seasonal activity and morphological changes in martian gullies abstract recent studies of martian dune and non dune gullies have suggested a seasonal control on present day gully activity the timing of current gully activity especially activity involving the formation or modification of channels which commonly have been taken as evidence of fluvial processes has important implications regarding likely gully formation processes and necessary environmental conditions in this study we describe the results of frequent meter scale monitoring of several active gully sites by the high resolution imaging science experiment hirise on the mars reconnaissance orbiter mro the aim is to better assess the scope and nature of current morphological changes and to provide improved constraints on timing of gully activity on both dune and non dune slopes our observations indicate that 1 gully formation on mars is ongoing today and 2 the most significant morphological changes are strongly associated with seasonal frost and defrosting activity observed changes include formation of all major components of typical gully landforms although we have not observed alcove formation in coherent bedrock these results reduce the need to invoke recent climate change or present day groundwater seepage to explain the many martian gullies with pristine appearance

middle oligocene extension in the mediterranean calabro peloritan belt southern italy insights from the aspromonte nappes pile the calabro peloritan belt constitutes the eastward termination of the southern segment of the alpine mediterranean belt this orogenic system was built up during the convergence between the eurasian and the african plates roughly directed north south since the upper cretaceous it was subsequently fragmented during the opening of the western mediterranean basins since oligocene times the curved shape of the calabro peloritan belt was acquired during the opening of the tyrrhenian basin since tortonian the origin kinematics and significance of the calabro peloritan tectonic pile are still debated our data in the aspromonte massif of southern calabria reveal an alpine history marked by two main superimposed kinematic regimes i a first phase corresponds to the piling up of basement nappes with a top to the se vergence i e in a direction orthogonal to the belt trend and towards the adriatic foreland this external vergence is similar to what is observed in both northeastern sicily and northern calabria in sicily the age of nappe piling is alpine as evidenced by pinched slices of mesozoic sediments in the aspromonte massif thrusting age is less constrained our data suggest remnants of late hercynian structuration before the alpine stacking ii a second phase corresponds to the thinning of the continental crust dated at around 30 ma by both geochronological and stratigraphical data this extension is mainly localized on two low angle detachment contacts with top to the ne displacement the lower one corresponds to the reworking of the former main nappe contact the upper one is a large detachment fault cutting across the pile from upper sedimentary levels down to metamorphic basement extension of similar alpine age and similar internal vergence has been already recognized in other parts of the calabro peloritan arc in the basement nappes of northeastern sicily and in the ophiolitic units of northern calabria coming back to the original geometry and position of the calabro peloritan belt before its bending and the opening of the liguro provencal and tyrrhenian basins we evidence a homogeneous oligocene ne sw extension all along the calabro peloritan segment of the alpine mediterranean belt this tectonometamorphic history is best explained within the framework of the continuous tertiary westward dipping subduction of the tethyan oceanic domain below the european active margin and the progressive eastward retreat of the apennine trench since oligocene times

geomaterials in cultural heritage this volume gives a broad view of the application of geoscience techniques to the study of monuments and objects from excavations and museums including their origin technique of manufacture age and conservation it reaffirms the important contribution of geosciences in the interdisciplinary approach to the study of complex materials such as minerals rocks glass metals mortar plaster slags and pottery the papers in this book cover three topics the study of pottery glass stone and mortar the application of raman spectroscopy to a wide variety of objects and the future of archaeometry interdisciplinary studies including field geology geophysics microscopy textural analysis physical methods and geochemistry are used to unlock information from the ancient materials such as the provenance of the raw materials the firing technology the ancient recipes and the alteration pathways

subaerial river bank erosion processes and their interaction with other bank erosion mechanisms on the river arrow warwickshire uk river bank erosion occurs primarily through a combination of three mechanisms mass failure fluvial entrainment and subaerial weakening and weathering subaerial processes are often viewed as preparatory processes weakening the bank face prior to fluvial erosion within a river basin downstream process domains occur with subaerial processes dominating the upper reaches fluvial erosion the middle and mass failure the lower reaches of a river the aim of this paper is to demonstrate that a subaerial processes may be underestimated as an erosive agent and b process dominance has a temporal as well as spatial aspect bank erosion on the river arrow warwickshire uk was monitored for 16 months december 1996 to march 1998 using erosion pins variations in the rate and aerial extent of erosion are considered with reference to meteorological data throughout the first 15 months all erosion recorded was subaerial resulting in up to 181 mm a 1 of bank retreat compared with 13 to 27 mm a 1 reported by previous researchers while the role of subaerial processes as preparatory is not contended it is suggested that such processes can also be erosive the three bank erosion mechanisms operate at different levels of magnitude and frequency and the river arrow data demonstrate this thus the concept of process dominance has a temporal as well as spatial aspect particularly over the short time periods often used for studying processes in the field perception of the relative efficacy of each erosive mechanism will therefore be influenced by the temporal scale at which the bank is considered with the advent of global climate change both these magnitude frequency characteristics and the consequent interaction of bank erosion mechanisms may alter it is therefore likely that recognition of this temporal aspect of process dominance will become increasingly important to studies of bank erosion processes copyright 2001 john wiley sons ltd

stability of streambanks formed in partially saturated soils and effects of negative pore water pressures the sieve river italy abstract streambanks of alluvial channels are usually composed of loose materials which are unsaturated in ambient conditions unsaturated soils are subject to negative pore water pressures which cause an apparent cohesion the latter is the main factor in allowing the stability of near vertical banks even during moderate in bank flow events the apparent cohesion can be strongly reduced as the material approaches full saturation therefore during the drawdown phase as the confining pressure of the water in the channel disappears a bank failure is likely to occur channel bed level lowering along the sieve river central italy has caused widespread bank instability a geomorphological reconnaissance of forms and processes was followed by in situ tests to determine the shear strength of the banks interpretation of the tests and a streambank stability analysis were based on concepts of soil mechanics for unsaturated soils in order to obtain relations between bank angle and height in limit equilibrium conditions a stability chart was obtained with curves for different apparent cohesion values and a stability analysis was performed taking into account the effects of flow events in order to investigate the pore pressure effects a series of piezo tensiometers were installed in a streambank of the sieve river data from a 1 year monitoring period show variations in pore water pressure and matric suction as a consequence of rainfall evapotranspiration and water stage variations a planar failure with a tension crack occurred in the upper cohesive part of the bank during december 1996 the safety factor has been expressed as a function of the geometry of the bank and of the shear strength of the material safety factor variations through time are therefore shown as a function of seasonal variations in matric suction

a physically based model to predict hydraulic erosion of fine grained riverbanks the role of form roughness in limiting erosion hydraulic erosion of bank toe materials is the dominant factor controlling the long term rate of riverbank retreat in principle hydraulic bank erosion can be quantified using an excess shear stress model but difficulties in estimating input parameters seriously inhibit the predictive accuracy of this approach herein a combination of analytical modeling and novel field measurement techniques is employed to improve the parameterization of an excess shear stress model as applied to the lower mekong river boundary shear stress is estimated using a model kean and smith 2006a 2006b for flow over the irregular bank topography that is characteristic of fine grained riverbanks bank erodibility parameters were obtained using a cohesive strength meter tolhurst et al 1999 the new model was used to estimate annual bank erosion rates via integration across the mekong s annual flow regime importantly the simulations represent the first predictions of hydraulic bank erosion that do not require recourse to calibration thereby providing a stronger physical basis for the simulation of bank erosion model predictions as evaluated by comparing simulated annual rates of bank toe retreat with estimates of bank retreat derived from analysis of aerial photographs and satellite imagery indicate a tendency to overpredict erosion root mean square error equals 0 53 m yr form roughness induced by bank topographic features is shown to be a major component 61 85 of the spatially averaged total shear stress and as such it can be viewed as an important factor that self limits bank erosion

long term monitoring of martian gully formation and evolution with mro hirise abstract gully landforms are commonly taken as evidence for surface liquid water in the recent geological history of mars repeat observations with the high resolution imaging science experiment hirise instrument on the mars reconnaissance orbiter demonstrate widespread activity in gullies in the southern hemisphere particularly in those with the freshest morphologies this activity includes substantial channel incision and large scale mass movements and constitutes ongoing gully formation rather than degradation of older landforms new apron deposits that are bright dark and neutrally toned have all been observed the timing of gully activity is seasonally controlled and occurs during the period when seasonal frost is present and defrosting these observations support a model in which currently active gully formation is driven mainly by seasonal co 2 frost gullies in the northern hemisphere are far less active than those in the south this may be due to the current timing of perihelion near the northern winter solstice integrated over time activity like that observed within the past few years appears capable of forming all of the martian gully landforms on timescales of millions of years additionally the current style and rate of activity is able to erase meter to decameter scale surface features that might have been uniquely produced by other processes during the last obliquity high 0 4 ma although it is impossible to rule out a past role for water in the formation of martian gullies a model in which gullies form only through currently active processes with little or no liquid water is consistent with our observations

identification of gully debris flow deposits in protonilus mensae mars characterization of a water bearing energetic gully forming process gullies are a class of geologically recent landform on mars that show evidence of downslope transport of sedimentary material from recessed alcoves through incised channels to distributary fans or aprons the mechanisms invoked to account for the formation of gullies on mars range from completely dry granular flows or landslides to debris flows that incorporate some component of liquid water to fluvial erosion and alluvial fan like deposition each of these processes requires different amounts of liquid water and produces different characteristic morphologies we report on the identification of unusual lobate structures present in proximity to gullies in protonilus mensae the lobes are up to 3 m thick and terminate in rounded snouts these lobate structures are present mostly downslope of gullies and can be traced upslope through channels to gully fan termini and in places onto gully fan surfaces crater dating indicates that the deposits formed recently potentially within the past 500 ka we use hrsc digital elevation models to constrain mechanical properties of the lobate deposits and to compare their formation environment to that of typical martian gullies the protonilus mensae lobate deposits are interpreted to indicate local dominance of wet debris flows in the formation of the observed gullies and lobes these observations are consistent with 1 top down melting of the ice component of the latitude dependent mantle terrain in which the gullies form and 2 initiation of debris flows by mobilization of the dusty lithic component of the mantle the suite of morphological observations diagnostic of wet debris flow processes suggests the identification of an unusual environment in which the wet debris flow formational end member is locally the dominant gully forming process elsewhere on mars gully morphology may be more consistent with a range of other water related sediment transport mechanisms including fluvial erosion hyperconcentrated flow and low strength mudflows that deposit as fans rather than lobes these results suggest that 1 gully forming processes involve liquid water 2 that the water source is associated with the martian latitude dependent mantle and 3 that a range of water related sediment transport processes is involved in gully formation

world wide delivery of river sediment to the oceans new data and new estimates from old data show that rivers with large sediment loads annual discharges greater than about 15 times 10 6 tons contribute about 7 times 10 9 tons of suspended sediment to the ocean yearly extrapolating available data for all drainage basins the total suspended sediment delivered by all rivers to the oceans is about 13 5 times 10 9 tons annually bedload and flood discharges may account for an additional 1 2 times 10 9 tons about 70 of this total is derived from southern asia and the larger islands in the pacific and indian oceans where sediment yields are much greater than for other drainage basins

mars south polar spring and summer behavior observed by tes seasonal cap evolution controlled by frost grain size thermal emission spectrometer tes observations of the recession phase of mars south polar cap are used to quantitatively map this recession in both thermal and visual appearance geographically nonuniform behavior interior to the cap is characterized by defining several small regions which exemplify the range of behavior for most of the cap while temperatures remain near the co2 frost point albedos slowly increase with the seasonal rise of the sun then drop rapidly as frost patches disappear over a period of 20 days a cryptic region remains dark and mottled throughout its cold period tes observations are compared with first order theoretical spectra of solid co2 frost with admixtures of dust and h2o the tes spectra indicate that the cryptic region has much larger grained solid co2 than the rest of the cap and that the solid co2 here may be in the form of a slab the mountains of mitchel remain cold and bright well after other areas at comparable latitude apparently as a result of unusually small size of the co2 frost grains we found little evidence for a significant presence of h2o although co2 grain size may be the major difference between these regions incorporated dust is also required to match the observations a self cleaning process carries away the smaller dust grains comparisons with viking observations indicate little difference in the seasonal cycle 12 martian years later the observed radiation balance indicates co2 sublimation budgets of up to 1250 kg m 2 regional atmospheric dust is common localized dust clouds are seen near the edge of the cap prior to the onset of a regional dust storm and interior to the cap during the storm

morphological modelling of rivers with erodible banks a bank erosion mechanism and provisions to account for the associated planform changes and input of bank erosion products are added to a two dimensional depth averaged model of river morphology the model is applied to a reach of the meandering gravel bed river oh e eger in the former state of czechoslovakia the agreement with observations is poor but this can be ascribed to shortcomings in the flow and bed topography submodels rather than to shortcomings in the bank erosion submodel better results are expected when a three dimensional flow model equations for sediment mixtures and a bank accretion mechanism are included this inclusion will have to be preceded by fundamental research on bank accretion mechanisms and on hiding and exposure effects in the relationship for the influence of gravity pull on sediment transport direction 1998 john wiley sons ltd

global documentation of gullies with the mars reconnaissance orbiter context camera and implications for their formation abstract hypotheses ranging from fluvial processes and debris flows to co 2 frost lubricated or entirely dry flows have been proposed for the formation of martian gullies in order to constrain these potential formation mechanisms we mapped the global distribution of gullies on mars using 54 000 images from the mars reconnaissance orbiter mro context camera ctx covering 85 of the martian surface at a resolution of 6 m pixel the results of this mapping effort confirm the results of studies using lower resolution and or less areally extensive datasets that gullies are confined to the martian mid to high latitudes 30 80 in both hemispheres we also find a clear transition in gully orientation with increasing latitude going from poleward facing to equator facing preference in general gullies are more developed on poleward facing walls and mid latitude gullies are more developed than those at higher latitudes gullies are also found to be strongly correlated with regions of distinct thermophysical properties of sand to pebble sized grains low albedo and higher thermal inertia these observations all point to climate insolation and thermal properties of the substrate playing key factors in gully formation on mars supporting either a melting ground ice or snowpack hypothesis as the source for water involved in gully formation

keys to gully formation processes on mars relation to climate cycles and sources of meltwater abstract advances in dating gullies on mars using superposition relationships and a stratigraphic marker horizon link gully chronostratigraphy to recent climate cycles new observations of gully morphology show the close association of gully source regions channels and fan deposits with well documented ice rich latitude dependent mantle deposits the deposition of which is interpreted to be coincident with recent ice ages on the basis of these close correlations we interpret the formative processes for mid latitude gullies to involve melting of these ice rich mantling deposits and the generation of an aqueous phase leading to fluvial activity continued monitoring of gullies by spacecraft in the current interglacial climate period 0 4 ma to the present will permit assessment of changing rates and styles of gully activity in the now largely depleted source areas

martian gullies a comprehensive review of observations mechanisms and insights from earth analogues upon their discovery in 2000 martian gullies were hailed as the first proof of recent i e less than a few million years flowing liquid water on the surface of a dry desert planet many processes have been proposed to have formed martian gullies ranging from liquid water seepage from aquifers melting of snow ice and frost to dry granular flows potentially lubricated by co2 terrestrial analogues have played a pivotal role in the conception and validation of gully formation mechanisms comparison with the terrestrial landscape argues for gully formation by liquid water debris flows originating from surface melting however limited knowledge of sediment transport by sublimation is a critical factor in impeding progress on the co2 sublimation hypothesis we propose avenues towards resolving the debate a laboratory simulations targeting variables that can be measured from orbit b applications of landscape evolution models c incorporation of the concept of sediment connectivity d using 3d fluid dynamic models to link deposit morphology and flow rheology and e a more intense exchange of techniques between terrestrial and planetary geomorphology including quantitative and temporal approaches finally we emphasize that the present may not accurately represent the past and that martian gullies likely formed by a combination of processes

present day seasonal gully activity in a south polar pit sisyphi cavi on mars abstract the large amount of multi temporal high resolution images acquired in the last few years offers the opportunity to identify morphological changes associated with recent geologic activity on the surface of mars in this study we focus on a single gully in sisyphi cavi located in the south polar region at 1 44 e and 68 54 s the gully incises the gullied equator facing slope of an isolated polar pit within an infilled impact crater it is important to notice that the following investigations describe the activity and modifications of an existing gully and not the formation of the gully itself high resolution image data analyses show new deposits at the terminus of the gully channel and on the gully apron within spring after solar longitudes of 236 of martian years my 29 and 31 our morphological investigations show that the identified new deposits were formed by dark flows through the entire gully deposited on top of the apron between solar longitudes l s 218 and 226 thermal data show a temperature increase between l s 218 and 226 near infrared spectral data show relatively constant band strengths of co 2 ice and h 2 o ice in this time range after the formation of the dark flows after l s 226 temperatures increase rapidly from 180 k to 270 k at l s 250 at this time spectral data indicate that all volatiles on the surface sublimated however an earlier beginning of sublimation when the dark flows were observed between l s 218 and 226 is likely due to the fact that the instruments can only show the last phase of sublimation decrease of volatile band strengths spectral modeling shows that from winter to mid spring the surface of the studied area is covered by translucent co 2 slab ice contaminated by minor amounts of h 2 o ice and dust furthermore our spectral modeling indicates that the dark material most likely flows on top of the co 2 slab ice cover three different scenarios were proposed to explain the identified dark flows including 1 flows supported by liquid h 2 o 2 flows supported by co 2 gas and 3 dry flows on the basis of our study we find that scenario 1 is unlikely because of the very low temperatures while scenario 2 is consistent with the observed beginning of co 2 ice sublimation in the study area it is unlikely because of the limitation of the activity to only one gully compared to surrounding gullies that share the same morphologies slope angles and volatile contents also with scenario 3 dry flows the activity of only one gully is difficult to explain thus we propose a mixture of scenario 2 and 3 dry flows supported by the ongoing sublimation of co 2 ice within the gully to be the most plausible scenario when the observed active gully comprises different source material than the surrounding gullies i e a higher content of probably sand sized material from outcrops located in the alcove

surface runoff features on mars testing the carbon dioxide formation hypothesis 1 fresh gully like features on mars strongly suggest that fluid flowed on the surface in the recent past here we consider the possibility that co2 vapor supported flows formed the gullies we find that neither condensed co2 nor co2 clathrate hydrate are likely to accumulate in significant quantities in the martian crust in addition if condensed co2 were present under lithostatic pressures exposure to the atmosphere would produce features analogous to terrestrial pyroclastic flows not surface runoff finally the source volume of co2 required to support a flow excludes clustered or episodic gully formation therefore we conclude that co2 cannot have formed the gullies in light of these results liquid water flow remains the preferred formation mechanism for the recent surface runoff features

geomorphic controls on contaminant distribution along an ephemeral stream sediment borne contamination in a watershed can be highly variable as a result of uvial processes operating over a range of time scales this study presents a detailed analysis of the distribution of one contaminant along an ephemeral stream after 55 years of sediment transport deposition and exchange by ash oods wastewater containing plutonium was discharged into the pueblo canyon watershed from 1945 until 1964 and plutonium concentrations in uvial deposits vary over ve orders of magnitude these variations can be attributed to three primary factors time since contaminant releases particle size sorting and mixing of sediment from different sources the highest concentrations occur in ne grained sediment deposits near the source that date to the period of ef uent releases and concentrations are lower in younger deposits in coarser grained deposits and in deposits farther downstream the spatial distribution of plutonium is strongly affected by longitudinal variations in the size of sediment deposits of different age a major aggradation degradation cycle in the lower canyon overlapped with the period of active ef uent releases and a signi cant portion of the total plutonium inventory is contained within large coarse grained deposits below ll terraces that post date 1945 the spatial pattern of contamination is thus determined by the speci c geomorphic history of the watershed in addition to processes of mixing and sorting during transport that occur in all uvial systems copyright 2004 john wiley sons ltd

dynamics of unusual debris flows on martian sand dunes 1 gullies that dissect sand dunes in russell impact crater often display debris flow like deposits in their distal reaches the possible range of both the rheological properties and the flow rates are estimated using a numerical simulation code of a bingham plastic flow to help explain the formation of these features our simulated results are best explained by a rapid debris flow for example a debris flow with the viscosity of 102 pa s and the yield strength of 102 pa can form the observed deposits with a flow rate of 0 5 m3 s sustained over several minutes and total discharged water volume on the order of hundreds of cubic meters which may be produced by melting a surface layer of interstitial ice within the dune deposits to several centimeters depth

formation of gullies on mars link to recent climate history and insolation microenvironments implicate surface water flow origin features seen in portions of a typical midlatitude martian impact crater show that gully formation follows a geologically recent period of midlatitude glaciation geological evidence indicates that in the relatively recent past sufficient snow and ice accumulated on the pole facing crater wall to cause glacial flow and filling of the crater floor with debris covered glaciers as glaciation waned debris covered glaciers ceased flowing accumulation zones lost ice and newly exposed wall alcoves continued as the location for limited snow frost deposition entrapment and preservation analysis of the insolation geometry of this pole facing crater wall and similar occurrences in other craters at these latitudes on mars shows that they are uniquely favored for accumulation of snow and ice and a relatively more rapid exposure to warmer summer temperatures we show that after the last glaciation melting of residual snow and ice in alcoves could have formed the fluvial channels and sedimentary fans of the gullies recent modeling shows that top down melting can occur in these microenvironments under conditions similar to those currently observed on mars if small amounts of snow or frost accumulate in alcoves and channels accumulation and melting is even more favored in the somewhat wetter relatively recent geological past of mars after the period of active glaciation

mass movements related to tectonics in the aspromonte massif southern italy abstract geomorphic and structural studies have been carried out on the headwaters of vallone colella torrent in an area intensely affected by mass movement phenomena on the aspromonte massif of southern italy rock types outcropping in the area are mostly gneiss and granitoids with subordinate presence of metarenites phyllites and biotite schists all lithologies experienced low grade metamorphism as indicated by petrographic analysis structural surveys performed at macroscopic and mesoscopic scale allowed recognition of several sets of discontinuities related to different deformation events the upper reaches of vallone colella torrent present a large active landslide zone the debris materials of which feed the debris flows along the drainage system towards the main valley mass movement phenomena are both shallow and deep seated the latter are limited to a sector of the study area while shallow processes are present throughout the landslide zone some considerations of the relationship between tectonics and mass movement are presented with particular reference to the presence of a large scale downthrown wedge bounded by structural surfaces on both sides of the valley located in the same area affected by deep seated phenomena

a new dry hypothesis for the formation of martian linear gullies long narrow grooves found on the slopes of martian sand dunes have been cited as evidence of liquid water via the hypothesis that melt water initiated debris flows eroded channels and deposited lateral levees however this theory has several short comings for explaining the observed morphology and activity of these linear gullies we present an alternative hypothesis that is consistent with the observed morphology location and current activity that blocks of co2 ice break from over steepened cornices as sublimation processes destabilize the surface in the spring and these blocks move downslope carving out leveed grooves of relatively uniform width and forming terminal pits to test this hypothesis we describe experiments involving water and co2 blocks on terrestrial dunes and then compare results with the martian features furthermore we present a theoretical model of the initiation of block motion due to sublimation and use this to quantitatively compare the expected behavior of blocks on the earth and mars the model demonstrates that co2 blocks can be expected to move via our proposed mechanism on the earth and mars and the experiments show that the motion of these blocks will naturally create the main morphological features of linear gullies seen on mars

measuring the in situ erosion shear stress of intertidal sediments with the cohesive strength meter csm the shear resistance of muddy sediments directly governs the susceptibility of the sediment to erosion by tidal and wave induced currents measurements of the natural erosion shear stress are important in modelling estuarine systems and in determining the possible impact of human disturbance a second generation erosion instrument the cohesive strength meter csm designed to measure the critical erosion shear stress ocr of intertidal sediments in situ is described the csm allows measurements of small scale spatial and temporal variation of sediment stability to be made on a scale and rapidity previously unachievable new features of specialized hardware are described and the instrument is empirically calibrated in terms of an equivalent horizontal bed shear stress using quartz sand some example results from recent field trials on the konigshafen sylt romo bight are presented the erosion characteristics of this intertidal flat varied on a cm scale due to the presence of patchy diatom biofilms areas with a diatom biofilm were more stable than those without giving a biostabilization index of 6 2

form drag in rivers due to small scale natural topographic features 2 irregular sequences 1 the size shape and spacing of small scale topographic features found on the boundaries of natural streams rivers and floodplains can be quite variable consequently a procedure for determining the form drag on irregular sequences of different sized topographic features is essential for calculating near boundary flows and sediment transport a method for carrying out such calculations is developed in this paper this method builds on the work of kean and smith 2006 which describes the flow field for the simpler case of a regular sequence of identical topographic features both approaches model topographic features as two dimensional elements with gaussian shaped cross sections defined in terms of three parameters field measurements of bank topography are used to show that 1 the magnitude of these shape parameters can vary greatly between adjacent topographic features and 2 the variability of these shape parameters follows a lognormal distribution simulations using an irregular set of topographic roughness elements show that the drag on an individual element is primarily controlled by the size and shape of the feature immediately upstream and that the spatial average of the boundary shear stress over a large set of randomly ordered elements is relatively insensitive to the sequence of the elements in addition a method to transform the topography of irregular surfaces into an equivalently rough surface of regularly spaced identical topographic elements also is given the methods described in this paper can be used to improve predictions of flow resistance in rivers as well as quantify bank roughness

a model for flow over two dimensional bed forms when non cohesive sediment is set in motion by a unidirectional flow waves of sand often result moreover these waves typically are asymmetrical with steep lee faces that produce flow separation behind each wave a wake region forms which grows in height and decays in strength with distance downstream producing a near bottom acceleration the no slip condition at the bed however requires an internal boundary layer to form beneath the wake region which retards the flow there the interaction of these flow processes produces a local maximum in the boundary shear stress downstream of a bump even over an otherwise flat bed because the erosion rate is proportional to the stress divergence for bed load and weak suspended load transport erosion will occur upstream of this point and desposition will occur downstream of it thus influencing the bottom shape herein the equations of motion are solved for the accelerating internal boundary layer beneath a wake the resulting velocity and boundary shear str

debris flows over sand dunes on mars evidence for liquid water 1 this study focuses on the formation and physical properties of the gullies observed over large martian dunes especially those of the russell crater 54 s 347 w geomorphic features like sinuosities and connections of the channels show that gullies over dunes involve flows with a significant proportion of liquid the occurrence of levees implies that these flows are debris flows with a yield strength characteristics of bingham plastic materials we apply terrestrial methods to estimate viscosity and velocity of these flows from levee size and sinuosities we obtain average velocities in the range of 1 to 7 m s 1 and apparent viscosities of 2 8 to 46 000 pa s with an average at 740 pa s compared with the 0 001 pa s of pure water these viscosities and velocities are in the range of terrestrial debris flows with a proportion of 10 to 40 of h2o these properties are typical of water holding debris flows but not of pure water surface runoff or co2 driven flows the debris flows over dunes are oriented on south facing slopes like other recent gullies meltwater from ground ice formed during a recent period of high obliquity is the more likely explanation for the formation of such flows over dunes

remote sensing and spatial analysis of aeolian sand dunes a review and outlook abstract for more than four decades remote sensing images have been used to document and understand the evolution of aeolian sand dunes early studies focused on mapping and classifying dunes recent advances in sensor technology and software have allowed investigators to move towards quantitative investigation of dune form evolution and pattern development these advances have taken place alongside progress in numerical models which are capable of simulating the multitude of dune patterns observed in nature the potential to integrate remote sensing rs spatial analysis sa and modeling to predict the future changes of real world dune systems is steadily becoming a reality here we present a comprehensive review of significant recent advances involving rs and sa our objective is to demonstrate the capacity of these technologies to provide new insight on three important research domains 1 dune activity 2 dune patterns and hierarchies and 3 extra terrestrial dunes we outline how several recent advances have capitalized on the improved spatial and spectral resolution of rs data the availability of topographic data and new sa methods and software we also discuss some of the key research challenges and opportunities in the application of rs and sa dune field including the integration of rs data with field based measurements of vegetation cover structure and aeolian transport rate in order to develop predictive models of dune field activity expanding the observational evidence of dune form evolution at temporal and spatial scales that can be used to validate and refine simulation models the development and application of objective and reproducible sa methods for characterizing dune field pattern and expanding efforts to quantify three dimensional topographic changes of dune fields in order to develop improved understanding of spatio temporal patterns of erosion and deposition overall our review indicates a progressive evolution in the way sand dunes are studied whereas traditional field studies of airflow and sand transport can clarify event based process form interactions investigators are realizing a synoptic perspective is required to address the response of dune systems to major forcings the integration and evolution of the technologies discussed in this review are likely to form a foundation for future advances in aeolian study

geomorphological evidence for transient water flow on vesta abstract vesta the second most massive asteroid has long been perceived as anhydrous recent studies suggesting the presence of hydrated minerals and past subsurface water have challenged this long standing perception yet direct geologic indications of water activity on vesta s surface were unexpected herein we show evidence that transient water flowed on the surface in a debris flow like process and left distinctive geomorphologic features based on detailed analysis of highest resolution 20 m pixel images obtained by the dawn spacecraft we identify a class of locally occurring interconnected and curvilinear gully networks on the walls of young

bank erosion of an incised upland channel by subaerial processes tasmania australia the headwaters of many rivers are characterized by gullies and incised streams that generate significant volumes of sediment and degrade downstream water quality these systems are characterized by harsh climates ephemeral flows that do not reach bank top and bare cohesive banks of clay and weathered bedrock we investigated the rates and processes of bank erosion in an incised canal that has such characteristics detailed measurements of bank position were made over two years with a purpose built groundprofiler and photo electronic erosion pins peeps stage height and turbidity were also monitored the bare banks eroded at 13 2 mm a 1 erosion is controlled by subaerial processes that loosen bank material observations show that needle ice growth is important in winter and desiccation of clays predominates in summer flows are unable to erode firm cohesive clays from the banks and erosion is generally limited by the availability of loosened material this produces strong hysteresis in turbidity during events peak turbidity is related to the number of days with low flow between events and not peak stage rehabilitation with a moderate cover of grass is able to prevent bank erosion by limiting the subaerial erosion processes projections of current erosion suggest that without vegetation cover the banks are unlikely to stabilize for many years copyright 2000 john wiley sons ltd

floodplain storage of mine tailings in the belle fourche river system a sediment budget approach arsenic contaminated mine tailings that were discharged into whitewood creek at lead south dakota from 1876 to 1978 were deposited along the floodplains of whitewood creek and the belle fourche river the resulting arsenic contaminated floodplain deposit consists mostly of overbank sediments and filled abandoned meanders along white wood creek and overbank and point bar sediments along the belle fourche river arsenic concentrations of the contaminated sediments indicate the degree of dilution of mine tailings by uncontaminated alluvium about 13 per cent of the 110 106 mg of mine tailings that were discharged at lead were deposited along the whitewood creek floodplain deposition of mine tailings near the mouth of whitewood creek was augmented by an engineered structure about 29 per cent of the mine tailings delivered by whitewood creek were deposited along the belle fourche river floodplain about 60 per cent of that sediment is contained in overbank deposits deposition along a segment of the belle fourche river was augmented by rapid channel migration the proportions of contaminated sediment stored along whitewood creek and the belle fourche river are consistent with sediment storage along the floodplains of perennial streams in other similar sized watersheds

generation and verification of theoretical rating curves in the whitewater river basin kansas 1 a new method for generating stage discharge relations rating curves for geomorphically stable channels is presented and applied to two streams in the whitewater river basin kansas the approach converts measurements of stage into discharge using a fluid mechanically based model the model does not use empirical roughness coefficients such as manning coefficients but rather determines channel roughness from field measurements of the 1 channel geometry 2 the physical roughness of the bed banks and floodplain and 3 the vegetation density on the banks and floodplain these measurements are used to calculate explicitly the drag on the small scale topographic features on the boundary the drag on the stems and branches of woody vegetation and the friction on the bed banks and floodplain the theoretical rating curves produced by the model for two study reaches which are near u s geological survey usgs streamflow gauging stations are in good agreement with direct measurements of discharge made by the usgs our method has the potential of providing accurate estimates of stream flows less expensively than conventional gauging methods in addition the method can be used to obtain more accurate discharge estimates than conventional indirect methods for determining discharge which are based on estimates of manning s coefficient

on the orbital forcing of martian water and co2 cycles a general circulation model study with simplified volatile schemes 1 variations in the martian water and co2 cycles with changes in orbital and rotational parameters are examined using the geophysical fluid dynamics laboratory mars general circulation model the model allows for arbitrary specification of obliquity eccentricity and argument of perihelion as well as the position and thickness of surface ice exchange of co2 between the surface and atmosphere is modeled generating seasonal cycles of surface ice and surface pressure water is allowed to exchange between the surface and atmosphere cloud formation is treated and both cloud and vapor are transported by modeled winds and diffusion exchange of water and co2 with the subsurface is not allowed and radiative effects of water vapor and clouds are not treated the seasonal cycle of co2 is found to become more extreme at high obliquity as suggested by simple heat balance models maximum pressures remain largely the same but the minima decrease substantially as more co2 condenses in the more extensive polar night vapor and cloud abundances increase dramatically with obliquity the stable location for surface ice moves equatorward with increasing obliquity such that by 45 obliquity water ice is stable in the tropics only ice is not spatially uniform but rather found preferentially in regions of high thermal inertia or high topography eccentricity and argument of perihelion can provide a second order modification to the distribution of surface ice by altering the temporal distribution of insolation at the poles further model simulations reveal the robustness of these distributions for a variety of initial conditions our findings shed light on the nature of near surface ice rich deposits at midlatitudes and low latitudes on mars

evidence for present day gully activity on the russell crater dune field mars 1 on the basis of high resolution imaging science experiment hirise images of two successive years we observed changes of a gully on the russell crater dune field within the first year the length of a 2 m wide incised gully channel grew about 50 m downslope and 120 m within in the second year gully activity occurred in early spring between ls 198 and 218 in the first year and between ls 192 and 221 in the second year based on the channel morphology spectral data and modeled surface temperatures the changes can be best explained with transient melting of small amounts of h2o ice triggering slurry flows consisting of sand mixed with liquid water

downslope sediment transport by boiling liquid water under mars like conditions experiments and potential implications for martian gullies gullies are widespread morphological features on mars for which current changes have been observed liquid water has been one of the potential mechanisms to explain their formation and activity however under present day martian conditions liquid water is unstable and should only be transiently present in small amounts at the surface yet little attention has been paid to the mechanisms by which unstable water transports sediment under low atmospheric pressure here we present the results of laboratory experiments studying the interaction between liquid water owing over a sand bed under mars like atmospheric pressure c 9 mbar the experiments were performed in a mars simulation chamber at the open university uk in which we placed a test bed of ne sand at a 25 slope we chose to investigate the in uence of two parameters the temperature of the water and the temperature of the sand we performed 27 experiments with nine different combinations of water and sand temperatures ranging from 278 to 297 k under all experimental conditions the water was boiling we investigated and compared the types and timing of sediment transport events and the shapes characteristics and volumes of the resulting morphologies in agreement with previous laboratory studies we found that more intense boiling increased the volume of sediment transported for a given volume of water we found four main types of sediment transport entrainment by overland ow grain ejection grain avalanches and levitation of saturated sand pellets our results showed that increasing sand temperature was the main driving parameter in increasing the sand transport and in modifying the dominant sediment transport mechanism the temperature of the water played a negligible or minor role apart from the duration of sand ejection and avalanches which lasted longer at low water temperature at low sand temperature the majority of the sand was transported by overland ow of the liquid water at higher sand temperatures the transport was dominated by processes triggered by the boiling behaviour of the water at the highest temperatures sediment transport was dominated by the formation of levitating pellets dry avalanches and ejection of the sand grains this resulted in a transport volume about nine times greater at a sand temperature of 297 k compared with 278 k our heat transfer scaling shows that the boiling behaviour will be enhanced under martian low gravity resulting in more ef cient transport of sediment by levitating sand pellets even at temperatures close to the triple point our results showed that the boiling intensity played an important role in the physics of sediment transport by liquid water this implied that the amount of water required to produce morphological changes at the surface of mars could be lower than previously estimated by assuming stable liquid water boiling is a critical process to be considered when assessing gully formation and modi cation mechanisms mobilized by liquid water our work could have similar implications for any water formed landform on mars which could include recurring slope lineae dark dune ows and slope streaks

riparian seed banks along the lower river dove uk their structure and ecological implications this paper investigates associations between the viable seed bank sediment properties and elevation on three eroding river banks along the lower reaches of the river dove derbyshire uk using both descriptive statistics and detrended correspondence analysis major contrasts are found in the abundance and floristic composition of the viable seed bank between the bank top bank face and bank toe and between the three study sites canonical correspondence analysis identifies associations between the floristic composition of the seed bank and the percent organic matter percent clay percent sand and median particle size of the soil matrix that contains the seeds the patterns revealed by the above analyses indicate i an increasing influence of fluvial processes hydrochory on the species composition of the seed bank with decreasing elevation ii a low abundance of viable seeds on unvegetated eroding bank sections suggesting limited long term storage of viable seeds within floodplain sediments and iii a very substantial seed bank where old channel sections provide a local depositional environment the implications of these observations for understanding the role of fluvial processes in riparian seed bank dynamics and their implications for riparian management are discussed

fluvial geomorphology on earth like planetary surfaces a review morphological evidence for ancient channelized flows fluvial and fluvial like landforms exists on the surfaces of all of the inner planets and on some of the satellites of the solar system in some cases the relevant fluid flows are related to a planetary evolution that involves the global cycling of a volatile component water for earth and mars methane for saturn s moon titan in other cases as on mercury venus earth s moon and jupiter s moon io the flows were of highly fluid lava the discovery in 1972 of what are now known to be fluvial channels and valleys on mars sparked a major controversy over the role of water in shaping the surface of that planet the recognition of the fluvial character of these features has opened unresolved fundamental questions about the geological history of water on mars including the presence of an ancient ocean and the operation of a hydrological cycle during the earliest phases of planetary history other fundamental questions posed by fluvial and fluvial like features on planetary bodies include the possible erosive action of large scale outpourings of very fluid lavas such as those that may have produced the remarkable canali forms on venus the ability of exotic fluids such as methane to create fluvial like landforms as observed on saturn s moon titan and the nature of sedimentation and erosion under different conditions of planetary surface gravity planetary fluvial geomorphology also illustrates fundamental epistemological and methodological issues including the role of analogy in geomorphological geological inquiry

identification of mars gully activity types associated with ice composition the detection of geologically recent channels at the end of the 20th century rapidly suggested that liquid water could have been present on mars up to recent times a mechanism involving melting of water ice during ice ages in the last several million years progressively emerged during years following the first observations of these gullies however the recent discovery of current activity within gullies now suggests a paradigm shift where a contemporary co2 ice based and liquid water free mechanism may form all gullies here we perform a survey of near infrared observations and construct time sequences of water and co2 ice formation and sublimation at active gully sites we observe that all major new erosive features such as channel development or lengthening systematically occur where and if applicable when co2 ice is observed or probable co2 ice layers are however estimated to be only 1 mm to 1 cm thick for low latitude sites which may have implication for potential formation mechanisms we also observe that part of current gully activity notably the formation of some new deposits is poorly compatible with the presence of co2 ice in particular all new bright deposits reported in the literature have a low co2 ice probability while water ice should be present at most sites our results confirm that co2 ice is a key factor controlling present day channel development on mars and show that other mechanisms potentially involving sublimation or melting of water ice are also contributing to current gully activity

detrital modes of the ionian forearc basin fill oligocene quaternary reflect the tectonic evolution of the calabria peloritani terrane southern italy abstract during oligocene neogene time the calabria peloritani terrane cpt a small block of continental lithosphere rifted from the southern margin of the eurasian continent and drifted southeastward to collide with the african continent along the leading edge of the cpt a late oligocene to quaternary mostly siliciclastic succession 2 000 meters thick was deposited in the ionian forearc basin the detritus forming the succession was derived directly from the erosion of the nearby cpt composed of hercynian plutons intruding metasedimentary host rocks contrary to most modern and ancient forearc basins penecontemporaneous volcanic detritus is virtually absent this results from rift related topographic barriers which separated the forearc basin from the associated volcanic arc in spite of an overall quartzofeldspathic continental block provenance the analysis of a large sandstone and conglomerate petrological dataset 228 samples points to three discrete detrital inputs of aphanitic lithic fragments in i late oligocene early miocene ii late messinian and iii quaternary times these petrological variations can be linked to independently determined tectonic events in the western mediterranean which likely modified the lithologic composition of the sediment source terranes input i documents the progressive widespread unroofing of the continental basement of the southern european margin when northwestward subduction of the remnants of the ligurian ocean began input ii is related to widespread intra messinian tectonism possibly due to out of sequence thrusting induced by isostatic readjustments of the perimediterranean orogenic wedges following the messinian drawdown input iii reflects the rapid vertical uplift experienced by the cpt since mid pleistocene time possibly the result of slab detachment along the ionian subduction zone this study indicates that detailed statistical analysis of the detrital modes of ancient terrigenous deposits can be used to identify the tectonic events affecting somewhat petrologically monotonous sediment source areas within small lithospheric terranes

large scale sedimentary recycling of tectonic melange in a forearc setting the ionian basin oligocene quaternary southern italy distinctive horizons of melange ranging in maximum thickness from a few tens to several hundreds of meters are conformably interbedded with the regularly stratified oligocene to quaternary predominantly marine deposits of the ionian forearc basin along the leading edge of the calabria peloritani microplate of southern italy these melange horizons were emplaced from the late early to the late miocene during collision of the southern and northern margins of the microplate with the passive margins of northern africa and the apulian platform respectively collisional deformation induced uplift of parts of the accretionary prism and ensuing sedimentary recycling of melange into the adjacent ionian forearc basin the thickest melange horizon can be traced for a distance 80 km with a consistent stratigraphic position within the forearc basin fill and ranges in thickness from 1 km near the collision zone to zero away from it it was emplaced in the late burdigalian and records oblique collision of the calabria peloritani microplate with the northern continental margin of africa in this context portions of the melange of the accretionary prism were extruded tectonically and gravitationally mobilized from southwest to northeast in the remaining undeformed parts of the forearc basin this interpretation is supported by 1 the overall geometry of the melange horizon pinching out away from the collision zone 2 its conformable contacts and chronostratigraphic relationships with the underlying and overlying stratigraphic units 3 its composition and 4 the absence of tectonic deformation at base and top of the horizon younger and thinner melange horizons are interbedded within the latest tortonian messinian succession and resulted from the erosion of thrust tip areas within the inner portion of the accretionary prism following incipient collision of the northern end of the microplate with the apulian platform integration of the results of this and other studies indicate that sedimentary recycling of large volumes of melange from accretionary prisms into forearc basins is an important process along both collisional and noncollisional active plate margins

debris flows on the great kobuk sand dunes alaska implications for analogous processes on mars abstract we observed niveo aeolian deposits denivation features and small meltwater induced debris flows that had formed at the great kobuk sand dunes northwestern interior alaska in late march 2010 this high latitude cold climate dune field is being studied as a planetary analog to improve our understanding of factors that may trigger debris flows on the lee slopes of martian aeolian dunes debris flows consisted of a sand and liquid water mixture that cascaded down the lee slopes of two barchanoid dunes on days when measured ground surface temperatures were below freezing we hypothesize that relatively dark sand on snow caused local hot spots where solar radiation could be absorbed by the sand and conducted into the underlying snow enabling meltwater to form and sand to be mobilized this investigation provides insights into the interactions between niveo aeolian deposition slope aspect and insolation thawing and initiation of alluvial processes these debris flows are morphologically similar to those associated with seasonal gullies or erosion tracks visible on the slopes of mid to high latitude dune fields in both martian hemispheres localized heating and thawing at scales too small for orbital sensors to identify may yield martian debris flows at current climate conditions

sand water flows on cold climate eolian dunes environmental analogs for the eolian rock record and martian sand dunes abstract sand water flows were observed on the slopes of cold climate eolian dunes in southwestern saskatchewan canada during episodes of intense thawing in the winters of 2004 and 2005 meltwater produced flows with varying grain water contents on slopes of active blowout hollows and parabolic dunes the sand water flows emplaced small structureless lobate and tongue shaped deposits and alluvial fans the greatest concentration of deposits occurred on south facing slopes which frequently thaw in winter from intense insolation transport modes ranged from high density viscous slurry flows to lowdensity hyperconcentrated flows the triggering cause of these flows is high pore water pressure that develops in thawed nearsurface sand due to impeded infiltration by frozen sand with pore ice at depth these observations broaden the environmental context of sand water flows on dunes and contribute to interpretations of these deposits in the eolian rock record and to recent alluvial features observed on martian sand dunes

mass wasting triggered by seasonal co2 sublimation under martian atmospheric conditions laboratory experiments sublimation is a recognized process by which planetary landscapes can be modi ed however interpretation of whether sublimation is involved in downslope movements on mars and other bodies is restricted by a lack of empirical data to constrain this mechanism of sediment transport and its in uence on landform morphology here we present the rst set of laboratory experiments under martian atmospheric conditions which demonstrate that the sublimation of co 2 ice from within the sediment body can trigger failure of unconsolidated regolith slopes and can measurably alter the landscape previous theoretical studies required co 2 slab ice for movements but we nd that only frost is required hence sediment transport by co 2 sublimation could be more widely applicable in space and time on mars than previously thought this supports recent work suggesting co 2 sublimation could be responsible for recent modi cation in martian gullies

landscape evolution in martian mid latitude regions insights from analogous periglacial landforms in svalbard periglacial landforms on spitsbergen svalbard norway are morphologically similar to landforms on mars that are probably related to the past and or present existence of ice at or near the surface many of these landforms such as gullies debris flow fans polygonal terrain fractured mounds and rock glacier like features are observed in close spatial proximity in mid latitude craters on mars on svalbard analogous landforms occur in strikingly similar proximity which makes them useful study cases to infer the spatial and chronological evolution of martian coldclimate surface processes the analysis of the morphological inventory of analogous landforms on svalbard and mars allows the processes operating on mars to be constrained different qualitative scenarios of landscape evolution on mars help to better understand the action of periglacial processes on mars in the recent past

erodibility of cohesive streambeds in the loess area of the midwestern usa excess stress parameters critical shear stress c and erodibility coefficient k d for degrading channels in the loess areas of the midwestern usa are presented based on in situ jet testing measurements critical shear stress and k d are used to define the erosion resistance of the streambed the jet testing apparatus applies hydraulic stresses to the bed and the resulting scour due to the impinging jet is related to the excess stress parameters streams tested were primarily silt bedded in texture with low densities which is typical of loess soils results indicate that there is a wide variation in the erosion resistance of streambeds spanning six orders of magnitude for c and four orders of magnitude for k d erosion resistance was observed to vary within a streambed from streambed to streambed and from region to region an example of the diversity of materials within a river system is the yalobusha river basin in mississippi the median value of c for the two primary bed materials naheola and porters creek clay formations was 1 31 and 256 pa respectively streambeds composed of the naheola formation are readily eroded over the entire range of shear stresses whereas only the deepest flows generate boundary stresses great enough to erode streambeds composed of the porters creek clay formation therefore assessing material resistance and location is essential in classifying and modelling streambed erosion processes of these streams

co2 sublimation in martian gullies laboratory experiments at varied slope angle and regolith grain sizes martian gullies were initially hypothesized to be carved by liquid water due to their resemblance to gullies on earth recent observations have highlighted significant sediment transport events occurring in martian gullies at times and places where co2 ice should be actively sublimating here we explore the role of co2 sublimation in mobilizing sediment through laboratory simulation in our previous experimental work we reported the first observations of sediment slope movement triggered by the sublimation of co2 frost we used a mars regolith simulant near the angle of repose the current study extends our previous work by including two additional substrates fine and coarse sand and by testing slope angles down to 10 we find that the mars regolith simulant is active down to 17 the fine sand is active only near the angle of repose and the coarse sand shows negligible movement using an analytical model we show that under martian gravity motion should be possible at even lower slope angles we conclude that these mass wasting processes could be involved in shaping martian gullies at the present day and intriguingly the newly reported co2 creep process could provide an alternative explanation for putative solifluction lobes on mars

laboratory simulations of martian gullies on sand dunes 1 small gullies observed on mars could be formed by groundwater seepage from an underground aquifer or may result from the melting of near surface ground ice at high obliquity to test these different hypotheses a cold room based laboratory simulation has been performed the experimental slope was designed to simulate debris flows on sand dune slopes at a range of angles different granulometry and permafrost characteristics preliminary results suggest that the typical morphology of gullies observed on mars can best be reproduced by the formation of linear debris flows related to the melting of a near surface ground ice with silty materials this physical modelling highlights the role of the periglacial conditions especially the active layer thickness during debris flow formation

topographic measurements of slope streaks on mars abstract slope streaks are enigmatic actively forming albedo features occurring on slopes in high albedo low thermal inertia dust rich equatorial regions on mars they are a specifically martian phenomenon with no direct analogs on the earth their morphology suggests that the streaks are initiated at their upslope tips and propagate down to their termini however the physical mechanism of their formation is uncertain we performed a large series of measurements of slopes associated with slope streaks using stereo pairs of high resolution orbital images obtained by hirise camera and generated several digital elevation models for selected streaks we found that 1 slopes at the upslope streak tips range widely however there is a strong indication that streaks can be initiated only on slopes steeper than 20 2 slopes of the streak termini show an even wider range with some streaks terminating at slopes as steep as their tips while others propagate all the way down to horizontal surfaces 3 the streaks can propagate stably for long many hundreds of meters distances and can turn following the topographic gradient on 10 15 slopes 4 no uphill propagation of streaks is detected over baselines of tens of meters 5 the slope streaks often propagate over 1 2 m high obstacles and can climb 1 2 m uphill over short meters distances we used these findings to assess the viability of two classes of hypotheses about slope streak formation mechanisms proposed earlier 1 dry some kind of run away avalanche like dry granular flow and 2 wet some kind of run away propagation of a front of percolating brines in the shallow subsurface no specific observation unambiguously proves or rejects either of the two mechanisms several of our findings are readily explained by the dry mechanism and cannot be easily explained with any kind of wet mechanism while other findings are closely consistent with the wet mechanism and are difficult to reconcile with the dry mechanism this situation might be explained by equifinality meaning that the streaks despite their similarity are formed by different physical processes alternatively some modifications to either the dry or wet mechanisms may be able to provide a coherent explanation it is also possible that new ideas are needed to understand the processes involved

evidence for very recent melt water and debris flow activity in gullies in a young mid latitude crater on mars abstract terrestrial debris flows and their deposits are mainly studied and monitored because of their hazardous nature on mars they may serve as geomorphologic indicators of transient liquid water we compared the morphology of debris flow like deposits within a young 0 2 ma mid latitude crater on mars with debris flow fans on svalbard as possible terrestrial analogues it was our objective to constrain whether dry granular flow or processes related to water saturation at or close to the surface were responsible for the formation of the deposits within the crater we found that the morphological attributes of the deposits on mars are very similar to debris flows in svalbard and include overlapping terminal lobes debris tongues and snouts debris flow fans scoured channels with medial deposits debris plugs and clearly defined lateral deposits levees furthermore the interior crater walls display a range of landforms indicating aspect dependent degradation ranging from debris flow dominated pole facing slopes to east and west facing single channel gullies and north facing talus cones granular flow our findings suggest that the debris flows are not related to impact induced heating and release of meltwater we further suggest that degradation of a latitude dependent dust ice mantling unit may only have played a minor role in this youthful terrain instead we propose that the debris flows are mainly formed by melting of very recent snow deposits after the termination of the last martian ice age as such they may represent some of the most recent geomorphological indicators of transient liquid water in the martian mid latitudes the distinct north south asymmetry in degradation further demonstrates that insolation controlled slope processes are surprisingly efficient on mars during the last

seasonality of present day martian dune gully activity martian slope gullies are argued to be evidence for recent liquid water flow on the surface of mars to explain the source of water a wide range of environmental conditions and processes has been invoked however a lack of information about the environmental context or timing of gully activity makes it difficult to evaluate the theories here we present new observations of extensive gully modification over the past 6 mars years within dune gullies with slope gully morphology observed activity within 18 gullies in 7 dune fields constrains timing to winter which is consistent with observed slope gully activity these observations show that fluvial processes are unlikely to cause present day martian dune gully activity and imply that co 2 frost accumulation may play the dominant role

examining the physical meaning of the bank erosion coefficient used in meander migration modeling widely used models of meander evolution relate migration rate to vertically averaged near bank velocity through the use of a coefficient of bank erosion e in applications to floodplain management problems e is typically determined through calibration to historical planform changes and thus its physical meaning remains unclear this study attempts to clarify the extent to which e depends on measurable physical characteristics of the channel boundary materials using data from the sacramento river california usa bend average values of e were calculated from measured long term migration rates and computed near bank velocities in the field unvegetated bank material resistance to fluvial shear k was measured for four cohesive and noncohesive bank types using a jet test device at a small set of bends for which both e and k were obtained we discovered that variability in k explains much of the variability in e the form of this relationship suggests that when modeling long term meander migration of large rivers e depends largely on bank material properties this finding opens up the possibility that e may be estimated directly from field data enabling prediction of meander migration rates for systems where historical data are unavailable or controlling conditions have changed another implication is that vegetation plays a limited role in affecting long term meander migration rates of large rivers like the sacramento river these hypotheses require further testing with data sets from other large rivers

initiation and flow conditions of contemporary flows in martian gullies understanding the initial and flow conditions of contemporary flows in martian gullies generally believed to be triggered and fluidized by co2 sublimation is crucial for deciphering climate conditions needed to trigger and sustain them we employ the ramms rapid mass movement simulation debris flow and avalanche model to back calculate initial and flow conditions of recent flows in three gullies in hale crater we infer minimum release depths of 1 0 1 5 m and initial release volumes of 100 200 m3 entrainment leads to final flow volumes that are 2 5 5 5 times larger than initially released and entrainment is found necessary to match the observed flow deposits simulated mean cross channel flow velocities decrease from 3 4 m s 1 to 1 m s 1 from release area to flow terminus while flow depths generally decrease from 0 5 1 m to 0 1 0 2 m the mean cross channel erosion depth and deposition thicknesses are 0 1 0 3 m back calculated dry coulomb friction ranges from 0 1 to 0 25 and viscous turbulent friction between 100 200 m s 2 which are values similar to those of granular debris flows on earth these results suggest that recent flows in gullies are fluidized to a similar degree as are granular debris flows on earth using a novel model for mass flow fluidization by co2 sublimation we are able to show that under martian atmospheric conditions very small volumetric fractions of co2 of 1 within mass flows may indeed yield sufficiently large gas fluxes to cause fluidization and enhance flow mobility

new insights into gully formation on mars constraints from composition as seen by mro crism over 100 martian gully sites were analyzed using orbital data collected by the compact reconnaissance imaging spectrometer for mars crism and high resolution imaging science experiment hirise on the mars reconnaissance orbiter mro most gullies are spectrally indistinct from their surroundings due to mantling by dust where spectral information on gully sediments was obtained a variety of mineralogies were identified their relationship to the source rock suggests that gully forming processes transported underlying material downslope there is no evidence for specific compositions being more likely to be associated with gullies or with the formation of hydrated minerals in situ as a result of recent liquid water activity seasonal co2 and h2o frosts were observed in gullies at mid to high latitudes consistent with seasonal frost driven processes playing important roles in the evolution of gullies our results do not clearly indicate a role for long lived liquid water in gully formation and evolution

the mekong from satellite imagery a quick look at a large river abstract physical datasets on rivers thousands of kilometres long can be efficiently and rapidly acquired through satellite imagery as large rivers commonly cross several tectonic and climatic zones their channels are composed of a number of units each with characteristic morphology and behaviour separating a large river into such units provides a framework for understanding the geomorphology of the river concerned allowing acquisition of information for environmental impact analysis and river management about 2500 km of the mekong river from the china border to the sea has been examined with spot satellite images with a selection of modis and ikonos scenes in support hydrological data of the mekong river commission hydrographic maps of the commission and field observations have been used to verify and extend the findings from the satellite imagery the technique provides a rapid and holistic conceptualisation of forms and functions along the derived eight unit classification of the mekong river such a framework is valuable for 1 determining selected aspects of the geomorphological behaviour of a large river system 2 rapidly analysing project related environmental impacts and 3 examining the geological evolution of the river investigating large rivers is difficult and resource consuming but satellite imagery provides an easy and rapid tool the cost of the images however may be high as a number of them are required for this type of analysis

present day gully activity in sisyphi cavi mars flow like features and block movements abstract the continuously increasing number of multi temporal high resolution images from the surface of mars offers the possibility for detailed studies of present day surface activity in this study we investigated all gullies in the sisyphi cavi region 355 e 71 s of the south polar region of mars this region is influenced by the seasonal deposition of a decimeters thick translucent slab ice in late autumn winter and its subsequent sublimation in spring we mapped all gullies n 17 760 and measured their orientations we also identified gullies with contemporary activity n 35 using multi temporal hirise images for martian years my 28 to 34 we observed two different kinds of activity 1 dark flow like features and 2 movement of blocks for both sediment was transported from the source region alcove and or flanks of channels down the gully using image data from hrsc ctx and hirise we monitored the general defrosting of the study region we also analyzed the maximum daytime surface temperatures of the complete study region based on tes data from mys 24 to 26 to identify the origin and triggering mechanism of the observed activity we used 1 detailed topographic investigations e g slope angles of two extensively gullied slopes based on two hirise dtms 2 identification of small scale displacements with digital image correlation dic and 3 orientation measurements of active gullies and comparison to non active gullies we found that for the active gullies studied activity happens at the end of spring between ls 225 and 250 this is consistent with the timing of final stages of defrosting in the region at this time some surfaces are already defrosted while others still host the seasonal slab ice cover for the surfaces with slab ice dark defrosting spots and flows if the surface is inclined are observed on dark dunes as well as on gully aprons and in gully channels these spots form when triggered by basal sublimation generated overpressure sediment entrained in co2 gas is transported through cracks within the ice and redeposited onto the frosted surface we compared and linked both morphologic features dark dune spots and dark flow like features and concluded that these features have comparable or even the same triggering mechanisms based on this extensive study the most plausible mechanism for ongoing gully activity can be divided into two steps 1 accumulation of material within gully channels via small dry flows on top of the slab ice comparable to dark dune spots flows 2 when a critical mass is reached the sediment flows down the still frosted gully on top of the sublimating ice or as a mixture of dry material and ice in a catastrophic flow the triggering factor for the movement of blocks remains unclear as their timing could not be constrained with the available data we identified headwall erosion in one gully in the study region whereas a discrete source could not be identified for the other sites suggesting multiple failure mechanisms could be active in such gullies finally through volume balance calculations we show that active gullies in sisyphi cavi could have been formed within decades to several tens of thousands of my but gully morphology indicates a much longer period for formation of the entire gully landform

recent debris flows on mars seasonal observations of the russell crater dune field 1 debris flows occur on slopes in the russell crater dune field the morphology of the erosion features resembles terrestrial viscous slurry flows mudflows and suggests that a flow of fine grained material mixed with liquid water might have been responsible for their formation seasonal mgs tes and moc imagery based observations of the dune field show 1 an annual frosting and defrosting cycle and 2 that liquid h2o could be stable within a limited time period in the summer of the southern hemisphere these observations lead to the conclusion that debris flows in the russell crater dune field may form under current climatic conditions by episodic or seasonal melting of small amounts of autumn winter condensed water ice

interfacial liquid water on mars and its potential role in formation of hill and dune gullies abstract gullies are among the most intriguing structures identified on the surface of mars most common are gullies located on the slopes of craters which are probably formed by liquid water transported by shallow aquifers heldmann j l carlsson e johansson h mellon m t toon o b 2007 icarus 188 324 344 two particular types of gullies are found on slopes of isolated hills and dunes the hill slope gullies are located mostly at 50 s which is at the high end of latitudes of bulk of the gullies found so far the dune gullies are found in several locations up to 65 s reiss d jaumann r kereszturi a sik a neukum g 2007 lunar planet sci xxxviii abstract 1993 but the best known are those in russel crater at 54 s the hill and dune gullies are longer than others making the aquifers explanation for their formation unlikely balme m mangold n baratoux d costard f gosselin m masson p pnet p neukum g 2006 j geophys res 111 doi 10 1029 2005je002607 recently it has been noted that thin liquid films of interfacial water can play a role in rheological processes on the surface of mars moehlmann d 2008 icarus 195 131 139 kereszturi a moehlmann d berczi sz ganti t kuti a sik a horvath a 2009 icarus 201 492 503 here we try to answer the question whether interfacial liquid water may occur on mars in quantities large enough to play a role in formation of gullies to verify this hypothesis we have calculated thermal models for hills and dunes of various steepness orientation and physical properties we find that within a range of average expected values of parameters it is not possible to have more than a few monolayers of liquid water at depths greater than a centimeter to create subsurface interfacial water film significantly thicker and hence to produce conditions for the slope instability parameters have to be chosen to have their extreme realistic values or an additional source of surface heating is needed one possibility for additional heating is a change of atmospheric conditions due to a local dust storm we conclude that if interfacial water is responsible for the formation of the hill slope gullies our results may explain why the hill gullies are rare

ripple migration and dune activity on mars evidence for dynamic wind processes 1 in this report we show evidence of widespread ripple migration over the stoss side of dark barchan dunes in nili patera on mars the measured average migration of 1 7 meters in less than 4 terrestrial months clearly indicates that active sand saltation is occurring in the study area in addition we document widespread changes in the dune base ground surface contact and in the slip face structures showing that not only the ripples but the whole dunes are actually migrating in the present day atmospheric setting these results provide unequivocal evidence of recent aeolian activity and suggest that other dunes and ripples on mars may also be active

geometry of a miocene submarine canyon and associated sedimentary facies in southeastern calabria southern italy outcrops of the stilo capo d9orlando formation latest oligocene early miocene along the southeastern coast of calabria southern italy expose a cross section orthogonal to paleoflow of the proximal part of a turbidite depositional system major erosion surfaces cutting into basement rocks define several submarine paleocanyons paleocanyon fills consist of large lenticular conglomerate bodies that are 200 580 m thick and 3 6 km wide the best example of these paleocanyons is located near the town of stilo where the geometric relationships between paleocanyon fill and adjacent slope deposits are well exposed at this locality a 460 m thick section of conglomerate cuts into the basement and is composed internally of smaller scale channel fills of poorly organized clast supported cobble to boulder conglomerate deposited mainly by high density turbidity flows the conglomerate is thickest near stilo and becomes progressively thinner southward where a wedge of mudrock intervenes between the basement and the conglomerate the mudrock wedge is composed of poorly bedded intensely bioturbated mudstone with slump structures and represents slope deposits bedding within the mudrock wedge is better defined in its stratigraphically higher part near the conglomerate body where thin bedded normally graded sandstone layers with climbing ripples horizontal lamination and general thickening toward the canyon axis are present these layers are the deposits of dilute turbidity currents that occasionally spilled over the canyon margins when the depression was nearly filled the conglomeratic canyon fill and the adjacent muddy slope deposits are both overlain by a laterally continuous sequence 160 m thick composed of two units of fine grained thin bedded turbidites alternating with two units of thicker sandstone and minor pebble conglomerate beds the paleocanyons probably originated as subaerial valleys in response to a major fall in relative sea level at 30 ma and were later submerged by a combination of relative sea level rise and concomitant tectonic activity the sharp transition between coarse grained canyon confined conglomerate and the overlying fine grained unconfined thin bedded turbidites exists throughout southern calabria and may represent the effect of a significant rise in relative sea level two other cycles of relative sea level changes probably resulting from local tectonic control are indicated by the upper part of the stilo capo d9orlando formation

periglacial mass wasting landforms on mars suggestive of transient liquid water in the recent past insights from solifluction lobes on svalbard abstract on earth periglacial solifluction is a slow mass wasting process related to freeze thaw activity we compare the morphology of small scale lobate features on mars to solifluction lobes in svalbard to constrain their processes of formation the analysis is based on high resolution satellite imagery of mars hirise 25 cm pxl aerial images of svalbard with a similar spatial resolution hrsc ax 20 cm pxl acquired through an air campaign in summer 2008 and ground truth obtained during two summer expeditions in 2009 and 2011 on svalbard we present a detailed study of two crater environments on mars displaying two types of lobate forms characterized as sorted clast banked and non sorted lobes on both svalbard and mars such lobes typically occur as clusters of overlapping risers lobe fronts pointing to differential velocities in the soil the martian small scale lobes have well defined arcuate risers and lobe treads surface lobe widths range between 14 and 127 m and tread lengths between 13 and 105 m riser height is estimated to be approximately 1 5 m the lobes on mars share the plan view morphology of solifluction lobes on svalbard and their morphometry is within the range of values of terrestrial solifluction lobes the lobes are distinct from permafrost creep landforms such as rock glaciers we show the results of a survey of 53 hirise images covering latitudes between 59 n and 81 n similar to svalbard the studied lobate features on mars occur in close spatial proximity to gullies and thermal contraction polygons the widespread distribution of the lobate forms in the northern hemisphere and their close association to ground ice and gullies are best explained by mass wasting processes related to frost creep gelifluction and or plug like flow this suggests a protracted process thousand to several thousands of years of freeze thaw activity at the northern high latitudes on mars age constraints on lobe deposits and superposition relationships with gullies and polygons imply a process involving liquid water within the last few million years

identifying the effects of parameter uncertainty on the reliability of riverbank stability modelling bank retreat is a key process in fluvial dynamics affecting a wide range of physical ecological and socioeconomic issues in the fluvial environment to predict the undesirable effects of bank retreat and to inform effective measures to prevent it a wide range of bank stability models have been presented in the literature these models typically express bank stability by defining a factor of safety as the ratio of driving and resisting forces acting on the incipient failure block these forces are affected by a range of controlling factors that include such aspects as the bank profile bank height and angle the geotechnical properties of the bank materials as well as the hydrological status of the riverbanks in this paper we evaluate the extent to which uncertainties in the parameterization of these controlling factors feed through to influence the reliability of the resulting bank stability estimate this is achieved by employing a simple model of riverbank stability with respect to planar failure which is the most common type of bank stability model in a series of sensitivity tests and monte carlo analyses to identify for each model parameter the range of values that induce significant changes in the simulated factor of safety these identified parameter value ranges are compared to empirically derived parameter uncertainties to determine whether they are likely to confound the reliability of the resulting bank stability calculations our results show that parameter uncertainties are typically high enough that the likelihood of generating unreliable predictions is typically very high 80 for predictions requiring a precision of 15 because parameter uncertainties are derived primarily from the natural variability of the parameters rather than measurement errors much more careful attention should be paid to field sampling strategies such that the parameter uncertainties and consequent prediction unreliabilities can be quantified more robustly

gullies and their relationships to the dust ice mantle in the northwestern argyre basin mars we investigated gullies and their relationships to the atmospherically derived dust ice mantle and aeolian features in the northwestern part of the argyre basin a detailed morphologic map of the argyre study region allowed us to constrain the stratigraphic relationships and relative ages of gullies in addition we investigated the morphologic characteristics and orientations of all gullies in the argyre study region maximum absolute ages for gullies were determined with crater size frequency distribution measurements of the dust ice mantle which is the source material of gullies in the study area gullies only evolve from this mantle probably by melting of its ice content two different morphologies of pristine and degraded gullies were identified mostly occurring on pole and equatorward facing slopes respectively we conclude that the morphologies and orientations were initiated either by a more rapid and extensive erosion of equatorward facing gullies or by at least two generations of gullies with generally older gullies on equatorward facing slopes and younger ones on pole facing slopes different intensities of solar insolation on equator and pole facing slopes might be responsible for the different development of pristine and degraded gullies gullies in the study area generally have ages 20 ma some uncratered and thus very young aeolian dunes are superposed by a few gullies in some locations indicating another even younger generation of gullies with an upper limit absolute model age of about 500 ka

formation of gullies on mars by debris flows triggered by co2 sublimation martian gully landforms resemble terrestrial debris flows formed by the action of liquid water and have thus been interpreted as evidence for potential habitable environments on mars within the past few millennia however ongoing gully formation has been detected under surface conditions much too cold for liquid water but at times in the martian year when a thin layer of seasonal co 2 frost is present and defrosting above the regolith these observations suggest that the co 2 condensation sublimation cycle could play a role in gully formation here we use a thermo physical numerical model of the martian regolith underlying a co 2 ice layer and atmosphere to show that the pores beneath the ice layer can be filled with co 2 ice and subjected to extreme pressure variations during the defrosting season the subsequent gas fluxes can destabilize the regolith material and induce gas lubricated debris flows with geomorphic characteristics similar to martian gullies moreover we find that subsurface co 2 ice condensation sublimation and pressurization occurs at conditions found at latitudes and slope orientations where gullies are observed we conclude that martian gullies can result from geologic dry ice processes that have no terrestrial analogues and do not require liquid water such dry ice processes may have helped shape the evolution of landforms elsewhere on the martian surface

using provenance data to assess archaeological landscapes an example from calabria italy abstract ceramic provenance studies have helped archaeologists examine trade and exchange in multiple scales the organization of production and even vessel function yet they may go even further to provide a venue for the examination of past people s perception of their landscape to do so a methodology is needed that links the choices prehistoric potters made as reflected in their ceramics with the choices their landscape could afford them as reflected in the extent and distribution of local clays and the physical chemical and mineralogical characteristics of these clays using the region of bova marina in southwestern calabria as a case study we have combined a raw materials survey with field and laboratory experiments along with chemical and mineralogical analyses of the collected sediments to understand the distribution and the physical chemical and mineralogical variability of locally available clays and provide baseline data against which prehistoric ceramic materials from the region may be compared we show that the local sediments can be divided into three major units based on their macroscopic mineralogical and chemical characteristics that correspond well with the major geological units outcropping in the study area while two of these units have internally consistent properties the third is variable

are different martian gully morphologies due to different processes on the kaiser dune field we describe and compare the morphology and activity of two types of gullies with different orientations collocated on the kaiser dune field in the southern hemisphere of mars large apron gullies and linear dune gullies the activity of large apron gullies follows an annual cycle i material collapse into the alcove mid autumn late winter as co2 condenses ii remobilization by mass flows late winter and iii continuous appearance of hundreds of digitate flows on the fan autumn winter we find that large apron gullies could form in hundreds of martian years in contrast linear dune gullies are active briefly in late winter when the co2 frost disappears their activity is characterized by the extension of channels the creation of pits and the darkening of the surface linear dune gullies are likely to form within one to tens of martian years we infer that insolation which influences the depth to ground ice and the amount of volatile deposited may be the factor differentiating large apron gullies and linear dune gullies sediment transport by co2 sublimation is a good candidate for the activity observed in all of these features however linear gullies could also be formed by brine release when the temperature rises abruptly after the removal of the co2 ice

quantitative analysis of the morphology of martian gullies and insights into their formation the process of formation of observed geologically recent gully features on mars has remained a topic of intense debate since their discovery in this study we performed quantitative morphological analysis on certain parameters of gullies from different settings such as crater walls terraces and sand dunes on the martian surface in addition to the meteor and xiuyan craters on the earth the morphometric parameters were measured for cross profiles which were extracted along each gully at certain intervals some interesting relationships among the parameters were determined which could provide us a comprehensive understanding of the morphologies of the gullies the results show that strong correlations exist among those parameters and the gullies are morphometrically similar except for a scale difference in different geologic settings the morphometric similarity implies that they were probably formed by some common processes on the other hand the morphometric differences indicate that the processes may have played different roles in the formation of the gullies the formation of gullies on the earth crater walls was heavily affected by surface flow and slippage and pre existing fractures and faults were also very influential in their formation we propose that gullies in martian crater walls and terraces should have a similar formation mechanism and they can probably account for most of gullies appearing on crater walls the morphometric differences between the gullies in sand dunes and other gully types are probably a result of the disparity in lithological settings which have significant influence on erosion ability even for the same agents

metastability of liquid water on mars abstract a simple model of local heat transport on mars demonstrates that transient melting of ice may occur in depressions and gullies nearly anywhere on the planet where thin ice is illuminated by normal incidence insolation an experiment has been performed to confirm the model of evaporation rate at low pressure reduction of radiative cooling due to gully geometry is shown to be important since appropriate meteorological topographic and optical conditions may occur on slopes nearly anywhere on the planet hydrological features such as gullies would likely form only where such ice might accumulate notably in sheltered locations at high latitudes it is suggested that cold trapping of winter condensation could concentrate a sufficient amount of ice to allow seasonal melting in gullies