structural asymmetry in martian impact craters as an indicator for an impact trajectory abstract impact crater formation is a highly dynamic and complex geological phenomenon methods of structural geology are capable of giving insights into deformation processes that occur during cratering while most deformation observed in craters exhibits a generally radial symmetry recent discoveries of non radial structural elements in the central uplifts of terrestrial craters have led to the suggestion that obliquely impacting projectiles can cause non radial deformation in the central subsurface area of the crater the lack of ejecta blankets as accepted indicators of an oblique impact on earth make it difficult to correlate the observed non radial structures with the impact direction therefore in this study three martian complex impact craters were selected that exhibit an oblique ejecta blanket and layered bedrock in the central uplift the central uplifts were structurally mapped using high resolution imaging science experiment hirise imagery and additional high resolution digital terrain models dtms structural data were evaluated and show a correlation between the orientation of at least two structural criteria and the direction of impact 1 the strike of upturned bedrock layers is on average perpendicular to the impact trajectory and 2 the majority of faults show a preferred trend parallel to the impact trajectory a fourth martian crater was examined as a counterexample which had a radial ejecta blanket and thus no indication of an oblique trajectory strike in this crater showed no preferred orientation these results will help to solidify the suggested correlation between non radial structural features in impact craters and the horizontal component of momentum transferred from an obliquely impacting projectile to the target

climate change signature of small scale parasequences from lateglacial holocene transgressive deposits of the arno valley fill abstract despite recent report of short term cyclicity from lateglacial holocene deposits of several coastal plains worldwide no precise documentation of the key factors controlling cyclic facies architecture has been made available by previous work detailed sedimentological analysis of a continuously cored borehole around the town of pisa in western tuscany provides evidence for the occurrence of three high frequency transgressive regressive cycles within the post last glacial maximum lgm transgressive succession 13 8 cal kyr bp of the arno incised valley fill these cycles which are bounded by lateral equivalents of marine flooding surfaces are 8 12 m thick and correspond to small scale parasequences micropalaeontological foraminifers and ostracods investigations based upon differentiation of eight microfossil associations allow to refine the stratigraphic framework emphasizing subtle changes in palaeosalinity across parasequence boundaries diagnostic changes in vegetation patterns driven by opposite climate conditions enable precise documentation of parasequence development as a function of climate change pollen spectra invariably show expansions of broad leaved forests at parasequence boundaries suggesting that rapid shifts to warmer climate conditions accompanied episodes of rapid sea level rise in contrast stillstand phases saw the development of cold temperate communities upper parts of parasequences suggesting transition to temporary colder climate conditions reconstruction of parasequence architecture on the basis of adjacent stratigraphic data combined with palaeoclimate characterization and radiometric dating enable identification within the transgressive arno valley body of three major regressive pulsations that are tentatively correlated with the most important cooling events of the post lgm period the sedimentary response to these short term phases of climatic cooling is clearly documented by episodes of widespread coastal plain and bay head delta progradation leading to partial estuary infilling and temporary establishment of continental environments in the proximal and central sectors of the valley

hillslope storage and rainfall amount thresholds as controls of preferential stormflow summary shallow saturated subsurface flow is a dominant runoff mechanism on hillslopes of headwater catchments under humid temperate climate its timing and magnitude is significantly affected by the presence of preferential pathways reliable prediction of runoff from hillslope soils under such conditions remains a challenge in this study a quantitative relationship between rainfall stormflow and leakage to bedrock for hillslopes where lateral preferential runoff represents a dominant part of the overall response was sought combined effects of temporal rainfall distribution and initial hillslope saturation antecedent moisture conditions on stormflow leakage to bedrock and overall water balance were evaluated by conducting simulations with synthetic rainfall episodes a two dimensional dual continuum model was used to analyze hydrological processes at an experimental hillslope site located in a small forested headwater catchment long term seasonal simulations with natural rainfall indicated that leakage to bedrock occurred mostly as saturated flow during major runoff events the amount of rainfall needed to initiate stormflow appeared as a dynamic hillslope property depending on temporal rainfall distribution initial hillslope storage and the spatial distribution of soil water within the hillslope no single valued rainfall threshold responsible for triggering stormflow was found rainfall stormflow as well as rainfall leakage relationships were found highly nonlinear for low initial hillslope saturations temporal rainfall distribution affected the amount of rainfall necessary to initiate stormflow more than it did the amounts of stormflow or leakage to bedrock in spite of a simple hillslope geometry with constant slope and parallel soil atmosphere and soil bedrock interfaces considered in the analysis the applied model predicted a hysteretic behavior of storage discharge relationship the results showed a mutual interplay of components of hillslope water balance exposing a nonlinear character of the hillslope response the study provided a quantitatively coherent insight in the hydraulic functioning of hillslopes where preferential flow constitutes a dominant part of stormflow

spatial modelling and uncertainty assessment of pyroclastic cover thickness in the sorrento peninsula assessing spatial variability of soil thickness is a critical issue for understanding and predicting slope processes the present work was aimed at estimating the spatial scales at which the variation of pyroclastic cover thickness occurs in a sample area in the sorrento peninsula italy stochastic simulation was used to understand the spatial variability of pyroclastic cover thickness on mount pendolo and to assess its spatial uncertainty in the study area covering about 0 7 km2 thickness measurements were collected using electrical resistivity tomography profiles continuous core drillings and steel rod penetrometric tests variographic analysis revealed the occurrence of an anisotropic behaviour along the n50 and n140 directions in the latter anisotropic direction a nested variogram was fitted including 1 a long range component which could be related to large scale factors like the curvature of the slope and contributing area and 2 a shorter scale variation which is probably associated with the occurrence of denudation processes or to the articulate cover bedrock interface to assess the spatial variability and uncertainty of pyroclastic cover thickness a stochastic simulation algorithm was used and 500 equally probable images of cover thickness were yielded the results showed that a better thickness distribution map can be drawn by simulating the data collected on the slope and at the footslope separately the approach also allowed delineating the areas characterized by greater uncertainty suggesting supplementary measurements to further improve the cover thickness distribution model thus reducing the uncertainty

a mass conservative method for the integration of the two dimensional groundwater boussinesq equation 1 this work presents a new conservative finite volume numerical solution for the two dimensional groundwater flow boussinesq equation which can be used for investigations of hillslope subsurface flow processes and simulations of catchment hydrology the boussinesq equation which is integrated for each grid element can take account of the local variations of topography and soil properties within the individual elements the numerical method allows for wetting and drying of the water table without ad hoc assumptions the stability and convergence of the method is shown to be guaranteed a priori by the properties of the solver itself even with respect to the boundary conditions an aspect that has been neglected in previous literature the numeric solutions are validated against some approximate analytical solutions and compared to those of another 1 d numerical solver of the boussinesq equation the solver capabilities are further explored with simulations of the panola experimental hillslope where the bedrock topography which is accurately known causes complex wetting and drying patterns in this situation the importance of a two dimensional description of subsurface flows to obtain properly simulated discharges becomes clear finally a comparison is made between the results of the presented algorithm and the output of the geotop hydrological distributed model which simulates variably saturated soils the findings of the comparison are discussed

tracer and hydrometric study of preferential flow in large undisturbed soil cores from the georgia piedmont usa we studied the temporal patterns of tracer throughput in the outflow of large 30 cm diameter by 38 cm long undisturbed cores from the panola mountain research watershed georgia tracer breakthrough was affected by soil structure and rainfall intensity two rainfall intensities 20 and 40 mm hr 1 for separate cl and br amended solutions were applied to two cores one extracted from a hillslope soil and one extracted from a residual clay soil on the ridge for both low and high rainfall intensity experiments preferential flow occurred in the clay core but not in the hillslope core the preferential flow is attributed to well developed interpedal macrochannels that are commonly found in structured clay soils characteristic of the ridge site however each rainfall intensity exceeded the matrix infiltration capacity at the top of the hillslope core but did not exceed the matrix infiltration capacity at the middle and bottom of the hillslope core and at all levels in the clay core localized zones of saturation created when rainfall intensity exceeds the matrix infiltration capacity may cause water and tracer to overflow from the matrix into macrochannels where preferential flow occurs to depth in otherwise unsaturated soil

cratering on titan impact melt ejecta and the fate of surface organics abstract we conduct three dimensional hydrodynamical simulations of hypervelocity impacts into the crust of titan to determine the fraction of liquid water generated under the reasonable assumption that the crust is largely water ice and to track the fate of the organic rich layer that is thought to overlie the ice over much of the surface impactors larger than a kilometer in diameter are only slightly affected by the atmosphere while those well under that size are strongly decelerated and broken up before reaching the surface impact of a 2 km diameter icy projectile into the crust at velocities of 7 km per second or higher and angles of impact between 30 and 45 generate about 2 5 melt by volume within the crater our results for the amount of aqueous melt generated in impacts on titan are broadly consistent with the analytic model developed by thompson and sagan 1992 although our numerical model allows us to more precisely quantify the fraction of melt and fate of the organics as a function of the impact parameters while much of the organic surface layer is heavily shocked and ejected from the immediate region of the crater a significant fraction located behind the oblique impact trajectory is only lightly shocked and is deposited in the liquid water at the crater base simple calculations suggest that the resulting aqueous organic phase may remain liquid for hundreds of years or longer enough time for the synthesis of simple precursor molecules to the origin of life

strength of the lithosphere of the galilean satellites abstract several approaches have been used to estimate the ice shell thickness on callisto ganymede and europa here we develop a method for placing a strict lower bound on the thickness of the strong part of the shell lithosphere using measurements of topography the minimal assumptions are that the strength of faults in the brittle lithosphere is controlled by lithostatic pressure according to byerlee s law and the shell has relatively uniform density and thickness under these conditions the topography of the ice provides a direct measure of the bending moment in the lithosphere this topographic bending moment must be less than the saturation bending moment of the yield strength envelope derived from byerlee s law the model predicts that the topographic amplitude spectrum decreases as the square of the topographic wavelength this explains why europa is rugged at shorter wavelengths 10 km but extremely smooth and perhaps conforming to an equipotential surface at longer wavelengths 100 km previously compiled data on impact crater depth and diameter schenk p m 2002 nature 417 419 421 on europa show good agreement with the spectral decrease predicted by the model and require a lithosphere thicker than 2 5 km a more realistic model including a ductile lower lithosphere requires a thickness greater than 3 5 km future measurements of topography in the 10 100 km wavelength band will provide tight constraints on lithospheric strength

impact crater formation in icy layered terrains on mars we present numerical simulations of crater formation under martian conditions with a single near surface icy layer to investigate changes in crater morphology between glacial and interglacial periods the ice fraction thickness and depth to the icy layer are varied to understand the systematic effects on observable crater features to accurately model impact cratering into ice a new equation of state table and strength model parameters for h2o are fitted to laboratory data the presence of an icy layer significantly modifies the cratering mechanics observable features demonstrated by the modeling include variations in crater morphometry depth and rim height and icy infill of the crater floor during the late stages of crater formation in addition an icy layer modifies the velocities angles and volumes of ejecta leading to deviations of ejecta blanket thickness from the predicted power law the dramatic changes in crater excavation are a result of both the shock impedance and the strength mismatch between layers of icy and rocky materials our simulations suggest that many of the unusual features of martian craters may be explained by the presence of icy layers including shallow craters with well preserved ejecta blankets icy flow related features some layered ejecta structures and crater lakes therefore the cratering record implies that near surface icy layers are widespread on mars

a low dimensional hillslope based catchment model for layered groundwater flow despite the strong interaction between surface and subsurface waters groundwater flow representation is often oversimplified in hydrological models for instance the interplay between local or shallow aquifers and deeper regional scale aquifers is typically neglected in this work a novel hillslope based catchment model for the simulation of combined shallow and deep groundwater flow is presented the model consists of the hillslope storage boussinesq hsb model representing shallow groundwater flow and an analytic element ae model representing deep regional groundwater flow the component models are iteratively coupled via a leakage term based on darcy s law representing delayed recharge to the regional aquifer through a low conductivity layer simulations on synthetic single hillslopes and on a two hillslope open book catchment are presented and the results are compared against a benchmark three dimensional richards equation model the impact of hydraulic conductivity hillslope plan geometry uniform convergent divergent and hillslope inclination 0 2 5 and 30 under drainage and recharge conditions are examined on the single hillslopes good matches for heads hydrographs and exchange fluxes are generally obtained with the most significant differences in outflows and heads observed for the 30 slope and for hillslopes with convergent geometry on the open book catchment cumulative outflows are overestimated by 1 4 heads in the confined and unconfined aquifers are adequately reproduced throughout the catchment whereas exchange fluxes are found to be very sensitive to the hillslope drainable porosity the new model is highly efficient computationally compared to the benchmark model the coupled hsb ae model represents an alternative to commonly used groundwater flow representations in hydrological models of particular appeal when surface subsurface exchanges local aquifer regional aquifer interactions and low flows play a key role in a watershed s dynamics copyright 2011 john wiley sons ltd

synthesis of the special issue the formation and evolution of ceres occator crater abstract the distinctive bright regions within occator crater are one of the most remarkable discoveries of the dawn mission s exploration of ceres the central region is named cerealia facula and the additional regions in the eastern crater floor are named vinalia faculae here we summarize and synthesize the results of this special issue which aimed to identify the driving forces behind the formation of occator and the faculae and thus lead us to a new understanding of the processes and conditions that occurred in ceres past and potentially in its present the investigations presented here used dawn data theoretical modeling and laboratory experiments to deduce the sequence of events that led to the formation of occator cerealia facula and vinalia faculae which are broken into stages 1 3 stage 1 occator s ejecta blanket terraces and hummocky crater floor material formed during and shortly after crater formation these features are located in many cerean complex craters however occator also contains the lobate materials and faculae which are unique to occator we interpret the lobate materials as a slurry of water soluble salts and boulders of unmelted silicates salts which flowed around the crater interior before solidifying at least portions of the lobate materials were solidified prior to the formation of the central pit which is suggested to form via the melted uplift model and provides insights into central pit formation across the solar system we propose the outer edge of cerealia facula formed shortly after the occator forming impact via impact induced hydrothermal brine deposition or via salt rich water fountaining perhaps sourced in a pre existing reservoir stage 2 the majority of cerealia facula is located within the central pit and is interpreted to have formed later at least 18 myr after the occator forming impact via multiple depositional events the cerealia facula forming brines may have flowed out of fractures in the walls of the central pit and or been driven to the surface by freezing of a subsurface reservoir and or deposited via salt rich water fountains further investigations are required to identify whether the formation of the majority of cerealia facula is driven by processes triggered by an impact i e an exogenic event or by a combination of impact driven and endogenic processes cryomagmatic intrusions are suggested to uplift the crater floor resulting in concentric floor fractures and an asymmetric dome injection of a similar material is proposed to inflate part of the lobate materials giving them a hummocky texture the resulting stresses formed fractures in the hummocky lobate material which allowed the vinalia faculae forming brines to travel to the surface where they ballistically erupted the central dome within the central pit was one of the last features to form by laccolithic intrusion or by volume expansion from freezing of volatiles or by extrusion of brines stage 3 mixing with ceres average materials and or space weathering darken the faculae over time cerealia facula and vinalia faculae are the brightest and freshest of the bright regions identified on ceres surface bright regions darken over time until their eventual erasure thus it is likely that faculae formation has occurred throughout ceres history but that occator s faculae are visible today because they are geologically young through synthesis of the studies presented in this special issue we find that entirely exogenic driving forces triggered by the impact or a combination of endogenic and impact derived forces could explain the formation of occator and its faculae whether activity is impact triggered and or endogenic in nature is a key question for all investigations of ceres and future studies may favor one possibility over the other the investigations presented in our special issue indicate ceres is an active world where brines have been mobile in the geologically recent past as such ceres is an intriguing world that we have only begun to explore

impact features on europa results of the galileo europa mission gem during the galileo europa mission gem impact features on europa were observed with improved resolution and coverage was compared with voyager or the galileo nominal mission we surveyed all primary impact features 4 km in diameter seen on europa through orbit e19 the transition from simple to complex crater morphology occurs at a diameter of about 5 km we calculated the transient crater dimensions and excavation depths of all craters surveyed the largest impact feature tyre probably had a transient crater depth between 5 and 10 km and transported material to the surface from a depth of not greater than 4 km craters 30 km in diameter such as manannan and pwyll formed within targets whose immediate subcrater materials exhibited nonfluid behavior on time scales of the impact event and that are capable especially in the case of pwyll of supporting significant local topographic loads such as a central peak these craters are nevertheless quite shallow with very subdued floors and we suspect that manannan and pwyll s small depth to diameter ratios are due to the isostatic adjustment of large scale topography facilitated by warm plastically deformable ice at depth morphological similarities between callanish and tyre strongly imply that conclusions reached regarding callanish in j moore et al 1998 icarus135 127 145 also apply to tyre which was that callanish is the consequence of impact into target materials that are mechanically very weak at depth new evidence that callanish s circumferential rings formed before the proximal ejecta became immobile implies a low viscosity substrate at the time of impact we also report additional evidence that a component of the proximal ejecta of callanish was emplaced as a fluid our observations of pwyll secondaries support the conclusions stated in alpert and melosh 1999 that impacts on icy bodies eject smaller fragments and that fragment size decreases more gradually as velocity increases than observed for impacts on silicate bodies at equivalent ejection velocities examination of pwyll s secondary craters reveals azimuthal variations with ejecta fragment sizes being larger near the center of a ray than off the ray our initial analysis of the characteristic size distribution of pwyll s secondary craters shows that they form a differential slope slightly shallower than 4 similar steep slopes for small craters on ganymede imply that small craters there are mostly formed by secondary impact and the jovian system may thus be deficient in small impacts relative to the environment of the terrestrial planets

evidence for an explosive origin of central pit craters on mars abstract kilometer scale pits are nested in the centers of many impact craters on mars as well as on icy satellites they have been inferred to form in the presence of a water ice rich substrate however the process es responsible for their formation is still debated previous models invoke origins by either explosive excavation of potentially water bearing crustal material or by subsurface drainage of meltwater and or collapse if explosive excavation forms central pits pit derived ejecta should be draped around the pits whereas internal collapse should not deposit significant material outside pit rims using visible wavelength images from the mars reconnaissance orbiter mro context camera ctx and high resolution imaging science experiment hirise instruments and thermal infrared images from the odyssey thermal emission imaging system themis instrument we conducted a survey to characterize in detail the global population of central pits in impact craters 10 km in diameter we specifically examined the morphology and thermophysical characteristics of the pits for evidence of pit ejecta our analysis of thermal images suggests that coarse grained materials are distributed proximally around many central pits on the floors of their host craters the decrease in average grain size with distance from pit rims is consistent with pit derived ejecta these observations and interpretations better support an explosive origin for central pits on mars than they do an origin of subsurface meltwater drainage and collapse of the overlying substrate a major weakness to previous explosive central pit formation models is the inability for them to form pits late enough in the impact process to be preserved to address this we present an alternative melt contact model where a central uplift brings ice bearing substrate into contact with impact melt to generate steam explosions and excavate central pits during the impact modification stage theoretical calculations show that more than enough thermal energy is available via impact melt from the host crater to form central pits by steam explosions and such explosions would require only a modest amount 2 6 by volume of uplifted water ice we therefore propose that central pits on mars could have formed explosively by the interaction of impact melt and subsurface water ice

hillslope dynamics modeled with increasing complexity summary few studies have investigated how much model complexity is needed to simulate both the hillslope outflow and the internal hillslope dynamics we studied the influence of model complexity on simulations for the panola mountain trenched hillslope we analyzed the influences of the inclusion of bedrock permeability variable soil depth and preferential flow on modeled hillslope responses we found that without the inclusion of bedrock leakage the long term subsurface flow response measured at the trenchface and the threshold relation between total precipitation and total subsurface flow could not be simulated adequately individual events could still be represented acceptably showing the importance of long time series for model calibration and validation the use of spatially constant bedrock conductivity allowed us to simulate spatially variable bedrock leakage rates because of the spatially variable depths of saturation without variable soil depth the spatial variability of subsurface flow along the trenchface and its temporal dynamics during events could not be represented in addition the spatial patterns of saturation at the soil bedrock interface did not agree with the observed patterns and responses to smaller events were underestimated inclusion of preferential flow mainly influenced the distribution of the maximum saturation depths at the soil bedrock interface and increased peak flows and recessions soil moisture measurements were less useful for model validation for the panola hillslope than measurements of the spatial patterns of saturation and subsurface flow we plea for a new blue print for the set up of hillslope experiments such that their data is useful for studies on hillslope model complexity and for model validation and rejection

numerical modeling for target water depth estimation of marine target impact craters 1 marine impacts can develop a crater in the seafloor if the target water depth is shallow in relation to the size of the impactor the geology of this marine target crater is influenced by the layer of water in the upper part of the target the influence increases with increased water depth the target water depth is essential when calculating the magnitude of the impact event as the seafloor crater merely expresses some of the expended energy the target water depth for a marine target crater is often estimated by facies analysis of sediments related to the impact crater unfortunately often with ambiguous results we propose to combine the conventional methods with numerical modeling of the target water depth based on the special target water related features of the crater we used geological data from the lockne crater as constraints in a simulation with the sova hydrocode the simulations were done for three different target water depths 200 m 500 m and 1000 m within the likely depth range for the middle ordovician sea in which the impact occurred in order to obtain the minimum estimated size of the lockne crater by an asteroid impact at 20 km s the water depth must have been slightly less than 1 km and the impactor radius must have been about 400 m it was not possible to generate a crater with the geological features of lockne for target water depths of less than about 500 m however the ratio may be further constrained by factors such as impactor density impact angle and impact velocity

pre quaternary orogen parallel extension in the southern apennine belt italy abstract the southern apennine fold and thrust belt differs from other parts of the peri tyrrhenian orogen in most of the peri tyrrhenian belt hinterland extension is oriented at a high angle to the orogen axis and appears to be related to rifting and formation of oceanic crust within the tyrrhenian basin the southern apennines share the late stage development of normal faults related to the opening of the tyrrhenian sea but also experienced an episode of extension parallel to the strike of the tectonic belt the orogen parallel extension was apparently formed in response to the increase in length of the deformed belt during arcuation arcuation ostensibly was related to asymmetrical rifting in the hinterland which was greater in the southern tyrrhenian sea than in areas to the north and proportionately greater shortening in the frontal parts of the southern belt as compared to regions in the north during arcuation extension was spatially concentrated within structural domains and was accomplished by displacement on low angle detachment faults cutting through a previously imbricated thrust stack during the miocene pliocene nnw sse extension in the interior of the southern appennine belt formed coveally with ene wsw shortening in the foreland longitudinal extension ceased in the pleistocene when younger high angle normal faults formed in response to the easterly migration of tyrrhenian sea rifting and ne sw extension associated with lithospheric stretching

impact cratering on titan ii global melt escaping ejecta and aqueous alteration of surface organics abstract new three dimensional hydrodynamic simulations of hypervelocity impacts into the crust of titan were undertaken to determine the fraction of liquid water generated on the surface of saturn s largest moon over its history and hence the potential for surface modification of hydrocarbons and nitriles by exposure to liquid water we model in detail an individual impact event in terms of ejecta produced and melt generated and use this to estimate melt production over titan s history taking into account the total flux of the impactors and its decay over time our estimates show that a global melt layer at any time after the very beginning of titan s history is improbable but transient melting local to newly formed craters has occurred over large parts of the surface local maxima of the melt are connected with the largest impact events we also calculate the amount of volatiles delivered at the impact with various impact velocities from 3 km s for possible hyperion fragments to 11 km s for jupiter family comets and their retention as a possible source of titan s atmosphere we find the probability of impact ejecta escaping titan with its modern dense and thick atmosphere is rather low and dispersal of titan organics throughout the rest of the solar system requires impactors tens of kilometers in diameter water ice melting and exposure of organics to liquid water has been widespread because of impacts but burial or obscuration of craters by organic deposits or cryovolcanism is aided by viscous relaxation the largest impactors may breach an ammonia water mantle layer creating a circular albedo contrast rather than a crater

large impact features on middle sized icy satellites abstract all of the large impact features of the middle sized icy satellites of saturn and uranus that were clearly observed by the voyager spacecraft are described new image mosaics and stereo and photoclinometrically derived digital elevation models are presented landforms related to large impact features such as secondary craters and possible antipodal effects are examined and evaluated of the large impacts odysseus on tethys appears to have had the most profound effect on its target satellite of any of the impact features we examined our modeling suggests that the odysseus impact may have caused the prompt formation of ithaca chasma a belt of tectonic troughs that roughly follow a great circle normal to the center of odysseus although other hypotheses remain viable we identify probable secondary cratering from tirawa on rhea we attribute a number of converging coalescing crater chains on rhea to a putative possibly relatively fresh 350 km diameter impact feature we examine the antipodes of odysseus the putative 350 km diameter rhean impact feature and tirawa and conclude that evidence from voyager data for damage from seismic focusing is equivocal although our modeling results indicate that such damage may have occurred we propose a number of observations and tests for cassini that offer the opportunity to differentiate among the various explanations and speculations reviewed and evaluated in this study

ganymede and callisto complex crater formation and planetary crusts new depth diameter d d rim and peak height and width measurements of fresh craters on ganymede and callisto are utilized to explore not only crater mechanics on icy satellites but intersatellite crater scaling and crustal properties and composition significant systematic differences in crater morphology on icy and rocky planets are confirmed simple to complex transition diameters on icy satellites including ganymede and callisto are much lower than those on rocky planets also complex crater depths and rim heights on ganymede and callisto are inherently 60 70 shallower than lunar complex craters despite similar surface gravity hence viscous relaxation is not as important as is generally assumed central peaks on most icy satellites are 1 2 km higher and considerably wider with respect to diameter than for similar sized lunar craters terracing and rim slumping is also rare in these craters central peaks in craters on ganymede and callisto larger than 15 km however are relatively small in both width and height however correlating with the occurrence of rim slumping thus central peak dimensions are an indirect indicator of the degree of rim slumping transition diameters for the occurrence of central peaks and rim slumps and for d d curve inflections for icy satellites scale approximately with the inverse of surface gravity except possibly at very low g the transition diameters for central peaks and for rim slumping differ however by 5 15 km on ganymede and callisto but by 50 or more km on the smaller icy satellites these large differences suggest that d d curves on icy satellites are comprised of three segments of decreasing slope one for smaller simple craters a second for central peak craters and a third for larger true complex craters with both central peaks and rim slumping the shallow slopes of d d curves on ganymede and callisto resemble that of the moon consistent with the occurrence of both central peaks and rim failure the high slopes of d d curves on the middle sized icy satellites indicate that they are middle segments consistent with the dominance of central peaks in those craters complex crater depths on icy satellites in general scale with the inverse of surface gravity the depths of all the observed large basin scale craters on these small satellites when scaled to ganymede gravity are very similar to those of complex craters on ganymede and callisto these large craters including odysseus 425 km diameter on tethys are probably true complex craters that have not undergone significant viscous relaxation ithaca chasma on tethys probably formed during the prompt collapse of the transient odysseus crater crater morphology is clearly controlled by both gravity and by large variations in material properties i e composition and should be useful in constraining bulk crustal composition i e ice rock ratios the similarity of various morphological transition diameters and complex crater depths on ganymede and callisto two geophysically very similar but geologically divergent large icy satellites indicates that the crusts of both bodies are dominated by water ice with only a minor rocky component

palaeoenvironmental reconstruction of late quaternary foraminifera and molluscs from the enea borehole versilian plain tuscany italy abstract foraminifera and molluscs from the 90 m deep enea borehole versilian plain central italy were studied for paleoenvironmental purposes palaeontological analyses integrated with u th and radiocarbon data helped to recognize late quaternary sea level changes and supplied results on tectonic mobility of the area the study highlighted four sedimentary phases the first phase consists of a shore environment attributed to mis 7 1 a hiatus corresponding to mis 6 is hypothesized at the top of this interval recognition of the paleo shoreline of mis 7 1 at 72 8 m signifies a vertical displacement due to the extensional tectonics of the apennine orogenesis the second phase consists of a transgressive succession with evidence of warm temperatures which was interpreted as part of the transgression leading to the mis 5 5 highstand the third phase includes sub aerial and lacustrine deposits radiocarbon dates and palaeoecological reconstruction led us to attribute this interval to mis 4 mis 3 and mis 2 the fourth phase begins with a lagoon environment attributable to holocene sea level rise and ends with marsh episodes signifying the progradation of the alluvial plain this reconstruction confirms the hypothesis of tectonic stability for the versilian area during the holocene

thickness constraints on the icy shells of the galilean satellites from a comparison of crater shapes a thin outer ice shell on jupiter s large moon europa would imply easy exchange between the surface and any organic or biotic material in its putative subsurface ocean1 2 3 4 the thickness of the outer ice shell is poorly constrained however with model dependent estimates ranging from a few kilometres5 6 to ten or more kilometres7 here i present measurements of depths of impact craters on europa ganymede and callisto that reveal two anomalous transitions in crater shape with diameter the first transition is probably related to temperature dependent ductility of the crust at shallow depths 7 8 km on europa the second transition is attributed to the influence of subsurface oceans on all three satellites3 8 9 which constrains europa s icy shell to be at least 19 km thick the icy lithospheres of ganymede and callisto are equally ice rich but europa s icy shell has a thermal structure about 0 25 0 5 times the thicknesses of ganymede s or callisto s shells depending on epoch the appearances of the craters on europa are inconsistent with thin ice shell models1 and indicate that exchange of oceanic and surface material could be difficult

candidate volcanic and impact induced ice depressions on mars abstract we present an analysis of two concentrically fractured depressions on mars one in northern hellas and the second in galaxias fossae volumetric measurements indicate that 2 4 km3 and 0 2 km3 of material was removed in order to form the north hellas and galaxias depressions the removed material is inferred to be predominantly water ice calorimetric estimates suggest that up to 103 105 m3 of magma would have been required to melt sublimate such a volume of ice under an ice magma interaction scenario this process would lead to subsidence and cracking of the surface which could produce the observed concentric fracture crevasse like morphology while the galaxias fossae landform morphology is consistent with an impact origin the large volume of removed material in north hellas is less consistent with an impact origin and is interpreted to have resulted from volcanic melting of ice the possibility of liquid water formation during or subsequent to volcanism or an impact could generate locally enhanced habitable conditions making these features tantalizing geological and astrobiological exploration targets

the central pit and dome at cerealia facula bright deposit and floor deposits in occator crater ceres morphology comparisons and formation abstract the prominent bright deposit cerealia facula ceres coincides with the central depression or central pit of the recently formed 92 km wide complex crater occator the central pit is 9 10 km wide and up to 1 km deep and is partially filled with a 700 m high 2 km wide dome the upper surface of the central dome is densely fractured but the flanks are not indicating that uplift of the dome surface occurred after the bright deposit was emplaced and primarily through uplift of the surface from below by laccolithic intrusion or volume expansion the pit is rimless except for two prominent massifs that flank it to the east and west this pit dome morphology bears a strong resemblance in morphology topography and dimensions to central pit craters observed on ganymede and callisto but is essentially absent on the similar sized ice rich moons of uranus saturn and pluto the lack of pit craters on midsize icy moons and the possible lack of central pit craters at the cold poles of ceres suggest that temperature is a significant controlling factor in central pit formation beyond the canonical inverse gravity scaling of complex crater transitions while renewed modeling will benefit from these new constraints the mapping of central pits on ceres including occator suggests that either the rheologically layered target model or more likely the melted central uplift model may be the most probable explanation for central pit formation on ceres lack of similar high resolution imaging on the galilean icy satellites precludes definitive evaluation of models there large volumes of lobate floor fill material at least 600 m thick in some places cover large areas of the southern and eastern floor of occator and small outcrops of this unit are found perched high on closed topographic depressions on the occator terrace zone and other higher areas of the crater floor the swirling and knobby surface textures of these lobate deposits are essentially indistinguishable from those on impact melt sheets on large lunar craters such as tycho these observations indicate that this unit is most likely an impact melt sheet formed from melted water ice admixed with unmelted particulate or dissolved phyllosilicates salts and or carbonates and large quantities of fragmented debris melt of ice phases within ceres crust is also supported by independent numerical models of impact at occator and would provide a ready source of fluids to promote hydrothermal deposition of the observed bright na carbonates on the surface of the central pit at occator if the deposit formed within a million years or so of impact the central dome finds analogs in salt domes on earth and pingos frost mounds on earth and mars which form by water and solute migration and freeze expansion later freezing of a central reservoir of volatiles beneath the central pit at occator or mobilization of ice or other phases during the cooling and refreezing process could explain the uplift of the central dome finally no changes were detected in the cerealia and vinalia facula bright deposits during the course of the prime dawn mapping mission placing additional constraints on their formation time and limits on ongoing activity

threshold relations in subsurface stormflow 2 the fill and spill hypothesis analysis of subsurface stormflow from 147 storms at the 20 m long trench in the panola mountain research watershed by tromp van meerveld and mcdonnell 2006a showed that there was a distinct 55 mm precipitation threshold for significant subsurface stormflow production this second paper in the series investigates the processes responsible for this threshold response we installed a dense spatial array of maximum rise crest stage gauges and recording wells on the hillslope and studied the temporal and spatial patterns of transient saturation at the soil bedrock interface and its relation to subsurface stormflow measured at the trench face results show that while transient groundwater developed on parts of the hillslope during events smaller than 55 mm it was not until more than 55 mm of rain fell before bedrock depressions on the hillslope were filled water spilled over microtopographic relief in the bedrock surface and the subsurface saturated areas became connected to the trench when connectivity was achieved the instantaneous subsurface stormflow rate increased more than fivefold compared to before the subsurface saturated areas were connected to the trench face total subsurface stormflow was more than 75 times larger when connectivity was achieved compared to when connectivity was not achieved the fill and spill hypothesis presented in this paper is a process explanation for the observed threshold behavior of tromp van meerveld and mcdonnell 2006a thereby linking patterns and processes

run off formation in a humid temperate headwater catchment using a combined hydrological hydrochemical and isotopic approach jizera mountains czech republic the formation of baseflow and stormflow was examined in the 1 18 km2 part of the headwater catchment uhli ska jizera mountains czech republic over the period 2007 2011 by means of run off data and environmental tracers 18o and sio2 the baseflow computed using the digital filter approach bflow contributes 67 to total streamflow and has a mean residence time of 12 3 months it is formed by groundwater discharge from the valley deluviofluvial granitic sediments in combination with soil water in weathered layers on hillslopes during rainfall and snowmelt periods the prevailing source of the groundwater is the infiltration of snowmelt water analysis of 20 run off events and their hysteretic patterns demonstrated that the stormflow water has a residence time of about 4 months and is generated by preferential flow on hillslopes combined by soil matrix drainage because of slower flow in the soil matrix the enrichment of pore water in sio2 is more pronounced the stormflow and snowmelt water flowing via preferential pathways of upslope minerals soils pushes the pre event groundwater through the pathways in wetlands to the stream and the wetland can be therefore considered as groundwater supplied this mechanism has been found to be typical for the groundwater supplied headwater catchments of the jizera mountains and can be also assumed in other mountainous headwaters of the granitic massif in central europe the main methodological contribution of this study are the residence time calculations stratified by baseflow and event flow identifying run off components of different travel times to streams and linking them with geochemical run off sources this achievement was possible because of a comprehensive dataset on hydrology stable isotopes and silica hydrochemistry in all relevant run off generation components this concept indicates that a possible long term change in snowmelt may affect the run off regime of headwater catchments to climate or land use changes copyright 2013 john wiley sons ltd

a proposed origin for palimpsests and anomalous pit craters on ganymede and callisto palimpsests and anomalous pit craters are two classes of craters found on the icy satellites ganymede and callisto that have no obvious counterparts among the crater populations found on rocky planets the distinct characteristics of palimpsests and anomalous pit craters in morphology morphometry and population statistics which differentiate them from the more numerous normal craters and basins on the icy satellites also preclude their origin as normal craters that have nearly vanished through viscous relaxation an alternate origin is proposed palimpsests are formed when the flow of material during the modification stage of crater formation is dominated by wet fluid flow as opposed to dry granular flow which forms normal craters conditions of wet modification flow occur when the volume of melt remaining in the crater attains a volume comparable to the volume of the transient crater by use of an impact model that includes 1 plausible impact velocity distributions 2 crater scaling in ice 3 shock melting in ice 4 thermal profiles as a function of time in ganymede and 5 cratering flow field constraints conditions for wet modification flow are found to occur for sufficiently large impacts or high velocity impactors the range of normal crater palimpsest transition diameters and the morphologic characteristics inferred from the impact model are consistent with the observed characteristics of palimpsests thus normal craters are inferred to result from the majority of impactors which have impact velocities near the average of 15 km s anomalous pit craters inferred to be transitional forms from intermediate velocity impactors at about 30 km s and palimpsests by impactors travelling in excess of about 40 km s the thermal state of the crust at the time of impact is a second order effect but sufficient to account for the difference in palimpsest population between ganymede and callisto if ganymede once had a liquid mantle while callisto remained unmelted and undifferentiated or solidified prior to the formation of the presently observed crater population

conceptualizing lateral preferential flow and flow networks and simulating the effects on gauged and ungauged hillslopes 1 one of the greatest challenges in the field of hillslope hydrology is conceptualizing and parameterizing the effects of lateral preferential flow our current physically based and conceptual models often ignore such behavior however for addressing issues of land use change water quality and other predictions where flow amount and components of flow are imperative dominant runoff processes like preferential subsurface flow need to be accounted for in the model structure this paper provides a new approach to formalize the qualitative yet complex explanation of preferential flow into a numerical model structure we base our examples on field studies of the well studied maimai watershed new zealand we then use the model as a learning tool for improved clarity into the old water paradox and reasons for the seemingly contradictory findings of lateral preferential flow of old water where applied line sources of tracer appear very quickly in the stream following application we evaluate the model with multiple criteria including ability to capture flow hydrograph composition and tracer breakthrough we generate output ensembles with different pipe network geometries for model calibration and validation analysis surprisingly the range of runoff response among the ensembles is narrow indicating insensitivity to specific pipe placement our new model structure shows that high transport velocities for artificial line source tracers can be reconciled with the dominance of preevent water during runoff events even when lateral pipe flow dominates response the work suggests overall that preferential flow can be parameterized within a process based model structure via the structured dialog between experimentalist and modeler

determining rates of chemical weathering in soils solute transport versus profile evolution abstract sio 2 fluxes associated with contemporary solute transport in three deeply weathered granitoid profiles are compared to bulk sio 2 losses that have occurred during regolith development climates at the three profiles range from mediterranean to humid to tropical due to shallow impeding alluvial layers at two of the profiles and seasonally uniform rainfall at the third temporal variations in hydraulic and chemical state variables are largely attenuated below depths of 1 2 m this allows current sio 2 fluxes below the zone of seasonal variations to be estimated from pore water concentrations and average hydraulic flux densities mean annual sio 2 concentrations were 0 1 1 5 mm hydraulic conductivities for the investigated range of soil moisture saturations ranged from 9 to 10 6 m s 1 estimated hydraulic flux densities for quasi steady portions of the profiles varied from 6 10 9 to 14 10 9 m s 1 based on darcy s law and field measurements of moisture saturations and pressure heads corresponding fluid residence times in the profiles ranged from 10 to 44 years total sio 2 losses based on chemical and volumetric changes in the respective profiles ranged from 19 to 110 kmoles sio 2 m 2 of land surface as a result of 0 2 0 4 ma of chemical weathering extrapolation of contemporary solute fluxes to comparable time periods reproduced these sio 2 losses to about an order of magnitude despite the large range and non linearity of measured hydraulic conductivities solute transport rates in weathering regoliths can be estimated from characterization of hydrologic conditions at sufficiently large depths the agreement suggests that current weathering rates are representative of long term average weathering rates in the regoliths

impact basin relaxation as a probe for the thermal history of pluto we investigate viscoelastic impact basin relaxation on pluto for a variety of thermal evolution scenarios encompassing both convective and conductive ice shells basins smaller than 200 km in diameter do not relax appreciably while relaxation fractions can be up to 60 for large impact basins the main control on basin relaxation is the amount of radiogenic heat produced in the rocky core our results are insensitive to the formation time of the basin the ice reference viscosity adopted and the presence absence of a subsurface ocean other volatiles such as co2 or nh3 if present in the ice shell in sufficient quantities could increase the predicted relaxation fraction of basins relaxation causes extensional stresses interior to the basin the orientation of the resulting tectonic features is controlled by the effective elastic thickness beneath the basin future observations of the relaxation states and tectonics of impact basins are therefore likely to provide a key constraint on pluto s thermal history

a global inventory of central pit craters on the moon distribution morphology and geometry abstract the origin of central pit craters on the moon has long been an enigma and a primary reason is that their geographic distribution and morphometric characteristics were unknown we investigated a global inventory of lunar central pit craters using high resolution image and topography data obtained from the lunar reconnaissance orbiter 56 certain and 35 probable central pit craters are found on both the lunar maria and highlands the certain pit craters are 9 57 km in diameter the average diameter ratio between the central pits and their parent craters is 0 12 and the average depth diameter ratio for the central pits is 0 072 with irregular shaped rims the central pits have conical profiles and some have flat floors the central pits occur on both crater floors and central peaks the floor pits are generally larger deeper and with more irregular shape compared with summit pits both the summit and floor pit craters have formed in every lunar stratigraphic epoch from nectarian to copernican target properties of background terrains affect the morphology and size of central pits but they do not determine whether or not a central pit forms during a cratering event the lunar central pits may have formed by deformation of central peaks caused by some mechanical processes during or soon after the cratering process of their parent craters

sea level change and volcano tectonic interplay the gulf of pozzuoli campi flegrei eastern tyrrhenian sea during the last 39 ka a geological study based on seismic profiles and sediment cores has been accomplished on the gulf of pozzuoli the marine sector of the campi flegrei an active volcanic area located west of the city of naples italy detailed seismo stratigraphic analysis led to the correlation between marine units and the on land volcanic deposits the absence of primary pyroclastic beds in cores highlights the role of the shallow marine environment in the reworking of the volcani clastic sediments the evolution of the area during the last 39 ka evidences the role of the eustatic change and volcano tectonic phenomena in the development of the local sedimentary record four main phases in the geological evolution have been distinguished in a first phase the emplacement of two volcanic units v1 between 60 and 39 ka and ci 39 ka took place a second phase developed between 39 and 15 ka and led to the formation of regressive depositional wedges fw and lw sedimentary bodies in the external sectors of the area outer shelf the eruption of the neapolitan yellow tuff 15 ka and the following eruptions that occurred up to 11 ka constitute the third phase during the fourth phase 11 ka to present generalized marine conditions were established in the area distribution and thickness of the sedimentary bodies formed during the latter time span are highly variable and constitute the result of a complex interplay between volcano tectonic movements and sea level change

ganymede crater dimensions implications for central peak and central pit formation and development the morphology of impact craters on the icy galilean satellites differs from craters on rocky bodies the differences are thought due to the relative weakness of ice and the possible presence of sub surface water layers digital elevation models constructed from galileo images were used to measure a range of dimensions of craters on the dark and bright terrains of ganymede measurements were made from multiple profiles across each crater so that natural variation in crater dimensions could be assessed and averaged scaling trends constructed the additional depth slope and volume information reported in this work has enabled study of central peak formation and development and allowed a quantitative assessment of the various theories for central pit formation we note a possible difference in the size morphology progression between small craters on icy and silicate bodies where central peaks occur in small craters before there is any slumping of the crater rim which is the opposite to the observed sequence on the moon conversely our crater dimension analyses suggest that the size morphology progression of large lunar craters from central peak to peak ring is mirrored on ganymede but that the peak ring is subsequently modified to a central pit morphology pit formation may occur via the collapse of surface material into a void left by the gradual release of impact induced volatiles or the drainage of impact melt into sub crater fractures

geology before pluto pre encounter considerations the cameras of new horizons will provide robust data sets that should be imminently amenable to geological analysis of the pluto system s landscapes in this paper we begin with a brief discussion of the planned observations by the new horizons cameras that will bear most directly on geological interpretability then we broadly review the major geological processes that could potentially operate on the surfaces of pluto and its major moon charon we first survey exogenic processes i e those for which energy for surface modification is supplied externally to the planetary surface impact cratering sedimentary processes including volatile migration and the work of wind we conclude with an assessment of the prospects for endogenic activity in the form of tectonics and cryovolcanism

early thermal profiles and lithospheric strength of ganymede from extensional tectonic features abstract estimates of the brittle lithosphere thickness derived from the width and spacing of extensional tectonic features coupled with lithospheric strength envelopes brittle and ductile yield stress versus depth appropriate for ice allow the quantitative determination of early thermal profiles and lithospheric strength and stability on ganymede furrows and grooves indicate brittle lithospheric thicknesses of 5 10 and 2 5 km respectively assuming that their spacing is controlled by an extensional instability or that their width is controlled by the intersection depth of their bounding faults plots of the brittle and ductile yield stress versus depth for the icy lithosphere of ganymede show a linear increase in brittle strength with depth to a maximum at the brittle ductile transition followed by an exponential decrease in ductile yield stress with depth because the depth to the brittle ductile transition depends primarily on the thermal gradient the thickness of the brittle lithosphere can be used to calculate early thermal profiles of 1 5 6 and 4 5 20 km during the formation of the furrows and grooves respectively lithospheric strength the integral of the yield stress versus depth curve varied from 30 125 gpa m when the furrows formed to 5 30 gpa m when the grooves formed which correspond to maximum yield stresses of 6 11 and 2 5 6 mpa respectively these results indicate that the thermal gradient and lithospheric strength varied laterally by as much as a factor of 5 and that ganymede cooled in a highly inhomogeneous manner with significant lateral thermal anomalies finally this analysis provides a straightforward explanation for the stability of large remnants of cratered terrain such as galileo regio that had a low thermal gradient and strong lithosphere in contrast to small remnants of cratered terrain that were fractured and broken up by grooved terrain as a result of higher thermal gradients and weaker lithospheres

oceans in the icy galilean satellites of jupiter abstract equilibrium models of heat transfer by heat conduction and thermal convection show that the three satellites of jupiter europa ganymede and callisto may have internal oceans underneath ice shells tens of kilometers to more than a hundred kilometers thick a wide range of rheology and heat transfer parameter values and present day heat production rates have been considered the rheology was cast in terms of a reference viscosity 0 calculated at the melting temperature and the rate of change a of viscosity with inverse homologous temperature the temperature dependence of the thermal conductivity k of ice i has been taken into account by calculating the average conductivity along the temperature profile heating rates are based on a chondritic radiogenic heating rate of 4 5 pw kg 1 but have been varied around this value over a wide range the phase diagrams of h2o ice i and h2o 5 wt nh3 ice have been considered the ice i models are worst case scenarios for the existence of a subsurface liquid water ocean because ice i has the highest possible melting temperature and the highest thermal conductivity of candidate ices and the assumption of equilibrium ignores the contribution to ice shell heating from deep interior cooling in the context of ice i models we find that europa is the satellite most likely to have a subsurface liquid ocean even with radiogenic heating alone the ocean is tens of kilometers thick in the nominal model if tidal heating is invoked the ocean will be much thicker and the ice shell will be a few tens of kilometers thick ganymede and callisto have frozen their oceans in the nominal ice i models but since these models represent the worst case scenario it is conceivable that these satellites also have oceans at the present time the most important factor working against the existence of subsurface oceans is contamination of the outer ice shell by rock rock increases the density and the pressure gradient and shifts the triple point of ice i to shallower depths where the temperature is likely to be lower then the triple point temperature according to present knowledge of ice phase diagrams ammonia produces one of the largest reductions of the melting temperature if we assume a bulk concentration of 5 wt ammonia we find that all the satellites have substantial oceans for a model of europa heated only by radiogenic decay the ice shell will be a few tens of kilometers thinner than in the ice i case the underlying rock mantle will limit the depth of the ocean to 80 100 km for ganymede and callisto the ice i shell on top of the h2o nh3 ocean will be around 60 to 80 km thick and the oceans may be 200 to 350 km deep previous models have suggested that efficient convection in the ice will freeze any existing ocean the present conclusions are different mainly because they are based on a parameterization of convective heat transport in fluids with strongly temperature dependent viscosity rather than a parameterization derived from constant viscosity convection models the present parameterization introduces a conductive stagnant lid at the expense of the thickness of the convecting sublayer if the latter exists at all the stagnant lid causes the temperature in the sublayer to be warmer than in a comparable constant viscosity convecting layer we have further modified the parameterization to account for the strong increase in homologous temperature and therefore decrease in viscosity with depth along an adiabat this modification causes even thicker stagnant lids and further elevated temperatures in the well mixed sublayer it is the stagnant lid and the comparatively large temperature in the sublayer that frustrates ocean freezing

soil thickness effect on hydrological and erosion characteristics under sloping lands a hydropedological perspective abstract soil thickness exerts a first order control on the hydrological processes of the hillslopes however from a hydropedological perspective the knowledge of soil thickness effect on hydrological and erosion characteristics under sloping lands is limited based on a comprehensive survey of an experimental watershed in the three gorges area of china five typical sloping land plots 2 m 1 m with different soil thickness were selected along a hillslope to investigate their hydrological processes and erosion response under three rainfall intensities 60 90 and 120 mm h 1 using a portable rainfall simulator the results can be summarized as follows 1 the surface flow coefficient was increased with increasing soil thickness especially under the event of 60 mm h 1 2 the subsurface flow of the 23 31 and 45 cm plots mainly took the form of preferential flow conversely the 59 and 76 cm plots mainly took the form of matrix flow 3 a prolonged low intensity rainfall is much more likely to facilitate deep percolation and subsurface flow than a short high intensity rainfall regardless of soil thickness 4 soil thickness and rock fragment cover were the most important factors than other soil properties in determining the hydrological and erosion behaviors thin soils showed higher infiltration capacity than thick soils due to their more distinct hydrological processes of subsurface flow and deep percolation rock fragment cover enhanced infiltration and served as a shield to protect the soil surface from detaching due to the synergies between thin soil thickness and high rock fragment cover thin soils displayed significantly lower erosion rates than thick soils in all rainfall events which increased from 211 g m 2 h 1 for the 23 cm plot with rainfall of 60 mm h 1 to 4220 g m 2 h 1 for the 76 cm plot with rainfall of 120 mm h 1 our study suggested that the emerging interdisciplinary field of hydropedology promotes synergistic integration of pedology e g watershed scale soil thickness investigation and soil profile description and hydrology e g rainfall simulation subsurface flow and deep percolation to enhance the holistic study of soil water interactions in the sloping lands with different soil thickness

the role of lateral pipe flow in hillslope runoff response an intercomparison of non linear hillslope response the importance of lateral pipe flow on runoff generation in wet steep hillslopes has been described in many case studies from around the world however most hillslope studies are done in isolation and usually focus on the idiosyncrasies of individual hillslope characteristics and pipe flow response at a single site consequently the first order controls on pipe flow responses remain poorly understood we present a new intercomparison of pipe flow response to storm rainfall at four well instrumented sites panola georgia usa toinotani kyoto japan jozankei hokkaido japan and hakyuchi tokyo japan our objective was to minimize the complexities of lateral pipe flow on hillslopes by looking for commonality across different hillslope types despite the large differences between the study sites in topography climate soil type and soil matrix hydraulic conductivity we found several common pipe flow responses to storm rainfall 1 the relationship between total rainfall amount and total pipe flow volume was highly non linear at each site 2 initiation of measurable pipe flow was threshold dependent controlled by the total rainfall amount and the pre storm wetness 3 once significant pipe flow response occurred the maximum pipe flow rate was sensitive to the measured rainfall intensity and 4 the ratio of total pipe flow to total hillslope discharge for each site was constant regardless of total rainfall amount once the precipitation threshold for significant pipe flow response was reached we used these results to develop a decision tree to determine the general conditions necessary for significant pipe flow to occur the controls derived from our comparisons agree largely with the controls reported by the previous individual hillslope pipe flow studies in the literature the commonality of response between our four very different forested hillslope settings indicates that site intercomparison may be effective for extracting common first order controls on complex hillslope processes we argue that a decision tree may be a useful organizational framework to summarize and organize comparative analyses and may provide a structure for defining the hierarchy of process controls necessary for model development

delta initiation and holocene sea level change example from the song hong red river delta vietnam abstract delta initiation and subsequent delta growth were investigated by using radiocarbon dated borehole cores from the song hong red river delta vietnam the sediments underlying the present delta plain record three depositional systems since the last glacial maximum fluvial estuarine and deltaic in ascending order the landward part of the initial delta was characterized by an active tide influenced accumulation of sandy sediments the seaward part of the initial delta is composed of muddy prodelta and seafloor sediments that accumulated slowly radiocarbon ages of molluscan shells and organic materials suggest that the transition from estuary to delta occurred at approximately 8500 cal years bp the transition was induced by deceleration of the postglacial sea level rise which was coeval with the delta initiation the stacking pattern of the delta system is very different from that of the estuary system the sediments of the estuary that developed during the rapid rise in sea level between 11000 and 8500 cal years bp display a retrogradational stacking pattern forming a thick transgressive systems tract on the other hand aggradational as well as progradational stacking with clinoform architecture characterized the delta system between 8500 and 6500 cal years bp as the sea level continued its slow rise progradation has been dominant during the last 6500 years because the cessation of sea level rise resulted in little accommodation being added the results of this study are similar to those for other major delta systems such as the changjiang and the ganges brahmaputra deltas despite large differences in sediment discharge tectonics basin size and coastal environment this implies that the postglacial sea level rise and the change in the rise rate markedly influenced the evolution of depositional systems at river mouths

shocked h2o ice thermal emission measurements and the criteria for phase changes during impact events 1 impact cratering events on icy planetary bodies may produce transient liquid water and vapor we present the first thermal emission measurements from shocked h2o ice and derive peak and post shock temperatures under shock pressures between 8 2 and 13 6 gpa initially 165 k ice is heated to between 673 and 1055 k in the time frame of the experiment the shocked h2o releases to the saturation vapor curve and does not achieve full decompression the temperature results are used to validate the new 5 phase h2o model equation of state eos the 5 phase eos is used to predict the critical shock pressures required to induce melting and vaporization of ice for a wide range of ambient pressures and temperatures impact events with velocities as low as 1 km s will initiate phase changes on icy surfaces thus shock induced melting and vaporization of ice is a widespread process in the solar system

titan s impact crater population after cassini abstract titan is saturn s largest moon and has a dynamic surface with methane rivers carved by an active hydrological cycle and sand seas shaped by aeolian processes one way to study the rates of these processes is by examining titan s impact craters because they provide quantitative constraints on the level of degradation with the end of the cassini mission in september 2017 we have reassessed the crater population using the entire cassini synthetic aperture radar sar dataset including 30 additional craters since the last assessment in 2012 for a total of 90 certain to possible impact craters on titan we adjust for incomplete coverage 69 of the moon by sar imaging using a monte carlo approach and find no major change in titan s inferred surface age from prior studies we then used the sartopo and stereo topography data sets to measure crater depths and diameters for the first time rim heights for twelve craters were also reported on average titan s craters are shown to be shallower with lower rims than those observed on similarly sized icy moons e g ganymede this suggests that the observed modification is due to a combination of sand and sediment infilling onto the crater floor and fluvial erosion of the rims with fluvial erosion playing a larger role than previously thought in crater degradation on titan

experimental studies on the effects of pipeflow on throughflow partitioning abstract recent research has revealed that natural soil pipes provide important pathways for sub surface movement of water and solutes as well as contributing to landslide initiation a benchscale experiment in a sloping box 1 m in length was conducted with a uniform sand to evaluate the effect of pipeflow on the overall hydrologic regime a single drainage pipe 13 mm inside diameter id composed of five 20 cm segments each with a different roughness coefficient manning s n was placed 5 cm above the base of the 12 8 sloping box roughness elements were arranged in four different spatial combinations during hydraulic experiments piezometric levels were highest and pipeflow was lowest when the high roughness n 0 325 portion of the pipe was located at the downslope end of the box measured values of pipeflow for different hydraulic gradients in each experiment were related to piezometric head above the pipe raised to the 0 32 0 42 power pipeflow was proportional to matrix flow in the soil above the pipe raised to the power of 0 4 0 6 these findings may be useful in estimating pipeflow in uniform soils and in validating two domain models involving preferential flow in soils

the effect of target properties on crater morphology comparison of central peak craters on the moon and ganymede we examine the morphology of central peak craters on the moon and ganymede in order to investigate differences in the near surface properties of these bodies we have extracted topographic profiles across craters on ganymede using galileo images and use these data to compile scaling trends comparisons between lunar and ganymede craters show that crater depth wall slope and amount of central uplift are all affected by material properties we observe no major differences between similar sized craters in the dark and bright terrain of ganymede suggesting that dark terrain does not contain enough silicate material to significantly increase the strength of the surface ice below crater diameters of 12 km central peak craters on ganymede and simple craters on the moon have similar rim heights indicating comparable amounts of rim collapse this suggests that the formation of central peaks at smaller crater diameters on ganymede than the moon is dominated by enhanced central floor uplift rather than rim collapse crater wall slope trends are similar on the moon and ganymede indicating that there is a similar trend in material weakening with increasing crater size and possibly that the mechanism of weakening during impact is analogous in icy and rocky targets we have run a suite of numerical models to simulate the formation of central peak craters on ganymede and the moon our modeling shows that the same styles of strength model can be applied to ice and rock and that the strength model parameters do not differ significantly between materials

environmental impact of the 1 8 ka taupo eruption new zealand landscape responses to a large scale explosive rhyolite eruption abstract large scale ignimbrite eruptions from rhyolitic caldera volcanoes can trigger geologically instantaneous changes in sedimentary systems over huge areas by either burying existing environments or overloading them with vast quantities of unconsolidated particulate material the post eruption readjustment of the landscape to such perturbations is one of the most dramatic processes in physical sedimentology exemplified here by the 1 8 ka taupo eruption in the central north island of new zealand this eruption generated voluminous fall deposits then climaxed with emplacement of a c 30 km 3 non welded ignimbrite over a near circular area of c 20 000 km 2 approximately 90 of the area but the headwaters of many of the north island s largest rivers were impacted by both the primary pyroclastic fall and flow material large scale post eruption remobilisation of this material coupled with the re establishment of fluvial systems occurred in a distinct sequence as recorded by the evolution of sedimentary facies in different sub environments following an initial period dominated by mass flows re establishment of fluvial systems began with the headward erosion of box canyons through the ponded ignimbrite deposits a process often associated with the break out of temporary lakes aggradational streams developed in these channels rapidly evolved from shallow ephemeral sediment laden outbursts associated with flash flood events to deeper permanent braided rivers before declining sediment yields led to retrenchment of single thread rivers and a return to pre eruption gradients and bedloads years to decades later typically the modern profile of many streams and rivers follow closely their pre eruption profiles and incision and erosion is overwhelmingly confined to the deposits of the eruption itself although the general remobilisation pattern is similar for all impacted river systems detailed studies of the waikato rangitaiki mohaka ngaruroro and whanganui catchments show that the relative timing and scale of each eruption response phase differs between each catchment these reflect differences in catchment physiography and hydrology and the volume and type of pyroclastic material deposited in each ultimately the landscape response reflects the relative spatial distributions of and the volumetric ratios between the volumes of pyroclastic debris water and accommodation space in the basin cf kataoka and manville this volume

how do disconnected macropores in sloping soils facilitate preferential flow runoff from hillslopes is generated by processes such as infiltration excess and saturation overland flow subsurface stormflow and subsurface return flow preferential flow through macropores can affect any one of these runoff generation processes field studies at the hitachi ohta experimental watershed in japan have noted that self organization processes may manifest the connectivity of such subsurface flow paths particularly via macropores from hillslopes to stream channels it is well established from soil physics principles that the connectivity of macropore networks depends on soil wetness and this has been shown experimentally at hitachi ohta where subsurface flow and streamflow respond to thresholds of wetness numerical solutions to the three dimensional richards equation are derived for a sloping soil block containing a population of disconnected macropores of various sizes shapes and orientations solutions for the case of steady water flux applied to the surface of the soil block are evaluated to determine the conditions where the disconnected macropores become active in the flow process results show that subsurface flow is directed through the preferential flow network in the saturated portion of the soil but bypasses the macropores in the drier regions the preferential flow network expands as the degree of saturation increases the expanding network of active macropores leads to less resistance to overall flow in the domain and access to increased volumes of the flow domain although the individual macropores are disconnected it is argued that large localized hydraulic gradients can potentially lead to preferred zones of subsurface erosion in addition to the importance of these findings related to stormflow generation in catchments they add support to the concept of self organization of subsurface flow systems in soils copyright 2010 john wiley sons ltd

measurement and analysis of lunar basin depths from clementine altimetry altimetric profiles from the clementine lidar are used to calculate the depths of 29 large craters and basins on the moon plotting the depths of the best preserved structures together with values for simple and complex craters measured in pre clementine studies reveals an inflection in the depth diameter d d curve in addition to the one revealed by pre clementine data this inflection occurs in the diameter range that corresponds to the morphologic transition from complex crater to basin the best empirical power law fit for basin depths is log10 d 0 41 log10 d 0 57 this relationship is characterized by a lower slope than that for complex craters demonstrating that this morphologic transition corresponds to a further decrease in the depth of an impact structure relative to its diameter with increasing size qualitative consideration of possible causes for the second inflection leads to the conclusion that it is most likely a consequence of a short term modification mechanism that influences fundamental crater morphology such as the increasing influence of gravity with diameter thicknesses of maria in the major basins are calculated by assuming that their unfilled depths would follow thed drelation results are compared with previous estimates and yield thicknesses that are generally greater than those determined by studies of flooded craters and less than those obtained from analysis of gravity

thickness of a europan ice shell from impact crater simulations several impact craters on jupiter s satellite europa exhibit central peaks on the terrestrial planets central peaks consist of fractured but competent rock uplifted during cratering therefore the observation of central peaks on europa indicates that an ice layer must be sufficiently thick that the impact events did not completely penetrate it we conducted numerical simulations of vapor and melt production during cratering of water ice layers overlying liquid water to estimate the thickness of europa s icy crust because impacts disrupt material well beyond the zone of partial melting our simulations put a lower limit on ice thickness at the locations and times of impact we conclude that the ice must be more than 3 to 4 kilometers thick

comparison of central pit craters on mars mercury ganymede and the saturnian satellites we report on the first results of a large scale comparison study of central pit craters throughout the solar system focused on mars mercury ganymede rhea dione and tethys we have identified 10 more central pit craters on rhea dione and tethys than have previously been reported we see a general trend that the median ratio of the pit to crater diameter dp dc decreases with increasing gravity and decreasing volatile content of the crust floor pits are more common on volatile rich bodies while summit pits become more common as crustal volatile content decreases uplifted bedrock from below the crater floor occurs in the central peak upon which summit pits are found and in rims around floor pits which may or may not break the surface peaks on which summit pits are found on mars and mercury share similar characteristics to those of nonpitted central peaks indicating that some normal central peaks undergo an additional process to create summit pits martian floor pits do not appear to be the result of a central peak collapse as the median ratio of the peak to crater diameter dpk dc is about twice as high for central peaks summit pits than dp dc values for floor pits median dpk dc is twice as high for mars as for mercury reflecting differing crustal strength between the two bodies results indicate that a complicated interplay of crustal volatiles target strength surface gravity and impactor energy along with both uplift and collapse are involved in central pit formation multiple formation models may be required to explain the range of central pits seen throughout the solar system

extensional detachment faulting on the tyrrhenian margin of the southern apennines contractional belt italy the tectonic evolution of the campania margin during the late pliocene pleistocene is characterized by extensional deformation coeval with the opening of the marsili oceanic basin the initial stages of stretching are represented in the analysed area by the development of low angle normal faults that extended the belt in the same direction as the direction of spreading recognized for the oceanic basin detachment faulting was accompanied by the onset of magmatic activity and by major uplifts that resulted in the accumulation of thick conglomerate successions in the half grabens that developed in the upper plate of the extensional detachment deformation continued during the mid pleistocene with the formation of strike slip and normal faults trending almost parallel to the spreading direction of the marsili basin these faults dissected the extensional detachment and promoted counter clockwise block rotations about vertical axes which accommodated the ese directed stretching of the marsili basin and the consequent sinistral shear imposed on the southern apennine chain the development of a regional detachment fault along the tyrrhenian margin of campania explains the complex patterns of subsidence and uplift that characterize this area during the pleistocene and fits well within the regional geodynamic framework of the southern tyrrhenian sea

long term retention of impact crater topography on ganymede previous analyses into viscous relaxation of impact craters on ganymede have predicted short characteristic relaxation times of the order of 100 myr or less for larger craters in disagreement with the apparent great ages of ganymede s terrains by applying improved understanding of rheologic parameters and initial crater shapes to a viscoelastic model we calculate upper limit zero heat flow relaxation times in excess of the age of the solar system eliminating this discrepancy these very long relaxation times are not due to elastic effects but are simply due to the effective viscosity of water ice at the appropriate temperatures and stresses

central pit and dome craters exposing the interiors of ganymede and callisto central pit craters on the large icy satellites ganymede and callisto are an unusual crater class perhaps related to the unusual properties of water ice the detailed morphology and dimensions of pit crater features differ from those of smaller normal complex craters on these two satellites pit crater depths appear to be constant regardless of diameter rim collapse is also restricted relative to that in lunar craters or smaller ganymede craters the floors of pits in craters larger than 60 km are occupied by smooth bright domes pit to crater and dome to crater diameter ratios increase linearly with crater diameter and are indistinguishable on ganymede and callisto and with terrain type or surface longitude the floors and central structures of young bright rayed pit craters such as osiris are covered by a thin uniformly bright impact melt or frost deposit thus domes and pits form rapidly on the time scale of the impact itself rather than by long term postimpact intrusion or extrusion the bright domes in pit craters are most simply explained as the uplift and exposure of relatively ice rich material from depths of 3 5 to 5 km during impact this process is almost directly analogous to the uplift and exposure of anamolous deep seated material observed in terrestrial and lunar craters the unusual pit morphology on icy satellites may be the result of impact into crust that is mechanically much weaker at shallow depth than on rocky bodies such as the moon because crater morphology is strongly dependent on ice rock composition the similarity of pit and dome dimensions on ganymede and callisto indicates that the structure and rheology of the crusts of these bodies down to depths of 10 km are very similar and have been for several b y pit crater morphology indicates that the crusts of both satellites are probably ice rich and differentiated

impact craters in the northern hemisphere of mars layered ejecta and central pit characteristics mars global surveyor mgs and mars odyssey data are being used to revise the catalog of large martian impact craters analysis of data in the revised catalog provides new details on the distribution and morphologic details of 6795 impact craters in the northern hemisphere of mars this report focuses on the ejecta morphologies and central pit characteristics of these craters the results indicate that single layer ejecta sle morphology is most consistent with impact into an ice rich target double layer ejecta dle and multiple layer ejecta mle craters also likely form in volatile rich materials but the interaction of the ejecta curtain and target produced vapor with the thin martian atmosphere may be responsible for the large runout distances of these ejecta pancake craters appear to be a modified form of double layer craters where the thin outer layer has been destroyed or is unobservable at present resolutions pedestal craters are proposed to form in an ice rich mantle deposited during high obliquity periods from which the ice has subsequently sublimated central pits likely form by the release of vapor produced by impact into ice soil mixed targets therefore results from the present study are consistent with target volatiles playing a dominant role in the formation of crater morphologies found in the martian northern hemisphere

impact craters on titan five certain impact craters and 44 additional nearly certain and probable ones have been identified on the 22 of titan s surface imaged by cassini s high resolution radar through december 2007 the certain craters have morphologies similar to impact craters on rocky planets as well as two with radar bright jagged rims the less certain craters often appear to be eroded versions of the certain ones titan s craters are modified by a variety of processes including fluvial erosion mass wasting burial by dunes and submergence in seas but there is no compelling evidence of isostatic adjustments as on other icy moons nor draping by thick atmospheric deposits the paucity of craters implies that titan s surface is quite young but the modeled age depends on which published crater production rate is assumed using the model of artemieva and lunine 2005 suggests that craters with diameters smaller than about 35 km are younger than 200 million years old and larger craters are older craters are not distributed uniformly xanadu has a crater density 2 9 times greater than the rest of titan and the density on equatorial dune areas is much lower than average there is a small excess of craters on the leading hemisphere and craters are deficient in the north polar region compared to the rest of the world the youthful age of titan overall and the various erosional states of its likely impact craters demonstrate that dynamic processes have destroyed most of the early history of the moon and that multiple processes continue to strongly modify its surface the existence of 24 possible impact craters with diameters less than 20 km appears consistent with the ivanov basilevsky and neukum 1997 model of the effectiveness of titan s atmosphere in destroying most but not all small projectiles

ejection behavior characteristics in experimental cratering in sandstone targets within the frame of the memin research unit multidisciplinary experimental and numerical impact research network impact experiments on sandstone targets were carried out to systematically study the influence of projectile mass velocity and target water saturation on the cratering and ejection processes the projectiles were accelerated with two stage light gas guns ernst mach institute onto fine grained targets seeberger sandstone with about 23 porosity collection of the ejecta on custom designed catchers allowed determination of particle shape size distribution ejection angle and microstructures mapping of the ejecta imprints on the catcher surface enabled linking of the different patterns to ejection stages observed on high speed videos the increase in projectile mass from 0 067 to 7 1 g correlates with an increase in the total ejected mass ejecta angles however are similar in range for all experiments the increase in projectile velocity from 2 5 to 5 1 km s 1 correlates with a total ejecta mass increase as well as in an increase in comminution efficiency and a widening of the ejecta cone a higher degree of water saturation of the target yields an increase in total ejecta mass up to 400 with respect to dry targets higher ejecta velocity and a steeper cone these data in turn suggest that the reduced impedance contrast between the quartz grains of the target and the pores plays a primary role in the ejecta mass increase while vaporization of water determines the ejecta behavior concerning ejecta velocity and particle distribution

fill and spill hillslope runoff representation with a richards equation based model integrated surface subsurface hydrological models isshms are well established numerical tools to investigate water flow and contaminant transport processes over a wide range of spatial and temporal scales however their ability to correctly reproduce the response of hydrological systems to natural and anthropogenic forcing depends largely on the accuracy of model parameterization including the level of detail in the representation of the bedrock this latter is typically incorporated in some way via the bottom boundary of the model domain issues of bedrock topography variable soil depth and the resulting hillslope storage distribution representation in isshms are vitally important but to date have received little attention a standard treatment of the bottom boundary especially in large catchment and continental scale applications is to model it as a flat or inclined e g parallel to the surface impermeable base sometimes with some simple leakage term this approach does not allow the model to correctly reproduce bedrock controlled threshold responses such as the fill and spill process as observed across many hillslope and catchment scale field studies it is still unclear whether richards equation based numerical models are actually able to generate such responses here we use a richards equation based model cathy to simulate internal transient subsurface stormflow dynamics observed at the well characterized panola experimental hillslope in georgia usa soil and bedrock properties were calibrated starting from values reported in previous studies at the site our simulation results show that the model was able to reproduce threshold mechanisms which in turn affected both the integrated and distributed hydrologic responses of the panola hillslope we then developed a set of virtual experiments with modified boundary conditions and base topography at the soil bedrock interface to explore the bedrock boundary control on transient groundwater flow patterns our results show that accurate representation of the lower boundary is crucial for isshm simulations of hillslope scale storm runoff and for connectivity of transient groundwater we summarize our findings with the development of a new bedrock topographic wetness index that takes into account the unsaturated infiltration dynamics the index is able to help represent the spatial variability of water table response over the bedrock surface compared to standard surface topography based indices this new index may be useful in larger scale isshm applications where an exact bedrock topography representation is not feasible or possible

hydrological processes letters topographic controls on subsurface storm flow at the hillslope scale for two hydrologically distinct small catchmetns controls on hillslope ow pathways are still not well understood despite the many di erent studies reported since the pioneering work of hewlett 1961 in a wide range of recent modelling studies it has been assumed that ow directions can be related to hydraulic gradients derived from surface topography this assumption leads to believable maps of predictions of soil saturation and is convenient because of the increasing availability of digital terrain maps dtms the validity of the resulting spatial patterns throughout the watershed however have not been fully assessed although see the discussion in beven et al 1995 and the recent studies of nyberg 1996 and crave and gascuel odoux 1997 this results from the di culty of obtaining adequate spatial coverage of hydrological variables and the scale problem of relating point measurements to predictions at the dtm grid scale recent hillslope analyses of soil moisture distributions have identi ed that ow paths do not necessarily converge to hollow regions anderson 1982 that they may require dynamic spatial representations barling et al 1994 and that their prediction using topographically derived indices have had mixed results burt and butcher 1986 moore and thompson 1996 spatial representations of topographically driven indices therefore need further exploration a possible way forward is to conduct more detailed studies of the dynamics of subsurface ow at the hillslope scale analysis of a natural hillslope combines integrated trench ow and point scale soil moisture measurements coupled with a detailed understanding of surface and subsurface features such data provide a more comprehensive assessment of the assumption used in many modelling studies that hillslope ow is controlled by surface topography in this letter we address the question of whether it is appropriate to use surface topography to describe hillslope ow paths or if it is not more appropriate to use subsurface gradients relating to the soil bedrock interface or the hydrologically impeding layer we present examples for two hillslopes in di erent hydrogeological climatic settings analyses of the distribution of topographic index patterns derived from digital terrain analysis for both surface and subsurface topography are related to observational patterns of subsurface storm ow along arti cial trench face sections

hillslope riparian stream connectivity and flow directions at the panola mountain research watershed to obtain a better understanding of water s journey from the hillslope to the stream water level time series from 26 groundwater wells in a hillslope riparian study area in the panola mountain res

late quaternary incision and deposition in an active volcanic setting the volturno valley fill southern italy abstract article history received 30 january 2012received in revised form 1 august 2012accepted 5 october 2012available online 17 october 2012editor g j weltjekeywords incised valleysequence stratigraphyforaminifer and ostracod analysisvolturno riverquaternary extensive illustration of depositional facies ostracod and foraminiferal assemblages and late quaternarystratigraphic architecture is offered for the rst time from beneath the modern coastal plain of volturnoriver the longest river in southern italy proximity to an active volcanic district including quiescent vesuviusvolcano provides an easily identi able stratigraphic marker campania grey tuff or cgt up to 55 m thick emplaced39 ky cal bpbyalarge volumeexplosivepyroclasticeruption identi cationoftopcgttoamaximumdepthof30 mallowstracingouttheshapeofa15 20 kmwidelatequaternarypalaeovalleyincisedbyvolturnoriver into the thick ignimbritic unit immediately after its deposition a terraced palaeotopography of the valley anksisreconstructedonthebasisofcoredata abovethebasal uvialdeposits theearlyholocenetransgressivefacies consist of asuite of estuarine freshwater to brackish deposits these are separated from overlyingtransgressive barrier sands by a distinctive wave ravinement surface upwards a distinctive shallowing upward succession of middle late holocene age is interpreted to re ect initiation and subsequent progradationof a wave dominated delta system with anking strandplains in response to reduced rate of sea level rise theturnaround from transgressive to highstand conditions is identi ed on the basis of subtle changes in themeiofauna theseenabletrackingofthemaximum oodingsurfaceintoitsupdip lagoonal estuarine counterpart thus highlighting the role of re ned palaeontological criteria as a powerf ul tool for high resolution sequence stratigraphic studies 2012 elsevier b v all rights reserved

central pit craters on ganymede central pit craters are common on mars ganymede and callisto and thus are generally believed to require target volatiles in their formation the purpose of this study is to identify the environmental conditions under which central pit craters form on ganymede we have conducted a study of 471 central pit craters with diameters between 5 and 150 km on ganymede and compared the results to 1604 central pit craters on mars diameter range 5 160 km both floor and summit pits occur on mars whereas floor pits dominate on ganymede central peak craters are found in similar locations and diameter ranges as central pit craters on mars and overlap in location and at diameters 60 km on ganymede central pit craters show no regional variations on either ganymede or mars and are not concentrated on specific geologic units central pit craters show a range of preservation states indicating that conditions favoring central pit formation have existed since crater retaining surfaces have existed on ganymede and mars central pit craters on ganymede are generally about three times larger than those on mars probably due to gravity scaling although target characteristics and resolution also may play a role central pits tend to be larger relative to their parent crater on ganymede than on mars probably because of ganymede s purer ice crust a transition to different characteristics occurs in ganymede s icy crust at depths of 4 7 km based on the larger pit to crater diameter relationship for craters in the 70 130 km diameter range and lack of central peaks in craters larger than 60 km diameter we use our results to constrain the proposed formation models for central pits on these two bodies our results are most consistent with the melt drainage model for central pit formation

late quaternary depositional architecture of po and tevere river deltas italy and worldwide comparison with coeval deltaic successions abstract po and tevere rivers form two of the most important deltas of the whole mediterranean area detailed investigations have been carried out in the last decade beneath the present delta plains of these two river systems using borehole data correlation with the aid of radiocarbon dates and other dating methods pollens archaeology a detailed sequence stratigraphic framework has been constructed in both areas especially for the last glacial interglacial cycle regional subsidence combined with short term sea level fluctuations of relatively high amplitude played a fundamental role in creating subtracting accommodation during the long phase of falling sea level which followed the tyrrhenian substage 5e transgressive event a discontinuous record of this phase is present in the subsurface of the po plain whereas poor or no preservation has been detected in the tevere area progradational lowstand wedges accumulated during the last glacial maximum mostly in the central part of the basins far from the present deltas and are lacking in the study areas where a hiatal surface is invariably recorded below the transgressive deposits glacioeustasy exerted a major control on sedimentation in both areas during the latest pleistocene holocene sea level rise infilling of fluvial valleys and rapid landward migration of barrier lagoon systems in the context of wave dominated estuaries characterized the transgressive phase in both po and tevere systems in place drowning and transgressive submergence mechanisms of barrier migration were effective predominantly between 13 5 and 9 ka bp in contrast shoreface retreat was dominant in the late transgressive phase the maximum flooding surface mfs can be traced physically from continental to marine deposits and has similar characteristics in the po and tevere river systems being marked by peat layers or lagoonal deposits at landward locations and by distinctive lithological characteristics and micro and macrofossils assemblages basinwards above the mfs the early highstand systems tract records initially the filling of the lagoons followed by the rapid progradation of wave dominate delta systems and flanking strandplains autocyclic processes such as distributary channel avulsion delta lobe abandonment and local subsidence due to sediment compaction were the fundamental controlling factors on sedimentation during deposition of the hst the stratigraphic architecture of the post glacial po and tevere delta complexes closely resembles the basic facies successions documented from coeval deposits of wave dominated and wave influenced clastic coasts both locally within the mediterranean area and in other parts of the world our study emphasizes however some additional features and major differences with previously published depositional models including i the development of backstepping wave dominated estuaries during transgression ii consistent changes through time in the mechanism of barrier migration iii a later construction of the delta systems with respect to what traditionally considered

a hybrid 3d hillslope hydrological model for use in earth system models hillslope scale rainfall runoff processes leading to a fast catchment response are not explicitly included in land surface models lsms for use in earth system models esms due to computational constraints this study presents a hybrid 3d hillslope hydrological model h3d that couples a 1 d vertical soil column model with a lateral pseudo 2d saturated zone and overland flow model for use in esms by representing vertical and lateral responses separately at different spatial resolutions h3d is computationally efficient the h3d model was first tested for three different hillslope planforms uniform convergent and divergent we then compared h3d with single and multiple soil columns with a complex physically based 3 d model and a simple 1 d soil moisture model coupled with an unconfined aquifer as typically used in lsms it is found that simulations obtained by the simple 1 d model vary considerably from the complex 3 d model and are not able to represent hillslope scale variations in the lateral flow response in contrast the single soil column h3d model shows a much better performance and saves computational time by 2 3 orders of magnitude compared with the complex 3 d model when multiple vertical soil columns are implemented the resulting hydrological responses soil moisture water table depth and base flow along the hillslope from h3d are nearly identical to those predicted by the complex 3 d model but still saves computational time as such the computational efficiency of the h3d model provides a valuable and promising approach to incorporating hillslope scale hydrological processes into continental and global scale esms

a comparison of simplified methods for routing topographically driven subsurface flow a series of numerical experiments are used to evaluate the accuracy of two approaches for modeling topographically driven subsurface flow suitable for inclusion in spatially distributed hydrologic models the first is an explicit grid cell by grid cell approach and the second is a statistical dynamic method widely used in topmodel both approaches were compared with analytical solutions to the kinematic wave equation for flow down an inclined plane of constant slope using a power law transmissivity function the hillslope discharge and water table profiles simulated by the explicit method were in good agreement with the analytic solution in all test cases the statistical dynamic method converged on the correct steady state solution but failed to reproduce accurately transient conditions the two algorithms were then compared using a 30 m dem representation of the mahantango pa basin and hourly precipitation measured at the site the agreement in discharge between the two methods improved with increasing soil thickness surface conductivity and power law exponent however the percent root mean squared difference rmsd in hourly discharge was above 20 percent in all cases the statistical dynamic model was then calibrated to discharge simulated by the explicit method calibration was most effective for soils with low power law exponents generally producing discharge hydrographs in closemore agreement for soils with linear transmissivity profiles however even under these conditions there are large discrepancies between local water table depths simulated by the two models the level of agreement is best during dry conditions and decreases during wetter conditions as the number of cells with surface soil saturation increases less

modeling the morphological diversity of impact craters on icy satellites abstract impact craters on icy satellites display a wide range of morphologies some of which have no counterpart on rocky bodies numerical simulation studies have struggled to reproduce the diversity of features such as central pits and transitions in crater depth with increasing diameter observed on the icy galilean satellites the transitions in crater depth at diameters of about 26 and 150 km on ganymede and callisto have been interpreted as reflecting subsurface structure using the cth shock physics code we model the formation of craters with diameters between 400 m and about 200 km on ganymede using different subsurface temperature profiles our calculations include recent improvements in the model equation of state for h 2 o and quasi static strength parameters for ice we find that the shock induced formation of dense high pressure polymorphs ices vi and vii creates a gap in the crater excavation flow which we call discontinuous excavation for craters larger than about 20 km discontinuous excavation concentrates a hot plug of material 270 k and mostly on the melting curve in the center of the crater floor the size and occurrence of the hot plug are in good agreement with the observed characteristics of central pit craters and we propose that a genetic link exists between them we also derive depth versus diameter curves for different internal temperature profiles in a 120 k isothermal crust calculated craters larger than about 30 km diameter are deeper than observed and do not reproduce the transition at about 26 km diameter calculated crater depths are shallower and in good agreement with observations between about 30 and 150 km diameter using a warm thermal gradient representing a convective interior hence the depth to diameter transition at about 26 km reflects thermal weakening of ice finally simulation results generally support the hypothesis that the anomalous interior morphologies for craters larger than 100 km are related to the presence of a subsurface ocean

impact breaching of europa s ice constraints from numerical modeling numerical simulations show that impactors can penetrate europa s ice creating conduits to the underlying ocean breaching becomes inevitable when transient cavity depth exceeds 90 of ice thickness results indicate that a 0 5 km comet would penetrate 5 km ice and a 5 km comet could breach 40 km ice thinner ice would be breached more frequently thicker ice less so but even the 40 km upper estimates for ice thickness would be penetrated by comets with recurrence intervals less than 250 ma if actual ice thickness is 8 13 km indicated by comparing europan and simulated crater geometries the ocean could be exposed by impactors in the range 0 7 1 5 km which have recurrence intervals 3 to 7 ma thus it seems that europa s ice has been penetrated often in the past and possibly in geologically recent time the largest known impact sites callanish and tyre probably represent transition from craters to penetrating impacts the geomorphic expression of full penetration must exist on the surface chaos terrain is a candidate astrobiological materials could be transported to the ocean via these impact created conduits

dome craters on ganymede voyager observations of ganymede show broad high albedo topographic domes situated within the central pits of some impact craters referred to in this study as dome craters of 56 dome craters identified on ganymede all but two can be placed into one of two classes based on the ratio of dome diameter to crater rim diameter two new hypotheses for the origin of the domes involving diapirism as an agent of dome formation are offered implicit in both hypotheses are possible regional heat flux variations under these scenarios relaxation of crater relief may not be homogeneous in space and or time and crater morphology may not be a consistent indicator of crater age plutonic intrusions within the upper lithospheres of ganymede and callisto may have played a far more important role in heat transport on these satellites than previously noted

modeling damage and deformation in impact simulations numerical modeling is a powerful tool for investigating the formation of large impact craters but is one that must be validated with observational evidence quantitative analysis of damage and deformation in the target surrounding an impact event provides a promising means of validation for numerical models of terrestrial impact craters particularly in cases where the final pristine crater morphology is ambiguous or unknown in this paper we discuss the aspects of the behavior of brittle materials important for the accurate simulation of damage and deformation surrounding an impact event and the care required to interpret the results we demonstrate this with an example simulation of an impact into a terrestrial granite target that produces a 10 km diameter transient crater the results of the simulation are shown in terms of damage a scalar quantity that reflects the totality of fragmentation and plastic strain both total plastic strain the accumulated amount of permanent shear deformation regardless of the sense of shear and net plastic strain the amount of permanent shear deformation where the sense of shear is accounted for damage and plastic strain are both greatest close to the impact site and decline with radial distance however the reversal in flow patterns from the downward and outward excavation flow to the inward and upward collapse flow implies that net plastic strains may be significantly lower than total plastic strains plastic strain in brittle rocks is very heterogeneous however continuum modeling requires that the deformation of the target during an impact event be described in terms of an average strain that applies over a large volume of rock large compared to the spacing between individual zones of sliding this paper demonstrates that model predictions of smooth average strain are entirely consistent with an actual strain concentrated along very narrow zones furthermore we suggest that model predictions of total accumulated strain should correlate with observable variations in bulk density and seismic velocity

the galilean satellites nasa s galileo mission to jupiter and improved earth based observing capabilities have allowed major advances in our understanding of jupiter s moons io europa ganymede and callisto over the past few years particularly exciting findings include the evidence for internal liquid water oceans in callisto and europa detection of a strong intrinsic magnetic field within ganymede discovery of high temperature silicate volcanism on io discovery of tenuous oxygen atmospheres at europa and ganymede and a tenuous carbon dioxide atmosphere at callisto and detection of condensed oxygen on ganymede modeling of landforms seen at resolutions up to 100 times as high as those of voyager supports the suggestion that tidal heating has played an important role for io and europa

the origin of lunar concentric craters abstract lunar concentric craters are a unique class of impact craters because the interior of the craters contains a concentric ridge but their formation mechanism is unknown in order to determine the origin of concentric craters we examined multiple working hypotheses which include eight impact related and endogenic processes we analyzed data sets that originated from instruments onboard clementine kaguya and the lunar reconnaissance orbiter to characterize the morphology spatial distribution composition and absolute model ages of 114 concentric craters concentric craters contain five key properties 1 a concentric ridge 2 anomalously shallow floors 3 their occurrence is concentrated near mare margins and in mare pond regions 4 the concentric ridge composition is similar to the surrounding area and 5 concentric crater ages are eratosthenian and older these five key properties served as constraints for testing impact related and endogenic mechanisms of formation we find that most impact related hypotheses cannot explain the spatial and age distribution of concentric craters as for endogenic hypotheses we deduce that igneous intrusions are the likely mechanism that formed concentric craters because of the close relationship between concentric craters and floor fractured craters and the concentration of both features near mare highland boundaries and in mare ponds furthermore we observe that floor fractured craters are common at crater diameters 15 km whereas concentric craters are common at crater diameters 15 km produce floor fractured craters

a depth versus diameter scaling relationship for the best preserved melt bearing complex craters on mars abstract we use topographic data to show that impact craters with pitted floor deposits are among the deepest on mars this is consistent with the interpretation of pitted materials as primary crater fill impactite deposits emplaced during crater formation our database consists of 224 pitted material craters ranging in size from 1 to 150 km in diameter our measurements are based on topographic data from the mars orbiter laser altimeter mola and the high resolution stereo camera hrsc we have used these craters to measure the relationship between crater diameter and the initial post formation depth depth was measured as maximum rim to floor depth d r but we also report the depth measured using other definitions the database was down selected by refining or removing elevation measurements from problematic craters affected by processes and conditions that influenced their d r d such as pre impact slopes topography and later overprinting craters we report a maximum deepest and mean scaling relationship of d r 0 347 0 021 d 0 537 0 017 and d r 0 323 0 017 d 0 538 0 016 respectively our results suggest that significant variations between previously reported mola based d r vs d relationships may result from the inclusion of craters that 1 are influenced by atypical processes e g highly oblique impact 2 are significantly degraded 3 reside within high strength regions and 4 are transitional partially collapsed by taking such issues into consideration and only measuring craters with primary floor materials we present the best estimate to date of a mola based relationship of d r vs d for the least degraded complex craters on mars this can be applied to crater degradation studies and provides a useful constraint for models of complex crater formation

pristine impact crater morphology on pluto expectations for new horizons abstract this paper combines previous cratering studies and numerical modeling of the impact process at different impact velocities to predict crater morphology on pluto as an icy body pluto s craters are expected to be similar in morphology to those on the icy satellites lesser depth diameter ratios d d shallower wall slopes and the development of central uplifts in craters of smaller rim to rim diameter than craters on rocky bodies of similar gravity the low impact velocity of the pluto system 2 km s 1 might cause deviation from this generalization as the simulations presented in this work suggest that decreasing impact velocity from 10 km s 1 to 2 km s 1 results in deeper craters larger d d and a simple to complex transition diameter at larger crater sizes than predicted based on gravity scaling alone d 6 km conversely decreasing impact velocity from 2 km s 1 to 300 m s 1 produced smaller d d akin to the lower d d noted for secondary craters this complex relationship between impact velocity and d d suggests that there might be a larger range of pristine simple crater depths on pluto than on bodies with higher mean impact velocity the low impact velocities and correspondingly low volumes of impact melt generated at pluto might prevent the occurrence or limit the size of floor pits if their formation involves impact melt water the presence or not of central floor pit craters on pluto will thus provide a valuable test of floor pit formation theories the presence of summit pits or concentric craters on pluto is plausible and would indicate the presence of layering in the near sub surface palimpsests multi ring basins and other crater morphologies associated with high heat flow are not expected and would have important implications for pluto s thermal history if observed by new horizons

the theoretical plausibility of central pit crater formation via melt drainage central pit craters are seen in large craters on some icy satellites and on mars we investigate the hypothesis that central pits form when impact melt drains into fractures beneath the impact crater for this process to occur the volume of melt generated during the impact the volume of void space in fractures beneath the impact crater and the volume of melt able to drain before the fractures freeze shut all must exceed the volume of the observed central pits we estimate the volume of melt generated using results from previous numerical modeling studies the fracture volume is estimated using gravity anomalies over terrestrial craters to estimate the amount of melt able to drain before freezing we consider flow through plane parallel fractures these calculations all suggest that enough liquid water could drain into fractured ice beneath a crater on ganymede to form a central pit on earth and the moon silicate impact melt will freeze before a large volume is able to drain so we do not expect to see central pits in impact craters in targets with no ice in summary we find our calculations are consistent with observed central pits in craters on ganymede and the lack of central pits in craters on earth and the moon

gypsies in the palace experimentalist s view on the use of 3 d physics based simulation of hillslope hydrological response as a fundamental unit of the landscape hillslopes are studied for their retention and release of water and nutrients across a wide range of ecosystems the understanding of these near surface processes is relevant to issues of runoff generation groundwater surface water interactions catchment export of nutrients dissolved organic carbon contaminants e g mercury and ultimately surface water health we develop a 3 d physics based representation of the panola mountain research watershed experimental hillslope using the tough2 sub surface flow and transport simulator a recent investigation of sub surface flow within this experimental hillslope has generated important knowledge of threshold rainfall runoff response and its relation to patterns of transient water table development this work has identified components of the 3 d sub surface such as bedrock topography that contribute to changing connectivity in saturated zones and the generation of sub surface stormflow here we test the ability of a 3 d hillslope model both calibrated and uncalibrated to simulate forested hillslope rainfall runoff response and internal transient sub surface stormflow dynamics we also provide a transparent illustration of physics based model development issues of parameterization examples of model rejection and usefulness of data types e g runoff mean soil moisture and transient water table depth to the model enterprise our simulations show the inability of an uncalibrated model based on laboratory and field characterization of soil properties and topography to successfully simulate the integrated hydrological response or the distributed water table within the soil profile although not an uncommon result the failure of the field based characterized model to represent system behaviour is an important challenge that continues to vex scientists at many scales we focus our attention particularly on examining the influence of bedrock permeability soil anisotropy and drainable porosity on the development of patterns of transient groundwater and sub surface flow internal dynamics of transient water table development prove to be essential in determining appropriate model parameterization copyright 2010 john wiley sons ltd

33 000 yr k ar dating of the volcano tectonic horst of the isle of ischia gulf of naples the gulf of naples corresponds to a tectonic sink connected with recent volcanic activity in the south campanian area phlegrean fields ischia and vesuvius at its extreme northwest the isle of ischia was early recognized as a volcano tectonic horst by rittmann1 previous data2 concluded that its uplift ended around 300 000 yr and that the green tuff formation of which it is predominantly composed had an age of some 700 000 yr but tectonic and morphological studies together with original tephrostratigraphical observations on the slope of the horst led us to do some new k ar datings these revealed that the 780 m uplift of the horst from the sea level is younger than 33 000 yr the green tuff which was considered to be the oldest volcanic unit in the island is now dated at 56 000 yr its eruption following the dismantlement of a first volcanic complex now dated as not older than 130 000 yr

holocene evolution of the song hong red river delta system northern vietnam abstract the song hong red river delta located on the western coast of the gulf of bac bo tonkin in the south china sea formed as a result of the song hong sediment discharge throughout the holocene the river s sedimentary basin upstream from the delta plain is not large the delta plain comprises emerged tidal mangrove flats formed during the sea level highstand at 2 3 m 6 4 cal kyr bp and a beach ridge strandplain with straight to lobate beach ridges on the landward and seaward sides of the delta plain respectively the delta affords us the opportunity to examine river mouth morphodynamics comprehensively in relation to sediment discharge and sea level changes in this paper we describe the holocene evolution of the song hong delta system and the river mouth morphodynamics on the basis of seven sediment cores each 30 70 m long taken from the delta plain during 1999 2001 and 101 radiocarbon dates obtained from the core sediments sediments from the seven cores consisting of incised valley fills since the last glacial maximum can be divided in ascending order into fluvial sediments composed of gravelly sand and mottled clay tide influenced estuarine sediments containing shell and wood fragments and deltaic sediments composed of tide influenced sand and mud deposits in which the contents of sand and wood fragments increase upward by applying sequence stratigraphic concepts a transgressive surface can be identified at the gravelly sand mottled clay boundary and the maximum flooding surface can be identified at the estuarine deltaic sediments boundary the lowstand systems tract transgressive systems tract and highstand systems tract record 15 15 9 and 9 0 cal kyr bp respectively during the past 9 kyr the majority of the sediment discharged by the song hong accumulated in the incised valley and enhanced progradation at the river mouth the river mouth prograded from the bay head toward the gulf and its morphology changed from funnel shaped 9 6 cal kyr bp to straight 6 2 cal kyr bp and finally to lobate 2 0 cal kyr bp the morphological change from a funnel shaped to straight coast is interpreted to have been closely related to a hydrologic regime shift from a tide dominated bay head setting to a wave influenced open coast setting the cessation of the sea level rise at 6 cal kyr bp may have played only a small role in the change of river mouth morphology because the progradation rate decelerated from 22 to 4 m yr instead of accelerating at that time the river mouth morphodynamic change from straight to lobate was largely caused by an increase in the song hong sediment discharge from 17 27 9 2 cal kyr bp to 49 million t yr 2 0 cal kyr bp as a result of anthropogenic deforestation along the upper reaches of the song hong