pipe vesicles an alternate model for their origin most pipe vesicles occur near the base of basaltic flows where they are interpreted to be traces left by ascending gas bubbles some basaltic pillows also contain pipe vesicles but in these pillows pipe vesicles have a radial distribution indicating that buoyancy cannot be a factor in their formation pipe vesicles do not extend through chilled glassy margins at the base of flows or rims of pillows but rather they form only where there has been significant crystallization indicating that the gas forming these vesicles is exsolved from the lava and is not derived from an external source pipe vesicles in flows and pillows are proposed to form by the exsolution of gas onto bubbles that are attached to the zone of solidification as this zone advances into the cooling lava continued exsolution of gas causes the bubbles to grow normal to the solidification front as pipes gas tubes formed in a similar manner can be seen in most ice cubes lava near the advancing tip of a pipe vesicle cools more rapidly than elsewhere because heat is able to transfer along the pipe by radiation pipe vesicles therefore grow into the lava as cold fingers they cease growing when separate gas bubbles nucleate ahead of them in the ever broadening zone of solidification lava need contain no more than 0 01 wt h 2 o for pipe vesicles to form in this way

apollo 16 regolith breccias characterization and evidence for early formation in the mega regolith all of the apollo 16 regolith breccias 8 specimens have been characterized in terms of their petrography grain size distribution porosity major and trace element composition noble gas contents and ferromagnetie resonance properties these breccias vary signkqcantly with respect to their density and porosity with the more dense breccias showing significant shock damage the regolith breccias resemble the soils in grain size distribution and in the relative proportions of major petrological components except agglutinates many of the breecias are compositionally different from the apollo 16 soils in that they lack an important marie component present in the soils although some groupings occur the petrologic and chemical compositions of the regolith breedas do not correlate with the station location of the samples all but one of the breceias show some evidence of irradiation at the lunar surface solar gases measurable fmr agglutinates and analyses made on grain size separates from two disaggregated breedas indicate that this irradiation occurred before compaction when the breccia material was finely disseminated on the surface however the concentrations of surface irradiation parameters solar gases fmr agglutinates for most breedas are far less than seen in any lunar soils or in regolith breccias from other apollo missions several breedas also contain unusually high trapped 4oar 36ar ratios of 8 12 and a significant fission xe component in excess of that expected from in situ production these observations suggest that the surface irradiation of these breedas occurred as early as 4 x 109 years ago we conclude that most of the apollo 16 regolith breedas were not formed from any known apollo 16 soil they appear to be well comminuted material that contains ancient regolith developed during the late stage heavy bombardment of the moon when large impacts were much more common relative to small impacts so that regoliths did not have time to significantly mature before being diluted by fresh ejecta and buffed this ancient megaregolith is significantly different from more recent lunar regolith but may be similar to asteroidal regoliths from which some brecciated meteorites have formed

lava fountain heights at pu u o o kilauea hawaii indicators of amount and variations of exsolved magma volatiles we review the factors determining lava fountain heights in hawaiian style basaltic eruptions such as those occurring during the recent series of eruptive episodes at the pu u o o vent east rift zone of kilauea volcano hawaii numerical solutions to the equations describing the fluid dynamics of such eruptions predict that lava fountain heights which are indicators of the velocity of magmas in vents should be controlled much more strongly by amounts of exsolved volatiles than by any other factors the next most important factor is the width of the conduit system which determines frictional losses and can be characterized by the volume flux of magma the diameter of the surface vent required to accommodate a given discharge i e instantaneous volume rate of eruption is also a function of exsolved magma volatile content but is less dependent on this factor than is the fountain height we simulate fountain heights for typical discharges at pu u o o and find implied exsolved gas contents very close to those determined by other methods the corresponding predicted vent diameters are comparable with and somewhat smaller than the observed diameter of the pu u o o vent the discrepancy is probably a consequence of processes occurring in the lava pond which is present over the vent during eruptions the variation of fountain height with time during eruptive episodes can be used as a measure of changing exsolved magma volatile content which can be related to processes occurring in the subsurface dike system

waves of bubbles in basaltic magmas and lavas initially homogeneous suspensions of bubbles in basaltic magmas and lava flows may become unstable and form rising waves or layers of bubbles we derive a set of model equations for the two phase bubble liquid system and present the results of a linear stability analysis and numerical simulations periodic vesicle layers are preserved in columbia liver flows with a spacing of 1 m the prediction of the stability analysis combined with a simple model for solidification of the lava suggests that vesicle layers may represent waves of bubbles formed within the flow the spacing of layers is determined by a balance between the growth of bubbles and hydrodynamic self diffusion vesicular layers preserved in columbia liver flows may thus form by hydrodynamic processes and do not require the repeated injection of fresh volatile rich magma or a periodic nucleation of bubbles waves of bubbles may also develop in magma chambers and conduits and could play a role in eruption dynamics

the role of salt marsh erosion in barrier island evolution and deterioration in coastal louisiana abstract barrier shoreline erosion in louisiana reaches over 33 ft yr 10 m yr and island area decreased by 40 between 1880 and 1979 salt marsh erosion is an important factor in evolutionary barrier shoreline development and is presently contributing both directly and indirectly to the deterioration of louisiana s barrier islands the marshes originally developed as fresh marshes associated with regression of mississippi river delta lobes after fluvial abandonment salinity gradually increased and natural habitat change occurred as subsidence of deltaic sediments and transgression of the coastline by marine processes proceeded the marsh surface is subjected to relative sea level rise and unless sufficient sedimentation maintains marsh elevation erosional processes become dominant increased inundation of marsh vegetation stresses even halophytic vegetation and ultimately leads to plant death examination of variations in marsh topography over an area of approximately 2 45 acres 1 hectare revealed marked variations in the frequency and duration of tidal inundation increased flooding of lower areas can be sufficient to cause plant death and the opening of marsh ponds fragmentation of the marsh by these subsidence induced processes is part of the evolution of morphostratigraphic forms in the mississippi deltaic plain from erosional headland with flanking barriers to barrier island arc coastal bays in the mississippi deltaic plain many of which originated as interdistributary bays before transgression are also expanding at the expense of the surrounding salt marshes measurements on the margins of terrebonne timbalier bay approximately 77 mi2 200 km2 in area show that the rate of marginal erosion varies according to the exposure of the bay shoreline to prevailing southeasterly winds and fetch length across the bay in the most exposed areas erosion rates of over 13 ft yr 4 m yr have been monitored and even the north facing bay shorelines of barrier islands experience erosion rates of up to 6 6 ft yr 2 m yr the expansion of coastal bays and the fragmentation of interior marshes by pond formation leads to escalation of marsh erosion and increased threats to barrier islands bay margins disintegrate to a series of small islands which are rapidly eroded by wave attack as islands disappear wave fetch across the bay lengthens and wave attack on these island shorelines as well as back barrier marshes increases erosion of back barrier marshes both deceases island area and reduces the foundation for landward migration of the barrier sand body plans to restore louisiana s barrier islands must address the problem of bay expansion and back barrier marsh erosion in order to maintain a viable barrier beach system

bubble migration and coalescence during the solidification of basaltic lava flows the initial size distribution of gas bubbles in lava flows is modified by bubble rise and coalescence during post eruptive cooling and crystallization a simple model which computes the effects of rise and coalescence accounts for observed features and may provide a means whereby the initial bubble size distribution can be inferred a model lava flow of assumed thickness viscosity and volume percentage of gas bubbles is given an initial bubble size distribution bubbles coalesce due to differences in their relative rise velocities using a gravitational collection kernel the process may be modeled by numerical integration of the stochastic collection equation which yields the change in the number density spectrum of the population from the number densities of all pairs of bubbles and their probabilities of collision bubbles rise and coalesce within a fluid interior sandwiched between fronts of crystallization that advance inward from top and bottom bubbles that are overtaken by the crystallization f

from alkali basalt to phonolite in hand size samples vapor differentiation effects in the bouzentes lava flow cantal france abstract the bouzentes lava flow is a 20 m thick alkali basalt flow emplaced during the last stage of formation of the cantal stratovolcano at 4 2 ma its upper part has 1 to 20 cm thick vesicle rich segregation sheets which recur every 0 1 2 m these horizontal veins are hawaiitic in composition they are characterized by hypertrophic development of their minerals pegmatoids and by glassy phonolitic segregation vesicles internal differentiation within the bouzentes lava flow was triggered by an unusually high water content as suggested by pre emptive iddingsite alteration of olivine phenocrysts the proposed model of formation of the segregation sheets includes the upward motion of diapirs of residual melt plus addition of vapor from the bottom of the central liquid lens to the base of the upper solidified crust of the cooling lava flow olivine settling appears to have been inhibited or at least retarded by upward migration of melt plus vesicles most of the features observed in bouzentes recall the internal differentiation processes usually described within thick hawaiian lava lakes the segregation vesicles are believed to result from an increase of gas solubility in residual melt during the crystallization process

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

magnetic properties of lunar materials meteorites luna and apollo returned samples abstract we present the first comprehensive study of the magnetic properties of lunar meteorites and compare them with measurements from apollo and luna returned samples 37 unpaired lunar meteorites were studied while new susceptibility measurements were performed on 88 luna soil and rock samples to complement published luna and apollo data new magnetic data were also obtained on 4 apollo mare basalt samples magnetic susceptibility and saturation remanence appear mainly controlled by the amount of metallic iron added by the regolith forming processes and meteoritic contamination as shown by a positive correlation with ni and ir content a decrease with depth in regolith core profiles and a decrease with increasing soil size fraction the three sources of lunar materials provide coherent range of magnetic properties although the much larger abundance of anorthositic highland samples in the meteorite collection allows one to better describe the properties of this major lunar lithology the observed range of saturation remanence implies that mare basalts cannot contribute significantly to the patchy lunar crustal magnetizations which must be attributed to superficial impact processed feldspathic or mafic lithologies

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

geochemistry and petrography of the macalpine hills lunar meteorites abstract macalpine hills 88104 and 88105 are anorthositic lunar meteorites recovered from the same area in antarctica which are demonstrated to be paired samples of the same fall petrographic studies of matrix and clasts show that mac88104 5 is a polymict breccia dominated by impact melt clasts it contains a small amount of highland impact glass and very few regolith glass spherules it is better classified as a fragmental breccia than a regolith breccia the bulk composition is ferroan mg 63 and highly aluminous al 2 o 3 28 ree and other incompatible element concentrations are very low compositions of anorthositic granulitic and impact melt breccia clasts are very similar to but distinct from matrix composition mac88104 5 is very similar in composition to the other anorthositic lunar meteorites but each of the meteorites is distinct the anorthositic lunar meteorites especially mac88104 5 and y82192 3 86032 are very similar to north ray crater feldspathic fragmental breccias in compositon and petrography these fragmental lunar meteorites may have been ancient deeply buried breccias from the megaregolith comparisons of chemical petrographic features and exposure histories suggest that the twelve lunar meteorites were derived from two to nine but probably four to seven impacts onto the lunar surface discrepancies between the proportions of lunar meteorites and results of apollo missions may be due to unrepresentative sampling lunar meteorites provide valuable new information on the nature of the lunar crust

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

lunar meteorites siderophile element contents and implications for the composition and origin of the moon abstract six lunar meteorites have thus far been discovered in antarctica although these meteorites are of undocumented lunar geographic provenance all other available lunar samples obtained from the apollo and luna programs came from a relatively minuscule region of the central nearside around which a polygon could be drawn covering just 4 7 of the lunar surface the five lunar meteorites that are now well studied represent at least two but probably three separate lunar source craters alha81005 and y791197 are probably from separate craters and compound meteorite y82192 6032 is certainly from a crater of its own at least alha81005 and y791197 and probably also at least in a loose sense y82192 6032 are highlands regolith breccias thus their compositions may be appropriately compared with compositions of apollo and luna highlands regolith samples compared with average highlands regolith samples from the central nearside apollo sites lunar meteorites have lower concentrations of siderophile elements in general and especially au ge and ni among anorthositic apollo samples i e mainly those from apollo 16 au ir and to a lesser extent ge ir ratios tend to be hyperchondritic most previous models for lunar regolith siderophile geochemistry assumed that the apollo 16 samples are representative of the overall lunar highlands such models tended to conclude that the hyperchondritic au ir and ge ir ratios were consequences of variations in the compositions of moon striking projectiles as a function of time it was even speculated that these temporal variations were consequences of the heterogeneous accretion of a moon with a general enrichment in refractory elements the lunar meteorites suggest that hyperchondritic au ir and ge ir are not general features of the highlands but peculiarities of the apollo 16 region or more generally the central nearside the high ni contents of the apollo 16 megaregolith substantially in excess of the ni implied by a model in which all meteoritic debris has an h chondritic ni ir ratio have been interpreted to imply that the mg rich fraction of the lunar crust is extremely ni rich and thus similar in siderophile geochemistry to terrestrial komatiites this coincidence has been interpreted as confirmation that the moon formed by modified fission from the earth s mantle after core formation plus late accretion effects had established the final siderophile pattern of the earth s mantle however the lunar meteorites and a survey of data for the luna 20 highlands regolith sample suggest that the high ni content of the apollo 16 regolith is strictly a peculiarity of the apollo 16 region and not a general feature of the moon s crust the anomalous siderophile composition of the central nearside regolith probably stems from a combination of regional heterogeneity in cratering projectile compositions plus regional enrichments in relatively labile siderophile elements most notably au ge and perhaps to a certain extent ni which might be loosely correlated with the anomalously high concentration of kreep over the central nearside

on the spectral peaks of volcanic tremor at stromboli abstract seismic activity at stromboli volcano is characterized by a variety of signals emanating from three vents for a long time the northwest vent has been in constant activity periodically large explosions occur and material is ejected beyond the crater walls these large explosions are accompanied by sonic and infrasonic pressure waves in the atmosphere and explosion quakes apart from large explosions there is constant activity in the form of continuous gas bursts which are related to low infrasonic pulses in the atmosphere and volcanic tremor we assume that volcanic tremor and low pressure infrasonics are generated by gas bubbles inside the volcanic conduit and accordingly we compute synthetic tremor by modeling the source function as a pressure variation in a spherical cavity that propagates through a finely layered medium by means of haskell s formalism to simulate a tremor we superpose in time domain a large number of such pulses of varying amplitudes and time delays according to the observed infrasonic series in addition to the spectral similarity the observed and synthetic tremor display the same autocorrelation and hurst exponents implying similar long term correlation we present strong evidence in favour of an interpretation of the spectral peaks of the volcanic tremor at stromboli in terms of resonances of the layered structure hence as a path effect rather than a source effect

trapped noble gases indicate lunar origin for antarctic meteorite the isotopic abundances of the noble gases he ne ar kr xe are reported for antarctic meteorite alha81005 it contains solar wind implanted gases whose absolute and relative concentrations are quite similar to lunar regolith samples but not to other meteorites alha81005 also contains a large excess 40ar component which is identical to the component in lunar fines implanted from the lunar atmosphere large concentrations of cosmogenic 21ne 82kr and 126xe in alha81005 indicate a total cosmic ray exposure age of 2 108 years the noble gas data alone are strong evidence for a lunar origin of this meteorite

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

experimental constraints on bubble interactions in rhyolite melts implications for vesicle size distributions we have studied interactions between bubbles of two distinct size classes in rhyolite melts experimentally decompressed between 200 and 80 mpa the first set of decompression bubbles has a size range rdec of 1 11 m and is formed from nucleation and growth upon isothermal decompression of the melt the larger populations of hydration bubbles are on average 30 40 m in radius rhyd and are formed from pore spaces present that were filled with water vapor during the saturation runs prior to the decompression experiments the first type of interaction results in the elongation of decompression bubbles oriented radially around the larger hydration bubbles the degree of elongation increases both as a function of distance and with increasing ratio of hydration to decompression bubble size rhyd rdec the second type of interaction studied results in a reduction of the size of decompression bubbles located within a range of distances from 10 to 65 m from a hydration bubble surface relative to the modal size of the unaffected bubbles in the same sample in addition within an average distance of 10 m melt next to the hydration bubble surface is depleted in decompression bubbles our results indicate that concentration gradients in the melt are probably responsible for bubble size reduction and the depleted zones because the predicted time scales for ostwald ripening are much longer than those of the experiments these effects persist even to the lowest ending pressures studied 80 mpa which indicates that size distributions of small bubbles may be affected by concentration gradients in the depleted melt shell surrounding large bubbles large bubbles present in an ascending magma prior to a subsequent nucleation event could therefore affect the growth of the smaller bubble population occurring within the depleted melt shell of the larger bubbles and produce a bimodal vesicle size distribution elongated decompression bubbles may be strained as a result of melt flowing away from the much larger hydration bubbles as they grow estimates of capillary number ca plotted against deformation df indicate that bubbles in water rich rhyolite melts are deformable even at small sizes 1 m and small values of ca our results show a different trend of df with ca than previous studies in non geological systems predict indicating that viscosity effects may be important the preservation of deformation textures depends strongly on relaxation time explaining the lack of deformation textures in less viscous natural lavas

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

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

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

segregation processes in vesiculating crystallizing magmas vesiculation of crystallising magma can produce either a mobile vesicular magma or a rigid network of crystals containing vesicular liquid where partially crystallized rigid mush underlies less crystallized magma such as near the base of a lava flow or in the cumulus pile of a magma chamber evolved interstitial melt and or gas may escape into the main body of magma the consequences of this may include contamination of the overlying liquid with gas and interstitial melt or intrusion of diapirs of vesicular evolved liquids to form vertical vesicle cylinders and other segregation features found in many basaltic lava flows and sills analog experiments were used to investigate some of the phenomena that can arise during vesiculation within a crystal mush which was simulated by pumping air through a porous plate that formed the floor of a container filled with a viscous liquid floored with a layer of glass beads experiments used either a single liquid or two stably stratified liquids with a liquid interface either coincident with the top of the porous layer of beads or slightly above the porous layer for a range of liquid viscosities and air flow rates vesiculation rates individual bubbles emerged from the top of the porous layer of beads and carried a thin trail of interstitial liquid into the overlying liquid the number of bubble trains leaving the surface of the porous bed increased with decreasing liquid viscosity and flow rate and with increasing bead size and hence with increasing permeability analog vesicle cylinders composed of diapirs of bubbly interstitial liquid were produced only when a layer of buoyant bubbly liquid lay above the surface of the porous layer the relative size of the bubbles and constrictions within the porous layer are argued to control whether individual bubbles leading to bubble trains or vesicular liquid leading to vesicle cylinders leaves the porous layer and hence whether vesicle cylinders can form

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

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

synneusis of kilauea iki olivines olivine phenocrysts in the picritic scoria that erupted from kilauea iki in 1959 occur as glomeroporphyritic aggregates of 2 16 crystals the compositions and three dimensional textures of the olivines vary within an aggregate and within individual lapilli the attachment of crystals from different environments indicates that these aggregates formed by synneusis the swimming together of crystals most of the crystals are attached along faces with their a crystallographic axes parallel and their c axes either parallel or perpendicular so that the structural mismatch and interfacial energy are minimized observed facial attachments are consistent with fluid dynamical interactions of crystals falling with their large 010 faces horizontal the aggregates formed in a liquid rich magma rough computations suggest that the minimum aggregation time could be on the order of minutes aggregation of very small crystals suggests that the yield strength was less than 3 dynes cm 2 the textures of the aggregates are similar to those of cumulate peridotites

bubbledrive 1 a numerical model of volcanic eruption mechanisms driven by disequilibrium magma degassing abstract we have developed a numerical model for magma dynamics in volcanic conduits that involves conduit flow driven by a detailed treatment of bubble growth the bubbledrive 1 model can be characterized by several unique aspects including treatment of the transient problem specific eruption triggers disequilibrium degassing a full scale bubble growth module and steady state eruption in the case of constant recharge from below the general conditions for the model are homogeneous two phase flow a simple fragmentation threshold pre existing bubbles and parameters corresponding to magma compositions of dacite and rhyolite the advantage of using a full scale bubble growth model in our treatment of conduit flow makes it possible to track the level of oversaturation throughout the conduit in space and time the model accounts for dynamic decompression in which the evolving interaction between decompression rate due to magma ascent and diffusive addition of gas into bubbles due to decreased solubility with decreasing pressure serves as the driving force of magma flow in the conduit the ability of the model to run the transient case enables us to explore specific triggers to initiate an eruption which proceeds with duration and eruption energy depending on conduit geometry and several other factors our numerical study revealed several notable features of volcanic systems that may shed additional light on natural systems each of the model runs was directed at elucidating specific aspects of eruptions and the suite of runs indicated some common features that may play a key role in all silicic eruptions we find that conduit geometry is critical in determining the nature of eruption conduits lacking a magma chamber have smooth and relatively quiet eruption styles conduits that include a magma chamber involve eruptions that start out like those without chambers but then evolve into a long and uniform eruption that ends with a violent explosion as the chamber is emptied the uniform phase is maintained by vesiculation within the chamber and the blast occurs when the fragmentation level descends down into the magma chamber resistance to flow imposed by the narrow conduit above the chamber acts as a buffer stabilizing the eruption during the steady state phase until the chamber is depleted in material discharge and vent velocity are proportional to the conduit chamber depth and are controlled by the initial concentration of dissolved volatiles maximum oversaturation is observed immediately below the fragmentation level of the magma column oversaturation at the vent remains remarkably constant at 1 wt of h2o for all cylindrical conduits with no recharge from below oversaturation at the vent is much more complex for conduits that contain magma chamber at 2 km depth our numerical study indicates that the primary factors that control eruption behavior are magma composition and conduit shape this suggests that future observation programs could provide valuable information by determining sub edifice structure so that better constraints on geometry can be derived

ferromagnetic resonance and magnetic properties of alha81005 seven chips of primarily matrix material from the antarctic meteorite alha81005 were analyzed by ferromagnetic resonance fmr and magnetic hysteresis techniques the fmr spectra of two chips have a resonance at g 2 1 that resembles the g 2 1 resonance that is characteristic of lunar soils thus the fmr spectra are consistent with the lunar regolith being a progenitor for the matrix material for the two chips is feo 5 units which is equivalent to a value for an immature lunar soil the total concentration of metallic iron is on the order of 0 11 equivalent wt which is within the observed range for apollo 16 rocks and soils

porosities of lunar meteorites strength porosity and petrologic screening during the meteorite delivery process porosity has been directly measured for eight lunar meteorite breccias and calculated for two more on the basis of literature density measurements lunar meteorite regolith breccias display systematically low porosity in comparison to otherwise analogous apollo regolith breccias among seven meteoritic regolith breccias porosity ranges from 1 to 11 and averages 7 5 1 3 2 whereas for 44 analogous apollo samples porosities mostly calculated from literature density data the average is 25 1 7 the origin of this disparity is enigmatic but the trend probably reflects mainly a bias in favor of strong compact breccias among fragments that manage to survive the violent process of launch to lunar escape velocity 2 38 km s in addition compaction during launch may play an important role the population of lunar meteorites is clearly not a random unmodified sample of lithic materials near the surface of the parent body

it takes three to tango 2 bubble dynamics in basaltic volcanoes and ramifications for modeling normal strombolian activity this is the second paper in a two part series examining numerical simula tions of buoyancy driven ow in the presence of large viscosity contrasts in the rst pa per we demonstrated that a combination of three numerical tools an extended ghost uid type method the level set approach and the extension velocity technique accurately simulate complex interface dynamics in the presence of large viscosity contrasts in this paper we use this three fold numerical method to investigate bubble dynamics in the conduits of basaltic volcanos with a focus on normal strombolian eruptions strombolian type activity named after the famously episodic eruptions at stromboli volcano is char acterized by temporally discrete fountains of incandescent clasts the mildly explosive nature of normal strombolian activity as compared to more eusive variants of basaltic volcanism is related to the presence of dissolved gas in the magma yielding a complex two phase ow problem we present a detailed scaling analysis allowing identication of the pertinent regime for a given ow problem the dynamic interactions between gas and magma can be clas sied into three non dimensional regimes based on bubble sizes and magma viscosity re solving the uid dynamics at the scale of individual bubbles is not equally important in all three regimes as long as bubbles remain small enough to be spherical their dy namic interactions are limited compared to the rich spectrum of coalescence and breakup processes observed for deformable bubbles in particular once inertia ceases to be neg ligible one key nding in our simulations is that both large gas bubbles and large conduit lling gas pockets slugs are prone to dynamic instabilities that lead to their rapid breakup during buoyancy driven ascent we provide upper bound estimates for the maximum sta ble bubble size in a given magmatic system and discuss the ramications of our results for two commonly used models of normal strombolian type activity the rise speed dependent rsd model and the collapsing foam cf model

formation of segregation structures in hafnarhraun pāhoehoe lobe sw iceland a window into crystal melt separation in basaltic magma to gain insights into crystal melt separation processes during basalt differentiation we have studied an 8 m thick p hoehoe lava lobe from the hafnarhraun lava flow field in sw iceland the lobe has abundant melt segregations porous cylindrical and sheet like structures generally interpreted as separated residual melts of a lava lobe we divide these melt segregations into three types based on morphology and composition vesicle cylinders vc type 1 horizontal vesicle sheets hvs1 and type 2 horizontal vesicle sheets hvs2 remarkably the studied vc are not simple residual melts generated by fractional crystallization but their composition points to removal of plagioclase from the parental lava hvs1 resemble vc but have fractionated more olivine ol plagioclase plg augite and have lost most if not all of their olivine phenocrysts hvs2 are fe rich and evolved corresponding to residual melts after 50 60 fractional crystallization of the lobe we suggest that the hafnarhraun vc formed in a two stage process firstly vc forming residual melt and vapor detached as rising diapirs from ol plg melt vapor mush near the lava base and later these vc diapirs accumulated ol phenocrysts and minor plg microphenocrysts in the lava core hvs1 represent accumulations of vc to the viscous base of the solidifying upper crust of the lobe and hvs2 formed as evolved vapor saturated residual melts seeped into voids within the upper crust such vapor aided differentiation here documented for the hafnarhraun lava may also apply to shallow crustal magma storage zones contributing to the formation of evolved basalts

two stage vesiculation in the cohassett flow of the grande ronde basalt south central washington the cohassett flow in south central washington is considered a possible host for a nuclear waste repository at the hanford site and is being investigated as part of the basalt waste isolation project the cohassett flow of the grande ronde basalt contains two vesicular zones separated by 24 m of dense sparsely vesicular basalt the vesicular zones represent accumulations of upward migrating bubbles sequentially frozen in by the downward passage of the upper solidification front the separation of the two zones suggests a hiatus in the exsolution of aqueous vapor from the lava the flow top vesicular zone formed during and immediately following emplacement of the flow from vapor bubbles nucleated during ascent and eruption whereas the internal vesicular zone formed after emplacement from bubbles apparently nucleated at the lower solidification front homogeneous nucleation of vapor was probably initially driven by large oversaturation pressures in the erupting lava after emplacement heterogeneous nucleation of vapor was probably initiated by crystallization in the margins of the flow

origin of vesicle layering and double imbrication by endogenous growth in the birkett basalt flow columbia river plateau abstract the 40 m thick birkett basalt pahoehoe flow at sentinel gap in the columbia river plateau has an unusually thick 15 m upper vesicular zone this zone includes a striking layering in which the layers have contrasted vesicle abundances and sizes most layers show a reverse grading of vesicle size and abundance the layering is interpreted to have grown endogenously by the cyclic injection of vesicular lava layers under the growing top crust accommodated by uplift of that crust grading of the layers resulted from vesicle growth and ascent each injection occurred at or near the boundary between vesicular and non vesicular lava of the preceding layer and split that layer into an upper vesicular part and a lower non vesicular part critical to this interpretation are 1 a pervasive foliation and lineation defined by the parallelism of strongly flattened and elongate vesicles transects the vesicle layers obliquely and 2 the magnetic fabric the anisotropy of magnetic susceptibility is oriented similarly to the vesicle foliation and also defines a cryptic foliation in the non vesicular zone having a dip opposed to that in the layered zone these foliations are interpreted to be opposed imbrications and indicate the flow azimuth of the lava they strongly support the concept of lava growth by successive thin sill like insertions of fresh vesicular lava between hot but static and effectively solid floor and roof

pipe vesicles in hawaiian basaltic lavas their origin and potential as paleoslope indicators study of several hawaiian tholeiitic volcanoes shows that pipe vesicles form only in thin pahoehoe flow units standing on a ground slope of less than about 4 the vesicles thus have potential as paleoslope indicators two examples are given of their use to deduce that the steep dip of certain intracaldera lavas is due to tilting pipe vesicles are attributed to gas bubbles rising through lava at a stage in its cooling history when it had acquired a yield strength of a few tens of n m 2 sufficient to prevent closure of lava behind the bubbles

alha 81005 meteorite chemical evidence for lunar highland origin based on the well established characteristic lunar and meteoritic ratios of feo mno cr2o3 v and k la and ree patterns alha 81005 meteorite is undoubtedly of lunar highland origin the alha 81005 meteorite is an anorthositic gabbro 72 pl and matches closely in chemical composition to apollo 15 15418 and luna 16 21013 highland rocks the rock is a non kreepy and vlt type the siderophiles au ni and ir content is high 1 5 cl equivalent and similar to other lunar highland breccias the clast has a different ancient meteorite component than the bulk and matrix the meteorite has a young terrestrial age implying a recent lunar cratering event therefore during major lunar basins formation in early eons the earth must have received a significant amount of lunar material which is now mixed in the crust the finding of a lunar meteorite lends credibility to the suggestion that snc achondrites may come from mars

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

antarctic meteorite alha 81005 a piece from the ancient lunar crust a 128 mg sample of the antarctic meteorite alha 81005 was analysed for major and trace elements by instrumental neutron activation techniques the meteorite or at least its major components may be older than 4 billion years and represent a piece of the ancient lunar crust before the formation of the large basins on the front side of the moon the evidence is derived from the low absolute content of incompatible elements and their slightly different fractionation pattern from kreep the dominant source for these elements on the front side the basically chondritic pattern of siderophile elements ni co ir au is clearly distinguished from younger basin related meteoritic components

internal differentiation of kutsugata lava flow from rishiri volcano japan processes and timescales of segregation structures formation article i nfo internal differentiation processes in a solidifying lava flow were investigated for the kutsugata lava flow from rishiri volcano in northern japan in a representative 6 m thick lava flow that was investigated in detail in this study segregation products darker than the host lavas manifested mainly in the form of pipes vesicle cylinders and layers vesicle sheets occurring around 0 5 2 3 m and 2 0 4 0 m above the base respectively both the cylinders and sheets are significantly richer in incompatible elements such as tio2 and k2o than the host lavas which suggest that these products essentially represent residual melt produced during solidification of the lava flow field observation and the geochemical features of the lavas suggest that the vesicle cylinders grew upward from near the base of the flow by continuous feeding of residual melt from the neighboring host lavas to the heads of the cylinders on the other hand the vesicle sheets were produced in situ in the solidifying lava flow as fracture veins caused by horizontal compression the vesicle cylinders have a remarkably higher mgo content up to 8 wt than the host lava b6 wt whereas the vesicle sheets display mgo depletion as low as 3 5 wt the relatively high mgo content of the vesicle cylinders cannot be explained solely by the mechanical mixing of olivine phenocrysts with the residual melt it is suggested that the vesicle cylinders were produced by the extraction of olivine bearing interstitial melt from an augite plagioclase network in the host lava whereas the vesicle sheets were formed by the migration of the residual melt from a crystal network consisting of plagioclase augite and olivine in the host lava into platy fractures we infer that this selective crystal fractionation for forming the vesicle cylinders resulted from processes in which abundant vesicles rejected from the upward migrating floor solidification front prevented olivine crystals from being incorporated into the crystal network in the host lava the vesicle cylinders are considered to have formed in 1 day after the lava flow came to rest while relatively large vesicle sheets n1 cm thick appeared much later after 9 days the formation of these segregation products was essentially complete within 20 days after the lava emplacement