experiments on conduit flow and eruption behavior of basaltic volcanic eruptions multiphase flow in basaltic volcanic conduits is investigated using analog experiments and theoretical approaches depending on gas supply large gas bubbles gas slugs may rise through basaltic magma in regimes of distinct fluid dynamical behavior ascent of single slugs supplied slugs fed from the gas source during ascent and periodic slug flow an annular flow regime commences at the highest gas supply rates a first set of experiments demonstrates that the growth of gas slugs due to hydrostatic decompression does not affect their ascent velocity and that excess pressure in the slugs remain negligible the applicability of theoretical formulae describing slug ascent velocity as a function of liquid and conduit properties is evaluated in a second set of experiments a third set of experiments with continuous gas supply into a cylindrical conduit are scaled to basaltic conditions over morton eotvos reynolds and froude numbers gas flow rate and liquid viscosity are varied over the whole range of flow regimes to observe flow dynamics and to measure gas and liquid eruption rates foam generation by slug bursting at the surface and partial slug disruption by wake turbulence can modify the bubble content and size distribution of the magma at the transition from slug to annular flow when the liquid bridges between the gas slugs disappear pressure at the conduit entrance drops by 60 from the hydrostatic value to the dynamic flow resistance of the annular flow which may trigger further degassing in a stored magma to maintain the annular flow regime until the gas supply is exhausted and the eruption ends abruptly magma discharge may also terminate when magma ascent is hindered by wall friction in long volcanic conduits and the annular gas flow erodes all magma from the conduit supplied slugs are found to reach much higher rise velocities than unsupplied slugs and to collapse to turbulent annular flow upon bursting at the surface a fourth set of experiments uses a conduit partially blocked by built in obstacles providing traps for gas pockets once gas pockets are filled rising gas slugs deform but remain intact as they move around obstacles without coalescence or significant velocity changes bursting of bubbles coalescing with trapped gas pockets causes pressure signals at least 3 orders of magnitude more powerful than gas pocket oscillation induced by passing liquid our experiments suggest a refined classification of strombolian and hawaiian eruptions according to time dependant behavior into sporadically pulsating lava fountains driven by stochastic rise of single slugs periodically pulsating lava fountains resulting from slug flow and quasi steady lava fountains oscillating at the frequency of annular flow turbulence

vesicularity of various types of pyroclastic deposits of campi flegrei volcanic field evidence of analogies in magma rise and vesiculation mechanisms abstract in order to investigate the factors controlling the style of explosive eruption in campi flegrei volcanic field image analyses of ash collected in all types of magmatic and hydromagmatic deposits have been carried out our results indicate that bubble shape size distribution and number density are not correlated with the eruptive styles moderate ash vesicularity and relatively high bubble number density suggest that in most cases magma rose with moderate gas oversaturation and in critical conditions near the transition between viscosity controlled and diffusivity controlled regimes in these conditions melt viscosity limited the bubble growth causing fragmentation to occur under the typical limits of gas volume fraction 75 85 for foam rupture the scarce deviation in vesicularity between pure magmatic and phreatomagmatic ashes suggests that the bubble growth was always arrested although not completed before the ultimate occurrence of magma water interaction and eruption thus magma flow rate and upper conduit events rather than conspicuous differences in magma vesiculation and ascent rate background likely controlled the eruptive style

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

north west european mis 11 malacological successions a framework for the timing of acheulean settlements apart from a few lacustrine sequences in north west europe the marine isotope stage mis 11 interglacial is mainly represented in fluvial sequences and is particularly well preserved in calcareous tufa formations these are favourable for the preservation of a range of fossil groups and several of them have yielded artefacts of acheulean affinity molluscan shells are the most abundant proxy occurring throughout these calcareous deposits they provide a valuable means for reconstructing the palaeoenvironments contemporaneous with human occupation allowing direct comparisons between sites the la celle tufa northern france provides the longest malacological succession which allows a detailed reconstruction of the development of forest cover successive arrivals of forest species first from an atlantic corridor and later from central and southern european routeways allow characterization of vegetational development the initial immigrants indicate the spread of closed habitats while a peak in the diversity of thermophilous snails corresponds to the optimum phase of deciduous forest expansion a subsequent decrease in forest molluscs together with expansion of hygrophilous species indicates the decline of closed canopy conditions the occurrence of critical forest species especially those now extinct or occurring far beyond their modern ranges provides a framework within which associated acheulean industries can be set

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

construction dynamics of a lava channel we use a kinematic gps and laser range finder survey of a 200 m long section of the muliwai a pele lava channel mauna ulu kilauea to examine the construction processes and flow dynamics responsible for the channel levee structure the levees comprise three packages the basal package comprises an 80 150 m wide a a flow in which a 2 m deep and 11 m wide channel became centred this is capped by a second package of thin 45 cm thick sheets of pahoehoe extending no more than 50 m from the channel the upper most package comprises localised a a overflows the channel itself contains two blockages located 130 m apart and composed of levee chunks veneered with overflow lava the channel was emplaced over 50 h spanning 30 may 2 june 1974 with the flow front arriving at our section 4 4 km from the vent 8 h after the eruption began the basal a a flow thickness yields effusion rates of 35 m3 s 1 for the opening phase with the initial flow advancing across the mapped section at 10 m min short lived overflows of fluid pahoehoe then built the levee cap increasing the apparent channel depth to 4 8 m there were at least six pulses at 90 420 m3 s 1 causing overflow of limited extent lasting no more than 5 min brim full flow conditions were thus extremely short lived during a dominant period of below bank flow flow depth was 2 m with an effusion rate of 35 m3 s 1 consistent with the mean output rate obtained from the total flow bulk volume of 23 54 m3 s 1 during pulses levee chunks were plucked and floated down channel to form blockages in a final low effusion rate phase lava ponded behind the lower blockage to form a syn channel pond that fed a a overflow after the end of the eruption the roofed over pond continued to drain through the lower blockage causing the roof to founder drainage emplaced inflated flows on the channel floor below the lower blockage for a further 10 h the complex processes involved in levee channel construction of this short lived case show that care must be taken when using channel dimensions to infer flow dynamics in our case the full channel depth is not exposed instead the channel floor morphology reflects late stage pond filling and drainage rather than true channel contained flow components of the compound levee relate to different flow regimes operating at different times during the eruption and associated with different effusion rates flow dynamics and time scales for example although high effusion rate brim full flow was maintained for a small fraction of the channel lifetime it emplaced a pile of pahoehoe overflow units that account for 60 of the total levee height we show how time varying volume flux is an important parameter in controlling channel construction dynamics because the complex history of lava delivery to a channel system is recorded by the final channel morphology time varying flow dynamics can be determined from the channel morphology developing methods for quantifying detailed flux histories for effusive events from the evidence in outcrop is therefore highly valuable we here achieve this by using high resolution spatial data for a channel system at kilauea this study not only indicates those physical and dynamic characteristics that are typical for basaltic lava flows on hawaiian volcanoes but also a methodology that can be widely applied to effusive basaltic eruptions

palaeoenvironmental dynamics of the mis 11 interglacial in north western europe based on the malacological succession from la celle seine valley france relationship with glacial refugia and palaeobiodiversity abstract in north western europe continental records of pleistocene interglacials are well preserved in fluvial sequences and particularly within calcareous tufas that formed at the top of the series they are the sole deposits recording the full optima tufas contain rich malacological communities that allow the detailed palaeoenvironmental history of past interglacials to be reconstructed several tufas have been investigated in the study area which have led to the recognition of the lyrodiscus fauna as a characteristic biostratigraphical signature of tufa sequences of mis 11 age in north western europe among these the site at la celle in the seine valley france is the only one where tufa has accumulated a substantial thickness almost 9 m in which the complete development of the lyrodiscus fauna is represented yielding a detailed record of the forest expansion during the mis 11 interglacial the la celle succession therefore provides a regional framework into which other sequences can be set shedding lights on various aspects of palaeoenvironmental dynamics biostratigraphy palaeogeography and palaeobiodiversity combined malacological and isotopic records from la celle demonstrate a close correlation between increasing temperatures and the development of forest land snail communities the palaeoecological framework of forest extension inferred from the malacological succession of la celle allows the shorter successions from northern france and south eastern england to be located within the maximum development of the humid forest biotope during mis 11c the order of occurrence of forest snails indicates that atlantic and central european refugia are the original sources of recolonizations for north western european sites strict mediterranean species reach the area only at the mis 11c climatic optimum many species present during mis 11c no longer live in this part of europe indicating a northward shift in the location of the modern alpine biodiversity hotspot

interpretation of porosity in dacite lava domes as ductile brittle failure textures abstract pores in dacite lavas of three volcanoes in japan unzen yakedake and daisen have characteristics unlike vesicles most of the pores have ragged walls marked by the protrusion of groundmass crystals and phenocrysts the shapes of these pores range from irregular to planar many pores occur in pressure shadows adjacent to phenocrysts some pores are crack like and pass around phenocrysts and have blunt terminations most of the pores are interpreted as the result of failure of the magma by flow during ductile brittle transition this phenomenon known as cavitation is well established in hydraulics and the material sciences cavitation of the lavas in this study was promoted by steep slope of emplacement subtle mechanical contrasts between bands and strain intensification around rigid crystals and lithic fragments cavitation in lava can extract volatiles from magma causing premature embrittlement and weakening cavitation is inferred to be critical to the initiation of lava front pyroclastic flows

the 1891 submarine eruption offshore pantelleria island sicily channel italy identification of the vent and characterization of products and eruptive style high resolution bathymetry and seafloor sampling have been used to characterize the 1891 submarine eruption of the pantelleria volcanic complex this submarine eruption has been documented mainly by historical reports describing basaltic scoria bombs floating on the sea surface i e lava balloons in this study the 1891 eruptive vent has been identified as a small cone volume of 700 000 m3 rising 90 m from 350 m w d and located within a newly discovered submarine volcanic field covering a wide area offshore from the nw coast of pantelleria recently kelly et al 2012 confirmed this location by a multibeam and rov survey pyroclasts from the 1891 eruption crop out directly on the seafloor and are fresh scoria clasts i e small bombs bomb fragments and lapilli and glass ash sized grains both have been characterized in their morphology textures and geochemistry the distinctive vesicularity and crystallization characteristics displayed by the scoriaceous pyroclasts reflect modes of degassing in both syn and posteruptive regimes these characteristics along with the distribution of deposits suggest for the strongest eruptive phase of the 1891 eruption a style analogous to hawaiian fountaining glass grains from a buoyant plume were dispersed northward from the vent up to distances of 1 5 km redirected by the levantine intermediate water the identification of the 1891 submarine eruptive vent offshore pantelleria as well as the features of erupted pyroclasts improve our knowledge of submarine explosive eruptions that occur at shallow intermediate depths and among these of the rare eruptions producing lava balloons

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

small catchments evolution on clayey hilly landscapes in central apennines and northern sicily italy since the late pleistocene abstract the study aims to define a possible evolutionary geomorphological model of small catchments i e

changes to the environment of intramontane basins in the light of malacological research of calcareous tufa podhale basin carpathians southern poland the profiles of calcareous tufa occurring in the podhale basin carpathians southern poland were subject to a detailed malacological analysis studies were carried out in 15 sites five of them represent the period of the late glacial and holocene and the remainder is tufa deposited during historical times on the basis of malacological analysis 10 faunistic assemblages were defined each developed under specific environmental and climatic conditions the observed sequences of molluscan assemblages in vertical profiles were the basis for paleoenvironmental reconstruction determining the main phases of climatic changes and the human impact on the natural environment the faunal sequence observed indicates a cold climate and the predominance of open habitats in the late glacial with progressing warming and the increasing significance of shaded habitats in the early and middle holocene as well as anthropogenic pressure in modern times the results of malacological analysis were complemented with determination of the age of deposits by radiocarbon dating and the results of palynological analyses conducted in the sites of peatbogs occurring in podhale the reconstruction indicates similarities and differences in the paleogeographic development of mountain and upland areas of central europe

electrical conductivity and pore space topology of merapi lavas implications for the degassing of porphyritic andesite magmas pore space topology is studied in recent compact angular blocks and scoria fragments om block and ash flow deposits of merapi volcano indonesia connected porosity and electrical conductivity of cored clay4 ee samples are measured in the laboratory at varying fluid salini ty the electrical brmation fiactor tortuosity and cementation index are derived and the pore space topology isbund to be porosity dependent the electrical flow pattern is controlled by crack like paths in compact angular block and by vesicles geometry in more porous scoria agments because merapi lavas are highly viscous and crystal rich we infer that the development of pore connectedness and vesicle coalescence is promoted by shear strain along with ascent rate considerations we conclude that degassing of merapi magma occurs mostly in the conduit during ascent

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

radiocarbon dating late quaternary loess deposits using small terrestrial gastropod shells constraining the ages and mass accumulation rates of late quaternary loess deposits is often difficult because of the paucity of organic material typically available for 14 c dating and the inherent limitations of luminescence techniques radiocarbon dating of small terrestrial gastropod shells may provide an alternative to these methods as fossil shells are common in loess and contain w12 carbon by weight terrestrial gastropod assemblages in loess have been used extensively to reconstruct past environmental conditions but have been largely ignored for dating purposes here we present the results of a multifaceted approach to understanding the potential for using small terrestrial gastropod shells to date loess deposits in north america first we compare highly resolved 14 c ages of well preserved wood and gastropod shells succineidae recovered from a holocene loess section in alaska radiocarbon ages derived from the shells are nearly identical to wood and plant macrofossil ages throughout the section which suggests that the shells behaved as closed systems with respect to carbon for at least the last 10 ka thousands of calibrated 14 c years before present second we apply 14 c dating of gastropod shells to late pleistocene loess deposits in the great plains using stratigraphy and independent chronologies for comparison the new shell ages require less interpretation than humic acid radiocarbon ages that are commonly used in loess studies provide additional stratigraphic coverage to previous dating efforts and are in correct stratigraphic order more often than their luminescence counterparts third we show that succineidae shells recovered from historic loess in the matanuska river valley alaska captured the 20th century 14 c bomb spike which suggests that the shells can be used to date late holocene and historicaged loess finally results from nebraska and western iowa suggest that similar to other materials shell ages approaching w40 ka should be viewed with caution as they may reflect trace amounts of contamination in sum our results show that small terrestrial gastropod shells especially from the succineidae family provide reliable ages for late quaternary loess deposits in north america published by elsevier ltd

the evolution of bubble size distributions in volcanic eruptions we review observations of bubble size distributions bsds generated during explosive volcanic eruptions and laboratory explosions as inferred from vesicle size distributions found in the end products unimodal polymodal exponential and power law bsds are common even in the absence of coalescence and both power law and exponential distributions have been generated in the same eruption to date theoretical models have proposed incompatible mechanisms for producing the various distributions we here present a unifying mechanism data from our laboratory analogue experiments suggest that power law distributions are associated with highly non equilibrium degassing a numerical model is developed in which bubbles nucleate repeatedly and grow in the spaces between those of previous generations where in a non equilibrium degassing scenario the volatile concentration remains high this process causes the bsd to evolve from unimodal through exponential into a power law the exponent of the power law is a measure of the number of nucleation events or the duration of the nucleation period compared with the timescale of bubble growth the mathematical inevitability of the evolution from unimodal poissonian to power law is discussed the findings may resolve the apparent contradiction between the equilibrium degassing conduit flow models and the non equilibrium degassing conditions derived from bubble growth models of explosive volcanic eruptions the process of ongoing nucleation is the mechanism whereby the volcanic system maintains near equilibrium in the case of rapid depressurisation and slow volatile diffusion

holocene succession patterns of land snails across temperate europe east to west variation related to glacial refugia climate and human impact abstract although holocene mollusc succession has been described from many temperate european sites no attempt to analyse diversity patterns across the continent from east to west has yet been done here we assembled and quantitatively analysed 54 most representative holocene successions categorized into five climatic and geomorphological regions these were defined along a longitudinal transect across temperate europe i e west carpathians bohemian massif west continental atlantic france and atlantic england we found a clear east west gradient in the holocene dynamic of land snail assemblages correlating mainly with the changes in strictly forest species richness representation of these species increased towards the east in accordance with known position of glacial refugia in the carpathian mountains the west carpathians acted as a unique refugium expressing the highest temporal stability of holocene snail assemblages with a sharp increase in strictly forest species richness already in the early holocene in contrast atlantic regions characterized by low elevation and low topographical heterogeneity were always poor in number of strictly forest species with no or only shallow increase of their richness in the holocene climatic optimum further reduction in the second half of the holocene along with the increase of strictly open country species richness correlates with higher human impact on mollusc faunas in lowland and flat regions these factors can explain the previously reported impoverishment of modern western european forest fauna and have apparently also contributed to regional diversity patterns throughout the holocene among the regions we found three types of successional trajectories in the composition changes of holocene molluscs mirroring the above mentioned east west gradient with the west carpathians having the most distinctive fauna our results show that distance from glacial refugia landscape topography and also human impact importantly shaped the species richness dynamic and successional pathways of holocene land snail fauna across temperate europe

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

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

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

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

molluscan and ostracod successions from dierden s pit swanscombe insights into the fluvial history sea level record and human occupation of the hoxnian thames abstract swanscombe kent is an internationally renowned hominin site located on the south bank of the river thames east of london the swanscombe sequence has been reconstructed from exposures at several localities from which important archaeological and palaeontological assemblages have been recovered the most important of these is barnfield pit where two stone tool industries clactonian and acheulian have been recorded in superposition together with three refitting pieces of a hominin skull associated with the acheulian dierden s pit ingress vale 0 5 km to the north of barnfield pit has also yielded palaeolithic artefacts but is best known as a source of abundant non marine molluscs and as the type locality for the water vole arvicola cantiana this paper describes the molluscan and ostracod successions through the dierden s pit sequence which shed light on important aspects of the fluvial sea level and archaeological histories of the thames during mis 11 a dramatic change occurs in the molluscan record at swanscombe marked by the appearance of the rhenish suite of freshwater molluscs which has previously been used to suggest confluence of the thames and rhine systems the rhenish suite occurs in the middle gravels at barnfield pit and throughout the shell bed at dierden s pit where the component species did not appear simultaneously but colonized the thames in an ordered sequence the occurrence of the rhenish suite provides a secure basis for correlation of important archaeological horizons at swanscombe which have previously been mis correlated on the basis of artefact typology moreover it enables correlation with other mis 11 sequences some of which clacton and east hyde can be directly linked to the pollen stratigraphy of the hoxnian the ostracod succession at dierden s pit provides the first clear evidence of increasing brackish influence at swanscombe and has formed the basis for palaeoclimatic reconstructions using the mutual ostracod temperature range motr method

middle pleistocene molluscan fauna from the valle giumentina abruzzo central italy palaeoenvironmental biostratigraphical and biogeographical implications abstract palaeoenvironmental reconstructions through the middle pleistocene sequence in the valle giumentina located in the abruzzo region of central italy are discussed the sampled sequence is 16 m thick and includes nine levels with lower palaeolithic industries the lithostratigraphy shows fluvio glacial sediments with interbedded colluvial deposits and volcanic tephras fine sediments are composed of calcareous sands and silts most of them yielding well preserved mollusc shells forty five samples at 10 cm resolution yielded 45 taxa which could be assigned to four biozones the oldest biozone vgm1 indicate an open environment which becomes a closed forest landscape developing under temperate conditions vgm2 after a decline of thermophilous species vgm3 mollusc assemblages indicate a dry open environment typical of a glacial period vgm4 all prehistoric occupation horizons occur during stable environmental episodes but under both temperate and cold climatic conditions the molluscan succession is allocated to the middle pleistocene on the basis of the occurrence of jaminia malatestae a well known italian species now extinct as well as the similarity of the molluscan record to that of case picconetto a well dated site nearby this attribution is supported by three tephra layers dated by 40ar 39ar at 556 6 531 5 and 456 2 ka the sequence is correlated with marine isotopic stages 14 13 and 12 four species of land snail azeca goodalli ruthenica filograna pagodulina pagodula nesovitrea hammonis occur beyond their modern range and are therefore of biogeographical interest these snails are western and central european in origin and their presence within the valle giumentina deposits highlight a north south gradient of colonization during pleistocene interglacial periods

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

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

the geotechnical effects of long human habitation 2000 years earthquake induced landslide hazard in the city of zefat northern israel abstract this work studies the effects of long human habitation on site geotechnical conditions it is focused on the city of zefat that is located on the borders of the dead sea transform in northern israel the city of zefat suffered severe damage and loss of life in historical earthquakes as a consequence of earthquake induced landslides eils in this work we evaluate the current eils hazard for the city of zefat using a gis based regional newmark analysis with calibration of the calculated newmark displacement representing eils hazard using maps of field evidence and historical documents testifying to slope instability that occurred in historical earthquakes we found that the core city of zefat is built on a layered anthropogenic material few meters deep which was deposited as a result of more than 2000 years of human habitation the anthropogenic material is mechanically weak susceptible to slope failure and to amplification of seismic shaking it is responsible for the city s devastation in historical earthquakes and it is the source for the current high seismic hazard as well our model shows that earthquakes of magnitudes mw 5 6 and 7 at distances of up to 10 km 50 km and more than 100 km respectively are likely to induce landslides in the core city of zefat the current engineering status of the city is poor and as a consequence severe damage and loss of life are expected in future earthquakes due to eils unless major engineering efforts are made cities in the eastern mediterranean with comparable long habitation histories e g jerusalem tiberias nablus amman are expected to have similar geotechnical problems in their old sections and are advised to take appropriate engineering steps to reduce damage and loss of life in future earthquakes evaluation of historical earthquake magnitudes based on reported local damage may however lead to overestimated magnitudes where the damaged sites are built on anthropogenic talus a common setting in the vicinity of the dead sea transform

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

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

geomorphological facies reconstruction of late quaternary alluvia by the application of fluvial architecture concepts abstract this paper investigates the methodical implications the benefits and the constraints of applying the fluvial architecture concept to late quaternary shallow subsurface alluvial deposits the focus is upon a typical small to mesoscale valley floor of the temperate zone the studied reach is part of the river wetter catchment 517 km 2 in central germany a large number of studies on late quaternary terrestrial paleoenvironmental change of the temperate zone refer to such small to mesoscale catchments which are mostly occupied by mixed to suspended load rivers as in many cases mostly coring based evidence is available the observation and measurement is limited to lithology and lithofacies boundaries facies geometry must be inferred moreover in those environments differences in lithofacies are obscured by a significantly reduced range of grain size distributions an example of an ancient channel belt of late glacial to holocene age serves to delineate the methodical practice and utility of the fluvial architecture approach field evidence is obtained from detailed cross sectional surveys and comprises descriptions of lithofacies structural pedogenetical biotic features munsell color and total organic carbon magnetic volume susceptibility cross sectional lithofacies information is represented by spatially attributed scaled borehole logs the example also accentuates the need for applying additional stratigraphical methods such as physical age determination macrofossil analysis and tephrological stratigraphy these methods form the basis to discern stacked channel facies and derive a diachrony of channel forms thus the adapted architecture approach provides a significant surplus of information on channel dimensions ages and channel floodplain interconnectedness distinct fluvial landforms such as channels levees abandoned channels swamps and floodplain flats can be highlighted a number of methodical constraints are discussed in detail e g the sharpness of channel element geometry and the underlying ordering of bounding surfaces moreover it is shown that the analytical process resembles an iterative looping process that is led by deduction many geomorphologists and multi disciplinary floodplain researchers collect sedimentary data but still neglect utilizing the potential of architectural analysis the study makes clear that sedimentological approaches used in big river floodplains also apply to small valleys in fact the procedures for facies reconstruction need to be adjusted to each individual case study alluvial architecture analysis provides the tools to reveal interconnectedness or disconnectedness of channel near channel and overbank fluvial landforms which is essential for a geomorphological understanding of floodplain evolution

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

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

holywell coombe folkestone a 13 000 year history of an english chalkland valley abstract holywell coombe is a valley cut into the scarp face of the north downs chalk cuesta near folkestone kent its geological importance stems from a highly fossiliferous sequence of lateglacial and holocene deposits that line the valley floor these have yielded a molluscan succession of particular importance providing a record of environmental change throughout the past 13 000 radiocarbon years waterlogging of the basal deposits has prevented oxidation leading to the preservation of a range of organic fossils such as plant and insect remains that normally do not survive in calcareous environments this enables linkage between faunal and vegetational records allowing the differential rates of response of particular groups to be critically compared the importance of the site was revealed in 1968 in trial pits connected with an aborted channel tunnel project resurrection of plans to build a tunnel led in 1987 to major rescue excavations and multidisciplinary investigations the results of which are reviewed here a three dimensional picture of the valley infill was established from a network of 180 boreholes critical parts of the sequence were investigated in specially excavated trenches and sections exposed during construction of the tunnel systematic sampling at a number of locations within the valley provided a palaeontological record from the full stratigraphical succession a number of lateglacial and holocene soils were found to be represented in the sequence including that formed during the allerod phase of the lateglacial interstadial the molluscan zonation scheme previously defined at holywell coombe and applicable over large areas of southern britain and possibly further afield has been refined and dated with greater precision the lateglacial sequence has been extended back to the early part of the lateglacial interstadial by this study and the site chronology is now underpinned by over 35 new radiocarbon dates quantitative palaeoclimatic reconstructions from beetle remains using the mutual climatic range method cover the period between 13 000 and 9000 yr bp the earliest sediments marsh deposits with thermophilous insect taxa and a species poor molluscan assemblage date from around 13 000 12 000 yr bp just before the end of this period changes in beetle faunas record climatic cooling heralding slope instability and the accumulation of thick colluvial deposits by 11 500 yr bp the climate had stabilized and slope movement had ceased allowing the formation of the allerod soil there followed a major deterioration to the arctic climate of the younger dryas during which renewed erosion from the valley sides brought further material onto its floor burying and sealing the earlier sediments the beginning of the holocene saw the onset of tufa formation around two dominant springs in the upper valley there was progressive development of forest hazel dominated woodland being established by 9500 yr bp there is some evidence for thinning of the forest canopy during the late mesolithic and neolithic but the major clearance occurred during the early bronze age causing renewed instability on slopes and consequent hillwash accumulation this final depositional phase continued with pauses marked by soil formation in the early bronze age and the iron age to the present day the hillwash seals structures relating to prehistoric human activity including plough marks and contains an extensive sequence of artefacts

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

magma degassing during the plinian eruption of novarupta alaska 1912 1 we have modeled the nucleation and isothermal growth of bubbles in dacite from the 1912 plinian eruption of novarupta alaska bubble growth calculations account for the exsolution of h2o and co2 beginning with bubble nucleation and ending when bubble sizes reproduced the observed size distribution of vesicles in novarupta pumice clasts assuming classical nucleation theory bubbles nucleated with a diameter of the order of 10 8 m and grew to sizes ranging from 10 6 m to greater than 10 3 m the typical range of vesicle sizes found in novarupta pumice the smallest vesicles in novarupta pumices are also the most abundant and bubbles with radii of 10 6 m to 10 5 m comprise almost 90 of the entire bubble population we find that these bubbles must have nucleated and grown to their final size within a few 100 milliseconds despite these extremely fast growth rates the pressures of exsolved volatiles contained within the bubbles remained high up to about 107pa in excess of ambient pressure assuming a closed system the potential energy of these compressed volatiles was sufficient to cause magma fragmentation even though only a fraction of the pre eruptive volatiles had exsolved unless the matrix glasses of novarupta pyroclasts retains a large fraction of pre eruptive volatiles the majority of magmatic volatiles 80 90 was likely lost by open system degassing between magma fragmentation and quenching

vesicles in thick komatiite lava flows kambalda western australia traditionally vesicles have been considered to be rare in komatiites however field studies at kambalda western australia and critical literature examination suggest that vesicle presence and content in komatiites are grossly underestimated at kambalda vesicles are observed in significant amounts up to 30 in internal horizons within komatiite lavas the vesicular horizons are inferred to represent bubbles frozen in place below the upper crust during multiple episodes of flow through of bubble rich lava we conclude that vesicle and crystal distribution are compatible with many komatiites being emplaced under laminar flow conditions analogous to models for basalt lava emplacement

molluscan successions from the holocene tufa of st germain le vasson normandy france and their biogeographical significance a detailed molluscan succession from a 10 m thick deposit of holocene tufa at st germain le vasson normandy provides the most complete record from northern france and has shed new light on the historical biogeography of several species of land snail the succession has been reconstructed from four profiles and a chronology provided by accelerator mass spectrometry radiocarbon dating of charcoal wood and shell the onset of tufa formation occurred after 9700 90 yr bp and persisted until 4213 77 yr bp the tufa appears to have accumulated at a remarkably constant rate 14 4 16 5 cm 100 yr 1 except for the upper levels where the rate increases fourfold the succession has been divided into six local molluscan zones an early assemblage consisting of ecologically tolerant species and those indicative of marshy grassland is replaced by a sequence of shade demanding taxa reflecting the encroachment of woodland shaded conditions persist until the end of the sequence but the most hygrophilous elements decline after 5422 60 yr bp zone 5 a change also reflected in the tufa lithology by the development of silty grey horizons notable species recovered from the tufa include acicula fusca vertigo substriata v alpestris v moulinsiana all rare or unknown living in northern france hygromia limbata a twentieth century introduction to britain was previously thought to be a relatively recent arrival in northern france but its record at st germain shows that it has been present in normandy since 6500 yr bp azeca goodalli another shade demanding species appeared at st germain much later just after 4420 65 yr bp several other species present in the tufa such as pomatias elegans no longer live on the site adding to the evidence for a distributional decline in normandy and elsewhere perhaps the most noteworthy record is that of leiostyla anglica between about 8500 yr bp and 5000 yr bp because this constitutes its only holocene occurrence from mainland europe following this discovery it seems likely that further holocene sites with l anglica may be found along the western seaboard of europe connecting populations in iberia with those of the british isles copyright 2004 john wiley sons ltd

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

late quaternary catchment evolution and erosion rates in the tyrrhenian side of central italy abstract this work assessed the geomorphological evolution and erosion rates in a small clayey catchment of tyrrhenian central italy providing chronological constraints for the fluvial deposits of the area for the first time the study area is the catchment of the formone stream a left tributary of the orcia river tuscany italy a 5 km long section of the valley up to its confluence with the orcia was studied it has an area of ca 12 km 2 and elevations between ca 300 and 600 m a s l two soil samples have been radiocarbon dated one was located at the top of a fluvial terrace 20 m above the present thalweg and the other was located near the water divide of a small tributary catchment they yielded ages of 2780 40 and 14 050 70 yrs b p respectively these chronological constraints allowed us to reconstruct the geomorphological evolution of the area through topographic and gis analyses and to estimate late quaternary erosion rates the ages provided a chronological reference for the terraced fluvial deposits of the formone and the upper orcia catchments the resultant erosion rates are consistent with those in the literature both for the tyrrhenian side of central italy and for mediterranean europe moreover the results confirmed that very intense erosion processes occurred as a consequence of the pleistocene holocene climatic change as observed in the peri adriatic belt of central italy

variations in hydration within perlitised rhyolitic lavas evidence from torfajokull iceland perlitic fractures form due to the hydration of glassy rhyolitic lavas perlitised lavas are also an important industrial commodity yet there has been little study on the mechanisms of outcrop perlitisation here the fracture populations perlitisation and volatile concentrations of subglacial rhyolitic glassy facies have been studied adding a quantitative dimension to previous qualitative studies samples include hyaloclastite perlitised and non perlitised obsidian and microcrystalline rhyolite which are all present in lava lobes at torfajokull iceland fractures formed through cooling increase in spacing with increased distance inwards from the margins of lobes the size distribution of perlitic beads is shown to follow a log normal distribution the degree of perlitisation and the total volatile content measured using thermogravimetric analysis tga of samples are shown to decrease with distance inwards from lobe margins in general increased perlitisation is accompanied by increased hydration although complexity exists within single outcrops the elevated total volatile content of perlite is shown to be due to hydration by environmental water with the structural location of the water changing as total volatile content increases

holocene molluscan succession from ne morocco palaeoenvironmental reconstruction and biogeographical implications abstract fluvio lacustrine holocene sequences from the semi arid region of eastern morocco are rich in shells and show similar sedimentary levels that could correspond to synchronous environmental variations the high diversity of moroccan continental malacofaunas makes them a very suitable fossil group for palaeoenvironmental reconstructions and palaeobiodiversity implications the malacological study of blirh is the first in morocco to be based on a systematic sampling providing a complete faunal record in order to reconstruct palaeoenvironmental successions three biozones have been recognized they illustrate occurrence of a marsh and a lake from shortly before 10 600 cal bp followed by an abrupt drying up around 5000 cal bp this dramatic environmental change is not synchronous with lithological variations as stated by previous studies based on geological and palynological records the blirh lacustrine phase fits into the humid period that follows full glacial hyperarid conditions during the latest pleistocene in north africa from 14 800 cal bp the abrupt shift to dry conditions around 5000 cal bp inferred from the malacological succession correlates with the contraction of saharan lakes during the last biozone despite disappearance of the main water body marshy species persist and demonstrate occurrence of very wet environments in the middle moulouya plateau until historical times several species currently absent from the region were found within the holocene assemblages at least two new species of aquatic molluscs hydrobiidae have been discovered sampling of modern malacofaunas from wells and springs in the area has demonstrated that one of them is still living in the water table the blirh malacological record provides an insight of the palaeo biogeographical changes affecting this group during the holocene and demonstrates the very recent increase of human impact on the regional biodiversity

humans in the hoxnian habitat context and fire use at beeches pit west stow suffolk uk a lower palaeolithic industry at beeches pit west stow suffolk occurs within an interglacial sequence that immediately overlies glacial deposits referable to the anglian lowestoft formation there is strong biostratigraphical evidence from both vertebrates and molluscs that the interglacial represented is the hoxnian mis 11 this conclusion is supported by uranium series dates from carbonate nodules 400 kyr tl dates from burnt flint 414 30 kyr and a range of amino acid racemisation data the archaeology consists of flint artefacts of acheulian character including many refitting examples charred material is abundant in three stratigraphical units and many bones and flints have been burnt indicating repeated occurrence of fire several discrete areas of burnt sediment appear to be hearths this interpretation is supported by 1 the intensity of burning 600 8008c implied by the charred and calcined bones 2 the intersection of two of the burnt areas implying separate burning events at slightly different overlapping locations 3 the discovery of two burnt flakes that refit onto an adjacent group that are unburnt indicating that the burning was highly localised and 4 the spatial distribution of artefacts respects the features interpreted as hearths suggesting fireside knapping fossils associated with the archaeology indicate occupation within closed deciduous forest in a fully temperate climate attractions to this unusual environment would have included the fresh water provided by springs a rich supply of potential food and a prolific source of good quality flint for tool manufacture the archaeological evidence therefore suggests that the site repeatedly served as an area of focused activities perhaps a home base during much of the interglacial the upper levels of the sequence provide clear faunal evidence of climatic deterioration during which human occupation and fire use persisted biostratigraphical correlations with other lower palaeolithic sites lend support to the suggestion that acheulian and clactonian industries occurred in britain during the same substage of the hoxnian although not necessarily at precisely the same time copyright 2006 john wiley sons ltd

in situ high pressure and high temperature bubble growth in silicic melts we present the first investigation of in situ high pressure and high temperature bubble growth in silicic melts in a hydrothermal diamond anvil cell a haplogranite melt 79 wt sio2 is hydrated then subjected to cooling and decompression with decreasing pressure water exsolves from the melt and bubbles grow the whole experiment is observed through an optical microscope and video recorded so that bubble nucleation bubble growth and the glass transition are directly monitored bubbles nucleate and expand in melt globules having radii from 15 to 70 m bubbles reached 3 6 9 1 m in radius within 6 1 11 7 s until the glass transition is attained while temperature decreases from 709 879 c to 482 524 c corresponding to decompressions from 7 0 21 9 to 3 4 15 2 kbar bubbles nucleated either in a single event occurring within the first second or in successive pulses over a period of up to 7 s when the melt globules are in contact with a diamond culet of the cell in these experiments bubble growth can be fitted to the cube root or a logarithm of time mainly ascribable to the combination of large water oversaturations due to rapid cooling and decompression at pressures of 3 4 15 2 kbar we measure glass transition temperatures that are 20 80 c higher than those calculated at atmospheric pressure

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

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

geochemical stratigraphy of lavas and fault block structures in the ametista do sul geode mining district parana volcanic province southern brazil abstract the parana volcanic province is the world s largest producer of amethyst geodes mostly from the ametista do sul mining district 20 by 30 km in southern brazil the description of the lava flows in the ametista do sul mining district and adjacent areas combined with flow by flow geochemistry and scintillometry defines the stratigraphy of the flows nine flows were identified in the ametista do sul region and four additional flows were identified in the frederico westphalen region totalizing 13 flows in the stratigraphy of the ametista do sul mining district six of the flows belong to pitanga magma type more than 3 wt tio 2 which occur at the base of the local stratigraphy and the other seven flows belong to paranapanema magma type 2 3 wt tio 2 at the top of the stratigraphy the amethyst bearing geodes occur in the uppermost three pitanga flows known as veia alta main producer veia do meio and veia baixa these flows were highly altered more than 60 vol to clay minerals by a low temperature alteration process the massive presence of clay minerals is an important component that controls the rheology of the rock transforming the basalt into a very low grade smectite and celadonite metabasalt two paranapanema flows coogamai and linha alta from ametista do sul were identified in a lower position at the base of the section in frederico westphalen which were correlated using scintillometry and flow by flow geochemistry in addition veia alta and veia do meio flows were also identified in lower positions compared to ametista do sul thus the identification of these flows in different places with different elevations is an evidence of the presence of downthrown blocks in a fault block structure lowering the stratigraphy more than 200 m to the west in four steps the tectonic patterns that generate this structure are three nw strike lineaments the identification of the coogamai flow at the base of the frederico westphalen region suggests that the veia alta geode hosting flow is below the ground or below the elevation of 250 m in this region these evidences show that the fault block structure is controlling vertically the deposit of amethyst bearing geodes and is of major significance in the exploration for new amethyst geode deposits in the region

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

environmental change in the vicinity of the neolithic wetland settlement pestenacker s germany during the last 6600 years abstract pestenacker and the adjacent neolithic wetland sites unfriedshausen and pestenacker nord in southern germany belonged to the altheim culture from around 5750 5350 years cal bp in contrast to contemporaneous pile dwellings the houses of pestenacker were constructed at ground level in a wetland environment only little is known about the environmental and hydrological conditions in the direct vicinity of the settlement and how they changed in time to find detailed answers to these questions stratigraphy sedimentology microfossils geochemistry and stable isotopes of a sediment profile immediately to the west of the settlement were studied an age model comprises five radiocarbon dates and dates the base of the profile to about 6600 years cal bp ostracods and aquatic gastropods were frequent only in the basal part of the profile ostracod taxa typical for open water conditions point to higher humidity especially at 6120 5860 years cal bp and 5750 5370 years cal bp sedimentology and organic carbon isotope data confirm this observation thereafter open water habitats disappeared while increasing numbers of non aquatic gastropods occur and soil formation is indicated by elevated 15 n values we conclude that during the time of settlement an open water body existed near by that disappeared shortly after the settlement was abandoned however the spatial extent of this water body still remains to be clarified

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

response of the selle river to climatic modifications during the lateglacial and early holocene somme basin northern france abstract research on lateglacial sequences from the selle valley leads to an overview of its evolution in relation to climatic variations between the end of the weichselian upper pleniglacial and the beginning of the holocene the first major modification of the fluvial morphology is dated at the upper pleniglacial lateglacial transition 13 000 14 c yr bp at that time the response to climatic improvement and environmental modifications is marked by downcutting and evolution from a braided river to a transitional river pattern bolling infilling in the newly created channels after a short cold phase recorded in a thin calcareous bed at the top of the bolling peat attributed to the older dryas dr ii the allerod is characterized by the deposition of organic overbank silts within a large single channel meandering system in lower slope environments this period is also marked by slow rates of colluvial accumulation and by the development of upbuilding soils allerod soil on the other hand the end of the lateglacial is characterised by the infilling of the whole valley by fine calcareous overbank silts during the younger dryas cold phase overflow of a large single channel and lateral input of chalk mud a second major downcutting phase occurs at the beginning of the holocene at around 10 000 bp in parallel with another rapid climatic improvement and the renewed spread of vegetation from a general point of view the evolution of fluvial environments in the selle valley is comparable with many other river valleys in nw europe showing that fluvial systems react very quickly to climatic variations of short duration 1000 to 100 years finally in the upper selle river incision events occur clearly before the main modifications of the vegetal cover they are most likely linked to a rapid shift in the balance between water discharge and sediment supply caused by climate modifications shift to more temperate and oceanic conditions and the resulting environmental changes cessation in aeolian sedimentation strong reduction of slope processes permafrost disappearance and soil development

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

scaling vesicle distributions and volcanic eruptions models of coalescence decompressive expansion of the later stages of bubble growth predict that for diverse types of volcanic products the vesicle number densities n v are of the scaling form text n left text v right propto text v text b 3 1 where v is the volume of the vesicles and b3 the 3 dimensional scaling power law exponent we analyze cross sections of 9 pumice samples showing that over the range of bubble sizes from 10 m to 3 cm they are well fit with b3 0 85 we show that to within experimental error this exponent is the same as that reported in the literature for basaltic lavas and other volcanic products the importance of the scaling of vesicle distributions is highlighted by the observation that they are particularly effective at packing bubbles allowing very high vesicularities to be reached before the critical percolation threshold a process which for highly stressed magmas would trigger explosion in this way the scaling of the bubble distributions allows them to be key actors in determining the rheological properties and in eruption dynamics

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

experimental study of bubble coalescence in rhyolitic and phonolitic melts abstract we have experimentally studied the process of bubble coalescence in rhyolite and phonolite melts of natural composition the experiments involved decompression of water saturated melts equilibrated at pressures and temperatures from 100 to 150 mpa and 775 to 840 c in vertically oriented rapid quench capable cold seal pressure vessels one type of experiments rhyolite mcr 100 120 150 and phonolite lsp 120 series approximates a static bubble coalescence case where we held the decompressed samples for 5 seconds to 4320 minutes 3 days before quenching the second type rhyolite lpc 100 series replicates an expanding bubble coalescence environment where we continually decompressed the experiments at a rate of 0 5 mpa s examining samples quenched at ending pressures between 10 and 80 mpa our static case mcr 100 120 and 150 and lsp 120 results show significant increases in the modal bubble sizes and in the sizes of the largest bubbles corresponding to measurable broadening in the size distributions their bubble number densities nv decrease as a function of hold time at their final pressures pf and can be fit well by power law functions our expanding case experiments lpc 100 show a significant drop in nv during the duration of the experiments that can be fit by an exponential equation as nv vs either time or pf average estimates of bulk coalescence rates indicate a 1 order of magnitude drop in nv for static case rhyolites in a 2 3 day period and 2 orders of magnitude for phonolites within a 3 day period despite a 2 order of magnitude difference in viscosity coalescene in the phonolite is only slightly faster than the rhyolite the expanding case experiments show a 1 order of magnitude drop in nv over 180 seconds thus nv s decrease 4 orders of magnitude faster in expanding vs static bubbly rhyolite melts our results imply that significant bubble coalescence can occur in rhyolite magmas at relatively fast 20 m s ascent rates in the conduit thus bubble interconnectivity leading to high permeability is possible during ascent bubble coalescence may occur during second boiling in magma bodies that are stalled in the crust the timescales over which this occurs is much faster than the estimated rise rates for bubbles to reach the top of the magma chamber

fragmentation mechanisms associated with explosive lava water interactions in a lacustrine environment rootless cones form when partially outgassed lava interacts explosively with external water the explosions represent an end member system that can elucidate mechanisms of explosive magma water interactions in the absence of magmatic fragmentation induced by outgassing the proportion of finely fragmented ejecta i e ash generated in rootless explosions may contribute significantly to the energy of the explosion even if the ash volume is small relative to coarser ejecta laboratory experiments indicate that the degree of melt water mixing and energy release are proportional to the abundance of blocky grains fragmented by brittle disintegration which effectively contribute thermal energy to the system to constrain the mechanisms and dynamics of rootless explosive activity we assess the nature and modes of fragmentation and ejecta characteristics through morphological textural and density analysis of rootless tephra associated with a p hoehoe lava flow in a lacustrine lake basin environment we observe strong correlations between the mean grain size and the mass percentage of both blocky negative power law trend and fluidal positive logarithmic tephra clasts of all sizes we interpret these trends as scale dependent fragmentation behavior due to the decreasing efficacy of hydrodynamic fragmentation as it occurs over finer scales especially over the ash size range additionally all analyzed beds contain fine ash sized blocky and mossy clasts which are thought to be diagnostic of a high transfer rate of thermal to mechanical energy characteristic of molten fuel coolant interactions these results agree with a recent model of rootless cone formation prior fragmentation theory and scaled laboratory experiments and therefore provide a field based analog for future experimental and modeling efforts

percolating magmas and explosive volcanism 1 magma under pressure rises in conduits depressurizes forms bubbles by the exsolution of gas and at void fractions p typically of the order of 0 7 can fragment and explode the study of overlapping geometrical units percolation theory predicts that at a critical volume fraction pc the size of the largest simply connected region becomes infinite we apply percolation theory to overlapping bubbles arguing that this geometric singularity at pc implies a physical singularity in the magma rheology this would imply that if the magma is under stress whether it is ductile or brittle this rapid development of a network of infinitely long bubbles triggers fragmentation and explosion classical monodisperse equal size continuum percolation theory predicts pc 0 2985 0 005 which is far from the observed values however it has recently been shown that the bubble distribution is a power law associated with a huge range of bubble sizes using monte carlo percolation simulations we show that distributions exhibiting the empirical exponents are very efficient at packing the bubbles drastically raising pc to the value 0 70 0 05 explosive volcanism is thus explained by singular rheology at pc index terms 3220 mathematical geophysics nonlinear dynamics 8414 volcanology eruption mechanisms 8429 volcanology lava rheology and morphology citation gaonac h h s lovejoy and d schertzer percolating magmas and explosive volcanism geophys res lett 30 11 1559 doi 10 1029 2002gl016022 2003

malacological sequence from profile of calcareous tufa in gron podhale basin southern poland as an indicator of the late glacial holocene boundary abstract rich assemblages of subfossil malacofauna were discovered in the profile of slope deposits and calcareous tufas at the gron site in the podhale basin in southern poland the detailed analysis of the composition of this fauna has made it possible to distinguish four types of assemblages their age was established by radiocarbon dating as well as by comparisons with other profiles the malacofauna represented almost exclusively by terrestrial species was used for the reconstruction of the changes in the environment during the sedimentation of the deposits the assemblages distinguished in the study provided the basis for stratigraphic considerations the oldest fauna characterized by a high proportion of cold loving species is typical of the younger dryas the remaining three assemblages are correspondingly linked with the early and middle holocene the evident differences in the composition and structure of the identified malacocoenoses enabled definition of the late glacial holocene boundary the wide geographical distribution of the selected molluscan assemblages enables supra regional correlation and provides an important premise for defining the regional malacostratigraphic subdivisions which can be successfully used to determine the age of deposits from this viewpoint the profile of calcareous tufas in gron represents a model location for central europe

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

late quaternary geomorphological evolution and erosion rates in the clayey peri adriatic belt central italy abstract this study analyses the geomorphological evolution during the last 20 000 years in two areas representative of the peri adriatic belt of central italy mt ascensione in the high hilly sector 600 1100 m a s l and the atri district in the hilly coastal sector up to ca 500 m a s l in both areas the lithostructural setting is characterized by an east verging monocline mainly composed of clayey formations the two areas are compared in relation to their morpho chronological aspects and geomorphological dynamics the results suggest two fundamental evolutionary phases 1 about 20 000 yr bp sedimentation occurred along the main valleys when the middle to upper portions of slopes were covered by colluvial deposits and 2 at the beginning of the holocene the climatic improvement triggered erosion along rivers producing deep and narrow valleys estimated denudation rates during the last 20 000 yr are 7 8 mm yr 1 for the mt ascensione area and 2 4 3 0 mm yr 1 for the atri district reflecting frequent landslides and fluvial erosion the rates are consistent with the data available in literature denudation rates double if we assume most of the erosion process took place after the beginning of the holocenic warming phase

lava effusion rate definition and measurement a review measurement of effusion rate is a primary objective for studies that model lava flow and magma system dynamics as well as for monitoring efforts during on going eruptions however its exact definition remains a source of confusion and problems occur when comparing volume flux values that are averaged over different time periods or spatial scales or measured using different approaches thus our aims are to 1 define effusion rate terminology and 2 assess the various measurement methods and their results we first distinguish between instantaneous effusion rate and time averaged discharge rate eruption rate is next defined as the total volume of lava emplaced since the beginning of the eruption divided by the time since the eruption began the ultimate extension of this is mean output rate this being the final volume of erupted lava divided by total eruption duration whether these values are total values i e the flux feeding all flow units across the entire flow field or local i e the flux feeding a single active unit within a flow field across which many units are active also needs to be specified no approach is without its problems and all can have large error up to 50 however good agreement between diverse approaches shows that reliable estimates can be made if each approach is applied carefully and takes into account the caveats we detail here there are three important factors to consider and state when measuring giving or using an effusion rate first the time period over which the value was averaged second whether the measurement applies to the entire active flow field or a single lava flow within that field and third the measurement technique and its accompanying assumptions

terrestrial environments during mis 11 evidence from the palaeolithic site at west stow suffolk uk abstract multidisciplinary investigations of the sequence at beeches pit west stow suffolk uk have a direct bearing the age of the hoxnian interglacial and its correlation with the continental holsteinian and with the global marine record at this site glacial deposits till and outwash gravels referable to the anglian lowestoft formation fill a subglacial channel cut in chalk bedrock above these glacial deposits a series of interglacial sediments occurs consisting of limnic tufaceous and colluvial silts lacking pollen but rich in shells ostracods and vertebrates lower palaeolithic flint artefacts of acheulian character have also been recovered including refitting examples charred material is abundant at certain horizons and many of the bones have been burned several discrete areas of burnt sediment are interpreted as hearths the molluscan fauna comprises some 78 taxa and includes species of considerable zoogeographical and biostratigraphical importance the land snail assemblage from the tufa consists of woodland taxa with no modern analogue including species that are either extinct e g zonitoides sepultus or which no longer live in britain e g platyla polita p similis neniatlanta pauli this is also the type locality of retinella lyrodiscus skertchlyi which belongs to a subgenus of zonitid land snail now living only on the canary islands there are indications from this fauna the lyrodiscus biome that the climate was wetter and perhaps warmer than the present day the vertebrate fauna is also noteworthy with species of open habitats such as rabbit oryctolagus cf cuniculus and of closed forest such as squirrel sciurus sp and garden dormouse eliomys quercinus present at different times the occurrence of southern thermophiles such as aesculapian snake zamenis longissimus indicates temperatures warmer than those of eastern england today the upper levels include much material reworked from the interglacial sediments although there is clear faunal evidence for climatic deterioration both the molluscan and vertebrate faunas suggest correlation of the interglacial sediments with the hoxnian uranium series dates from the tufa 455 ka bp tl dates from burnt flints 414 30 ka bp and a range of amino acid racemization data all support correlation of this interglacial with mis 11 however four osl dates from sand beneath the interglacial sequence yield a mean age of 261 31 ka bp far younger than all other age determinations and far younger than implied by the biostratigraphy archaeologically the site is unusual in showing prolonged human occupation within closed deciduous forest and evidence for controlled use of fire in a lower palaeolithic context biostratigraphical correlations with other lower palaeolithic sites support the suggestion that acheulian and clactonian industries both occurred in southern britain during the same substage of the hoxnian although not necessarily at precisely the same time the characteristics of the mis 11 interglacial in britain are discussed in the light of evidence from beeches pit and elsewhere

δ13c δ18o and deposition rate of tufa in xiangshui river sw china implications for land cover change caused by climate and human impact during the late holocene

spatter stability constraining accumulation rates and temperature conditions with experimental bomb morphology we have developed the first experimental methodology to create a volcanic spatter pile using molten basalt this method permits reproduction of thermal conditions that yield the wide variety of spatter morphologies observed in nature the morphology of the clasts is most strongly controlled by the time the clast spends above the glass transition temperature which is in turn affected by the rate of accumulation and cooling of the deposit also spatter piles that remain hotter over longer durations experience increased fusion between clasts less void space between clasts and generally larger aspect ratios our experimental method successfully replicated natural microcrystal textures rheology and clast size work is still therefore required to achieve realistic vesicle distribution and deposit void space based on presented experimental work we estimate emplacement conditions of southern idaho spatter vents to have been 850 900 c with eruption temperatures closer to 1000 1100 c the rapid decrease from eruption temperature to effective emplacement temperature is the result of clast flight as well as equilibrating with the cooler surrounding material the morphology of the natural clasts matches experiments that have accumulation rates of 2 5 4 5 m h which also is consistent with the few measurements made at active eruptions finally we provide a constraint on the temperatures and accumulation rates that can lead to the construction of fused spatter features as well as provide the steps for future experiments to investigate other aspects such as compression impact and larger sizes of spatter formation by adapting our methodology

a relation between lava discharge rate thermal insulation and flow area set using lidar data 1 a simple linear relation can be used to link time averaged discharge rate tadr and lava flow area a the relation applies to given insulation conditions as described by the characteristic flow surface temperature te and will vary from case to case depending on rheological and topographic influences on flow spreading most flows have insulation conditions that change through time modifying the relationship between tadr and area as insulation conditions evolve using lidar data we can define tadr the flow area that the discharge feeds and te allowing generation of a case specific relation to convert satellite data derived flow areas to tadr for etna s 2006 lava flow field we obtain a relation whereby tadr 5 6 10 6 a for well insulated conditions te 100 c and tadr 1 5 10 4 a for poorly insulated conditions te 600 c

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

bubble development in explosive silicic eruptions insights from pyroclast vesicularity textures from raoul volcano kermadec arc critical to understanding explosive eruptions is establishing how accurately representative pyroclasts are of processes during magma vesiculation and fragmentation here we present data on densities and vesicle size and number characteristics for representative pyroclasts from six silicic eruptions of contrasting size and style from raoul volcano kermadec arc we use these data to evaluate histories of bubble nucleation coalescence and growth in explosive eruptions and to provide comparisons with pumiceous dome carapace material density vesicularity distributions show a scarcity of pyroclasts with 65 75 vesicularity however pyroclasts closest to this vesicularity range have the highest bubble number density bnd values regardless of eruptive intensity or style clasts with vesicularities greater than this 65 75 pivotal vesicularity range have decreasing bnds with increasing vesicularities interpreted to reflect continuing bubble growth and coalescence clasts with vesicularities less than the pivotal range have bnds that decrease with decreasing vesicularity and preserve textures indicative of processes such as stalling and open system degassing prior to vesiculation in a microlite rich magma or vesiculation during slow ascent of degassing magma bubble size distributions bsds and bnds show variations consistent with 65 75 representing the vesicularity at which vesiculating magma is most likely to undergo fragmentation consistent with the closest packing of spheres we consider that the observed vesicularity range may reflect the development of permeability in the magma through shearing as it flows through the conduit these processes can act in concert with multiple nucleation events generating a situation of heterogeneous bubble populations that permit some regions of the magma to expand and bubbles to coalesce with other regions in which permeable networks are formed fragmentation preserves the range in vesicularity seen as well as any post fragmentation pre quenching expansion which may have occurred we demonstrate that differing density pyroclasts from a single eruption interval can have widely varying bnd values corresponding to the degree of bubble maturation that has occurred the modal density clasts the usual targets for vesicularity studies have likely undergone some degree of bubble maturation and are therefore may not be representative of the magma at the onset of fragmentation

lateglacial palaeoenvironments and palaeoclimates from conty and houdancourt northern france reconstructed from beetle remains abstract two lateglacial insect sequences are described a from conty in the selle valley and b from houdancourt in the oise valley both in northern france these investigations are part of a multidisciplinary investigation involving archaeology sedimentology geomorphology geochronology and palaeontology pollen macroscopic plant remains vertebrates molluscs and insect fossils the sequences of insect assemblages date from the latter part of the bolling to the end of the allerod periods environmental analysis of these faunas shows that rivers with riffles and pools meandered across flood plains the river was extensively fringed with reedy vegetation the only trees growing close to the river were of salix and or populus all the insect assemblages indicate that the thermal climates during the bolling and allerod periods were similar to one another and during both periods were very nearly as warm as that of the present day no insect fossils were recovered from the sediments attributed to the older dryas interval though other evidence from these sites suggests that this event was decidedly colder than those immediately preceding and succeeding it comparisons are made between lateglacial climatic patterns in northern france with those elsewhere in europe

molluscan and ostracod biostrati graphy of holocene tufa in the test valley at bossington hampshire uk holocene tufa deposits in the test valley hampshire uk have been examined as part of a wider project into prehistoric activity and landscape change in the central southern chalklands molluscan and ostracod analysis on three tufa sequences shows that the tufa began developing around 9300 bp in open marsh open woodland environment although one of the sequences boss 10 demonstrates a wooded environment throughout another sequence boss 360n 60e indicates that the initial woodland is followed by reversion to more open conditions both profiles then show a short drier woodland phase subsequent to this one of the profiles then shows wetter woodland conditions developing boss 10 the other boss 360n 60e more open wetland deposition rates are comparable to tufa deposits elsewhere and indicate that the short lived drier woodland phase perhaps lasted only a few hundreds of years there are also indications of woodland clearance associated with a charcoal peak although no causal mechanism can be proposed the formation of substantial portions of holocene tufa deposits within open or only a lightly wooded landscapes has not previously been documented for southern britain where generally tufa holocene has been shown to have formed in densely wooded conditions through the tufa deposits the ostracod and research molluscan evidence are in accord and provide detailed hydrological and environmental information respectively fine sampling 1 cm units allowed a temporal resolution of perhaps around 20 years per sample it is clear that the tufas studied here formed as groundwater fed paludal deposits within the valley bottom

sedimentation of holocene tufa influenced by the neolithic man an example from the sąspowska valley southern poland abstract a complex of inactive tufas the thickness of which reaches 3 5 m was studied in the lowermost segment of the s spowska valley in the krakow upland ojcow national park poland five fluvial tufa barrages were recognized they are composed of moss tufa and stromatolitic tufa accompanied with oncoidal rudstone and detrital tufa interbarrage ponded areas were filled with detrital tufa lutite and subordinately oncoidal rudstone limestone gravel and peat like deposit radiocarbon dates suggest that the tufa formed during subboreal boreal and atlantic time the main difference between the tufa in the s spowska valley and contemporaneous tufas in other valleys of the krakow upland is the higher amount of non carbonate fraction in the former other lower and middle holocene tufas of the krakow upland are composed mainly or exclusively of carbonate fraction the non carbonate fraction in fluviatile tufas in the s spowska valley resulted from erosion of loess cover in the upper part of the catchment the erosion was related to local activity of neolithic flint miners who cleared forest at a local scale dug shafts in loess cover and exploited flints from underlying weathered residuum of jurassic limestone consequently they made copious amounts of loose material available for transport down the valley and subsequent trapping within the tufa depositional system

structural analysis of flow related textures in lavas abstract the textures of coherent volcanic rocks including lavas and volcanic intrusives commonly contain features that are attributed to flowage previous applications of structural analysis to volcanic rocks are expanded here to provide a framework for analysis textures defined as the crystallinity granularity and shapes and arrangements of the components crystals glass and voids of a rock together with structures defined as individual features composed of the disposition attitude arrangement or relative positions of the components of a rock are first described second the spatial fabrics shapes and arrangements of the components of a rock and the orientation of textures and structures are identified third textures structures and fabrics are placed in the spatial and temporal geological context finally detailed interpretations of the kinematics and rheology of structures and fabrics is made leading to an integrated flow history of the rock illustrative case studies include rhyolite from the basal part of the tertiary minyon falls dome northeastern new south wales australia which has a texture comprising planar domains of differing crystal abundance flow bands multiple folds of these domains relatively homogeneous crystal alignment parallel to the fold axes and microfolding of these domains in the zone of interaction between phenocrysts and matrix including retrorotation of phenocrysts on short limbs of inequant folds trachyte dykes on fraser island queensland australia have a texture comprising crystal alignment planar concentration domains banding two planar domains of crystal alignment interpreted to be conjugate shear zones phenocrysts influence the spacing and distribution of the domains and interacted with shear zones by undergoing small amounts of rotation the shear zones overprinted a homogeneous crystal alignment during the last stage of flow before solidification as a result of dilatant granular interactions lava from miocene submarine banded silicic mafic domes on katsurajima on the coast of the shimane peninsula southwestern japan has a texture comprising crystal alignment irregular domains interpreted as the result of quenching local internal deformation of crystals including brittle boudinage and elongate vesicles and amygdales dacite from the late stages of the 1991 1995 eruption of mount unzen in western kyushu japan has a texture comprising crystal alignment deformation of phenocrysts and their surrounding matrix producing voids by mechanical means with the possible involvement of vapour phases the pervasive mechanical failure of the flowing magma may have triggered frontal collapse and the ensuing pyroclastic eruptions a spectrum of increasingly intense flow related textures can be recognised from simple planar alignments of crystals and vesicles to overprinting effects and domainal textures such as banding and shear zones and deformed domains pervasive ductile tearing and ultimately brittle fracture record flow during the transition from ductile magma to brittle rock the development of these flow related textures is controlled by the interplay of driving forces magma pressure gravity and resisting forces viscosity where driving forces are strong flow related textures are well developed when viscous resistance exceeds the driving forces flow and the development of flow related textures ceases