volcanic plumes and wind jetstream interaction examples and implications for air traffic abstract volcanic plumes interact with the wind at all scales on smaller scales wind affects local eddy structure on larger scales wind shapes the entire plume trajectory the polar jets or jetstreams are regions of high generally eastbound winds that span the globe from 30 to 60 in latitude centered at an altitude of about 10 km they can be hundreds of kilometers wide but as little as 1 km in thickness core windspeeds are up to 130 m s modern transcontinental and transoceanic air routes are configured to take advantage of the jetstream eastbound commercial jets can save both time and fuel by flying within it westbound aircraft generally seek to avoid it using both an integral model of plume motion that is formulated within a plume centered coordinate system bent as well as the active tracer high resolution atmospheric model atham we have calculated plume trajectories and rise heights under different wind conditions model plume trajectories compare well with the observed plume trajectory of the sept 30 oct 1 1994 eruption of kliuchevskoi volcano kamchatka russia for which measured maximum windspeed was 30 40 m s at about 12 km tephra fall patterns for some prehistoric eruptions of avachinsky volcano kamchatka and inyo craters ca usa are anomalously elongated and inconsistent with simple models of tephra dispersal in a constant windfield the avachinsky deposit is modeled well by bent using a windspeed that varies with height two potentially useful conclusions can be made about air routes and volcanic eruption plumes under jetstream conditions the first is that by taking advantage of the jetstream aircraft are flying within an airspace that is also preferentially occupied by volcanic eruption clouds and particles the second is that because eruptions with highly variable mass eruption rate pump volcanic particles into the jetstream under these conditions it is difficult to constrain the tephra grain size distribution and mass loading present within a downwind volcanic plume or cloud that has interacted with the jetstream furthermore anomalously large particles and high mass loadings could be present within the cloud if it was in fact formed by an eruption with a high mass eruption rate in terms of interpretation of tephra dispersal patterns the results suggest that extremely elongated isopach or isopleth patterns may often be the result of eruption into the jetstream and that estimation of the mass eruption rate from these elongated patterns should be considered cautiously

the 1815 tambora ash fall implications for transport and deposition of distal ash on land and in the deep sea tambora volcano lies on the sanggar peninsula of sumbawa island in the indonesian archipelago during the great 1815 explosive eruption the majority of the erupted pyroclastic material was dispersed and subsequently deposited into the indian ocean and java sea this study focuses on the grain size distribution of distal 1815 tambora ash deposited in the deep sea compared to ash fallen on land grain size distribution is an important factor in assessing potential risks to aviation and human health and provides additional information about the ash transport mechanisms within volcanic umbrella clouds grain size analysis was performed using high precision laser diffraction for a particle range of 0 2 m 2 mm diameter the results indicate that the deep sea samples provide a smooth transition to the land samples in terms of grain size distributions despite the different depositional environments even the very fine ash fraction 10 m is deposited in the deep sea suggesting vertical density currents as a fast and effective means of transport to the seafloor the measured grain size distribution is consistent with an improved atmospheric gravity current sedimentation model that takes into account the finite duration of an eruption in this model the eruption time and particle fall velocity are the critical parameters for assessing the ash component depositing while the cloud advances versus the ash component depositing once the eruption terminates with the historical data on eruption duration maximum 24 h and volumetric flow rate of the umbrella cloud 1 5 2 5 1011 m3 s as input to the improved model and assuming a combination of 3 h plinian phase and 21 h co ignimbrite phase it reduces the mean deviation of the predicted versus observed grain size distribution by more than half 9 4 to 3 7 if both ash components are considered

estimating volcanic plume heights from depositional clast size 1 tephra deposits retain a considerable amount of information about the nature of volcanic eruptions with plume height commonly inferred from maximum clast size measurements however current methods for inferring plume height from maximum clast size lose some of the accuracy in measurements made in the field and have limited application when trying to constrain the uncertainty in these parameters here a predictive numerical model is used to determine plume height from maximum clast size found in a deposit plume height is an essential parameter for inferring eruption magnitude as it is explicitly related to mass eruption rate we investigate the effects of different atmospheric and wind profiles allowing the input conditions to be location specific for each eruption the use of a predictive model reduces the uncertainty in determining plume height as it retains the detail of measurements made in the field and incorporates the uncertainty in these measurements in the results in the form of a probability distribution we have applied this approach to fall deposits from the 1991 eruption of pinatubo one of the few plinian eruptions in which the true height of the plume is well known the predicted plume heights are in good agreement with those found from satellite measurements this new approach provides a method for determining plume height from poorly preserved fall deposits from which a limited amount of data can be sampled leading to large uncertainties in the field measurements

comparative proximal features of the main plinian deposits campanian ignimbrite and pomici di base of campi flegrei and vesuvius abstract the proximal plinian fall deposits of the campanian ignimbrite ci 38 ky fedele et al 2008 and pomici di base pdb 18 ky bertagnini et al 1998 have been investigated in order to understand the contribution of each part of the plume to the proximal sedimentation following houghton et al 2004b we consider three main transport regimes jet phase producing facies fb buoyant region of the plume producing facies fa and direct lateral ejection producing facies fc as well documented in medial locations sparks et al 1992 1997 ernst et al 1996 transport regimes can develop different facies even in proximal locations according to the dynamics of the eruptive column our proximal deposits show stratification and diffuse bedding allowing us to introduce two new facies stratified fa sfa and diffuse bedded fb dbfb these facies retain the transport regime previously proposed for fa buoyant plume and fb jet phase but their lithological features are influenced by near vent depositional conditions lithology and sedimentological data grain size componentry maximum clasts suggest that most of the sedimentation occurred mainly from the buoyant plume with simultaneous contribution from the other two different dynamic regimes coarse clasts falling from the lower margins of the plume strongly affected the sedimentation of the ci proximal fall deposit with a minor contribution from lithic clasts ballistically emplaced and partial collapses of the plume forming pyroclastic density currents in contrast the pdb proximal fall deposit was strongly affected by coarse clasts emplaced directly from the vent through parabolic trajectories with very little contribution of material emplaced from the lower part of the plume these differences can be attributed to different vent conduit processes acting during the eruptions

impact of the lateral blast on the spatial pattern and grain size characteristics of the 18 may 1980 mount st helens fallout deposit the 18 may 1980 eruption of mount st helens started with a lateral blast that fed a pyroclastic surge which then uplifted to form a co blast plume thirty minutes later plinian activity started at the vent and fluctuated in intensity for 9 h the resulting fallout deposit documented to 600 km from vent presents some striking features 1 displacement of the overall deposit to the north of the vent 2 a secondary thickness and mass maximum at 300 km from vent 3 a total grain size distribution dominated by fine ash 62 wt of the deposit 63 m and 4 individual grain size distributions that vary dramatically in the crosswind direction from strongly bimodal in the south to skewed unimodal in the north results from a new deconvolution of the individual grain size distributions show that they are a combination of a coarse subpopulation that decreases in size with distance from vent and a constant fine subpopulation with a mean of 15 m relative proportions of each subpopulation vary asymmetrically in the crosswind directions with the fine subpopulation preponderant toward the north and the coarse one dominating the south of the deposit both reach their absolute maxima in mass on the deposit axis componentry analyses of selected samples show that blast derived material is greatly enriched toward the north of the deposit these results indicate that the co blast plume dispersed fine grained material over great distances and dominated the fine subpopulation comparison with reanalysis data of atmospheric wind fields and satellite images of the spreading ash cloud suggests contrasting ash transport and depositional processes for the early co blast plume and the later vent derived plinian plumes the co blast plume is displaced to the north it had a high overshoot height and eastward dispersion via strong winds low in the stratosphere 10 15 km the plinian plumes were lower and dispersed most of the material to the southeast as the direction of high velocity winds shifted just before the late climactic plinian eruptive phase fine ash fine subpopulation was deposited continuously throughout the deposit with an increase of sedimentation rate 300 km from the vent where there is a secondary maximum in the deposit mass and thickness fine ash probably settled by a combination of enhanced sedimentation mechanisms including not only aggregation but also gravitational convective instabilities of cloud base hydrometeor formation and destruction and entrainment of small particles by larger ones finally we show that half of the deposit by mass in the medial area was deposited by the co blast plume and that a significant proportion of the mount st helens fallout deposit is nonjuvenile which has implications for the magmatic budget of this eruption

formation of high grade ignimbrites part ii a pyroclastic suspension current model with implications also for low grade ignimbrites analogue experiments in part i led to the conclusion that pyroclastic flows depositing very high grade ignimbrite move as dilute suspension currents in the thermo fluid dynamical model developed the degree of cooling of expanded turbulent pyroclastic flows dynamically evolves in response to entrainment of air and mass loss to sedimentation initial conditions of the currents are derived from column collapse modeling for magmas with an initial h2o content of 1 3 wt erupting through circular vents and caldera ring fissures the flows spread either longitudinally or radially from source up to a runout distance that increases with higher mass flux but decreases with higher gas content temperature bottom slope and coarser initial grain size progressive dilution by entrainment and sedimentation causes pyroclastic currents to transform into buoyant ash plumes at the runout distance the ash plumes reach stratospheric heights and distribute 30 80 of the erupted material as widespread co ignimbrite ash pyroclastic suspension currents with initial mass fluxes of 107 1012 kg s can spread for tens of kilometers with only limited cooling although they move as supercritical strongly entraining currents for the eruption conditions considered here with increasing eruption mass flux cooling during passage through the fountain diminishes while cooling during flow transport increases the net effect is that eruption temperature exerts the prime control on emplacement temperature pyroclastic suspension currents can form welded ignimbrite across their entire extent if eruption temperature is to 1 3 tmw the minimum welding temperature high eruption rates a large fraction of fine ash and a ring fissure vent favor the formation of extensive high grade ignimbrite for very hot eruptions producing sticky partially molten pyroclasts analysis of particle aggregation systematics shows that factors favoring longer runout also favor more efficient aggregation which reduces runout as a result very high grade ignimbrites cannot spread more than a few tens of kilometers from their source in cooler pyroclastic currents particles do not aggregate and the sedimentation process may involve re entrainment of particles which potentially leads to more extensive cooling and longer runout such effects however are only significant when net erosion of substrate occurs model results can be employed to estimate mass flux and duration of ignimbrite eruptions from measured ignimbrite masses and aspect ratios the model also provides an alternative explanation of the observed decrease in h lratios with ignimbrite mass

the effects of sediment supply and concentrations on the formation timescale of martian deltas abstract we used a comprehensive 2 d and 3 d basin filling morphodynamical model to explore the effects of changing hydrologic and sedimentary conditions on delta formation under martian conditions spatial and temporal deposition of sediment into a body of standing water was simulated using event based time stepping e g seasons river and sediment discharge were calculated using the darcy weisbach equation for width and depth averaged flow velocity and well known and tested terrestrial sediment transport predictors modified for application to martian flows a range in sediment grain sizes was determined from both landers and orbiting spacecraft data in order to include grain sizes typical of mars and yet representative of the martian deltas several different scenarios of seasonal river discharge and sediment supply were explored to encompass a range of possible formation conditions with the ability to track sediment as it is transported throughout the basin it is apparent that non negligible amounts of material are moved beyond the delta forming region this loss of sediment increased with river discharge increasing the gap between the calculated and modeled formation timescales these results have important implications for the formation timescales of the deltas and the small number of identifiable deltas on mars today formation timescales that consider only the supply of sediment to the system and do not take into account factors affecting deposition and delta formation are underestimates of the actual amount of time needed to form the deposits the lack of identifiable deltas in many paleolakes is likely a result of significant sediment transport beyond the channel mouth causing the expected delta deposit to be draped throughout the basin

the timing of martian valley network activity constraints from buffered crater counting abstract valley networks concentrations of dendritic channels that often suggest widespread pluvial and fluvial activity have been cited as indicators that the climate of mars differed significantly in the past from the present hyperarid cold desert conditions some researchers suggest that the change in climate was abrupt while others favor a much more gradual transition thus the precise timing of valley network formation is critical to understanding the climate history on mars we examine thirty valley network incised regions on mars including both cratered upland valley networks and those outside the uplands and apply a buffered crater counting technique to directly constrain when valley network formation occurred the crater populations that we derive using this approach allow assessment of the timing of the last activity in a valley network independent of the mapping of specific geological units from these measurements we find that valley networks cluster into two subdivisions in terms characteristics and age 1 valley network activity in the cratered highlands has an average cessation age at the noachian hesperian boundary and all valleys that we crater counted are early hesperian or older no evidence is found for valley networks in the cratered uplands of late hesperian or amazonian age the timing of the cessation of cratered upland valley network activity at the noachian hesperian boundary also corresponds to a decline in the intensity of large crater formation and degradation and to the apparent end of phyllosilicate type weathering 2 a few valley network incised regions formed outside of the cratered uplands on volcanic edifices in association with younger impact craters and on the rim of valles marineris we applied our buffered crater counting technique to four such valleys on the volcanoes ceraunius tholus hecates tholus and alba patera and on the rim of echus chasma and find that each has distinctive and different late hesperian or early amazonian ages indicating that valley networks formed from time to time in the post noachian period unlike the cratered upland valley networks these isolated occurrences are very local and have been interpreted to represent local conditions e g snowpack melted during periods of intrusive volcanic activity in contrast to a gradual cessation in the formation of valley networks proposed by some workers our new buffered crater counting results indicate a relatively abrupt cessation in the formation of the widespread cratered upland valley networks at approximately the end of the noachian followed only by episodic and very localized valley network formation in later mars history very likely due to specific conditions e g local magmatic heating these valley network ages and correlations are thus consistent with a major change in the near surface aqueous environment on mars at approximately the noachian hesperian boundary the noachian environment supported surface running water and fluvial erosion across mars in the cratered uplands enhanced crater degradation and a weathering environment favoring the formation of phyllosilicates the hesperian amazonian environment was more similar to the hyperarid cold desert of today with valley networks forming only extremely rarely and confined to localized special conditions sources of water for these latter occurrences are likely to be related to periodic mobilization and equatorward migration of polar volatiles due to variations in spin axis orbital parameters and to periodic catastrophic emergence of groundwater

crystal settling in a vigorously converting magma chamber there has been much debate concerning the mechanism of fractional crystallization in magma chambers the traditional hypothesis of crystal settling has been widely replaced by the concept of in situ crystallization coupled with compositional convection observations from layered intrusions however are equivocal1 4 doubts have been raised about crystal settling on theoretical grounds because convective velocities in magma chambers are often much greater than the crystal settling velocities predicted by stokes law5 but there has been no experimental study of crystal settling in such vigorous convection here we present physical considerations and laboratory experiments which show that the phenomenon of particle settling in these conditions can be accounted for by a simple theory application of this theory to crystal settling in magma chambers suggests that crystal settling may be an efficient differentiation mechanism at least in basaltic magma chambers despite large convective velocities

hydraulic modeling of the tributary and the outlet of a martian paleolake located in the memnonia quadrangle we present a steady state hydraulic model of the tributary and the outlet of a martian paleolake located in the memnonia quadrangle between 167 0 0 w and 167 30 0 w longitude and between 9 25 0 s and 9 45 0 s latitude the mars express high resolution stereo camera hrsc digital elevation model h31850000da4 with a spatial resolution of 75 m is used to describe the geometrical features of the hydraulic system a steady state hydraulic model through a monte carlo procedure is adopted to investigate the assumption that the tributary lake outlet hydraulic system was acting simultaneously during its last water related evolutionary phase through our analysis we infer the roughness coefficient and the discharge of both the tributary and the outlet channels geomorphic evidence such as river terraces were used to constrain the water discharge and the manning s roughness coefficient thereby obtaining estimates of the water level in the lake during the last evolutionary phase of the system our analysis of the outlet reveals a median paleodischarge of 7135 m3 s 1 and a median manning s roughness coefficient of 0 067 m 1 3 s tributary analysis provides a median flow and a median roughness coefficient of 6405 m3 s 1 and 0 123 m 1 3 s respectively moreover the hydraulic analysis suggests that the paleolake water surface level was 1397 m median value hrsc elevation which is consistent with the observed paleoshoreline the results imply that the tributary the lake and the outlet were hydraulically synchronized therefore confirming the presence of a connected water system this study demonstrates that hydraulic analysis can provide valuable information regarding ancient martian water fluxes

the influence of diffusive convection on sedimentation from buoyant plumes abstract diffusive convection driven by the differential diffusion of density altering fluid properties may enhance the scavenging of particles from natural buoyant plumes for single phase fluid solute heat systems this phenomenon has been extensively studied because salt fingering generated at the oceanic thermocline is a major mechanism of salt transport in the oceans however the influence of this process on particle laden plumes for example fluvial plumes in lakes and estuaries volcanic clouds and seafloor hydrothermal plumes is largely unknown in this paper we present direct experimental measurements of the interfacial particle flux at the plume base which can be applied to predict particle scavenging from natural buoyant plumes particle flux is measured using a light attenuation technique employing a chain of photodiodes which average concentration over a large number of fingers the results are in good general agreement with earlier studies based on finger velocity flux measurements cover a wide range of conditions from those where diffusive convection dominates to those where settling and diffusive convection are of a similar magnitude for very small particles double diffusive salt finger theory is applicable to two component particulate systems as suggested by earlier studies green t 1987 the importance of double diffusion to the settling of suspended material sedimentology 34 319 331 two component diffusive convection theory is extended to three components in order to predict particle scavenging from marine fluvial plumes which involve the diffusion of sediment salt and heat for larger particles which settle significantly the flux can be approximated by adding the double diffusive and settling fluxes a theory to predict particle transport through the lower layer and sedimentation at the bed is developed based on the observation of strong convection below the plume application of our theory and experimental results indicates that while double diffusion may significantly influence the longitudinal distribution and vertical sorting of deposits from lacustrine plumes the diffusive convection process is generally insignificant in marine plumes observational evidence for lacustrine double diffusion based on water column measurements is presented

probabilistic modeling of tephra dispersal hazard assessment of a multiphase rhyolitic eruption at tarawera new zealand 1 the tarawera volcanic complex comprises 11 rhyolite domes formed during five major eruptions between 17 000 b c and a d 1886 the first four of which were predominantly rhyolitic the only historical event erupted about 2 km3 of basaltic tephra fall a d 1886 the youngest rhyolitic event erupted a tephra fall volume more than 2 times larger and covered a wider area northwest and southeast of the volcano a d 1315 kaharoa eruption we have used the kaharoa scenario to assess the tephra fall hazard from a future rhyolitic eruption at tarawera of a similar scale the plinian phase of this eruption consisted of 11 discrete episodes of vei 4 we have developed an advection diffusion model tephra that allows for grain size dependent diffusion and particle density a stratified atmosphere particle diffusion time within the rising plume and settling velocities that include reynolds number variations along the particle fall simulations are run in parallel on multiple processors to allow a significant implementation of the physical model and a fully probabilistic analysis of inputs and outputs tephra is an example of a class of numerical models that take advantage of new computational tools to forecast hazards as conditional probabilities far in advance of future eruptions three different scenarios were investigated for a comprehensive tephra fall hazard assessment upper limit scenario eruption range scenario and multiple eruption scenario hazard curves and probability maps show that the area east and northeast of tarawera would be the most affected by a kaharoa type eruption

primary and secondary fragmentation of crystal bearing intermediate magma abstract crystal rich intermediate magmas are subjected to both primary and secondary fragmentation processes each of which may produce texturally distinct tephra of particular interest for volcanic hazards is the extent to which each process contributes ash to volcanic plumes one way to address this question is by fragmenting pyroclasts under controlled conditions we fragmented pumice samples from soufriere hills volcano shv montserrat by three methods rapid decompression in a shock tube like apparatus impact by a falling piston and milling in a ball mill grain size distributions of the products reveal that all three mechanisms produce fractal breakage patterns and that the fractal dimension increases from a minimum of 2 1 for decompression fragmentation primary fragmentation to a maximum of 2 7 by repeated impact secondary fragmentation to assess the details of the fragmentation process we quantified the shape texture and components of constituent ash particles ash shape analysis shows that the axial ratio increases during milling and that particle convexity increases with repeated impacts we also quantify the extent to which the matrix is separated from the crystals which shows that secondary processes efficiently remove adhering matrix from crystals particularly during milling abrasion furthermore measurements of crystal size distributions before using x ray computed tomography and after by componentry of individual grain size classes decompression driven fragmentation show not only that crystals influence particular size fractions across the total grain size distribution but also that free crystals are smaller in the fragmented material than in the original pumice clast taken together our results confirm previous work showing both the control of initial texture on the primary fragmentation process and the contributions of secondary processes to ash formation critically however our extension of previous analyses to characterisation of shape texture and componentry provides new analytical tools that can be used to assess contributions of secondary processes to ash deposits of uncertain or mixed origin we illustrate this application with examples from shv deposits

settling driven convection a mechanism of sedimentation from stratified fluids convection driven by sediment particles may play an important role in sedimentation from the base of buoyant hypopycnal plumes for example fluvial plumes in stratified estuaries and lakes black smokers on the ocean floor volcanic clouds and coastal currents in addition to the well known double diffusive convection mechanism another mode of convective instability development is by settling across the density interface we performed laboratory experiments to investigate this fingering convective instability mechanism and its effect on particle distribution in the water column and deposition at the bed a simple theoretical model of finger formation at a fluid density interface is developed based on an analogy with thermal plume formation at a flat heated plate this model which involves a thickening interface layer that becomes gravitationally unstable relative to the ambient fluid is in good agreement with measurements of finger size and instability wavelength from visualization experiments since fingering at the density interface drives larger scale convection in the fluid below a mass balance model of the lower layer assuming strong mixing i e uniform sediment concentration is successfully applied to predict sediment concentration in the water column and deposition at the bed strong mixing can be assumed since convective velocities are usually much greater than the particle fall velocities as convection proceeds the sediment concentrations in the two layers approach each other and convection will die out using the model equations we develop analytical expressions for the time when convection ceases and the portion of sediment remaining in the water column

on the relationship between eruption intensity and volcanic plume height insights from three dimensional numerical simulations abstract height of plumes generated during explosive volcanic eruptions is commonly used to estimate the associated eruption intensity i e mass eruption rate mer in order to quantify the relationship between plume height and mer we performed a parametric study using a three dimensional 3d numerical model of volcanic plumes for different vent sizes the results of five simulations indicate that the flow pattern in the lower region of the plume systematically changes with vent size and hence with mer for mers 7 kg s 1 the flow in the lower region has a jet like structure the jet like regime for mers 10 8 kg s 1 the flow shows a fountain like structure the fountain like regime the flow pattern of plumes with 4 10 7 kg s 1 8 kg s 1 shows transitional features between the two flow regimes within each of the two flow regimes the plume height increases as the mer increases whereas plume heights remain almost constant or even decrease as mer increases in the transitional regime as a result the jet like and fountain like regimes show distinct relationships of plume height and mer the different relationships between the two regimes reflect the fact that the efficiency of entrainment of ambient air in the jet like regime is substantially lower than that in the fountain like regime it is suggested that in order to estimate eruption intensity from the observed plume heights it is necessary to take the different flow regimes depending on mer into account

paleohydrology of eberswalde crater mars abstract eberswalde crater mars contains a well preserved fluvial distributary network in a likely deltaic setting the meandering inverted paleochannels and closed drainage basin of this deposit support relatively well constrained estimates of channel forming discharge over an individual event flood timescale runoff production event and annual timescales and longevity of deposition geologic timescale during the late hesperian to early amazonian epochs the width and meander dimensions of two inverted paleochannels reflect the channel forming discharge from event floods 200 to 400 m 3 s the deposit surface indicates the level 1400 to 1350 m and surface area 410 to 810 km 2 of the likely paleolake and the topography and mapped extent of tributaries constrain the watershed area 5000 to 17 000 km 2 based on these results and terrestrial empirical constraints on evaporation and sediment concentration we evaluated three hypothetical water sources meltwater liberated by the nearby holden crater impact continuous deposition over 10 1 10 2 years intermittent rainfall or snowmelt during finite periods controlled by orbital evolution deposition over 10 4 10 6 years and highly infrequent runoff or melting of accumulated snowpacks following distant impacts or secular changes in orbital parameters local impact generated runoff and highly infrequent rainfall or snowmelt require unreasonably high and low rates of evaporation respectively to maintain the paleolake level the local impact hypothesis alternatively depends on one flooding episode with very high concentrations of fluvial sediment that are inconsistent with morphologic considerations multiple primary impact craters in the area postdate holden ejecta but were later dissected indicating fluvial erosion long after the holden impact intermittent rainfall of 1 cm day and seasonal snowmelt are both consistent with our results over a deposition timescale totaling 10 4 10 6 years

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

errors in martian paleodischarges skew interpretations of hydrologic history case study of the aeolis dorsa mars with insights from the quinn river nv abstract changes in martian fluvial geomorphology with time stratigraphic age including decreases in paleochannel widths suggest waning paleodischarges through time where fluvial landforms do not preserve paleochannel widths e g meander deposits other landform dimensions i e radius of curvature may be used to estimate paleodischarges in the aeolis dorsa region topographically inverted and stacked fluvial deposits wide meander point bars overlain by thin channel fills preserve ostensible evidence of decreasing paleodischarges through time however a robust paleohydraulic analysis of these distinct deposits requires knowledge of the accuracy of a terrestrial based empirical relationship that estimates channel width from point bar radius of curvature we assess the accuracy of this radius width relationship by applying it to a well studied terrestrial analog the quinn river nevada we find that radii of curvature from the quinn river exceed the values predicted from the empirical relationship these anomalously high radii are associated with greater resistance in the channel cut banks indicating that bank strength is a confounding factor in the radius width relationship some deposits in the aeolis dorsa include irregular meander morphologies suggesting variably resistant channel banks and overestimates of both paleochannel widths and paleodischarges furthermore the morphometry of the overlying thin channel fills suggests their widths have been eroded such that their paleodischarges are underestimates these overestimates and underestimates when considered together suggest little change in paleodischarge during the stratigraphic transition from meander deposits to channel fills this work demonstrates the importance of terrestrial analog studies for revealing confounding factors in martian fluvial systems and cautions against simplistic interpretations of martian fluvial history the discovered inaccuracies of paleodischarge estimates expose sources of uncertainty in the extant paleodischarge data that bias inferences toward waning hydrologic activity through time

modeling tephra dispersal in absence of wind insights from the climactic phase of the 2450 bp plinian eruption of pululagua volcano ecuador the determination of eruptive parameters is crucial in volcanology not only to document past eruptions but also for tephra fallout hazard assessments in most tephra fallout studies eruptive parameters have been determined either by empirical techniques or analytical models but the uncertainty of such parameters is usually not well described we have applied both empirical and analytical models to characterize the climactic phase of the 2450 bp plinian eruption of pululagua bf2 layer and explore the variations in the total erupted mass column height and total grain size distribution both approaches yield comparable results in the total mass of tephra erupted 4 5 1 5 1011 kg while they show some discrepancies for the determination of the column height 36 20 km from empirical techniques and 30 20 km from analytical techniques the total grain size distribution of the bf2 layers varies with the different techniques used for the calculation and significantly affects the outputs of analytical models furthermore the determination of the total grain size distribution depends strongly on the number and spatial distribution of the sample location inverting tephra fallout deposits on the total accumulation or thickness gives a good constraint on the total mass erupted but not on the column height however inverting on individual grain size classes better constrains the possible range of column heights but cannot resolve particle release height results from the inversion on individual grain size classes show that large diffusion coefficients are necessary to model the bf2 layer and might be required to model proximal tephra deposits in order not to overestimate the total erupted mass additionally we used a statistical method smoothed bootstrap approach to quantify the uncertainty in eruptive parameters such as column height and total erupted mass our uncertainty analysis yields a mean total erupted mass of 4 5 0 3 1011 kg and a mean column height of 30 3 km results from the uncertainty analysis compare well with results from other approaches finally although the climactic phase of the 2450 bp plinian eruption of pululagua occurred in relatively calm atmospheric conditions our results show that the dispersion of the bf2 layer was influenced by slight northeasterly wind conditions

three empirical methods for the calculation of distal volume of tephra fall deposits abstract three empirical methods for the calculation of distal tephra fall volumes are presented and tested the three methods allow calculation of approximate distal tephra fall volumes under different conditions and abundances of field data all methods use proximal data to extrapolate the distal situation they are based on i shape and dispersal axis of proximal isopachs method of ellipses ii break in slope distance on log t vs a diagram where one distal isopach is available method of a ip with one distal isopach and iii distal thinning rate and break in slope distance on log t vs a diagram method of k 1 vs a ip the application of the three methods to published data of 23 32 eruptions in which it is possible to define at least two segments on the log t vs a diagram yields different results the method of ellipses yields good results if the thickness of reconstructed distal isopachs is greater than about 1 cm whereas the method of a ip with one distal isopach is more accurate if the distal isopach has a thickness below the half thickness at the break in slope distance t t ip the method of distal thinning rate k 1 vs break in slope distance a ip allows calculation of distal thinning rate and break in slope distance from only proximal data in this case calculated distal volumes approximate the actual one only if the deposits have a proximal volume total volume ratio greater than 0 7 otherwise they must be considered as minimum values to be added to the proximal volumes an empirical correlation between proximal thinning rate k and column height h t 7 6 k 0 47 r 0 90 is also presented column heights calculated in this way are within 20 of the observed published values in 94 of the examined cases

interior channels in martian valley networks discharge and runoff production the highland valley networks are perhaps the most compelling evidence for widespread fluvial activity on mars 3 5 ga however determining the hydrology of these features has been difficult owing to poor image resolution and the lack of available topographic data new orbital imaging reveals 21 late stage channels within valley networks which we use to estimate formative discharges and to evaluate water supply mechanisms we find that channel width and associated formative discharge are comparable to terrestrial valley networks of similar area and relief for 15 narrow channels in basin filling networks likely episodic runoff production rates up to centimeters per day and first order formative discharges of 300 3000 m 3 s are similar to terrestrial floods supplied by precipitation geothermal melting of ground ice would produce discharges 100 times smaller per unit area and would require pulsed outbursts to form the channels in four large valleys with few tributaries wider channels may represent large subsurface outflows or paleolake overflows as these four channels originate at breached basin divides and or near source regions for the catastrophic outflow channels

the variation of large magnitude volcanic ash cloud formation with source latitude 1 very large magnitudes of explosive volcanic eruptions can produce giant ash clouds with diameters of hundreds to thousands of kilometers these ash clouds are controlled by gravity and rotational forces leading to a more radially constrained shape than clouds produced by smaller eruptions here we develop a dynamic model of the formation of large ash clouds that are produced by eruptions of constant intensity and finite duration incorporating source latitude eruption type magnitude and intensity the cloud grows as a stratified intrusion in the stratosphere to an equilibrium shape that approximates an ellipsoid of revolution rotating anticyclonically as a solid body at sufficient large distances from the equator more generally the structure of the cloud is determined by the source latitude s and the parameter ys ys nd0 1 2 wherein ys is the distance of the source from the equator is the north south gradient of the coriolis frequency n is the buoyancy frequency of the stratosphere and d0 is the maximum cloud thickness a steady solution for an equilibrium cloud exists if ys lies above a boundary that ranges from 2 at the equator to 0 at the pole these clouds move westward at an increasing rate with decreasing latitude below this boundary steady solutions appear not to exist and the nature of the breakdown of the solution at the boundary suggests that the cloud or part of it moves toward and across the equator the above parameters may be expressed in terms of latitude and cloud volume which enables the model to be applied to the ash clouds of past large magnitude eruptions the results suggest that the behavior of clouds formed from plinian phases with eruption magnitudes m 6 5 they could achieve interhemispheric transport from most latitudes for clouds from co ignimbrite sources for m 8 it is possible from most latitudes

controls on the channel width of rivers implications for modeling fluvial incision of bedrock on the basis of the manning equation and basic mass conser vation principles we derive an expression for scaling the steady state width w of river channels as a function of discharge q channel slope s roughness n and width to depth ratio a w 5 a a1 2 2 3 3 8 q 3 8 s 23 16 n 3 8 we propose that channel width to depth ratio in addition to roughness is a function of the material in which the channel is developed and that where a river is con fined to a given material width to depth ratio and roughness can be assumed constant given these simplifications the expression emulates traditional width discharge relationships for rivers incis ing bedrock with uniformly concave fluvial long profiles more sig nificantly this relationship describes river width trends in terrain with spatially nonuniform rock uplift rates where conventional discharge based width scaling laws are inadequate we suggest that much of observed channel width variability in river channels confined by bedrock is a simple consequence of the tendency for water to flow faster in steeper reaches and therefore occupy smaller channel cross sections we demonstrate that using conventional scaling relationships for channel width can result in underestima tion of stream power variability in channels incising bedrock and that our model improves estimates of spatial patterns of bedrock incision rates

characteristics of tephra fall from eruptions at sakurajima volcano revealed by optical disdrometer measurements we investigated the main characteristics of tephra fall from the eruptions at sakurajima volcano in southern kyushu japan by using an optical disdrometer for simultaneous measurement of particle size and fall velocity measurements were carried out for 2 years at one station located 2 5 km south of the active crater this made it possible to detect 76 tephra fall events with the detection rate of the tephra events from these south directed eruption clouds being about 25 from the relationship between particle diameter and fall velocity we were able to estimate morphological parameters of volcanic particles measurements of temporal change in the tephra fall for each minute revealed that both the tephra diameter and fall velocity gradually decrease with time during each event where the ranges of the diameter and velocity for the events with south directed eruption clouds were 0 336 2 04 mm and 1 40 6 24 m s 1 respectively by using temporal changes in the diameter and velocity we estimated travel time and distance for the tephra falling from a release point in the eruption cloud to the station and found a positive correlation between the travel distance and column height for the south directed clouds with a determination coefficient of 0 498 for linear fitting the comparison between tephra data and seismic data revealed that episodic increases in the tephra diameter and fall velocity were correlated with a drastic increase in amplitude of explosion earthquake or tremor these results indicate that disdrometer measurements can provide valuable information about the quantitative features of the tephra fall and are useful for detecting changes in the magnitude of eruption if a number of suitably placed instruments are deployed

greater contrast in martian hydrological history from more accurate estimates of paleodischarge correlative width discharge relationships from the missouri river basin are commonly used to estimate fluvial paleodischarge on mars however hydraulic geometry provides alternative and causal width discharge relationships derived from broader samples of channels including those in reduced gravity submarine environments comparison of these relationships implies that causal relationships from hydraulic geometry should yield more accurate and more precise discharge estimates our remote analysis of a martian terrestrial analog channel combined with in situ discharge data substantiates this implication applied to martian features these results imply paleodischarges of interior channels of noachian hesperian 3 7 ga valley networks have been underestimated by a factor of several whereas paleodischarges for smaller fluvial deposits of the late hesperian early amazonian 3 0 ga have been overestimated thus these new paleodischarges significantly magnify the contrast between early and late martian hydrologic activity width discharge relationships from hydraulic geometry represent validated tools for quantifying fluvial input near candidate landing sites of upcoming missions

valleys in pit craters on mars characteristics distribution and formation mechanisms abstract new observations of central pit craters on mars reveal that some craters contain prominent interior valley networks that drain into their central pit in this study we catalog the distribution of pit craters with associated valleys and characterize in detail five diverse well preserved examples in some instances sedimentary deposits we interpret as either alluvial fans or deltas are found in the central pits and evidence suggests that at least some of these pits once contained lakes fluvial activity within the five pit craters we detail appears to have occurred relatively late in mars history during the hesperian or amazonian periods for this reason further understanding the formation mechanisms of these valleys has important implications for the history of water on mars

grain size variation of tephra derived from volcanic umbrella clouds the relationships among the thickness and grain size of tephra fall deposits and the volumetric flow rate of their source umbrella clouds are analytically obtained the logarithm of the ratio of the probability distribution function based on grain size inr f in fall deposits at two localities from the vent r 1 and r 2 respectively has a linear relationship with the particle settling velocity v as in 1n r f frac pi r 2 2 r 1 2 nu q 1n a where q is the volumetric flow rate of the umbrella cloud and a is a constant for a given pair of localities the volumetric flow rate of the umbrella cloud can be estimated from granulometric data using this formula generally the thickness distance relationship of tephra fall deposits depends on the initial grain size distribution and the volumetric flow rate of the umbrella cloud the empirical relationship of the exponential thinning behaviour can be extrapolated towards infinite distance only for a specific initial grain size which is similar to a log normal distribution with 2 5 otherwise it holds only in a limited range of distances in applying these results to the 1991 eruption of mt pinatubo it is shown that the volumetric flow rate of the umbrella cloud during the climactic phase of 15 june was approximately 5x1010 m3 s which is fairly consistent with the expansion rate of the umbrella cloud observed in the satellite images

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

parametric estimation of phase and group slownesses from sonic logging waveforms sonic logging waveforms consist of a mixture of nondispersive waves such as the p and s headwaves and dispersive waves such as the stoneley and pseudo rayleigh waves in monopole logging and the flexural wave in dipole logging conventionally slowness dispersion curves of various waves are estimated at each frequency independent of data at other frequencies this approach does not account for the fact that slowness dispersion functions in sonic logging are continuous and in most cases smooth functions of frequency we describe a parametric slowness estimation method that uses this property by locally approximating the wavenumber of each wave as a linear function of frequency this provides a parametric model for the phase and group slownesses of the waves propagating across the receiver array the estimation of phase and group slownesses is then carried out by minimizing the squared difference between the predicted and observed waveforms the minimization problem is nonlinear and is solved by an it

late hesperian to early amazonian midlatitude martian valleys evidence from newton and gorgonum basins 1 numerous shallowly incised valleys extend from the upper interior rims of newton and gorgonum basins across smooth interior basin deposits these valleys are a few meters to 300 m wide and may have experienced discharges over all or most of their width implying that they are in fact incised channels in newton crater these valleys extend up to 75 km to near the center of the basin floor in gorgonum basin the valleys terminate at what we interpret to be a former ice covered lake these valleys appear to be examples of scattered shallowly incised valleys found throughout the midlatitudes of mars superimposed upon the widespread mantling deposits within the region on the basis of crater count age dating the interior valleys in newton and gorgonum basins were formed at about the hesperian to amazonian transition the runoff through the valleys may have occurred due to episodic melting of snow and ice that had accumulated on the crater rims temperatures warm enough to cause extensive melting may have occurred during optimal orbital and obliquity configurations because of intensive volcanism releasing greenhouse gasses or as a result of a brief episode of warming from a large impact somewhere on mars the valleys were formed at about the same time as major outflow channels were active along the highlands lowlands boundary water delivered to the northern lowlands by the outflow channels may have been recycled as snow and ice deposits within the martian midlatitudes the episodic melting of such deposits may have formed the midlatitude valleys

fluvial sedimentary deposits on mars ancient deltas in a crater lake in the nili fossae region 1 new spacecraft observations in the nili fossae region of mars reveal two valley networks 80 and 200 km long that each formed distributary fans as they entered an ancient 40 km diameter impact crater an outlet channel on the eastern crater rim lying at an elevation above the fans suggests these fans formed as subaqueous deltas in a crater lake water flowing in the valley networks entered the crater and deposited the fans and ponded to a maximum depth of about 450 m the lake then overtopped and breached the crater rim incising it and dropping the lake level by 100 m geological evidence combined with the volume of water necessary to fill the crater suggests the duration of flow through this system was prolonged the existence of the deposits described here implies that the early martian environment supported overland flow and ponding of water for an extended period of time

an inclined vulcanian explosion and associated products vulcanian explosions generate some of the most hazardous types of volcanic phenomena including pyroclastic density currents non vertical directionality of an explosion promotes asymmetrical distribution of proximal hazards around the volcano although critical such behaviour is relatively uncommon and has been seldom documented here we present for the first time evidence both from geophysical monitoring and field survey data that records the occurrence of such an event thermal imagery captures a vulcanian explosion at soufriere hills volcano montserrat which occurred during a large partial lava dome collapse in february 2010 and was inclined at about 25 from the vertical in a northerly direction pyroclastic products were preferentially distributed to the north and included an unusual pumice boulder deposit that we propose was formed by a dilute pyroclastic density current pumice flow deposits and a proximal lapilli and block fallout lobe the inclined nature of the explosion is attributed to the asymmetric geometry around the vent the explosion derived pyroclastic density currents had notably lower velocities than those associated with lateral blasts which we suggest result from a separate and distinct mechanism these inclined explosions present an additional mechanism that is able to generate directed pyroclastic density currents with consequent implications for hazard assessment

a coupled model for dispersal of tephra during sustained explosive eruptions abstract we present a model for fallout of tephra based on approximate analytical solutions of the advection diffusion transport equation as usual the model requires the distribution of mass throughout the eruptive column as a boundary condition an input which is normally imposed ad hoc by means of analytical expressions we propose an alternative way to assess this input based on coupling the model of fallout with already existing simple models for volcanic plumes flow along the volcanic conduit and magma chamber withdrawal the final outcome is a one way coupled model that involves all the spatial domains simultaneously and has a good compromise between physical accuracy and computational efficiency the coupled model outputs not only maps of isopachs but also several relevant eruptive parameters such as column height mass eruption rate or duration of the eruption time dependency is introduced via a quasi steady approach that is considering a succession of steady states we apply the model to simulate the 2 ka subplinian eruption of montana blanca tenerife island

the effects of topography on sedimentation from particle laden turbulent density currents abstract we present results from a series of laboratory experiments that illustrate the influence of changes in channel topography depth or width on the sedimentation patterns produced by steady particle laden currents on a planar surface in a channel with constant width such currents created deposits that thinned exponentially with distance as long as a current was not blocked to produce a bore topographic features consisting of constrictions ridges and sudden openings caused no significant deviation from exponential deposit thinning or discontinuity in thickness even when there was a transition in flow regime caused by the topographic feature changes in the channel width did affect the distance over which the deposit thinned with the deposits associated with wider parts of the channel thinning more rapidly with distance in contrast if the topographic change was large enough to partially reflect the flow producing an upstream propagating bore then the deposit did not thin exponentially the results are consistent with a model in which the current is assumed to be turbulent and well mixed in this case sedimentation occurs at a rate proportional to the channel width the settling speed of the particles and their concentration within the current and inversely proportional to the current discharge such a model predicts that as a flow passes through a topographic control that does not produce a bore the deposit continues to thin exponentially even if the flow undergoes a transition from the subcritical to the supercritical regime the results suggest that in natural systems changes in current speed and flow regime do not in themselves produce changes in deposit thickness or gradient in thickness unless the flow is partially blocked and a fraction of the flow is reflected upstream

on the ability of pyroclastic flows to scale topographic obstacles we present a simple analysis of momentum dissipation in a pyroclastic flow with high initial velocity and show that the deceleration is inversely proportional to the volumetric flow rate consequently for a given mass flow rate dense flows slow down more rapidly than dilute flows the analysis ignores density stratification and flow unsteadiness and assumes that deceleration is due to turbulent dissipation alone but the results have implications for a wide range of flow regimes we apply our analysis to the distribution of the 1800 year old deposits of the taupo pyroclastic flow the velocity of which is constrained by the height of topographic obstacles that it scaled the volumetric flow rate required to maintain velocities high enough to overtop the rugged topography is consistent with a dilute flow but strongly argues against the dense flow hypothesis the same conclusion applies to other pyroclastic flow deposits distributed over rugged terrain

hesperian age for western medusae fossae formation mars the medusae fossae formation mff on mars is an intensely eroded deposit north of the cratered highlands it is widely thought that mff materials were emplaced through ignimbrite eruptions recent geologic mapping of western mff identified outliers of mff materials well beyond the previously mapped western extent for the deposit including outliers close to gale crater we report counts of impact craters on the mff units that have implications for our understanding of the general history of mff and the uppermost layered materials on the gale crater mound

insights into eruption dynamics from the 2014 pyroclastic deposits of kelut volcano java indonesia and implications for future hazards abstract on 13 to 14 february 2014 a 4 h long vei 4 eruption occurred at kelut volcano java indonesia pyroclastic density currents pdcs and extensive ash fall led to 7 fatalities and disruption to flights across the asia pacific region new sedimentological descriptions of the pyroclastic deposits from the 2014 eruption were compared with eyewitness and satellite reports to elucidate temporal variations in eruptive dynamics the stratigraphy of the deposits is presented in 3 stages associated with two eruptions that occurred approximately 15 30 min apart stage 1 pdc deposits originate from the smaller onset eruption the pdc deposits from stage 2 and tephra fall deposits from stage 3 originate from the second plinian eruption during the onset eruption stage 1 low energy pdcs were produced that ran out to 70 by vol pdc deposits ran out to 4 7 km from the vent the deposits reflect an increased output of fresh fragmented magma and some conduit widening evidenced by dense lithic fragments vent instabilities and incorporation of dense material into basal margins of the plume led to the marginal collapse and formation of these pdcs stage 3 occurred in the final hour at the peak of the plinian eruption around 01 00 to 02 00 and produced reversely graded lapilli fall deposits with 90 vol pumice from a 26 km high plume this indicates that there was a sustained flux of juvenile magma to the now open vent system and expansion and fragmentation of the gas rich magma was at its most efficient our study of the eruptive sequence of kelut provides some constraints on predicted patterns for future explosive activity critical for further hazard assessment of the volcano since 1901 kelut has erupted on intervals of 1 to 23 years and the 2014 event characterises a typical explosive style of eruption that alternates regularly with effusive dome formation and collapse events this pattern depends on the dynamics of magma renewal to the system and degassing conditions in the shallow magma reservoir and upper conduit if this pattern holds and the next eruption occurs within the next two decades a return of prolonged dome growth could be anticipated

dynamics of wind affected volcanic plumes the example of the 2011 cordon caulle eruption chile the 2011 cordon caulle eruption represents an ideal case study for the characterization of long lasting plumes that are strongly affected by wind the climactic phase lasted for about 1 day and was classified as subplinian with plumes between 9 and 12 km above the vent and mass flow rate mfr on the order of 107 kg s 1 eruption intensity fluctuated during the first 11 days with mfr values between 106 and 107 kg s 1 this activity was followed by several months of low intensity plumes with mfr 106 kg s 1 plume dynamics and rise were strongly affected by wind during the whole eruption with negligible upwind spreading and sedimentation the plumes that developed on 4 6 and 20 22 june can be described as transitional i e plumes showing transitional behavior between strong and weak dynamics while the wind clearly dominated the rise height on all the other days resulting in the formation of weak plumes individual phases of the eruption range between volcanic explosivity indices veis 3 and 4 while the cumulative deposit related to 4 7 june 2011 is associated with veis 4 and 5 crosswind cloud and deposit dispersal of the first few days are best described by a linear combination of gravitational spreading and turbulent diffusion with velocities between 1 and 10 m s 1 downwind cloud velocity for the same days is best described by a linear combination of gravitational spreading and wind advection with velocities between 17 and 45 m s 1 results show how gravitational spreading can be significant even for subplinian and small moderate eruptions strongly advected by wind and with low richardson number and low mfr

fluvial erosion and post erosional processes on titan the surface of titan has been revealed by cassini observations in the infrared and radar wavelength ranges as well as locally by the huygens lander instruments sand seas recently discovered lakes distinct landscapes and dendritic erosion patterns indicate dynamic surface processes this study focus on erosional and depositional features that can be used to constrain the amount of liquids involved in the erosional process as well as on the compositional characteristics of depositional areas fluvial erosion channels on titan as identified at the huygens landing site and in radar and visible and infrared mapping spectrometer vims observations have been compared to analogous channel widths on earth yielding average discharges of up to 1600 m3 s for short recurrence intervals that are sufficient to move centimeter sized sediment and significantly higher discharges for long intervals with respect to the associated drainage areas this roughly translates to 1 150 cm day runoff production rates with 10 years recurrence intervals and by assuming precipitation this implies 0 6 60 mm h rainfall rates thus the observed surface erosion fits with the methane convective storm models as well as with the rates needed to transport sediment during cassini s t20 fly by the vims observed an extremely eroded area at 30 w 7 s with resolutions of up to 500 m pixel that extends over thousands of square kilometers the spectral characteristics of this area change systematically reflecting continuous compositional and or particle size variations indicative of transported sediment settling out while flow capacities cease to account for the estimated runoff production and widespread alluvial deposits of fine grained material release of area dependent large fluid volumes are required only frequent storms with heavy rainfall or cryovolcanic induced melting can explain these erosional features

the quetzalapa pumice a voluminous late pleistocene rhyolite deposit in the eastern trans mexican volcanic belt the study area is located in the east part of the trans mexican volcanic belt in the las cumbres volcanic complex lcvc which lies between two large stratovolcanoes pico de orizaba 5700 m a s l to the south and cofre de perote 4200 m a s l to the nne the most conspicuous structure of the lcvc is a 4 km diameter circular crater with a dacitic dome in the center which constitutes the remains of a destroyed stratovolcano the quetzalapa pumice qp was produced by a plinian eruption that was dated by the 14c method at 20 000 yr bp the eruptive sequence consists predominantly of pumice fall deposits and scarce intra plinian pyroclastic flow deposits which crop out on the west flank of the lcvc the absence of post plinian ignimbrite deposits is striking the deposits are well sorted clast supported with reverse grading at the base with a medium to high accessory lithics content the maximum average thickness of the deposit in the proximal areas is about 15 m and has been divided into three members the basal member bm 2 m thick with four submembers bmf1 bmf2 bmf3 and bmafl the intermediate member im 10 m thick with two submembers impf and imaf and the upper member um 3 m thick with four submembers umpl umsdf umwaf and umpls the predominant component of the fall deposits is a white highly vesiculated pumice with 71 sio2 content plagioclase is the most abundant mineral followed by 1 3 mm long biotite phenocrysts the accessory lithics are lavas mostly of andesitic composition their abundance increases toward the uppermost levels of the sequence we calculate a minimum volume of 8 4 km3 2 22 km3 dense rock equivalent for the entire qp deposit isopach and isopleth maps show that the im deposit has an elongated distribution with a nne ssw direction whereas the um deposit has a circular distribution we estimate a maximum eruptive column height for the im of 20 km field studies and isopach and isopleth maps indicate that the eruptive column was affected by a strong wind previous studies located the qp source in the las cumbres crater however based on the isopach and isopleth distribution and the lack of pumice fall deposits inside the las cumbres crater we consider that the qp emission center is located on the west flank of the lcvc and was buried by its own pumice fall deposits it coincides with an explosion crater called la capilla formed during the closing phase of the qp eruption a pumice fountain model is proposed to explain the observed sequence of deposits according to this model the material was emitted through a hose type conduit during a monogenetic eruption of rhyolitic composition this kind of volcanic activity is not extensively reported in the literature

distal enhanced sedimentation from volcanic plumes insights from the secondary mass maxima in the 1992 mount spurr fallout deposits some tephra fallout deposits show an increase of mass and thickness at distances from the source 100 km areas of secondary mass maximum asmm which demonstrates distal enhanced sedimentation from volcanic plumes we explore development of the asmms during the 1992 august and september mount spurr eruptions usa by combining eld data on the spatial distribution of mass and grain size with 1 simulations of individual particle settling through a homogeneous and horizontally strati ed atmosphere and 2 mesoscale models of the three dimensional wind eld that include the effect of the underlying topography the crosswind and downwind variations of deposit characteristics indicate that the increase of sedimentation at the asmms is not formed solely because of preferential settling of small ash particles 125 m as commonly assumed in aggregation models instead asmm grain sizes correspond to the ne modes of the bimodal total grain size distributions there also appears to be a link between the asmm and the topography the mass local minima occur across the windward ank of 2 km high mountain ranges while the asmms spread on the leeward ank mesoscale models of the three dimensional wind eld show vertical oscillations in the wind over mountainous regions which may enhance mechanisms of en masse sedimentation aggregation hydrometeor formation and particle boundary layers as well as strong spatial variations of the horizontal wind eld in the lower troposphere our study demonstrates the importance of using grain size as well as mass data to constrain the complex processes responsible for particle sedimentation from volcanic plumes

pervasive aqueous paleoflow features in the aeolis zephyria plana region mars abstract a survey of themis visible wavelength images in the aeolis zephyria plana region over the two western lobes of the equatorial medusae fossae formation mff shows 150 sinuous ridges having a variety of morphologies and contexts to systematize investigation we use a classification scheme including both individual ridge and ridge network types as well as associations with impact craters and fan shaped features the morphology of the ridges their location downslope from higher topography e g crater rims and scarps and their association with fan shaped forms indicate that most sinuous ridges formed through overland aqueous flow analysis of observations by individual ridge type leads to interpretation of most of these sinuous ridges as inverted fluvial channels or floodplains and a few as possible eskers with the origin of the remaining ridges under continuing investigation about 15 of the sinuous ridges are associated with impact craters but data analysis does not support a genetic relationship between the craters and the sinuous ridges instead analysis of one sinuous ridge network associated with a crater indicates that the water source for the network was atmospheric in origin namely precipitation runoff the broad areal distribution of these 150 ridges and the network morphologies in particular the branched and subparallel types suggest that an atmospheric water source is generally applicable to the population of sinuous ridges as a whole this concentration of sinuous ridges is the largest single population of such landforms on mars and among the youngest these ridges are situated at a paleoscarp between cerberus palus and the aeolis highlands suggesting that the precipitation that formed them was orographic in origin the ages of the equatorial mff units in which this population of sinuous ridges is found imply that this orographic rain and or snow fell during some period from the late hesperian through the middle amazonian

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

particle segregation of an eruption plume as revealed by a comprehensive analysis of tephra dispersal theory and application abstract a new way to deduce particle segregation in an uprising eruption column is developed this method subdivides an eruption column into horizontal slices and particle dispersal from each column slice is calculated using an advection diffusion model named tephra2 a grid search is employed to obtain the particle segregation from each column slice and other unknown parameters vent position diffusion coefficient and particle density the initial conditions for the calculation were mass loading data collected on the ground wind profile and minimum empirical parameters this method is applied to the 1986b eruption of izu oshima volcano japan which was a sub plinian eruption with a vertically uprising column of 10 km high a previous study of this eruption employed a gravity current model which assumes that most of the tephra segregation took place at the column umbrella transition and at the base of the umbrella cloud the gravity current model was used to calculate the base height of the umbrella cloud from the mass loading distribution on the ground and the calculated base height 7 9 km is consistent with the observed column height however the present study shows that most of the particles segregated from the lower parts of the column 1 3 km high and no significant fallout from the upper part of the column was observed even though the segregation pattern is different between the present and past studies the total mass and total grain size distribution are similar this coincidence is attributed to the use of the same decay function of mass loading in both models both assume the exponential decay of mass loading as a function of the area enclosed by the isopleth although the physical meaning of the decay rate is different in the two models this conclusion also implies that the shape of the decay function itself cannot be used to determine which model is appropriate in describing the source column however the applicability of the gravity current model should be justified when the decay rate is low and when an unreasonably high diffusion coefficient is obtained by inversion techniques that use advection diffusion models the new approach of this study also enables the calculation of the total mass and total grain size distribution without hand drawn isopleth maps and uses all of the point data with error evaluations for each point data the calculation results e g the erupted mass are shown with associated errors

constraining particle size dependent plume sedimentation from the 17 june 1996 eruption of ruapehu volcano new zealand using geophysical inversions weak subplinian plinian plumes pose frequent hazards to populations and aviation yet many key parameters of these particle laden plumes are to date poorly constrained this study recovers the particle size dependent mass distribution along the trajectory of a well constrained weak plume by inverting the dispersion process of tephra fallout we use the example of the 17 june 1996 ruapehu eruption in new zealand and base our computations on mass per unit area tephra measurements and grain size distributions at 118 sample locations comparisons of particle fall times and time of sampling collection as well as observations during the eruption reveal that particles smaller than 250 m likely settled as aggregates for simplicity we assume that all of these fine particles fell as aggregates of constant size and density whereas we assume that large particles fell as individual particles at their terminal velocity mass fallout along the plume trajectory follows distinct trends between larger particles d 250 m and the fine population d 250 m that are likely due to the two different settling behaviors aggregate settling versus single particle settling in addition we computed the resulting particle size distribution within the weak plume along its axis and find that the particle mode shifts from an initial 1 mode to a 2 5 mode 10 km from the vent and is dominated by a 2 5 to 3 mode 10 180 km from vent where the plume reaches the coastline and we do not have further field constraints the computed particle distributions inside the plume provide new constraints on the mass transport processes within weak plumes and improve previous models the distinct decay trends between single particle settling and aggregate settling may serve as a new tool to identify particle sizes that fell as aggregates for other eruptions

hydrology of early mars valley network incision 1 widespread occurrences of valley networks on mars provide geomorphic evidence for an active hydrologic cycle to constrain the climatic conditions capable of forming the valley networks a hydrological model was used to analyze the valley incision depth and volume of eroded valleys because the absolute magnitudes of precipitation runoff and evaporation are uncertain we have used the ratio of these quantities the x ratio to express climatic conditions the spatial distribution and strength of the correlations between 1 the estimated depth and volume of eroded material and 2 estimated flood magnitude and valley gradients were investigated as a function of the assumed x ratio we also conducted an analysis of conditions required to have appreciable discharge in selected valley networks which provided the most definitive constraint on martian paleoclimate the other methods show a relatively weak dependency of incision depths and volumes upon the assumed x ratio the multiple regression analyses indicate that incision depth is strongly influenced by gradient and weakly related to modeled flood discharge the factors determining relative depth of incision depend partly on the type of channel bed however postflow modification of the valley networks by mass wasting cratering aeolian infilling and ice related processes precludes direct determination of bed morphology our hydrological analyses suggest that climatic conditions on early mars were at least as moist as those that occurred in the great basin region of the u s when large lakes were present during the pleistocene in terms of the balance of runoff and lake evaporation

sedimentation of tephra by volcanic plumes i theory and its comparison with a study of the fogo a plinian deposit sao miguel azores sedimentation of ejecta from volcanic plumes has been studied as a function of distance from the source in the fogo a plinian deposit sao miguel azores the fogo a trachytic pumice deposit is reversely graded and can be divided into two parts on the basis of pumice colour abundance of syenite accessory lithic clasts and distribution the lower syenite poor part was dispersed to the south and was clearly influenced by wind the upper syenite rich part is coarsegrained and has a nearly symmetrical distribution around the vent elongation of isopachs to the east indicate a weak wind influence the grain size variations of lithic and crystal components in the upper coarse part were studied total accumulation and accumulation per unit area expressed in kg m2 show good fits to a gaussian function at distances greater than 7 km for grain diameters less than 2 cm these results agree with a theoretical model for a radially spreading turbulent current moving over a quiescent fluid the gaussian coefficient is shown to be a function of grain size and the flow rate of material into the umbrella region of the eruption column the coefficient is therefore also a function of column height the column height deduced from these data is 21 km which is in broad agrrement with the column height of 27 km deduced from maximum clast dispersal using the method of carey and sparks 1986 the accumulation of clasts larger than 2 cm agrees with a theory for the fallout of clasts from the margins of the ascending eruption column which treats the plume as a succession of large eddies that decrease their mass of particles as an exponential function of time calculations are also presented for the influence of the radial inflow of surrounding air into the column on the deposition of clasts these calculations constrain the wind speed during the later part of the fogo a eruption to be at most a few metres per second the study has allowed four different dynamic categories of clast behaviour to be recognised in eruption columns

inverted fluvial features in the aeolis zephyria plana region mars formation mechanism and initial paleodischarge estimates 1 a subset of the sinuous ridges srs in the aeolis zephyria plana azp region of mars has been previously hypothesized to be inverted fluvial features although the precise induration and erosion mechanisms were not specified morphological observations and thermal inertia data presented here support this hypothesis a variety of mechanisms can cause inversion and identification of the specific events that lead to fluvial sr formation can provide insights into the sedimentological geochemical and climatic processes of the region reconnaissance of two terrestrial lava capped ridges suggests some criteria that may be used to identify inverted fluvial features formed by lava infill on mars but these criteria are not satisfied by the majority of the azp fluvial srs armoring also appears inconsistent with terrestrial analogs layering and surface textures of fluvial srs indicate that the most likely induration mechanism was geochemical cementation of fluvial sediments and that the primary erosional mechanism that exposed the fluvial srs was aeolian abrasion this analysis of formation mechanism provides a foundation for estimating paleodischarge using an empirical form discharge approach to which we have applied scaling for martian gravity for those fluvial srs meeting a set of criteria for accurate paleodischarge estimates paleodischarge values generally range between 101 and 103 m3 s 1 the largest of these initial estimates are comparable to paleodischarge estimates for some late stage noachian fluvial channels on mars and provide a constraint on the atmospheric conditions at this equatorial location during the late hesperian to early amazonian time frame

downstream variations in the width of bedrock channels field surveys of channel width w and drainage area a in bedrock channel reaches reveal relationships where w 5 ca b similar to the classic hydraulic geometry of alluvial channels data from five mountain channel networks support the assumption used in many landscape evolution models that an alluvial hydraulic geometry relationship where b 5 0 3 0 5 holds for bedrock channel systems although there is substantial local variability in channel width in bedrock channel systems there is no systematic difference in width versus drainage area relations for the surveyed bedrock and alluvial reaches in sedimentary lithologies in coastal oregon and washington in contrast bedrock channels were narrower and therefore had deeper flow than alluvial channels with equal drainage areas in the granite and limestone terrain of the yuba river california in addition data from the mokelumne river show that bedrock channel width decreases substantially downstream at the contact between relatively weak limestone and more erosion resistant granite but that channel slope does not change appreciably across contacts between these two lithologies data from coastal oregon drainage basins further show systematic channel widening after flood flows and debris flow impacts we conclude that downstream variations in the width of bedrock channels generally follow traditional hydraulic geometry relations but also reflect the local influence of longitudinal patterns of bedrock erosivity and disturbance history

digital elevation models for topographic characterisation and flood flow modelling along low gradient terminal dryland rivers a comparison of spaceborne datasets for the rio colorado bolivia abstract many dryland rivers are terminal systems with small channels undergoing prominent downstream size reductions before ending on channelless floodplains in wetlands or at playa margins spaceborne digital elevation models dems provide potential for assessing subtle topographic and hydrodynamic changes in these low gradient low relief settings but challenges are posed by limitations in vertical and horizontal accuracy this study evaluates the use of different spaceborne dems for topographic characterisation and flood flow modelling of the low gradient

sedimentation from gravity currents generated by turbulent plumes sedimentation from radially spreading gravity currents generated at the top of ascending sediment laden plumes is described by a model which assumes that sediment is dispersed homogeneously by turbulence in the gravity current resulting in an exponential decrease in the concentration of sediment with time as particles settle out of the lower boundary of the current for radial spreading this model predicts a gaussian distribution of sediment accumulation away from the source with an exponential constant b which depends on flow rate q and particle settling velocity v b nv q in the experiments described sedimentation occurs from gravity currents generated by ascent of buoyant particle laden plumes of fresh water in a tank of salty water the sediment accumulation shows close agreement with the theoretical model and the gaussian decay constant b can be determined from a maximum in the accumulated mass of sediment per unit distance and from the slope of the line in s s0 br2 where r is the radial distance s is the sediment mass flux per unit area and s0 is the value of s at r 0 data from the dispersal of volcanic ejecta from a large c 24 km high plinian eruption column in the azores also show good agreement with the theory confirming that it is general and independent of scale and the nature of the fluid the experimental data also show a change in sedimentation behaviour at distances from the source corresponding to the corner of the plume where it diverts into a lateral gravity current and there is an abrupt decrease in vertical velocity sedimentation of coarse grain sizes between the source and the corner occurs from the inclined plume margins and does not behave as predicted by the theoretical model

a laboratory study of ash flows hot ash flows propagate from volcanic vents during some explosive volcanic eruptions as a flow entrains and heats ambient air and simultaneously deposits pyroclasts part of the flow may become less dense than the air and ascend from the flow if entrainment of air is more important than sedimentation in controlling the flowbehaviour then a large buoyant ash cloud may form above the flow conversely if sedimentation of particles dominates then a much smaller fraction of the particles are able to ascend in the buoyant cloud we have carried out a series of analog laboratory experiments to simulate the motion and buoyancy generation in dilute ash flows propagating along the ground the first series of experiments investigated buoyancy generation through entrainment using mixtures of methanol ethylene glycol and water the second series examined the role of sedimentation upon the generation of buoyancy using particle laden fresh water currents propagating in a saline ambient fluid the experiments showed that the rate of entrainment increases while the sedimentation rate decreases as the downward slope of the terrain increases suggesting that massive ash laden clouds are more likely to rise from flows traveling on steeper slopes changes in slope angle also control the motion of ash flows the experiments suggest that flow separation and hydraulic jumps resulting from sudden changes in slope angle can enhance entrainment or sedimentation and increase buoyancy observations of the the interactions of ash flows with topography at redoubt volcano in april 1990 and at mount st helens on may 18 1980 are consistent with our laboratory observations

the formation of high grade ignimbrites i experiments on high and low concentration transport systems containing sticky particles high grade ignimbrites are thought to be deposited by pyroclastic flows at temperatures exceeding minimum welding temperature or even solidus temperature corresponding pyroclastic flow particles range from plastic to partially liquid and are able to aggregate or coalesce this contrasts with particles in pyroclastic flows producing unwelded ignimbrite which are capable of elastic grain interactions the low aspect ratio and great areal extent of high grade ignimbrites requires transport in a particulate state either by a high concentration mass flow facilitated by fluidizing gas reducing internal friction or by b expanded turbulent flow of low but downward increasing concentration this paper presents experiments designed to investigate the effects of plastic to liquid particles on these two contrasting transport mechanisms gas fluidization experiments using polyethyleneglycole peg powders heated above minimum sintering tms and melting tm temperatures cover a wide range of fluidization velocities umf ua 0 6 ut but are always in the bubbly fluidization regime similar to fluidized ignimbrite ash where particle volume concentration outside the bubbles is high 10 1 when the powders reach a critical temperature tm t tms defluidization by catastrophic particle aggregation immediately commences in both stationary and laterally moving fluidized beds as well as in experiments using mixtures of high and low tm 30 wt peg powders when t tms of the lower tm powder this indicates that extended particulate transport at t tms is not possible at such high particle concentrations in the turbulent flow experiments liquid sprays of molten peg or water vertically injected into a high re 104 horizontal air flow form a low concentration 10 5 to 10 4 turbulent suspension current proximal formation of partially coalesced aggregates which settle faster than individual particles causes the measured downstream decay of sedimentation rate to be steeper than predicted by theory of single solid particle sedimentation from turbulent suspensions as particles become finer downstream and coalescence efficiency decreases in response to cooling more distally formed aggregates become too small and rare to modify sedimentation rate decay from that of suspension flows containing solid particles the key difference between the two transport systems is particle concentration c since particle collision rate rcoll c2 collision rates in fluidized beds are so high that all particles immediately aggregate when coalescence efficiency 1 ecoal 0 is larger than 10 3 low concentration suspensions on the other hand require much higher values of ecoal for significant aggregation to occur dilute pyroclastic flows will have higher particle volume fractions 10 3 than the experimental currents but then viscous pyroclasts should have lower coalescence efficiencies than peg droplets experimental results thus support an expanded turbulent transport mechanism of pyroclastic flows generating extensive high grade ignimbrite sheets

tephra sedimentation during the 2010 eyjafjallajokull eruption iceland from deposit radar and satellite observations the april may 2010 eruption of eyjafjallajokull volcano iceland was characterized by a nearly continuous injection of tephra in the atmosphere that affected various economic sectors in iceland and caused a global wide interruption of air traffic eruptive activity during 4 8 may 2010 was characterized based on short duration physical parameters in order to capture transient eruptive behavior of a long lasting eruption i e total grainsize distribution erupted mass and mass eruption rate averaged over 30 minute activity resulting 30 minute total grainsize distribution based on both ground and msg seviri satellite measurements is characterized by mdphi of about 2 phi and a fine ash content of about 30wt accumulation rate varied by two orders of magnitude with an exponential decay away from the vent whereas mdphi shows a linear increase until about 18 km from vent reaching a plateau of about 4 5 phi between 20 56 km associated mass eruption rate is in between 0 6 1 2 x 10 5 kg s 1 in situ sampling showed how fine ash mainly fell as aggregates of various typologies about 5 to 9 wt of the erupted mass remained in the cloud up to 1000 km from the vent suggesting that nearly half of the ash 7 phi settled as aggregates within the first 60 km particle sphericity and shape factor varied between 0 4 and 1 with no clear correlation with size and distance from vent our experiments also demonstrate how satellite retrievals and doppler radar grainsize detection can provide real time description of the source term but for a limited particle size range

comparative study between rivers in tarim basin in northwest china and evros vallis on mars abstract the morphometric characteristics of the kaidu river and keriya river in the extremely arid tarim basin and the evros vallis on mars were compared to study the formation of the dendritic evros vallis which has great significance for exploring ancient climate of mars the following results were obtained a the average sinuosities of kaidu river keriya river and evros vallis are 1 17 1 35 and 1 32 respectively b the average bifurcation ratios are 3 84 4 73 and 3 43 respectively c the average stream length ratios are 2 21 3 86 and 2 08 respectively d the stream frequencies are 0 017 0 028 and 0 002 respectively e the drainage densities are 0 195 km 1 and 0 217 km 1 and 0 048 km 1 respectively f the stream gradients are 3 74 7 03 and 1 63 respectively g the stream fractal dimensions are 1 70 1 0 and 1 68 respectively paleodischarge estimations at different stream segments of evros vallis support the hypothesis that the v bend area that joints the eastern and western segments possibly has a tectonic origin geomorphological evidence e g tributaries from high resolution images and stream morphometric parameters from a comparative analysis e g concave upward longitudinal profile and stream fractal dimension support previous hypothesis that evros vallis is a mature drainage system formed by precipitation driven surface runoff this drainage process occurred either in a continuously warm wet climate that lasted long enough on early mars or in regional hydrologic cycles consisting of precipitation and occasionally returned runoff in intermittently clement climates

evaluation of paleohydrologic models for terrestrial inverted channels implications for application to martian sinuous ridges abstract fluvial systems can be preserved in inverted relief on both earth and mars few studies have evaluated the applicability of various paleohydrological models to inverted fluvial systems the first phase of this investigation focused on an extensive spanning 12 km inverted paleochannel system that consists of four sandstone capped carbonate cemented sinuous ridges within the early cretaceous cedar mountain formation located southwest of green river utah morphologic and sedimentologic observations of the exhumed paleochannels were used to evaluate multiple numerical models for reconstructing paleofluvial hydrological parameters another objective of the study was to determine whether aerial or orbital observations yield model results that are consistent with those constrained by field data the models yield an envelope of plausible dominant discharge values 100 500 m 3 s reflecting the limitations of the approach and no single model can be used to reliably estimate paleodischarge on mars landforms with attributes consistent with inverted channels have been identified in spite of differences in the formation history between these martian landforms and the terrestrial analog described here including potential differences in cement composition and the erosional agent that was responsible for relief inversion these numerical models can be applied with modification to the martian landforms and yield an envelope of plausible values for dominant discharge

dynamics of the major plinian eruption of samalas in 1257 a d lombok indonesia the 1257 a d caldera forming eruption of samalas lombok indonesia was recently associated with the largest sulphate spike of the last 2 ky recorded in polar ice cores it is suspected to have impacted climate both locally and at a global scale extensive fieldwork coupled with sedimentological geochemical and physical analyses of eruptive products enabled us to provide new constraints on the stratigraphy and eruptive dynamics this four phase continuous eruption produced a total of 33 40 km3 dense rock equivalent dre of deposits consisting of i 7 9 km3 dre of pumiceous plinian fall products ii 16 km3 dre of pyroclastic density current deposits pdc and iii 8 9 km3 dre of co pdc ash that settled over the surrounding islands and was identified as far as 660 km from the source on the flanks of merapi volcano central java widespread accretionary lapilli rich deposits provide evidence of the occurrence of a violent phreatomagmatic phase during the eruption with a peak mass eruption rate of 4 6 108 kg s a maximum plume height of 43 km and a dispersal index of 110 500 km2 the 1257 a d eruption stands as the most powerful eruption of the last millennium eruption dynamics are consistent with an efficient dispersal of sulphur rich aerosols across the globe remarkable reproducibility of trace element analysis on a few milligrammes of pumiceous tephra provides unequivocal evidence for the geochemical correlation of 1257 a d proximal reference products with distal tephra identified on surrounding islands hence we identify and characterise a new prominent inter regional chronostratigraphic tephra marker

insights into surface runoff on early mars from paleolake basin morphology and stratigraphy we present observations on the morphology and stratigraphy of more than 400 paleolake basins on mars we show that there are two distinct classes of martian paleolake basins 1 paleolakes fed by regionally integrated valley networks n 251 and 2 paleolakes fed by isolated inlet valleys not integrated into broader regional drainage systems n 174 we conclude that valley network fed paleolakes primarily formed prior to approximately the noachian hesperian boundary ca 3 7 ga while isolated inlet valley paleolakes primarily formed later in martian history all 174 isolated inlet valley paleolakes are closed basin lakes however there are surprisingly few 31 valley network fed closed basin lakes compared to a large number 220 of valley network fed open basin lakes this observation is consistent with declining levels of fluvial activity over time on the martian surface our results imply that during the era of valley network formation 90 of topographic basins breached by an inlet valley had sufficiently high ratios of water influx to losses to fill overtop and form an outlet valley this conclusion provides an important constraint on the balance between surface runoff production and water losses on early mars that must be satisfied by any model of the early martian climate and hydrologic cycle

an automatic procedure to forecast tephra fallout tephra fallout constitutes a serious threat to communities around active volcanoes reliable short term forecasts represent a valuable aid for scientists and civil authorities to mitigate the effects of fallout on the surrounding areas during an episode of crisis we present a platform independent automatic procedure with the aim to daily forecast transport and deposition of volcanic particles the procedure builds on a series of programs and interfaces that automate the data flow and the execution and subsequent postprocess of fallout models firstly the procedure downloads regional meteorological forecasts for the area and time interval of interest filters and converts data from its native format and runs the calmet diagnostic model to obtain the wind field and other micro meteorological variables on a finer local scale 3 d grid defined by the user secondly it assesses the distribution of mass along the eruptive column commonly by means of the radial averaged buoyant plume equations depending on the prognostic wind field and on the conditions at the vent granulometry mass eruption rate etc all these data serve as input for the fallout models the initial version of the procedure includes only two eulerian models hazmap and fall3d the latter available as serial and parallel implementations however the procedure is designed to incorporate easily other models in a near future with minor modifications on the model source code the last step is to postprocess the outcomes of models to obtain maps written in standard file formats these maps contain plots of relevant quantities such as predicted ground load expected deposit thickness and for the case of or 3 d models concentration on air or flight safety concentration thresholds