dating the quaternary progress in luminescence dating of sediments abstract luminescence dating comprises a collection of numerical age techniques that are among the most significant chronological tools currently used in quaternary research this paper briefly reviews the key historical developments in luminescence dating from its roots in thermoluminescence dating of heated minerals to the development of optical dating methods for sunlight exposed sediments we describe the principles and practicalities of the various techniques commonly used in luminescence dating including multiple aliquot single aliquot and single grain procedures and we discuss some of the latest approaches to recognising and minimising potential errors in age estimation e g by means of component analysis and dose distribution methods in optical dating the overview also introduces the other papers in this special issue of quaternary science reviews which address a selection of important issues in basic research technique development and application of luminescence dating to critical questions in the geological and archaeological sciences illustrated with examples from around the world and the last million years of earth history

growth of volcanic ash aggregates in the presence of liquid water and ice an experimental approach key processes influencing the aggregation of volcanic ash and hydrometeors are examined with an experimental method employing vibratory pan aggregation mechanisms of aggregation in the presence of hail and ice pellets liquid water 30 wt and mixed water phases are investigated at temperatures of 18 and 20 c the experimentally generated aggregates examined in hand sample impregnated thin sections sem imagery and x ray microtomography closely match natural examples from phreatomagmatic phases of the 27 ka oruanui and 2010 eyjafjallajokull eruptions laser diffraction particle size analysis of parent ash and aggregates is also used to calculate the first experimentally derived aggregation coefficients that account for changing liquid water contents and subzero temperatures these indicate that dry conditions 1 in contrast liquid saturated conditions 15 20 wt liquid promote less size selective processes crystalline ice was also capable of preferentially selecting volcanic ash 31 m under liquid free conditions in a two stage process of electrostatic attraction followed by ice sintering however this did not accumulate more than a monolayer of ash at the ice surface these quantitative relationships may be used to predict the timescales and characteristics of aggregation such as aggregate size spectra densities and constituent particle size characteristics when the initial size distribution and water content of a volcanic cloud are known the presence of an irregularly shaped millimeter scale vacuole at the center of natural aggregates was also replicated during interaction of ash and melting ice pellets followed by sublimation fine grained rims were formed by adding moist aggregates to a dry mixture of sub 31 m ash which adhered by electrostatic forces and sparse liquid bridges from this we infer that the fine grained outer layers of natural aggregates reflect recycled exposure of moist aggregates to regions of volcanic clouds that are relatively dry and dominated by 31 m ash

determining the burial time of single grains of quartz using optically stimulated luminescence abstract in the optical dating of sediments it is usually assumed that the optically stimulated luminescence osl signal has been completely reset by light exposure prior to burial this assumption is often not valid one approach to testing and perhaps circumventing this assumption is to examine the apparent date of last exposure to daylight of individual sediment grains this paper reports on the application for the first time of 2 new measurement protocols to the estimation of the radiation dose received during burial for individual quartz grains from an aeolian deposit of known age 10 000 year old which is considered likely to have been completely reset by sunlight at deposition additive dose laboratory doses added to the burial dose before osl measurement and regenerative dose doses added after measurement of osl from burial dose single aliquot protocols are applied to 28 and 25 individual grains respectively each grain provides an independent estimate d e of the burial dose the average d e from the additive dose protocol 21 8 1 1 gy is in good agreement with the average from the regenerative dose protocol 23 8 1 0 gy both agree well with 1 13 multiple grain regenerative dose single aliquot measurements each on 1 mg sub samples of 23 9 0 3 gy 2 9 multiple grain additive dose single aliquot measurements also on 1 mg sub samples of 22 4 0 7 gy and 3 one previously published multiple aliquot additive dose estimate of 23 5 0 6 gy using 52 sub samples each of 5 mg the resulting optical ages are in good accord with 14 c and thermoluminescence age determinations the distribution of equivalent doses in the single grains is however unexpectedly large 23 of mean d e given the very likely complete resetting of the osl signal at deposition possible reasons are discussed and it is concluded that heterogeneity in beta dosimetry is the most likely explanation the single grain optical dating protocols reported here allow a detailed examination of the dose distribution in very small samples thus they should enable accurate dates to be obtained for sediments and soils that contain poorly bleached or mixed age components as well as deposits in which quartz grains are present in extremely low abundance

low electrical resistivity associated with plunging of the nazca flat slab beneath argentina beneath much of the andes oceanic lithosphere descends eastward into the mantle at an angle of about 30 ref 1 a partially molten region is thought to form in a wedge between this descending slab and the overlying continental lithosphere as volatiles given off by the slab lower the melting temperature of mantle material2 this wedge is the ultimate source for magma erupted at the active volcanoes that characterize the andean margin but between 28 and 33 s the subducted nazca plate appears to be anomalously buoyant3 4 as it levels out at about 100 km depth and extends nearly horizontally under the continent1 5 6 above this flat slab volcanic activity in the main andean cordillera terminated about 9 million years ago as the flattening slab presumably squeezed out the mantle wedge5 6 but it is unknown where slab volatiles go once this happens and why the flat slab finally rolls over to descend steeply into the mantle 600 km further eastward here we present results from a magnetotelluric profile in central argentina from which we infer enhanced electrical conductivity along the eastern side of the plunging slab indicative of the presence of partial melt this conductivity structure may imply that partial melting occurs to at least 250 km and perhaps to more than 400 km depth or that melt is supplied from the 410 km discontinuity consistent with the transition zone water filter model of bercovici and karato7

iconic imagery pleistocene rock art development across northern australia there is general agreement that the peopling of sahul was achieved sometime before 45 000 years ago with most parts of the continent colonised by 30 000 rock art both engraved and painted is present in all areas where these early people left their mark did this artistic endeavour come with these people or was this an expression of being in sahul certainly there are aspects like the cupules and hand stencils which have parallels outside the continent however there are many features that suggest separate artistic traditions and conventions that were present and have continued since these early times spread over an area greater than one million sq km 386 000 sq miles stretching in an arc over 2 000 km from the pilbara coast through the kimberley and into arnhem land is a vast body of rock art that demonstrates there to be differentiation in the symbolic structuring of people s lives relatively early after colonisation this supports the notion that regionalisation within sahul is not simply a holocene expression

volcanic ash clusters tephra rafts and scavengers abstract much of the volcanic ash deposited in the vicinity of pullman washington from the may 18th eruption of mt st helens in 1980 fell in the form of composite ash clusters 0 25 to 0 5 mm in diameter particles in the clusters ranged from sub micron to more than 40 microns in size the porous clusters rafted large ash particles great distances and scavenged particles of all sizes as the wind blew them eastward the result is poorly sorted ash deposits as far as 644 km east missoula within individual clusters textural relationships suggest that both mechanical interlocking and electrostatic attraction played a role in cluster formation the clusters are very fragile and may never be preserved in the stratigraphic record but it is suggested that this kind of ash transport may well have occurred in the geologic past documentation of this ash cluster fall will promote a better understanding of the physical aspects of the downwind distribution of fine grained volcanic ash the poor size sorting in some ancient ash deposits may thus be explained

stable isotope ratios of carbon in phytoliths as a quantitative method of monitoring vegetation and climate change the 13c 12c ratios of occluded carbon within opal phytoliths from the northern great plains show potential as a basis for paleoclimatic reconstruction a significant correlation exists between the carbon isotopic composition of a host plant and that of the organic matter in its phytoliths the 13c 12c ratios for phytoliths from surface layers of soils along climatic gradients reflect the current proportions of c3 and c4 plants variations in the 13c values of phytoliths with soil depth are caused by a variety of processes burial of soil surface by dust bioturbation and possible illuviation by percolating water also contributions of phytoliths by dust and roots have unknown isotopic effects the 13c values of phytoliths from soils increase with decreasing 14c age suggesting that the proportion of c4 plants in this region has increased during the holocene phytoliths of apparent mid holocene age suggest exclusive dominance by c4 plants which agrees with paleoclimatic interpretations of an arid middle holocene climate

gas aerosol ash interaction in volcanic plumes new insights from surface analyses of fine ash particles the reactions occurring between gases aerosols and silicate ash particles in volcanic eruption plumes remain poorly understood despite the fact that they are at the origin of a range of volcanic environmental atmospheric and health effects in this study we apply x ray photoelectron spectroscopy xps a surface sensitive technique to determine the chemical composition of the nearsurface region 2 10 nm of nine ash samples collected from eight volcanoes in addition atomic force microscopy afm is used to image the nanometer scale surface structure of individual ash particles isolated from three samples we demonstrate that rapid acid dissolution of ash occurs within eruption plumes this process is favoured by the presence of fluoride and is believed to supply the cations involved in the deposition of sulphate and halide salts onto ash afm imaging also has permitted the detection of extremely thin 10 nm coatings on the surface of ash this material is probably composed of soluble sulphate and halide salts mixed with sparingly soluble fluoride compounds the surface approach developed here offers promising aspects for better appraising the role of gas aerosol ash interaction in dictating the ability of ash to act as sinks for various volcanic and atmospheric chemical species as well as sources for others c 2007 elsevier b v all rights reserved

a prognostic turbulence scheme for the nonhydrostatic plume model atham the presented turbulence scheme was developed for the active tracer high resolution atmospheric model atham to parameterize the effect of subgrid scale turbulence in contrast to the commonly used assumption of local isotropy in high resolution atmospheric modeling this scheme differentiates between horizontal and vertical turbulent exchange to represent the strong influence of buoyancy forces and vertical transports its computational efficiency is similar to classical turbulent kinetic energy approaches while preserving one of the main feature of higher order schemes the present extensions to include anisotropic effects in a turbulent kinetic energy approach do not need any ad hoc assumptions and are equivalent to the classical formulation in the isotropic limit the presence of high tracer concentrations in a particle laden plume is taken into account as well as supersonic effects at low mach numbers the turbulent exchange coefficients used in the equations of motion are derived from a set of three coupled differential equations for the horizontal and vertical turbulent energy and the turbulent length scale no turbulent equilibrium is assumed all turbulent quantities are treated prognostically numerical simulations of convective plumes of a typical plinian volcanic eruption with the nonhydrostatic plume model atham reveal that a complex treatment of turbulent quantities is necessary in order to capture the bulk characteristics of the plume such as the plume height the horizontal extent and plume development in time anisotropic effects of turbulence have a significant impact on the stability and internal structure of the plume for the first time results from a fully three dimensional simulation of a volcanic plume are presented because of its general formulation the presented turbulence scheme is suitable for a wide range of atmospheric applications

injection of gases into the stratosphere by explosive volcanic eruptions 1 explosive eruptions can inject large amounts of volcanic gases into the stratosphere these gases may be scavenged by hydrometeors within the eruption column and high uncertainties remain regarding the proportion of volcanic gases which eventually reach the stratosphere these are caused by the difficulties of directly sampling explosive volcanic eruption columns and by the lack of laboratory studies in the extreme parameter regime characterizing them using the nonhydrostatic nonsteady state plume model active tracer high resolution atmospheric model atham we simulated an explosive volcanic eruption we examined the scavenging efficiency for the climatically relevant gases within the eruption column the low concentration of water in the plume results in the formation of relatively dry aggregates more than 99 of these are frozen because of their fast ascent to low temperature regions consideration of the salinity effect increases the amount of liquid water by one order of magnitude but the ice phase is still highly dominant consequently the scavenging efficiency for hcl is very low and only 1 is dissolved in liquid water however scavenging by ice particles via direct gas incorporation during diffusional growth is a significant process the salinity effect increases the total scavenging efficiency for hcl from about 50 to about 90 the sulfur containing gases so2 and h2s are only slightly soluble in liquid water however these gases are incorporated into ice particles with an efficiency of 10 to 30 despite scavenging more than 25 of the hcl and 80 of the sulfur gases reach the stratosphere because most of the particles containing these species are lifted there sedimentation of the particles would remove the volcanic gases from the stratosphere hence the final quantity of volcanic gases injected in a particular eruption depends on the fate of the particles containing them which is in turn dependent on the volcanic and environmental conditions

two dimensional electrical section beneath the eastern margin of japan sea 1 four ocean bottom electromagnetometers provided seafloor geoelectromagnetic data for more than nine months in order to reveal mantle dynamics beneath the eastern margin of japan sea where several large and hazardous earthquakes have repeatedly occurred so far high quality magnetotelluric mt data from the seafloor array together with those of four additional land sites in northeast japan were analyzed and carefully corrected for topographic bathymetric effects to extract two dimensional 2d mt responses at each site here we show how the 2d electrical section derived by inverting the corrected 2d mt responses depicts fluid injection deep into the wedge and back arc mantle by the cold and fast subducting pacific plate a high conductivity anomaly found beneath the sado ridge at depths ranging from 150 to 200 km may be direct field evidence that supports water transportation from the earth s surface to the wedge and back arc mantle in the form of serpentinite

a review of tephra transport and dispersal models evolution current status and future perspectives abstract tephra transport models try to predict atmospheric dispersion and sedimentation of tephra depending on meteorology particle properties and eruption characteristics defined by eruption column height mass eruption rate and vertical distribution of mass models are used for different purposes from operational forecast of volcanic ash clouds to hazard assessment of tephra dispersion and fallout the size of the erupted particles a key parameter controlling the dynamics of particle sedimentation in the atmosphere varies within a wide range largest centimetric to millimetric particles fallout at proximal to medial distances from the volcano and sediment by gravitational settling on the other extreme smallest micrometric to sub micrometric particles can be transported at continental or even at global scales and are affected by other deposition and aggregation mechanisms different scientific communities had traditionally modeled the dispersion of these two end members volcanologists developed families of models suitable for lapilli and coarse ash and aimed at computing fallout deposits and for hazard assessment in contrast meteorologists and atmospheric scientists have traditionally used other atmospheric transport models dealing with finer particles for tracking motion of volcanic ash clouds and eventually for computing airborne ash concentrations during the last decade the increasing demand for model accuracy and forecast reliability has pushed on two fronts first the original gap between these different families of models has been filled with the emergence of multi scale and multi purpose models second new modeling strategies including for example ensemble and probabilistic forecast or model data assimilation are being investigated for future implementation in models and or modeling strategies this paper reviews the evolution of tephra transport and dispersal models during the last two decades presents the status and limitations of the current modeling strategies and discusses some emergent perspectives expected to be implemented at operational level during the next few years improvements in both real time forecasting and long term hazard assessment are necessary to loss prevention programs on a local regional national and international level

high flying diatoms widespread dispersal of microorganisms in an explosive volcanic eruption explosive eruptions create a transient bridge between the solid earth and atmosphere frequently injecting volcanic aerosols to stratospheric levels although known to disrupt terrestrial and aquatic ecosystems at the surface the role of explosive volcanism in airborne transport of microscopic organisms has never been characterized this study documents abundant freshwater diatoms microskeletons of siliceous algae in widespread tephra from the 25 4 ka oruanui eruption of taupo volcano new zealand by matching the tephra hosted species assemblages to those in coerupted clasts of lacustrine sediment we demonstrate that 0 6 km 3 of diatom remains were incorporated during magma water interaction with a lake system overlying the vents and were dispersed along with fi ne ash particles hundreds of kilometers downwind one of the dominant species cyclostephanos novaezeelandiae is endemic to new zealand s north island and serves as a unique identifi er of the eruptive source region our results suggest that dispersal of microorganisms may be an overlooked feature of a number of ancient and modern eruptions and indicate a novel pathway of microbe transport in airborne volcanic plumes we conclude that the biogenic signatures contained within distal tephras have potential application in the characterization of eruption dynamics location and environmental settings of volcanic source areas

water on venus new insights from tremolite decomposition abstract venus is an extremely hot and dry planet with very little water in its atmosphere and no standing water on its surface however if venus had had more water in the past as the high d h ratio implies hydrous minerals might have formed we present the first experimental study that examines the decomposition rate of hydrous minerals specifically tremolite with applications to venus we predict that tremolite can survive decomposition on venus over geologic time scales at current and at higher surface temperatures thus if future spacecraft can detect tremolite this discovery could serve as evidence of a wetter venusian history

evidence of enso mega drought triggered collapse of prehistory aboriginal society in northwest australia the kimberley region of northwest australia contains one of the world s largest collections of rock art characterised by two distinct art forms the fine featured anthropomorphic figures of the gwion gwion or bradshaw paintings and broad stroke wandjina figures luminescence dating of mud wasp nests overlying gwion gwion paintings has confirmed an age of at least 17 000 yrs b p with the most recent dates for these paintings from around the mid holocene 5000 to 7000 yrs b p radiocarbon dating indicates that the wandjina rock art then emerged around 3800 to 4000 yrs b p following a hiatus of at least 1200 yrs here we show that a mid holocene enso forced collapse of the australian summer monsoon and ensuing mega drought spanning approximately 1500 yrs was the likely catalyst of this change in rock art the severity of the drought we believe was enhanced through positive feedbacks triggered by change in land surface condition and increased aerosol loading of the atmosphere leading to a weakening or failure of monsoon rains this confirms that pre historic aboriginal cultures experienced catastrophic upheaval due to rapid natural climate variability and that current abundant seasonal water supplies may fail again if significant change in enso occurs

optical dating of tibetan human hand and footprints an implication for the palaeoenvironment of the last glaciation of the tibetan plateau 1 the tibetan plateau is a cold and arid environment with poor archaeological finds it is generally assumed to have been covered by ice sheet during the last ice age nineteen handprints and footprints of homo sapiens on hot spring travertine and the remnant of a fireplace have been found at an elevation of 4200 m on the tibetan plateau based on the optically stimulated luminescence of quartz extracted from samples of the baked and unheated travertine the age of the prints and the fireplace are around 20 000 these finds suggest that there were humans living in this area around the time of the last glacial maximum lgm and that the ice sheet did not cover the entire tibetan plateau at this time

electrical conductivity anisotropy of deformed talc rocks and serpentinites at 3 gpa abstract the electrical conductivity anisotropy of deformed natural talc rocks and serpentinites was investigated using a kawai type multi anvil press in the temperature range of 500 1000 k at 3 gpa the electrical conductivities of the samples were measured by an impedance analyzer with a frequency range of 10 3 10 6 hz along three sample directions the direction parallel to the lineation of oriented minerals x direction the direction perpendicular to the lineation on the foliation plane y direction and the direction perpendicular to the foliation z direction for both rock types electrical conductivities parallel to the x and the z directions were the highest and the lowest respectively electrical conductivities of talc rocks and serpentinites were at least two orders of magnitude lower than previous reports electrical conductivities of the serpentinites were higher than those of the talc rocks electrical conductivity anisotropy for the talc rocks was stronger than that for the serpentinites at the same oxygen buffer condition electrical conductivity and its anisotropy of the serpentinites become higher with higher oxygen fugacity the activation enthalpy of talc rocks was the lowest 0 59 ev in the x direction and highest 0 68 ev in the z direction the activation enthalpies of the serpentinites in different directions show similar values about 0 74 ev and 0 68 ev for the experiments using mo and ni electrodes respectively impedance spectra for both rock types show the presence of two conduction paths grain interior and grain boundary conductions the total electrical conductivities were reduced by grain boundary conduction electrical conductivities of hydrous minerals show strong dependence on hydrogen concentration and hydrogen mobility the conduction mechanism probably was proton migration through extrinsic vacancies derived from a presence of ferric iron perpendicular to the c axis of the crystals and through interstitial mechanisms parallel to the c axis in both warm and cold subduction zones high electrical conductors 10 1 5 s m cannot be explained by the presence of talc or serpentinites the electrical conductivity anisotropy in a subduction zone would be inconspicuously small within one order unless we consider other well aligned high conductive phases

electrical structure of the central cascadia subduction zone the emslab lincoln line revisited abstract the emslab experiment was an ambitious onshore offshore magnetotelluric mt transect of the cascadia subduction zone when completed 1985 1988 it was the largest experiment of its kind modeling and inversion capabilities at the time were however not sufficiently sophisticated to handle a fully regularized inversion of the data including the seafloor data and bathymetric constraints with the main final model presented based on trial and error forward modeling of the responses moreover new data collected as part of the earthscope usarray program are of higher quality due to improvements in instrument technology and augment the original emslab data set presenting an opportunity to revisit the structure in this part of the subduction system we have integrated the original wide band mt data as well as several long period stations from the original emslab data set and invert these in conjunction with emslab seafloor responses and new earthscope data on land this new composite data set has been analyzed in several ways within a two dimensional geometry in which conductivity is assumed to be invariant along a strike direction roughly coincident with that of the subduction zone we have solved for fully smooth regularized models as well as solutions that allow discontinuities in conductivity along the top surface of the descending slab finally we have tested specific features in the emslab model notably a moderately shallow 30 km depth forearc conductor a feature similar to this shallow conductor is a consistent and required feature in our new inversion models but the new models highlight the connection between the slab and what is interpreted to be an accumulation of aqueous fluids in the deep crust the depth 40 km at which the conductor intersects the slab suggests that the fluids are released by the transition of hydrous basalt to eclogite at upper greenschist facies and higher metamorphic grade the nose of the mantle wedge has a conductivity consistent with a dry peridotite composition and thermal models of the system at a depth of around 80 km the mantle intersecting the slab shows a slight increase in conductivity this increase is not sufficient to require the presence of melt but a conductor indicative of melt can be inserted into the model at this depth without compromising the fit

electrical conductivity of tremolite under high temperature and pressure implications for the high conductivity anomalies in the earth and venus we measured the electrical conductivity of tremolite over a range of pressures 1 0 1 5 and 2 0 gpa and temperatures 648 1373 k at temperatures lower than 1173 k the electrical conductivity of tremolite was 0 001 s m but once the dehydroxylation reaction took place at 1173 k we observed a significant increase in the electrical conductivity the electrical conductivity continued to increase until it reached its maximum value of 1 s m at a temperature of 1373 k which we attributed to dehydroxylation in the tremolite samples the electrical behavior was altered by the physical breakdown of the tremolite structure rather than the oxidation process the decomposition of tremolite resulted in the creation of diopside enstatite and quartz to explain some anomalous conductivity measurements we propose that iron free amphibole experiences a dehydroxylation mechanism that differs from the dehydroxylation mechanism observed in iron bearing amphiboles our conductivity analyses indicate that the observed increase in the electrical conductivity in deep subduction regions at depths of 180 km is driven by the dehydroxylation of tremolite and by the mixing of lherzolite and tremolite in the upper mantle using our data and previously published temperature gradient data we were able to extrapolate reasonable electrical conductivity values for the surface and interior of venus

measurements of wave velocity and electrical conductivity of an amphibolite from southwestern margin of the tarim basin at pressures to 1 0 gpa and temperatures to 700 c comparison with field observations summary in situ measurements of elastic wave velocities and electrical conductivities in the three structural directions normal to foliation z perpendicular to lineation in foliation y and parallel to lineation x for an amphibolite collected from southwestern margin of the tarim basin northwest china were carried out in the laboratory the elastic wave velocity was measured with thecombinedtransmission reflectionmethodatpressuresupto1 0gpa atroomtemperature and temperatures up to 700 c at 1 0 gpa and the electrical conductivity was measured with the impedance spectroscopy from 250 to 700 c at 1 0 gpa the experimentally determined data included compressional vp and shear wave velocities vs velocity anisotropy av intrinsic pressure and temperature derivatives of vp and vs electrical conductivity electrical conductivity anisotropy a and the parameters of the arrhenius relationship elastic wave velocities increase in the structural directions z y x with vp of 6 63 6 78 and 6 95 km s 1 and vs of 3 75 3 82 and 3 96 km s 1 for z y and x respectively at pressure of 1 0 gpa elastic wave velocities increase linearly with pressure at room temperature and pressures between 0 25 and 1 0 gpa and decrease linearly with increasing temperature at 1 0 gpa the pressure coefficients of the sample are in the range of 0 1883 0 2308 km s 1 gpa 1 for vp and 0 1149 0 1678 km s 1 gpa 1 for vs the temperature coefficients are in the range of 2 09 2 35 10 4 km s 1 gpa 1 for vp and 1 28 1 68 10 4 km s 1 gpa 1 for vs t he electrical conductivity increases with increasing temperature consistent with the arrhenius relationship activation energies for the three structural directions of the amphibolite are in the range of 0 71 0 75 ev the amphibolite shows velocity anisotropy 4 15 4 86 per cent for vp and 5 29 5 84 per cent for vs at 0 25 1 0 gpa and electrical conductivity anisotropy 11 1 25 2 per cent based on the regional crust model and geothermal gradient velocity and electrical conductivity depth profiles were calculated for the sample these profiles were then compared with those derived from seismic reflection refraction data and from electromagnetic data our results showed that the amphibolite sample has vp and vs in agreement with those of the middle and lower crust obtained from seismic reflection refraction data and in accord with that of the lower crust deduced from electromagnetic data the lower crust of the electromagnetic crust model is roughly equivalent to the middle and lower crust layers of the seismic crust model therefore it is suggest that the amphibolite may be one of the constituents of the present middle and lower crust in the tarim basin

metamorphic amphiboles composition and coexistence amphiboles have long been key players in metamorphic petrology the concept of facies was developed for rocks of basaltic composition eskola 1920 1939 fyfe et al 1958 and within this concept amphiboles had a leading role the first appearance of amphiboles the presence of amphiboles of certain compositions or last appearance of amphiboles that are replaced by pyroxene bearing assemblages mark a number of major facies boundaries the transition from greenschist to amphibolite facies is marked in part by hornblende replacing actinolite and the granulite facies is defined by the breakdown of hornblende to orthopyroxene bearing assemblages the blueschist facies is defined by the appearance of glaucophane while the transition from blueschist facies to eclogite facies conditions is indicated by the breakdown of glaucophane to omphacitic pyroxene bearing assemblages references to amphibole names actinolite glaucophane or rocks characterized by certain amphiboles amphibolite hornblende figure prominently in six facies names turner 1981 liou et al 1985 oh et al 1988 evans 1990 peacock 1993 a large part of the literature that is devoted to metamorphic petrology of amphiboles concerns reactions which produce amphiboles from more hydrated mafic igneous rocks or lead to the destruction of amphiboles as they break down to form anhydrous or nearly anhydrous mineral assemblages consequently amphiboles can be thought of as occupying the wide intermediate portion of p t xfluid space in which metamorphic rocks are found the number of citations of the published amphibole nomenclature serves as a yardstick meterstick of the interest in amphiboles and a minimum estimate of the amount of literature devoted to this mineral two versions of the nomenclature of amphiboles have appeared 1978 and 1997 leake 1978 leake et al 1997 and they have been cited a over 2300 times in the past 28 years this works out to a minimum

age of barrier canyon style rock art constrained by cross cutting relations and luminescence dating techniques rock art compels interest from both researchers and a broader public inspiring many hypotheses about its cultural origin and meaning but it is notoriously difficult to date numerically barrier canyon style bcs pictographs of the colorado plateau are among the most debated examples hypotheses about its age span the entire holocene epoch and previous attempts at direct radiocarbon dating have failed we provide multiple age constraints through the use of cross cutting relations and new and broadly applicable approaches in optically stimulated luminescence dating at the great gallery panel the type section of bcs art in canyonlands national park southeastern utah alluvial chronostratigraphy constrains the burial and exhumation of the alcove containing the panel and limits are also set by our related research dating both a rockfall that removed some figures and the rock s exposure duration before that time results provide a maximum possible age a minimum age and an exposure time window for the creation of the great gallery panel respectively the only prior hypothesis not disproven is a late archaic origin for bcs rock art although our age result of a d 1 1100 coincides better with the transition to and rise of the subsequent fremont culture this chronology is for the type locality only and variability in the age of other sites is likely nevertheless results suggest that bcs rock art represents an artistic tradition that spanned cultures and the transition from foraging to farming in the region

optical and radiocarbon dating at jinmium rock shelter in northern australia the jinmium rock shelter is located in the kimberley region of northern australia claims for ancient rock art and an early human presence at this site1 were based on thermoluminescence ages of 50 75 thousand years kyr for quartz sands associated with buried circular engravings pecked cupules and on thermoluminescence ages of 116 176 kyr for the underlying artefact bearing deposits here we report substantially younger optical ages for quartz sand and ages based on measurements of radioactive carbon in charcoal fragments from the occupation deposit using conventional multiple grain optical dating methods we estimate that the base of the deposit is 22 kyr however dating of individual grains shows that some have been buried more recently the single grain optical ages indicate that the jinmium deposit is younger than 10 kyr this result is in agreement with the late holocene ages obtained for the upper two thirds of the deposit from radiocarbon measurements we suggest that some grains have older optical ages because they receivedinsufficient exposure to sunlight before burial the presence of such grains in a sample will cause age overestimates using multiple grain methods whether using thermoluminescence or optical dating

progress towards single grain optical dating of fossil mud wasp nests and associated rock art in northern australia here we report on investigations into optical dating of fossil mud wasp nests as a means of constraining the ages of overlying and underlying rock paintings in northern australia we describe the application of a dual signal regenerative dose approach using the easy to bleach fast and hard to bleach slow components of optically stimulated luminescence osl emitted by individual sand sized grains of quartz extracted from two nests a modern nest 2 yr old and a nest dated by 14c to about 30 000 calendar years 30 ka for the modern nest most of the palaeodoses obtained from both the fast and slow components are consistent with a zero age while the 14c dated nest yielded an age of 27 1 1 5 ka from those grains that yielded concordant palaeodoses from the fast and slow components as measured by linearly modulated osl our findings indicate that a dual signal approach permits grains that were fully bleached by sunlight at the time of nest construction and that have since remained concealed in the light safe core of a nest to be distinguished from a grains that were incompletely bleached before nest construction and b grains embedded in the continuously light exposed exterior portion of a nest we conclude that reliable optical ages for small mud wasp nests associated with ancient rock art may be obtained using the dual signal approach and the light safe grains

the 12 900 years bp laacher see eruption estimation of volatile yields and simulation of their fate in the plume we estimated the volatile emissions of the 12 900 years bp eruption of laacher see volcano germany using a modified petrological method glass inclusions in phenocrysts and matrix glasses sampled over the laacher see tephra profile were analysed by synchrotron x ray fluorescence microprobe and electron microprobe to obtain the emitted masses of halogens sulphur and water these data were used to initialize the numerical plume model atham in order to investigate the fate of volcanic gases in the plume and to estimate volatile masses injected into the stratosphere the scavenging efficiency of each volatile component depends on its interactions with both liquid water and ice we found a scavenging efficiency of c 5 for the sulphur species and of only c 30 for hydrogen halides despite their high water solubility our simulations showed that the greatest fraction of hydrometeors freeze to ice due to the fast plume rise and great height of the eruption column for the dry atmospheric conditions of the laacher see eruption the amount of liquid water was not sufficient to completely scavenge hcl and hbr so that a large proportion could reach the stratosphere

particle fallout thermal disequilibrium and volcanic plumes we develop a model of a volcanic eruption column that includes the effects of fallout of pyroclasts and thermal disequilibrium we show that clast fallout with no thermal disequilibrium has only a small effect upon the column however disequilibrium changes column behaviour significantly and can even induce collapse our results may explain the lower plume heights and less widely dispersed fallout of cone forming eruptions contrasted with sheet forming eruptions the model also predicts that the transition from the gas thrust to the convective region in a column results in an inflection in dispersal curves that some features of the stratigraphy common to many fall deposits may result from column velocity structure and that there may exist a region near the volcanic vent in which maximum pyroclast size does not decrease significantly with distance

tremolite new enthalpy and entropy data from a phase equilibrium study of the reaction tremolite 2 diopside 1 5 orthoenstatite β quartz h2o

a 28 000 year old excavated painted rock from nawarla gabarnmang northern australia we report new archaeological excavations from northern australia revealing part of a charcoal design likely to be c 28 000 years old and chrono stratigraphically constrained within the period 15 600 45 600 cal bp on a small rock slab fallen from the ceiling at the rockshelter of nawarla gabarnmang in jawoyn country arnhem land this represents the oldest confirmed pictograph in australia

electrical conductivity of enstatite as a function of water content implications for the electrical structure in the upper mantle abstract the electrical conductivity of ca free aluminous enstatite with various water contents has been determined at a pressure of 3 gpa in a kawai type multi anvil apparatus impedance spectroscopy was performed for both hydrogen doped and undoped samples in a frequency range from 0 1 hz to 1 mhz to examine the effect of water on conductivity two conduction mechanisms were identified for hydrogen undoped samples at temperature of 1000 1723 k and for hydrogen doped samples at relatively lower temperature range of 500 900 k to minimize dehydration of samples for the hydrogen undoped samples the activation enthalpy is around 1 9 ev at the higher temperatures range 1300 k suggesting that the dominant charge transfer mechanism is fe 2 fe 3 hopping small polaron conduction for the hydrogen doped samples measured below 900 k the activation enthalpy decreases from 1 11 to 0 70 ev and the conductivity values systematically increase with increasing water content suggesting that proton conduction is the dominant conduction mechanism taking hopping conduction and water content dependence of activation enthalpy for proton conduction into account all electrical conductivity data were fitted to the formula 0 h exp h h kt 0 p c w exp h p 0 c w 1 3 kt where 0 is pre exponential factor c w is the water content in weight percent h is the activation enthalpy h p 0 is the activation enthalpy for proton conduction at very low water concentration is the geometrical factor k is the boltzmann constant t is absolution temperature and subscripts h and p represent hopping and proton conductions respectively using the present results a laboratory based conductivity depth profile in the earth s upper mantle has been constructed as a function of water content comparison of our model with the currently available geophysical observations beneath the eastern pacific rise indicates that hydrous aluminous enstatite cannot account for the high conductivity anomaly at the top of the asthenosphere as well as hydrous olivine

improved prediction and tracking of volcanic ash clouds abstract during the past 30 years more than 100 airplanes have inadvertently flown through clouds of volcanic ash from erupting volcanoes such encounters have caused millions of dollars in damage to the aircraft and have endangered the lives of tens of thousands of passengers in a few severe cases total engine failure resulted when ash was ingested into turbines and coating turbine blades these incidents have prompted the establishment of cooperative efforts by the international civil aviation organization and the volcanological community to provide rapid notification of eruptive activity and to monitor and forecast the trajectories of ash clouds so that they can be avoided by air traffic ash cloud properties such as plume height ash concentration and three dimensional ash distribution have been monitored through non conventional remote sensing techniques that are under active development forecasting the trajectories of ash clouds has required the development of volcanic ash transport and dispersion models that can calculate the path of an ash cloud over the scale of a continent or a hemisphere volcanological inputs to these models such as plume height mass eruption rate eruption duration ash distribution with altitude and grain size distribution must be assigned in real time during an event often with limited observations databases and protocols are currently being developed that allow for rapid assignment of such source parameters in this paper we summarize how an interdisciplinary working group on eruption source parameters has been instigating research to improve upon the current understanding of volcanic ash cloud characterization and predictions improved predictions of ash cloud movement and air fall will aid in making better hazard assessments for aviation and for public health and air quality

volcanic particle aggregation in explosive eruption columns part ii numerical experiments abstract the goal of this paper is to determine the parameters that control the aggregation efficiency and the growth rate of volcanic particles within the eruption column numerical experiments are performed with the plume model atham active tracer high resolution atmospheric model in this study we employ the parameterizations described in a companion paper this issue the presence of hydrometeors promotes the aggregation of ash particles which strongly increases their fall velocities and thus their environmental impact the tephra mass is about two orders of magnitude greater than that of hydrometeors during typical plinian eruptions without interaction of external water ice is highly dominant in comparison to liquid water 99 by mass this is caused by the fast column rise 100 m s 1 on average to very cold altitudes most particles occur in the form of frozen aggregates with low ice content the collection efficiency is governed by the availability of hydrometeors acting as adhesives at the particles surface in our study and wet ash particles have a higher sticking capacity than icy ones therefore aggregation is fastest during the eruption within the column when limited regions of liquid water exist and when particle concentrations are very high of the order of 10 5 cm 3 increased humidity in the background atmosphere generally leads to enhanced ice formation but shows only a weak influence on the aggregation process first sensitivity studies showed however a significant increase of the liquid water fraction when considering salinity effects the availability of water or ice at the particles surfaces is also governed by the surface properties the porosity and permeability of ash which are not well established to date particle growth is significantly enhanced for greater differences in the sizes and fall velocities among particles as gravitational capture becomes more efficient our experiments indicate a major influence of the erupted particle size distribution first sensitivity studies show that electrostatic forces result in a significant enhancement of aggregated particles the present exploratory study provides new insights into the sensitivity of the ash aggregation process to a number of key parameters our results indicate the need of further constraining particle composition size porosity permeability and surface properties at low temperatures by in situ observations in the laboratory and in the field in addition further research on electrostatic aggregation would be desirable

the nature origins and distribution of ash aggregates in a large scale wet eruption deposit oruanui new zealand abstract this study documents the processes and products of volcanic ash aggregation in phreatomagmatic phases of the 25 4 ka oruanui supereruption from taupo volcano new zealand detailed textural and stratigraphic relationships of aggregates are examined in six of the ten erupted units which range from relatively dry styles of eruption and deposition units 2 5 to mixed units 6 7 8 and dominantly wet unit 3 aggregate structures and grain size distributions shift abruptly over vertical scales of cm to dm providing diagnostic features to identify deposits emplaced primarily as vertical fallout or pyroclastic density currents pdcs the six categories of ash aggregates documented here are used to infer distinct volcanic and meteorological interactions in the eruption cloud related to dispersal characteristics and mode of emplacement our field observations support the notion of brown et al 2010 origin of accretionary lapilli within ground hugging density currents evidence from pyroclastic couplets on tenerife geol soc am bull 122 305 320 that deposits bearing matrix supported accretionary lapilli with concentric internal structure and abundant rim fragments are associated with emplacement of pdcs however on the basis of grain size distributions and field relationships it is inferred that these types of ash aggregates formed their ultrafine ash dominantly 100 km from vent it is inferred that ambient meteorological conditions play a more important role in ash fallout in these cases entrainment of moist air and distal subsidence and melting of ice carried by the plume are both likely to have contributed to the observed features of late stage aggregation in the drier phases of eruption these observations suggest that proximal column influenced aggregation processes which weaken with distance from source are overprinted by secondary later stage aggregation mechanisms farther downwind

use of motion estimation algorithms for improved flux measurements using so 2 cameras abstract article history received 3 april 2014accepted 18 august 2014available online xxxxkeywords so 2 uxso 2 cameraplume speedplume modellingoptical owmotion estimation so 2 cameras are rapidly gaining popularity as a tool for monitoring so 2 emissions from volcanoes severaldifferent so 2 camera systems have been developed with varying patterns of image acquisition in space timeand wavelength despite this diversity there are two steps common to the work owsofmostofthesesystems aligning images of different wavelengths to calculate apparent absorbance and estimating plume transportspeeds both of which can be achieved using motion estimation algorithms here we present two suchalgorithms adualtreecomplexwavelettransform basedalgorithmandthefarnebackopticalflowalgorithm weassesstheiraccuracyusingasyntheticdatasetcreatedusingthenumericcloud resolvingmodelatham andthen apply them to real world data from villarrica volcano both algorithms are found to perform well and theatham simulations offer useful datasets for benchmarking and validating future algorithms 2014 the authors published by elsevier b v this is an open access article under the cc by license http creativecommons org licenses by 3 0

electrical conductivity of dense hydrous magnesium silicates with implication for conductivity in the stagnant slab abstract electrical conductivities of dense hydrous magnesium silicates dhms phase a super hydrous phase b sub and phase d were measured by means of impedance spectroscopy in the frequency range of 10 1 106 hz at temperatures up to 775 700 and 700 k and pressures of 10 18 and 22 gpa respectively for all phases the increase in electrical conductivity with temperature follows the arrhenian formula 0 exp h k t the pre exponential factors 0 and activation enthalpies h of phase a sub and phase d yield values of 7 28 0 82 s m and 0 77 0 01 ev 292 48 s m and 0 83 0 01 ev and 1342 154 and 0 75 0 01 ev respectively higher pressure dhms phases show higher conductivity values the electrical conductivities of phase d and super hydrous phase b are about two and one orders of magnitude higher than that of phase a in the same temperature range respectively although the proton conduction is considered to be a dominant mechanism there is no clear relationship between water content and conductivity rather the conductivity of dhms phase is closely related to the o o distance the conductivity depth profiles for a cold subduction zone were constructed based on the phase proportion predicted in the descending slab the results show distinctly lower conductivity values than those geophysically observed beneath the northeastern china and the philippine sea where the cold slab stagnates in the mantle transition zone consequently the dhms phases themselves cannot be a main contributor to enhance the conductivity in the stagnant slab dehydration of the stagnant slab would strongly enhance the conductivities in the transition zone beneath northeastern china and philippine sea

cross dating th u 14c of calcite covering prehistoric paintings in borneo abstract we present the first application of cross dating th u measured by thermo ionization mass spectrometry tims and 14c measured by accelerator mass spectrometry ams of calcite covering prehistoric paintings th u age estimates of cave drapery range from 9800 to 27 300 yr b p while conventional 14c age is estimated between 9900 and 7610 yr b p depending on the dead carbon correction the age discrepancy is attributed to a disturbance of th u and or 14c geochemical systems showing the limits of the geochronological approach applied to this kind of material for the th u system the poor consistency of u data u content 234u 238u activity ratios and apparent ages argue for open system conditions for 14c system variation of the dead carbon fraction dcf and a possible mixing of successive generations of calcite could account for age discrepancy nevertheless one sample shows concordant ages for the two methods compatible ages through corrections for open system conditions are assumed for other samples then the cross dating suggests 9900 yr as the minimum age of the piece of drapery the underlying painting must be older this study of rock art demonstrates the presence of a pleistocene population before 9900 yr in the southeast of borneo whereas previously the only population in evidence in this area was of austronesian type from 5000 to 6000 yrs ago

ascent dynamics of large phreatomagmatic eruption clouds the role of microphysics 1 we examine the impact of abundant surface water interaction on the development of volcanic clouds from large scale 108 kg s 1 magma phreatomagmatic eruptions presenting the first 2 d large eddy simulations of wet volcanic plumes that incorporate the effects of microphysics the active tracer high resolution atmospheric model was forced with field derived inputs from an exceptionally large phreatomagmatic eruption the 27 ka oruanui supereruption taupo volcano new zealand surface water contents were varied from 0 to 40 wt for eruptions with equivalent magma eruption rates of 1 3 108 and 1 1 109 kg s 1 our findings confirm that increased surface water has a pronounced impact on column stability leading to transitional column behavior and hybrid clouds resulting from simultaneous ascent of material from stable columns and pyroclastic density currents pdcs contrary to the suggestion of previous workers however abundant surface water does not systematically lower the spreading level or maximum height of volcanic clouds owing to vigorous microphysics assisted lofting of pdcs the simulated behavior and ash cloud dimensions provide a close match to field evidence from the oruanui case study cloud heights from the collapsing eruption columns also show a notable sensitivity to changes in the altitude of the tropopause while ambient humidity primarily impacts the abundance of airborne hydrometeors particularly ice associated with the volcanic clouds general relationships between eruption style meteorological conditions and the resulting vertical profiles of volcanic emissions outlined here could also be adapted for use in operational volcanic ash forecasting and deposit reconstruction techniques already in existence

low frequency electrical response of polycrystalline olivine compacts grain boundary transport the complex electrical impedance of sintered polycrystalline compacts of san carlos olivine grain size 75 180 m has been determined over the frequency range 104 to 10 4 hz at temperatures between 800 and 1400 c at the fo2 of the wustite magnetite buffer complex plane plots im z vs re z show separate effects of grain interior and grain boundary conductivity grain interior transport controls the response above 102 hz whereas grain boundary transport dominates between 102 and 10 2 hz overall response of the compacts is modeled with an equivalent circuit in which parallel rc circuit elements representing grain interior and grain responses act in series bulk dc conductivity is lower than either grain interior or grain boundary conductivity alone inversion of magnetotelluric profiles that employ lower bulk conductivities of the grain interior grain boundary system yield upper mantle temperature estimates 30 to 50 c higher than those based on single crystal values

luminescence dating of rock art and past environments using mud wasp nests in northern australia mud nesting wasps are found in all of the main biogeographical regions of the world1 2 3 and construct nests that become petrified after abandonment nests built by mud dauber and potter wasps in rock shelters in northern australia1 4 often overlie and occasionally underlie prehistoric rock paintings mud nests contain pollen spores and phytoliths from which information about local palaeovegetation can be gleaned here we report a new application of optical dating5 6 7 using optically stimulated luminescence osl and accelerator mass spectrometry ams 14c dating of pollen8 to determine the ages of mud wasp nests associated with rock paintings in the kimberley region of western australia9 10 optical dating of quartz sand including the analysis of individual grains embedded in the mud of fossilized nests shows that some anthropomorphic paintings are more than 17 000 years old reconstructions of past local environments are also possible from the range of pollen and phytolith types identified this approach should have widespread application to studies of rock art dating and late quaternary environmental change on continents where mud wasps once lived and other sources of palaeoecological information are absent

optical dating of sediments a new method for dating sediments is proposed which determines the time since the sediment was last exposed to sunlight an argon ion laser is used to excite electrons from thermally stable light sensitive traps and the subsequent luminescence used as a measure of the past radiation dose two sample sequences spanning the periods 0 700 kyr and 0 6 kyr show steadily increasing luminescence with age an age of 62 8 kyr is obtained for a silt radiocarbon dated at 58 8 0 3 kyr problems were found with two much younger samples

deep electrical structure of the northern cascadia british columbia canada subduction zone implications for the distribution of fluids long period magnetotelluric data have been used to image the deep electrical structure of the cascadia subduction zone in british columbia canada zones of elevated electrical conductivity were found in both the forearc and backarc regions and are interpreted as a consequence of the fluid release from subducting slab a shallow zone of high conductivity beneath vancouver island is likely due to fluids that are trapped above the subducting plate east of this structure is a conductive 0 03 s m forearc mantle wedge that also exhibits low seismic velocities and may be serpentinized a free fluid phase is required to account for this enhanced conductivity elevated conductivities are observed in the upper mantle throughout the backarc 0 01 s m and strongly support the hypothesis of a shallow convecting asthenosphere this enhanced upper mantle conductivity can be explained by either hydrogen ion diffusion in olivine minerals or by a few percent partial melting 4

magnetotelluric image of the fluid cycle in the costa rican subduction zone fluids entering the subduction zone play a key role in the subduction process they cause changes in the dynamics and thermal structure of the subduction zone1 and trigger earthquakes when released from the subducting plate during metamorphism fluids are delivered to the subduction zone by the oceanic crust and also enter as the oceanic plate bends downwards at the plate boundary however the amount of fluids entering subduction zones is not matched by that leaving through volcanic emissions4 or transfer to the deep mantle implying possible storage of fluids in the crust here we use magnetotelluric data to map the entire hydration and dehydration cycle of the costa rican subduction zone to 120 km depth along the incoming plate bend we detect a conductivity anomaly that we interpret as sea water penetrating down extensional faults and cracks into the upper mantle along the subducting plate interface we document the dehydration of sediments the crust and mantle we identify an accumulation of fluids at 20 30 km depth at a distance of 30 km seaward from the volcanic arc comparison with other subduction zones5 14 indicates that such fluid accumulation is a global phenomenon although we are unable to test whether these fluid reservoirs grow with time we suggest that they can account for some of the missing outflow of fluid at subduction zones

a model for wet aggregation of ash particles in volcanic plumes and clouds 2 model application 1 the occurrence of particle aggregation has a dramatic effect on the transport and sedimentation of volcanic ash the aggregation process is complex and can occur under different conditions and in multiple regions of the plume and in the ash cloud in the companion paper costa et al develop an aggregation model based on a fractal relationship to describe the rate particles are incorporated into ash aggregates the model includes the effects of both magmatic and atmospheric water present in the volcanic cloud and demonstrates that the rate of aggregation depends on the characteristics of the initial particle size distribution the aggregation model includes two parameters the fractal exponent df which describes the efficiency of the aggregation process and the aggregate settling velocity correction factor e which influences the distance at which distal mass deposition maxima form both parameters are adjusted using features of the observed deposits here this aggregation model is implemented in the fall3d volcanic ash transport model and applied to the 18 may 1980 mount st helens and the 17 18 september 1992 crater peak eruptions for both eruptions the optimized values for df 2 96 3 00 and e 0 27 0 33 indicate that the ash aggregates had a bulk density of 700 800 kg m 3 the model provides a higher degree of agreement than previous fully empirical aggregation models and successfully reproduces the depositional characteristics of the deposits investigated over a large range of scales including the position and thickness of the secondary maxima

the bolivian altiplano conductivity anomaly 1 a long period magnetotelluric study was carried out in the central andes between latitudes 19 5 s and 21 s along two almost parallel profiles of 220 and 380 km length respectively the investigation area extends from the pacific coast to the southern altiplano plateau in the back arc of the south american subduction zone the main geoelectrical structure resolved is a broad and probably deep reaching highly conductive zone in the middle and deeper crust beneath the high plateau although the data show deviations from two dimensionality a two dimensional approach is justified for large parts of the profiles sensitivity studies were carried out in order to constrain the depth extent another electrically conductive structure was resolved in the middle crust of the chilean forearc thought to be connected with the precordillera fault system the andean continental research program ancorp seismic reflection profile carried out along the same line at 21 s revealed highly reflective zones below the altiplano in good correlation with the upper boundary of the altiplano conductor this highly conductive domain also coincides with low seismic velocities and a zone of an elevated vp vs ratio and although not well resolved with low qp seismic quality factors taking into account the enhanced heat flow and a derived temperature model the most probable explanation lies in the assumption of granitic partial melts the good conductor below the volcanic arc which was found in regions farther south at 22 s gradually vanishes toward the north this is consistent with the results of seismic tomography concerning qp values and a gap of recent volcanism

experiments on gas ash separation processes in volcanic umbrella plumes abstract we present a series of analogue laboratory experiments which simulate the separation of ash and gas and the formation of secondary intrusions from finite volcanic umbrella plumes we examined the lateral spreading of mixtures of freshwater and particles released into a laboratory tank containing a uniformly stratified aqueous solution for times smaller than the sedimentation time of particles through the intrusion the current remains coherent and intrudes laterally as some of the particles settle into the underlying ambient fluid a layer of particle depleted fluid develops below the upper surface of the current and the density of the residual fluid is reduced over longer times the intrusion ceases to be coherent with small fingers of relatively buoyant particle depleted fluid rising from the upper part of the intrusion into the overlying fluid meanwhile the lateral motion of the injected solution induces a return flow in the ambient fluid which sweeps some of the particles sedimenting from the lower surface of the intrusion inwards as a result relatively dense particle laden fluid collects below the intrusion and then sinks into the underlying fluid eventually this fluid reaches a new neutral buoyancy height where it intrudes to form a second laterally spreading current below the original intrusion the process then repeats to form further weaker intrusions below these results of the separation of the ash and volcanic gas in an umbrella plume are consistent with field observations at sakurajima volcano where positively charged plumes thought to consist of volcanic gas have been observed above negatively charged plumes of ash this work also suggests that volcanic aerosols may form up to a kilometer above the original injection height of the ash in a strong wind shear this could result in very different trajectories of the ash and gas and so be important for evaluating the impact of ash plumes on both aviation safety and volcanic aerosol formation the separation of the ash from the umbrella plume after a time of order 10 3 10 4 s corroborates recent models of the may 18 1980 eruption at mount st helens that after a few hours the motion of the ash was simply controlled by wind dispersal and gravitational settling the complex motion of the sedimenting ash may also explain some of the observations of multiple intrusions in short lived umbrella plumes such as observed at redoubt alaska in april 1990

the el chichon stratospheric cloud solid particulates and settling rates sampling of the el chichon stratospheric cloud in early may and in late july 1982 showed that a significant proportion of the cloud consisted of solid particles between 2 m and 40 m size in addition many particles may have been part of larger aggregates or clusters that ranged in size from 50 m the majority of individual grains were angular aluminosilicate glass shards with various amounts of smaller adhering particles surface features on individual grains include sulfuric acid droplets and larger 0 5 m to 1 m sulfate gel droplets with various amounts of na mg ca and fe the sulfate gels probably formed by the interaction of sulfur rich gases and solid particles within the cloud soon after eruption ca sulfate laths may have formed by condensation within the plume during eruption or alternatively at a later stage by the reaction of sulfuric acid aerosols with ash fragments within the stratospheric cloud a wilson huang formulation for the settling rate of individual particles qualitatively agrees with the observed particle size distribution for a period at least four months after injection of material into the stratosphere this result emphasizes the importance of particle shape in controlling the settling rate of volcanic ash from the stratosphere

optical dating in archaeology thirty years in retrospect and grand challenges for the future in 1982 when richard klein first became one of the editors of this journal the luminescence dating community was embarking on a new phase of exploratory research attention was turning from the use of thermoluminescence tl dating to estimate the time of last heating of archaeological objects such as pottery and burnt flint to the tl dating of unheated sediments that had been transported by wind and then deposited on the landscape this revolutionary development enabled the extension of tl dating to sedimentary deposits in a variety of environmental settings and to the multitude of archaeological sites that lack suitably heated artefacts in sediment dating the age of most interest is usually the time elapsed since grains of quartz or feldspar were last exposed to sunlight as the energy of the sun s rays is sufficient to evict electrons from their light sensitive traps these traps are steadily refilled after sediment deposition and the longer the grains remain buried the more tl they will emit when measured in 1985 huntley and colleagues proposed optical dating as a simpler and superior means of stimulating the light sensitive traps in quaternary sediments and this is now the principal luminescence based method of dating geological and archaeological deposits optical dating is an umbrella term for an armada of acronyms the most common in archaeological contexts being osl optically stimulated luminescence tt osl thermally transferred osl irsl infrared stimulated luminescence and pirir post infrared irsl all of these variants are founded on the same basic tenet measurement of a light sensitive signal to determine typically the last time that sediment grains were sun bleached but each approach has its virtues and vices in this paper we review this family of luminescence dating techniques and look back on 30 years of optical dating in archaeology some of the more interesting and important achievements are highlighted including the critical insights gained in the last two decades from osl measurements of individual grains of quartz we also look to the future of optical dating in archaeological contexts efforts to extend the age limits of optical dating to older hominin and archaeological sites will remain a key goal and understanding how archaeological sites of all ages form and evolve over time could be improved greatly by combining micromorphology analysis with optical dating of undisturbed intact sediments the latter poses a series of particularly formidable technical challenges but if the past is any guide to the future then we can expect optical dating to illuminate much more of human history before celebrating its golden jubilee

early evolution of a stratospheric volcanic eruption cloud as observed with toms and avhrr this paper is a detailed study of remote sensing data from the total ozone mapping spectrometer toms and the advanced very high resolution radiometer avhrr satellite detectors of the 1982 eruption of el chichon mexico the volcanic cloud atmosphere interactions in the first four days of this eruption were investigated by combining ultraviolet retrievals to estimate the mass of sulfur dioxide in the volcanic cloud krueger et al 1995 with thermal infrared retrievals of the size optical depth and mass of fine grained 1 10 m radius volcanic ash wen and rose 1994 our study provides the first direct evidence of gravitational separation of ash from a stratospheric gas rich plinian eruption column and documents the marked differences in residence times of volcanic ash and sulfur dioxide in volcanic clouds the eruption column reached as high as 32 km carey and sigurdsson 1986 and was injected into an atmosphere with a strong wind shear which allowed for an observation of the separation of sulfur dioxide and volcanic ash the upper more sulfur dioxide rich part of the cloud was transported to the west in the stratosphere while the fine grained ash traveled to the south in the troposphere the mass of sulfur dioxide released was estimated at 7 1 109 kg with the mass decreasing by approximately 4 1 day after the peak the mass of fine grained volcanic ash detected was estimated at 6 5 109 kg amounting to about 0 7 of the estimated mass of the ash which fell out in the mapped ash blanket close to the volcano over the following days 98 of this remaining fine ash was removed from the volcanic cloud and the effective radius of ash in the volcanic cloud decreased from about 8 m to about 4 m

influence of particle aggregation on deposition of distal tephra from the may 18 1980 eruption of mount st helens volcano the may 18 1980 eruption of mount st helens msh produced an extensive ashfall deposit in washington idaho and montana with a minumum volume of 0 55 km3 tephra an unusual feature of the deposit is the occurrence of a second thickness maximum 325 km ene of msh near ritzville washington grain size and component abundance analysis of samples along the main dispersal axis indicates that ash in this region is very fine grained mean size 22 m poorly sorted polymodal and rich in glass shards and pumice fragments a computer simulation of ash fallout from an atmospherically dispersed eruption plume was developed to evaluate various hypotheses for the origin of the distal ash characteristics particularly the thickness versus distance relationship the model was constrained by observations of the eruption column height elevation of major ash transport lateral spreading of the eruption plume and atmospheric wind structure in the vicinity of msh results of different simulations indicate that the second thickness maximum cannot be attributed to either decreased wind velocities over central washington or injection of fine ash above the horizontal wind velocity maximum near the tropopause for the model to fit the observed characteristics of the deposit significant particle aggregation of ash finer than 63 m must be invoked the best fit occurs when ash less than 63 m is aggregated into particles several hundred microns in diameter with a settling velocity of 0 35 m s support for this process comes from the observation and collection of fragile ash clusters of similar size which fell at pullman washington during the may 18 eruption sorem 1982 the premature fallout of fine ash as particle aggregates is a fundamental process in the origin of the grain size characteristics variations in component abundances and thickness versus distance relationship of the may 18 msh ash fall deposit

atmospheric electric potential gradient measurements of ash clouds generated by pyroclastic flows at unzen volcano japan atmospheric electric potential gradient measurements were made at two localities simultaneously during pyroclastic flow events on september 25 1993 at unzen volcano immediately after generation of the pyroclastic flows the potential gradients showed a positive anomaly that was followed by a negative anomaly the magnitude of the positive anomalies were nearly equal at the two measurement localities whereas the magnitude of the negative anomalies at the measurement locality close to the axis of the ash cloud was larger than the magnitude at the off axis measurement locality these differences may be accounted for by the differences in the distance between the ash cloud and each measurement locality it is suggested that the height to the positive charge was sufficiently larger and the height to the negative charge was sufficiently smaller than the horizontal distance between the two measurement localities our results suggest that the upper part of the ash cloud which contained volcanic gases and or relatively fine ash carried a net positive charge and the lower part of ash cloud which contained relatively coarse ash carried a net negative charge this charge distribution in the ash clouds generated by pyroclastic flows is more consistent with the results reported for vulcanian plumes from sakurajiama volcano lane and gilbert 1992 lane et al 1995 and asama volcano hatakeyama and ishikawa 1946 than any other cases

towards single grain esr dating of sedimentary quartz first results abstract in optically stimulated luminescence dating apparent ages of individual grains are thought to reflect a wide distribution of initial bleaching levels in hard to bleach sediments although having a larger age range up to 1 ma and beyond this approach has not been used yet in electron spin resonance esr dating here we report on the first results of esr measurements on single sedimentary quartz grains initial bleaching levels are evaluated for two different river meuse deposits in limburg ne belgium measurements were done with a q band esr spectrometer on transparent quartz grains of sufficiently large diameter 0 5 0 7 mm single crystal esr properties were used to identify different esr active centres in about 50 of the selected grains an al and or ti li signal was detected and the latter has been selected for further measurements artificial bleaching experiments show a strong signal decrease with uv light exposure after gamma ray irradiation a number of different signal intensity vs artificial dose curves could be observed exponential growth exponential saturation linear with inflexion points and unclear ones many grains show increasing esr signals with doses up to 1000 gy suggesting that the age range could be extended over 1 ma covering the middle pleistocene and part of the early pleistocene accumulated doses of individual grains were calculated using the additive dose method the results show a large dose distribution of individual grains for both deposits it is concluded that insufficiently bleached grains can be detected using single grain esr measurements of sedimentary quartz in a fluvial environment

a review of rock art dating in the kimberley western australia this paper critically reviews the various approaches used to estimate the age of the rock art in the kimberley region of western australia they include i the relative superimposition of styles ii the use of diagnostic subject matter depictions of extinct animals stone tool technology introduced european and asian objects and animals iii the recovery of a painted slab from a dated archaeological unit iv radiocarbon dating of beeswax figures charcoal pigments organic matter in overlying mineral deposits and accreted paint layers oxalate rich crusts and amorphous silica skin pollen grains from an overlaying mud wasp nest and v optically stimulated luminescence osl dating of quartz grains from overlying mud wasp nests future directions for rock art dating in the kimberley include uranium series dating of overlying and underlying mineral deposits

moist convection and the injection of volcanic ash into the atmosphere if unsaturated water vapor is carried upward by a volcanic eruption column it may eventually become saturated owing to the decrease in temperature of the column as it expands through decompression and transfers heat to entrained air heat released as a result of the subsequent condensation of water vapor causes the air within the column to expand we show that this increases the buoyancy and therefore the total height of rise of the column the increase in height is significant in relatively small sub plinian and strombolian eruptions in which mass eruption rates lie in the range 103 to 106 kg s in such eruptions the latent heat released as the entrained water vapor condenses may provide the main source of heat which drives the ash and clasts upward the height of rise then becomes relatively insensitive to the mass flux erupted at the vent and depends primarily upon the vapor loading of the atmosphere in a moist atmosphere ash may rise several kilomtres higher than in an eruption of comparable strength in a dry environment moist convection leads to much wider ash dispersal particularly from very small eruptions subsequently rain flushing of ash from umbrella clouds may result from the water which forms through the condensation of entrained vapor the ash provides natural condensation nuclei for some of this entrained vapor whose mass may be much greater than that of the ash in small columns 107 kg s the latent heat released by condensation of vapor is relatively small in comparison with the thermal energy provided by the hot clasts and therefore moisture has no significant effect upon the eruption column dynamics furthermore the mass of water vapor originating from the erupted volatiles is usually comparable to or greater than that entrained from the ambient air our model also shows that if the erupting mixture becomes buoyant then the eruption columns associated with phreatomagmatic eruptions ascend nearly as high as plinian columns with the same mass eruption rate this is because the water which is vaporized by the hot ash at the source condenses higher in the column and thereby restores its latent heat to the ascending ash

effect of water on the electrical conductivity of lower crustal clinopyroxene 1 the electrical conductivity of lower crustal clinopyroxene was measured at 6 12 kbar 250 1000 c and ni nio buffer conditions the dependence of electrical conductivity on water content was studied using both natural and preannealed samples separated from a fresh xenolith granulite with water contents from 0 to 375 ppm an end loaded piston cylinder apparatus and a solarton 1260 impedance gain phase analyzer were used in the study over a frequency range of 0 01 106 hz to obtain the complex impedance spectra the results show that the influence of pressure is very weak relative to temperature and water content and that two distinct mechanisms with different activation enthalpies dominate electrical conduction under dry and wet conditions for the dry sample the activation enthalpy is 102 kj mol and the main charge carriers are small polarons i e hopping of electron holes between ferrous and ferric irons for wet samples the electrical conductivity is significantly enhanced with an activation enthalpy of 70 kj mol and the charge carriers are likely to be protons under hydrous conditions the activation enthalpies are nearly independent of water content and the conductivity is a function of water content with an exponent of 1 as a major constituent of granulites with 60 modal volume in some regions clinopyroxene containing minor amounts of water may contribute significantly to the high electrical conductivity in the lower crust especially under stable continental regions

electrical conductivity beneath the bolivian orocline and its relation to subduction processes at the south american continental margin 1 a long period magnetotelluric data set was obtained during 2002 and 2004 in the central andes to study the deep electrical conductivity structure in the region of the bolivian orocline between latitudes 17 s and 19 s the profile extends from the coastal cordillera in northernmost chile crosses the volcanic arc and the altiplano high plateau in central bolivia and ends in the eastern cordillera two dimensional inversion revealed several well defined conductivity anomalies in upper crustal levels the conductive sedimentary basins of the central altiplano and the resistive arequipa block beneath the western altiplano are imaged earlier seismological and magnetotelluric investigations on the southern altiplano inferred a large highly conductive partially molten body in the mid to deep crust it was assumed that this structure would be underlying the entire plateau but this is not the case according to the new models instead the most prominent feature in the new investigation area is a high conductivity zone at upper mantle depths below the high plateau which may be interpreted as an image of partial melts and fluids triggered by water supply from the subducting nazca slab this conductor would be in accordance with the standard subduction scenario it is however laterally offset by almost 100 km from the volcanic arc in contrast the deep crust and upper mantle beneath the arc is moderately resistive both observations may hint at an emerging shift of the magmatic fluid system in the central andes

origin of accretionary lapilli within ground hugging density currents evidence from pyroclastic couplets on tenerife aggregation of airborne particles is an important way in which the atmosphere is cleansed of fine dust particles such as following explosive eruptions and meteorite impacts we identify successive stages in the growth history of particle aggregates based upon well preserved ash aggregate bearing pyroclastic layers on tenerife the layers are persistently organized into couplets made up of a lower ignimbrite layer and an upper widespread coignimbrite ash fall layer the upper part of each ignimbrite contains whole and fragmented concentric laminated accretionary lapilli whereas the overlying coignimbrite ash fall layer lacks accretionary lapilli and is composed of framework supported smaller and nonlaminated ash pellets sometimes slightly deformed or partly disaggregated the pellets resemble the cores of the larger accretionary lapilli in the underlying ignimbrite layer these field relations are repeated numerous times in several different successions and they indicate that ash pellets not accretionary lapilli form within the coignimbrite ash plumes some pellets fell directly to the ground producing coignimbrite ash fall layers but others settled into pyroclastic density currents where they accreted successive concentric laminations of fine ash as they circulated through the variously turbulent levels of the stratified current and heat of the lower part of the current dried and partly lithified them into brittle accretionary lapilli the fully formed whole and broken accretionary lapilli were then deposited from the current along with ash and pumice lapilli numerous ignimbrite veneers on tenerife have the form of ash layers a few centimeters thick that drape topography and locally contain matrix supported accretionary lapilli most volcanoes lack laterally continuous field exposure and such accretionary lapilli bearing layers might be mistaken for ash fall deposits we highlight the value of careful distinction between different types of ash aggregate facies when interpreting the origin of pyroclastic deposits for example during hazard assessments

the effect of total grain size distribution on the dynamics of turbulent volcanic plumes abstract the impact of explosive volcanic plumes on climate and on air traffic strongly depends on the concentration and grain size distribution gsd of pyroclastic fragments injected into the atmosphere accurate and robust modelling of the evolution of gsd during pyroclast transport from the vent to the ash cloud is therefore crucial for the assessment of major volcanic hazards analysis of field deposits from various recent plinian eruptions shows that their total gsd is well described by a power law as expected from the physics of magma fragmentation with an exponent d ranging from 3 0 to 3 9 by incorporating these measured gsd into the initial conditions of a steady state 1d model of explosive eruption columns we show that they have a first order impact on the dynamical behaviour of explosive eruption columns starting from an initial value of d the model tracks the evolution of gsd in the column and calculates the dynamical consequences of particle sedimentation the maximum height reached by the column one of the first order results relevant to aircraft safety changes by 30 for mass fluxes of 10 7 kg s 1 or larger and by 45 85 for mass fluxes between 105 and 10 7 kg s 1 depending on exponent d we compare our predictions to a specially assembled set of geologic field data and remote sensing observations from 10 plinian eruptions for which maximum column height and mass flux are known independently the incorporation of realistic power law gsd in the model greatly improves the predictions which opens new perspectives for estimation of ash load and gsd in volcanic clouds from near real time measurements available from satellite payloads our results also contribute to the improvement of volcanic source term characterization that is required input for meteorological dispersion models

the electrical conductivity of lherzolite between 700oc and 1200oc and time over a period of 1700 hours are reported for a lherzolite nodule from mount porndon australia analysis of complex impedance collected at 100 hz 1 khz and 10 khz indicates that there is significant frequency dispersion in this rock at temperatures below 900oc 1000oc by choosing the resistance of an equivalent parallel rc network at the frequency having minimum phase the effect of dispersion is largely avoided conductivity as a function of time collected following changes in fo2 at 1010 and 1200oc has been analyzed to determine the diffusivity of defects relating fo2 to the electrical conduction mechanism in olivine the diffusivities so obtained are in remarkably good agreement with those determined from strain measurements during creep tests which implies that magnesium vacancies are the rate limiting step for conductivity reequilibration after fo2 changes a longer term process is observed in this rock in which the conductivity drifts upward or downward with a time constant of hundreds of hours after initial reequilibration to gas mix fo2 changes we speculate that this long term drift could be related to equilibration of the iron distribution between coexisting olivine and pyroxene as a function of fo2 the sense is an increase in conductivity olivine gains iron at low fo2 and vice versa the lherzolite conductivity data are not significantly different from measurements made on olivine single crystals and polycrystals even though the rock contains about 34 modal pyroxene this consistency of laboratory measurements of electrical conductivity of olivines from many localities and geological settings supports the use of recent models relating mantle temperature with electrical conductivity in the interpretation of mantle geo electromagnetic soundings

partial melting below the magmatic arc in the central andes deduced from geoelectromagnetic field experiments and laboratory data abstract magnetotelluric and geomagnetic deep soudings in northern chile revealed a pronounced high conductivity zone hcz below the western cordillera which constitutes the present magmatic arc with active volcanism of the south american continental margin conductivities in the range of 1 s m are observed the anomalously high conductivities in a broad depth range from approximately 20 km to at least 60 km are interpreted in terms of partial melting other geophysical observations such as a zone of low seismic velocities lvz at similar depths high heat flow values 100 mw m2 and a pronounced negative anomaly in the residual gravity field are also considered impedance spectroscopic laboratory experiments up to and in the temperature range of partial melting were performed under controlled oxygen fugacities at sub solidus temperatures electrical behavior is described by defect electrons with an activation energy of 1 34 ev and a conductivity of 2 5 ms m at 900 c model calculations using a modified brick layer model mbl were compared with experimental observations a good agreement between calculations and experiments is achieved with an electrical resistivity of the melt phase of 7 s m at 1250 c assuming an activation energy of 1 ev the same mbl model is used to calculate melt proportions beneath the western cordillera between 14 and 27 vol of interconnected melt are necessary to explain the observed hcz the stability of the melt rich crust is explained by a dynamic melting crystallisation behavior during crustal anatexis and by magma filled dikes

fluid and deformation regime of an advancing subduction system at marlborough new zealand newly forming subduction zones on earth can provide insights into the evolution of major fault zone geometries from shallow levels to deep in the lithosphere and into the role of fluids in element transport and in promoting rock failure by several modes the transpressional subduction regime of new zealand which is advancing laterally to the southwest below the marlborough strike slip fault system of the northern south island is an ideal setting in which to investigate these processes here we acquired a dense high quality transect of magnetotelluric soundings across the system yielding an electrical resistivity cross section to depths beyond 100 km our data imply three distinct processes connecting fluid generation along the upper mantle plate interface to rock deformation in the crust as the subduction zone develops massive fluid release just inland of the trench induces fault fracture meshes through the crust above that undoubtedly weaken it as regional shear initiates narrow strike slip faults in the shallow brittle regime of interior marlborough diffuse in width upon entering the deeper ductile domain aided by fluids and do not project as narrow deformation zones deep subduction generated fluids rise from 100 km or more and invade upper crustal seismogenic zones that have exhibited historic great earthquakes on high angle thrusts that are poorly oriented for failure under dry conditions the fluid deformation connections described in our work emphasize the need to include metamorphic and fluid transport processes in geodynamic models

electrical conductivity of lawsonite and dehydrating fluids at high pressures and temperatures lawsonite is a calcium aluminum bearing hydrous silicate mineral with caal2si2o7 oh 2 h2o stoichiometry it is thermodynamically stable in the hydrated oceanic crust low velocity anomalies observed in the cold subducted slabs have been related to the unusual shear wave velocities of lawsonite eclogite however electrical conductivity of lawsonite at high pressure and temperature remains unknown in this study we measured the electrical conductivity of lawsonite at 7 gpa and temperatures ranging from 298 k 1320 k at 1173 k the electrical conductivity of lawsonite is around 10 1 s m a sharp increase of electrical conductivity is observed at temperatures exceeding the dehydration 1258 k the high electrical conductivity up to 101 s m observed in our experiments is due to the presence of highly conductive fluid and could explain the low resistivity observed at 150 250 km depths in subduction zone settings such as ne japan northern and central chile

volcanic particle aggregation in explosive eruption columns part i parameterization of the microphysics of hydrometeors and ash abstract the aggregation of volcanic ash particles within the eruption column of explosive eruptions has been observed at many volcanoes it influences the residence time of ash in the atmosphere and the radiative properties of the umbrella cloud however the information on the processes leading to aggregate formation are still either lacking or very incomplete we examine the fate of ash particles through numerical experiments with the plume model atham active tracer high resolution atmospheric model in order to determine the conditions that promote ash particle aggregation in this paper we describe the microphysics and parameterization of ash and hydrometeors in a companion paper this issue we use this information in a series of numerical experiments the parameterization includes the condensation of water vapor in the rising eruption column the formation of liquid and solid hydrometeors and the effect of latent heat release on the eruption column dynamics are considered the interactions of hydrometeors and volcanic ash within the eruption column that lead to aggregate formation are simulated for the first time within a rising eruption column the microphysical parameterization follows a modal approach the hydrometeors are described by two size classes each of which is divided into a liquid and a frozen category by analogy with the hydrometeor classification we specify four categories of volcanic ash particles we imply that volcanic particles are active as condensation nuclei for water and ice formation ash can be contained in all categories of hydrometeors thus forming mixed particles of any composition reaching from mud rain to accretionary lapilli collisions are caused by gravitational capture of particles with different fall velocity coalescence of hydrometeor ash aggregates is assumed to be a function of the hydrometeor mass fraction within the mixed particles the parameterization also includes simplified descriptions of electrostatics and salinity effects

electric potential gradient changes during explosive activity at sakurajima volcano japan we report electric potential gradient measurements carried out at sakurajima volcano in japan during 1 explosions which generated ash plumes 2 steam explosions which produced plumes of condensing gases and 3 periods of ashfall and plume induced acid rainfall sequential positive and negative deviations occurred during explosions which generated ash plumes however no deflections from background were found during steam explosions during periods of ashfall negative electric potential gradients were observed while positive potential gradients occurred during fallout of plume induced acid rain from the same eruption these results suggest that a dipole arrangement of charge develops within plumes such that positive charges dominate in the volcanic gas rich top and negative charges in the following ash rich part of the plume the charge polarity may be reversed for other volcanoes hatakeyama and uchikawa 1952 we suggest that charge is generated by fracto emission donaldson et al 1988 processes probably during magma fragmentation within the vent rather than by frictional effects within the plume

charge structure in volcanic plumes a comparison of plume properties predicted by an integral plume model to observations of volcanic lightning during the 2010 eruption of eyjafjallajokull iceland observations of volcanic lightning made using a lightning mapping array during the 2010 eruption of eyjafjallajokull allow the trajectory and growth of the volcanic plume to be determined the lightning observations are compared with predictions of an integral model of volcanic plumes that includes descriptions of the interaction with wind and the effects of moisture we show that the trajectory predicted by the integral model closely matches the observational data and the model well describes the growth of the plume downwind of the vent analysis of the lightning signals reveals information on the dominant charge structure within the volcanic plume during the eyjafjallajokull eruption both monopole and dipole charge structures were observed in the plume by using the integral plume model we propose the varying charge structure is connected to the availability of condensed water and low temperatures at high altitudes in the plume suggesting ice formation may have contributed to the generation of a dipole charge structure via thunderstorm style ice based charging mechanisms though overall this charging mechanism is believed to have had only a weak influence on the production of lightning

the human colonisation of australia optical dates of 53 000 and 60 000 years bracket human arrival at deaf adder gorge northern territory the date at which people entered australia has important implications for the debate on modern human origins thermoluminescence dates of 50 60 ka reported for initial occupation of the malakunanja ii site in northern australia have been used as a means of calibrating the rate of mitochondrial and nuclear dna evolution in modern humans optical dating of unburnt quartzose sediments from a rock shelter site nauwalabila i lindner site in deaf adder gorge 70 km south of malakunanja ii provides new evidence for the timing of the colonisation of the continent optical dates were determined for several stratigraphic levels within a 3 m deep excavation in which flaked stone artefacts and ground pigments were found in primary depositional setting the lowest human occupation levels are bracketed by dates of 53 4 5 4 ka and 60 3 6 7 ka while the upper levels show good agreement between optical and calibrated 14c age estimates high quality haematite with ground facets and striations is associated directly with the 53 ka level and indicates the use of pigments by these early australians the optical dates independently confirm evidence for the colonisation of northern australia shortly after 60 ka and should be seen in the context of this region as having been a likely entry route for the first human movements into sahul

transport of atmospheric water vapor by volcanic eruption columns contrary to assumptions often made in the literature explosive volcanic eruptions are capable of transporting significant amounts of water into the stratosphere in addition to the magmatic water component atmospheric water vapor is entrained by the column at lower levels a theoretical model for the conservation of mass momentum and thermal energy of four separate components dry air water vapor liquid condensates and solid particles is used to determine the extent of atmospheric water redistribution we examine the effects of water vapor condensation on dynamical characteristics and ambient water vapor transport a simple technique is presented for deriving canonical forms for the complex system of ordinary differential equations governing the column components solutions of this model are presented that show the influence of different volcanic boundary conditions and a range of ambient water vapor distributions on transport of the buoyant column we show that the water component vapor liquid of small eruption columns rising through a wet atmosphere is dominated by entrained water whereas larger columns are dominated by the magmatic water this is due in part to the proportionately smaller entrainment surface area in relation to the control volume for the larger columns we also show that a maintained column with an initial mass flux of 2 7 108 kg s 1 erupted into a wet atmosphere would inject 96 mt of water vapor into the stratosphere over 24 hours comparable to the annual input from methane oxidation or 100 midlatitude thunderstorms this increase may accelerate the conversion of simultaneously erupted volcanic so2 into sulfuric acid

luminescence dating in less than ideal conditions case studies from klasies river main site and duinefontein south africa abstract luminescence dating results are reported for two south african archaeological sites where changes in the dose rate through time are apparent a subtraction procedure involving analysis of both quartz and potassium feldspar extracts is applied to detect and correct for these changes at the middle stone age site of klasies river the dose rate changes inferred from geologic evidence for shell dissolution turn out not to be significant having occurred rapidly after deposition the dates here range from 50 115 ka in broad agreement with other evidence the important howiesons poort component here appears to date somewhat later about 55 60 ka than at several other sites in south africa at the acheulian site of duinefontein the dose rate changes also thought to be caused by shell dissolution are on the other hand very significant the subtraction ages here 125 300 ka agree with independent chronological assessments

geophysical constraints on partial melt in the upper mantle this paper addresses the conditions under which partial melt can exist in the mantle in order to be observed as a geophysical anomaly typical observed anomalies are high electrical conductivity of the order of 0 1 s m or greater velocity decreases of 7 10 seismic q values less than 100 and a frequency band for seismic effects in the region near 1 hz existing theories of electrical conduction in partial melts and of frequency dependent seismic properties together with recent measurements of melt electrical conductivity viscosity and partial melt texture can be used to establish requirements for melt to be observed by geophysical methods from electrical anomalies mainly sensitive to melt volume and its interconnection one can require a minimum melt fraction of several percent at temperatures close to the solidus 1150 1300 c however seismic models demand only a small volume in very flattened shapes aspect ratio 0 001 melt fraction 0 1 further if melt configuration permits seismic dissipation in bulk that is there exist flattened voids intersecting more or less equant voids then it is possible to infer melt fractions for elastic anomalies that are consistent with the several percent required for electrical anomalies observed equilibrium textures of partly melted peridotite together with inferred melt solid surface energies suggest that melt on a grain size scale in a gravitational field segregates into a strongly anisotropic pattern thus if partial melt causes mantle geophysical anomalies it should exist in a variety of void shapes and probably of sizes while the association of electrical and elastic anomalies with indications of reduced density volcanism and high heat flow makes the hypothesis of partial melting an attractive explanation the minimum physical requirement is for existence of relatively high temperature

radiocarbon dating of pollen by accelerator mass spectrometry radiocarbon dating of bulk sediments has been the standard method for establishing chronologies in the studies of lake sediment cores which have contributed significantly to our knowledge of late quaternary paleo environments these bulk sediment dates are presumed to be direct ageindicators for the speciments e g pollen or macrofossils which are actually being studied however several recent studies have reinforced long standing apprehensions concerning this presumption in this study we demonstrate for the first time the radiocarbon dating of pollen concentrate samples by accelerator mass spectrometry the dates obtained by this method should provide more reliable radiocarbon chronologies for paleo environmental studies than have been obtainable by bulk sediment dating