basaltic magma reservoirs factors controlling their rupture characteristics and evolution the manner in which magma enters and leaves a magma reservoir is a fundamental aspect of magmatic activity a quantitative model is developed to evaluate the variation of stress acting on the wall of a magma reservoir as a function of depth factors assessed include the size of the reservoir its depth of burial the strength of the country rocks and the variation with depth of the densities of the magma and country rocks it is shown that small magma reservoirs with halfheights less than 1 km centered at levels of neutral buoyancy can grow in all directions with nearly equal ease by injecting dikes into their surroundings at the sites of wall ruptures in larger reservoirs with half heights greater than 2 km however the stress required to cause wall failure is much less at the depth corresponding to the center of the reservoir than it is near the top or bottom thus larger reservoirs are likely to grow predominantly sideways by lateral dike injection in these cases vertical growth will not be important unless significant accumulation of low density material can occur in the upper part of the reservoir the formation of a low density layer due to gas exsolution or chemical differentiation of the magma can facilitate failure of the roof and upward dike migration from a mature reservoir as the reservoir grows and evolves through time the increasing magma pressure head at the depth corresponding to the center of the reservoir means that the amount of gas exsolution or chemical differentiation required to allow the occurrence of vertical dike emplacement also increases ultimately a vertical reservoir size is reached beyond which the excess stress required to cause lateral dike injection is so much less than that required to cause vertical injection that essentially no further vertical growth of the reservoir will occur the reservoir will thus develop a more laterally elongate shape with time the final aspect ratio will then depend mainly on the supply rate of magma to the reservoir from the mantle

degassing processes at stromboli volcano inferred from short lived disequilibria 210 pb 210 bi 210 po in volcanic gases abstract volcanic aerosols and gases released by three active craters at stromboli volcano have been regularly collected since 1985 in this paper we present new evidence of the high volatility of some nuclides among radon daughters 210pb 210bi and 210po which are strongly fractionated leading to significant radioactive disequilibria in volcanic exhalations the very low volcanic activity in october 1996 allowed a separate sampling of each crater plume for the first time remote sampling of the bulk plume were also performed these data show that the chemical composition of volcanic aerosols remains constant within the first few hundred meters from their source vents ensuring the validity of remote sampling when the activity does not allow one to approach the active craters moreover it appears that there is no differentiation of gases from one crater to another suggesting that the geometry of the upper plumbing system of the volcano is rather simple gases being directly emitted from a shallow magma chamber without significant cooling inside the edifice on the basis of the assumption of a continuously replenished shallow magma reservoir in steady state we propose a dynamic model of degassing accounting for the variations of radionuclide contents and ratios observed in the gas phase since 1985 this model allows us to relate these variations to changes in the magma chamber dynamics namely the magma residence time inside the chamber and the escape time of gases from it both parameters being closely linked to the volcanic activity while gases are always emitted within a few hours after bubble nucleation suggesting that the chamber is no deeper than a few hundred meters magma residence time varies from less than 20 days during eruptive periods highly explosive or effusive periods to more than 200 days before the 1985 eruption the latter figure is explained by the storage at shallow depth of a poorly renewed magma batch that fed the eruption the variations of the residence time observed over the studied period suggest that the steady state dynamics of the stromboli magma chamber is sustained for rather short periods of a few months at most on basis of the knowledge of the deep undegassed magma supply and the magma residence time we estimate the volume of the shallow magma chamber at about 7 2 10 5 m 3 the good agreement of our results with previous estimates based on both geochemical and geophysical studies suggests that the measurement of radioactive disequilibria in the gas phase provides a robust tool for a deeper understanding of the volcanic activity and the magma dynamics beneath active volcanoes

martian surface simulations computer generated surfaces have been created to aid in imaging landing and rover studies for mars and the moon they are also being applied to the study of cratering histories the surfaces are generated in steps which attempt to mimic geologic episodes surface roughness is realized fractally while craters and other specific features have shapes and distributions dictated by observation surface materials are assigned appropriate albedos making the images more realistic with the inclusion of correlations between crater and rock distributions the simulations are beginning to acquire a predictive capability

trace element degassing and enrichment in the eruptive plume of the 2000 eruption of hekla volcano iceland during its last eruption in february 2000 hekla volcano iceland emitted a sub plinian plume that was condensed and scavenged down to the ground by heavy snowstorms offering the unique opportunity to study the chemistry of the gaseous plume released during highly explosive eruptions in this paper we present results on trace element and minor volatile species sulfates chlorides and fluorides concentrations in snow samples collected shortly after the beginning of the eruption the goal of this study is to better constrain the degassing and mobility of trace elements in gaseous emissions trace element volatility at hekla is quantified by means of enrichment factors ef relative to be well known volatile trace elements e g transition metals heavy metals and metalloids are considerably enriched in the volcanic plume of hekla their abundances are governed by the primary magmatic degassing of sulfate and or halide compounds which are gaseous at magmatic temperature their volatility is however slightly lower than in basaltic systems most likely because of the lower magma temperature and higher magma viscosity at hekla more surprisingly refractory elements e g ree th ba and y are also significantly enriched in the eruptive plume of hekla where their apparent volatility is two orders of magnitude higher than in mafic systems in addition ree patterns normalized to the hekla 2000 lava composition show a significant enrichment of hree over lree suggesting the presence of ree fluorides in the volcanic plume such enrichments in the most refractory elements and ree fractionation are difficult to reconcile with primary degassing processes since ree fluorides are not gaseous at magma temperature ree enrichments at hekla could be attributed to incongruent dissolution of tephra grains at low temperature by f rich volcanic gases and aerosols within the eruptive plume this view is supported by both leaching experiments performed on hekla tephra and thermodynamic considerations on ree mobility in hydrothermal fluids and modeling of glass dissolution in f rich aqueous solutions tephra dissolution may also explain the observed enrichments in other refractory elements e g th y and ba and could contribute to the degassing mass balance of some volatile trace elements provided they are mobile in f rich fluids it thus appears that both primary magmatic degassing and secondary tephra dissolution processes govern the chemistry of eruptive plumes released during explosive eruptions

experimental study of bubble growth in stromboli basalt melts at 1 atm abstract volcanic eruptions are characterized by intense degassing thus it is imperative to have high quality laboratory data to constrain degassing mechanisms in order to investigate bubble formation and growth at 1 atm degassing experiments using a stromboli basalt were performed on the gsecars x ray beamline at the advanced photon source volatile bearing glasses were synthesized at 1250 c and 1000 mpa in a piston cylinder with h 2 o or mixtures of h 2 o co 2 they were then heated in situ on the x ray beamline at 1 atm bubble growth was observed in situ using x ray radiography the 3d bubble size distributions in the quenched samples and a natural stromboli pumice were studied by synchrotron x ray microtomography the results show that bubble nucleation and growth in basaltic melts are volatile concentration dependent bubbles can easily form in melts initially containing high volatile concentrations the effect of co 2 on bubble nucleation and growth becomes significant at large co 2 concentrations of 880 to 1480 ppm but is not important at lower concentrations multiple nucleation events occur in most of these degassing experiments and they are more pronounced in more supersaturated melts bubble growth is controlled by viscosity near glass transition temperatures and by diffusion at higher temperatures bubbles begin to pop 10 to 20 s after a foam is developed at vesicularities of 65 to 83 bubble size distributions follow power law relations at vesicularities of 1 to 65 and bubble size distributions evolve from power law relations to exponential relations at vesicularities of 65 to 83 this evolution is associated with the change from far from equilibrium degassing to near equilibrium degassing during far from equilibrium degassing multiple nucleation events are pronounced and possibly account for the generation of power law relations when the system reaches near equilibrium degassing coalescence is dominant and leads to the formation of bubbles of similar size therefore bubble size distributions are described by exponential relations

bubble coalescence in basaltic lava its impact on the evolution of bubble populations morphological properties bubble number density porosity mean radius specific surface area of vesicular rocks provide quantitative information on the rates of bubble nucleation growth and coalescence in magmas when measured as a function of time such data are useful in constraining the timing and style of gas release during volcanic eruptions volcanic rocks commonly show strong zonation with respect to bubble size and porosity indicating a variation in the amount of bubble growth and coalescence preserved within a single sample morphological properties and bubble size distributions bsd s were measured in a suite of zoned alkali basalts using image analysis and the data were compared to theoretical predictions our data indicate that at porosities greater than 35 extensive coalescence occurred during the growth of bubbles with restricted nucleation at lower porosities vesiculation is dominated by nucleation and diffusion with no coalescence the interiors of many of our samples have undergone 4 7 binary coalescence events after eruption in a time of around 15 min the ostwald ripening effect has not significantly modified the bsd s

relationship between gases and volcanic activity of mount etna in 1986 the long lived 222rn decay products 210pb 210bi and 210po have been monitored in the plumes of several vents at mount etna sicily from may to october 1986 the results show that the four main craters of this volcano emit gases whose compositions are different from each other the 210bi 210pb ratios for the plumes have similar mean values close to 25 which correspond to a degassing time of 1 5 to 2 7 days according to the model of lambert et al 1985 86 in contrast 210po 210pb ratios have very different mean values in each plume 35 at the voragine crater 20 at the bocca nuova crater and 14 at the south east crater these figures enable us to calculate proportions of deep magma of 50 29 and 19 in the degassing cells of these craters respectively moreover the se crater appears to be a secondary degassing vent not directly related to the main magma reservoir the evolution of these ratios has been related to variations in volcanic activity

spongy pahoehoe in hawaii a study of vesicle distribution patterns in basalt and their significance a well defined pahoehoe lava type that is very common medially and distally in hawaii is characterized by a high concentration and fairly uniform distribution of spherical or near spherical vesicles measurements of vesicle sizes and concentrations have been made on ten of these spongy pahoehoe lava flow units the vesicles increase in size toward the middle accompanied by a moderate increase in lava porosity the close approach to bilateral symmetry on either side of the horizontal median plane and the common occurrence of a median gas blister shows that no significant upward movement of vesicles occurred suggesting that the lava possessed a yield strength and was more or less static olivine phenocrysts when present are however concentrated in the lower half of the same flow units showing that the lava previously lacked a significant yield strength the vesicles are regarded as early inherited from the vent but the size characteristics of the vesicle population are a late formed feature vesicles grew in static lava mostly by coalescence and it is postulated that coalescence was promoted by the presence of abundant diktytaxitic voids which punctured the walls of contiguous vesicles zones in which the vesicle concentration is lower and the vesicles are larger and strongly deformed interrupt the symmetry of some spongy pahoehoe units and gas blisters higher than the median plane occur in many examples these zones are interpreted to result from late stage shearing and point to a mechanism by which vesicles may be eliminated from a lava

bubble coalescence in basalt flows comparison of a numerical model with natural examples gas accumulation in magma may be aided by coalescence of bubbles because large coalesced bubbles rise faster than small bubbles the observed size distribution of gas bubbles vesicles in lava flows supports the concept of post eruptive coalescence a numerical model predicts the effects of rise and coalescence consistent with observed features the model uses given values for flow thickness viscosity volume percentage of gas bubbles and an initial size distribution of bubbles together with a gravitational collection kernel to numerically integrate the stochastic collection equation and thereby compute a new size spectrum of bubbles after each time increment of conductive cooling of the flow bubbles rise and coalesce within a fluid interior sandwiched between fronts of solidification that advance inward with time from top and bottom bubbles that are overtaken by the solidification fronts cease to migrate the model predicts the formation of upper and lower vesicle rich zones separated by a vesicle poor interior the upper zone is broader more vesicular and has larger bubbles than the lower zone basaltic lava flows in northern california exhibit the predicted zonation of vesicularity and size distribution of vesicles as determined by an impregnation technique in particular the size distribution at the tops and bottoms of flows is essentially the same as the initial distribution reflecting the rapid initial solidification at the bases and tops of the flows many large vesicles are present in the upper vesicular zones consistent with expected formation as a result of bubble coalescence during solidification of the lava flows both the rocks and model show a bimodal or trimodal size distribution for the upper vesicular zone this polymodality is explained by preferential coalescence of larger bubbles with subequal sizes vesicularity and vesicle size distribution are sensitive to atmospheric pressure because bubbles expand as they decompress during rise through the flow the ratio of vesicularity in the upper to that in the lower part of a flow therefore depends not only on bubble rise and coalescence but also on flow thickness and atmospheric pressure application of simple theory to the natural basalts suggests solidification of the basalts at 1 0 0 2 atm consistent with the present atmospheric pressure paleobathymetry and paleoaltimetry are possible in view of the sensitivity of vesicle size distributions to atmospheric pressure thus vesicular lava flows can be used to crudely estimate ancient elevations and or sea level air pressure

remote sensing studies of the lomonosov fleming region of the moon 1 lomonosov fleming is a 620 km pre nectarian impact basin centered at 19 n 105 e clementine multispectral images and a variety of spacecraft photographs were used to investigate the composition and origin of geologic units in the region mare basalt deposits in the lomonosov fleming region are small and exhibit varying degrees of highlands contamination four previously unrecognized dark mantle deposits of probable pyroclastic origin were identified and mapped a major expanse of cryptomare was mapped in and around the lomonosov fleming basin spectral and chemical data obtained for dark haloed craters dhc established that these impact craters excavated mare basalt from beneath higher albedo highlands rich surface units the buried basalts exposed by dhcs in the region exhibit a variety of compositions which range from very low titanium basalt to intermediate tio2 mare basalt nectarian aged units with subjacent cryptomare are much more extensive than imbrian aged deposits with underlying basalt at least some of the buried mare basalts in the region may have been emplaced during pre nectarian time while both impact basins and craters played a role in cryptomare formation by transporting highlands material to mare surfaces the evidence indicates that most of the cryptomare inside the basin are of the distal basin ejecta type the enhanced feo and tio2 abundances exhibited by these cryptomare surfaces usually light plains units demonstrate that ballistic erosion and sedimentation played an important role in their formation

resolved hapke parameter maps of the moon we derived spatially resolved near global hapke photometric parameter maps of the moon from 21 months of lunar reconnaissance orbiter camera lroc wide angle camera wac multispectral observations using a novel tile by tile method 1 latitude by 1 longitude bins the derived six parameters w b c bs0 hs and p for each tile were used to normalize the observed reflectance standard angles i g 60 e 0 instead of the traditional angles i g 30 e 0 within each tile resulting in accurate normalization optimized for the local photometric response each pixel in the seven color near global mosaic 70 s to 70 n and 0 e to 360 e was computed by the median of normalized reflectance from large numbers of repeated observations uv 50 and visible 126 on average the derived mosaic exhibits no significant artifacts with latitude or along the tile boundaries demonstrating the quality of the normalization procedure the derived hapke parameter maps reveal regional photometric response variations across the lunar surface the b c henyey greenstein double lobed phase function parameters maps demonstrate decreased backscattering in the maria relative to the highlands except 321 nm band probably due to the higher content of both smfe submicron iron and ilmenite in the interiors of back scattering agglutinates in the maria the hs angular width of shadow hiding opposition effect map exhibits relatively lower values in the maria than the highlands and slightly higher values for immature highland crater ejecta possibly related to the variation in a grain size distribution of regolith

first microwave map of the moon with chang e 1 data the role of local time in global imaging abstract among recent lunar orbiters only the chinese chang e 1 ce 1 was equipped with a passive microwave radiometer mrm to measure the natural microwave emission from the lunar surface the microwave emission characterized by a frequency dependent brightness temperature tb is related to the physical temperature and dielectric properties of the lunar surface by measuring the brightness temperature at different frequencies detailed thermal behavior and properties of the lunar surface can be retrieved using ce 1 s microwave data we present here a set of microwave maps of the moon constructed through a rescaling of tb to noontime or midnight the adopted processing technique helps to reduce the effect of mixing up the temporal and spatial variations introduced by the satellite s localized measurements which cover different locations of the globe at different lunar local times the resulting maps show fine structures unseen in previous microwave maps that disregarded the local time effect we discussed the new features revealed and their possible connections with the lunar geology

explosive volcanic eruptions ix the transition between hawaiian style lava fountaining and strombolian explosive activity the commonest eruption styles of basaltic volcanoes involve hawaiian lava fountaining or intermittent strombolian explosions we investigate the ways in which magma rise speed at depth magma volatile content and magma viscosity control which of these eruption styles takes place we develop a model of the degree of coalescence between gas bubbles in the magma which allows us to simulate the transition between the two extreme styles of activity we find that magma rise speed is the most important factor causing the transition with gas content and viscosity also influencing the rise speed at which the transition occurs counter to intuitive expectations a decrease in gas content does not cause a transition from hawaiian to strombolian activity but instead causes a transition to passive effusion of vesicular lava rather a change from hawaiian to strombolian style requires a significant reduction in magma rise speed

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

ages and stratigraphy of mare basalts in oceanus procellarum mare nubium mare cognitum and mare insularum accurate estimates of mare basalt ages are necessary to place constraints on the duration and the flux of lunar volcanism as well as on the petrogenesis of lunar mare basalts and their relationship to the thermal evolution of the moon we performed new crater size frequency distribution measurements in order to investigate the stratigraphy of mare basalts in oceanus procellarum and related regions such as mare nubium mare cognitum and mare insularum we used high resolution clementine color data to define 86 spectrally homogeneous units within these basins which were then dated with crater counts on lunar orbiter iv images our crater size frequency distribution measurements define mineralogical and spectral surface units and offer significant improvements in accuracy over previous analyses our data show that volcanism in the investigated region was active over a long period of time from 3 93 to 1 2 b y a total of 2 7 b y volumetrically most of the basalts erupted in the late imbrian period between 3 3 and 3 7 b y and we see evidence that numerous units have been resurfaced during the eratosthenian period significantly less basalt was erupted depending on the absolute model ages that one can assign to the lunar chronostratigraphic systems five units might be of copernican age younger basalts are generally exposed in the center of the investigated area that is closer to the volcanic centers of the aristarchus plateau and marius hills older basalts occur preferentially along the northwestern margin of oceanus procellarum and in the southeastern regions of the studied area i e in mare cognitum and mare nubium combining the new data with our previously measured ages for basalts in mare imbrium serenitatis tranquillitatis humorum australe and humboldtianum we find that the period of active volcanism on the moon lasted 2 8 b y from 4 b y to 1 2 b y on the basis of the basalts dated so far which do not yet include the potentially young basalts of mare smythii e g schultz and spudis 1983 we conclude that oceanus procellarum not only exhibits the widest range of ages of all investigated basins but probably also is the location of some of the youngest basalts on the lunar surface

in situ degassing study on crystal bearing stromboli basaltic magmas implications for stromboli explosions 1 three dimensional crystal and bubble sizes and distributions in experimentally produced vesicular crystal bearing stromboli basalts and natural scoria were studied with x ray microtomography ct at high 1 85 m and low 5 46 9 0 m resolution the permeabilities from lattice boltzmann lb simulations and experimental measurements are about 1 2 orders of magnitude higher than in aphyric stromboli basalts at porosity 31 6 55 3 we propose that the higher permeability in crystal bearing samples results in highly efficient degassing in shallow highly porphyritc hp magma as opposed to the deeper aphyric lp magma in paroxysmal explosions the lp magma flows up in a cylindrical conduit due to the density and viscosity difference between the two magmas this type of convection can cause the lp magma with exsolved gas to be efficiently transferred through the overlying hp magma potentially resulting in the more violent paroxysmal explosions

volcanic and impact deposits of the moon s aristarchus plateau a new view from earth based radar images lunar pyroclastic deposits reflect an explosive stage of the basaltic volcanism that filled impact basins across the nearside these fine grained mantling layers are of interest for their association with early mare volcanic processes and as possible sources of volatiles and other species for lunar outposts we present earth based radar images at 12 6 and 70 cm wavelengths of the pyroclastic deposit that blankets the aristarchus plateau the 70 cm data reveal the outlines of a lava flow complex that covers a significant portion of the plateau and appears to have formed by spillover of magma from the large sinuous rille vallis schroteri the pyroclastics mantling these flows are heavily contaminated with rocks 10 cm and larger in diameter the 12 6 cm data confirm that other areas are mantled by 20 m or less of material and that there are numerous patches of 2 cm and larger rocks associated with ejecta from aristarchus crater some of the radar detected rocky debris is within the mantling material and is not evident in visible wavelength images the radar data identify thick rock poor areas of the pyroclastic deposit best suited for resource exploitation

radioactive isotopes and trace elements in gaseous emissions from white island new zealand abstract measurements of the radioactivity of gases released by white island volcano show variations in 210 po concentrations with temperature in fumarolic gases and this is interpreted to be due to dilution of magmatic gases with vapours derived from an envelope of acid brines surrounding the vent system the degassing model derived for mount etna emissions is tested on white island magmatic gases the results are a short degassing time 2 days small degassing magma volume 5 10 6 m 3 and the following estimations of emanation coefficients pb 1 bi 2 7 cd 0 05 and cu 0 07 the initial content of s in the magma is estimated to be within the range 300 600 mg kg fluxes of trace metals kg day emitted by the volcano are estimated to be pb 125 bi 6 cu 300 and cd 9

brightness temperature calculation of lunar crater interpretation of topographic effect on microwave data from chang e in order to quantitatively interpret topographic effect on chang e ce microwave data a detailed method to compute brightness temperature tb over a lunar crater is proposed which incorporated the effect of surface tilts the method improves the effective solar irradiance model of the lunar surface to obtain the temperature profile of the lunar crater the calculated tb at 37 ghz with the proposed computation method which is based on three digital elevation models dems from different sources are consistent with the observed tb from the ce 2 microwave radiometer the simulated behavior of tb across crater hercules reproduces the tb undulation observed by ce in a single swath tb is significantly affected by the lunar dust of a lunar crater and affected by albedo and emissivity in a lesser degree based on the explanation with simplified models the tb variation over a crater is proved to be significantly affected through physical temperature by the crater shape described by dems with the simplified crater model the amplitude of the tb oscillatory curves is proved to depend on the crater shape

h2o and halogen f cl br behaviour during shallow magma degassing processes abstract degassing paths of silicic h2o rich magmas during explosive plinian and dome forming eruptions may be represented in simple evolution diagrams relating the residual volatile content of the melt to the volume ratio of gas over melt vg vl these parameters are measurable in erupted magma fragments they are used for interpreting the h2o and halogen contents determined in a series of variously degassed volcanic clasts from the 650 y b p eruption at mt pelee martinique fwi which is characterized by the succession of a dome extrusion and a plinian activity h2o degassing of plinian pumice clasts are modeled by an equilibrium closed system evolution which allows to calculate the partition coefficients of halogen between the aqueous fluid and the rhyolitic melt d v l i 1 for f 10 1 5 for cl and 3 7 1 for br at around 900 c the strong increase of the dv li values of cl and br during dome extrusion is explained by an open system degassing model with a simultaneous crystallization of the melt some significant br enrichments relative to cl in dome fragments are attributed to interactions with an hydrothermal fluid close to seawater in composition the models allow calculation of cl and br contents of aqueous fluids generated by the different degassing paths cl contents are 0 5 mol l for closed system evolution and vary between 0 2 and 1 mol l during open system evolutions these fluids are able to extract significant amounts of chloride complexed metals and silica from the magma during dome forming eruptions they also may generate mineralization of the wall rocks or the rising dome itself e g silica precipitation which may seal the volcanic system and be responsible for the dome explosivity and the transition from dome forming to plinian eruptive style the cl br ratio of initial melts of p1 eruption 250 is much lower than the basaltic and exospheric ratios 400 suggesting that strong cl br fractionation may occur during the production or the differentiation of subduction related magmas

magma budgets and steady state activity of vulcano and stromboli we present three models for magma budget during steady state volcanic activity by which non erupted magma is emplaced as dykes or cumulates or crystallises in place using gas and thermal data we apply our models at vulcano to calculate degassing cooling and crystallisation of magma at a rate of 40 375 kg s 1 within a magma body with an upper surface at a 2 km depth at stromboli we calculate a steady magma supply of 300 1300 kg s 1 to shallow 1 km depths

interactions between bubbles in magmas and lavas effects of bubble deformation the interactions between two deformable bubbles are studied in order to determine the effects of deformation on bubble dynamics and to determine the limits in which the effects of deformation can be ignored deformation due to hydrodynamic interactions with other bubbles leads to alignment of horizontally offset bubbles and thus an enhanced rate of coalescence bubble alignment may produce spatial inhomogeneities in bubble concentrations in magmas which implies temporal variations in the concentration and size of bubbles in erupting magmas and spatial variations in solidified lavas an approximate quantitative model for the rate of coalescence of deformable bubbles is developed based on a series of experiments the effects of deformation can be ignored if the largest bubbles have radii less than about 5 mm in silicate magmas

remote sensing and geologic studies of the balmer kapteyn region of the moon 1 the balmer kapteyn b k region is located just east of mare fecunditatis on the east limb of the moon it is centered on the balmer kapteyn basin a pre nectarian impact structure that exhibits two rings approximately 225 km and 450 km in diameter clementine multispectral images and lunar prospector lp gamma ray spectrometer grs data were used to investigate the composition age and origin of geologic units in the region a major expanse of cryptomare was mapped within the b k basin spectral and chemical data obtained for dark haloed craters dhcs established that these impact craters excavated mare basalt from beneath higher albedo highland rich surface units the buried basalts exposed by dhcs in the region are dominated by low titanium mare basalts the fresh dhc feo values 15 0 15 7 wt that best represent those of buried mare basalts are well within the range of values exhibited by high alumina mare basalts while most cryptomare deposits occur beneath surfaces that range in age from imbrian to nectarian it is possible that some mare flows were emplaced during pre nectarian time most cryptomare deposits in the b k region were formed by the contamination of mare surfaces by highland rich distal ejecta from surrounding impact craters these balmer type cryptomare deposits are usually associated with light plains units major lp grs feo enhancements are associated with cryptomaria in the balmer kapteyn lomonosov fleming schiller schickard and mendel rydberg regions

effusion rate trends at etna and krafla and their implications for eruptive mechanisms abstract using effusion rates obtained from ground and satellite based data we build a data set of 381 effusion rate measurements during effusive activity at etna and krafla between 1980 and 1999 this allows us to construct detailed effusion rate curves for six fissure fed eruptions at etna and krafla and four summit fed eruptions at etna these define two trends type i and ii type i trends have effusion rates that rise rapidly to an initial peak before declining more slowly resulting in an exponential decrease in eruption rate and declining growth in cumulative volume type ii trends are characterised by steady effusion and eruption rates and hence a linear increase in cumulative volume the former is typical of fissure eruptions and can be explained by tapping of an enclosed pressurised system the latter are typical of persistent etnean summit eruptions plus one persistent effusive eruption at stromboli 1985 1986 examined here and can be explained by overflow of the time averaged magma supply we use our effusion rate data to assess the magma balance at etna 1980 1995 and krafla 1975 1984 between 1980 and 1995 etna was supplied at a time averaged rate of 6 8 2 3 m 3 s 1 of which 13 was erupted at krafla 817 30 10 6 m 3 was erupted and intruded during 1975 1984 and the ratio of erupted to intruded volume was 0 3 at etna there is evidence for intrusion of the unerupted magma within and beneath the edifice as well as storage in the central magma column at krafla unerupted magma was intruded into a rift zone but an increasing proportion of the supply was erupted from 1980 onwards a result of the rift zone capacity being reached magma intruded prior to an eruptive event may also be entrained and or pushed out during eruption to contribute to the initial high effusion rate phases of type i events the detail in our effusion rate curves was only possible using a thermal approach which estimates effusion rates using satellite data we look forward to analysing satellite derived effusion rate trends in real time using data from current and soon to be launched sensors

vesiculation of basaltic magma during eruption vesicle size distributions in vent lavas from the pu9u9o9o kupaianaha eruption of kilauea volcano are used to estimate nucleation and growth rates of h 2 o rich gas bubbles in basaltic magma nearing the earth9s surface 120 m depth by using well constrained estimates for the depth of volatile exsolution and magma ascent rate nucleation rates of 35 9 events cm 3 s 1 and growth rates of 3 2 x 10 4 cm s are determined directly from size distribution data the results are consistent with diffusion controlled growth as predicted by a parabolic growth law this empirical approach is not subject to the limitations inherent in classical nucleation and growth theory and provides the first direct measurement of vesiculation kinetics in natural settings in addition perturbations in the measured size distributions are used to examine bubble escape accumulation and coalescence prior to the eruption of magma

gas transport model for the magmatic system at mount pinatubo philippines insights from 210pb 226ra abstract measurements of 226ra 210pb disequilibria in eruptive products have the potential to track the accumulation or loss of volatiles in magmatic systems on timescales of decades because the intermediate nuclide 222rn follows the gas phase we present measurements of 210pb 226ra disequilibria for whole rock samples representing a time sequence of tephra through the june 15 1991 cataclysmic eruption of mount pinatubo volcano philippines mount pinatubo volcano is a dacitic system that did not significantly vent gases at the surface prior to eruption and we can therefore isolate the 210pb 226ra disequilibria due to gas accumulation without complications due to 222rn loss during degassing pyroclastic samples have 210pb 226ra 0 ranging from 1 01 to 1 10 averaging 1 06 a sample of the post climactic dome has 210pb 226ra 0 1 12 previous uranium series degassing studies have suggested that 210pb excesses are created by rapid volatile transport carrying the intermediate daughter 222rn and subsequent volatile accumulation and decay of 222rn to 210pb however bubbles in viscous dacite magma cannot rise at speeds needed to provide a flux of 222rn large enough to cause measurable disequilibria in the 210pb 226ra system in addition there is little evidence for magmatic sources large enough to supply a rapid flux of 222rn therefore we present a model in which 210pb 226ra disequilibria is established during basaltic recharge of the pinatubo reservoir the relatively low viscosity of basaltic magma allows for differential gas motion and the production of 210pb excess in localized basaltic melt transport of volatiles and 210pb rich basalt through a crystal matrix and the formation of bubble plumes in the dacitic reservoir produces a mixed magma with 210pb excess through this mechanism the timescale of gas transport and accumulation is constrained not by the half life of 222rn 3 8 days but rather by the half life of 210pb 22 6 years bubble plume motion preserves disequilibria and creates a zone of eruptable dacite with 210pb excess alleviating the need for gas transport on very short time scales using the rate of decay of 210pb coupled with published trace element data we present a quantitative investigation of this new conceptual model and propose that changes in 210pb values with time may suggest changing conditions of magma supply at volcanoes

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

formation of propagation pattern in two phase flow systems with application to volcanic eruptions summary the hydrodynamic behaviour of a two phase system with different densities and viscosities is investigated assuming that both phases are continuous phases and incompressible and that no phase change occurs mass and momentum conservation equations describe the relative motion of the two phases under the gravitational force when the inertia term is not negligible using the derived equations the stability of a spatially constant structure along gravity is examined in the one dimensional case for an infinite system without boundaries where the basic state is taken as constant velocity and volume fractions two special cases are considered the first is a gas liquid system where the density of one of the phases is neglected the second is a deformable solid liquid system where the densities of the two phases are taken to be the same except for the calculation of the buoyancy force the linear stability analysis shows that a small perturbation always generates a propagating wave which grows unstably with a characteristic wavelength since the spatially uniform structure of a two phase system is always unstable the growth pattern should be observed in nature if the growth rate and spatial scale of the system are suitable the dependence of the wavelength and growth rate on parameters is divided intc two regimes in one regime the wavelength which equals the compaction length and growth rate depend on the typical pore size in the other regime on the other hand they do not depend on the typical pore size but only on the kinematic viscosity of the liquid phase and the volume fraction given the frictional law which regime a real system chooses depends on a nondimensional parameter the first case gas liquid system is applied to magma effusion in an eruption style volcano the system consisting of a silicate liquid phase and a gas phase can have a wavelength from metres to tens of metres and a growth rate from the order of less than a second to 1 week depending on viscosities typical pore size and volume fraction as a result the rhythm and discreteness of magma effusion observed at volcanic eruptions may be explained by the mechanism presented here the theory provides a relation between the observed period of the magma effusion rate the mixture exit velocity of gas plus magma and the volume fraction of magma given the frictional law using the relation the mixture exit velocity is estimated from the observed period for the 1986 izu oshima eruption the applicability to partially molten systems in the mantle and the core and basic assumptions are discussed

planetary cratering 2 studies of saturation equilibrium a realistic computer model has been developed to display images of imaginary cratered surfaces taking into account empirically measured input size distributions of primary and secondary craters ejecta blanket morphology including feathering with distance obliteration due to ejecta from outside the imaged area lighting effects etc the model allows us to track surface evolution of morphology as new craters are added using the model as well as lunar photos we have studied the approach to saturation equilibrium defined as a condition when no further proportionate increase in crater density occurs as input cratering increases we find that an identifiable saturation equilibrium occurs close to a level previously identified for this state hartmann 1984 typically fluctuating around a crater density from 0 4 to 2 times that level this result is fairly robust vis a vis the range of model parameters we have chosen flooding basin ejecta blankets and other obliterative effects can introduce structure and oscillations within this range even after saturation equilibrium is achieved these findings may constrain or revise certain earlier interpretations of satellite and planet surface evolution and impactor populations which were predicated on the assumed absence of saturation equilibrium in our fourth experimental run we found that suppression of sandblasting by subresolution impacts allows the smallest secondaries to rise above the saturation equilibrium line a result that might be relevant to a similar situation on gaspra and perhaps some other asteroids

merapi volcano central java indonesia a case study of radionuclide behavior in volcanic gases and its implications for magma dynamics at andesitic volcanoes for more than 20 years volcanic gases have been regularly collected at merapi volcano indonesia and have been subsequently analyzed for their 210pb 210bi and 210po activities and so2 contents these new results show the high volatility of the three radionuclides in andesitic gases although their emanation coefficients 0 94 3 5 and 53 for 210pb 210bi and 210po respectively are significantly lower than those observed at basaltic volcanoes this emphasizes the major role of magma temperature on the degassing of these metals which are mainly transported in volcanic gases as pb chloride compounds and as bi and po metallic species radioactive disequilibria between 210pb 210bi and 210po in the gas phase are characteristic of degassing processes and gas paths within the edifice gases released at both gendol and woro fumarolic fields are of magmatic origin but their radionuclide content is strongly altered by secondary processes chemical reactions with surrounding brines and deposition of sublimates in the ground high temperature gases collected in the summit gas plume are of pure primary magmatic origin and are likely directly tapped in the degassing reservoir gases arising from the growing domes are strongly depleted in the most volatile isotopes and gas species this suggests that magma mostly degasses at depth in open system explaining why the volcano usually undergoes no explosive eruptions the gas flux at merapi is sustained by a deep magma supply which is twice the extrusion rate of lava unerupted degassed magma thus progressively accumulates beneath the summit yielding an overpressure which can trigger dome collapse without precursor

measurement of bubble size distributions in vesiculated rocks with implications for quantitative estimation of eruption processes abstract this paper outlines methods for determining a bubble size distribution bsd and the moments of the bsd function in vesiculated clasts produced by volcanic eruptions it reports the results of applications of the methods to 11 natural samples and discusses the implications for quantitative estimates of eruption processes the analysis is based on a quantitative morphological stereological method for 2 dimensional imaging of cross sections of samples one method determines with some assumptions the complete shape of the bsd function from the chord lengths cut by bubbles the other determines the 1st 2nd and 3rd moments of distribution functions by measurement of the number of bubbles per unit area the surface area per unit volume and the volume fraction of bubbles comparison of procedures and results of these two distinct methods shows that the latter yields rather more reliable results than the former though the results coincide in absolute and relative magnitudes results of the analysis for vesiculated rocks from eleven subplinian to plinian eruptions show some interesting systematic correlations both between moments of the bsd and between a moment and the eruption column height or the sio2 content of magma these correlations are successfully interpreted in terms of the nucleation and growth processes of bubbles in ascending magmas this suggests that bubble coalescence does not predominate in sub plinian to plinian explosive eruptions the moment moment correlations put constraints on the style of the nucleation and growth process of bubbles the scaling argument suggests that a single nucleation event and subsequent growth with any kind of bubble interaction under continuous depressurization which leads to an intermediate growth law between the diffusional growth r m t 2 3 at a constant depressurization rate and the ostwald ripening r m t 1 3 under a constant pressure where rm and t are the mean radius of bubble and the effective time of diffusion respectively occurred in the eruptions it is emphasized that the bsd in vesiculated rocks from terrestrial volcanoes can be used to estimate quantitatively eruption processes such as the initial saturation pressure and magma ascent velocity in a volcanic conduit

a multispectral geological study of the schrodinger impact basin1 schrodinger basin is a well preserved peak ring basin located on the lunar farside along the rim of the much larger south pole aitken spa basin the relatively young age lower imbrian series

a simple model of 222rn accumulation leading to 210pb excesses in volcanic rocks while most rocks from active volcanoes display 210pb 226ra activity ratios lower than or close to the equilibrium value of 1 several other have ratios much higher than 1 transfer of 222rn by magmatic volatiles has often been advocated to explain both 210pb deficits and excesses we develop here a model to account for 210pb excesses through 222rn accumulation we show that large 210pb excesses can be readily obtained even for moderate ratios of degassing magma over accumulating magma in a closed system model where the 222rn atoms produced by decay of 226ra in the degassing magma are continuously extracted by a gas phase for a given duration of volatile transfer relative 210pb excesses are expected to be much larger than 210pb deficits this model is applied to samples from santorini aegean arc and surtsey iceland both of which show high 210pb 226ra ratios of 6 7 and 2 3 respectively at the time of eruption the agreement with field data suggests that 222rn accumulation leading to 210pb excesses might be a rather common process in zoned magma chambers as well as in individual lava flows and that it can be described by a closed system model

atmospheric 210 po anomaly as a precursor of volcano eruptions 1 due to its high volatility 210po can be effectively released from active volcanoes prior to their explosions a continuous record of the fallout rate of 210po versus that of 210pb in northern taiwan reveals that most of the 210po was derived from pre eruption gas emission of philippines mayon volcano in the past two years from this observation we suggest that if a global network can be properly designed it may be possible to employ 210po anomaly as a precursor of volcano eruptions worldwide

lunar mare volcanism stratigraphy eruption conditions and the evolution of secondary crusts abstract lunar mare basalt deposits cover 17 of the lunar surface occur preferentially in topographic lows on the nearside and have a total volume estimated at 1 107 km3 analysis of returned samples and photogeologic and remote sensing studies shows that mare volcanism began prior to the end of heavy bombardment the period of cryptomare formation in pre nectarian times and continued until the copernican period a total duration approaching 3 5 4 ga stratigraphic analyses show that the flux was not constant but peaked in early lunar history during the imbrian period which spans the period 3 85 3 2 ga average volcanic output rate during this peak period was about 10 2 km 3 a very low relative to the present global terrestrial volcanic output rate and comparable to the present local output rates for individual volcanoes such as vesuvius and kilauea hawaii volcanic landforms indicate that many eruptions were of high volume and long duration some eruptions associated with sinuous rules may have lasted of the order of a year and emplaced 103 km3 of lava representing the equivalent in one year of about 70 000 years at the average flux shallow magma chambers were uncommon the nearsidefarside mare deposit asymmetry can be readily explained by differences in crustal thickness magma ascending from the mantle or from a buoyancy trap at the base of the crust should preferentially extrude to the surface on the nearside but should generally stall and cool in dikes in the farside crust extruding only in the deepest basins the occurrence of farside maria within craters whose diameter is generally near to or less than the thickness of the crust may be accounted for by the difference between local and regional compensation dikes that establish pathways to the surface on the nearside should have very high volumes comparable to the volumes associated with many observed flows and sinuous rilles an abundance of dikes should exist in the lower crust of the moon many more than those feeding surface eruptions the upper limit is 37 50 of the crust by volume the presence and abundance of such dike swarms have important implications for the interpretation of the average composition of the lunar crust and the composition of basin and crater ejecta the interplay between thermal contraction and differentiation leads to net cooling and ultimate contraction of the outer portions of the moon resulting in a regional horizontal compressive stress acting on the lunar crust in addition overall cooling and deepening of sources require the production of ever larger volumes of magma in order to reach the surface with time stresses became high enough so that few dikes could open to the surface causing eruptive activity to be severely diminished in the eratosthenian and perhaps to cease in the copernican period lower stress levels are required to terminate eruptive activity on the lunar farside consistent with the imbrian age of the farside maria and the nearside location of the youngest maria lunar mare deposits provide an example of the transition from primary crusts to secondary crusts and illustrate the significance of several factors in the evolution of secondary crusts such as crustal density variations in crustal thickness presence of impact basins state and magnitude of stress in the lithosphere and general thermal evolution these factors are also responsible for the extremely low volcanic flux even during periods of peak extrusion

fragmentation in kimberlite products and intensity of explosive eruption the explosive eruption of kimberlite magma is capable of producing a variety of pyroclast sizes shapes and textures however all pyroclastic deposits of kimberlite comprise two main types of pyroclasts 1 pyroclasts of kimberlite with or without enclosed olivine crystals and 2 olivine crystals which lack coatings of kimberlite here we propose two hypotheses for how kimberlite magmas are modified due to explosive eruption 1 olivine crystals break during kimberlite eruption and 2 kimberlite melt can be efficiently separated from crystals during eruption these ideas are tested against data collected from field study and image analysis of coherent kimberlite and fragmental kimberlite from kimberlite pipes at diavik nt olivines are expected to break because of rapid pressure changes during the explosive eruption disruption of kimberlite magma and pyroclast production is driven by ductile deformation processes rather than by brittle fragmentation the extent to which melt separates from olivine crystals to produce kimberlite free crystals is a direct consequence of the relative proportions of gas melt and crystals lastly the properties of juvenile pyroclasts in deposits of pyroclastic kimberlite are used to index the relative intensity of kimberlite eruptions a fragmentation index is proposed for kimberlite eruption based on a crystal size distributions of olivine and on b ratios of selvage free olivine pyroclasts to pyroclasts of kimberlite with or without olivine crystals

strombolian explosions 2 eruption dynamics determined from acoustic measurements strombolian activity consists of a series of explosions due to the breaking of a large overpressurized bubble at the surface of the magma column acoustic pressure due to sound waves has been measured and analyzed at stromboli for more than 50 explosions three parts can be distinguished in the acoustic pressure waveform which are related to the behavior of the bubble before during and after its bursting before the sharp rise in acoustic pressure the signal is dominated by waves with a frequency of 2 hz which develop on the nose of the bubble they produce sound in air by imposing a rapid motion to the interface and one could detect a bubble travelling in the uppermost 30 m of the magma column when the bubble reaches the air magma interface its strong vibration driven by a large overpressure inside the gas generates the main event with a frequency around 9 hz after the bubble has burst kinematic waves of frequency around 4 5 hz are the main source of sound they develop at the surface of the magma left on the conduit side the three types of motion although determined independently give consistent results furthermore combining the results obtained for the two types of kinematic waves the magma viscosity is estimated to be of 300 65 pa s which is in good agreement with petrological constraints and corroborates the validity of our analysis this suggests that acoustic measurements constitute a powerful tool in the understanding of eruption dynamics

ages of mare basalts on the lunar nearside the chronology of lunar volcanism is based on radiometric ages determined from apollo and luna landing site samples regional stratigraphic relationships and crater degradation and size frequency distribution data for units largely defined prior to the end of the apollo program here we report on new crater size frequency distribution data for 139 spectrally and morphologically defined basalt units which are exposed in six nearside impact basins australe tranquillitatis humboldtianum humorum serenitatis and imbrium crater size frequency distribution measurements are a statistically robust and accurate method to derive absolute model ages of unsampled regions of the moon compared to crater degradation ages crater size frequency ages performed on spectrally defined units offer significant improvements in accuracy our investigation showed that 1 in the investigated basins lunar volcanism was active for at least 1 5 2 0 b y starting at about 3 9 4 0 b y and ceasing at 2 0 b y 2 most basalts erupted during the late imbrian period at about 3 6 3 8 b y 3 significantly fewer basalts were emplaced during the eratosthenian period 4 basalts of copernican age were not found in any of the investigated basins 5 lunar basin filling volcanism probably started within 100 m y after the formation of the individual basins we also assessed the relationship between impact basin age and the history of mare basalt emplacement in these basins we found that 1 in all pre nectarian basins australe and tranquillitatis as well as in the humboldtianum basin which is of nectarian age the distribution of surface ages is clearly dominated by only a single peak in the number of erupted units at 3 6 3 8 b y 2 in the younger basins humorum serenitatis and imbrium a second peak at 3 3 3 5 b y is observed 3 basalt eruptions younger than 2 6 b y occur only intermittently and 4 in the youngest basins serenitatis and imbrium we see an extended period of active basin filling volcanism 1 5 1 6 b y which is 500 m y longer than in the australe and humorum and even 1 0 b y longer than in tranquillitatis and humboldtianum

analysis of chang e 2 brightness temperature data and production of high spatial resolution microwave maps of the moon abstract the microwave radiation passively emitted from the moon is valuable for investigating the physical properties of the lunar regolith microwave maps which can reveal subsurface characteristics at depths of centimeters to meters give clues to understanding the evolution of the lunar surface china s chang e 2 ce 2 spacecraft carried a microwave radiometer mrm and conducted passive microwave remote sensing of the moon at 3 7 8 19 35 and 37 ghz 10 3 84 1 55 and 0 81 cm wavelengths during 2010 2011 brightness temperature tb data derived from the mrm orbital observations cover the entire moon and the time coverage is over a complete lunation in this paper we use spherical harmonic fits to model the tb variation as functions of local time and latitude using these fits we normalized the day and nighttime tb data measured at various local times into noon time and midnight conditions the spatial sampling of the normalized tb maps is 6 km pixel much higher than ground based observations and higher resolution than the mrm maps derived from chang e 1 by removing the variation in tb related to local time and latitude we produced a series of microwave maps that reveal differences in the properties of the regolith across the lunar surface the microwave behavior of various lunar surface features can be explained primarily by differences in the microwave loss tangent of the materials for example we find that the high ti maria have high daytime tb and exhibit lower nighttime tb than the other maria as a result of the high dielectric loss tangent of ilmenite the ilmenite rich materials are less transparent to microwaves and hence emissions emerge from closer to the surface which is heated strongly in the day and cools quickly at night most fresh craters correspond to low tb spots in the nighttime microwave maps in contrast to their behavior as hot spots in nighttime infrared data suggesting that the higher loss tangent of rocks compared to soils suppresses microwave emission at night the aristarchus plateau has a lower loss tangent relative to its surroundings because it is blanketed by fine grained rock poor pyroclastic material the pyroclastic blanket is more transparent to microwaves than the nearby maria causing the plateau to have relatively cool daytime tb and warm nighttime tb as a consequence of microwave emissions that originate at greater depths the orientale basin is another prominent anomaly in the microwave maps indicating that orientale materials differ in thermophysical and or dielectric properties from typical highland lithologies brightness temperature differences among prominent rayed craters indicate that the very youngest crater rays e g giordano bruno have lower thermal inertia than older but still optically immature rays e g tycho

beginning and end of lunar mare volcanism mare volcanism on the moon is commonly attributed to an important but relatively short lived epoch of internal heating after 3 900 myr bp but before about 2 500 myr bp refs 1 2 although some studies suggested that mare volcanism had started earlier3 5 than times indicated by dated lunar samples only recently have photogeological spectral and geochemical data6 8 documented the importance of a pre 4 000 myr bp epoch similarly early earth based geological mapping revealed a bright rayed crater lichtenberg superposed by mare units9 thereby indicating that mare volcanism must have extended to times significantly more recent than 3 100 myr bp lunar orbital photography confirmed this inferred strati graphical relationship10 but crater statistics indicated that the youngest units were at least twice the age of copernicus or between 1 700 and 2 000 myr bp refs 11 13 we present here the inferred distribution and style of the early phases of mare volcanism based on current evidence and conclude that certain regions of the moon underwent two distinct pulses of igneous activity we then examine crater statistics for the post lichtenberg mare unit and other selected units and conclude that mare volcanism extended to a time comparable with that of the copernicus impact or 1 myr bp these reassessments of the oldest and youngest maria provide new constraints on geophysical models of the internal thermal history of the moon

a rock model for the cold and hot spots in the chang e microwave brightness temperature map thermal anomaly spots both hot and cold have been found in the global 37 ghz brightness temperature tb map of the moon based on the chang e ce microwave radiometer measurements to explain their origin a rock model is proposed to simulate the tb variation against latitude along the profile of a fresh crater in a single track way which is selected to highlight the topographic effect and avoid any modification to the data a mixed upper layer made up of rock and soil regolith and dust was employed into our previous multilayer model the thermal properties thermal conductivity and heat capacity of the mixture layer are presumed to be linear with the fraction of rocks given that high frequency 37 ghz measurements are chosen only the meter size and larger rocks of the upper mixed layer are considered to avoid scattering effects several fresh craters poor rich in ilmenite are selected as testing sites despite uncertainties in parameters such as rock abundance ra and iron and titanium abundances three conclusions can be reached from these cases 1 ra has a significant effect on both the tb value and tb variation trend against latitude its contribution over some craters may be as high as 15 k 2 the simulations based on our rock model fit the ce observations better than those when rocks are not included and 3 the rock and ilmenite contributions could be the main cause for the cold and hot spots found in the ce microwave map

long lived volcanism on the lunar farside revealed by selene terrain camera we determined model ages of mare deposits on the farside of the moon on the basis of the crater frequency distributions in 10 meter resolution images obtained by the terrain camera on selene selenological and engineering explorer kaguya most mare volcanism that formed mare deposits on the lunar farside ceased at 3 0 billion years ago suggesting that mare volcanism on the moon was markedly reduced globally during this period however several mare deposits at various locations on the lunar farside also show a much younger age clustering at 2 5 billion years ago these young ages indicate that mare volcanism on the lunar farside lasted longer than was previously considered and may have occurred episodically

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

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

vesiculation of may 18 1980 mount st helens magma the may 18 1980 eruption of mount st helens washington produced both white and gray pumice similar in composition but varying in phenocryst microlite and vesicle content the white pumice has fewer phenocrysts no microlites and higher vesicularity and is thus less dense than the gray in addition vesicles in the white pumice are larger and more interconnected than those in the gray both white and gray have effective crystal free vesicularities 85 7 and 72 2 respectively close to the traditionally accepted fragmentation vesicularity of 75 77 given that the two pumice types were erupted concurrently for several phases of the eruption and therefore probably had similar eruption paths we suggest that differences in vesicularity and vesicle size distributions result from the presence or absence of microlites the presence of microlites in the gray pumice not only increased the magma viscosity and effective vesicularity but appears to have aided bubble nucleation and hindered bubble expansion and coalescence thus magmas with microlites may fragment at a lower bulk vesicularity than those without microlites fragmented microlite bearing clasts are also likely to expand less after fragmentation and therefore more closely preserve the bubble distribution and structure at the time of magma fragmentation

elevated gas flux and trace metal degassing from the 2014 2015 fissure eruption at the barðarbunga volcanic system iceland the 2014 bar arbunga rifting event in iceland resulted in a 6 month long eruption at holuhraun this eruption was characterized by high lava discharge rate and significant gas emission the so2 flux for the first 3 months was measured with satellite sensors and the petrologic method high resolution time series of the satellite data give 1200 kg s that concurs with 1050 kg s obtained from melt inclusion minus degassed lava sulfur contents scaled to the mass of magma produced a high purity gas sample with elevated s cl due to limited chlorine degassing reveals a similar degassing pattern of trace metals as observed at k lauea hawai i and erta ale ethiopia this suggests a common degassing mechanism at mantle plume related volcanoes the trace metal fluxes calculated from trace element to sulfur ratios in the gas sample and scaled to the sulfur dioxide flux are 1 2 orders of magnitude stronger at holuhraun than k lauea and erta ale in contrast volcanoes at convergent margins etna and stromboli italy have 1 2 orders of magnitude higher trace element fluxes most likely caused by abundant chlorine degassing this emphasizes the importance of metal degassing as chlorine species short lived disequilibria between radon daughters 210pb 210bi 210po measured in the gas suggest degassing of a continuously replenished magma batch beneath the eruption site earlier and deep degassing phase of carbon dioxide and polonium is inferred from low 210po 210pb in the gas consistent with magma transfer rate of 0 75 m s

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

volumetric characteristics of lava flows from interferometric radar and multispectral satellite data the 1995 fernandina and 1998 cerro azul eruptions in the western galapagos we have used a suite of remotely sensed data numerical lava flow modeling and field observations to determine quantitative characteristics of the 1995 fernandina and 1998 cerro azul eruptions in the western galapagos islands flank lava flow areas volumes instantaneous effusion rates and average effusion rates were all determined for these two eruptions for which only limited syn eruptive field observations are available using data from spot topsar ers 1 and ers 2 we determined that the 1995 fernandina flow covers a subaerial area of 6 5 106 m2 and has a subaerial dense rock equivalent dre volume of 42 106 m3 field observations atsr satellite data and the flowgo numerical model allow us to determine that the effusion rate declined exponentially from a high of 60 200 m3 s 1 during the first few hours to 5 m3 s 1 prior to ceasing after 73 days with a mean effusion rate of 4 16 m3 s 1 integrating the atsr derived exponentially declining effusion rate over the eruption duration produces a total subaerial submarine dre volume of between 27 and 100 106 m3 the range in values being due to differing assumptions about heat loss characteristics only values in the higher part of this range are consistent with the independently derived subaerial volume using spot topsar ers 1 and ers 2 data we determine that the 1998 cerro azul flow is 16 km long covers 16 km2 and has a dre volume of 54 106 m3 flowgo produces at vent velocity and effusion rate values of 11 m s 1 and 600 m3 s 1 respectively the velocity value agrees well with the 12 m s 1 estimated in the field the mean effusion rate total dre volume duration was 7 47 m3 s 1 dike dimensions fissure lengths and pressure gradients along the conduit based on magma chamber depth estimates of 3 5 km produce mean effusion rates for the two eruptions that range over nearly four orders of magnitude the range being due to uncertainty in the magma viscosity dike dimensions and pressure gradient between magma chamber and vent although somewhat consistent with mean effusion rates from other techniques their wide range makes them less useful the exponentially declining effusion rates during both eruptions are consistent with release of elastic strain being the driving mechanism of the eruptions our results provide independent input parameters for previously published theoretical relationships between magma chamber pressurization and eruption rates that constrain chamber volumes and increases in volume prior to eruption as well as time constants of exponential decay during the eruption the results and theoretical relationships combine to indicate that at both volcanoes probably 25 30 of the volumetric increase in the magma chamber erupted as lava onto the surface in both eruptions the lava flow volumes are less than 1 of the magma chamber volume

lunar cryptomaria physical characteristics distribution and implications for ancient volcanism cryptomaria lunar volcanic deposits obscured by crater and basin impact ejecta can provide important information about the thermal and volcanic history of the moon the timing of cryptomare deposition has implications for the duration and flux of mare basalt volcanism in addition knowing the distribution of cryptomaria can provide information about mantle convection and lunar magma ocean solidification here we use multiple datasets e g m3 lola lroc diviner to undertake a global analysis to identify the general characteristics e g topography surface roughness rock abundance albedo etc of lunar light plains in order to better distinguish between ancient volcanic deposits cryptomaria and impact basin and crater ejecta deposits we find 20 discrete regions of cryptomaria covering approximately 2 of the moon which increase the total area covered by mare volcanism to 18 of the lunar surface comparisons of light plains deposits indicate that the two deposit types volcanic and impact produced are best distinguished by mineralogic data on the basis of cryptomaria locations the distribution of mare volcanism does not appear to have changed in the time prior to its exposed mare basalt distribution there are several hypotheses explaining the distribution of mare basalts which include the influence of crustal thickness mantle convection patterns asymmetric distribution of source regions kreep distribution and the influence of a proposed procellarum impact basin the paucity of farside mare basalts means that multiple factors such as crustal thickness variations and mantle convection are likely to play a role in mare basalt emplacement

the 2007 eruption of stromboli volcano insights from real time measurement of the volcanic gas plume co2 so2 ratio abstract the recent eruption of stromboli in february april 2007 offered a unique chance to test our current understanding of processes driving the transition from ordinary persistent strombolian to effusive activity and the ability of instrumental geophysical and geochemical networks to interpret and predict these events here we report on the results of two years of in situ sensing of the co 2 so 2 ratio in stromboli s volcanic gas plume in the attempt to put constraints on the trigger mechanisms and dynamics of the eruption we show that large variations of the plume co 2 so 2 ratio range 0 9 26 preceded the onset of the eruption since december 2007 interrupting a period of relatively steady and low ratios time averaged ratio 4 3 lasting from at least may to november 2006 by contrasting our observations with numerical simulations of volcanic degassing at stromboli derived by use of an equilibrium saturation model we suggest that the pre eruptive increase of the ratio reflected an enhanced supply of deeply derived co 2 rich gas bubbles to the shallow plumbing system this larger than normal ascent of gas bubbles was likely sourced by a 1 3 km deep gas melt separation region probably a magma storage zone and caused faster convective overturning of magmas in the shallow conduit an increase in the explosive rate and in seismic tremor and finally the collapse of the la sciara del fuoco sector triggering the effusive phase the high co 2 so 2 ratios up to 21 observed during the effusive phase and particularly in the days and hours before a paroxysmal explosion on march 15 2007 indicate the persistence of the same gas source and suggest that de pressurization of the same 1 3 km deep magma storage zone could have been the trigger mechanism for the paroxysm itself

farside gravity field of the moon from four way doppler measurements of selene kaguya the farside gravity field of the moon is improved from the tracking data of the selenological and engineering explorer selene via a relay subsatellite the new gravity field model reveals that the farside has negative anomaly rings unlike positive anomalies on the nearside several basins have large central gravity highs likely due to super isostatic dynamic uplift of the mantle other basins with highs are associated with mare fill implying basalt eruption facilitated by developed faults basin topography and mantle uplift on the farside are supported by a rigid lithosphere whereas basins on the nearside deformed substantially with eruption variable styles of compensation on the near and farsides suggest that reheating and weakening of the lithosphere on the nearside was more extensive than previously considered

hierarchical classification for the topography analysis of asteroid 4179 toutatis from the chang e 2 images abstract high spatial resolution images of the near earth asteroid 4179 toutatis are provided by a successful flyby of the chang e 2 spacecraft these optical images give us a chance to closely observe the surface of this asteroid however some local low contrast regions in the chang e 2 images limit the accuracy of the topography recognition to solve this problem a hierarchical classification method is suggested and developed to assist the topography analysis for toutatis based on the chang e 2 optical images the proposed method first classifies the image at both the macro level and the micro level respectively then topography of toutatis can be explored by using the hierarchical classification result experimental results demonstrate that the method cannot only provide a new perspective to analyze topography objects reported previously but also reveal some new characteristics at low contrast regions namely two new topographic characteristics are revealed one is a connection region with a particular spectral value locating at the corner of the large lobe and the other is an object seeming like a fixed star at the background of the images

gravity changes and passive so2 degassing at the masaya caldera complex nicaragua an understanding of the mechanisms responsible for persistent volcanism can be acquired through the integration of geophysical and geochemical data sets by interpreting data on micro gravity ground deformation and so2 flux collected at masaya volcano since 1993 it is now clear that the characteristically cyclical nature of the activity is not driven by intrusion of additional magma into the system rather it may be due in large part to the blocking and accumulation of gas by restrictions in the volcano substructure the history of crater collapse and formation of caverns beneath the crater floor would greatly facilitate the trapping and storage of gas in a zone immediately beneath san pedro and the other craters another mechanism that may explain the observed gravity and gas flux variations is the convective overturn of shallow pre existing degassed cooled dense magma that is replaced periodically by lower density hot gas rich magma from depth buoyant gas rich magma rises from depth and is emplaced near the surface resulting in the formation and fluctuation of a low density gas rich layer centred beneath nindiri and santiago craters as this magma vigorously degasses it must cool increase in density and eventually sink five stages of activity have been identified at masaya since 1853 and the most recent data suggest that the system may have been entering another period of reduced degassing in 2000 this type of analysis has important implications for hazard mitigation because periods of intense degassing are associated with poor agricultural yields and reduced quality of life a better understanding of persistent cyclically active volcanoes will allow for more effective planning of urban development and agricultural land use

dynamics of deep submarine silicic explosive eruptions in the kermadec arc as reflected in pumice vesicularity textures abstract despite increasing recognition of silicic pumice bearing deposits in the deep marine environment the processes involved in explosive silicic submarine eruptions remain in question here we present data on bubble sizes and number densities number of bubbles per unit of melt matrix for deep submarine erupted pumices from three volcanoes healy raoul sw and havre along the kermadec arc sw pacific to investigate the effects of a significant 1 km overlying water column and the associated increased hydrostatic pressure on magma vesiculation and fragmentation we compare these textural data with those from chemically similar subaerially erupted pyroclasts from nearby raoul volcano as well as submarine erupted tangaroan fragments derived by non explosive buoyant detachment of foaming magma from macauley volcano also along the kermadec arc deep submarine erupted pumices are macroscopically similar colour density texture to subaerial or shallow submarine erupted pumices but show contrasting microscopic bubble textures deep submarine erupted pyroclasts have fewer small

understanding magmatic processes at telica volcano nicaragua crystal size distribution and textural analysis telica volcano in nicaragua currently exhibits persistent activity with continuous seismicity and degassing yet it has not produced lava flows since 1529 to provide insight into magma chamber processes including replenishment and crystallization crystal size distribution csd profiles of plagioclase feldspar phenocrysts were determined for quaternary telica basalts and basaltic andesites textural analysis of 14 highly crystalline lavas 20 vol phenocrysts indicates that the samples are dominated by sieve textured plagioclase feldspar phenocrysts whose origin requires thermochemical disequilibrium within the magmatic system the csd curves display an inverse relationship between phenocryst length and population density concave up patterns observed for the telica lava samples can be represented by linear segments that define two crystal populations a steeply sloping segment for small crystals 1 5 mm in length the two crystal populations may be explained by magma replenishment and a mixing model in which a mafic magma is introduced to a stable chamber that is petrologically and geochemically evolving residence times calculated using the defined linear segments of the csd curves suggest these magmatic processes occur over timescales on the order of decades to centuries the crystal size distribution and textural analysis advocate for the current persistent activity as being consistent throughout telica s historic and prehistoric eruptive periods and driven by replenishment of mafic magma

escape of unradiogenic osmium during sub aerial lava degassing evidence from fumarolic deposits piton de la fournaise reunion island abstract this study presents new re os isotope and elemental data in gas condensates and corresponding lavas in order to examine the geochemical behavior of these two elements during magma degassing at piton de la fournaise reunion island gas sublimates formed between 2007 and 2011 at temperature ranging from 400 to ca 100 c include na k sulfate aphthitalite na sulfate thenardite ca cu sulfate e g gypsum ca mg al fe fluoride e g ralstonite and native sulfur the high temperature deposits show trace element typical of volcanic gas with high enrichment in re 24 to 79 ppb almost two order of magnitude higher than the corresponding lavas but with os abundances similar to those of the lavas 14 132 ppt in contrast the os contents of the low temperature fluoride deposits 13 77 ppb are higher than any of the other condensates the fluorides are also enriched in re albeit to lesser extent than os 2 9 15 3 ppb based on high temperature samples the fluid melt partition coefficients estimated for re and os are 100 80 and 1 2 respectively considering 1 of fluid loss these partition coefficients translate into emanation coefficients of 0 50 0 17 0 65 for re and 0 01 0 0 03 for os these results indicate that re unlike os is highly volatile at piton de la fournaise osmium isotopic compositions of samples collected at medium and low temperature 187 os 188 os between 0 130 0 135 and plot within the range of the april 2007 lava flow and the historical lavas of piton de la fournaise i e 0 130 0 137 however the highest temperature condensates na k sulfates with t of 384 400 c yield lower 187 os 188 os ratios i e 0 124 0 129 within the field of mantle signal such unradiogenic compositions are best explained if old mantle sulfides occur in lavas and contribute to volcanic gases within the general frame of osmium mantle geochemistry loss of unradiogenic os during magmas degassing could help to explain osmium isotope disequilibrium between lavas and melting residues

fractionation of metals in volcanic emissions abstract the enrichment of some metals al mg na k cu zn cd in volcanic gases is measured by an emanation coefficient ex relating the amount of the element x in lavas and in aerosols ex is determined in the volcanic emissions of mount etna sicily with regard to that of210pb the accuracy of the results is limited by the geochemical behavior of common lead compared to that of210pb concerning the most volatile species it appears that practically all the volcanic aerosols are produced by evaporation followed by gas to particle conversion and the spattered fraction appears to be negligible

observations of seismic volcanic signals at stromboli volcano italy abstract digital recordings of ground motion during a seismic operation organized at stromboli volcano italy from may 31 1986 to june 26 1986 have been studied the amplitude of background seismic noise is greater at the summit than at the base of the volcano and the spectra calculated on different days are dominated by at least two frequencies 2 0 and 6 0 hz with subdominant frequencies at 4 1 4 8 and 8 hz according to their waveform and their spectral content three types of discrete volcanic signals are distinguishable the first type is characterized by a dominant frequency at 2 hz and a subdominant frequency at 4 1 hz the second type also has a dominant peak frequency at 2 hz with two important subdominant frequencies at 5 and 8 hz the type 3 has a sharp dominant frequency at 6 hz and subdominant frequency at 3 2 hz the frequencies observed for discrete signals and ground noise suggest that they are produced by the same repeated mechanism which probably has a volcanic origin the discrete signals are linked to explosions at the active vents within the craters

eruption of basalt and andesite lava degasses 222rn and 210po activities of 222rn and 210po were measured in a september 1983 basic andesite lava from arenal and a november 1983 basalt from kilauea starting 3 and 1 days after eruption respectively in both cases in growth patterns show that all rn volatalized during eruption po degassing also was complete at kilauea but only 84 10 at arenal

lunar regolith thermal behavior revealed by chang e 1 microwave brightness temperature data abstract microwave brightness temperature data obtained by the chinese chang e 1 lunar orbiter are analyzed with the lunar diurnal variations filtered resulting maps from the high frequency microwave channel show lunar topographic signatures with close similarity to those seen in clementine s lunar topography maps while the low frequency channels reveal intriguing lunar surface properties not previously observed here we focus on two characteristics displayed by the filtered brightness temperature maps in the high frequency maps the existence of an anti correlation between daytime and nighttime brightness temperature deviations in certain regions especially in the lunar maria and in the low frequency maps the appearance of cold spots which correspond with the hot spots observed in the infrared during lunar eclipses

volcanic emission of radionuclides and magma dynamics 210pb 210bi and210po the last decay products of the238u series are highly enriched in volcanic plumes relative to the magma composition moreover this enrichment varies over time and from volcano to volcano a model is proposed to describe 8 years of measurements of mt etna gaseous emissions the lead and bismuth coefficients of partition between gaseous and condensed phases in the magma are determined by comparing their concentrations in lava flows and condensated volatiles in the case of volatile radionuclides an escaping time is calculated which appears to be related to the volcanic activity finally it is shown that that magma which is degassing can already be partly degassed it should be considered as a mixture of a few to 50 of deep non degassed magma with a well degassed superficial magma cell

lunar iron and titanium abundance algorithms based on final processing of clementine ultraviolet visible images the clementine mission to the moon returned global imaging data collected by the ultraviolet visible uvvis camera this data set is now in a final state of calibration and a five band multispectral digital image model dim of the lunar surface will soon be available to the science community we have used observations of the lunar sample return sites and stations extracted from the final dim in conjunction with compositional information for returned lunar soils to revise our previously published algorithms for the spectral determination of the feo and tio2 content of the lunar surface the algorithms successfully normalize the effects of space weathering so that composition may be determined without regard to a surface s state of maturity these algorithms permit anyone with access to the standard archived dim to construct high spatial resolution maps of feo and tio2 abundance such maps will be of great utility in a variety of lunar geologic studies

variability of alkali and heavy metal fluxes released by mt etna volcano sicily between 1991 and 1995 abstract we regularly collected volcanic gases and aerosols at mt etna volcano over a long period 1991 1995 and measured their chemical composition by icp ms based on these data we present new evidence on the high volatility of both alkali and some heavy metals in contrast both lanthanides and actinides are not produced as significant gaseous compounds at magmatic temperatures and can be used as tracers of spattered materials all metals of each chemical family maintained systematic trends during the study period at both summit craters and effusive vents located in the valle del bove during the 1991 1993 eruption during the eruption we observed high metal enrichments at effusive vents these enrichments seem to be characteristic of the secondary degassing of a magma previously degassed under the summit area lower metal enrichments are recorded in aerosols sampled in summit crater plumes according to the primary degassing type occurring at these vents while a primary degassing type still occurs at both bocca nuova and voragine during the post eruptive period sud est crater exhibits a transition from primary to secondary type according to the variations of the volcanic activity level we confirm that the alkali metals fractionate systematically within their family as they cross the melt vapour interface the heavier members being always more enriched than the lighter ones in aerosols we also show that this fractionation is not related to the volcanic activity and the degassing type but seems to be a significant feature of the alkali family itself estimation of new emanation coefficients for rubidium caesium tin and thallium 0 07 0 15 0 50 and 21 respectively yields annual outputs around 1000 t yr 60 t yr 240 t yr and 1600 t yr respectively mount etna is a very important source of metals injected into the atmosphere contributing to the global volcanic budget about 16 for heavy metals and 19 for alkali metals in eruptive periods and only 2 and 4 respectively in quiet periods

degassing of metals and metalloids from erupting seamount and mid ocean ridge volcanoes observations and predictions recently it has been reported that the element polonium degasses from mid ocean ridge and seamount volcanoes during eruptions published and new observations on other volatile metal and metalloid elements can also be interpreted as indicating significant degassing of magmatic vapors during submarine eruptions this process potentially plays an important role in the net transfer of chemical elements from erupting volcanoes to seawater in addition to that arising from sea floor hydrothermal systems in this paper a framework is constructed for predicting and assessing semiquantitatively the potential magnitude and chemical fingerprints in the water column of metal and metalloid degassing using 1 predictions from a summary of element volatilities during mafic subaerial volcanism worldwide and 2 limited data from submarine volcanic effusives the latter include analyses of polonium and trace metals in near volcano water masses sampled following a submarine eruption at loihi seamount hawaii 1000 m bsl in 1996 the element volatility predictions and observations show good agreement considering the limited dataset some of the highest volatility main group and transition element enrichments in seawater over loihi are predicted by the degassing mass transfer model i present when expanded to cover all submarine volcanic activity it is predicted that exit fluxes of these elements are up to 102 103 greater by degassing than by normal mor hydrothermalism in contrast mor exit fluxes of low volatility alkali and alkaline earth elements are likely 102 106 greater from hydrothermal inputs degassing inputs to the ocean are probably highly episodic occurring almost entirely during eruptions these are times of enhanced and abnormal hydrothermalism as well although major hydrothermal and degassing events may not be chemically recognizable in real water masses as wholly distinct entities it is nevertheless possible to predict to what extent each process flavors the effluents of the other degassing at mid ocean ridges may explain a variety of observations previously ascribed to complexities occurring during hydrothermal venting and or fluid ascent in the buoyant hydrothermal plumes above ridges

lunar impact basins new data for the western limb and far side orientale and south pole aitken basins from the first galileo flyby compositional aspects of impact basin materials can be analyzed using multispectral image data acquired by the galileo solid state imaging ssi experiment during the december 1990 lunar encounter these data provide important information on the spectral properties of the western lunar limb and parts of the far side the ssi images cover the wavelength range 0 4 1 0 m allowing measurement of spectral slope and estimation of the strength of the 1 m absorption due to iron in the mafic minerals olivine and pyroxene among deposits of the 930 km diameter orientale basin exterior ejecta comprising the hevelius formation is relatively homogeneous and spectrally similar to mature apollo 16 soils suggesting an upper crustal source the centrally located maunder formation is distinct from the younger mare basalts but comparable to the hevelius formation in its spectral reflectance properties supporting an interpretation as basin impact melt the montes rook formation located in an annulus between the maunder and the hevelius shows a slightly stronger mafic absorption and may be the deepest crustal material excavated the distal orientale deposits show local mafic enhancements in the schiller schickard and mendel rydberg regions interpreted to represent pre orientale mare deposits or cryptomaria intermixed with overlying basin ejecta in this case maria of sizes comparable to those presently observed were widespread in this region before the orientale impact mixing model analyses are consistent with the ballistic erosion and sedimentation model for ejecta emplacement in the distal regions beyond the continuous ejecta deposit on the southern lunar farside a huge area with an enhanced mafic absorption corresponds to the interior and rim of the pre nectarian south pole aitken impact basin 2000 2500 km in diameter the anomaly is interpreted to be due to several factors including excavation into the more mafic lower crust and the presence of extensive early volcanic fill cryptomare similar to that seen in ancient basins such as smythii and australe these results show that although basin forming events are an important factor in producing lateral heterogeneities in crustal composition and in modifying preexisting deposits such as cryptomaria the majority of material in even the largest basins was excavated from crustal levels our results suggest a gradational vertical crustal stratigraphy consisting of an uppermost mixed crustal layer of anorthosite basin ejecta and cryptomaria deposits generally corresponding to the megaregolith an upper crustal layer of anorthosite and a lower more noritic layer many of the basic questions remaining from this study could be addressed by global high resolution geochemical and mineralogical data obtained by polar orbiting spacecraft

stability of foams in silicate melts bubble coalescence and the spontaneous disruption of high porosity foams in silicate melts are the result of physical expulsion of interpore melt syneresis leading to bubble coalescence and diffusive gas exchange between bubbles melt expulsion can be achieved either along films between pairs of bubbles or along plateau borders which represent the contacts between 3 or more bubbles theoretical evaluation of these mechanisms is confirmed by experimental results enabling us to quantify the relevant parameters and determine stable bubble size and critical film thickness in a foam as a function of melt viscosity surface tension and time foam stability is controlled primarily by melt viscosity and time melt transport leading to coalescence of bubbles proceeds along inter bubble films for smaller bubbles and along plateau borders for larger bubbles thus the average bubble size accelerates with time in silicate melts the diffusive gas expulsion out of a region of foam is effective only for water and even then only at small length scales as the diffusion of co2 is negligible the results of our analyses are applicable to studies of vesicularity of lavas melt degassing and eruption mechanisms

evolution transfer and release of magmas and volcanic gases an introduction abstract in this introduction recent progress in the study of the evolution transfer and release of magmas and volcanic gases is briefly reviewed based on discussions at the mag2007 international conference held in taipei taiwan in april 2007 the meeting pooled the diverse expertise of igneous and volcanic gas geochemists this special issue which presents six case studies covering a range of topics from variations in mantle source compositions to the nature of volcanic degassing reflects that diversity

image processing of explosive activity at stromboli abstract a new way to study the dynamics of explosive behaviour at different vents of stromboli volcano is proposed the method is based on computer processing of images taken by an infrared film camera at a rate of 4 pictures per second each picture has been digitized by use of an image scanner with a 75 d p i dots per inch resolution and 256 levels of gray then processed and the total mass of the ejected material has been calculated for each photograph with this procedure the flux of ejected matter throughout every single explosive event has been reconstructed the analysis of trajectories made on adequate samples of ejecta has allowed us to evaluate the ejection velocity the mode of the mass flux distribution and the mean value of the velocities calculated for individual particles quantify the kinetic energy of an explosion vents nos 1 and 3 which remained active after the last effusive eruption of 1985 1986 show several explosive patterns the energy of which is measured the observed flux distributions have been checked both numerically and experimentally by modelling impulsive events the computer simulations of the mass distributions have allowed us to speculate on the possible explosive dynamisms two different models have been used a single impulse model confirms the behaviour actually shown by one of the two vents while the behaviour of the other is better depicted by a cumulative trend of successive impulses in rhythmic sequence moreover through the experimental approach we have had the opportunity to test the overall resolution of the method the observed matter flux distribution has then been associated to the seismic signals in order to correlate the dynamics involved in the explosions with the seismic source mechanisms

iron abundances on the lunar surface as measured by the lunar prospector gamma ray and neutron spectrometers i global measurements of iron abundances on the lunar surface are presented using data from the lunar prospector lp gamma ray spectrometer grs and neutron spectrometer ns in this study we derive relative iron abundances from the low altitude high spatial resolution 45 km 2 lp data using the 7 6 mev neutron capture gamma ray doublet as part of the lp grs analysis we demonstrate the importance of accounting for variations in neutron number density across the lunar surface by measuring neutron fluxes using lp ns data in a first step of comparing the lp grs data with previously published iron abundances inferred from clementine spectral reflectance csr data we show that the existing csr feo data are nonlinear with respect to the lp relative iron abundances we use the lp data to linearize the relationship between the csr and the relative iron values then recalibrate the csr data to iron abundance using returned soil abundances we then correlate the csr data except for major anomalies with the lp relative iron measurements to convert the lp data to absolute iron abundances when we compare the lp grs and revised csr data sets we find a very good correspondence there are two locations mare tranquillitatis and south pole aitken spa basin that show major discrepancies suggesting that the csr data are locally overestimating iron abundances in both these regions the discrepancies identified by the lp grs csr comparison are possibly explained by mineralogical differences that are not accounted for in the csr to feo calibration in regards to our understanding of the moon the lp data have found the following i there exist large expanses of mare basalt in the western mare regions that have very high iron abundances 22 23 wt feo that are underrepresented but not absent from the returned sample collection and are highly unusual for mare soils which typically contain a significant amount of highlands contamination 2 the low iron abundances in the lunar highlands 5 feo wt are consistent with a previous analysis using thermal and epithermal neutrons and with the idea that the lunar crust formed by a relatively simple magma ocean process 3 the comparison of lp and csr derived iron abundances suggests that the material within spa basin is similar to a norite type rock without an enriched mantle feo signature 4 a comparison of lp and csr data at tycho crater shows a large discrepancy such that the csr data show moderate iron abundances of 8 9 wt feo while the lp data show very low iron abundances of 3 4 wt feo this discrepancy cannot yet be easily explained by any known process