changes in the hydrothermal system at loihi seamount after the formation of pele s pit in 1996 sulfide and sulfate minerals recovered from loihi seamount during pisces v submersible dives in october 1996 are the first occurrence of high temperature hydrothermal mineralization documented for ocean island volcanoes millimeter to centimeter sized particles recovered in talus deposits on the north rim of the newly formed pele9s pit consist of aggregates of pyrite marcasite pyrrhotite wurtzite and barite the barite occurs as single clear euhedral crystals or as acicular radial crystal clusters on sulfide or rock fragments the mineral assemblage and the composition of the sulfide phases are similar to those of hydrothermal sulfide from mid ocean spreading centers the sulfide assemblage confirms the presence of high temperature fluids 250 c in the loihi hydrothermal system the sulfide samples are not pieces of broken chimney or basal mound structures or stockwork from lower levels in the hydrothermal system the euhedral crystals and homogeneous compositions suggest rapid precipitation from a high temperature plume injected into cold seawater along fractures and fissures that define the north wall of the new pit crater formed during the seismic swarm in july and august 1996

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

crystal morphologies in pillow basalts implications for mid ocean ridge processes abstract we present the results of a detailed petrological study of a sparsely phyric basalt mapco ch98 dr11 dredged along the mid atlantic ridge 30 41 n the sample contains microphenocrysts of olivine that display four different rapid growth morphologies comparison of these morphologies with those obtained in dynamic crystallization experiments allows us to constrain the thermal history of the sample the dendritic morphology swallowtail chain and lattice olivine is directly related to the final quenching during magma seawater interaction in contrast the three other morphologies namely the complex polyhedral crystal the closed hopper and the complex swallowtail morphology result from several cycles of cooling heating corresponding to a maximum degree of undercooling of 20 25 c during crystal growth these thermal variations occurred before eruption and are interpreted to be the result of turbulent convection in a small magmatic body beneath the ridge the results suggest that the mid atlantic ridge is underlain by a mush zone that releases batches of liquid during tectonic segregation aphyric basalts are emitted during eruptions controlled by the tectonic activity whereas phyric basalts correspond to small fractions of magma from the mush zone mobilized by reinjections of primitive magmas

coupled textural and compositional characterization of basaltic scoria insights into the transition from strombolian to fire fountain activity at mount etna italy strombolian and fire fountain activities represent a common expression of explosive basaltic eruptions however the transition between these two eruptive styles and their source mechanisms are still debated we use textural and compositional studies to characterize pyroclastic material from both the strombolian and hawaiian style fire fountain phases of the january june 2000 etna activity we find that basaltic scoria presents distinctive textural and compositional features that reflect different modes of magma vesiculation and crystallization in the two eruptive regimes overall magma that forms strombolian scoria is far more crystallized less vesicular and more evolved indicating strong volatile depletion and longer residence time before being erupted fire fountain scoria indicates a fast rising magma with evidence of moderate syneruptive volatile exsolution the new textural and compositional data set is integrated with previous volcanological and geophysical investigations to provide further insights into the dynamics of fire fountains and to frame the transition from strombolian explosions to fire fountain activity into a model that may apply to future eruptions at mount etna as well as other active basaltic volcanoes

groundwater salinization in semi arid zones an example from nador plain tipaza algeria the groundwater of nador plain has been overexploited during the last two decades the goal was to meet the demands of intensive agricultural activities and at the same time the supply of drinking water as a result the dynamic balance between freshwater and seawater has been disturbed and the quality of the groundwater has deteriorated the degradation of the groundwater quality is characterized by salinization phenomena in this project the analysis of the piezometric map indicates a piezometric water level of 0 m inside the plain the chemical analysis of major ions in the groundwater was carried out on the water samples of 24 wells it indicates an electrical conductivity of water exceeding 1 500 s cm and chloride concentrations exceeding 500 mg l in the downstream of the plain presently the groundwater in this coastal sector is used neither for drinking water nor for irrigation in this study 35 vertical electrical soundings ves were carried out in the area with geoelectrical sections and maps of iso resistivity created to delineate the zones that are affected by saltwater intrusion the findings suggest that saltwater intrusion has reached a distance of approximately 1 600 m inside the aquifer

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

pumping management of coastal aquifers using analytical models of saltwater intrusion 1 analytical models of saltwater intrusion in coastal aquifers of finite size are developed and utilized in an optimization methodology for determining the optimal pumping rates the models are based on the sharp interface approximation and the ghyben herzberg relation the governing equations are expressed in terms of a single potential and are solved analytically using the method of images to account for the aquifer boundaries the analytical models consider ambient flow and surface recharge the results are compared to numerical simulations indicating a good match as the number of images is increased the objective of optimization is to maximize the total pumping from the aquifer and a set of constraints protect the wells from saltwater intrusion the constraints are expressed using the analytical saltwater intrusion models two different constraint formulations are investigated the toe constraint formulation protects the wells from saltwater intrusion by not allowing the toe of the interface to reach the wells this formulation results in a nonlinear optimization problem which is solved using sequential quadratic programming sqp the potential constraint formulation on the other hand protects the wells by maintaining a potential at the wells larger than the toe potential this formulation results in a linear optimization problem which is solved using the simplex method several simulation runs indicate that the optimal solution is very sensitive to variations of recharge rates hydraulic conductivity heterogeneities etc the linear programming formulation besides being computationally simpler provides a safer solution than the nonlinear formulation

effectiveness of geophysical surveys for water wells relocation in overexploited aquifers the example of maggiore and traversola valleys northwestern italy aquifer overexploitation is a common problem in drinking water management this will become more and more important given the general reduction of water resources to overcome overexploitation one of the most adopted solutions is the relocation of extraction wells to establish the positions of new wells a precise knowledge of the hydrogeological setting is required specific surveys are therefore necessary to obtain information over wide investigation zones geophysical methods particularly electromagnetic and electrical can be useful with this aim in the present paper a case history on the combined use of electric resistivity tomography and time domain electromagnetic soundings is reported surveys have been performed within the maggiore and traversola valleys to investigate the uppermost part of the quaternary deposits hosting the near surface aquifer the electromagnetic data have been inverted with a spatially constrained approach by assuming a quasi 1d model of the subsurface geophysical surveys allowed for depicting the depth and lateral continuity of the supposed aquifer level in the surveyed area up to a depth of about 200 m and proposing potential positions for well relocation

aquifer characterization using shallow geophysics in the keritis basin of western crete greece effective management of groundwater resources is a well known problem in several areas around the world it is especially important to areas suffering from an intrinsic lack of fresh water such as islands detailed study of available aquifers is of particular interest in the highly touristic greek island of crete the increasing water demand makes water resources management extremely important for sustainable development this is the case in the prefecture of chania in western crete where there has been a lack of success of many different groundwater management plans that have been produced over the years and submitted for application to water management authority the inefficiency of the management plans is verified by the continuous water shortage reported every year which forces the public authorities to transfer water from far away sources and wells until today there are only geological data as well as information from the borehole logs therefore the current work is focused to study in detail the tectonic and hydrogeological characteristics of the keritis watershed to make a correlation of the available geoenvironmental information with the geophysical data of the study aquifer transient electromagnetic soundings were conducted to obtain detailed information about the tectonic hydrogeological hydrolithological and geometrical characteristics of the aquifer under investigation in addition optimum areas of water well drilling were identified to minimize the uncertainty and the total cost economical managerial etc of future groundwater surveys

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

petrology and geochronology of basalt breccia from the 1996 earthquake swarm of loihi seamount hawaii magmatic history of its 1996 eruption samples of basalt were collected during the rapid response cruise to loihi seamount from a brec cia that was probably created by the july to august 1996 loihi earthquake swarm the largest swarm ever recorded from a hawaiian volcano 210 po 210 pb dating of two fresh lava blocks from this breccia indicates that they were erupted during the first half of 1996 making this the first documented historical eruption of loihi sonobuoys deployed during the august 1996 cruise re corded popping noises north of the breccia site indicat ing that the eruption may have been continuing during the swarm all of the breccia lava fragments are tho leiitic like the vast majority of loihi s most recent lav as reverse zoning at the rim of clinopyroxene pheno crysts and the presence of two chemically distinct oliv ine phenocryst populations indicate that the magma for the lavas was mixed just prior to eruption the trace element geochemistry of these lavas indicates there has been a reversal in loihi s temporal geochemical trend although the new loihi lavas are similar isotopically and geochemically to recent kilauea lavas and the man tle conduits for these two volcanoes appear to converge at depth distinct trace element ratios for their recent lavas preclude common parental magmas for these two active volcanoes the mineralogy of loihi s recent tho leiitic lavas signify that they crystallized at moderate depths f8 9 km within the volcano which is approx imately 1 km below the hypocenters for earthquakes from the 1996 swarm taken together the petrological and seismic evidence indicates that loihi s current magma chamber is considerably deeper than the shal low magma chamber f3 4 km in the adjoining active shield volcanoes

what makes hydromagmatic eruptions violent some insights from the keanakāko i ash kilauea volcano hawai i abstract volcanic eruptions at the summit of kilauea volcano hawai i are of two dramatically contrasting types 1 benign lava flows and lava fountains and 2 violent mostly prehistoric eruptions that dispersed tephra over hundreds of square kilometers the violence of the latter eruptions has been attributed to mixing of water and magma within a wet summit caldera however magma injection into water at other volcanoes does not consistently produce widespread tephras to identify other factors that may have contributed to the violence of these eruptions we sampled tephra from the keanak ko i ash the most recent large hydromagmatic deposit and measured vesicularity bubble number density and dissolved volatile content of juvenile matrix glass to constrain magma ascent rate and degree of degassing at the time of quenching bubble number densities 9 10 4 1 10 7 cm 3 of tephra fragments exceed those of most historically erupted kilauean tephras 3 10 3 1 8 10 5 cm 3 and suggest exceptionally high magma effusion rates dissolved sulfur average 330 ppm and water 0 15 0 45 wt concentrations exceed equilibrium saturation values at 1 atm pressure 100 150 ppm and 0 09 respectively suggesting that clasts quenched before equilibrating to atmospheric pressure we interpret these results to suggest rapid magma injection into a wet crater perhaps similar to continuous uprush jets at surtsey estimates of reynolds number suggest that the erupting magma was turbulent and would have mixed with surrounding water in vortices ranging downward in size to centimeters such fine scale mixing would have ensured rapid heat exchange and extensive magma fragmentation maximizing the violence of these eruptions

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

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

explosive deep water basalt in the sumisu backarc rift eruption of 1 million year old tholeiitic basalt 1800 meters below sea level 18 megapascals in a backarc rift behind the bonin arc produced a scoriaceous breccia similar in some respects to that formed during subaerial eruptions explosion of the magma is thought to have produced frothy agglutinate which welded either on the sea floor or in a submarine eruption column the resulting 135 meter thick pyroclastic deposit has paleomagnetic inclinations that are random at a scale of 2 5 meters high magmatic water content which is about 1 3 percent by weight after vesiculation contributed to the explosivity

generation of fine hydromagmatic ash by growth and disintegration of glassy rinds 1 the deposits of mafic hydromagmatic eruptions are more fine grained and variable in vesicularity than dry magmatic deposits blocky equant shapes of many hydromagmatic clasts also contrast with droplet thread and bubble wall morphology of dry magmatic fragments small 180 m blocky hydromagmatic pyroclasts have traditionally been interpreted to result from discrete vapor explosions although such explosions tend to occur only under certain conditions this paper considers a process of hydromagmatic ash formation that involves repeated growth and disintegration of glassy rinds on pyroclast surfaces as they deform within turbulent flows this process termed turbulent shedding may occur during the expansion phase of vapor explosions or during turbulent but nonexplosive mixing of magma with water steam or water sprays the occurrence of turbulent shedding and the resulting fragment sizes depend on the timescale for rind growth and the timescale between disturbances that remove or disintegrate glassy rinds turbulent shedding is directly observable in some small littoral jets at kilauea calculations suggest that in the presence of liquid water or water sprays glassy rinds having a thickness of microns to millimeters should form in milliseconds to seconds this is similar to the timescale between turbulent velocity fluctuations that can shred lava globules and remove such rinds the fraction of a deposit consisting of fine ash should increase with the duration of this process large scale surtseyan jets generate hundreds or thousands of shedding events bubble bursts or tephra jets at kilauea s coast may produce only a few

texture analysis of volcanic rock samples quantitative study of crystals and vesicles shape preferred orientation from x ray microtomography data abstract in the texture analysis of volcanic rocks the preferred orientation of the constituents can provide useful information for the interpretation of the processes involved in the rock formation we present here a new data analysis technique based on x ray microtomography measurements and on shape preferred orientation analysis to obtain the orientation distribution functions of the constituents of volcanic rocks this procedure proved to be very suitable for volcanic samples where diffraction based techniques developed for crystallographic preferred orientation studies are of limited utilization in addition to the fact that they cannot provide any information about vesicles or bubbles moreover the analysis performed directly in three dimensions 3d overcomes the problems that usually occur when employing stereological methods for the analysis of the images obtained via microscopy based techniques in this study two scoriae from stromboli and etna and a tube pumice from campi flegrei were measured via x ray microtomography and then the resulting volumes were analyzed following the proposed procedure results highlight little preferred orientation for the vesicles in the two scoria samples whereas the pumice shows a marked preferred orientation crystals also divided by mineral species were taken into account as well and in the two scoria samples there is no crystal preferred orientation in contrast with the pumice where crystal preferred orientation features are very similar to the ones found for the vesicles overall we found strong differences in preferred orientation weak for vesicles in scoriae showing an axial symmetry with the axis parallel to the elongation axis of the sample and a stronger and more complex orientation texture in the pumice sample for both crystals and vesicles the promising results obtained suggest that this procedure is potentially very useful for the analysis of preferred orientation in volcanic rocks and geomaterials in general

direct video and hydrophone observations of submarine explosive eruptions at nw rota 1 volcano mariana arc 1 extraordinary video and hydrophone observations of a submarine explosive eruption were made with a remotely operated vehicle in april 2006 at a depth of 550 560 m on nw rota 1 volcano in the mariana arc the observed eruption evolved from effusive to explosive while the eruption rate increased from near zero to 10 100 m3 h during the peak in activity cyclic explosive bursts 2 6 min long were separated by shorter non eruptive pauses lasting 10 100 s the size of the ejecta increased with the vigor of the explosions a portable hydrophone deployed near the vent recorded sounds correlated with the explosive bursts the highest amplitudes were 50 db higher than ambient noise at frequencies between 10 and 50 hz the acoustic data allow us to quantify the durations amplitudes and evolution of the eruptive events over time the low eruption rate high gas lava ratio and rhythmic eruptive behavior at nw rota 1 are most consistent with a strombolian eruptive style we interpret that the eruption was primarily driven by the venting of magmatic gases which was also the primary source of the sound recorded during the explosive bursts the rhythmic nature of the bursts can be explained by partial gas segregation in the conduit and upward migration in a transitional regime between bubbly flow and fully developed slug flow the strongest explosive bursts were accompanied by flashes of red glow and oscillating eruption plumes in the vent apparently caused by magma seawater interaction and rapid steam formation and condensation this is the first time submarine explosive eruptions have been witnessed with simultaneous near field acoustic recordings

insights into the dynamics of mafic magmatic hydromagmatic eruptions from volatile degassing behaviour the hverfjall fires iceland abstract the style and intensity of hydromagmatic activity is governed by a complex interplay between the relative volumes of magma and water that interact their relative viscosities the depth of subsurface explosions the substrate properties and the vent geometry fundamental questions remain however regarding the role of magmatic vesiculation in determining the dynamics of magma water interaction mwi petrological reconstructions of magmatic degassing histories are commonly employed to interpret the pre and syn eruptive conditions during dry magmatic eruptions but the application of similar techniques to hydromagmatic activity has not yet been fully explored in this study we integrate glass volatile measurements s cl h2o and co2 with field observations and microtextural measurements to examine the relationship between degassing and eruptive style during the hverfjall fires fissure eruption iceland here coeval fissure vents produced both dry magmatic jar ba sholar scoria cone complex and variably wet hydromagmatic hverfjall tuff ring activity generating physically distinct pyroclastic deposits with contrasting volatile signatures matrix glass volatile concentrations in hydromagmatic ash 883 172 1 ppm s 0 45 0 03 1 wt h2o 20 ppm co2 are consistently elevated relative to magmatic ash and scoria lapilli 418 93 1 ppm s 0 12 0 48 1 wt h2o co2 below detection and overlap with the range for co erupted phenocryst hosted melt inclusions 1522 127 1 ppm s 165 27 1 ppm cl measurements of hydromagmatic glasses indicate that the magma has degassed between 17 and 70 of its initial sulfur prior to premature quenching at variably elevated confining pressures by comparing volatile saturation pressures for both magmatic and hydromagmatic glasses and how these vary through the eruptive stratigraphy we place constraints on the conditions of mwi crucially our data demonstrate that the magma was already vesiculating when it encountered groundwater at depths of 100 200 m and that the external water supply was sufficient to maintain mwi throughout the eruption with no significant vertical or lateral migration of the fragmentation surface we propose that development of an in vent water sediment slurry provides a mechanism through which the elevated confining pressures of 1 6 2 6 mpa or up to 6 mpa accounting for uncertainty in co2 below analytical detection could be maintained and buffered throughout the eruption whilst enabling vertical mixing and ejection of fragmented juvenile and lithic material from a range of depths importantly these results demonstrate that the volatile contents of hydromagmatic deposits provide valuable records of 1 the environment of mwi e g groundwater versus surface water vertical migration of the fragmentation level and 2 the state of the magma at the time of fragmentation and quenching we further suggest that the volatile content of tephra glasses provides a reliable alternative or additional indicator of a hydromagmatic origin particularly for reduced ocean island basalts where late stage volatile saturation and degassing s h2o occurs over a pressure range relevant to typical mwi environments

vesiculation and crystallization under instantaneous decompression numerical study and comparison with laboratory experiments abstract vesiculation and crystallization in ascending magmas are key processes that control the eruption behavior and they interplay each other through the water exsolution process we conducted a numerical study in order to quantitatively understand the water exsolution and crystallization processes in natural eruptions decompression history is unknown and in laboratory experiments the amount of decompression is constant with time the numerical results which take into account homogeneous or heterogeneous nucleation and growth of bubbles with varying diffusivity of water viscosity and the amount of decompression provide a quantitative understanding of their control on bubble formation and water exsolution in the constant amount of decompression the bubble nucleation in the homogeneous nucleation can be divided into two regimes the diffusion control regime and viscosity control regime depending on the modified peclet number and the effective supersaturation in the cases of both homogeneous and heterogeneous nucleations the bubble growth is controlled by diffusion or viscosity depending on the modified peclet number and bubble number density the water exsolution rate which is controlled by the modified peclet number in the viscosity control regime and by the bubble number density and diffusive driving force in the diffusion control regime acts as an effective cooling rate in a decompression induced crystallization process a comparison of the numerical results with the results of laboratory experiments suggests that water exsolution proceeds by the diffusion limited growth of bubbles under disequilibrium vesiculation through the heterogeneous nucleation of bubbles and this in turn controls the crystallization kinetics of microlite with the homogeneous nucleation of microlite and the diffusion limited growth of crystal the several orders of variation of microlite number density with the amount of decompression in laboratory experiments can be interpreted as the effect of the amount of decompression on the driving force for the diffusive bubble growth that controls the water exsolution rate

a geophysical and geochemical approach for seawater intrusion assessment in the acquedolci coastal aquifer northern sicily vertical electrical sounding ves surveys and chemical analyses of groundwater have been executed in the coastal plain of acquedolci northern sicily with the aim to circumscribe seawater intrusion phenomena this urbanized area is representative of a more general problem interesting most of mediterranean littoral areas where intensive overdraft favors a heavy seawater intrusion through the coastline aquifer resistivity seems decisively to be conditioned by the chlorine and magnesium content in the main aquifer of the region schlumberger ves together with piezometric and chemical physical information of groundwater allowed us to perform hydrogeological and geophysical elaborations to propose the occurrence of a relatively narrow belt marked by fresh salt water mixing in the considered plain pollution risk studies have been already realized by authors with the proposal to identify by parametric and synthetic zoning of significant hydrogeological elements the most vulnerable sectors in detail an intrinsic vulnerability mapping has been already performed applying the well known sintacs system this paper intends to give in this sector of sicily an example of integration of different methodologies showing the role of geophysics to describe the degradation of aquifers on the whole as well as to assess their pollution risk better

influence of fo2 and cooling rate on the kinetics and energetics of fe rich basalt crystallization cooling rate and fo2 are each varied over several orders of magnitude in a matrix of 1 atm constant rate cooling experiments using synthetic basalt the modes and compositions of olivine pyroxene and titanomagnetite are sensitive to oxygen fugacity ranging from qfm 4 to qfm 5 log units whereas their textures respond to the degree of undercooling as modulated by cooling rate ranging from 2 8 to 231 c h 1 key results pertain to the trends in mineral composition melt differentiation and

primary clinopyroxene spherulites in basaltic lavas from the pacific antarctic ridge fresh glassy basaltic andesite samples recovered from the northern part of the pacific antarctic ridge contain abundant spherulites consisting of arrays of closely packed clinopyroxene fibers the spherulites frequently enclose elongated vesicles that are tear drop shaped or tailed the long axes of the elongated vesicles were found to be always parallel to the orientation of the surrounding crystal fibers in several cases elongated vesicles having different orientations are hosted by a single spherulite the existence of elongated vesicles provides unequivocal evidence that a significant proportion of the clinopyroxene fibers must have crystallized directly from a supercooled liquid at temperatures above the glass transition moreover the absence of fractures within the spherulites and the surrounding glass as well as the observed nucleation of clinopyroxene fibers at vesicle walls are interpreted to be consistent with a primary origin of the clinopyroxene spherulites based on these textural observations it has to be concluded that spherulites do not represent a diagnostic texture for the devitrification of volcanic glass that occurs below the glass transition temperature

subaqueous eruption and emplacement of the shinjima pumice shinjima moeshima island kagoshima bay sw japan abstract the shinjima pumice is a fines depleted pumice lapilli tuff emplaced several thousands years ago at about 100 140 m below sea level this 40 m thick deposit comprises many poorly defined flow units which are 1 10 m thick diffusely stratified and showing upward coarsening of pumice clasts with a sharp to transitional base parallel to wavy diffuse stratifications are commonly represented by alignment of pumice clasts especially in the lower half of the flow units pumice clasts of block to coarse lapilli size commonly have thermal contraction cracks best developed on the surfaces demonstrating that they were hot but cooled down to the ambient temperatures prior to their emplacement these features are suggestive of the direct origin of the shinjima pumice from subaqueous eruptions a theoretical consideration on the behavior of subaqueous eruption plumes and hot and cold pumice clasts suggests that subaqueous eruption plumes commonly collapse by turbulent mixing with the ambient water and are transformed into water logged mass flows

heat source or heat sink what dominates behavior of non explosive magma water interaction 1 much of the volcanism on earth takes place in subaqueous settings where magma has direct contact with a water reservoir of restricted or quasi unrestricted volume in order to assess the intensity and timescale of non explosive interaction of magmatic melts and water experiments representing these settings were performed natural volcanic samples were remelted and poured as a continuous jet into a water filled calorimeter where the melt interacts with its coolant the rapid cooling results in granulation i e brittle failure of the material granulation needs energy which is taken from the thermal input of the hot melt energy used in granulation was found to require 5 20 of the melt s initial heat content this energy loss fraction is insensitive to variations in coolant and melt temperatures but instead depends on the melt s thermomechanical properties however analysis of the experimentally produced granulate indicates a strong correlation between the initial coolant temperature i e the heat sink and the grain size distribution but also shows variations due to material properties the maximum of the grain size distribution was determined to change from a diameter of 1 mm up to 4 mm due to coolant temperature increase properties of the heat source melt dominate the efficiency of the process whereas both heat sink and source characteristics determine the products

seawater intrusion and associated processes in a small coastal complex aquifer castell de ferro spain an attempt to identify the hydrogeochemical processes that accompany current or past intrusion of seawater in the castell de ferro coastal aquifer se spain was made using ionic deltas ionic ratios and saturation indices alluvial and coastal quaternary sediments and triassic marbles constitute this complex aquifer cation exchange dolomitization and calcite dissolution were identified as operating in the aquifer the cation exchange processes in the detrital materials are different from those in the marbles in addition it was determined that while the processes of marine intrusion associated with periods of low groundwater levels still persist in the detrital aquifer in the carbonate sector the flushing process characteristic of wetter conditions has begun

syn and post fragmentation textures in submarine pyroclasts from lō ihi seamount hawai i abstract the extent and timing of vesiculation and microlite formation in ascending basaltic melts are relatively well understood for subaerial eruptions but they have not been studied thoroughly for submarine eruptions this is largely due to a lack of samples of appropriate volume and grain size we present a quantitative textural evaluation of coarse lapilli from two cone forming deposits at 1 km depth on l ihi seamount hawai i collected during a sampling intensive submersible dive series in 2006 lapilli from the deposits named the northern and southern cones have modal bulk vesicularities of 55 and 42 respectively and vesicle populations dominated by sub spherical non interconnected vesicles with number densities on the order of 10 4 to 10 5 cm 3 clasts of modal vesicularity have margin parallel zonation with seawater quenched rims interpreted to preserve syn fragmentation magmatic textures in microlite free sideromelane glass enclosing post fragmentation tachylitic interiors with vesicle and microlite textures that progressively coarsen from rim to core degassing scenarios are linked to syn fragmentation vesicle textures to demonstrate that both magmas degassed in dominantly closed systems diffusion controlled cooling rates of basaltic pyroclasts in contact with water are linked to post fragmentation evolution of vesicle and microlite textures to make inferences about transportation and dispersal of the pyroclasts in low submarine jets the textural analysis shows that the northern and southern cone eruptions were not strictly analogous to any classical subaerial eruption type they were uniquely submarine with ambient seawater playing a crucial role in the processes of degassing vesiculation crystallization and dispersal

comprehensive hydro geophysical prospecting to delineate fresh water zone in the coastal aquifer south india abstract the integrated hydrogeophysical surveys were used to discriminate between fresh and saline groundwater in the coastal aquifer zones of lower vellar river basin south india which is considered to be the main source of groundwater in the basin geologically the basin consists of tertiary and quaternary formation in order to delineate the freshwater aquifer zone sixty nine 69 ves locations were surveyed by schlumberger electrode arrangement and eight 8 scanning surveys were conducted by multi electrode scanning method the ves results reflect that the overall resistivity ranges from 0 01 to 12 670 m and thickness varies from 0 49 to 49 9 m with a maximum of four subsurface layers the dominant curve types are h and qh followed by kh 8 and k 6 the pseudo sections prepared to understand the variations of subsurface characteristics and to delineate potential fresh saline water aquifer zones in the basin whereas the scanning surveys results showed resistivity ranges from 1 to 500 m the resistivity 20 60 m was considered as freshwater aquifer zone and observed at six locations at varying depths the both the ves and scanning results were correlated with existing borewell lithology and it showed reliable matching the results of this survey identified the freshwater aquifer zones 20 60 m in central and south central part of the basin with high potential aquifer thickness and optimum yield this integrated hydrogeophysical methods proved to be an excellent solution for delineation of fresh water aquifer zone and could be applied to any other basins with similar lithological conditions

groundwater salinization in the azores archipelago portugal groundwater salinization in coastal regions causes severe constraints to water supply and economic losses to society worldwide in the azores archipelago groundwater abstraction in wells drilled in coastal aquifers is very important for water supply and quality problems have been reported therefore a groundwater chemistry dataset from wells was compiled to study groundwater salinization in these aquifers waters are mainly of the na cl type presenting a slightly acidic to slightly alkaline character with a ph between 5 63 and 8 50 median 7 40 electrical conductivity measurements range from 127 to 9 670 s cm median 862 suggesting highly variable mineralization with higher values observed on santa maria sao miguel pico graciosa and sao jorge islands the major ion composition reflects the contribution of seawater to the groundwater compositional evolution which is essentially explained by seawater intrusion into wells in many samples exchange reactions of na k for ca2 mg2 are associated with salinization the seawater fraction in groundwater composition reaches a maximum of 22 5 these results are extremely challenging to water managers in the azores because failure to comply with national water quality regulations and with european union groundwater directive requirements often occurs

management of coastal aquifers based on nonlinear optimization and evolutionary algorithms abstract a method of assessing the optimum pumping rates of coastal aquifers based on nonlinear optimization and evolutionary algorithms ea is developed the objective is to maximize the total pumping rate while protecting the wells from sea water intrusion the formulation of the constraints is based on numerical simulation of the freshwater flow equations the simulation model is based on the sharp interface and the ghyben herzberg approximation and is applicable to unconfined aquifers and steady state flow the single potential formulation of water resour res 12 1976 1165 is followed and the governing equations are solved numerically using finite differences the numerical model can handle aquifers of complex shapes nonuniform hydraulic conductivity nonuniform distribution of surface recharge etc the constraints are nonlinear with respect to the decision variables resulting in a nonlinear optimization problem two optimization methods are investigated specifically sequential quadratic programming sqp and evolutionary algorithms ea sqp requires less computer time than ea but can get stuck on local optimum solutions the simulation and optimization methodology is applied to a real unconfined coastal aquifer in the greek island of kalymnos for determining the optimal pumping rates while protecting the wells from sea water intrusion

extensive volcaniclastic deposits at the mid atlantic ridge axis results of deep water basaltic explosive volcanic activity a recent mapping survey followed by submersible diving investigations revealed the existence of extensive volcaniclastic deposits on three adjoining progressively deeper segments of the mid atlantic ridge south west of the azores the maximum water depth at which subaqueous magmatic and hydro magmatic explosive processes can occur is controversial this discovery provides fundamental constraints on the dynamics of deep subaqueous volcanic eruptions using multibeam bathymetry sonar image interpretations submersible observations volcaniclastic sample descriptions and chemical analysis evidence of extensive deep water up to 1700 m magmatic explosive activity of basalt at the axis of a spreading mid ocean ridge is documented for the first time

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

vesiculation and quenching during surtseyan eruptions at hunga tonga hunga ha apai volcano tonga surtseyan eruptions are shallow to emergent subaqueous explosive eruptions that owe much of their characteristic behavior to the interaction of magma with water the difference in thermal properties between water and air affects the cooling and postfragmentation vesiculation processes in magma erupted into the water column here we study the vesiculation and cooling processes during the 2009 and 2014 2015 surtseyan eruptions of hunga tonga hunga ha apai volcano by combining 2 d and 3 d vesicle scale analyses of lapilli and bombs and numerical thermal modeling most of the lapilli and bombs show gradual textural variations from rim to core the vesicle connectivity in the lapilli and bombs increases with vesicularity from fully isolated to completely connected and also increases from rim to core in transitional clasts we interpret the gradual textural variations and the connectivity vesicularity relationships as the result of postfragmentation bubble growth and coalescence interrupted at different stages by quenching in water the measured vesicle size distributions are bimodal with a population of small and large vesicles we interpret this bimodality as the result of two nucleation events one prefragmentation with the nucleation and growth of large bubbles and one postfragmentation with nucleation of small vesicles we link the thermal model with the textural variations in the clasts showing a dependence on particle size leidenfrost effect and initial melt temperature in particular the cooling profiles in the bombs are consistent with the gradual textural variations from rim to core in the clasts likely caused by variations in time available for vesiculation before quenching

shallow magma mingling driven strombolian eruptions at mt yasur volcano vanuatu 1 mt yasur volcano vanuatu has been increasingly recognized for its high frequency strombolian eruptions strombolian activity is often regarded as a product of the rapid ascent of gas slugs originating from a deep magma which mingle with a batch of shallow magma upon eruption heterogeneous crystal distribution as well as bimodal bubble size distributions in the eruptive products generally supports this view here the strombolian activity at mt yasur is analyzed a rheological investigation indicates that the basaltic andesitic eruptive products contain an apparently homogeneous glass phase and yet exhibit evidence of a distinct range of glass transition temperatures with multiple peaks occurring in individual samples such anomalous behavior is proposed to result from the mingling of magmas with contrasting oxidation states the unstable nature of the measured glass transition behavior leads us to the inference that mingling is located in the shallow parts of the eruptive conduits partly driven by rejuvenation of material slumped from the crater walls into an open conduit system the dynamics of this process may expose the periodicity of the eruptions themselves

lava bubble wall fragments formed by submarine hydrovolcanic explosions on lō ihi seamount and kīlauea volcano glassy bubble wall fragments morphologically similar to littoral limu o pele have been found in volcanic sands erupted on l ihi seamount and along the submarine east rift zone of k lauea volcano the limu o pele fragments are undegassed with respect to h2o and s and formed by mild steam explosions angular glass sand fragments apparently form at similar and greater depths by cooling contraction granulation the limu o pele fragments from l ihi seamount are dominantly tholeiitic basalt containing 6 25 7 25 mgo none of the limu o pele samples from l ihi seamount contains less than 5 57 mgo suggesting that higher viscosity magmas do not form lava bubbles the dissolved co2 and h2o contents of 7 of the limu o pele fragments indicate eruption at 1200 300 m depth 120 30 bar these pressures exceed that generally thought to limit steam explosions we conclude that hydrovolcanic eruptions are possible with appropriate pre mixing conditions at pressures as great as 120 bar

new field and laboratory evidence for the origin of hyaloclastite flows on seamount summits new field observations with the submersible alvin and photographic evidence from a study of the summits of seamounts near the east pacific rise show that hyaloclastite deposits occur commonly hyaloclastite outcrops were found on six volcanoes at depths from 1240 to 2500 m these new observations plus laboratory study of new hyaloclastite specimens extend the results of previous studies most of the hyaloclastite samples are of hydrovolcanic eruptive origin but a few show evidence of a predominantly sedimentary origin primarily from morphology we identify several vent areas from which hyaloclastite presumably erupted the surface appearance of the hyaloclastite deposits varies with distance to these vents leading us to propose a facies model for deep sea hyaloclastites on seamount summits hyaloclastites of hydromagmatic origin exhibit weak normal grading and bedding parallel alignment of platy shards they consist of blocky sliver and fluidal basalt glass shards and lithics in a matrix that contains pelagic sediment the shards themselves are remarkably free of even the tiniest crystals and are usually chemically homogeneous we propose that the shards form mainly by cooling contraction granulation but cannot rule out the possibility of limited steam explosivity hyaloclastites are closely associated with submarine pahoehoe and we propose that a very rapid eruption rate promoting clastic dominated versus flow dominated eruptive behavior is the dominant control on hyaloclastite formation we propose that shard formation occurs during submarine lava fountaining gravitational instability of the resulting slurry of shards sea water and possibly steam causes gravity flow that carries the shards outward from the vent further field and modelling studies are needed to test these ideas and more quantitatively constrain the ascent mechanism eruption dynamics and deposition of deep sea hyaloclastites

sediment sorting in the deposits of turbidity currents created by experimental modeling of explosive subaqueous eruptions abstract deposits of turbidity currents induced by subaqueous volcanic eruptions are increasingly recognized in settings ranging from lakes to the deep sea these eruption fed density currents have high current temperatures and low density particles which affect current dynamics and deposit features field data indicate that deposit thickness and grain size decrease downflow at a changing rate this trend is similar for deposits of noneruptive turbidity currents but with volcanic activity the deposits often exhibit a break in slope of the profile of deposit thickness and grain size distribution here we present laboratory results on density currents that address the effects of variations in grain density and water temperature on flow properties and depositional processes parallel runs were performed under identical flow conditions using quartz sand and pyroclastic sediment each grain type was used in one series of runs in which a hot density current enters a cold environment and one series in which

the structure of basaltic scoria and reticulite and inferences for vesiculation foam formation and fragmentation in lava fountains in this investigation pyroclast structures are used to constrain degassing in basaltic lava fountains vesicle size shape number density interconnectedness and packing character are quantified and related to 1 the kinetics of bubble nucleation and growth 2 the structural evolution of magmatic foams and 3 the influence of vesiculation rate on magma fragmentation measurements made on a diverse suite of pyroclasts from kilauea volcano indicate that basaltic foams evolve through an initially disordered closed celled spherical state to a well ordered open celled polyhedral state as the vesicularity rises from 75 to 98 the structural changes occur rapidly 10 s in the conduit and fountain in response to an intense vesiculation burst vesicle size distribution systematics indicate bubble nucleation rates 2 104 events cm 3s 1 that are approximately three orders of magnitude greater than those found for effusive eruptive activity bubble growth rates 9 10 4 cm s exceed effusive estimates by a factor of 3 the observed runaway rate of bubble production indicates strong supersaturations at the onset of nucleation we speculate that the rise speed of the magma as it reaches the level where significant volatile exsolution begins determines the intensity of the vesiculation burst and hence the vigor of the eruption rapid expansion and acceleration of the magma under these conditions may provide the impetus for fragmentation

volcaniclastic deposits from the north arch volcanic field hawaii explosive fragmentation of alkalic lava at abyssal depths submarine explosive eruptions are generally considered to become less likely with increasing depth due to the increasing hydrostatic pressure of the overlying water column volcaniclastic deposits from the north arch volcanic field north of oahu have textural characteristics of explosive fragmentation yet were erupted in water depths greater than 4 200 m

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

application of resistivity and gpr techniques for the characterization of the coastal litho stratigraphy and aquifer vulnerability due to seawater intrusion abstract the objective of this study is to identify geological properties and structural settings allowing salt water intrusion to the aquifers in oceanic originated rock formations of the south andaman island to evaluate the impact of seawater in groundwater aquifer several geophysical surveys using ground penetrating radar gpr and resistivity sounding were performed through the most significant sites located near coastal areas tidal channels and agriculture land high resolution gpr images were obtained and combined with resistivity sounding which allows to identify the mixing transition zone of fresh and saline groundwater and also successfully delineated the structural geometry and litho stratigraphic details of aquifers we show that the sedimentary formations are highly susceptible to seawater intrusion than the mantle originated ophiolites further potential impacts from seawater intrusion are higher along the west coast than the east coast because of macro pore tendency of soils allows seawater filtration

3d particle size distributions from 2d observations stereology for natural applications abstract we have developed a general formulation for stereological analysis of particle distributions which is applicable to any particle size or size distribution not limited to log normal unimodal etc we have applied numerical techniques to define intersection probability distributions for any shapes previously only known for spheres and quantified the errors involved in using spherical coefficients for various non spherical particles this stereological technique is based on knowing the probability distribution of random cross sections through various particles so that small circle cross sections can be subtracted from an observed population to provide the 3d size distribution of particles the results indicate that the most important parameter controlling calculated size distribution is particle aspect ratio for a distribution of particles with a specific aspect ratio or range of aspect ratios variations of particle form spherical vs cubic rectangular vs elliptical do not alter the results so the technique can be applied to a range of particle shapes applications can be made in a petrology volcanology and other fields only a few of which can also be treated using expensive x ray techniques

pyroclast textures of the ilchulbong wet tuff cone jeju island south korea abstract jeju island is a quaternary shield volcano situated approximately 95 km south of the korean peninsula comprising holocene late pleistocene phreatomagmatic deposits and shield forming basaltic to trachytic lavas that overlie early mid pleistocene marine sedimentary and hydrovolcanic deposits ilchulbong tuff cone is among the youngest hydrovolcanic centres on the island formed along the shoreline from a surtseyan style eruption involving interaction of magma with external water we have analysed lapilli from selected sites on the volcanic edifice in terms of vesicle population texture shape and size and quantitatively with reference to bulk vesicularity vesicle number density vesicle dimensions and distributions the lapilli range in total vesicularity from low 15 35 to high 50 80 values and show a modest range of vesicle number densities n v number of vesicles per unit rock volume between 2 26 10 3 and 6 97 10 3 vesicles mm 3 such vesicle number densities are higher than those typical of strombolian n v between 9 3 10 1 and 1 3 10 3 vesicles mm 3 stromboli 2002 lautze and houghton 2007 and hawaiian eruptions and more similar to those of plinian n v between 1 5 and 2 5 10 3 vesicles mm 3 tarawera sable et al 2009 eruptions the lapilli studied were not strongly quenched and we infer that the high vesicle number densities reflect a late nucleated bubble population related in origin and formed in response to high levels of microlite growth in the ilchulbong magma prior to final ascent

pumping optimization in saltwater intruded coastal aquifers this paper investigates the hydraulic issues of pumping well optimization in saltwater intruded coastal aquifers the well field includes freshwater outflow pumping wells and a recharge canal the objective is to maximize the total pumping rate subject to the constraint of no intrusion of the saltwater front into the wells analytical solutions are presented for one well two well and one well with recharge canal problems for problems involving multiple pumping wells a structured messy genetic algorithm is used to search for the optimal solution

diverse basalt types from loihi seamount hawaii loihi seamount is the southeasternmost active volcano in the hawaiian emperor volcanic chain the seamount is considered representative of the early phase of hawaiian volcanism because of its youth small size and location near the melting anomaly seventeen dredge stations recovered transitional basalt alkalic basalt and basanite in addition to the expected tholeiitic basalt four flows of alkalic basalt contain common small dunite xenoliths the recovered samples have thin palagonite rinds and almost no manganese on the glassy surfaces we estimate that the lavas are less than about 4 000 yr old and many are less than 1 000 yr old loihi seamount is apparently in a transitional growth phase between the early eruption of alkalic lavas and the commonly observed subaerial tholeiitic eruptive phase previously thought to dominate hawaiian volcanism from inception until the postcaldera collapse alkalic stage

quench rates in air water and liquid nitrogen and inference of temperature in volcanic eruption columns we applya geospeedometer previouslydeveloped in this lab to investigate cooling rate profiles of rhy olitic samples initiallyheld at 720 750 c and quenched in water liquid nitrogen and air for quench of mm size samples in liquid nitrogen and in air the cooling rate is uniform and is controlled byheat transfer in the quench medium instead of heat conduction in the sample the heat transfer coefficient in static air decreases with increasing sample size for quench of mm size samples in water heat transfer in water is rapid and the cooling rate is largelycontrolled byheat conduction in the sample our experimental results are roughlyconsistent with previous calculations for cooling in air and in water although constant heat transfer coefficients were used in these calculations but cooling rate in liquid nitrogen is only1 8 2 3 times that in static air and slower bya factor of 2 than calculated byprevious authors cooling rate in compressed airflow is about the same as that in liquid nitrogen the experimental results are applied to interpret cooling rates of pyroclasts in ash beds of the most recent eruptions of the mono craters cooling rates of pyroclasts are inversely correlated with sample size and slower than those in air the results indicate that the hydrous species concentrations of the pyroclasts were frozen in the eruption column rather than inside ash beds or in flight in ambient air from the cooling rates we infer eruption column temperature in a region where and at a time when hydrous species concentrations in a pyroclast were locked in the temperature ranges from 260 to 570 c for the most recent eruptions of mono craters these are the first estimates of temperatures in volcanic eruption columns the abilityto estimate cooling rates and eruption column temperatures from eruptive products will provide constraints to dynamic models for the eruption columns 2002 elsevier science b v all rights reserved

poseidic explosive eruptions at loihi seamount hawaii much remains unknown about submarine explosive eruptions their deposits are found to great depths in all the world s oceans but eruptions are typically described by analogy to a subaerial nomenclature that ignores the substantial and inevitable infl uences of hydrostatic pressure and magma water interaction at submerged edifi ces here we explore magmatic volatile exsolution and magma water interaction for a pyroclastic cone forming eruption at 1 km depth on loihi seamount hawaii we examine vesicle textures in lapilli the physical manifestation of degassing dissolved volatiles in matrix glasses and olivine hosted glass inclusions the geochemical record of ascent and volatile exsolution and fi ne ash morphology the evidence for if and how external water assisted in fragmentation this approach allows a submarine explosive eruption style to be defi ned the magma achieved 40 vesicularity through almost perfectly closed system volatile exsolution from 3 km below the vent which accelerated and weakened the melt allowing it to be fragmented by explosive magma water interaction we introduce the name poseidic for this end member style of submarine basalt explosivity poseidic eruptions are identifi able from measurable features in pyroclasts and are possible at all subaqueous basaltic volcanoes

cooling and crystallization of lava in open channels and the transition of pāhoehoe lava to a ā samples collected from a lava channel active at kilauea volcano during may 1997 are used to con strain rates of lava cooling and crystallization during early stages of flow lava erupted at near liquidus tem peratures f1150 7c cooled and crystallized rapidly in upper parts of the channel glass geothermometry indi cates cooling by 12 14 7c over the first 2 km of trans port at flow velocities of 1 2 m s this translates to cooling rates of 22 50 7c h cooling rates this high can be explained by radiative cooling of a well stirred flow consistent with observations of non steady flow in proximal regions of the channel crystallization of plag ioclase and pyroxene microlites occurred in response to cooling with crystallization rates of 20 50 per hour crystallization proceeded primarily by nucleation of new crystals and nucleation rates of f10 4 cm 3 s are similar to those measured in the 1984 open channel flow from mauna loa volcano there is no evidence for the large nucleation delays commonly assumed for plagioclase crystallization in basaltic melts possibly a reflection of enhanced nucleation due to stirring of the flow the transition of the flow surface morphology from pahoehoe to a aoccurred at a distance of 1 9 km from the vent at this point the flow was thermally stratified with an interior temperature of f1137 7c and crystallinity of f15 and a flow surface tempera ture of f1100 7c and crystallinity of f45 a afor mation initiated along channel margins where crust was continuously disrupted and involved tearing and clotting of the flow surface both observations suggest that the transition involved crossing of a rheological threshold we suggest this threshold to be the develop ment of a lava yield strength sufficient to prevent vis cous flow of lava at the channel margin we use this concept to propose that a aformation in open chan nels requires both sufficiently high strain rates for con tinued disruption of surface crusts and sufficient groundmass crystallinity to generate a yield strength equivalent to the imposed stress in hawai i where lava is typically microlite poor on eruption these combined requirements help to explain two common observations on a aformation a a aflow fields are generated when effusion rates are high thus promoting crustal disruption and b under most eruption conditions lava issues from the vent as pahoehoe and changes to a aonly after flowing some distance thus permitting sufficient crystallization

hydrochemical geophysical and multivariate statistical investigation of the seawater intrusion in the coastal aquifer at phetchaburi province thailand abstract seawater intrusion in coastal regions is an imperative ecological issues and results in an undesirable consequence on future groundwater resources to assess and mitigate seawater intrusion the affected aquifers need to be characterized by integrating geophysical investigation and multivariate statistical analysis of hydrochemical data seawater intrusion into coastal aquifers at cha am district in phetchaburi province thailand as a model area that is adversely affected by this problem was evaluated the vertical electrical sounding ves survey study was conducted at 80 locations and then 47 ves locations were used to create four pseudo cross section lines in a west east direction the geophysical results were described together with the hydrochemical analysis of 57 groundwater samples revealed that seawater intrusion occurred in the quarternary colluvial sediment aquifer at an average depth of 50 60 m a resistivity value of

vesiculation and fragmentation history in a submarine scoria cone forming eruption an example from nishiizu izu peninsula japan an uplifted 50 m thick half dissected submarine emplaced below wave base scoria cone occurs as dipping beds in coastal outcrops at nishiizu on the izu peninsula in japan concentrically outward dipping weakly stratified ungraded framework supported thin to very thick beds consist of brown coarse tuff to scoria lapilli tuff with outsized fluidal bombs throughout accessory lithic clasts chiefly occur in the lowermost visible beds scoria bombs have quenched margins weak bread crust textures and their vesicle number densities decrease inward which is indicative of fast surface cooling composite textures in the scoria bombs indicate recycling and agglutination of quenched and semi molten pyroclasts at the submarine vent in contrast to weak concentric gradations in vesicle size distribution in the bombs lapilli have asymmetrical gradients in vesicle size distribution indicating that they are fragments of coarser quenched lumps three grain size modes characterise the nishiizu brown scoria with coarse magma lumps ejected during magmatic fragmentation and quench jointed upon contact with seawater to be subsequently fragmented into lapilli and coarse ash by various styles of fragmentation where seawater plays a critical role the cone was constructed by slow moving fallout fed granular flow creep fed directly by suspension settling focused at the crater rim but extending onto the cone flanks with only minor resedimentation by granular flows nishiizu deposits yield an exceptional record of eruption and sedimentation dynamics during submarine cone building activity and in this study we compare their vesiculation and fragmentation mechanisms with those of potential subaerial analogues

fallout of pyroclastic debris from submarine volcanic eruptions volcanic fallout deposits on land being widespread and accessible for study have received much attention and have revealed a great deal about subaerial eruption mechanisms in contrast virtually nothing is known about equivalent deposits produced by submarine volcanoes despite the probable abundance of such material in today s oceans and in accreted volcanic arc terrains many submarine deposits may form by the fallout of debris to the sea floor downcurrent from the umbrella region of submarine eruption columns experiments on water saturated pumice and pieces of rock lithics show that particles settling to the sea floor at terminal velocities of 10 to 50 centimeters per second will display conspicuous bimodality of particle diameters pieces of pumice may be five to ten times as large as codeposited lithic fragments similar material erupted into the air and deposited on land displays less well developed bimodality pumice diameters are generally two to three times as large as associated lithics submarine fallout deposits are therefore distinctive and may be used to indicate a subaqueous origin for some of the great thicknesses of nonfossiliferous volcanic debris contained in ancient volcanic terrains worldwide whose environment of deposition has been uncertain

micro porous pyroclasts reflecting multi vent basaltic andesite plinian eruptions at mt tongariro new zealand abstract mt tongariro is a multi vent volcanic complex in the central north island of new zealand constructed along the axis of an active graben its five largest known explosive eruption episodes occurred 11 000 years ago during a 200 year long paroxysm during these stable plinian and collapsing sub plinian columns erupted from multiple sequential and synchronous vents along the graben axis we examined the spatially varying eruption dynamics during the 200 year paroxysm through the lens of pyroclastic textures each eruption episode produced micro vesicular basaltic andesitic juvenile lapilli with high vesicle number densities and high groundmass crystallinity textural characteristics indicate that pressurisation via second boiling drove eruptions and rhyolite like melt viscosities promoted brittle failure highly variable and mingled textures within individual juvenile lapilli evidence diverse conditions developed across the conduit during the eruption foamy magma rose rapidly through the conduit core driving explosive vigour and dragged and sheared gas poor crystallised magma from the conduit margins consistent with the northward widening graben the most stable plinian eruptions occurred at northern vents under highest extensional stresses and possibly widest most stable conduits by contrast collapsing unstable eruption columns occurred at southern vents where mainly degassed and crystalline magma erupted at lower ejection rates through narrower unstable and shifting conduits these data collectively show how spatial variations in structure and tectonics may strongly influence explosive eruption style

degassing and microlite crystallization of basaltic andesite magma erupting at arenal volcano costa rica abstract volcanoes can erupt explosively in plinian style or effusively as lava flows most models for such ranges in activity are based on silicic magma which may not be appropriate for less viscous basic magma although basic magma erupting at arenal volcano has not varied significantly in bulk composition the volcano has exhibited a full range in eruptive style from plinian activity in 1968 to strombolian bursts to lava flows we examined groundmass textures of samples erupted over that range of activity to investigate the controls on the variability microlite textures in lavas collected both hot rapid quenched and cold show that most samples have textures that are overprinted by crystallization as a result of cooling despite that overprint microlites in the plinian sample have unique crystal morphologies and vesicles that are much smaller and more spherical than those in the other samples we interpret those differences as recording a change in degassing style as a result of changing ascent rate in the conduit to constrain the potential changes in ascent rate a limited number of decompression experiments were run at rates from 0 0013 to 0 25 mpa s crystal textures and morphologies vary greatly as decompression rates change and compared to our observed differences in the natural groundmass it appears that magma erupted in the plinian event decompressed between 0 0013 and 0 025 mpa s whereas magma erupted in non plinian events decompressed slower than 0 0013 mpa s the change in eruptive style from explosive plinian to lava effusion thus resulted from an order of magnitude decrease in magma ascent rate plinian magma probably rose too quickly to allow bubbles to coalesce and allow the magma to degas efficiently whereas at other times magma rose more slowly which allowed bubbles to coalesce and gas to escape leading to less explosive activity

linking variable explosion style and magma textures during 2002 at stromboli volcano italy microtextural characteristics of fresh ejecta from stromboli volcano were examined from three periods of differing eruption style and intensity in 2002 activity shifted from relatively weak and infrequent ash charged explosions during january through may into two broad cycles of waxing activity in june through late september and late september through december followed by the onset on 28 december of the 2002 2003 effusive eruption analyzed sets of lapilli from may september october and 28 december show contrasts in the physical properties of magma resident in the shallow conduit during this range of activity three distinct textures are observed among the analyzed pyroclasts low density ld with an abundance of subspherical bubbles the presence of large irregularly shaped bubbles and a light to transparent glass matrix transitional texture tt with an intermediate number of subspherical bubbles a high frequency of large irregularly shaped bubbles and a honey colored glass matrix and high density hd with sparse relatively small bubbles conspicuous large irregular bubbles and a dark glass matrix observational and quantitative data density vesicle size indicate that these textures are linked through variable residence time in stromboli s shallow conduit with an ongoing evolution from ld to hd magma calculations suggest that residual ld magma will evolve to hd texture in a period of hours to days contrasting amounts of the ld tt and hd magmas are present in each sample with the most tt in may the most ld in september october and the most hd in december this implies that the shallow magma had a different rheology at each collection period the viscosity of ld and hd magmas are calculated to be in the range of 2 000 to 2 600 and 3 000 to 5 000 pa s respectively which with their changing proportions must have implications for rates of bubble slug ascent and processes of fragmentation this study suggests that an increasing maturity of magma in stromboli s shallow conduit with resultant increase in viscosity feeds back to reduce the intensity of explosions whereas a steady flux of ld magma favors more powerful explosions

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

crestal overtop and washover sedimentation on a fringing sandy gravel barrier coast carnsore point southeast ireland abstract storm sedimentation on a fringing sandy gravel barrier system in southeast ireland is examined recent wave overtopping and overwashing during severe onshore storms have resulted in a distinctive pattern of crest and backbarrier sedimentation this is not easily matched with available models of washover sedimentation drawn from the barrier islands of the eastern united states beach crest overtopping occurs at heights up to 6 m mhws and is related to the development of upper beach swash ramps that are plastered against storm wave eroded dune scarps located at the barrier crest ramp sediments comprise coarse basal beach gravels overlain by coarsening upward units and finally topped by distinctive seawarddipping fine grit coarse sand couplets in places where ramps reach the dune cre t overtopping swash has deposited a fine marine gravel veneer

deep submarine pyroclastic eruptions theory and predicted landforms and deposits submarine pyroclastic eruptions at depths greater than a few hundred meters are generally considered to be rare or absent because the pressure of the overlying water column is sufficient to suppress juvenile gas exsolution so that magmatic disruption and pyroclastic activity do not occur consideration of detailed models of the ascent and eruption of magma in a range of sea floor environments shows however that significant pyroclastic activity can occur even at depths in excess of 3000 m in order to document and illustrate the full range of submarine eruption styles we model several possible scenarios for the ascent and eruption of magma feeding submarine eruptions 1 no gas exsolution 2 gas exsolution but no magma disruption 3 gas exsolution magma disruption and hawaiian style fountaining 4 volatile content builds up in the magma reservoir leading to hawaiian eruptions resulting from foam collapse 5 magma volatile content insufficient to cause fragmentation normally but low rise speed results in strombolian activity and 6 volatile content builds up in the top of a dike leading to vulcanian eruptions we also examine the role of bulk interaction steam explosivity and contact surface steam explosivity as processes contributing to volcaniclastic formation in these environments we concur with most earlier workers that for magma compositions typical of spreading centers and their vicinities the most likely circumstance is the quiet effusion of magma with minor gas exsolution and the production of somewhat vesicular pillow lavas or sheet flows depending on effusion rate the amounts by which magma would overshoot the vent in these types of eruptions would be insufficient to cause any magma disruption the most likely mechanism of production of pyroclastic deposits in this environment is strombolian activity due to the localized concentration of volatiles in magma that has a low rise rate magmatic gas collects by bubble coalescence and ascends in large isolated bubbles which disrupt the magma surface in the vent producing localized blocks bombs and pyroclastic deposits another possible mode of occurrence of pyroclastic deposits results from vulcanian eruptions these deposits being characterized by the dominance of angular blocks of country rocks deposited in the vicinity of a crater should be easily distinguishable from strombolian and hawaiian eruptions however we stress that a special case of the hawaiian eruption style is likely to occur in the submarine environment if magmatic gas buildup occurs in a magma reservoir by the upward drift of gas bubbles in this case a layer of foam will build up at the top of the reservoir in a sufficient concentration to exceed the volatile content necessary for disruption and hawaiian style activity the deposits and landforms are predicted to be somewhat different from those of a typical primary magmatic volatile induced hawaiian eruption specifically typical pyroclast sizes might be smaller fountain heights may exceed those expected for the purely magmatic hawaiian case cooling of descending pyroclasts would be more efficient leading to different types of proximal deposits and runout distances for density flows would be greater potentially leading to submarine pyroclastic deposits surrounding vents out to distances of tens of meters to a kilometer in addition flows emerging after the evacuation of the foam layer would tend to be very depleted in volatiles and thus extremely poor in vesicles relative to typical flows associated with hawaiian style eruptions in the primary magmatic gas case we examine several cases of reported submarine volcaniclastic deposits found at depths as great as 3000 m and conclude that submarine hawaiian and strombolian eruptions are much more common than previously suspected at mid ocean ridges furthermore the latter stages of development of volcanic edifices seamounts formed in submarine environments are excellent candidates for a wide range of submarine pyroclastic activity due not just to the effects of decreasing water depth but also to 1 the presence of a summit magma reservoir which favors the buildup of magmatic foams enhancing hawaiian style activity and episodic dike emplacement which favors strombolian style eruptions and 2 the common occurrence of alkalic basalts the co2 contents of which favor submarine explosive eruptions at depths greater than tholeiitic basalts these models and predictions can be tested with future sampling and analysis programs and we provide a checklist of key observations to help distinguish among the eruption styles

salinization processes in the unconfined aquifer of bou areg ne morocco a geostatistical geochemical and tomographic study hydrogeological and geochemical data in conjunction with the results of an electrical imaging tomographic survey were examined to determine the main factors and mechanisms controlling the groundwater chemistry and salinity of the unconfined aquifer of bou areg on the mediterranean coast of ne morocco in addition statistical and geochemical interpretation methods were used to identify the distribution of the salinity multivariate statistical analysis cluster and principal component factors revealed the main sources of contamination groups a b and c in the cluster analysis and factors 1 3 factor 1 ce cl k so42 and mg2 factor 2 ca2 hco3 and ph factor 3 no3 represent the signature of seawater intrusion in the coastal zone the influence of marly gypsum outcrops in the upstream zone and anthropogenic sources respectively the ionic delta the ionic ratio the saturation index and stuyfzand s method were applied to evaluate geochemical processes the results obtained indicate on the one hand the phenomenon of salinization in both the coastal and the upstream zones and on the other the dilution of groundwater by recharge cation exchange is shown to modify the concentration of ions in groundwater locally with respect to salinization processes in the coastal zone the results of electrical imaging tomography show that salinity increases both with depth and laterally inland from the coastline due to seawater intrusion

single explosions at stromboli in 2002 use of clast microtextures to map physical diversity across a fragmentation zone abstract a combination of fortuitous eruptive and wind conditions at stromboli volcano in september 2002 enabled the collection of samples of multiple lapilli from individual observed explosions these ejecta present the first opportunity to analyze the vesicularity of material ejected in a single strombolian explosion samples of between 40 and 92 lapilli were collected from each of six sequential explosions on 30 september 2002 and 28 lapilli were obtained from a single explosion 24 h later 1 october density measurements and microtextural observations show that considerable heterogeneity existed within each of the seven samples centimeter to millimeter size bubble rich and bubble poor zones are present and are in places mingled together these data confirm that the shallow conduit at stromboli is a texturally diverse environment at the instant of a single explosion and that a similar range of heterogeneity can persist through closely spaced sequences of explosions on a timescale of hours and probably days despite the dynamic processes of ascent of melt and decoupled gas phases

eruption dynamics of popping rock from vesicle morphologies the textures elongation parameters and size distribution of vesicles frozen in a section of popping rock glass are presented these show that the vesicles in this particular piece of popping rock were deformed during eruption the degree of vesicle elongation is consistent with a velocity gradient across the section of between 0 8 and 4 s 1 this would suggest that magma rise speeds for popping rock were in excess of 1 m s 1 there are examples of vesicles fragmenting and coalescing preserved in the glass vesicle fragmentation occurs at comparatively low capillary number 0 3 vesicle overpressuring due to rapid decompression is thought to result in low capillary number fragmentation the vesicle size distribution the number of vesicles in a given size interval per unit volume of magma of this section suggests that continuous vesicle nucleation and growth took place in the magma consistent with two other popping rock sections studied previously minor vesicle coalescence has occurred in two of the sections the results from all the sections suggest that these three sections experienced a similar growth rate g and growth interval of g 0 1 mm and had similar initial bubble densities 200 mm 4

reevaluation of vesicle distributions in basaltic lava flows a fundamental dichotomy in the study of basaltic lava flows is that observations of active flows are restricted to flow surfaces yet older flows are often exposed only in vertical cross section cross sectional exposures of an inflated basaltic sheet flow emplaced in kalapana hawaii from 1990 to 1991 provide an unusual opportunity to merge these two viewpoints permitting the development of the internal structure of the flow to be viewed in the context of its known emplacement history we demonstrate that fundamental features of the flow structure a thick upper vesicular crust that diminishes downward in overall vesicularity a dense flow interior and a thin lower vesicular zone are generated through syn emplacement cooling of upper and lower flow crusts both the inverse correlation of overall vesicularity and vesicle size and the constant relative thickness of the upper vesicular zone are unique to inflated flows and permit a reinterpretation of flows previously interpreted to be ponded rapidly emplaced identification of inflation in turn implies near horizontal paleoslopes and permits estimates of flow duration based on upper flow crust thickness

fluidal clast breccia generated by submarine fire fountaining trooper creek formation queensland australia abstract a distinctive monomictic breccia composed of fluidal and blocky basaltic andesite clasts occurs in a cambro ordovician submarine volcanic succession in northern queensland australia associated with this fluvial clast buccia facies are coherent facies and coarse and fine breccia facies of the same composition the fluidal clast breccia facies is internally massive and 250 m thick varying only in the ratio of fluidal clasts to blocky clasts fluidal clasts range in size from 2 cm to 170 cm and have moderately to highly vesicular cores and thick up to 1 cm non vesicular formerly glassy rims blocky clasts are highly vesicular to non vesicular subaqueous fire fountain breccias are distinguished from subaerial fire fountain breccias by thick glassy margins on fluidal clasts the lack of welding and agglutination and the distinctive association of highly vesicular fluidal clasts with non vesicular angular blocky clasts recognition of submarine fire fountain breccias in volcanic successions constrains the eruption style proximity tens of metres to source and environment of deposition

petrology of basalts from loihi seamount hawaii abstract loihi seamount is the southeasternmost active volcano of the emperor hawaii linear volcanic chain it comprises a spectrum of basalt compositional varieties including basanite alkali basalt transitional basalt and tholeiite samples from four dredge collections made on scripps institution of oceanography benthic expedition in october 1982 are tholeiite the samples include highly vesicular olivine rich basalt and dense glass rich pillow fragments containing olivine and augite phenocrysts both quartz normative and olivine normative tholeiites are present minor and trace element data indicate relatively high abundances of low partition coefficient elements e g ti k p rb ba zr and suggest that the samples were derived by relatively small to moderate extent of partial melting of an undepleted mantle source olivine composition mgo cr and ni abundances and mg mg fe are typical of moderately fractionated to relatively unfractionated primary magmas the variations in chemistry between samples cannot be adequately explained by low pressure fractional crystallization but can be satisfied by minor variations in extent of melting if a homogeneous source is postulated alternatively a heterogeneous source with variable abundances of certain trace elements or mixing of liquids may have been involved data for 3 he 4 he presented in a separate paper implies a mantle plume origin for the helium composition of the loihi samples there is little variation in the helium isotope ratio for samples having different compositions and textures the helium data are not distinctive enough to unequivocally separate the magma sources for the tholeiitic rocks from the other rock types such as loihi alkalic basalts and the whole source region for loihi may have a nearly uniform helium compositions even though other element abundances may be variable complex petrologic processes including variable melting fractional crystallization and magma mixing may have blurred original helium isotopic signatures

the miocene costa giardini diatreme iblean mountains southern italy model for maar diatreme formation on a submerged carbonate platform in this paper we present a model for the growth of a maar diatreme complex in a shallow marine environment the miocene age costa giardini diatreme near sortino in the region of the iblei mountains of southern sicily has an outer tuff ring formed by the accumulation of debris flows and surge deposits during hydromagmatic eruptions vesicular lava clasts accretionary lapilli and bombs in the older ejecta indicate that initial eruptions were of gas rich magma abundant xenoliths in the upper late deposited beds of the ring suggest rapid magma ascent and deepening of the eruptive vent is shown by the change in slope of the country rock the interior of the diatreme contains nonbedded breccia composed of both volcanic and country rock clasts of variable size and amount the occurrence of bedded hyaloclastite breccia in an isolated outcrop in the middle lower part of the diatreme suggests subaqueous effusion at a low rate following the end of explosive activity intrusions of nonvesicular magma forming plugs and dikes occur on the western side of the diatreme and at the margins close to the contact between breccia deposits and country rock they indicate involvement of volatile poor magma possibly during late stages of activity we propose that initial hydromagmatic explosive activity occurred in a shallow marine environment and the ejecta created a rampart that isolated for a short time the inner crater from the surrounding marine environment this allowed explosive activity to draw down the water table in the vicinity of the vent and caused deepening of the explosive center a subsequent decrease in the effusion rate and cessation of explosive eruptions allowed the crater to refill with water at which time the hyaloclastite was deposited emplacement of dikes and plugs occurred nonexplosively while the breccia sediment was mostly still soft and unconsolidated locally forming peperites the sheltered low energy lagoon filled with marine limestones mixed with volcaniclastic material eroded from the surrounding ramparts ultimately lagoonal sediments accumulated in the crater until subsidence or erosion of the tuff ring caused a return to normal shallow marine conditions

combined application of electrical resistivity and shallow groundwater sampling to assess salinity in a shallow coastal aquifer in benin west africa summary motivated by prior field and numerical results suggesting possible movement of salinity towards public water supply wells serving cotonou benin this work examines the combined use of direct push chemical sampling electrical resistivity tomography ert and vertical electrical sounding ves to assess the distribution of saline waters in a complex coastal aquifer direct push sampling data allowed delineation of shallow salinity and provided chemical signatures useful in defining possible sources of the salinity complementary ert data revealed local heterogeneity in the subsurface resistivity largely related to variability in the depth to salinity along the survey line despite this local variability interpretation of ves data using a layered model proved reasonably robust for estimating the depth of the contact between fresh and salt waters where field conditions allowed all three measures to be performed in close proximity there was general agreement among the ert ves and direct sampling data in terms of indication of locations of shallow salinity combined with interpretation of the local geology the data lead to the conclusion that the distribution of salinity is related to aquifer heterogeneity but that the coastal region likely does not pose an immediate threat to the well field beyond implications for coastal benin these results demonstrate that combining electrical resistivity surveys direct push sampling and geologic interpretation allows initial characterization of complex coastal aquifers under the constraint of limited field data

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

comparison of aquifer vulnerability assessment techniques application to the neblon river basin belgium five different methods for assessing intrinsic aquifer vulnerability were tested in a case study and their results compared the test area was a slightly karstified district in the condroz region of belgium the basin covers about 65 km2 and the karst aquifer provides a water supply of about 28 000 m3d 1 the methods tested were epik doerfliger et al 1999 drastic aller et al 1987 german method von hoyer and sofner 1998 god foster 1987 and isis civita and de regibus 1995 the results are compared and critically examined from the analysis it seems that reducing the number of parameters is unsatisfactory due to the variety of geological conditions the various methods produce very different results at any given site as only physically based methods can be checked for their reliability it is clear that future vulnerability mapping techniques must incorporate such methods

shallow seated explosions in the construction of the motukorea tuff ring auckland new zealand evidence from lithic and sedimentary characteristics at least 52 eruption centres are scattered within the 360 km2 auckland volcanic field avf motukorea now an island in the waitemata harbour is one of 39 avf volcanoes that experienced a phreatomagmatic explosive phase before a magmatic phase the volcano erupted through a 200 300 m thick consolidated mudstone sandstone sequence of the miocene waitemata group which overlies the waipapa terrane greywacke basement detailed field descriptions of the sedimentary characteristics of the early phreatomagmatic deposits were carried out along with examination of lithics the ejecta ring deposit comprises 55 to 60 vol lithics of which waitemata group fragments constitute approximately 90 vol whereas 10 vol are waipapa fragments suggesting a dominance of shallow fragmentation the sedimentary characteristics of the stratigraphic sequence at motukorea suggest a dominance of wet surges at the beginning of the eruption with progression into drier sequences upwards this is reflected in increasing inter bedded juvenile pyroclast dominated fall deposits up sequence these characteristics are attributed to the changing hydrogeological conditions within the diatreme and the host rocks these findings shed light on the eruption dynamics of phreatomagmatic eruptions through consolidated rocks in the avf and enable the depiction of a scenario of future eruptions within the field in similar substrates

submarine eruption near socorro island mexico geochemistry and scanning electron microscopy studies of floating scoria and reticulite abstract products of an underwater eruption near socorro island in the ne pacific were observed directly on january 29 1993 ten days after precursors were first recorded by sofar sound fixing and ranging hydrophones located in hawaii and tahiti eruptive activity was noticed from boats and ships as small steam plumes rising from the sea at an area centered at 18 48 n 111 05 w 2 4 km nw of punta tosca and 4 6 km ssw of cape henslow on socorro island the observed steam was produced by 1 3 m large blocks of hot dark grey highly vesiculated basalt rising buoyantly to the surface from two submarine shallow vents at 210 and 30 m depth tens of blocks accompanied by bubbles could be observed rising to the surface in irregular pulses these scoriaceous blocks remained floating at the surface until they would crack into smaller pieces by thermal contraction emitting hissing noises from vapourizing seawater in contact with the hot interior of the blocks steam jets several metres in height were produced and occasionally blocks were propelled laterally by the steam jet depending on vesicularity and permeability blocks remained floating and drifting with the surface current for 1 15 minutes before sinking back floating rocks covered an area of about 6000 m2 this intermittent activity has been observed ever since and has not stopped as of april 1994 buoyant scoria and reticulite are indicative of volatile mostly co2 supersaturation and exsolution in the magma prior to rapid quenching which inhibits loss of volatiles by bubble escape a high velocity ascent of low viscosity magma in a relatively narrow conduit is also required to prevent substantial gas escape and allow formation of reticulite the buoyant scoria is most probably ejected by intermittent lava fountaining at fixed vents as a result of changes in eruption velocities due to changes in the exsolved gas content of the lava between january and july 1993 floating blocks of scoria and reticulite were collected on several occasions from the surface of the sea for chemical and mineralogical analyses major and minor element analyses including ree as well as electron microprobe analyses of different phases revealed that the composition of the emitted lava has not changed through time blocks of basalt sio2 45 47 are highly vitric and vesicular with tabular anorthite phenocrysts up to 3 mm in length and minor grains of forsteritic olivine ree and trace element composition of these rocks suggest an anomalous mantle source for the erupted alkali basalt lava the ongoing eruption will either continue in a similar fashion as described and eventually cease or built up a mound that reaches the surface and forms an island with accompanying change in eruptive style

the fragmentation threshold of pyroclastic rocks in response to rapid decompression porous magma may fragment explosively this occurs when the melt can no longer withstand forces exerted upon it due to the overpressure in included bubbles this occurs at a critical pressure difference between the bubbles and the surrounding magma in this study we have investigated this pressure threshold necessary for the fragmentation of magma here we present the first comprehensive high temperature experimental quantification of the fragmentation threshold of volcanic rocks varying widely in porosity permeability crystallinity and chemical composition we exposed samples to increasing pressure differentials in a high temperature shock tube apparatus until fragmentation was initiated experimentally we define the fragmentation threshold as the minimum pressure differential that leads to complete fragmentation of the pressurized porous rock sample our results show that the fragmentation threshold is strongly dependent on porosity high porosity samples fragment at lower pressure differentials than low porosity samples the fragmentation threshold is inversely proportional to the porosity of the other factors permeability likely affects the fragmentation threshold at high porosity values whereas chemical composition crystallinity and bubble size distribution appear to have minor effects the relationship for fragmentation threshold presented here can be used to predict the minimum pressure differential necessary for the initiation or cessation of the explosive fragmentation of porous magma

phreatomagmatic eruptions through unconsolidated coastal plain sequences maungataketake auckland volcanic field new zealand abstract maungataketake is a monogenetic basaltic volcano formed at 85 89 ka in the southern part of the auckland volcanic field avf new zealand it comprises a basal 1100 m diameter tuff ring with a central scoria spatter cone and lava flows the tuff ring was formed under hydrogeological and geographic conditions very similar to the present the tuff records numerous density stratified wet base surges that radiated outward up to 1 km decelerating rapidly and becoming less turbulent with distance the pyroclastic units dominantly comprise fine grained expelled grains from various sedimentary deposits beneath the volcano mixed with a minor component of juvenile pyroclasts 35 vol subtle lateral changes relate to deceleration with distance and vertical transformations are minor pointing to stable explosion depths and conditions with gradual transitions between units and no evidence for eruptive pauses this volcano formed within and on 60 m thick plio pleistocene poorly consolidated highly permeable shelly sands and silts kaawa formation capped by near impermeable water saturated muds tauranga group these sediments rest on moderately consolidated miocene aged permeable turbiditic sandstones and siltstones waitemata group magma water fuelled thermohydraulic explosions remained in the shallow sedimentary layers excavating fine grained sediments without brittle fragmentation required on the whole the resulting cool wet pyroclastic density currents were of low energy the unconsolidated shallow sediments deformed to accommodate rapidly rising magma leading to development of complex sill like bodies and a range of magma water contact conditions at any time the weak saturated sediments were also readily liquefied to provide an enduring supply of water and fine sediment to the explosion loci changes in magma flux and or subsequent stabilisation of the conduit area by a lava ring barrier led to ensuing strombolian and fire fountaining eruption phases future eruptions in littoral environments around auckland are likely to be of this type producing base surges that rapidly decrease in energy over short runout distances 1 km

quantification of vesicle characteristics in some diatreme filling deposits and the explosivity levels of magma water interactions within diatremes abstract vesicles within juvenile fragments in mafic pyroclastic deposits contain important information about the state of the magma at the time of fragmentation there have been few vesicle studies of juvenile pyroclasts from mafic phreatomagmatic deposits however and none we can find from maar diatreme volcanoes in this paper we document the vesicularity and vesicle population characteristics of juvenile fragments sampled from non bedded lithified deposits of the coombs hills diatreme complex part of the ferrar large igneous province antarctica the diatreme filling pyroclastic deposits dominated by lapilli tuffs and tuff breccias contain typically abundant lithic clasts derived mostly from the enclosing sedimentary sequence and several types of juvenile clasts ranging from blocky to fluidal or raggy in the samples measured 77 80 of the juvenile pyroclasts ranging in size from 0 5 mm to fine lapilli is in the non vesicular to incipiently vesicular range fluidal or rag shaped juvenile clasts some circular vesicles and the lack of microlites all suggest that the coombs hills magma had a relatively low viscosity prior to fragmentation despite the basaltic andesite composition this low viscosity allowed parts of the magma to be fragmented in a non brittle fashion during phreatomagmatic explosions and to form fluidal clasts phreatomagmatic explosions in diatremes can therefore produce diverse types of juvenile clasts simultaneously and the proportions of each will depend on the explosivity of the magma water slurry interaction and other factors recycling of fragments is also thought to be an important factor in generating mixtures of different types of juvenile fragments in diatremes

incipient melt segregation as preserved in subaqueous pyroclasts melt segregation is the extraction of residual melt from the rigid but permeable network of growing crystals with which it co evolved it is recognized as an effective mechanism of igneous differentiation that acts over many geologic time and length scales here we present evidence for rapid melt segregation in subaqueous basaltic pyroclasts segregation produced intravesicular extrusions i e partly hollow balloons of glass penetrating the walls of earlier formed vesicles set in a microcrystalline groundmass the segregation process can be described as a form of gas filter pressing where microlite crystallization produced local gradients in volatile supersaturation and vapor pressure that drove melt extrusion into adjacent vesicles unlike in previously described segregation features the structures presented here are shown to have formed after the extruded melt became enriched in fast diffusing h2o but before it became measurably enriched or depleted in slower diffusing major elements we show that melt segregation of this embryonic type must occur in seconds rather than in the days to centuries required for similar processes to occur in lava flows or magma chambers and that it occurs within the short time scales that characterize explosive fragmentation of basaltic melt

explosive submarine eruptions driven by volatile coupled degassing at lō ihi seamount hawai i abstract there is a growing body of information on submarine explosive eruptions but important questions remain about their causes and diversity magmatic degassing influences eruption dynamics but a paucity of appropriate samples from submarine pyroclastic deposits has limited thorough analysis of this process we present major element and volatile analyses of matrix glasses and olivine hosted glass inclusions from a submarine scoria cone the northern cone at 1060 m below sea level on l ihi seamount hawai i to quantitatively constrain ascent and degassing processes and infer the magmatic plumbing geometries that permit submarine explosive eruption of basalt in deep water olivine crystals form two populations the first consists of a single crystal fo86 8 88 6 bearing inclusions of high fe tholeiitic glass 1 18 to 1 28 wt h2o 182 to 505 ppm co2 major element concentrations indicate that these high fe inclusions represent parental melt that subsequently evolved by crystal fractionation to form the erupted bulk melt the second population consists of variably zoned crystals bearing low fe inclusions with lower volatile contents 0 63 to 0 74 wt h2o 29 to 176 ppm co2 low fe inclusions are not geochemically related to the bulk melt and their host crystals are interpreted as xenocrysts entrained from shallow storage the northern cone magma experienced strongly volatile coupled closed system where bubbles remain in physical contact with the melt from which they have grown ascent from at least 1 5 km deep in the conduit retention of co2 in bubbles facilitated strong exsolution of h2o and s exsolution of h2o dominated the vesiculation and acceleration of ascending melt accounting for the measured 47 to 65 vesicles in lapilli co2 played an essential chemical role but negligible physical role in driving magma ascent our results contradict the common interpretation that high hydrostatic pressures require submarine explosive eruptions to be strombolian driven by the accumulation and buoyant decoupling of co2 rich fluids comparison to volatile data from other explosive and effusive eruption products on l ihi indicates that explosivity is controlled primarily by the style of degassing rather than magma type or initial volatile content magmas that ascend directly from source to vent under volatile coupled conditions retain maximum explosive potential conversely magmas that degas under open system conditions or ascend from shallow reservoirs will have their explosive potential diminished as exsolved volatile fluids are lost to hydrothermal systems this latter path appears to be the most common at l ihi causing most magmas to erupt effusively

groundwater monitoring at a building site of the tidal flood protection system mose in the lagoon of venice italy to protect venice against tidal flooding the mose system experimental electro mechanic module has been under construction since 2003 this safeguarding system is composed of four batteries of mobile barriers at the lagoon s inlets lido malamocco chioggia which will be lifted before the occurrence of exceptional high tides 1 10 m above the mean sea level isolating the venetian lagoon from the sea the end of the construction work is foreseen by 2016 in this paper the results of the groundwater monitoring at the building site of punta sabbioni at the lido inlet are described a large dewatered basin tura formerly occupied by the sea and close to the shoreline was used for the precasting of the mobile barriers and the impact of groundwater control was therefore monitored in the phreatic and shallow confined aquifers although a slurry wall barrier was excavated to isolate the tura a drawdown cone in the confined aquifer was observed extending to 1 km from the construction site in contrast the phreatic aquifer was only influenced by tides rainfall and evapotranspiration and the slurry wall of the tura had a positive effect of decreasing the groundwater salinity by limiting the seawater intrusion as confirmed by the electrical conductivity profiles measured inside the piezometers the monitoring activity was successful in assessing the impacts of the construction work on the aquifer system and in distinguishing them from the effects of natural driving forces

electrical methods ves and ert for identifying mapping and monitoring different saline domains in a coastal plain region alt emporda northern spain summary the spatial variability through time of the degree of salinity of soils and groundwater is a major issue concerning the sustainable management of water resources the problem is accentuated in coastal plain areas where saline bodies of different origin coexist we present an extensive geoelectrical resistivity dataset collected in the alt emporda clastic coastal aquifer system ne spain integrating the results of field campaigns undertaken within a period of more than two decades the dataset is unique in the literature and comprises highly valuable information for the investigation of saline domains the joint application of vertical electrical sounding ves and electrical resistivity tomography ert methods allowed the identification of saline domains and monitoring their evolution through time geophysical data gathered during field campaigns in 1982 2002 and 2010 were calibrated and interpreted on the basis of soil and groundwater physico chemical analyses and hydrogeological stratigraphic and geomorphological data the results illustrate the potential of electrical resistivity methods at differentiating saline domains in coastal aquifer areas and at modelling their configuration and evolution although the ves data processing allows solving the one dimensional resistivity structure of the subsurface the inversion imposes a 1d layered model thus interpretation of two dimensional structures is subject to the interpolation between discrete measures in contrast ert data offer a continuous 2d image of the resistivity distribution both laterally and in depth given that the bulk resistivity of the medium is extremely sensitive to salt content the ert profiles permitted identifying and determining the geometry of hyper saline areas characterized by resistivities of less than 5 m the study demonstrates the efficiency of the electrical methods to map subsurface conductive zones and illustrates how the accurate knowledge of the hydrogeological pattern results critical to meet this objective