extreme detached dust layers near martian volcanoes evidence for dust transport by mesoscale circulations forced by high topography modeling suggests that thermal circulations over mars s highest volcanoes transport water vapor and dust from the surface into the middle atmosphere forming detached layers in these constituents intense vertical mixing also takes place in regional and global dust storms which can generate detached layers that are extreme in both altitude and magnitude here we employ observations by the mars climate sounder mcs on board mars reconnaissance orbiter taking advantage of improved vertical coverage in mcs s aerosol retrievals to discover a new class of extreme detached dust layers eddls observed during minimal dust storm activity and furthermore distinguished by their potentially large and measurable horizontal extent 1000 km these eddls cluster near olympus mons and the tharsis montes from which they likely originate the existence of these eddls suggests that vertical mixing by topographic circulations can be much stronger than previously modeled and more frequent than previously observed

decrypting silicic magma plug fragmentation at azufral crater lake northern andes insights from fine to extremely fine ash morpho chemistry azufral sw colombia is a dangerous silicic volcano hosting a crater lake which serves as an excellent example of an incipient plug disruption through phreatomagmatism we studied the youngest succession of dilute pyroclastic density currents pdcs onlapping the north eastern crater rim scanning electron microscopy coupled with energy dispersive x ray spectroscopy was used to carry out an automated single particle analysis of fine to extremely fine ash we were able to obtain fast and accurate chemical analysis and imaging of 15 098 particles within the 250 63 m and the 63 32 m size ranges the 2d form and roughness parameters were determined for 4895 juvenile glassy particles and validated by 3d micro x ray computer tomography there are two end members of high group 1 and low group 2 roughness juvenile glassy particles group 1 comprises high roughness glass particles with solidity values as low as 0 34 in 2d and 0 33 in 3d and convexity values as low as 0 33 in 2d and 0 26 in 3d group 2 comprises low roughness glass particles with 2d solidity values 0 79 and 3d solidity values typically 0 58 in this group 2d convexity values are 0 68 and 3d convexity values are 0 71 both end members are mostly discriminated by the 2d concavity index 0 14 to 0 77 in group 1 vs 0 05 0 35 in group 2 the remaining group 3 comprises particles of intermediate roughness values in this study we show how an incipient plug developed over a short repose time might be subjected to only a few cycles of vesicle nucleation collapse and densification retaining the characteristics of juvenile glass each glassy juvenile ash type defined by a particular morphology roughness and microtexture can be linked to a density stratified conduit model in azufral the capping and conduit lining dense regions and the permeable zones of the incipient plug likely cracked the newly formed cracks could allow hydraulic forcing caused by external water and induce phreatomagmatic interaction this interaction favoured the fine fragmentation of the plug while enhancing ongoing magmatic processes finally the variations of bulk componentry provided clues on dilute pyroclastic density current transport and physical fractionation processes by secondary fragmentation elutriation and interaction with the crater rim

kaikoura canyon new zealand active conduit from near shore sediment zones to trench axis channel kaikoura canyon is one of a few major active conduits between a near shore sediment transport system and a deep ocean channel it is the sink for mobile zones of gravel sand and mud that migrate northwards off northeastern south island new zealand it is presently the primary source for the 1500 km long hikurangi channel which supplies overbank turbidites to a filled trench an ocean plateau basin and a distal fan drift swath data seismic profiles side scan sonographs aerial photographs cores grab samples and current meter data are used to define the shape and texture of the canyon and adjacent shelf in order to better understand how coastal processes and canyon interact to supply sediment to the deep ocean kaikoura canyon is 60 km long up to 1200 m deep and generally u shaped in profile its head is within 500 m of the shore and within 200 m of rocky projections from the shore platform in a mountain backed bay without large rivers the canyon head incises the 18 m depth contour and boulders pebble gravel and megarippled coarse sand reach the canyon rim fine sand migrating northward along the shelf under the influence of waves and currents is trapped in a southward projecting canyon head gully which incises the thickest part of the holocene sediment prism it is estimated that about 1 5 106 m3 of sediment falls into the canyon head each year tensional fractures around the canyon rim suggest that sediments in the canyon head gully are unstable gravel turbidites with post last glacial age shells are at or near the seabed in the lower canyon but are blanketed by many thin silt and sand possibly storm generated turbidites in the upper canyon the top gravel contains a twig that is about 170 years old suggesting that the last major collapse in the canyon head coincides with many onshore rockfalls triggered by rupture of a major strike slip plate boundary fault in about 1833 an underlying gravel is about 300 years old and may again coincide with fault rupture most of the large earthquake triggered failures may ignite to form self perpetuating autosuspension flows that feed a 1500 km long deep sea turbidite channel

textured dust storm activity in northeast amazonis southwest arcadia mars phenomenology and dynamical interpretation abstractdust storms are mars s most notable meteorological phenomenon but many aspects of their structure and dynamics remain mysterious the cloud top appearance of dust storms in visible imagery varies on a continuum between diffuse hazy and textured textured storms contain cellular structure and or banding which is thought to indicate active lifting within the storm some textured dust storms may contain the deep convection that generates the detached dust layers observed high in mars s atmosphere this study focuses on textured local dust storms in a limited area within northeast ne amazonis and southwest sw arcadia planitiae 25 40 n 155 165 w using collocated observations by instruments on board the mars global surveyor mgs and mars reconnaissance orbiter mro satellites in northern fall and winter this area frequently experiences dust storms with a previously unreported ruffled texture that resembles wide mixed layer rolls in earth s atmosphere a resemblance that is supported by h

the analysis of the influence of pumice shape on its terminal velocity 1 pumice particles represent the basic ingredient of many large explosive eruptions and form as a result of magma fragmentation inside the conduit at the onset of eruption fragmental pumices are expelled at high velocity from the crater by the overpressure of gas liberated on explosion the resulting multiphase flow is forced through atmosphere by a variety of transportation mechanisms and pumices eventually decouple from the gas flow settling down to form pyroclastic deposits here we propose new experimental data of terminal velocity together with a quantitative shape analysis of a wide range of pumice particles the resulting model allows predicting the terminal velocity of pumice by means of easily measured particle characteristics with an average error of 12 which compares favourably with previous models

an observational overview of dusty deep convection in martian dust storms abstractdeep convection as used in meteorology refers to the rapid ascent of air parcels in earth s troposphere driven by the buoyancy generated by phase change in water deep convection undergir

high resolution 3d analyses of the shape and internal constituents of small volcanic ash particles the contribution of sem micro computed tomography sem micro ct abstract the morphology of small volcanic ash particles is fundamental to our understanding of magma fragmentation and in transport modeling of volcanic plumes and clouds until recently the analysis of 3d features in small objects 20 m3 3 5 m in diameter can be successfully reconstructed and quantified in addition new functionalities of the blob3d software were developed to allow the particle shape factors frequently used as input parameters in ash transport and dispersion models to be calculated this study indicates that sem micro ct is very well suited to quantify the various aspects of shape in fine volcanic ash and potentially also to investigate the 3d morphology and internal structure of any object

first evidence of a distal early holocene ash layer in eastern mediterranean deep sea sediments derived from the anatolian volcanic province article i nfo a hitherto unknown distal volcanic ash layer has been detected in a sediment core recovered from the southeastern levantine sea eastern mediterranean sea radiometric stratigraphic and sedimentological data show that the tephra here termed as s1 tephra was deposited between 8970 and 8690 cal yr bp the high silica rhyolitic composition excludes an origin from any known eruptions of the italian aegean or arabian volcanic provinces but suggests a prevailing central anatolian provenance we compare the s1 tephra with proximal to medial distal tephra deposits from well known mediterranean ash layers and ash fall deposits from the central anatolian volcanic field using electron probe microanalyses on volcanic glass shards and morphological analyses on ash particles we postulate a correlation with the early holocene dikkartin dome eruption of erciyes dag volcano cappadocia turkey so far no tephra of the central anatolian volcanic province has been detected in marine sediment archives in the eastern mediterranean region the occurrence of the s1 tephra in the south eastern part of the levantine sea indicates a wide dispersal of pyroclastic material from erciyes dag more than 600 km to the south and is therefore an important tephrostratigraphical marker in sediments of the easternmost mediterranean sea and the adjacent hinterland

the distribution composition and particle properties of mars mesospheric aerosols an analysis of crism visible near ir limb spectra with context from near coincident mcs and marci observations the compact reconnaissance imaging spectral mapper crism onboard the mars reconnaissance orbiter mro obtains pole to pole observations i e full mro orbits of vertical profiles for visible near ir spectra 0 4 4 0 m which are ideally suited to identifying the composition and particle sizes of mars ice and dust aerosols over 50 100 km altitudes in the mars mesosphere within the coverage limitations of the crism limb data set a distinct compositional dichotomy is found in mars mesospheric ice aerosols co2 ice clouds appear during the aphelion period of mars orbit solar longitudes ls 0 160 at low latitudes 20s 10n over specific longitude regions meridiani valles marineris and at typical altitudes of 55 75 km apart from faint water ice hazes below 55 km mesospheric h2o ice clouds are primarily restricted to the perihelion orbital range ls 160 350 at northern and southern mid to low latitudes with less apparent longitudinal dependences mars mesospheric co2 clouds are presented in crism spectra with a surprisingly large range of particle sizes cross section weighted radii reff 0 3 to 2 2 m the smaller particle sizes reff 1 m appear concentrated near the spatial latitude and altitude boundaries of their global occurrences crism spectra of mesospheric co2 clouds also show evidence of iridescence indicating very narrow particle size distributions effective variance veff 0 03 and so very abrupt co2 cloud nucleation furthermore these clouds are sometimes accompanied by altitude coincident peaks in 1 27 m o2 dayglow which indicates very dry cold regions of formation mesospheric water ice clouds generally exhibit small particle sizes reff 0 1 0 3 m although larger particle sizes reff 0 4 0 7 m appear infrequently on average water ice cloud particle sizes decrease with altitude over 50 80 km in the perihelion mesosphere water ice mass appears similar in clouds over a large range of observed cloud particle sizes with particle number densities increasing to 10 cm 3 for reff 0 2 m near coincident mars climate sounder mcs temperature and aerosol profile measurements for a subset of crism mesospheric aerosol measurements indicate near saturation h2o and co2 conditions for ice clouds and distinct mesospheric temperature increases associated with mesospheric dust loading dayside 3 pm mesospheric co2 clouds with larger particle sizes reff 0 5 m scatter surface infrared emission in mcs limb infrared radiances as well as solar irradiance in the mcs solar band channel scattering of surface infrared emission is most strikingly presented in nighttime 3 am mcs observations at 55 60 km altitudes indicating extensive mesospheric nighttime co2 clouds with considerably larger particle sizes reff 7 m mesospheric co2 ice clouds present cirrus like waveforms over extensive latitude and longitude regions 10 10 as revealed in coincident mars color imager marci nadir imaging solar tides gravity waves and the large orbital variation of the extended thermal structure of the mars atmosphere influence all of these behaviors mesospheric dust aerosols appear infrequently over the non global planet encircling dust storm era of the crism limb data set 2009 2016 and exhibit smaller particle sizes reff 0 2 0 7 m relative to dust in the lower atmosphere one isolated case of an aphelion ls 96 mesospheric dust layer with large dust particle sizes reff 2 m over syria planum may reflect high altitude non local transport of dust over elevated regions

surface area porosity and water adsorption properties of fine volcanic ash particles our understanding on how ash particles in volcanic plumes react with coexisting gases and aerosols is still rudimentary despite the importance of these reactions in influencing the chemistry and dynamics of a plume in this study six samples of fine ash 500 a all the specimens had similar pore size distributions with a small peak centered around 50 a these findings suggest that fine ash particles have relatively undifferentiated surface textures irrespective of the chemical composition and eruption type adsorption isotherms for water vapour revealed that the capacity of the ash samples for water adsorption is systematically larger than predicted from the nitrogen adsorption a s values enhanced reactivity of the ash surface towards water may result from i hydration of bulk ash constituents ii hydration of surface compounds and or iii hydroxylation of the surface of the ash the later mechanism may lead to irreversible retention of water based on these experiments we predict that volcanic ash is covered by a complete monolayer of water under ambient atmospheric conditions in addition capillary condensation within ash pores should allow for deposition of condensed water on to ash particles before water reaches saturation in the plume the total mass of water vapour retained by 1 g of fine ash at 0 95 relative water vapour pressure is calculated to be 10 2 g some volcanic implications of this study are discussed

characterization of shape and terminal velocity of tephra particles erupted during the 2002 eruption of etna volcano italy in this paper we present a complete morphological characterization of the ash particles erupted on 18 december 2002 from etna volcano italy the work is based on the acquisition and processing of bidimensional digital images carried out by scanning electron microscopy sem to obtain shape parameters by image analysis we measure aspect ratio ar form factor ff compactness cc and rectangularity rt of 2065 ash particles with size between 0 026 and 1 122 mm we evaluate the variation of these parameters as a function of the grain size ash particles with a diameter of 0 250 mm are subelongate we find that on average particles with a diameter of 0 50 mm are angular using this morphological analysis and an empirical relation between the drag coefficient cd and reynolds number re of wilson and huang earth planet sci lett 44 311 324 1979 we calculate the terminal settling velocities vwh the comparisons between these velocities and those calculated with the formula of kunii and levenspiel fluidization engineering wiley new york pp 97 1969 vkl which considers ash particles as spheres show that vkl are in average 1 28 greater than vwh hence we quantify the systematic error on the spatial distribution of the mass computed around the volcano carried out by tephra dispersal models when the particles are assumed to be spherical

plasma observations during the mars atmospheric plume event of march april 2012 we present initial analyses and conclusions from plasma observations made during the reported mars plume event of march april 2012 during this period multiple independent amateur observers detected a localized high altitude plume over the martian dawn terminator the cause of which remains to be explained the estimated brightness of the plume exceeds that expected for auroral emissions and its projected altitude greatly exceeds that at which clouds are expected to form we report on in situ measurements of ionospheric plasma density and solar wind parameters throughout this interval made by mars express obtained over the same surface region but at the opposing terminator measurements in the ionosphere at the corresponding location frequently show a disturbed structure though this is not atypical for such regions with intense crustal magnetic fields we tentatively conclude that the formation and or transport of this plume to the altitudes where it was observed could be due in part to the result of a large interplanetary coronal mass ejection icme encountering the martian system interestingly we note that the only similar plume detection in may 1997 may also have been associated with a large icme impact at mars

conditions for the ignition of catastrophically erosive turbidity currents comment abstract gary parker s 1982 paper title above is compared with my own 1979 paper interaction between velocity and effective density in turbidity flow phase plane analysis with criteria for autosuspension the mathematical models in these papers agree in several fundamental particulars where they differ the two models usually complement rather than contradict one another

mars orbiter camera observations of martian dust devils and their tracks september 1997 to january 2006 and evaluation of theoretical vortex models 1 a multiyear planet wide survey of martian dust devils was conducted using observations from mars global surveyor mars orbiter camera acquired through 21 january 2006 a total of 223 350 images were surveyed and 11 456 dust devils were seen in 0 4 of the images 11 5 in the southern and 88 5 in the northern hemisphere dust devils were observed at latitudes from 71 9 s to 62 2 n over a range of surface albedos am 0 11 0 22 and elevations from hellas 8750 m to arsia mons 17 250 m the light and dark toned streaks created by dust devils were observed from 80 s to 80 n and changed on timescales as short as 1 month at mid to high latitudes seasonal changes in streak patterns contribute to the seasonal wave of darkening observed telescopically from earth dust devils were observed in all seasons in both hemispheres with the exception of ls 202 8 281 5 in the north peak activity occurred during midsummer in each hemisphere five regions in amazonis syria claritas meridiani and gusev were monitored regularly amazonis had the largest dust devils and was the most active planet wide with annual activity occurring from ls 8 5 197 interannual variability resulted from dust storms and planet encircling dust hazes which were observed to initiate and abate dust devil activity there was no evidence suggesting dust devils cause or lead to initiation of dust storms model derived tangential wind speeds of large vortices were 20 m s 1 at 20 m above the surface dust flux calculations suggest that dust devils are a contributor to the background dust opacity observed through northern spring and summer

a comparative study of daytime thermally induced upslope flow on mars and earth abstract several characteristics of thermally induced mesoscale upslope flow on mars and its comparison with that on earth were investigated using both analytical and numerical model approaches the conclusions obtained from the analytical and the numerical evaluations for mars are generally in agreement the main conclusions are i the intensity of the martian summer daytime upslope flow with a moderate slope reaches nearly 10 m s 1 and its depth is about 5 km ii the longwave radiation flux divergence heating within the lower boundary layer of mars has a nonnegligible contribution to the intensity of the upslope flows and iii on mars the values of upslope wind speed are typically about 2 5 times larger than on earth under similar conditions the depth of the daytime upslope flow and the air temperature increase near the surface are 3 to 4 times larger the vertical eddy exchange coefficient for heat and momentum is about 10 times larger on mars

synchrotron x ray computed microtomography studies on vesiculated basaltic rocks synchrotron x ray computed microtomography cmt was applied to five basalt samples from different locations in order to determine the microgeometrical structures and physical properties of vesicles two vesiculated basaltic lavas and one calcite filled vesiculated basaltic lava were collected from the lesotho highland south africa and two basaltic scoria tephra were taken from the lungkuan volcano group in northeast china they were examined with cmt on the x27c beam line of the brookhaven national synchrotron light source the voxel size varied from 10 to 20 m depending on the chosen field of view of the tomographic instrument a fast filtered back transform ffbt algorithm was employed in the tomographic reconstruction a 3d image geometry analysis package was used to measure the vesicularity specific surface area and interconnectivity of the vesicles the results of the analyses showed that the bubbles have roughly spheroidal forms of different sizes vesicularity ranged from 45 for lavas to 80 for scoria at least 90 of the vesicles are interconnected specific surface area was determined both by counting voxel faces and by use of two point correlation functions

identifying magma water interaction from the surface features of ash particles the deposits from explosive volcanic eruptions those eruptions that release mechanical energy over a short time span1 are characterized by an abundance of volcanic ash2 3 this ash is produced by fragmentation of the magma driving the eruption and by fragmenting and ejecting parts of the pre existing crust host rocks interactions between rising magma and the hydrosphere oceans lakes and ground water play an important role in explosive volcanism4 5 because of the unique thermodynamic properties of water that allow it to very effectively convert thermal into mechanical energy although the relative proportion of magma to host rock fragments is well preserved in the pyroclastic rocks deposited by such eruptions it has remained difficult to quantitatively assess the interaction of magma with liquid water from the analysis of pyroclastic deposits2 3 4 5 here we report the results of a study of natural pyroclastic sequences combined with scaled laboratory experiments we find that surface features of ash grains can be used to identify the dynamic contact of magma with liquid water the abundance of such ash grains can then be related to the water magma mass ratios during their interaction

quantitative discrimination of magma fragmentation and pyroclastic transport processes using the fractal spectrum technique abstract the morphology of volcanic particles can yield insight into magma fragmentation transport processes and style of eruption however the complexity and variability of volcanic particle shapes make quantitative characterization difficult the technique applied in this study is based on fractal geometry which has been successfully used to characterize a wide variety of particles and shapes here fractal data is produced by dilation of the 2 d particle boundary to produce a full spectrum of fractal dimensions over a range of scales for each particle multiple fractal dimensions which can be described as a fractal spectrum curve are calculated by taking the first derivative of data points on a standard richardson plot use of multiple fractal dimensions results in more effective discrimination than expressions of shape based on one or two fractal dimensions quantitative comparisons are carried out using multivariate statistical techniques such as cluster and principal components analysis applications to samples from well documented eruptions e g mt st helens 1980 tambora 1815 surtsey 1963 64 indicate that the fractal spectrum technique provides a useful means of characterizing volcanic particles and can be helpful for identifying the products of specific fragmentation processes volatile exsolution phreatomagmatic quench granulation and modes of volcanic transport deposition tephra fall pyroclastic flow blast surge

surface area and volume measurements of volcanic ash particles by sem stereoscopic imaging abstract surface area of volcanic ash particles is of great importance to research including plume dynamics particle chemical and water reactions in the plume modelling i e plume shape particle interactions dispersion etc remote sensing of transport and so 2 hcl h 2 o co 2 levels forecasting plume location and transportation and deposition of ash particles the implemented method presented in this study offers new insights for surface characterization of volcanic ash particles on macro pore regions surface area and volumes of volcanic ash particles were measured using digital elevation models dem reconstructed from stereoscopic images acquired from different angles by scanning electron microscope sem the method was tested using glycidyl methacrylate gma micro spheres which exhibit low spherical imperfections the differences between measured and geometrically calculated surface areas were introduced for both micro spheres and volcanic ash particles in order to highlight the probable errors in modelling on volcanic ash behaviour the specific surface areas of volcanic ash particles using this method are reduced by half from mean values of 0 045 m 2 g to 0 021 m 2 g for the size increment 63 m to 125 m ash particles mostly have higher specific surface area values than the geometric forms irrespective of particle size the specific surface area trends of spheres and ash particles resemble for finer particles 63 m approximation to sphere and ellipsoid have similar margin of error for coarser particles 125 m but both seem to be inadequate for representation of real ash surfaces

quantitative shape measurements of distal volcanic ash 1 large scale volcanic eruptions produce fine ash 200 m which has a long atmospheric residence time 1 hour or more and can be transported great distances from the volcanic source thus becoming a hazard to aircraft and public health ash particles have irregular shapes so data on particle shape size and terminal velocities are needed to understand how the irregular shaped particles affect transport processes and radiative transfer measurements in this study a methodology was developed to characterize particle shapes sizes and terminal velocities for three ash samples of different compositions the shape and size of 2500 particles from 1 distal fallout 100 km of the 14 october 1974 fuego eruption basaltic 2 the secondary maxima 250 km of the 18 august 1992 spurr eruption andesitic and 3 the miocene ash hollow member nebraska rhyolitic were measured using image analysis techniques samples were sorted into 10 to 19 terminal velocity groups 0 6 59 0 cm s using an air elutriation device grain size distributions for the samples were measured using laser diffraction aspect ratio feret diameter and perimeter measurements were found to be the most useful descriptors of how particle shape affects terminal velocity these measurement values show particle shape differs greatly from a sphere commonly used in models and algorithms the diameters of ash particles were 10 120 larger than ideal spheres at the same terminal velocity indicating that irregular particle shape greatly increases drag gas adsorption derived surface areas are 1 to 2 orders of magnitude higher than calculated surface areas based on measured dimensions and simple geometry indicating that particle shapes are highly irregular correction factors for surface area were derived from the ash sample measurements so that surface areas calculated by assuming spherical particle shapes can be corrected to reflect more realistic values

quantitative scanning electron microscope analysis of volcanic ash surfaces application to the 1982 1983 galunggung eruption indonesia qualitative analyses of volcanic ash are time consuming and subjective whereas quantitative analyses are methodical and automated not only volcanic ash particles but also many natural particles have been widely described and quantified by their outlines the qualitative data of volcanic ash surfaces need to be expressed quantitatively supported by supplementary methods such as statistical analysis and artificial intelligence well defined surface descriptors can be applied to volcanic ash particles in this study roughness and texture descriptors of pyroclastic material from the 1982 1983 eruption of galunggung java indonesia were used to describe the vesicle surfaces of the particles alteration intensity and or fine particle abundance these parameters are important for distinguishing the products of magmatic eruptions from those of phre atomagmatic eruptions further application of this method may allow these descriptors to be easily converted to alteration grade vesicularity index intensity of the fragmentation mechanism and relative proportions of the pyroclast types hence discrimination between products of different fragmentation mechanisms may permit forecasting of volcanic hazards

mapping the mesospheric co2 clouds on mars mex omega and mex hrsc observations and challenges for atmospheric models this study presents the latest results on the mesospheric co2 clouds in the martian atmosphere based on observations by omega and hrsc onboard mars express we have mapped the mesospheric co2 clouds during nearly three martian years of omega data yielding a cloud dataset of 60 occurrences the global mapping shows that the equatorial clouds are mainly observed in a distinct longitudinal corridor at seasons ls 0 60 and again at and after ls 90 a recent observation shows that the equatorial co2 cloud season may start as early as at ls 330 three cases of mesospheric midlatitude autumn clouds have been observed two cloud shadow observations enabled the mapping of the cloud optical depth 0 01 0 6 with median values of 0 13 0 2 at 1 m and the effective radii mainly 1 3 m with median values of 2 0 2 3 m of the cloud crystals the hrsc dataset of 28 high altitude cloud observations shows that the observed clouds reside mainly in the altitude range 60 85 km and their east west speeds range from 15 to 107 m s two clouds at southern midlatitudes were observed at an altitude range of 53 62 km the speed of one of these southern midlatitude clouds was measured and it exhibited west east oriented speeds between 5 and 42 m s the seasonal and geographical distribution as well as the observed altitudes are mostly in line with previous work the lmd mars global climate model shows that at the cloud altitude range 65 85 km the temperatures exhibit significant daily variability caused by the thermal tides with the coldest temperatures towards the end of the afternoon the gcm predicts the coldest temperatures of this altitude range and the season ls 0 30 in the longitudinal corridor where most of the cloud observations have been made however the model does not predict supersaturation but the gcm predicted winds are in fair agreement with the hrsc measured cloud speeds the clouds exhibit variable morphologies but mainly cirrus type filamented clouds are observed nearly all hrsc observations and most of omega observations in 15 of omega observations clumpy round cloud structures are observed but very few clouds in the hrsc dataset show similar morphology these observations of clumpy cumuliform type clouds raise questions on the possibility of mesospheric convection on mars and we discuss this hypothesis based on convective available potential energy calculations

applications of x ray computed tomography in the geosciences x ray computed tomography ct is a technique that allows non destructive imaging and quantification of internal features of objects it was originally developed as a medical imaging technique but it is now also becoming widely used for the study of materials in engineering and the geosciences x ray ct reveals differences in density and atomic composition and can therefore be used for the study of porosity the relative distribution of contrasting solid phases and the penetration of injected solutions as a non destructive technique it is ideally suited for monitoring of processes such as the movement of solutions and the behaviour of materials under compression because large numbers of parallel two dimensional cross sections can be obtained three dimensional representations of selected features can be created in this book various applications of x ray ct in the geosciences are illustrated by papers covering a wide range of disciplines including petrology soil science petroleum geology geomechanics and sedimentology

spatial analysis of mount st helens tephra leachate compositions implications for future sampling strategies tephra particles in physically and chemically evolving volcanic plumes and clouds carry soluble sulphate and halide salts to the earth s surface ultimately depositing volcanogenic compounds into terrestrial or aquatic environments upon leaching of tephra in water these salts dissolve rapidly previous studies have investigated the spatial and temporal variability of tephra leachate compositions during an eruption in order to gain insight into the mechanisms of gas tephra interaction which emplace those salts however the leachate datasets analysed are typically small and may poorly represent the natural variability and complexity of tephra deposits here we have conducted a retrospective analysis of published leachate analyses from the 18 may 1980 eruption of mount st helens washington analysing the spatial structure of the concentrations and relative abundances of soluble ca cl na and s across the deposits we have identified two spatial features 1 concentrated tephra leachate compositions in blast deposits to the north of the volcano and 2 low s cl and na cl ratios around the washington idaho border by reference to the bulk chemistry and granulometry of the deposit and to current knowledge of gas tephra interactions we suggest that the proximal enrichments are the product of pre eruptive gas uptake during cryptodome emplacement we speculate that the low s cl and na cl ratios reflect a combination of compositional dependences on high temperature so2 uptake and preferential hcl uptake by hydrometeor tephra aggregates manifested in terrestrial deposits by tephra sedimentation and fallout patterns however despite our interrogation of the most exhaustive tephra leachate dataset available it has become clear in this effort that more detailed insights into gas tephra interaction mechanisms are prevented by the prevalent poor temporal and spatial representativeness of the collated data and the limited characterisation of the tephra deposits future leachate studies should aim to extensively sample across tephra deposit limits whilst simultaneously characterising deposit stratigraphy and tephra chemistry mineralogy and granulometry taking steps to ensure the quality and comparability of collected leachate datasets

laboratory measurements of heterogeneous co2 ice nucleation on nanoparticles under conditions relevant to the martian mesosphere clouds of co2 ice particles have been observed in the martian mesosphere these clouds are believed to be formed through heterogeneous nucleation of co2 on nanometer sized meteoric smoke particles msps or upward propagated martian dust particles mdps large uncertainties still exist in parameterizing the microphysical formation process of these clouds as key physicochemical parameters are not well known we present measurements on the nucleation and growth of co2 ice on sub 4 nm radius iron oxide and silica particles representing msps at conditions close to the mesosphere of mars for both particle materials we determine the desorption energy of co2 to be fdes 18 5 0 2 kj mol 1 corresponding to fdes 0 192 0 002 ev and obtain m 0 78 0 02 for the contact parameter that governs heterogeneous nucleation by analyzing the measurements using classical heterogeneous nucleation theory we did not find any temperature dependence for the contact parameter in the temperature range examined 64 k to 73 k by applying these values for msps in the martian mesosphere we derive characteristic temperatures for the onset of co2 ice nucleation which are 8 18 k below the co2 frost point temperature depending on particle size this is in line with the occurrence of highly supersaturated conditions extending to 20 k below frost point temperature without the observation of clouds moreover the sticking coefficient of co2 on solid co2 was determined to be near unity we further argue that the same parameters can be applied to co2 nucleation on upward propagated mdps

high resolution three dimensional imaging of coal using microfocus x ray computed tomography with special reference to modes of mineral occurrence abstract samples of coal from the sydney and bowen basins of eastern australia have been imaged at high resolution using a large field 3d microfocus x ray computed tomography ct system with special but not exclusive attention to evaluating the modes of occurrence of the mineral matter within the coal the samples imaged were 110 mm 25 mm 19 mm 10 mm and 4 mm in size yielding voxel dimensions of 54 30 12 6 and 3 m respectively data collection was carried out using a helical stage providing images with 20002 voxels in the horizontal x y plane and up to 3500 voxels high three dimensional image blocks derived from the scans were examined as cross sections along orthogonal planes and as perspective images manipulated to be viewed from any angle imaging after saturating the coal with x ray attenuating brine was also carried out to highlight the distribution of connected micro pores and cleats and improve the detail of features seen within the samples features evaluated within the coals included the size and three dimensional distribution of siderite nodules and different types of mineral infillings in petrifactions of maceral components individual macerals could also be identified within the coal based partly on x ray density and partly on the associated porosity and structure in some cases high resolution images enabled the nature of individual plant particles to be identified within the coal samples mineral filled cleats and open fractures were also evaluated including the origin of radiating fracture patterns around siderite nodules in vitrinite in some cases several generations of cleat and or fractures could be distinguished and the sequence of their formation and infilling was interpreted complementary analyses of the mineral matter in the samples were carried out using x ray diffraction as well as examination of polished sections by optical microscopy examination images obtained from the ct scans were also registered against sem edx and qemscan images of polished sections prepared from the same samples after scanning providing a more definitive basis for identifying the different components and for integrating ct data with results from other petrographic and electron microscope studies

quaternary mud turbidites from the south shetland trench west antarctica recognition and implications for turbidite facies modelling a piston core from the basinal part depth of 5188 m of the south shetland trench west antarctica yielded a terrigenous mud section 11 m long which can be subdivided with great precision into turbidite and hemipelagite layers mud turbidites mean bed thickness 44 cm alternate regularly with and are best distinguishable from their hemipelagite host mean bed thickness 17 cm by the following features i sharp basal contacts ii terrigenous sand free textures except basal well sorted silt laminae and the absence of outsized ice rafted components iii a laminated little to non bioturbated internal structure iv distinct textural and compositional grading and v marked steps on water content and sediment density logs mud turbidites recovered from the south shetland trench differ from an earlier model mud turbidite sequence by their i excessive about six times larger bed thickness ii complex internal organization manifested in multiple repetitions up to four of the same structural interval s in sequential or nonsequential order iii distinctive very fine grained cap of highly porous clay rich in fragments of siliceous biogenics iv widespread zones of penesyndepositional deformation and v evidence of flow reversals these features are interpreted to record deposition from large muddy turbidity currents subjected to flow transformations including soliton and or seiche related reversals induced by ponding and interactions of the flow with the topographical confinements of the trench it is concluded that contained muddy turbidites cannot be adequately modelled using published sequences differentiation of single model and contained mud turbidites offers obvious advantages in basin analysis and in understanding the plethora of turbidity current related depositional mechanisms of deep sea mud

quantitative 3d petrography using x ray tomography application to bishop tuff pumice clasts abstract textures are traditionally studied using the petrographic microscope which limits observations to 2d sections of 3d objects given the difficulty in retrieving information on shapes sizes and spatial distribution of objects in 3d from random sections a method that can yield observations in 3d is highly desirable x ray tomography yields a 3d map of the linear x ray attenuation coefficient which is a function of the atomic number and density of the material and the x ray energy used based on the compositional contrasts between different phases various phases can be identified in a rock pumice clasts characterized by isolated crystals surrounded by a low density matrix are ideal for the application of this technique we present our first results obtained using x ray tomography for pumice clasts from the bishop tuff samples studied are from units f7 and f8 and are representative of the variability in density and crystal contents observed in the early erupted bishop tuff data were collected on the geosoilenvironcars beamline at the advanced photon source argonne national laboratory using a 22 kev monochromatic x ray beam image analysis was performed using the software blob3d brightness contrasts in the resulting images allow the separation of magnetite sanidine quartz including minor plagioclase glass and vesicles crystals smaller than 5 voxels in diameter cannot be quantified properly mostly due to noise in the images this constrains the spatial resolution of the resulting images such that there is a trade off between sample size and spatial resolution we employed two runs with samples of varying sizes 5 and 10 mm to obtain adequate resolution voxel sizes ca 8 and 17 m we have previously studied quartz size distributions in bishop pumice clasts using a crushing sieving and winnowing procedure the agreement between our new and previous results is excellent quartz size distributions obtained using the tomography data are concave upward on population density vs size plots and resemble the size distributions for all quartz crystals including both whole crystals and fragments these size distributions were probably generated by fragmentation through which large crystals were converted in a larger number of small crystals petrographic observations suggest fragmentation occurred mostly under magmatic conditions sanidine size distributions are similar to those observed for quartz magnetite size distributions are typically linear indicating a simple magmatic history in contrast with the tektosilicates

dusty deep convection in the mars year 34 planet encircling dust event dusty convection convective activity powered by radiative heating of dust is a ubiquitous phenomenon in mars s atmosphere but is especially deep that is impactful on the middle atmosphere and widespread during planet encircling dust events pede that occur every few mars years my yet the relative roles of dusty deep convection and global dynamics such as the principal meridional overturning cell pmoc and the radiative tides in dust storm development and the vertical transport of dust and water are still unclear here observations from the mars climate sounder on board mars reconnaissance orbiter mro mcs are used to study dusty deep convection and its impact on middle atmospheric water content during the my 34 pede commenced june 2018 additional context is provided by mro mcs observations of the my 28 pede commenced june 2007 this investigation establishes that a few localized centers of dusty deep convection in the tropics formed in the initial phases of both pede simultaneously with a substantial increase in middle atmospheric water content the growth phase of the my 34 pede was defined by episodic outbreaks of deep convection along the acidalia and utopia storm tracks as opposed to less episodic more longitudinally distributed convective activity during the my 28 pede the most intense convection during both pede was observed in southern eastern tharsis where mro mcs observed multiple instances of deep convective clouds transporting dust to altitudes of 70 90 km these results suggest that martian pede typically contain multiple convectively active mesoscale weather systems

the meteorology of gale crater as determined from rover environmental monitoring station observations and numerical modeling part ii interpretation abstract numerical modeling results from the mars regional atmospheric modeling system are used to interpret the landed meteorological data from the rover environmental monitoring station onboard the mars science laboratory rover curiosity in order to characterize seasonal changes throughout the martian year simulations are conducted at ls 0 90 180 and 270 two additional simulations at ls 225 and 315 are explored to better understand the unique meteorological setting centered on ls 270 the synergistic combination of model and observations reveals a complex meteorological environment within the crater seasonal planetary circulations the thermal tide slope flows along the topographic dichotomy mesoscale waves slope flows along the crater slopes and mt sharp and turbulent motions all interact in nonlinear ways to produce the observed weather ls 270 is shown to be an anomalous season when air within and outside the crater is well mixed by strong flushing northerly flow and large amplitude breaking mountain waves at other seasons the air in the crater is more isolated from the surrounding environment the potential impact of the partially isolated crater air mass on the dust water noncondensable and methane cycles is also considered in contrast to previous studies the large amplitude diurnal pressure signal is attributed primarily to necessary hydrostatic adjustments associated with topography of different elevations with contributions of less than 25 to the diurnal amplitude from the crater circulation itself the crater circulation is shown to induce a suppressed boundary layer

the fractal and multifractal dimension of volcanic ash particles contour a test study on the utility and volcanological relevance abstract image processing analysis is used to check the ability of the fractal dimension for quantitatively describing the shape of volcanic ash particles digitized scanning electron microscopy images of fine pyroclasts from the eruptions of monte pilato rocche rosse lipari italy are investigated to test the efficiency of the fractal dimension to discriminate between particles of different eruptive processes multivariate analysis of multiple fractal components allows distinction between magmatic particles and phreatomagmatic particles which however is less significant than the discrimination obtained in previous studies by the use of simple adimensional shape parameters approximation of the actual particle boundary and the not rotation invariant nature of the fractal data frequently result in a significant scatter of data points in the mandelbrot richardson plot such behavior obscures in some cases the actual information of particle shape and renders the discriminating power of fractal analysis less effective than classical shape descriptors data less affected by scatter reveal that phreatomagmatic particles of the monte pilato rocche rosse eruptions are true mono fractals whereas magmatic particles are multifractals the textural small scale fractal of magmatic particles is similar to the fractal dimension value of phreatomagmatic particles and is attributed to the rheological behavior of melt upon brittle fragmentation the structural large scale fractal of magmatic particles refers to the walls of ruptured vesicles that lay on the particle outline the high difference between the values of the textural and structural fractals of magmatic particles of the monte pilato rocche rosse eruptions suggests two distinct and independent processes in the formation of such pyroclasts at the scales corresponding to the textural fractal the fragmentation process is independent of vesicles magmatic fragmentation is not simply related to growth expansion interference and explosion of vesicles but to a brittle cracking of the highly viscous melt likely related to rapid decompression

the grain size dependency of vesicular particle shapes strongly affects the drag of particles first results from microtomography investigations of campi flegrei fallout deposits abstract acknowledging the grain size dependency of shape is important in volcanology in particular when dealing with tephra produced and emplaced during and after explosive volcanic eruptions a systematic measurement of the tridimensional shape of vesicular pyroclasts of campi flegrei fallout deposits agnano monte spina astroni 6 and averno 2 eruptions varying in size from 8 00 to 0 016 mm has been carried out by means of x ray microtomography data show that particle shape changes with size especially for juvenile vesicular clasts since it is dependent on the distribution and size of vesicles that contour the external clast outline two drag laws that include sphericity in the formula were used for estimating the dependency of settling velocity on shape results demonstrate that it is not appropriate to assume a size independent shape for vesicular particles in contrast with the approach commonly employed when simulating the ash dispersion in the atmosphere

vertical distribution of dust and water ice aerosols from crism limb geometry observations 1 near infrared spectra taken in a limb viewing geometry by the compact reconnaissance imaging spectrometer for mars crism on board the mars reconnaissance orbiter provide a useful tool for probing atmospheric structure specifically the observed radiance as a function of wavelength and height above the limb enables the vertical distribution of both dust and water ice aerosols to be retrieved more than a dozen sets of crism limb observations have been taken so far providing pole to pole cross sections spanning more than a full martian year radiative transfer modeling is used to model the observations taking into account multiple scattering from aerosols and the spherical geometry of the limb observations both dust and water ice vertical profiles often show a significant vertical structure for nearly all seasons and latitudes that is not consistent with the well mixed or conrath v assumptions that have often been used in the past for describing aerosol vertical profiles for retrieval and modeling purposes significant variations are seen in the retrieved vertical profiles of dust and water ice aerosol as a function of season dust typically extends to higher altitudes 40 50 km during the perihelion season than during the aphelion season 20 km and the hellas region consistently shows more dust mixed to higher altitudes than other locations detached water ice clouds are common and water ice aerosols are observed to cap the dust layer in all seasons

volcanic ash leachates a review and recommendations for sampling methods tephra in plumes can scavenge and thereby rapidly deposit volatiles including sulphur halogen and metal species these may then be leached e g by rainfall potentially releasing heavy loadings to soils and water bodies several eruptions have resulted in contamination of pasture sometimes with serious impacts on livestock water quality has also been an issue in some areas affected by tephra fall this work synthesises the literature on volcanic ash leachates and considers the controls on volatile adsorption general trends emerge for basaltic intermediate and silicic tephra as well as for variable particle size and transport distance the applications of ash leachate data to plume gas geochemistry calculation of volatile budgets and environmental impact assessment are evaluated comparisons for different eruptions are hampered by disparities in leachate analysis techniques a standardised methodology is therefore proposed to facilitate future health impact assessment and volcanological interpretation of results from different sites

the role of syn eruptive vesiculation on explosive basaltic activity at mt etna italy abstract we investigated the dynamics of explosive activity at mt etna between 31 august and 15 december 2006 by combining vesicle studies in the erupted products with measurements of the gas composition at the active summit crater the analysed scoria clasts present large connected vesicles with complex shapes and smaller isolated spherical vesicles the content of which increases in scoriae from the most explosive events gas geochemistry reports co 2 so 2 and so 2 hcl ratios supporting a deep derived gas phase for fire fountain activity by integrating results from scoria vesiculation and gas analysis we find that the highest energy episodes of mt etna activity in 2006 were driven by a previously accumulated co 2 rich gas phase but we highlight the lesser role of syn eruptive vesicle nucleation driven by water exsolution during ascent we conclude that syn eruptive vesiculation is a common process in etnean magmas that may promote a deeper conduit magma fragmentation and increase ash formation

mars equatorial mesospheric clouds global occurrence and physical properties from mars global surveyor thermal emission spectrometer and mars orbiter camera limb observations 1 we report the occurrence of a new type of cloud in the mars dayside 1300 1400 local time atmosphere apparent as high altitude 60 to 80 km vertically discrete aerosol scattering layers mars global surveyor mgs limb observations from the thermal emission spectrometer tes visible channel indicate peak frequencies at the beginning and end of the aphelion northern summer season ls 30 and 150 where they are confined to equatorial 15 s 15 n latitudes and two longitude ranges 40 e 2 w and 50 w 120 w limb images from the mgs mars orbiter camera moc indicate significant horizontal variations in these mars equatorial mesospheric mem clouds on 20 50 km scales on the basis of the distribution of projected limb heights mem clouds exhibit peak optical depths over 70 75 km altitudes that are substantial nadir vis of order 0 01 for the low pressure region of formation 1 bar averaged tes limb infrared spectral 5 40 m and solarband radiance profiles corresponding to mem occurrence indicate dust aerosols reff 1 5 2 0 m vis 0 4 at 0 25 km altitudes capped by water ice clouds reff 1 5 2 0 m vis 0 2 at 20 45 km altitudes the lack of detectable infrared radiances at mem cloud heights precludes distinction of water versus co2 ice but indicates 1 m particle sizes for water or 1 5 m for co2 ice compositions more recent mars express observations point toward mars mesospheric co2 clouds although current dynamical and radiative models do not indicate sufficiently cold temperatures at mem cloud locations to produce daytime co2 saturation conditions

a multiannual record of gravity wave activity in mars s lower atmosphere from on planet observations by the mars climate sounder abstract gravity waves in mars s atmosphere strongly affect the general circulation as well as middle atmospheric cloud formation but the climatology and sources of gravity waves in the lower atmosphere remain poorly understood at earth the statistical variance in satellite observations of thermal emission above the instrumental noise floor has been used to enable measurement of gravity wave activity at a global scale here is presented an analysis of variance in calibrated radiance at 15 4 m 635 665 cm 1 from off nadir and nadir observations by the mars climate sounder mcs on board mars reconnaissance orbiter mro a major expansion in the observational data available for validating models of martian gravity wave activity these observations are sensitive to gravity waves at 20 30 km altitude with wavelength properties h 10 100 km z 5 km that make them likely to affect the dynamics of the middle and upper atmosphere we find that 1 strong moderately intermittent gravity wave activity is scattered over the tropical volcanoes and throughout the middle to high latitudes of both hemispheres during fall and winter 2 gravity wave activity noticeably departs from climatology during regional and global dust storms and 3 strong intermittent variance is observed at night in parts of the southern tropics during its fall winter but frequent co 2 ice clouds prevents unambiguous attribution to gw activity the spatial distribution of wave activity is consistent with topographic sources being dominant but contributions from boundary layer convection and other convective processes are possible

predicting the cation exchange capacity of reservoir rocks from complex dielectric permittivity measurements abstractdimensional analysis was performed to understand the physics of ionic dispersion in reservoir rocks and to identify the factors influencing the cation exchange capacity cec of these rocks dimensional analysis revealed the existence of a general relation independent of the unit system between two dimensionless groups denoted as the cationic dispersion number 1 and the conductivity number 2 the former group 1 stands for the ratio of the cec to the electrical double layer dispersion the latter group 2 represents the ratio of the low frequency ionic conductivity to the high frequency electronic polarization complex dielectric permittivity measurements on 121 water saturated sandstone and carbonate rock samples were used to validate the dimensionless groups in retrospect dimensional analysis was useful in identifying variables influencing the cec of hydrocarbon rocks in particular these variables consist of rock porosity specific surface area and five other parameters of the cole cole

the origin evolution and trajectory of large dust storms on mars during mars years 24 30 1999 2011 abstract mars daily global maps mdgm derived from the mars global surveyor mgs mars orbiter camera moc and mars reconnaissance orbiter mro mars color imager marci are used to study the distribution and evolution of large dust storms over the period from mars years 24 30 1999 2001 large storms are defined here as discrete dust events visible in image sequences extending over at least 5 sols mars days and where the dust covers areas beyond the origination region a total of 65 large dust storms meeting these criteria are identified during the observational period and all are observed during the l s 135 30 seasonal window dust storms originating in the northern and southern hemispheres appear to form two distinct families all but two of the storms originating in the northern hemisphere are observed in two seasonal windows at l s 180 240 and l s 305 350 while all but two of those originating in the southern hemisphere are observed during l s 135 245 none of the large dust storms originating in the northern hemisphere are observed to develop to global scale but some of them develop into large regional storms with peak area 1 10 7 km 2 and duration on the order of several weeks in comparison large dust storms originating in the southern hemisphere are typically much smaller except notably in the two cases that expanded to global scale the 2001 and 2007 global storms distinct locations of preferred storm origination emerge from the dust storm image sequences including acidalia utopia arcadia and hellas a route trajectory graph for the observed sequences is provided the routes are highly asymmetric between the two hemispheres in the south for non global dust storms the main routes are primarily oriented eastwest whereas in the north the routes are primarily north south and zonally concentrated into meridional channels in a few impressive cases storms originating in the northern hemisphere are observed to flush through acidalia and utopia across the equator and then branch in the low and mid southern latitudes the origin of the 2007 global dust storm is ambiguous from the imaging data immediately prior to the global storm a dust storm sequence from chryse is identified this storm s connection to the explosive expansion observed to start from noachis west hellas is unclear due to image coverage this paper further identifies and describes three different styles of dust storm development which we refer to as consecutive dust storms sequential activation and merging the evolution of a given dust storm sequence can exhibit different combinations of these growth styles at different stages of development dust storm sequences can overlap in time which makes them good candidate to grow into larger scale

three dimensional grain fabric measurements using high resolution x ray computed tomography abstract high resolution x ray computed tomography hrxct provides detailed imagery of the interiors of rocks up to hand sample size non destructively and in three dimensions new tools described here allow these data to be used for analysis of grain fabrics two separate sets of measurement techniques have been developed the first concentrates on quantifying individual crystals phenocrysts porphyroblasts or other discrete objects or void spaces within a sample quantifiable properties include location size shape orientation and contact relationships with adjacent objects the second set of techniques performs a more general fabric analysis on any distinguishable component in a sample a fabric tensor can be computed based on a number of metrics including the star volume distribution svd star length distribution sld and mean intercept length mil methods the fabric tensors provide principal component directions and magnitudes which in turn provide a measure of degree of anisotropy and shape indices because the svd and sld measure only the material of interest whereas the mil is also influenced by spatial distribution results can be divergent for sparse phases also introduced is a three dimensional rose diagram that can be viewed interactively and inspected to reveal further details about non orthogonal directional components these techniques are demonstrated through analysis of a garnet kyanite schist from mica dam british columbia

the seasonal behavior of water ice clouds in the tharsis and valles marineris regions of mars mars orbiter camera observations abstract the mars global surveyor mars orbiter camera was used to obtain global maps of the martian surface with equatorial resolution of 7 5 km pixel in two wavelength ranges blue 400 450 nm and red 575 625 nm the maps used were acquired between march 15 1999 ls 110 and july 31 2001 ls 205 corresponding to approximately one and a quarter martian years using the global maps cloud area in km2 has been measured daily for water ice clouds topographically corresponding to olympus mons ascraeus mons pavonis mons arsia mons alba patera the western valles marineris canyon system and for other small surface features in the region seasonal trends in cloud activity have been established for the three tharsis volcanoes olympus mons and alba patera olympus ascraeus and pavonis mons show cloud activity from about ls 0 220 with a peak in cloud area near ls 100 one of our most interesting observational results is that alba patera shows a double peaked feature in the cloud area with peaks at ls 60 and 140 and a minimum near ls 100 arsia mons shows nearly continuous cloud activity the altitudes of several of these clouds have been determined from the locations of the visual cloud tops and optical depths were measured for a number of them using the disort code of stamnes et al 1988 appl opt 27 2502 2509 several aspects of the observations e g cloud heights effects of increased dust on cloud activity are similar to simulations in richardson et al 2002 j geophys res 107 5064 a search for short period variations in the cloud areas revealed only indirect evidence for the diurnal cloud variability in the afternoon hours unambiguous evidence for other periodicities was not found

glaciations and paleoclimate of mount erciyes central turkey since the last glacial maximum inferred from 36cl cosmogenic dating and glacier modeling abstract forty four boulders from moraines in two glacial valleys of mount erciyes 38 53 n 35 45 e 3917 m central turkey dated with cosmogenic chlorine 36 36cl indicate four periods of glacial activity in the past 22 ka 1 ka 1000 calendar years last glacial maximum lgm glaciers were the most extensive reaching 6 km in length and descending to an altitude of 2150 m above sea level these glaciers started retreating 21 3 0 9 ka 1 ago they readvanced and retreated by 14 6 1 2 ka ago lateglacial and again by 9 3 0 5 ka ago early holocene the latest advance took place 3 8 0 4 ka ago late holocene using glacier modeling together with paleoclimate proxy data from the region we reconstructed the paleoclimate at these four discrete times the results show that lgm climate was 8 11 c colder than today and moisture levels were somewhat similar to modern values with a range between 20 more and 25 less than today the analysis of lateglacial advance suggests that the climate was colder by 4 5 6 4 c based on up to 1 5 times wetter conditions the early holocene was 2 1 4 9 c colder and up to twice as wet as today while the late holocene was 2 4 3 c colder and its precipitation amounts approached to similar conditions as today our paleoclimate reconstructions show a general trend of warming for the last 22 ka and an increase of moisture until early holocene and a decrease after that time the recent glacier terminates at 3450 m on the northwest side of the mountain it is a remnant from the last advance possibly during the little ice age repeated measurements of glacier length between 1902 and 2008 reveal a retreat rate of 4 2 m per year which corresponds to a warming rate of 0 9 1 2 c per century

martian dust storms 1999 mars orbiter camera observations the mars orbiter camera on board the mars global surveyor from march 9 1999 ls 107 where ls is the areocentric longitude of the sun measured in degrees from mars northern spring equinox to december 31 1999 ls 274 has obtained 7 5 km pixel 1 daily global maps of the martian surface in two wavelength bands blue 400 450 nm and red 575 625 nm visual inspection of these maps during the 1999 dust storm season has resulted in the detection of 783 dust storms ranging in size from local 102 km2 to regional 1 6 106 km2 no global storms were observed the difference in the numbers of dust storms occurring in the two hemispheres north 343 south 440 was not statistically significant fifty percent of the regional size dust storms formed as a result of the merger of two or more smaller local storms the regional storms from ls 207 to ls 223 were observed to move from the northern hemisphere into the southern hemisphere between 30 w and 50 w longitude this cross equatorial transport of dust suggests the location of the low lying southward flowing branch of the hadley circulation observations show that dust storms occur in several regions on mars at the two polar cap edges at the base of high elevation regions in the northern hemisphere near the polar hood during northern fall and at mid latitudes in both hemispheres specific regions such as solis planum and hesperia which were regions of significant dust activity in the past showed almost no dust storm activity in 1999 suggesting that regional dust sources are variable over a 20 year time frame one region of exceptional activity not noted previously was the arcadia amazonis border however other regions such as near elysium mons acidalia chryse hellas noachis argyre cimmeria and sirenum again were active dust storm regions relative dust opacities were modeled for 117 red wavelength events and ranged from 0 54 diffuse haze to 2 13 concentrated local events from the dust opacities we estimated the north polar sedimentation rate to be 6 0 10 10 4 g cm 2 yr 1 a factor of 40 smaller than previous estimates from the two 1977 global dust storms pollack et al 1979 along with the global dust mass loading 2 6 4 0 10 4 g cm 2 and cross equatorial dust mass loading 3 6 10 4 g cm 2 the 1999 cross equatorial mass dust loading suggests that the southern hemisphere subtropical latitudes require at least 2 3 martian years to replenish their dust sources before global storms can form

origin of a zone of anomalously high porosity in the subduction inputs to nankai trough abstract one poorly understood feature of the subduction inputs to the nankai trough subduction zone sw japan is a stratigraphic interval with an anomalously high porosity zone hpz which is up to 240 m thick and located within the clay and volcanic ash rich shikoku basin facies to investigate the origin of their peculiar physical properties we integrated logging while drilling lwd data shipboard density measurements and visual descriptions of core samples recovered from four drill sites of the ocean drilling program and integrated ocean drilling program we combined those observations with scanning electron microscopy sem and laboratory consolidation tests on both hpz samples and artificial mixtures of ash glass shards smectite and vesicular pumice smectite lwd data indicate that the hpz mudstones have a large proportion of dispersed volcanic ash 20 30 the consolidation tests show that the rate of porosity loss with increasing effective stress consolidation behavior is consistent among hpz specimens and matches artificial mixtures containing up to 60 volcanic material however absolute values of porosity remain higher for hpz samples compared to artificial mixtures so processes in addition to the mechanical effects of volcanic clasts must be contributing we suggest that hydration and partial dissolution turns clusters of volcanic glass into aggregates with distinct microfabric sem images confirm the presence of strengthened grain to grain contacts which probably inhibit the collapse of the intra aggregate pore space the aggregates behave like grains so that cohesive strength of the bulk sediment and rate of porosity loss remain nearly unchanged during burial the two step diagenetic process of dissolution and precipitation depends critically on a threshold abundance of fine grained dispersed volcanic ash pumice older units in the shikoku basin with only traces of dispersed ash show no such effects hpzs should be expected in other subduction zones with similar compositional and diagenetic prerequisites

surface area and volume measurements of volcanic ash particles using micro computed tomography micro ct a comparison with scanning electron microscope sem stereoscopic imaging and geometric considerations volcanic ash particles are important components of explosive eruptions and their surface textures are the subject of intense research characterization of ash surfaces is crucial for understanding the physics of volcanic plumes remote sensing measurements of ash and aerosols interfacial processes modelling transportation and deposition of tephra and characterizing eruptive styles a number of different methods have been used over the years to arrive at surface area estimates the more common methods include estimates based on geometric considerations geometric surface area and physisorption of gas molecules on the surface of interest physical surface area in this study micro computed tomography micro ct which is a non destructive method providing three dimensional data enabled the measurement of surface area and volume of individual ash particles results were compared with the values obtained from sem stereoscopic imaging and geometric considerations surface area estimates of micro ct and sem stereoscopic imaging are similar with surface area volume ratios sa v of 0 0368 and 0 0467 respectively ash particle surface textures show a large deviation from that of simple geometric forms and an approximation both to spheres and ellipsoids do not seem adequate for the representation of ash surface sem stereoscopic and or micro ct imaging are here suggested as good candidate techniques for the characterization of textures on macro pore regions of ash particles

three dimensional investigation of volcanic textures by x ray microtomography and implications for conduit processes 1 synchrotron x ray computed microtomography ct was applied for the first time to clasts of pumice and scoria generated by active explosive volcanoes characterized by a range of eruptive styles mild strombolian to plinian and magmatic composition basaltic to trachytic the obtained two dimensional 2d tomographic images corresponding to sample views at different rotation angles were processed to reconstruct three dimensional 3d volumes and then used to make 3d measurements of vesicularity vesicle number density volume and connectivity for quantitative characterization of the investigated tephras the results indicate a positive correlation between vesicle number density and eruption intensity that is used to investigate modes of magma degassing in explosive eruptions in addition the vesicle geometry affecting the connected gas flow pathways in pyroclasts from strombolian eruptions is determined and related to the known permeabilities implications on the dynamics of explosive eruptions is discussed and ultimately used to quantitatively discriminate between different eruptive styles

simulation of the atmospheric thermal circulation of a martian volcano using a mesoscale numerical model mesoscale 100 km atmospheric phenomena are ubiquitous on mars as revealed by mars orbiter camera images numerical models provide an important means of investigating martian atmospheric dynamics for which data availability is limited but the resolution of general circulation models which are traditionally used for such research is not sufficient to resolve mesoscale phenomena to provide better understanding of these relatively small scale phenomena mesoscale models have recently been introduced here we simulate the mesoscale spiral dust cloud observed over the caldera of the volcano arsia mons by using the mars regional atmospheric modelling system our simulation uses a hierarchy of nested models with grid sizes ranging from 240 km to 3 km and reveals that the dust cloud is an indicator of a greater but optically thin thermal circulation that reaches heights of up to 30 km and transports dust horizontally over thousands of kilometres

conditions for the ignition of catastrophically erosive turbidity currents abstract the basic impediment to a clear understanding of eroding and depositing turbidity currents has been the lack of a proper formulation of bed sediment entrainment this problem is addressed herein a detailed analysis indicates that the bagnold criterion is necessary but insufficient for self sustaining turbidity currents the analysis reveals two possible equilibrium states a relatively low velocity ignitive state and a high velocity dense catastrophic state a stability analysis indicates that the ignitive state is unstable flows below it invariably die out and flows above it ignite i e accelerate and entrain sediment to the catastrophic state which is stable the ignitive state thus defines the criterion for a self sustaining turbidity current estimates of the catastrophic state suggest that it is highly erosive and competent to scour out submarine canyons

valles marineris cloud trails 1 distinctive cloud trails are identified in mars reconnaissance orbiter mars color imager marci images over specific locations associated with valles marineris and noctis labyrinthus and at perihelion solar longitudes l s 230 260 high contrast surface shadows are well defined as cast from their eastern margins supporting altitude and optical depth determinations these relatively high altitude clouds 40 50 km exhibit narrow latitudinal widths 25 75 km in comparison to extended longitudinal dimensions 400 1000 km marci multispectral imaging of cloud surface shadows in five wavelength channels 260 320 437 546 and 653 nm yields the wavelength dependence of cloud extinction optical depth revealing a range of small cloud particle sizes r eff 0 2 0 5 m and moderate cloud optical depths 0 03 0 10 visible and 0 1 0 2 ultraviolet local time and temporal sampling characteristics of marci cloud images indicate that these clouds develop very rapidly in afternoon hours 1300 1500 lt reach their full longitudinal extents within 2 h time scales and often reoccur on successive afternoons mars global surveyor mars orbital camera imaging in previous mars years indicates these clouds are annually repeating these observed characteristics suggest a cloud formation mechanism that is specific to 50 km horizontal and vertical scales transports water vapor and dust upward from lower levels exists during the afternoon and is likely associated with the mesoscale atmospheric circulations induced by the near equatorial canyons of mars cloud particles formed in such updrafts would then be rapidly transported westward in the strong retrograde zonal circulation of the subsolar middle atmosphere in this season

estimating the 3d shape of volcanic ash to better understand sedimentation processes and improve atmospheric dispersion modelling abstract the sedimentation rate of volcanic ash through the atmosphere influences its travel distance with important implications for aviation and health the fall velocity of a particle depends on its size and density but also shape and volcanic ash is not spherical to capture the sedimentation of ash atmospheric dispersion models use empirical drag equations calibrated using geometric shape descriptors however particle shape data are scarce and there is no standard method of shape measurement in addition shape measurements are not always available during an eruption when dispersion models are used operationally to forecast ash hazard we assess the variability in the shape of volcanic ash from icelandic eruptions using x ray computed tomography to consider how good different drag equations and shape descriptors are at representing the sedimentation of volcanic ash we compare calculated fall velocities to measured fall velocities of volcanic ash in air in a settling column we then suggest the best drag equations and shape descriptors for use in atmospheric dispersion models we find that shape dependent drag equations produce more accurate results than a spherical approximation however accurate drag calculations based on the shape descriptor sphericity which is a function of surface area require the imaging resolution to be within the range of 102 105 voxels per particle where a voxel is a volumetric pixel as surface area is sensitive to imaging resolution we suggest that the large scale form of the particle impacts sedimentation more than small scale surface roughness shape descriptors based on ratios between principal axis lengths are more practical as they are less variable among particle size classes and much less sensitive to imaging resolution finally we use particle shape data from this study and literature sources to make recommendations on default values for use with atmospheric dispersion models where no shape data are available

image processing analysis in reconstructing fragmentation and transportation mechanisms of pyroclastic deposits the case of monte pilato rocche rosse eruptions lipari aeolian islands italy abstract a quantitative study of particle morphology of samples from monte pilato rocche rosse deposits lipari aeolian islands italy shows a significant variability in particle structure and texture the study consisted of image processing techniques and multivariate statistical methods in analysis of the quantitative particle morphology data with the goal of identifying the genetic processes responsible for the formation of the deposits from these investigations we numerically define the form of the clasts thus avoiding subjectivity in the classification of clast morphology starting from this clast definition we then construct diagrams in which clasts due to different genetic processes i e magmatic vs hydromagmatic fragmentation are discriminated based on simple nondimensional parameters the application of the methods used seems to be of general interest in discriminating the fragmentation and transportation dynamics responsible for the formation of pyroclastic deposits