ezinu quadrangle analyzed by the dawn mission abstract we studied the surface composition of ceres within the limits of the ezinu quadrangle in the ranges 180 270 e and 21 66 n by analyzing data from dawn s visible and near infrared data from the visible and infrared mapping spectrometer and from multispectral images from the framing camera our analysis includes the distribution of hydroxylated minerals ammoniated phyllosilicates carbonates the search for organic materials and the characterization of physical properties of the regolith the surface of this quadrangle is largely homogenous except for small high albedo carbonate rich areas and one zone on dark lobate materials on the floor of occator which constitute the main topics of investigation 1 carbonate rich surface compositions are associated with h2o ice rich crust weaker absorption bands of hydroxylated and ammoniated minerals over the carbonate rich areas can be explained by higher abundances of carbonates at the topmost surface 2 dark smooth lobate materials at the foot of occator s northeastern wall possibly reveal fresh slumping of phyllosilicate rich materials with fine grain size or local enrichment in carbon rich materials such as tholins 3 the deeper absorption band depth of oh and nh4 on the rim of several impact craters is one observation that is consistent with a stratification of the phyllosilicate abundance that has been inferred previously from global investigations

seismic heterogeneity of mt etna structure and activity a dense seismic array maintained temporarily for 7 weeks provides an approach to deducing the 3 d heterogeneity of the structure of the upper crust beneath mt etna volcano from the inversion of p and s wave arrivals of local earthquakes independent data from a different source array geometry using waves generated by distant shots at sea confirm a main lateral variation a high velocity body underlies part of the volcano its contrast with the surrounding thick sedimentary pile and its location extending from the present summit to the southeast suggests that it may have been built by the development and migration of past eruptive centres followed by caldera collapse local low velocity anomalies near its sharp western edge may be associated with presently active features

magma ascent simulations of etna s eruptions aimed at internal system definition the internal system of etna was studied by employing a nonequilibrium two phase flow model of magma ascent which accounts for different gas magma flow regimes and gas loss to surrounding conduit fractures when the magma pressure exceeds the local lithostatic pressure simulations of different phases of the 1974 and 1989 eruptions of etna with different flow regimes in conduits suggest that the pyroclastic strombolian lava fountaining and effusive lava flow activity can be modeled by effectively accounting for different physical processes of magma ascent results from simulations and geophysical and geological data suggest that magma ascent at etna may occur along a central conduit or inclined conduits from a magma storage region located from 8 to 9 km below the summit depending on the regional tectonic stresses and characteristics of the magma supply system the results also suggest the existence of a structurally weak zone from 1 to 4 km below the summit where magma may accumulate and from which fracture systems and magma ascent with gas loss to fractures may propagate to the eruptive vents at the surface the predicted excess magmatic pressure over lithostatic in the upper regions of conduits without gas loss to fractures suggests fracturing of the volcanic edifice during initial stages of eruptions and subsequent magma ascent and gas loss along these fractures modeling of the changes of activity at etna requires significant new efforts in geophysics aimed at high resolution internal system definition

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

the 1989 1990 activity of etna magma mingling and ascent of h2oclsrich basaltic magma evidence from melt inclusions abstract the melt inclusions in olivine phenocrysts from basaltic tephra erupted by etna volcano during the 1989 1990 eruptive period were investigated for major elements cl and s by electron microprobe fluorine by pigme particule induced gamma ray emission and h 2 o by sims the results indicate the ascent of basaltic magmas with different k 2 o concentrations possibly related to different feeding dykes lk basaltic melt inclusions rich in cl s and h 2 o are trapped in olivine fo 84 from the 1990 tephra and represent the early crystallization stage their composition in major elements is quite similar to those of most of the historic and even pre etnean alkali basalts but significantly lower in k 2 o compared with the 1989 1990 lavas only scarce hk basaltic melt inclusions were observed in the outer rim fo 79 6 of reversely zoned olivine phenocrysts and correspond to late crystallization stage at low pressure high sulfur concentration s 0 3 wt is a general characteristic of the etnean basaltic magmas with h 2 o s ratio as high as 7 the volatile abundances of the etna primitive basalts were computed at 1 45 wt for h 2 o 0 17 wt for cl and 0 047 wt for f with a high cl f ratio close to 3 6 the 1989 lava samples with cl at 660 90 ppm and f at 770 30 ppm have suffered a significant cl loss the possible behaviour of the volatile phase as co 2 h 2 o even cl is discussed with h 2 o and chlorine late degassing and an active role of h 2 o during the lava fountaining activity

mineralogical mapping of the kerwan quadrangle on ceres abstract the ceres surface is globally composed of mg phyllosilicates ammoniated clays carbonates and dark components to obtain a more detailed mineralogical and geological investigation the dwarf planet surface has been divided into fifteen quadrangles the aim of this work is to investigate the abundance of phyllosilicates and ammoniated clays in the kerwan quadrangle classified as ac h 7 and spanning from 22 s to 22 n in latitude and from 72 e to 144 e in longitude maps of band depth distribution at 2 7 m and 3 1 m have been performed and compared with a map of geometric albedo estimated at 1 2 m phyllosilicates and ammoniated clays generally correlate in the kerwan quadrangle even if departure from this behavior is observed in the floor of kerwan inamahari and homsuk craters the greatest abundance of ammoniated phyllosilicates is found in rao and kerwan ejecta while bonsu and tafakula floors are the most depleted in volatile as well as inamahari and dantu ejecta six bright spots are detected in the kerwan quadrangle and the one richest in carbonate is related to dantu ejecta in the southeast region some younger features such as rao or kerwan ejecta show deeper band depths than older terrain a contrast trend with respect to the entire ceres surface since this correlation is observed in a few other places on other quadrangles but not on the entire ceres surface it is possible that recent impact events could have been masked this correlation

kuroshio sea surface height fluctuations observed simultaneously with inverted echo sounders and topex poseidon sea surface height anomalies measured by inverted echo sounders with pressure gauges ies pgs and topex poseidon are compared at six locations in the northwest pacific near the kuroshio where it separates from the japanese coast the instruments are positioned along a topex poseidon descending ground track near 35 n 143 e good correlation is found between measurements with best agreement near the kuroshio where the range of sea surface height change is largest correlations between ies pg and topex poseidon sea surface height variations range from 0 70 to 0 97 tides modeled and removed from the topex poseidon data at the inverted echo sounder sites compare well with tides measured by the ies pgs topex poseidon and ies pg data are complementary in describing mesoscale variability in the kuroshio region

the geomorphology of ceres introduction observations of ceres the largest object in the asteroid belt have suggested that the dwarf planet is a geologically differentiated body with a silicate core and an ice rich mantle data acquired by the dawn spacecraft were used to perform a three dimensional characterization of the surface to determine if the geomorphology of ceres is consistent with the models of an icy interior rationale instruments on dawn have collected data at a variety of resolutions including both clear filter and color images digital terrain models have been derived from stereo images a preliminary 1 10 m scale geologic map of ceres was constructed using images obtained during the approach and survey orbital phases of the mission we used the map along with higher resolution imagery to assess the geology of ceres at the global scale to identify geomorphic and structural features and to determine the geologic processes that have affected ceres globally results impact craters are the most prevalent geomorphic feature on ceres and several of the craters have fractured floors geomorphic analysis of the fracture patterns shows that they are similar to lunar floor fractured craters ffcs and an analysis of the depth to diameter ratios shows that they are anomalously shallow compared with average ceres craters both of these factors are consistent with ffc floors being uplifted due to an intrusion of cryomagma kilometer scale linear structures cross much of ceres some of these structures are oriented radially to large craters and most likely formed due to impact processes however a set of linear structures present only on a topographically high region do not have any obvious relationship to impact craters geomorphic analysis suggests that they represent subsurface faults and might have formed due to crustal uplift by cryomagmatic intrusion domes identified across the ceres surface present a wide range of sizes 100 km basal shapes and profiles whether a single formation mechanism is responsible for their formation is still an open question cryovolcanic extrusion is one plausible process for the larger domes although most small mounds 10 km diameter are more likely to be impact debris differences in lobate flow morphology suggest that multiple emplacement processes have operated on ceres where three types of flows have been identified type 1 flows are morphologically similar to ice cored flows on earth and mars type 2 flows are comparable to long runout landslides type 3 flows morphologically resemble the fluidized ejecta blankets of rampart craters which are hypothesized to form by impact into ice rich ground conclusion the global trend of lobate flows suggests that differences in their geomorphology could be explained by variations in ice content and temperature at the near surface geomorphic and topographic analyses of the ffcs suggest that cryomagmatism is active on ceres whereas the large domes are possibly formed by extrusions of cryolava although spectroscopic analysis to date has identified water ice in only one location on ceres the identification of these potentially ice related features suggests that there may be more ice within localized regions of ceres crust figure 1 dawn high altitude mapping orbit imagery 140 meters per pixel of example morphologic features a occator crater arrows point to floor fractures b linear structures denoted by arrows c a large dome at 42 n 10 e visible in the elevation map d a small mound at 45 5 s 295 7 e e type 1 lobate flow arrows point to the flow front analysis of dawn spacecraft framing camera image data allows evaluation of the topography and geomorphology of features on the surface of ceres the dwarf planet is dominated by numerous craters but other features are also common linear structures include both those associated with impact craters and those that do not appear to have any correlation to an impact event abundant lobate flows are identified and numerous domical features are found at a range of scales features suggestive of near surface ice cryomagmatism and cryovolcanism have been identified although spectroscopic analysis has currently detected surface water ice at only one location on ceres the identification of these potentially ice related features suggests that there may be at least some ice in localized regions in the crust 1 pending yes

rheological properties of basaltic lavas at sub liquidus temperatures laboratory and field measurements on lavas from mount etna models of many magmatic processes require accurate data on the rheological properties of lava at sub liquidus temperatures laboratory measurements of the rheological properties of basalts erupted on mount etna in 1983 were made at various crystal concentrations in a specially designed furnace using a haake rotovisco viscometer attached to a spindle designed to eliminate slippage at the melt spindle interface measurements were made at strain rates between 0 3 and 5 s 1 over the range of eruption temperatures on mount etna 1084 1125 c at temperatures above 1120 c the 1983 lava behaves as a newtonian fluid at lower temperatures the lava is a thixotropic pseudoplastic fluid with a maximum yield strength of 78 pa at a temperature of 1087 c in view of its low yield strength over this temperature range the theological behaviour of the lava approximates to that of a power law fluid apparent viscosities at unit shear strain rates increase from 150 pa s at 1125 c to 3000 pa s at 1084 c unit strain rate apparent viscosities measured in the field using a rotating vane viscometer range from 1385 pa s to 1630 pa s these values are in close agreement with those measured at the same temperature in the laboratory and with those calculated theoretically from the physico chemical properties of the lava

mount etna dense array local earthquake p and s tomography and implications for volcanic plumbing inversion for the three dimensional velocity structure of mount etna is performed with a data set of arrival times of p and s waves of local earthquakes from temporary dense arrays of three component seismographs a high v p body revealed by the original tomography without nearby stations is confirmed and its image is sharpened using new velocity constraints provided by refraction data synthetic tests of v p and v p v s and comparison with an independent artificial source tomography with a fundamentally different geometry consistently calibrate the significance threshold of the resolution indicators the trustworthy part of the image shows a high v p body centered under the southern part of valle del bove above the 6 km below sea level deep basement which extends towards sea level and may be rooted in or through the crust it has a large contrast of over 1 km s with the surrounding sediments and sharp lateral limits and can thus be regarded as made of intrusive material of magmatic origin the massive high v p body is heterogeneous in v p v s the regions inside it where v s is relatively low can then be suspected of containing a proportion of melt or be fractured and act as pressure links or transport zones such features may be structurally linked and appear to be activated in eruptive phenomena by taking into account the heterogeneities in structure and physical state retrieved by seismic tomography a succession of seismic events deformational episodes and geochemical variation in lavas can be discussed with respect to the well observed eruptions

the 1983 mount etna eruption thermochemical and dynamical inferences thermochemical calculations and laboratory phase equilibration experiments on lavas of the 131 day 1983 mt etna flank eruption of 0 1 km3 were undertaken to investigate possible systematic variations in inferred melt phenocryst equilibration conditions as a function of time the 1983 mt etna lavas are multiply saturated plagioclase clinopyroxene and olivine the dominant phenocrysts occur in the ratio 1 1 2 1 4 melts glasses plot close to the plagioclase saturated olivine clinopyroxene low pressure cotectic on a walker o hara diopside forsterite silica diagram suggesting equilibration of melt and phenocrysts in a high level magma reservoir total pressures temperatures and dissolved h2o concentrations were calculated using the isoactivity method of carmichael and coworkers based on about 300 elelctron microprobe analyses of coexisting olivine clinopyroxene and plagioclase phenocrysts microphenocrysts and groundmass microlites for samples collected 6 46 and 125 days after the start of the eruption total pressures pt temperatures and h2o contents based on representative olivine clinopyroxene pairs are 140 mpa 1105 c 2 4 wt h2o 255 mpa 1112 c 1 0 wt h2o and 85 mpa 1096 c 1 8 wt h2o respectively for the early 283 middle i83 and late l83 samples corresponding equilibration depths are in the range 3 to 10 kilometers plagioclase feldspar phenocrysts while showing more evidence of disequilibrium provide compatible estimates of pt and t when analysis is restricted to the low anorthite mode of the plagioclase frequency composition histograms 133 mpa and 1115 c 260 mpa and 1117 c and 103 mpa and 1104 c repectively for 283 i83 and l83 the pre eruptive i e in situ temperature pressure gradient calculated from olivine clinopyroxene equilibria is 10 6 k kbar this compares well with independent estimates of the temperature pressure derivative of the pseudo invariant point composition 10 to 12 k kbar in both model e g diopside forsterite anorthite presnall et al 1978 and natural e g walker et al 1979 grove et al 1982 systems apparently magma within the etna reservoir was in a quasiequilibrium state buffered by its multiply saturated character immediately preceding eruption the temporal variation of computed pt t and h2o concentrations for melt phenocryst equilibrium agrees well with predictions based on simulations of the withdrawal of magma from a body zoned with respect to dissolved h2o provided the temporal record of magma discharge is taken into account discharge varied by a factor of about 100 during the sample collection interval the intermediate pt but high h2o content inferred for sample 283 reflects the withdrawal of h2o enriched magma during an early phase of high average discharge of about 3 50 m3 s before evaculation isochrons became quasistationary the high pt and relatively dry i83 magma reflects the deepening of the evacuation isochrons after 50 days of intermediate discharge with the development of quasi stationary isochrons in time and space sample l83 from day 125 near the end of the eruption reflects the shoaling of evacuation isochrons hence low pt and relatively high h2o content associated with the observed low 0 5 m3 s discharge our results show that thermochemical modeling efforts provide important opportunities for testing the predictions of magma with drawal simulations

cratering on ceres implications for its crust and evolution introduction thermochemical models have predicted that the dwarf planet ceres has to some extent formed a mantle moreover due to viscous relaxation these models indicate that ceres should have an icy crust with few or no impact craters however the dawn spacecraft has shown that ceres has elevation excursions of 15 km cliffs graben steep sided mountains and a heavily cratered surface rationale we used dawn s framing camera to study the morphology size frequency and spatial distribution of the craters on ceres these data allow us to infer the structure and evolution of ceres outer shell results a large variety of crater morphologies are present on ceres including bowl shaped craters polygonal craters floor fractured craters terraces central peaks smooth floors flowlike features bright spots secondary craters and crater chains the morphology of some impact craters is consistent with water ice in the subsurface although this might have favored relaxation there are also large unrelaxed craters the transition from bowl shaped simple craters to modified complex craters occurs at diameters of about 7 5 to 12 km craters larger than 300 km are absent but low pass filtering of the digital elevation model suggests the existence of two quasi circular depressions with diameters of 570 km 125 56 e and 19 60 n and 830 km 24 76 w and 0 5 n craters are heterogeneously distributed across ceres surface with more craters in the northern versus the southern hemisphere the lowest crater densities are associated with large well preserved southern hemisphere impact craters such as urvara and yalode because the low crater density lcd terrain extends across a large latitude range in some cases e g urvara and yalode 18 n and 75 s kerwan 30 n and 46 s its spatial distribution is inconsistent with simple relaxation driven by warmer equatorial temperatures we instead propose that impact driven resurfacing is the more likely lcd formation process although we cannot completely rule out an internal endogenic origin we applied two different methodologies to derive absolute model ages from observed crater size frequency distributions the lunar derived model adapts the lunar production and chronology functions to impact conditions on ceres taking into account impact velocities projectile densities current collision probabilities and surface gravity the asteroid derived model derives a production function by scaling the directly observed object size frequency distribution from the main asteroid belt extended to sizes 5 km by a collisional model to the resulting size frequency distribution of cerean craters using similar cerean target parameters as the lunar derived model by dating a smooth region associated with the kerwan crater we determined absolute model ages of 550 million and 720 million years depending on which chronology model is applied conclusion crater morphology and the simple to complex crater transition indicate that ceres outer shell is likely neither pure ice nor pure rock but an ice rock mixture that allows for limited relaxation the heterogeneous crater distribution across the surface indicates crustal heterogeneities and a complex geologic evolution of ceres there is evidence for at least some geologic activity occurring in ceres recent history figure 1 spatial density of craters larger than 20 km on ceres crater rims are shown as black solid circles blue indicates areas with lcds yellow and red represent more highly cratered areas the smallest dashed ellipse denotes the idealized former rim of an extremely degraded impact crater at 48 9 e and 44 9 s which is barely recognizable in imagery but apparent from the global digital elevation model also shown as dashed circles are the outlines of two large putative basins unambiguously recognized basins 300 km in diameter are missing and there are several areas with lcds associated with large impact craters e g yalode urvara kerwan ezinu vinotonus dantu and two unnamed craters northeast and southeast of oxo areas a and b are topographic rises with central depressions that also show lcds thermochemical models have predicted that ceres is to some extent differentiated and should have an icy crust with few or no impact craters we present observations by the dawn spacecraft that reveal a heavily cratered surface a heterogeneous crater distribution and an apparent absence of large craters the morphology of some impact craters is consistent with ice in the subsurface which might have favored relaxation yet large unrelaxed craters are also present numerous craters exhibit polygonal shapes terraces flowlike features slumping smooth deposits and bright spots crater morphology and simple to complex crater transition diameters indicate that the crust of ceres is neither purely icy nor rocky by dating a smooth region associated with the kerwan crater we determined absolute model ages amas of 550 million and 720 million years depending on the applied chronology model 1 pending yes

melt inclusion investigation of the volatile behaviour in historic alkali basaltic magmas of etna crystallization paths of basaltic 1763 eruption and hawaiitic 1865 and 1329 eruptions scoria from etna were deduced from mineralogy and melt inclusion chemistry the volatile behaviour was investigated through the study of melt inclusions trapped in the phenocrysts and those of the whole rocks and the matrix glasses the results from the 1763 eruption point to the early crystallization of olivine fo 81 7 from a water rich alkaline basalt with high cl 1750 2000 ppm and s 2100 2400 ppm concentrations the hawaiitic melt inclusions trapped in olivine fo 74 salite and plagioclase are characterized by a decrease in cl k2o and s k2o ratios in each investigated system there is good correlation between k2o and p2o5 in the whole rocks cl ranges from 980 to 1680 ppm from basaltic to hawaiitic lavas whereas s 110 136 ppm remains low cl and s behaviour in the 1763 magma suggests an early degassing stage of cl and s with co2 and a water rich gaseous phase for a pressure close to 100 mpa consistent with a permanent outgassing at the summit craters of etna during the eruption the sulphur remaining in the hawaiitic liquid is lost and the degassing of chlorine is limited such a degassing model can be extended to the 1865 and 1329a d eruptions

an investigation of the bluish material on ceres the dwarf planet ceres shows spatially well defined regions which exhibit a negative blue spectral slope between 0 5 and 2 5 m comparisons with planetary bodies known to exhibit a blue slope and spectral properties of materials identified on ceres surface based on infrared wavelength signatures indicate the spectral changes could be related to physical properties of the surface material rather than variations in its composition the close association of bluish surface regions to fresh impact craters implies a possible relationship to an impact triggered alteration and or space weathering processes the bluish regions could be linked with blankets of ultra fine grains and partly amorphous phyllosilicates which form larger agglomerates due to the sticky behavior of impact induced phyllosilicate dust and or the amorphization of the ejecta material during the impact process space weathering processes micro meteoritic impacts temperature changes cause a reversal of the agglutination process and a re crystallization of the surface material with time resulting in a reddening of the spectral slope

thermochronological evolution of an intra plate magmatic event inferred from an integrated modeling approach a case study in the westerwald germany abstract a lava sample from the tertiary westerwald volcanic field was selected for a detailed study using various analytical techniques in combination with petrological thermodynamic and diffusion modeling to extract information related to the thermochronological evolution of a magmatic event before eruption the lava sample contains large olivine phenocrysts which are compositionally zoned and two coexisting but chemically distinct melts a host melt with basaltic composition and small spherical pockets of a less abundant trachytic melt globules the sample was analyzed by electron microprobe x ray fluorescence xrf x ray diffraction xrd and electron backscatter diffraction ebsd the primary melt of the host lava was determined using the program primelt2 xls partial fractional crystallization of olivine was modeled using the program alphamelts timescale and cooling rate were retrieved by fitting the measured fe mg zoning along two directions in four olivine grains from the host lava using a 3 d numerical diffusion model the measured variation of ca is also consistent with a chemical diffusion process while a numerical growth model applied to the same olivines does not appear to explain the fe mg zoning chemical zoning of major elements in the melt globules were reproduced with a multicomponent diffusion model the results of this study show that the host magma fractionated about 9 of olivine in a first stage then the crystallization proceeded without further separation of mineral phases modeling of diffusion in the olivine crystals suggests that this second stage lasted at least 5 yrs and the temperature of the melt decreased from 1120 1150 c to 1090 c during this time according to the results of the multicomponent diffusion model applied to the melt globules the coexistence of the two melts was extremely short less than few hours possibly recording the assimilation of the globules during eruption or cooling of the whole system on the surface

mechanisms for ground surface fracturing and incipient slope failure associated with the 2001 eruption of mt etna italy analysis of ephemeral field data abstract during the july august 2001 eruption of mt etna development of extensional fractures faults and grabens accompanied magma intrusion and subsequent volcanic activity during the first days of the eruption we performed an analysis of attitude displacement and propagation of fractures and faults exposed on the ground surface in two sites torre del filosofo and valle del leone located along the same fracture system in the region surrounding the valle del bove depression on the eastern flank of mt etna fractures and faults formed as the consequence of a shallow intruding dyke system that fed the several volcanic centres developed along the fracture system the investigated sites differ in slope attitude and in geometrical relationships between fractures and slopes in particular the fracture system propagated parallel to the gentle slope

simulations of magma ascent and pyroclast dispersal at vulcano aeolian islands italy abstract two phase flow models of magma ascent in volcanic conduits and pyroclast dispersal in the pressure and temperature stratified atmosphere were employed to study the consistency of the palizzi pumice fall eruption phase and the last eruption of vulcano with modeling predictions the input data for magma ascent modeling were constrained by the limited availability of petrological volcanological and geophysical data and consisted of magma composition crystal content conduit geometry and pressure and temperature of magma in the magma chamber the magma ascent model was used to establish the locations of magma exsolution and fragmentation levels gas and pyroclast velocities pressure and pyroclast volumetric fractions at the exits of conduits of different diameters and lengths the vent exit conditions of gas and pyroclasts corresponding to different magma compositions and conduit geometry were employed in the pyroclastic dispersion modeling to establish the distribution of gas and pyroclasts in the atmosphere and along the slopes of the volcano during the first few minutes of the eruptions in order to determine the volcanic column and flow behavior along the slopes of the volcano the results from simulations showed that the palizzi pumice fall eruption phase and the last eruption of vulcano which produced bread crust bombs are consistent with magma ascent and pyroclastic dispersion models using the available volcanological petrological and geophysical data as well as the modeling results an eruptive scenario of each cycle of vulcano was hypothesized where the chemical characteristics of new magma supply into the volcanic system and magma remaining in the system after preceding eruptions mechanical characteristics of the magma ascent pathways and the conditions of aquifers surrounding these pathways determine the duration of phreatic phreatomagmatic magmatic and lava flow activities within each cycle the modeling results also suggested that the palizzi pumice fall eruption phase ejected magma with a dissolved water content of about 2 wt from a vent diameter of about 30 m and that the dissolved water content in magma during the last eruption of vulcano ranged between 1 and 2 wt detailed modeling of various eruptive phases and adequate volcanic hazard assessment at vulcano not only requires the development of magma water interaction and hydrothermal circulation models but also the collection of modeling oriented volcanological petrological and geophysical data

modeling the effects of eruptive and seismic activities on flank instability at mount etna italy 1 the identification and evaluation of trigger mechanisms for volcano flank instabilities and or collapse represent a key issue for risk assessment in densely populated volcanic areas as well as in long distance settings particularly in case of island or coastal volcanoes here we address quantitatively the effects of external seismic and inner magmatic forcing on the stress strain state associated to flank instabilities at mount etna sicily southern italy by means of a 2 d finite difference method numerical modeling modeled seismic actions include strong near field strong far field and low magnitude near field earthquakes magmatic actions consider the inner pressure changes induced by energetic lava fountains in the summit crater area and subvertical and oblique dike ascent below the summit area model results are validated in light of available monitoring data and recent eruptive activity numerical results show that the main strain effects are produced by high magnitude near field earthquakes expected return time of 103 yrs and by vertical uprise of a magma dike below the volcano summit area maximum displacements in the order of tens of centimeters may involve the summit area up to some 106 m3 m over some kilometers laterally stress releases up to 107 pa may affect a limited portion of the magmatic conduit thus favoring major effusive flank eruptions major catastrophic events such as volcano flank collapse should not be expected by applying either individually or combined the aforementioned actions

an experimental study of the kinetics of decompression induced crystallization in silicic melt 1 experiments were conducted to study the temporal evolution of feldspar crystallization kinetics during isothermal decompression pinatubo dacite was held at 780 c 220 mpa fo2 nno 2 h2o saturated conditions for an equilibration period decompressed to final pressures pf ranging from 175 to 5 mpa and then held for 0 3 931 hours according to the plagioclase liquidus curve in ph2o t space for the relevant melt composition these decompressions impose effective undercoolings teff of 34 266 c growth of preexisting phenocrysts and newly formed sparse microlites dominate crystallization at 75 pf 150 mpa teff 34 93 c and equilibrium crystal modes are achieved in 168 hours microlite nucleation is the dominant transformation process for 10 pf 50 mpa teff 125 241 c and chemical equilibrium is not attained by 168 hours under these conditions slow steady decompressions typically produced normally zoned euhedral and planar faceted feldspar crystals although anhedral morphologies were produced at very low pf contrary to expectation slowly decompressed samples were usually further from chemical equilibrium than rapidly decompressed samples after similar durations below the initial pressure although counterintuitive these trends are consistent with new constraints on the relative rates of feldspar nucleation and growth controlled by teff and melt viscosity experienced during each decompression path analysis of liquid to solid transformation kinetics using ttt style diagrams shows that crystallization occurs most rapidly at 100 mpa by a crystal growth mechanism the next most efficient crystallization conditions are at 25 mpa in a crystal nucleation dominated regime

magmatic processes revealed by textural and compositional trends in merapi dome lavas syn eruptive degassing of volcanoes may lead to syn eruptive crystallization of groundmass phases we have investigated this process using textural and compositional analysis of dome material from merapi volcano central java indonesia samples included dome lavas from the 1986 88 1992 93 1994 and 1995 effusive periods as well as pyroclastic material deposited by the november 1994 dome collapse with total crystallinities commonly in excess of 70 phenocrysts 1 microlites the liquids present in merapi andesites are highly evolved rhyolitic at the time of eruption feldspar microlites in dome rocks consist of plagioclase cores ab63an29or8 surrounded by alkali feldspar rims ab53an5or42 compositional pairs which are not in equilibrium a change in the phase relations of the ternary feldspar system caused by degassing best explains the observed transition in feldspar composition a small proportion of highly vesicular airfall tephra grains from the 1994 collapse have less evolved glass compositions than typical dome material and contain rimless plagioclase microlites suggesting that the 1994 collapse event incorporated less degassed partially liquid magma in addition to fully solidified dome rock as decompression drives volatile exsolution rates of degassing and resultant microlite crystallization may be governed by magma ascent rate microlite crystallinity is nearly identical among the 1995 dome samples an indication that similar microlite growth conditions ph2 o and temperature were achieved throughout this extrusive period however microlite number density varied by more than a factor of four in these samples and generally increased with distance from the vent low vent ward microlite number densities and greater microlite concentrations down flow probably reflect progressively decreasing rates of undercooling at the time of crystal nucleation during extrusion of the 1995 dome comparison between dome extrusion episodes indicates a correlation between lava effusion rate and microlite number density suggesting that extrusion slowed during 1995 crystal textures and compositions in the 1992 93 and 1994 domes share the range exhibited by the 1995 dome suggesting that transitions in crystallization conditions i e rates of undercooling determined by effusion rate are cyclic q 2000 elsevier science b v all rights reserved

the structure and transport of the gulf stream at 73 w abstract between september 1980 and may 1983 16 sections of temperature and velocity were obtained with the pegasus instrument along a transect crossing the gulf stream at 73 w the mean temperature and velocity fields of the upper 2000 meters were calculated the transport above 2000 meters calculated from the sections had a mean of 87 8 17 3 106 m3 s 1 a comparison with mass flux measurements obtained by previous investigators at cape fear indicated that the addition to the transport of the stream in the region was uniform with depth above 800 meters the mean inflow measured at the pegasus line was found to be uniform above 800 meters and to decrese substantially below this depth the increase in transport at the line estimated from the mean cross stream velocity field was 15 4 5 8 106 m3 s 1 per 100 km downstream distance the temporal fluctuation of the pegasus transport measurements was consistent with an annual cycle with a maximum in april the mean eddy kinetic energy at the surface

spectral investigation of quadrangle ac h 3 of the dwarf planet ceres the region of impact crater dantu abstract mapping ceres surface composition in the dantu region located between 21 66 n and 90 180 e offers the unique possibility to investigate changes in the surface composition related to different stratigraphic levels of ceres crust dantu is located in a huge depression named vendimia planitia which possibly represents a completely degraded impact basin formed in the beginning of ceres geological history most parts of this depression are characterized by strong phyllosilicate absorptions which are stronger than elsewhere on ceres surface this spectral signature possibly is related to the material emplaced at the time of the vendimia impact event excavating material from deeper regions of ceres crust subsequent impacts in this basin reach far deeper into ceres crust than any impact events outside of vendemia planitia which could explain the spectral signature of dantu possibly pointing to a higher concentration of ammonium bearing phyllosilicates in ceres deeper crust spectral differences with respect to the small fresh craters on dantu s floor are probably related to grain size effects causing a bluish visible slope as observed by fresh impact craters on other places on ceres the local enrichment of carbonates in the dantu area could also be associated with the impact event and may have been formed by additional impact triggered and or post impact alteration processes

olivine growth rates in a tholeiitic basalt an experimental study of melt inclusions in plagioclase abstract basaltic glass inclusions trapped in plagioclase phenocrysts an 84 are remnant of their parent magmatic liquid they can be used as natural reactors for the experimental investigation of olivine growth rate as a function of temperature the growth of one olivine nucleus can be observed at constant temperature supercooling from 15 to 150 c have been investigated growth habits vary from equant to feather in qualitative agreement with previous studies growth rates vary from 10 m s 1 to 6 10 7 m s 1 they vary with the direction the growth process planar or dendritic and the degree of supercooling chemical analysis of crystal overgrowth and the remaining liquid composition enables a mass balance calculation which confirms the rates determined optically the small number of results obtained so far does not permit to draw inferences on the growth mechanisms

an approach to problems on energy sources at mount etna based on seismological and volcanological data based on seismograms from the most continuously operating station of the seismic network at mt etna monte vetore 1665 m a s l the energy release patterns through time have been obtained for volcanic tremors and earthquakes which occurred between 1978 1982 both energies range between 1011 1013 j a but their release patterns are not strictly correlated to each other considering only the eruptions which occurred during the same time span the amount of thermal energy released and the associated potential energy needed to raise the magma to the surface from a 2 km deep hydrostatic equilibrium level were estimated to be about 1017 and 1015 j a respectively the computed energies for earthquakes and tremors are at least one order of magnitude less than what is needed to match a model of magma transport based solely on the jerky propagation of melt filled cracks the energy needed to raise the magma to the surface could be supplied by expanding gases in the upper levels of the magma column and or by tectonic stresses acting on shallow batches of magma

the contemporaneous emission of low k and high k trachybasalts and the role of the ne rift during the 2002 eruptive event mt etna italy mount etna volcano erupted almost simultaneously on its northeastern and southern flanks between october 27 and november 3 2002 the eruption on the northeastern flank lasted for 8 days while on the southern flank it continued for 3 months the northeastern flank eruption was characterized by the opening of a long eruptive fracture system between 2 900 and 1 900 m a s l a detailed survey indicates that the fractures direction shifted during the opening from n10w at the ne crater 2 900 m to n45e at its lowest portion 1 900 m and that distinct magma groups were erupted at distinct fracture segments based on their petrological features three distinct groups of rocks have been identified the first group high potassium porphyritic hkp is made up of porphyritic lavas with a porphyritic index p i of 20 32 and k2o content higher than 2 wt the second group is represented by lavas and tephra with low modal phenocryst abundance p i 20 named here oligo phyric low phyric and k2o content higher than 2 wt hko high potassium oligophyric the third group low potassium oligophyric lko consists of tephra with oligophyric texture p i 20 but k2o content 2 wt k rich magmas hkp and hko are similar to the magma erupted on the southern flank and geochemical variations within these groups can be accounted for by a variable degree of fractionation from a single parent magma the k poor magma lko erupted only in the upper segment of the fracture cannot be placed on the same liquid line of descent of the hk groups and it is similar to the magmas that fed the activity of etna volcano prior to the eruption of 1971 this is the first time since then that a magma of this composition has been documented at mt etna thus providing a strong indication for the existence of distinct batches of magma whose rise and differentiation are independent from the main conduit system the evolution of this eruption provides evidence that the ne rift plays a very active role in the activity of mt etna volcano and that its extensional tectonics allows the intrusion and residence of magma bodies at various depths which can therefore differentiate independently from the main open conduit system

experimental constraints on magma ascent rate for the crater flat volcanic zone hawaiite phase equilibria and isothermal constant rate decompression experiments conducted on a hawaiite from the crater flat volcanic zone near yucca mountain nevada provide insight into the dynamics of magma transport for this magmatic province h 2 o contents up to 4 6 wt in melt inclusions the lack of plagioclase phenocrysts and the presence of amphibole all suggest that phenocrysts and melt in the crater flat volcanic zone were equilibrated at near water saturated conditions during ascent comparison of decompression induced crystallization of plagioclase microlites in experiments with natural tephra implies that magma ascent rates for the region are 0 04 m s if the magmas are water saturated estimates of minimum ascent rates increase if the magmas are water undersaturated a two stage process is needed to generate reaction rims found on natural amphibole suggesting that small batches of magma were briefly stored 3 5 days at depths as shallow as 800 m prior to eruption

the dyke swarm of mount calanna etna italy an example of the uppermost portion of a volcanic plumbing system a new multidisciplinary study combining geology petrography and geochemistry on the rocks of the isolated hill of mount calanna mount etna italy has provided evidence for the existence of a dyke swarm formed by more than 200 dykes distributed over an area of 0 7 km2 with an intensity of intrusion up to 40 all bodies are deeply altered and the geological and mesostructural surveying of 132 dykes revealed that they intruded in e w direction with an average dip of 60 the faults affecting the outcrop have in general an e w strike and dip of 55 these have all normal motion and have been interpreted as coeval with the dykes this interpretation contrasts with the previous hypothesis that considered mount calanna as a thrust resulting from compressive deformation resulting from the gravitational spreading of the volcanic edifice mount calanna is here interpreted as the uppermost portion of a vertically extensive magmatic plexus that fed the eruptive activity of one or more eruptive center s sited in the valle del bove area measurements of the apparent densities on 23 dykes and host rock samples give an average value of 2 420 kg m3 for the entire complex 15 lower than the density expected for hawaiitic magma placing an important constraint on the geophysical identification of similar structures considering that mount etna is not an old eroded edifice but an active and growing volcano the exposure of this subvolcanic structure can be regarded as exceptional its geometry and physical characteristics can be thus regarded as an interesting example of the present day shallow plumbing system of mount etna as well as of other basaltic volcanoes

dynamics of degassing at kilauea volcano hawaii at kilauea volcano hawaii the recent long lived eruptions of mauna ulu and pu u o o have occurred in two major stages defining a characteristic eruptive pattern the first stage consists of cyclic changes of activity between episodes of fire fountaining and periods of quiescence or effusion of vesicular lava the second stage consists only of continuous effusion of lava we suggest that these features reflect the dynamics of magma degassing in a chamber which empties into a narrow conduit in the volcano chamber gas bubbles rise through magma and accumulate at the roof in a foam layer the foam flows toward the conduit and its shape is determined by a dynamic balance between the input of bubbles from below and the output into the conduit the foam thickness is proportional to lq e2 l g 1 4 where l and l are the viscosity and density of magma e is the gas volume fraction in the foam g is the acceleration of gravity and q is the gas flux the bubbles in the foam deform under the action of buoyancy and the maximum permissible foam thickness is hc 2 e lgr where is the coefficient of surface tension and r is the original bubble radius if this critical thickness is reached the foam collapses into a large gas pocket which erupts into the conduit foam accumulation then resumes and a new cycle begins the attainment of the foam collapse threshold requires a gas flux in excess of a critical value which depends on viscosity surface tension and bubble size hence two different eruption regimes are predicted 1 alternating regimes of foam buildup and collapse leading to the periodic eruption of large gas volumes and 2 steady foam flow at the roof leading to continuous bubbly flow in the conduit the essential result is that the continuous process of degassing can lead to discontinuous eruptive behavior data on eruption rates and repose times between fountaining phases from the 1969 mauna uiu and the 1983 1986 pu u o o eruptions yield constraints on three key variables the area of the chamber roof must be a few tens of square kilometers with a minimum value of about 8 km2 magma reservoirs of similar dimensions are imaged by seismic attenuation tomography below the east rift zone close to the roof the gas volume fraction is a few percent and the gas bubbles have diameters lying between 0 1 and 0 6 mm these estimates are close to the predictions of models for bubble nucleation and growth in basaltic melts as well as to the observations on deep submarine basalts the transition between cyclic and continuous activity occurs when the mass flux of gas becomes lower than a critical value of the order of 103 kg s in this model changes of eruptive regime reflect changes in the amount and size of bubbles which reach the chamber roof

cluster analysis of soil co2 data from mt etna italy reveals volcanic influences on temporal and spatial patterns of degassing soil co2 concentration data were collected periodically from july 2001 to june 2005 from sampling site grids in two areas located on the lower flanks of mt etna volcano paterno and zafferana etnea santa venerina cluster analysis was performed on the acquired data in order to identify possible groups of sites where soil degassing could be fed by different sources in both areas three clusters were recognised whose average co2 concentration values throughout the whole study period remained significantly different from one another the clusters with the lowest co2 concentrations showed time averaged values ranging from 980 to 1 170 ppm vol whereas those with intermediate co2 concentrations showed time averaged values ranging from 1 400 to 2 320 ppm vol and those with the highest concentrations showed time averaged values between 1 960 and 55 430 ppm vol we attribute the lowest co2 concentrations largely to a biogenic source of co2 conversely the highest co2 concentrations are attributed to a magmatic source whereas the intermediate values are due to a variable mixing of the two sources described above the spatial distribution of the co2 values related to the magmatic source define a clear direction of anomalous degassing in the zafferana etnea santa venerina area which we attribute to the presence of a hidden fault whereas in the paterno area no such oriented anomalies were observed probably because of the lower permeability of local soil time series analysis shows that most of the variations observed in the soil co2 data from both areas were related to changes in the volcanic activity of mt etna seasonal influences were only observed in the time patterns of the clusters characterised by low co2 concentrations and no significant interdependence was found between soil co2 concentrations and meteorological parameters the largest observed temporal anomalies are interpreted as release of co2 from magma batches that migrated from deeper to shallower portions of etna s feeder system the pattern of occurrence of such episodes of anomalous gas release during the observation period was quite different between the two studied areas this pattern highlighted an evident change in the mechanism of magma transport and storage within the volcano s feeder system after june 2003 interpreted as magma accumulation into a shallow 8 km depth reservoir

seismic patterns and fluid dynamic features preceding and accompanying the january 15 1990 eruptive paroxysm on mt etna italy abstract on the basis of data collected during a seismological investigation carried out on mt etna italy during a phase of the volcanic activity marked by progressive transition from strombolian bursts to effusive paroxysms at the se crater january 1990 three types of seismic regime have been recognized they are interpreted to be linked to modifications in the regimes of volcanic gases and vapours within the upper levels of the magma column as suggested by recent studies on the dynamics of magmatic fluids our analysis also reveals that the use of usual seismic parameters such as the temporal patterns associated with the occurrence of discrete low frequency events spindles and the coefficient m of the ishimoto iida law can furnish information about variations in the behaviour of the system before the irreversible evolution of the volcanic activity toward eruptive paroxysms

origin of anorthosite by textural coarsening quantitative measurements of a natural sequence of textural development the textures of plagioclase crystals within large olivine oikocrysts preserve the sequence of the formation of anorthosite such textures have been quantified in a troctolite anorthosite from the proterozoic lac st jean anorthosite complex canada crystal size distributions csds indicate that initially plagioclase nucleated and grew in an introduction environment of linearly increasing undercooling producing a straight the textures of plutonic rocks are one of their most line csd during this phase latent heat of crystallization was striking aspects but they have been little used to elucidate largely removed by circulation of magma through the porous crystal petrological processes as compared with chemical and mush by about 25 solidification the crystallinity was such that isotopic methods where used discussion has tended it reduced but did not eliminate the circulation of magma resulting to be qualitative in contrast to quantitative chemical in the retention of more latent heat within the crystal pile the methods hence reducing the weight of this approach temperature rose until it was buvered by the solution of plagioclase indeed it is not possible to verify physical models if close to the liquidus temperature of plagioclase nucleation of quantitative data are not available quantitative textural plagioclase was inhibited and conditions were suitable for textural studies of volcanic rocks are becoming more common coarsening of both plagioclase and olivine to occur ostwald and these methods are applied here to the development ripening in this process small crystals were resorbed whereas of anorthosite larger crystals grew from both material recycled by the resorption of quantitative textural studies of plutonic rocks really crystals smaller than the critical size and new material brought in started with jackson s studies of the stillwater complex by the circulating magmatic fluid the results of this process resemble in 1961 jackson 1961 he measured crystal size disthose of high temperature metasomatism but there is no necessity for tributions but did not record the area that he measured a magmatic fluid with a diverent composition the shapes of the hence his data cannot be completely compared with plagioclase csds fit better the communicating neighbours equation of modern data his pioneering work was not really followed textural coarsening rather than the classic lifshitz slyozov wagner up and since then most studies have looked only at equation as do other examples drawn from the literature if olivine average or typical crystal sizes these data are much started to nucleate at a higher temperature than plagioclase then less revealing of petrological processes than crystal size during the textural coarsening phase olivine would have been more distributions partly because they only give one parameter undercooled than plagioclase and would have had a higher maximum for each sample the few existing studies of crystal size growth rate in these conditions olivine would coarsen more rapidly distributions in plutonic rocks have not treated than plagioclase and engulf it hence the order of crystallization plagioclase determined from the textures would be the reverse of the order of one problem especially pertinent to quantitative texfirst nucleation of the two phases from equilibrium phase diagrams tural studies is the way that many igneous petrologists maintenance of the temperature near the plagioclase liquidus may look at rocks they commonly try to reconstruct how a rock has formed by examining the final fully crystallized also inhibit the nucleation and growth of other phases

one two and three phase viscosity treatments for basaltic lava flows 1 lava flows comprise three phase mixtures of melt crystals and bubbles while existing one phase treatments allow melt phase viscosity to be assessed on the basis of composition water content and or temperature two phase treatments constrain the effects of crystallinity or vesicularity on mixture viscosity however three phase treatments allowing for the effects of coexisting crystallinity and vesicularity are not well understood we investigate existing one and two phase treatments using lava flow case studies from mauna loa hawaii and mount etna italy and compare these with a three phase treatment that has not been applied previously to basaltic mixtures at etna melt viscosities of 425 30 pa s are expected for well degassed 0 1 w h2o and 135 10 pa s for less well degassed 0 4 wt h2o melt at 1080 c application of a three phase model yields mixture viscosities 45 crystals 25 35 vesicles in the range 5600 12 500 pa s this compares with a measured value for etnean lava of 9400 1500 pa s at mauna loa the three phase treatment provides a fit with the full range of field measured viscosities giving three phase mixture viscosities upon eruption of 110 140 pa s 5 crystals no bubble effect due to sheared vesicles to 850 1400 pa s 25 30 crystals 40 60 spherical vesicles the ability of the three phase treatment to characterize the full range of melt crystal bubble mixture viscosities in both settings indicates the potential of this method in characterizing basaltic lava mixture viscosity

population density and zoning of olivine phenocrysts in tholeiites from kauai hawaii the population density of olivine phenocrysts of the tholeiites display an exponential variation which is typical of igneous as well as contact metamorphic rocks the exponential variation is explained by a new growth probability model which is consistent with experimental work the forsterite content of the olivine phenocrysts decreases with decreasing size various phenocryst features suggest that the tholeiites first crystallized slowly in a magma chamber after which they underwent crystallization for a short period of time in a feeder dyke before eruption took place

the geology of the nawish quadrangle of ceres the rim of an ancient basin herein we present the geology of the nawish quadrangle located in the equatorial region of dwarf planet ceres named after one of the most prominent craters of the area geologic mapping was based on the image mosaics and digital terrain models derived from dawn framing camera data interpretation of geologic units was supported by supplemental data such as the multi spectral color images from the framing camera and the spectral parameters derived from the visible and infrared spectrometer vir data as well as dawn gravity data there is not a primary feature that dominates the geology of nawish quadrangle but rather several terrains overlap and their relations explain the geology of the area crater size frequency distributions show that nawish quadrangle is dominated by two distinct time domains the central and eastern part of the quadrangle is topographically elevated which we define as cratered highlands and contains the older domain the western lowlands show two younger domains related to impact craters kerwan and dantu including the kerwan smooth material and dantu ejecta this variation of elevation within the nawish quadrangle is more than the half of the global topographic altitude variation on ceres analysis and comparison of the topography of the nawish quadrangle with surrounding ones shows that this quadrangle is dominated by the topography of the rim sector of a large 800 km ancient impact basin most likely the putative vendimia planitia the nawish quadrangle thus represents a sector of ceres which has not undergone large scale post kerwan intermediate age events but rather represents a place on ceres where a well preserved relict of old cerean crust can be studied together with ejecta from more recent impact events

distribution of hydrogen peroxide in the northwest pacific ocean 1 hydrogen peroxide h2o2 is a reactive oxygen intermediate involved in the cycling of metals and dissolved organic matter because little is known of its distribution in the north pacific ocean we determined h2o2 in surface waters continuously and obtained vertical profiles at nine stations during a cruise from japan to hawaii surface water h2o2 varied from less than 10 to more than 250 nmol dm 3 a diel cycle in surface water h2o2 25 nmol dm 3 was observed only on one day during the monthlong cruise this is contrary to expectations based on the usual assumption of photo production as the dominant input of h2o2 experiments were also conducted during the cruise to examine both photo production and dark decay the net rate of photo production at a station near hawaii was determined to be 8 nmol dm 3 h 1 similar to rates reported for the central atlantic ocean and antarctic however this maximum estimate of photo production is also similar to probable rates of h2o2 input by other mechanisms biological production and rain the pseudo first order rate constant for dark decay varied from 0 1 to 0 2 d 1 which is toward the low end of previous reports of h2o2 decay rates and was observed to increase proportionately to the dissolved organic carbon concentration taken together these results suggest that photo production of h2o2 in open ocean waters may be less important than previously thought and therefore h2o2 is likely less of an indicator of the photo chemical reactivity of surface waters than hoped for furthermore we observed that the h2o2 inventory for the upper 200 m of the water column has a maximum at midlatitudes we suggest that this results from diminished inputs at high latitude as well as increased decay rates at low latitudes

mineralogy and temperature of crater haulani on ceres we investigate the region of crater haulani on ceres with an emphasis on mineralogy as inferred from data obtained by dawn s visible infrared mapping spectrometer vir combined with multispectral image products from the dawn framing camera fc so as to enable a clear correlation with specific geologic features haulani which is one of the youngest craters on ceres exhibits a peculiar blue visible to near infrared spectral slope and has distinct color properties as seen in multispectral composite images in this paper we investigate a number of spectral indices reflectance spectral slopes abundance of mg bearing and nh4 bearing phyllosilicates nature and abundance of carbonates which are diagnostic of the overall crater mineralogy plus a temperature map that highlights the major thermal anomaly found on ceres in addition for the first time we quantify the abundances of several spectral endmembers by using vir data obtained at the highest pixel resolution 0 1 km the overall picture we get from all these evidences in particular the abundance of na and hydrous na carbonates at specific locations confirms the young age of haulani from a mineralogical viewpoint and suggests that the dehydration of na carbonates in the anhydrous form na2co3 may be still ongoing

evidence for a north pacific deep western boundary current four current meter moorings arrayed across the japan trench near 35 n yielded 2 years of deep current velocities in the vicinity of the kuroshio where it separates from the japanese coast one and 2 year means are interpreted in the context of other observations including concurrent hydrography as well as the results of earlier investigations principal findings are as follows the presence of a persistent southward deep western boundary current 1 2 cm s 1 along the slope 2000 4000 m inshore of the japan trench a generally northward deep flow 4 cm s 1 over the trench beneath the kuroshio and southward and eastward deep flows farther southeast of the kuroshio separation these deep mean flows particularly the one inshore of the japan trench may be partly of thermohaline origin eddy driven local recirculations and bottom intensification are also likely

textural and geophysical characterization of explosive basaltic activity at villarrica volcano 1 villarrica volcano chile is one of the most active volcanoes in south america its activity is currently characterized by continuous degassing from a summit lava lake vent punctuated by explosive events during november 2004 a multidisciplinary experiment was deployed for a 10 d period to define the style of emission and infer shallow conduit dynamics at this basaltic center this involved collection of thermal seismic and infrasonic data to describe the background activity confined inside the crater and use of samples to texturally and chemically characterize the ejecta from more energetic explosions able to attain the crater rim the background activity was characterized by gas bursting with a frequency of 9 events per minute this involved emission of gas puffs fed by bubble bursting with larger bursts emplacing sheets of magma onto the lower crater walls the ejecta population from the more energetic events was characterized by the coexistence of both scoriae and golden pumice these two types of clasts have different textures but identical glass compositions suggesting that they underwent different conduit histories the golden pumice is interpreted as the expanding inner part of a short lived jet fed by a rapidly ascending magma batch the scoria forms the outer portion of the jet and comprises degassed material entrained during passage of the fresh batch through material residing in the upper most portion of the conduit we thus have a largely degassed upper column that feeds persistent bubble bursting through which fresh batches occasionally rise to feed events of relatively higher energy

geologic mapping of the ac 11 sintana quadrangle assessing diverse crater morphologies abstract a geologic map at a scale of 1 1 000 000 of the ac 11 sintana quadrangle 21 66 s and 0 90 e from the dwarf planet ceres and based on data from nasa s dawn spacecraft was produced as part of a geologic mapping campaign in order to investigate the surface structure stratigraphy composition and surface modifying processes the sintana quadrangle is geologically dominated by cratered terrain with morphologically distinct crater types the most prominent craters sintana hamori jarimba tupo annona and darzamat have complex structures including smooth crater material covering their floors collapsed crater walls forming terraces and central ridges multiple gravity driven blocky mass wasting features indicate post impact crater modification and are indicative of an ice rich subsurface in which there is no topographic or structural evidence of endogenic activity visible in the quadrangle absolute age estimates suggest that the entire surface in the quadrangle was resurfaced 1 1 ga ago possibly by kerwan related impact induced melting

glass forming ability and crystallisation behaviour of sub alkaline silicate melts abstract the intrinsic solidification behaviour and glass forming ability gfa of natural sub alkaline silicate melts have been experimentally quantified via cooling induced solidification approach gfa is measured by the critical cooling rate rc the rate at which a melt solidifies 2 area of crystals cooling rates of 9000 1800 180 60 7 and 1 c h have been run between 1300 c super liquidus region and 800 c quenching temperature at air f o 2 and ambient p for six silicate melts with compositions ranging from basalt b to rhyolite r i e b 100 b 80 r 20 b 60 r 40 b 40 r 60 b 20 r 80 and r 100 and water contents comprised between 53 b 100 and 384 b 20 r 80 ppm the ranges of cooling rates and chemical compositions used in this study are the broadest ever investigated in the earth sciences the phase proportions area were determined by image analysis on about 500 back scattered electron images collected over different magnifications phases are glass clinopyroxene cpx spinel sp and plagioclase plg sp is ubiquitous with abundance of few area and nucleates earlier than silicate crystals cpx solidifies in all runs except in r 100 and its abundance follows asymmetric broad gaussian like trends with tails towards low rates as a function of cooling rate moving from b 100 to b 40 r 60 these trends conserve their shape but shift progressively to lower cooling rates and mineral abundances plg crystallises only at low cooling rates and in sio 2 poor compositions run products with low amounts of crystals 5 area clearly show that cpx preferentially nucleates on surfaces of sp whereas a significant crystallisation of cpx 5 area is observed with decreasing cooling rate and with changing composition from b 100 to b 20 r 80 the crystallisation of silicate crystals is related to the chemical diffusivity of components in the melt also the initial crystallisation of plg occurs preferentially on cpx in general the amount of crystals decreases as the cooling rate increases however in some cases the amount of crystals remains constant or even decreases for b 80 r 20 with decreasing cooling rate rc values change over 5 orders of magnitude being 100 b 20 r 80 b 40 r 60 b 60 r 40 and b 80 r 20 and b 100 respectively the variation of rc can be modelled through nbo t nonbridging oxygen per tetrahedron parameter by the following equation rc a 1 e nbo t b c where a b and c are fitting parameters equal to 9214 0 297 and 0 040 respectively similarly to other glass forming liquids network metallic and molecular systems rc for natural sub alkaline silicate melts is inversely related to the reduced glass transition parameter trg trg tg tm and can be quantified with the equation rc a trg b where a and b are 1 19 10 4 and 28 7 respectively these results may be used to retrieve the solidification conditions of aphyric degassed and oxidised lavas in addition our data provide general constrains on the crystallisation kinetics of natural crystal bearing silicate melts erupted on earth e g lavas with phenocrysts the relationship between crystal content and cooling rate suggests that the solidification path induced by degassing can be also complex and nonlinear the growth of crystals with size up to 1 mm from a nearly anhydrous superheated silicate melt indicates that variable cooling conditions of lavas have to be accounted to discriminate among minerals formed before during and after eruptions moreover our results can be used to design glass ceramics from naturally available easy to find low cost starting materials

the feeding of the eruptive activity of etna volcano the regional stress field as a constraint to magma uprising and eruption an analysis of the structural lineaments as observed on the middle and upper slopes of etna volcano was made with the aim of checking stress distribution within the volcanic structure

near bottom currents and their relation to the transport in the kuroshio extension 1 near bottom current structure in the area of the kuroshio extension is examined using lowered adcp data obtained along 146 25 e and 152 30 e the flow of the kuroshio extension reaches the ocean floor with a shift of the current to the right with depth the near bottom currents have speeds of over 10 cm s westward deep counter currents are observed to the north and south of the near bottom kuroshio extension the eastward kuroshio extension transport is 163 sv across 146 25 e and 113 sv across 152 30 e larger than previous studies because the contribution of the barotropic flow is twice that of the geostrophic flow the downstream variation of the transport suggests the kuroshio extension strength increases after separating from the coast of japan and decreases before 152 30 e however temporal variability could also contribute to the different transport estimates

transitions between explosive and effusive eruptions of silicic magmas water rich silicic magmas may erupt explosively giving rise to massive columns of fragmented ash1 5 or effusively as viscous bubbly lavas to form lava domes6 8 complex cycles of explosive and effusive eruptions are often observed8 12 although these two eruption mechanisms have been modelled independently1 8 the conditions under which a volcano exhibits a particular style of eruption are not known and the transitions between eruption styles are poorly understood by modelling the ascent of magma along a permeable conduit we show here that for small magma chamber overpressures the style of eruption explosive or effusive is dependent on the magma flow rate we also identify a critical overpressure above which only explosive eruptions occur complex eruption sequences follow naturally for example if a shallow magmatic system is supplied with magma at an intermediate flow rate the eruption will be slow and effusive until the chamber over pressure becomes too large an explosive eruption then relieves the overpressure and an effusive eruption style resumes we suggest that monitoring of temporal variations in chamber overpressure for example by measuring ground deformation can be used to assess whether a passively effusing volcano has the potential to erupt explosively

volcanic tremor at mt etna italy preceding and accompanying the eruption of july august 2001 the july 17 august 9 2001 flank eruption of mt etna was preceded and accompanied by remarkable changes in volcanic tremor based on the records of stations belonging to the permanent seismic network deployed on the volcano we analyze amplitude and frequency content of the seismic signal we find considerable changes in the volcanic tremor which mark the transition to different styles of eruptive activity e g lava fountains phreatomagmatic activity strombolian explosions in particular the frequency content of the signal decreases from 5 hz to 3 hz at our reference station etf during episodes of lava fountains and further decreases at about 2 hz throughout phases of intense lava emission the frequency content and the ratios of the signal amplitude allow us to distinguish three seismic sources i e the peripheral dike which fed the eruption the reservoir which fed the lava fountains and the central conduit based on the analysis of the amplitude decay of the signal we highlight the migration of the dike from a depth of ca 5 km to about 1 km between july 10 and 12 after the onset of the effusive phase the distribution of the amplitude decay at our stations can be interpreted as the overall result of sources located within the first half kilometer from the surface although on a qualitative basis our findings shed some light on the complex feeding system of mt etna and integrate other volcanological and geophysical studies which tackle the problem of magma replenishment for the july august 2001 flank eruption we conclude that volcanic tremor is fundamental in monitoring mt etna not only as a marker of the different sources which act within the volcano edifice but also of the diverse styles of eruptive activity

crystal size distribution in magmatic rocks proposition of a synthetic theoretical model the crystal size distribution csd corresponds to the number of crystals of a mineral per unit volume within a series of defined size intervals many crystal size distributions in igneous systems are straight lines when plotted on the classical diagram of ln population density versus size other common csds are concave down on such graphs for the low size values the effect of growth rate on csds seems to be small and nucleation apparently increases exponentially with time although magmatic systems are always multiphase only a few csd studies deal with several phases on the basis of the few available published examples it seems that the parallelism defined as y spacing constancy of the normalized csds i e where the crystal lengths are normalized to the greatest length for each phase is a common feature in igneous systems the aim of our modelling is to propose a mathematical framework to unify the csd typology to explain the common occurrence of straight lines on the classical csd diagram and the y spacing constancy of the normalized csds for multiphase rocks and also to provide a convenient tool to easily test petrogenetic scenarios through efficient computer simulations the bulk balance modelling is based on a square matrix having for coefficients the number of nuclei of one phase by the crystallized volume of another phase this interaction matrix is the mainspring of our csd modelling which requires straightforward assumptions about the uniformity of crystal shape and growth 1 at each time every crystal of a phase has the same shape and 2 the one dimensional growth rate of a crystal is independent of its size consequently the values of the normalized csd are linked together by means of an integral equation for the most part the behaviour of the csds theoretically obtained with a constant matrix may also be observed in computer simulations of more general cases this extended approach makes feasible the application of the model to natural cases concave down shapes for the lowest size are classically interpreted as a consequence of the ending of crystallization by roughly taking into account crystal interactions during the growth process through the concept of mean clutter we successfully simulate such concave down csds

eruptive history of the late quaternary ciomadul csomad volcano east carpathians part i timing of lava dome activity located at the southern tip of the intra carpathian volcanic range in romania and composed of a dozen dacitic lava domes the ciomadul csomad volcanic complex is the youngest eruptive centre of the carpatho pannonian region whereas in the last decade the explosive history of ciomadul since 50 ka has been well constrained by numerous studies the chronology of the dome sequence still lacks robust chronological constraints and an extended analysis of all available data here we apply a detailed k ar dating approach to refine the chronology of the lava dome eruptions using the unspiked k ar cassignol gillot technique our dating focused on the most voluminous central part of the lava dome complex new eruption ages were determined following a strict separation of 10 g of groundmass from about 3 kg of unaltered sample rocks thereby isolating material whose cooling was contemporaneous with the eruption the newly applied methodology mainly consisting of a double full preparation first at larger grain size 0 4 mm and then at 100 m provides an appropriate procedure to separate suitable material to obtain the k ar age of the eruption i e the sample s groundmass in which there is no risk of the presence of older inherited crystals our new geochronological data set gives an improved insight into the temporal construction of the ciomadul volcanic complex where due to the method applied here all ages are younger than those from previous studies that used whole rock k ar ages our new results show that ciomadul s volcanic activity began with the construction of the south eastern peripheral domes from ca 850 ka to 440 ka after a ca 250 ky long repose period the activity resumed in the northern part at around 200 ka with subsequent domes emplaced between 200 and 130 ka aligned roughly north south in the western central part of the complex following a 30 ky long quiescence period the eastern central domes formed between 100 and 60 ka in addition to the chronological history of lava dome volcanism we also investigated the sequence of crystallization of mineral phases present in the lavas with respect to the modification of eruption ages ages obtained on pure minerals plagioclase amphibole and biotite are systematically older than those obtained on groundmass showing that most of them formed up to 1 85 myr before eruption in a long lived pre ciomadul magmatic system crystal size distribution csd data support the age contrasts between juvenile groundmass and older inherited minerals after injection of new magma and convective mixing with crystal clots ascent of the resulting mixture led to eruptions of material representing contrasting ages

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

resolved spectrophotometric properties of the ceres surface from dawn framing camera images we present a global spectrophotometric characterization of the ceres surface using dawn framing camera fc images we identify the photometric model that yields the best results for photometrically correcting images corrected fc images acquired on approach to ceres were assembled into global maps of albedo and color generally albedo and color variations on ceres are muted the albedo map is dominated by a large circular feature in vendimia planitia known from hst images li et al 2006 and dotted by smaller bright features mostly associated with fresh looking craters the dominant color variation over the surface is represented by the presence of blue material in and around such craters which has a negative spectral slope over the visible wavelength range when compared to average terrain we also mapped variations of the phase curve by employing an exponential photometric model a technique previously applied to asteroid vesta schroder et al 2013b the surface of ceres scatters light differently from vesta in the sense that the ejecta of several fresh looking craters may be physically smooth rather than rough high albedo blue color and physical smoothness all appear to be indicators of youth the blue color may result from the desiccation of ejected material that is similar to the phyllosilicates water ice mixtures in the experiments of poch et al 2016 the physical smoothness of some blue terrains would be consistent with an initially liquid condition perhaps as a consequence of impact melting of subsurface water ice we find red terrain positive spectral slope near ernutet crater where de sanctis et al 2017 detected organic material the spectrophotometric properties of the large vendimia planitia feature suggest it is a palimpsest consistent with the marchi et al 2016 impact basin hypothesis the central bright area in occator crater cerealia facula is the brightest on ceres with an average visual normal albedo of about 0 6 at a resolution of 1 3 km per pixel six times ceres average the albedo of fresh bright material seen inside this area in the highest resolution images 35 m per pixel is probably around unity cerealia facula has an unusually steep phase function which may be due to unresolved topography high surface roughness or large average particle size it has a strongly red spectrum whereas the neighboring less bright vinalia faculae are neutral in color we find no evidence for a diurnal ground fog type haze in occator as described by nathues et al 2015 we can neither reproduce their findings using the same images nor confirm them using higher resolution images fc images have not yet offered direct evidence for present sublimation in occator

mineralogical analysis of quadrangle ac h 10 rongo on the dwarf planet ceres abstract quadrangle ac h 10 rongo lat 22 s to 22 n lon 288 360 e shows a fairly homogeneous topography with the presence of notable elevations such as ahuna mons liberalia mons and part of samhain and uhola catenae the deepest areas correspond to the rongo crater region the areas between samhain and uhola catenae and the region of the quadrangle south of ahuna mons a substantial variability in the 2 7 m band depth distribution is observed across the rongo quadrangle indicating an east west gradient in the abundance of mg phyllosilicates the nh4 phyllosilicates distribution appears quite homogeneous except some localized regions such as crater haulani s ejecta the flanks of ahuna mons and crater begbalel the two band depths at 2 7 and 3 1 m display an overall low correlation suggesting a variable degree of mixing between mg phyllosilicates and nh4 phyllosilicates at the local scale mineralogical phases other than phyllosilicates are observed quadrangle rongo includes sodium carbonate rich regions such as the flanks of ahuna mons the ejecta of xevioso crater located in the southern edge of liberalia mons and crater begbalel which often display a reduction in both the 2 7 and 3 1 m band depths associated with an increased band depth at 4 m related to the presence of na rich carbonate phases this suggests recent hydrothermal activity in this area due to several episodes of cryovolcanism or impacts that unveiled a peculiar composition in the shallow subsurface alternatively the crust in this region might show a variable degree of compactness such that the formation of na carbonates is favored only in specific locations de sanctis et al 2016 ruesch et al 2016 zambon et al 2017 from a geological standpoint quadrangle ac h 10 rongo shows a correlation between its two main geologic units platz et al 2017 and the distribution of mg phyllosilicates suggesting a link between geology and mineralogy in this area

dione s spectral and geological properties abstract we present a detailed analysis of the variations in spectral properties across the surface of saturn s satellite dione using cassini vims data and their relationships to geological and or morphological characteristics as seen in the cassini iss images this analysis focuses on a local region on dione s anti saturnian hemisphere that was observed by vims with high spatial resolution during orbit 16 in october 2005 the results are incorporated into a global context provided by vims data acquired within cassini s first 50 orbits our results show that dione s surface is dominated by at least one global process bombardment by magnetospheric particles is consistent with the concentration of dark material and enhanced co 2 absorption on the trailing hemisphere of dione independent of the geology local regions within this terrain indicate a special kind of resurfacing that probably is related to large scale impact process in contrast the enhanced ice signature on the leading side is associated with the extended ejecta of the fresh impact crater creusa 49 n 76 w although no geologically active regions could be identified dione s tectonized regions observed with high spatial resolution partly show some clean h 2 o ice implying that tectonic processes could have continued into more recent times

distribution of icy particles across enceladus surface as derived from cassini vims measurements abstract the surface of enceladus consists almost completely of water ice as the band depths of water ice absorptions are sensitive to the size of particles absorptions can be used to map variations of icy particles across the surface the visual and infrared mapping spectrometer vims observed enceladus with a high spatial resolution during three cassini flybys in 2005 orbits en 003 en 004 and en 011 based on these data we measured the band depths of water ice absorptions at 1 04 1 25 1 5 and 2 m these band depths were compared to water ice models that represent theoretically calculated reflectance spectra for a range of particle diameters between 2 m and 1 mm the agreement between the experimental vims and model values supports the assumption that pure water ice characterizes the surface of enceladus and therefore that variations in band depth correspond to variations in water ice particle diameters our measurements show that the particle diameter of water ice increases toward younger tectonically altered surface units with the largest particles exposed in relatively fresh surface material the smallest particles were generally found in old densely cratered terrains the largest particles 0 2 mm are concentrated in the so called tiger stripes at the south pole in general the particle diameters are strongly correlated with geologic features and surface ages indicating a stratigraphic evolution of the surface that is caused by cryovolcanic resurfacing and impact gardening

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

baroclinic transport of the kuroshio extension between 141 e and 165 e using a water mass based climatology of temperature and salinity geostrophic transports derived from dynamic height differences across the width of the kuroshio extension are presented the dynamic height differences are obtained by calculating dynamic heights in the warmer water mass south of the kuroshio and the cooler water mass north of the kuroshio the mean baroclinic transport is examined between 141 e and 165 e relative to several pressure levels the baroclinic transports are sensitive to the selection of the northern and southern boundaries the baroclinic transports increase from 141 e to about 145 e and decline east of 145 e the computed seasonal variation of the longitudinally averaged baroclinic transport shows a minimum during spring and a broad maximum from july to november

mineralogy of the occator quadrangle abstract we present an analysis of the areal distribution of spectral parameters derived from the vir imaging spectrometer on board nasa dawn spacecraft specifically we studied the occator quadrangle of ceres which is bounded by latitudes 22 s to 22 n and longitudes 214 e to 288 e as part of the overall study of ceres surface composition reported in this special publication the spectral parameters used are the photometrically corrected reflectance at 1 2 m the infrared spectral slope 1 1 1 9 m and depths of the absorption bands at 2 7 m and 3 1 m that are ascribed to hydrated and ammoniated materials respectively we find an overall correlation between 2 7 m and 3 1 m band depths in agreement with ceres global behavior and band depths are shallower and the spectral slope is flatter for younger craters probably due to physical properties of regolith such as grain size spectral variations correlated with the tali geological unit also suggest differences in physical properties the deepest band indicating enrichment of ammoniated phyllosilicates are associated with ejecta generated by impacts that occurred in southern quadrangles the most peculiar region of this quadrangle is the occator crater 20 n 240 e the internal crater area contains two faculae which are the brightest areas on ceres due to exposure of sodium carbonates and by two types of ejecta dark and bright with different spectral properties probably due to different formation evolution or age

the spectral parameter maps of ceres from nasa dawn vir data abstract this article presents the spectral parameter maps used in this surface composition of ceres special issue the definition and use of spectral parameters has always played a fundamental role in understanding the properties and composition of a planetary surface mapping proper spectral parameters shows the global mineralogical diversity across ceres in this work we discuss the production process of ceres spectral parameter maps derived by the data of the visible and infrared mapping spectrometer vir onboard nasa s dawn mission we describe the data processing of the vir spectra and the procedure to retrieve the geometries latitude longitude and illumination angles of the acquired data spectra and geometries are used to project and mosaic this data to produce geographic information system compatible spectral parameters maps of ceres an overview of the variability of the data across the quadrangles is given addressing the specific analysis to each quadrangle mapping paper included in this special issue

distribution of phyllosilicates on the surface of ceres the dwarf planet ceres is known to host phyllosilicate minerals at its surface but their distribution and origin have not previously been determined we used the spectrometer onboard the dawn spacecraft to map their spatial distribution on the basis of diagnostic absorption features in the visible and near infrared spectral range 0 25 to 5 0 micrometers we found that magnesium and ammonium bearing minerals are ubiquitous across the surface variations in the strength of the absorption features are spatially correlated and indicate considerable variability in the relative abundance of the phyllosilicates although their composition is fairly uniform these data along with the distinctive spectral properties of ceres relative to other asteroids and carbonaceous meteorites indicate that the phyllosilicates were formed endogenously by a globally widespread and extensive alteration process

crystal size distribution systematics and the determination of magma storage times the 1959 eruption of kilauea volcano hawaii abstract the theory of crystal size distribution csd theory is based on a steady state population balance that monitors the flux of crystals growing into and out of specificed size categories in precipitating solutions the conservation equation describing this balance permits crystal growth and nucleation rates to be determined directly from crystal size distribution data in this investigation it is shown that csd analysis can alternatively be used to calculate the residence time of crystals in the system or in volcanologic terms the magma storage time prior to eruption if the characteristic crystal growth rate can be independently determined or estimated the crystal size data needed for storage time determinations are easily obtained from thin sections of glassy eruption samples and the mathematical calculations are relatively simple analysis of the errors inherent in this new technique predicts storage estimates accurate to within an order of magnitude

northwest africa 032 product of lunar volcanism mineralogy major element compositions of minerals and elemental and oxygen isotopic compositions of the whole rock attest to a lunar origin of the meteorite northwest africa 032 nwa 032 an unbrecciated basalt found in october 1999 the rock consists predominantly of olivine pyroxene and chromite phenocrysts set in a crystalline groundmass of feldspar pyroxene ilmenite troilite and trace metal whole rock shock veins comprise a minor but ubiquitous portion of the rock undulatory to mosaic extinction in olivine and pyroxene phenocrysts and micro faults in groundmass and phenocrysts also are attributed to shock several geochemical signatures taken together indicate unambiguously that nwa 032 originated from the moon the most diagnostic criteria include whole rock oxygen isotopic composition and ratios of fe mn in the whole rock olivine and pyroxene a lunar origin is documented further by the presence of fe metal troilite and ilmenite zoning to extremely fe rich compositions in pyroxene the ferrous oxidation state of all fe in pyroxene and the rare earth element pattern with a well defined negative europium anomaly this rock is similar in major element chemistry to basalts from apollo 12 and 15 but is enriched in light rare earth elements and has an unusually high th sm ratio some apollo 14 basalts yield a closer match to nwa 032 in rare earth element patterns but have higher concentrations of al2o3 ar ar step release results are complex but yield a whole rock age of ca 2 8 ga suggesting that nwa 032 was extruded at 2 8 ga or earlier this rock may be the youngest sample of mare basalt collected to date noble gas concentrations combined with previously collected radionuclide data indicate that the meteorite exposure history is distinct from currently recognized lunar meteorites in short the geochemical and petrographic features of nwa 032 are not matched by apollo or luna samples nor by previously identified lunar meteorites indicating that it originates from a previously unsampled mare deposit detailed assessment of petrographic features olivine zoning and thermodynamic modelling indicate a relatively simple cooling and crystallization history for nwa 032 chromite spinel olivine and pyroxene crystallized as phenocrysts while the magma cooled no faster than 2 c hr based on the polyhedral morphology of olivine comparison of olivine size with crystal growth rates and preserved fe mg diffusion profiles in olivine phenocrysts suggest that olivine was immersed in the melt for no more than 40 days plumose textures in groundmass pyroxene feldspar and ilmenite and fe rich rims on the phenocrysts formed during rapid crystallization cooling rates 20 to 60 c hr after eruption

timing of optical maturation of recently exposed material on ceres on ceres multispectral imaging data from the dawn spacecraft show a distinct bluish characteristic for recently exposed material from the subsurface in for example crater ejecta ejecta blankets of presumably old craters show a more reddish spectrum we selected areas in which fresh material from the cerean subsurface was exposed at a specific time in the past and no later geologic process is expected to have changed its surface composition or its cratering record for each area we determined two color ratios and the crater retention age the measured color ratios show an exponential diminishment of the bluish characteristic over time although the cause of the color change remains uncertain the time dependent change in spectral properties is evident which could help identify the process

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

the formation and evolution of bright spots on ceres the otherwise homogeneous surface of ceres is dotted with hundreds of anomalously bright predominantly carbonate bearing areas termed faculae with bond albedos ranging from 0 02 to 0 5 here we classify and map faculae globally to characterize their geological setting assess potential mechanisms for their formation and destruction and gain insight into the processes affecting the ceres surface and near surface faculae were found to occur in four distinct geological settings associated predominantly with impact craters 1 crater pits peaks or floor fractures floor faculae 2 crater rims or walls rim wall faculae 3 bright ejecta blankets and 4 the mountain ahuna mons floor faculae were identified in eight large deep and geologically young asteroid derived model adm ages of 420 60 ma craters occator haulani dantu ikapati urvara gaue ernutet and azacca the geometry and geomorphic features of the eight craters with floor faculae are consistent with facula formation via impact induced heating and upwelling of volatile rich materials upwelling excavation of heterogeneously distributed subsurface brines or their precipitation products or a combination of both processes rim wall faculae and bright ejecta occur in and around hundreds of relatively young craters of all sizes and the geometry of exposures is consistent with facula formation via the excavation of subsurface bright material possibly from floor faculae that were previously emplaced and buried a negative correlation between rim wall facula albedo and crater age indicates that faculae darken over time models using the ceres crater production function suggest initial production or exposure of faculae by large impacts subsequent dissemination of facula materials to form additional small faculae and then burial by impact induced lateral mixing which destroys faculae over timescales of less than 1 25 gyr cumulatively these models and the observation of faculae limited to geologically young craters indicate relatively modern formation or exposure of faculae indicating that ceres surface remains active and that the near surface may support brines in the present day

cryogenic flow features on ceres implications for crater related cryovolcanism craters on ceres such as haulani kupalo ikapati and occator show postimpact modification by the deposition of extended plains material with pits multiple lobate flows and widely dispersed deposits that form a diffuse veneer on the preexisting surface bright material units in these features have a negative spectral slope in the visible range making it appear bluish with respect to the grey toned overall surface of ceres we calculate the drop height to runout length ratio of several flow features and obtain a coefficient of friction of 0 1 the results imply higher flow efficiency for flow features on ceres than for similar features on other planetary bodies with similar gravity suggesting low viscosity material the special association of flow features with impact craters could either point to an impact melt origin or to an exogenic triggering of cryovolcanic processes