viscous flow features on the surface of mars observations from high resolution mars orbiter camera moc images 10 5 10 7 years of the material our shear stress estimates of 10 1 5 10 2 5 mpa yield strain rates on the order of 10 11 10 16 s 1 which are within the superplastic flow regime of ice mean annual surface temperatures age constraints and strain estimates show that it is possible for a meters thick ice dust mixture to undergo viscous deformation under past or present surface conditions for ice grain sizes 10 mm the meters thick layer in which the viscous flow features formed is morphologically similar to a degraded meters thick ice dust surface deposit dissected mantle terrain locations of the viscous flow features dissected mantle terrain and recent gullies are concentrated in the midlatitude regions and all three show identical distributions as a function of latitude with the maximum frequency of occurrence at 40 n and s the strong association between these small scale flow features and the dissected mantle terrain large scale viscous flow features and recent gullies imply that deposition deformation and removal of ice rich materials has played an important role in the modification of the surface in the midlatitudes of mars during the amazonian and possibly longer index terms 5470 planetology solid surface planets surface materials and properties 5416 planetology solid surface planets glaciation 1863 hydrology snow and ice 1827 1823 hydrology frozen ground 8168 tectonophysics stresses general keywords viscous flow viscous creep dissected mantle terrain ice rich deposits mars climate recent gullies

recent climate cycles on mars stratigraphic relationships between multiple generations of gullies and the latitude dependent mantle reconstructions of the orbital parameters of mars spanning the last 20 myr combined with global circulation models predict multiple cycles of accumulation and degradation of an ice rich mantle in the mid latitudes driven primarily by insolation at the poles during periods when obliquity was more than ten degrees greater than it is today i e 35 while evidence of an ice rich latitude dependent mantle ldm consistent with these predictions is abundant features indicative of cycles of emplacement and degradation of this unit are isolated and rare in addition fundamental physical properties of the ldm such as paleo thickness maxima have not been determined gullies which are sinuous channels found on steep slopes in mid and high latitudes interact with the ldm and provide a stratigraphic feature useful for documenting both cyclical emplacement removal and thickness estimates in past climate regimes in the southern hemisphere where gullies are most common we present extensive evidence of 1 cyclical degradation and removal of gullies in the lower mid latitudes 30 40 s and 2 burial and exhumation of inverted gully channels in the transitional latitude band between dissected and preserved ldm 40 50 s which can only be accounted for if an additional tens of meters of ldm were present at these locations during channel formation these relationships support a model in which end to end gully evolution is controlled by the behavior of the ldm at lower latitudes gullies incise an ice rich substrate and are removed when that ice becomes unstable and at higher latitudes gullies are buried by successive emplacement of ldm where ice remains stable near the surface further the presence of dormant buried gullies implies that present day activity within gullies likely to be controlled by the behavior of co 2 frost is insufficient to explain the entire gully population and that conditions conducive to increased gully activity preceded the most recent phase of ldm emplacement

emplacement of sandstone intrusions during contractional tectonics abstract sandstone injections are created by the forceful emplacement of remobilized sand in response to increases in overpressure however the contribution provided by horizontal compressive stress to the build up in overpressure and the resulting emplacement of sand injection complexes is still to be substantiated by robust field observations an opportunity to address this issue occurs in central california where a large volume of sandstone intrusions record regionally persistent supra lithostatic pore pressure detailed fieldwork allows sandstone filled thrusts to be recognized and for the first time permits us to demonstrate that some sandstone intrusions are linked to contractional deformation affecting the western border of the great valley basin fluidized sand was extensively injected along thrust surfaces and also fills local dilatant cavities linked to thrusting the main aims of this paper are to provide detailed descriptions of the newly recognized syn tectonic injections and describe detailed cross cutting relationships with earlier sandstone injection complexes in the study area finally an evolutionary model consisting of three phases of sand injection is provided in this model sand injection is linked to contractional tectonic episodes affecting the western side of the great valley basin during the early middle cenozoic this study demonstrates that sand injections driven by fluid overpressure may inject along thrusts and folds and thereby overcome stresses associated with regional contractional deformation it is shown that different generations of sand injection can develop in the same area under the control of different stress regimes linked to the evolving mountain chain

a hydrological continuum in permafrost environments the morphological signatures of melt driven hydrology on earth and mars abstract this paper examines relationships between the morphology of cold desert hydrological features and the water sources and it relates the formation of diagnostic deposits and erosion patterns to environmentally controlled patterns of discharge in particular three sets of landforms found in the mcmurdo dry valleys of antarctica are compared to similar features on mars antarctic streams rivers to amazonian valleys terrestrial gullies to martian gullies and water tracks to recurring slope lineae similarities in landform morphology are highlighted for each set hydrological characteristics are aggregated or calculated and they are shown to scale comparably across the landforms for the terrestrial and martian groups accordingly a hydrological continuum is proposed linking the magnitude and the persistence of water sources in cold desert environments to flow response and the formation of diagnostic landforms this concept provides a framework for examining the relationships between climate hydrology and geomorphology in the cold desert environments of these two worlds

debris flows and water tracks in northern victoria land continental east antarctica a new terrestrial analogue site for gullies and recurrent slope lineae on mars although the present environmental conditions on mars prohibit the generation of significant volumes of liquid water observations of several very young landforms such as gullies and recurrent slope lineae have been interpreted as signals for aqueous processes to explore the range of conditions under which such features can be formed on earth a field site in northern victoria land east antarctica was geomorphologically investigated despite the small size of the icefree area the site displays gullies water tracks and other traces of liquid water the gullies show clear evidence of sediment transport by debris flows and are typical of paraglacial processes on steep slopes in a recently deglaciated area water tracks appear in different forms and seem to recur seasonally in the austral summer melting of snow and surface glacier ice is the major water source for both debris flows and water tracks the observations presented here highlight the potential for hyperarid polar deserts to generate morphogenetically significant amounts of meltwater the gullies are morphologically analogous to martian gullies and water tracks on steep slopes appear very similar to recurrent slope lineae the observations suggest that even small icefree sites in continental antarctica may enable observations which can serve as a basis for working hypotheses in mars analogue studies and future field work should consider more areas in antarctica in addition to the mcmurdo dry valleys to search for mars analogue landforms

flow characteristics of large eruption triggered debris flows at snow clad volcanoes constraints for debris flow models abstract theoretical modelling is not yet adequate to predict the behavior of debris flows which can be an extremely hazardous hydrologic process commonly associated with volcanic eruptions particularly at snow clad stratovolcanoes to provide a realistic basis for modelling the behavior of large 1000 m3 s debris flows this paper summarizes kinematic volumetric and hydraulic characteristics of ten large historic volcanic debris flows from four different volcanoes although debris flows larger than these are known to have occurred in the past the ten summarized here define a practical upper range in magnitude of more typical flows to be considered for future hazard prediction peak flow velocities of the ten debris flows studied were indirectly measured to be between about 5 and 20 m s on gradients of 0 005 to 0 25 m m but locally they were as great as 40 m s hydraulic average depths were as great as 25 m but were more commonly between 5 and 15 m in channels up to 400 m wide computed peak discharges volumetric flow rates were as high as 105 m3 s and total volumes were as much as 108 m3 total flow volumes increased by as much as four times in relatively steep channels as eroded sediment was incorporated into the debris flows flows generally achieved supercritical flow and deposited minimal volumes of sediment on gradients steeper than 0 02 m m subcritical flow and active deposition predominated on gradients less than 0 01 m m although flows travelled tens of kilometers on such low gradients while laying down deposits total distances travelled as debris flows were as far as 120 km

the comparison of topographic long profiles of gullies on earth to gullies on mars a signal of water on mars the topographic signature of a landform can give important clues as to its formation process here we have used topographic long profiles to study the process of gully formation on mars we studied topographic long profiles of gullies on earth to 1 confirm that previously published generalisations of how long profile shape varies with process also applies at the kilometre scale of martian gullies and 2 use as a direct comparison with the martian data we have compared 24 fluvial and 22 debris flow long profiles of terrestrial gullies derived from laser altimeter and gps measurements to 78 long profiles of a range of gullies on mars derived from a stereo photogrammetry point matching technique we have confirmed that this manual point matching technique is reliable for the martian data by comparison with full digital elevation models we used nine different characteristics of the long profiles including slope and curvature parameters to perform a canonical discriminant analysis which allowed us to identify the variables most important for differentiating between fluvial and debris flow gullies on earth in agreement with published literature for larger scale features we found that terrestrial debris flow gullies tend to be steeper and less concave than fluvial gullies we have found that gully long profiles on mars can resemble long profiles of terrestrial gullies formed by either fluvial or debris flow processes with slightly more affinity to fluvial systems gullies on mars can only be weakly separated from those on earth they can be separated from terrestrial fluvial gullies on curvature parameters and from terrestrial debris flow gullies by slope parameters in addition we have found that different alcove types identified from planview morphology are also distinctive in terms of their long profile morphology gullies which incise back into the bedrock are more similar to terrestrial debris flows whereas polar pit gullies are most similar to terrestrial fluvial gullies our findings suggest that the presence of a bedrock alcove promotes debris flow behaviour in gullies on mars

surge zones in the moine thrust zone of nw scotland abstract the caledonian thrust zones of assynt show several examples of large fault bounded structures surge zones up to 8 km 2 in extent which have moved further than adjacent rocks extensional faults can be traced into strike slip faults and then to contractional imbricate faults there are also zones of extensional and contractional flow as shown by strained bioturbation marks in the cambrian pipe rock several other low angle extensional fault zones have been recognized along the length of the moine thrust zone notably in the kinlochewe district recognition of these extensional faults and local surge zones has solved several local problems such as the lack of continuity of the glencoul thrust and the out of sequence character of some of the large low angle faults though the thrust propagation direction was generally from east to west in the transport direction several of the eastern faults have been reactivated later and locally cut down as extensional faults the so called moine thrust shows extensional fault movement at several localities along its length the extensional structures and the surge zones suggest that body forces have been important in driving the faults rather than just a push from the rear the moines and moine thrust zone were presumably driven to the wnw by gravity spreading and thinning of the main scottish caledonides

ideas about the surface runoff features on mars in their report evidence of recent groundwater seepage and surface runoff on mars 30 june p 2330 1 malin and edgett propose that the seepage and flow of water may have occurred on mars in the recent geologic past on the basis of the observation of a large number of channel features on

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

testing the water hypothesis quantitative morphological analysis of terrestrial and martian mid latitude gullies abstract although martian gullies resemble terrestrial counterparts two conflicting hypotheses exist for their formation still invoke fluvial processes on the one hand or lubricated co 2 flows on the other in this work we compared the quantitative morphology of terrestrial gullies known to have formed by liquid water and mid latitude martian gullies in the martian southern hemisphere we also compared these results with measurements of martian dry ravines adjacent to the gullies our results show a similarity between martian and terrestrial gully formation supporting the hypothesis that liquid water was involved in their erosion our results show dry ravines differ morphologically from gullies further suggesting fluidised flows as a likely origin of the latter variations in the relationships across various terrestrial and martian gullies indicate the significance of local environmental and geological conditions our work supports the idea that martian gullies may not have been formed by just one single process but may have evolved through a more complex interaction of processes and environment

numerical modeling of self channeling granular flows and of their levee channel deposits when not laterally confined in valleys pyroclastic flows create their own channel along the slope by selecting a given flowing width furthermore the lobe shaped deposits display a very specific morphology with high parallel lateral levees a numerical model based on saint venant equations and the empirical variable friction coefficient proposed by pouliquen and forterre 2002 is used to simulate unconfined granular flow over an inclined plane with a constant supply numerical simulations successfully reproduce the self channeling of the granular lobe and the levee channel morphology in the deposits without having to take into account mixture concepts or polydispersity numerical simulations suggest that the quasi static shoulders bordering the flow are created behind the front of the granular material by the rotation of the velocity field due to the balance between gravity the two dimensional pressure gradient and friction for a simplified hydrostatic model competition between the decreasing friction coefficient and increasing surface gradient as the thickness decreases seems to play a key role in the dynamics of unconfined flows the description of the other disregarded components of the stress tensor would be expected to change the balance of forces the front s shape appears to be constant during propagation the width of the flowing channel and the velocity of the material within it are almost steady and uniform numerical results suggest that measurement of the width and thickness of the central channel morphology in deposits in the field provides an estimate of the velocity and thickness during emplacement citation mangeney a f bouchut n thomas j p vilotte and m o bristeau 2007 numerical modeling of self channeling granular flows and of their levee channel deposits

geomorphology landslide boost from entrainment the mechanisms that govern the growth of debris flows are largely unclear hampering efforts to assess natural hazards in landslide prone areas experiments suggest that high bed water content increases flow velocity and mass entrainment in landslides

lidar derived morphology of the 1993 lascar pyroclastic flow deposits and implication for flow dynamics and rheology abstract pumice flows are potentially destructive volcanic events that derive from eruption column collapse and whose dynamics are poorly understood the challenges in studying these flows include the lack of constraints on the dynamics kinematics and initial conditions that control their emplacement we present a morphological study of the distal deposits lobes of the pumice flows resulting from the 1993 eruption at lascar chile the surface geometry of the lobes was measured in detail using a lidar device which allowed for detailed characterisation of their morphology consisting of central channel and lateral levees and terminal frontal snout in particular we find that the ratio of channel levee height as a function of the ratio of the distance between levees total width of the lobe has a characteristic curve for these pumice flow lobes our analysis of several of the lascar pumice lobe deposits south east sector identified several dimensionless groups of the available parameters which when compared against published results from both experimental and numerical investigations allowed us to constrain crucial kinematic and dynamic information on the terminal phase of the pumice flows notably we estimate the velocity of the terminal phase of pumice flows to be 5 10 m s froude numbers of 1 5 2 are comparable with values found for experimental granular flows height width aspect ratios for the levee channel section of the pumice lobes are similar to those for experimental flows although these same aspect ratios for the snout are much larger for the natural deposits than their small scale analogues finally we discuss the possible emplacement dynamics of the terminal lascar 1993 pumice flows a pseudo reynolds number based on the velocity estimation is found to be up to 100 times larger for the pumice flows than experimental scale flows this suggests that the flow retarding frictional forces for large scale flows are relatively unimportant compared to flows at smaller scales mechanical effects such as fluidisation mobilisation of material lying on the slopes over which they propagate and lubrication due to polydispersivity could provide an explanation for their ability to propagate on shallow slopes 6 11

formation of recent martian gullies through melting of extensive water rich snow deposits the observation of gullies on mars indicates the presence of liquid water near the surface in recent times1 2 which is difficult to reconcile with the current cold climate gullies have been proposed to form through surface runoff from subsurface aquifers1 3 or through melting of near surface ice under warmer conditions4 but these gullies are observed to occur preferentially in cold mid latitudes2 where the presence of liquid water is less likely and on isolated surfaces where groundwater seepage would not be expected making both potential explanations unsatisfactory here i show that gullies can form by the melting of water rich snow that has been transported from the poles to mid latitudes during periods of high obliquity within the past 105 to 106 years refs 5 6 melting within this snow7 can generate sufficient water to erode gullies in about 5 000 years my proposed model for gully formation is consistent with the age and location of the gullies and it explains the occurrence of liquid water in the cold mid latitudes as well as on isolated surfaces remnants of the snowpacks are still present on mid latitude pole facing slopes and the recent or current occurrence of liquid water within them provides a potential abode for life

deep groundwater circulation through the high arctic cryosphere forms mars like gullies we report here the discovery of the northernmost known perennial spring located in the polar desert of the canadian high arctic average precipitation 75 5 mm yr average annual air temperature 19 7 c the high discharge spring 520 l s has also anomalously high temperatures 9 0 c despite occurring in a region of low geothermal gradient and thick 400 m permafrost active erosion at the spring outlet forms gullies with alcove channel apron morphology remarkably similar to archetypal gullies observed on mid latitude regions of mars geochemical and isotopic data show a meteoric origin for the waters demonstrating that deep circulating groundwater systems can form active connections through the cryosphere to the subsurface even in the absence of thermal anomalies this discovery challenges current understanding of high latitude permafrost hydrology

laboratory simulation of debris flows over sand dunes insights into gully formation mars gully morphology often summarized as comprising an alcove channel and debris apron is one of the key elements used to support the argument for liquid water in the recent past on mars nevertheless the processes that create different gully morphologies on both mars and earth are not fully understood one of the puzzling morphologic attributes of martian dune gullies is their apparent lack of an apron or terminal deposit which has caused debate about their formation process several physical processes such as runoff debris flows granular flows and sliding blocks falling downslope could explain the formation of these gullies in this work we focus on the role of liquid in the substrate as well as in the flow and choose to experimentally test the plausibility of this hypothesis we performed a series of analogue experiments to investigate the formation of gullies on sand dune like substrates we used controlled flows of water over an inclined sand box to produce gully like forms ice rich sedimentary substrates were used including substrates that included a thin liquid water saturated thawed layer an active layer above the ice saturated zone to give an analogue for a periglacial environment we quantitatively demonstrate that debris flow processes in periglacial experiments are conducive to the formation of narrow and long channels with small terminal deposits with perched channels by re analysis of martian elevation data for dune gullies on mars we have found good evidence that such terminal deposits could exist our experiments revealed that increased water content in the thawed layer above the frozen bed increases flow length due to the subsequent reduction in infiltration capacity water is incorporated into the flow by erosion of the wet thawed layer sand plus water and by drainage of the thawed layer using a mars environment simulation chamber we found that atmospheric pressure conditions seem to have a limited influence on the morphology of the flows our experimental investigation allowed the reproduction of terrestrial debris flow and martian gully morphologies suggesting that a substrate that is resistant to infiltration could be present beneath the dune gullies on mars we suggest that like in our laboratory experiments the presence of ice at shallow depth is a possible explanation for the formation of these morphologies and that a wet thawed layer is a possible explanation for the long flow length

the facing of faults it is proposed that the usage of the term structural facing be extended to include fault structures fault facing is defined as the direction in a fault plane which is at right angles to the trace of the bedding and is directed towards the younger beds certain types of faulted structures are found to have diagnostic patterns of facing variation

flow of variably fluidized granular masses across three dimensional terrain 1 coulomb mixture theory rock avalanches debris flows and related phenomena consist of grain fluid mixtures that move across three dimensional terrain in all these phenomena the same basic forces govern motion but differing mixture compositions initial conditions and boundary conditions yield varied dynamics and deposits to predict motion of diverse grain fluid masses from initiation to deposition we develop a depth averaged three dimensional mathematical model that accounts explicitly for solid and fluid phase forces and interactions model input consists of initial conditions path topography basal and internal friction angles of solid grains viscosity of pore fluid mixture density and a mixture diffusivity that controls pore pressure dissipation because these properties are constrained by independent measurements the model requires little or no calibration and yields readily testable predictions in the limit of vanishing coulomb friction due to persistent high fluid pressure the model equations describe motion of viscous floods and in the limit of vanishing fluid stress they describe one phase granular avalanches analysis of intermediate phenomena such as debris flows and pyroclastic flows requires use of the full mixture equations which can simulate interaction of high friction surge fronts with more fluid debris that follows special numerical methods described in the companion paper are necessary to solve the full equations but exact analytical solutions of simplified equations provide critical insight an analytical solution for translational motion of a coulomb mixture accelerating from rest and descending a uniform slope demonstrates that steady flow can occur only asymptotically a solution for the asymptotic limit of steady flow in a rectangular channel explains why shear may be concentrated in narrow marginal bands that border a plug of translating debris solutions for static equilibrium of source areas describe conditions of incipient slope instability and other static solutions show that nonuniform distributions of pore fluid pressure produce bluntly tapered vertical profiles at the margins of deposits simplified equations and solutions may apply in additional situations identified by a scaling analysis assessment of dimensionless scaling parameters also reveals that miniature laboratory experiments poorly simulate the dynamics of full scale flows in which fluid effects are significant therefore large geophysical flows can exhibit dynamics not evident at laboratory scales

sinuous gullies on mars frequency distribution and implications for flow properties recent gullies on mars are suspected to be the result of liquid water bearing flows a formation from wet flows has been challenged by studies invoking granular dry flows our study focuses on the sinuous shapes observed for some of the recent martian gullies sinuous gullies are found in locations and slopes of 10 15 similar to straight gullies and they are therefore related to the same formation processes numerical simulations of granular flows are performed here by introducing topographic variations such as obstacles roughness or slope changes that could possibly generate flow sinuosity none of these simulations was able to reproduce sinuous shapes on a slope lower than 18 with friction angles typical of dry granular material the only way to simulate sinuous shapes is to create small amplitude periodic variations of the topography of the deposit an origin not supported by current martian imagery given the presence of sinuosity in natural terrestrial debris flows we have concluded that sinuous martian gullies are better reproduced by liquid water bearing debris flows sinuous shapes in leveed flows are used to derive mechanical parameters from several martian gullies using photoclinometry values in yield strength of 100 2200 pa velocities of 1 1 3 3 m s 1 and viscosities from 40 to 1040 pa s are found which are all within the range of values for terrestrial debris flows with various proportions of liquid water 20 40

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

morphometry of bedrock meltwater channels on antarctic inner continental shelves implications for channel development and subglacial hydrology abstract expanding multibeam bathymetric data coverage over the last two decades has revealed extensive networks of submarine channels incised into bedrock on the antarctic inner continental shelf the large dimensions and prevalence of the channels implies the presence of an active subglacial hydrological system beneath the past antarctic ice sheet which we can use to learn more about inaccessible subglacial processes here we map and analyse over 2700 bedrock channels situated across 100 000 km2 of continental shelf in the western antarctic peninsula and amundsen sea to produce the first inventory of submarine channels on the antarctic inner continental shelf morphometric analysis reveals highly similar distributions of channel widths depths cross sectional areas and geometric properties with subtle differences between channels in the western antarctic peninsula compared to those in the amundsen sea at 75 3400 m wide 3 280 m deep 160 290 000 m2 in cross sectional area and typically 8 times as wide as they are deep the channels have similar morphologies to tunnel valleys and meltwater channel systems observed from other formerly glaciated landscapes despite differences in substrate geology and glaciological regime we propose that the antarctic bedrock channels formed over multiple glacial cycles through the episodic drainage of at least 59 former subglacial lakes identified on the inner continental shelf

outflow channels with deltaic deposits in ismenius lacus mars abstract a connected series of outflow channels in the ismenius lacus quadrangle are identified for the first time and characterized using high resolution stereo camera images of mars express the context camera images of mars reconnaissance orbiter and the topography of the mars observer laser altimeter these channels named okavango valles which stretch over 400 km south to north and join the northern plains were identified from braided channels scour groove marks poorly sinuous valleys and depositional landforms discharge rates were estimated to 0 1 5 10 6 m 3 s 1 from analysis of the topography of scour marks pathways of channels segments were extracted from topography showing a unique source at a breached crater rim suggesting overflow from ponded depressions a series of delta fans are observed inside depressions along the channel pathways the presence of these deltas formed in former bodies of water is a compelling argument for formation of this outflow channel system by fluvial flows the similarity of these flows with other outflow channels on mars proves that volcanically related outflows cannot explain all such features in addition this study also shows that catastrophic floods are able to create fan deltas in transient lakes this example has to be taken into account in the interpretation of late stage fans associated with poorly branched valleys and single channels

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

possible open system hydraulic pingos in and around the argyre impact region of mars abstract we report the observation of possible hydraulic open system pingos osps at the mid latitudes 37 s in and around the argyre impact basin osps are perennial water ice cored mounds they originate and evolve in periglacial and pro glacial landscapes on earth where intra or sub permafrost water under hydraulic artesian pressure uplifts localised sections of surface or near surface permafrost that then freezes in situ we invoke three lines of evidence in support of our analogue based interpretation 1 similarities of shape size and summit traits between terrestrial osps and the martian mounds 2 clustered distribution and the slope side location of the mounds consistent with terrestrial permafrost environments where osps are found and 3 spatially associated landforms putatively indicative of periglacial and glacial processes on mars that characterise osp landscapes on earth this article presents five osp candidate locations and nests these mound locations within a new geological map of the argyre impact basin and margins it also presents three periglacial hypotheses about the possible origin of the water required to develop the mounds alternative non periglacial formation hypotheses also are considered however we show that their robustness is not equal to that of the periglacial ones

gliding and overthrust nappe tectonics in the barberton greenstone belt abstract regional recumbent folds inverted stratigraphy nappes and olistostromes are described from the southern part of the 3 3 3 5 ga barberton greenstone belt overthrusting of thin rigid silicified slabs with minimum dimensions of 25 km2 and up to 500 m in thickness occurred over minimum distances of 86 km more ductile and coherent units were overfolded up to at least 2 km during their emplacement the glide planes on which these nappes travelled were zones of high fluid pressures related to hydrothermal fluid circulation patterns driven by heat sources from igneous intrusions the upwelling areas of the geothermal convection cells were sites of mud pools and hydrothermal vents which may mark the trailing edges pull aparts of the overthrust units progressive silica and carbonate precipitation due to decreasing temperatures within the zones of fluid migration distant from the areas of high heat flow probably acted as built in braking systems below the travelling slabs active sedimentation and metasomatism during this tectonism indicates a protracted history for the evolution of the greenstone belt the recognition of nappe and overthrust tectonics in the barberton belt processes which may have been commonplace in archaean terrains necessitates a re evaluation of the stratigraphy of this belt

mobility and topographic effects for large valles marineris landslides on mars 1 recent experiments on dry granular flows over horizontal plane bare some similarities with large martian landslides observed in valles marineris vm however martian normalized runout are twice as large as those that observed in dry granular flow experiments numerical simulations on theoretical 2d and real 3d topographies reconstructed from remote sensing data show that slope effects significantly reduce the shift between experimental results and martian observation however topography effects are not strong enough to explain the high mobility of martian landslides as a result other physical and or geological processes should play a key role into the dynamics of martian landslides a new mobility is defined that makes it possible to characterize the dynamics of the flow regardless of the geometry of the released mass and of the underlying topography

erosion and mobility in granular collapse over sloping beds 1 we describe laboratory experiments of granular material flowing over an inclined plane covered by an erodible bed designed to mimic erosion processes of natural flows travelling over deposits built up by earlier events two controlling parameters are the inclination of the plane and the thickness of the erodible layer we show that erosion processes can increase the flow mobility i e runout over slopes with inclination close to the repose angle of the grains r by up to 40 even for very thin erodible beds erosion efficiency is shown to strongly depend on the slope of the topography entrainment begins to affect the flow at inclination angles exceeding a critical angle c r 2 runout distance increases almost linearly as a function of the thickness of the erodible bed suggesting that erosion is mainly supply dependent two regimes are observed during granular collapse a first spreading phase with high velocity followed by a slow thin flow provided either the slope or the thickness of the erodible bed is high enough surprisingly erosion affects the flow mostly during the deceleration phase and the slow regime the avalanche excavates the erodible layer immediately at the flow front waves are observed behind the front that help to remove grains from the erodible bed steep frontal surges are seen at high inclination angles over both rigid or erodible bed finally simple scaling laws are proposed making it possible to obtain a first estimate of the deposit and emplacement time of a granular collapse over a rigid or erodible inclined bed

amazonian modification of moreux crater record of recent and episodic glaciation in the protonilus mensae region of mars abstract morphologic characteristics of ice rich landforms in the martian mid latitudes record evidence for significant modification of the landscape in response to spin axis orbital parameter driven shifts in the late amazonian climate these landforms are spatially distributed across the mid latitudes and their co existing presence has so far not been observed from a single crater to infer how exactly a terrain has been modified while mars was undergoing major moderate minor shifts in its late amazonian climate we have therefore carried out an in depth investigation of moreux crater 135 km centered at 41 66 n 44 44 e in the protonilus mensae region for identification of features associated with recent and episodic glacial events and for emphasizing the role played by these glacial events in the modification of the crater evidence for extensive modification of the surfaces over crater rim wall and around central peak by emplacement of multiple scales of ice rich landforms that represents large history of glacial activities was found from our results we document phases of major moderate minor glacial activities within the crater as 1 piedmont lobes lobate debris aprons linear valley fills 1 ga 100 ma 2 viscous flow features 30 0 1 ma and 3 gullies thermal contraction crack polygons 2 1 0 4 ma the form and distribution of the random valleys observed within moreux suggests their formation by pressure induced melting and flow occurring beneath an extensive layer of ice we also suggest that central peak of moreux probably acted as the locus for accumulation of ice snow and the diversity of glacial periglacial features within the crater was possibly controlled by differences in the amount of accumulated ice snow and the rate at which the terrain responded to the shifts in climate during subsequent periods of obliquity changes taken together these ice rich deposits within moreux suggest that sequential modification of the crater surfaces over the rim wall and around central peak has occurred over the last tens of millions of years of martian history this new evidence thus adds another well documented case to rapidly accumulating evidences for widespread glacial activity in the middle latitudes of mars in recent martian history

modeling crater topography and albedo from monoscopic viking orbiter images 1 methodology a new photoclinometric technique for extraction of topographic data from single planetary images is presented that overcomes many previous limitations of photoclinometry the procedure fully compensates for oblique viewing geometry prevalent in spacecraft images albedo variations have been one of the most serious obstacles in the application of photoclinometry to planetary surfaces this problem is overcome in the topographic solution by simultaneously utilizing brightness data from a pair of profiles both segments are assumed to have the same topographic and albedo variations along their lengths profile directions are chosen where the orientation of downslope or upslope is obvious thus resolving a major ambiguity in photoclinometry this requirement is particularly easy to satisfy for craters and not very difficult for many irregular features an additional procedure is presented that eliminates even the requirement of topographic symmetry along the pair of profiles if two profiles have the same relief but their shapes are very different another method can be used in an iterative process to derive topographic profiles however this procedure does require that the albedo not vary along the profiles test results indicate that both procedures have an accuracy and precision of approximately 2 for slopes of typical bowl shaped craters which translates to approximately 5 for depths

geologically recent gully polygon relationships on mars insights from the antarctic dry valleys on the roles of permafrost microclimates and water sources for surface flow we describe the morphology and spatial relationships between composite wedge polygons and mars like gullies consisting of alcoves channels and fans in the hyper arid antarctic dry valleys adv as a basis for understanding possible origins for martian gullies that also occur in association with polygonally patterned ground gullies in the adv arise in part from the melting of atmospherically derived wind blown snow trapped in polygon troughs snowmelt that yields surface flow can occur during peak southern hemisphere summer daytime insolation conditions ice cemented permafrost provides an impermeable substrate over which meltwater flows but does not significantly contribute to meltwater generation relationships between contraction crack polygons and sedimentary fans at the distal ends of gullies show deposition of fan material in polygon troughs and dissection of fans by expanding polygon troughs these observations suggest the continuous presence of meters thick ice cemented permafrost beneath adv gullies we document strong morphological similarities between gullies and polygons on mars and those observed in the adv inland mixed microclimate zone on the basis of this morphological comparison we propose an analogous top down melting model for the initiation and evolution of martian gullies that occur on polygonally patterned mantled surfaces

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

the role of arcuate ridges and gullies in the degradation of craters in the newton basin region of mars abstract a survey of craters in the vicinity of newton basin using high resolution images from mars global surveyor and mars odyssey was conducted to find and analyze examples of gullies and arcuate ridges and assess their implications for impact crater degradation processes in the phaethontis quadrangle mc 24 we identified 225 craters that contain these features of these 188 had gullies on some portion of their walls 118 had arcuate ridges at the bases of the crater walls and 104 contained both features typically on the same crater wall a major result is that the pole facing or equator facing orientation of these features is latitude dependent at latitudes 44 s equator facing orientations for both ridges and gullies are prevalent but at latitudes

the terminology of structures in thrust belts abstract a review of structures and geometric relationships recognized in thrust belts is presented a thrust is defined as any contractional fault a corollary being that thrusts must cut up section in their transport direction flats are those portions of a thrust surface which were parallel to an arbitrary datum surface at the time of displacement and ramps are those portions of thrusts which cut across datum surfaces ramps are classified on the basis of their orientation relative to the thrust transport direction and whether they are cut offs in the hangingwall or footwall of the thrust lateral variations in the form of staircase trajectories are joined by oblique or lateral ramps which have a component of strike slip movement an array of thrusts which diverge in their transport direction may form by either of two propagation models these are termed piggy back propagation which is foreland directed and overstep propagation which is opposed to the thrust transport direction an array of thrust surfaces is termed an imbricate stack and should these surfaces anastamose upwards a duplex will result the fault bounded blocks are termed horses a duplex is bounded by a higher roof thrust and a lower floor thrust the intersection of any two thrust planes is termed a branch line thrusts can be classified on the basis of their relationship to asymmetric fold limbs which they cut a further classification arises from whether a particular thrust lies in the hangingwall or footwall of another one the movement of thrust sheets over corrugated surfaces or the local development of thrust structures beneath will fold higher thrust sheets these folds are termed culminations and their limbs are termed culmination walls accommodation of this folding may require movement on surfaces within the hangingwall of the active thrust these accommodation surfaces are termed hangingwall detachments and they need not root down into the active thrust this category of detachment includes dip slip hangingwall drop faults which are developed by differential uplift of duplex roofs and out of the syncline thrusts which develop from overtightened fold hinges back thrusts as well as forming as hangingwall detachments may also form due to layer parallel shortening above a sticking thrust or by rotation of the hangingwall above a ramp

influence of the scar geometry on landslide dynamics and deposits application to martian landslides received 24 january 2011 revised 23 june 2011 accepted 30 june 2011 published 4 october 2011 1 landslides dynamics prediction remains difficult in spite of a considerable number of studies the runout distance is widely used in analysis of landslide dynamics and in the calibration of the rheological parameters involved in numerical modeling however the unknown impact of the significant uncertainty in the shape of the initial released mass on the runoutdistanceandontheoverallshapeofthedepositraisesquestionsabouttherelevanceof these approaches the impact of the initial scar geometry on flow and distribution of the deposits is studied here using satellite data and numerical modeling of theoretical landslides and martian landslides informed by geomorphological analysis by varying the initial scar geometry from spoon shaped to steep wall geometry our results show that the runout distance is a very robust parameter that is only slightly affected by the change in the geometry of the initial scar on the contrary the lateral extent of the deposit is shown to be controlled by the scar geometry providing unique insights into the initial landsliding conditionsonmarsandmakesitpossibletoaccuratelyrecoverthevolumeinitiallyinvolved an essential ingredient for volume balance calculation a feedback analysis of valles marineris landslides can be drawn showing good agreement between numerical results and geomorphological analysis the geometry of the initial scar inferred from numerical modeling is strongly correlated with the regional tectonic history in valles marineris area

a comparison of semiarid and subhumid terrestrial gullies with gullies on mars implications for martian gully erosion abstract comparison of martian hillside gullies with terrestrial analogues is a productive method for gaining an understanding of how surface processes operate on mars and on earth as well as their similarities and differences here we compare gullies within a semiarid region of island lagoon near woomera australia and periglacial gullies located at pasture hill new zealand with the martian gullies in noachis terra we discovered that fluvial processes dominate erosion at the terrestrial sites though in different forms concentration of overland flow and the presence of a resistant cap rock have played a key role in the location and shape of the island lagoon gullies the presence of steeper slopes and a greater abundance of volatiles such as water frost and snowmelt at pasture hill have helped carve channels equivalent in size to the martian gullies and the interaction of frost dry flows snowmelt and debris flows has led to a complex regime of gully erosion and deposition the observation of similar features on mars suggests that martian gully formation is not necessarily restricted to a single process in addition gully slopes are closely related to those of their host escarpment as well as the thickness of erodible material and presence of bedrock traditional indicators of water related activity such as slope and sinuosity need to be placed into the context of the environment of the study site

slope instabilities in dolomieu crater reunion island from seismic signals to rockfall characteristics 1 the seismic signals of hundreds of rockfalls within dolomieu crater piton de la fournaise volcano reunion island have been analyzed to investigate a possible link between physical rockfall generating processes and associated seismic signal features moreover indirect observation of rockfalls via the seismic signals they generate can provide useful data for studying volcanoes and the temporal variations of their structure an increase in the number of rockfall events and their volumes might be an indicator of structural weakness and deformation of the volcano associated with potential eruptive activity the study focuses on a 10 month period following the 6 april 2007 crater floor collapse within dolomieu crater from may 2007 to february 2008 for granular flows a scaling law is revealed between seismic energy and signal duration a semiempirical approach based on both analytical analysis and numerical simulation of these flows shows that a similar scaling law exists between the difference of potential energy computed for an event and its propagation times and also emphasizes the effect of local topography on this scaling law simulated and observed data were compared to evaluate the proportion of potential energy dissipated in the form of seismic waves and confirm a direct link between the seismic energy and potential energy of a given granular flow the mean ratio of seismic to potential energy is of the order of 10 4 comparable to the range of values observed in previous studies a simple method based on these ratios is proposed to estimate the volumes of rockfalls from their seismic signal observed seismic energy and the frequency of rockfalls decreased at the beginning of the studied period and reached a stable level in july thus suggesting a postcollapse relaxation time of dolomieu crater structure of about 2 months from seismic signal analysis which is confirmed by deformation data the total rockfall volume over the study period is estimated to be 1 85 mm3

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

a hydrological analysis of terrestrial and martian gullies implications for liquid water on mars abstract understanding the role and amounts of liquid water involved in martian gully formation is critical in studies of the martian hydrosphere and climate we performed hydrological analyses using the manning and darcy weisbach equations in order to infer flow velocities and discharge rates from channels at two gully sites in noachis terra mars the results of these analyses were compared with analogous hillside gullies in australia we found the velocities and discharge rates for the terrestrial gullies to be comparable to velocities and discharge rates of some small martian gully channels in contrast velocity and discharge in some larger martian gullies were almost an order of magnitude higher equating with catastrophic flows on earth we postulate that the larger gully channels were more likely formed by a number of smaller flows in a similar manner observed in some terrestrial gullies a scenario that does not require vast amounts of liquid water to be stable under martian conditions in addition we found that post fluvial channel widening may have acted on the martian gullies probably by dry mass wasting leading to larger channels than were originally carved by liquid water future hydrological analyses of martian gullies will lead to a greater understanding of the relative importance of dry mass wasting compared to liquid water erosion

topography of valley networks on mars from mars express high resolution stereo camera digital elevation models 1 martian valley networks have been identified mainly in the noachian heavily cratered uplands the geometry of valley networks can be studied using mars orbiter laser altimeter mola altimetry which is sufficient to map large valleys without a detailed 3 d shape of valley networks imaging from the mars express high resolution stereo camera hrsc is used to generate digital elevation models dems with resolution 50 m and vertical accuracy 60 m we studied valleys near huygens crater and in the aeolis region both in the noachian bedrock and on the west echus plateau in hesperian bedrock hrsc dems in these areas show that 1 drainage density is 3 times higher than is observed in mola data 2 degree of ramification is 1 order more than with mola 3 transverse valley profiles show a v shape more accurately and a minimum depth of 20 m and 4 higher drainage density shows greater headward extension that is not correlated to greater valley depth the deepest valleys 400 m are found in the huygens region where the density in the dem is 0 1 km 1 compared to shallow valleys 100 m of the echus region where the density is higher 0 3 km 1 these regional differences are due to spatially variable preservation and bedrock lithology longitudinal profiles suggest variations in duration of activity profile concavity is only developed in some noachian terrains valleys visible in hrsc images correspond to topographic features in dems showing the same geometry as terrestrial valleys thought to be formed by overland flows and seepage

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

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

thrust tectonics of s devon the tectonics of the area from start point to chudleigh sw england are shown to be dominated by northward verging thrust nappes two major thrusts are postulated the dartmouth antiform is considered to be a major thrust structure not a fold structure as previously interpreted the torquay limestones are allochthonous and part of a klippe of a major thrust nappe with a minimum displacement of 13 km northwards a progressive and diachronous sequence of deformation has been established with deformation starting in the s and moving n many of the folds and cleavages are probably related to the strains developed locally in thrust tips and may have no regional correlation more intense and complex deformation is found in the s compared to the n the diachroneity is also reflected in the k ar mineral ages in the s at start point southward verging backfolding is the last significant hercynian deformation phase folding the thrust nappes

the stereographic analysis of facing abstract facing directions represent an accurate means by which tectonic structure and sedimentary way up may be related a simple method is presented for determining facing directions accurately using a stereonet once determined larger amounts of facing data can be quickly collated and analysed using similar techniques to those employed for other lineations an example is given for some sheath fold structures in the moine rocks of sutherland n scotland

multi agent gully processes evidence from the monaro volcanic province australia and in terra cimmeria mars abstract comparison of the similarities and differences between terrestrial and martian hillside gullies promotes understanding of how surface processes operate on both planets here we tested the viability of subsurface flow of water as a process affecting gully evolution we compared gullies within the monaro volcanic province near cooma new south wales australia to gullies possessing strong structural control near gasa crater terra cimmeria mars although cursory examination of the monaro gullies initially suggested strong evidence for aquifer erosion detailed field surveys showed the evidence to be ambiguous instead a complex regime of erosion dependent on multiple conditions and processes such as local geology surface runoff dry mass wasting and animal activity emerged we found the morphology of gullies near gasa crater to be consistent with erosion caused by liquid water while also being heavily influenced by the local environment including slope and geology additionally erosion at the martian site was not consistent with evidence of subsequent smaller scale erosion and channel modification by dry mass wasting local conditions thus play an important role in gully evolution further highlighting that processes forming martian gullies may be more diverse than initially thought

simulation of tsaoling landslide taiwan based on saint venant equations over general topography the 1999 chi chi earthquake triggered the catastrophic tsaoling landslide in taiwan the geomorphological change measured from the data of the 1989 and 2000 aerial photos reveals that the scar and deposit volumes are about 0 126 km3 and 0 15 km3 respectively the debris material ran over a distance of 1 6 km with 500 m descent in elevation in this paper we use the continuum model of hydraulic flow shaltop2d based on the equations of bouchut and westdickenberg to simulate numerically the landslide dynamics when the mass is moving the flow is assumed hydrostatic with a basal coulomb friction the best fit is obtained using the basal friction angle equal to 6 the only parameter of the simulation uniformly applied in the calculation domain the landslide front reaches the chinshui river valley the foothill of the slope within only about 25 s after initiation and the motion settles in about 113 s the maximum speed is estimated 75 m s the spreading of the deposit agrees well with the field measurement

formation of recent martian debris flows by melting of near surface ground ice at high obliquity the observation of small gullies associated with recent surface runoff on mars has renewed the question of liquid water stability at the surface of mars the gullies could be formed by groundwater seepage from underground aquifers however observations of gullies originating from isolated peaks and dune crests question this scenario we show that these landforms may result from the melting of water ice in the top few meters of the martian subsurface at high obliquity our conclusions are based on the analogy between the martian gullies and terrestrial debris flows observed in greenland and numerical simulations that show that above freezing temperatures can occur at high obliquities in the near surface of mars and that such temperatures are only predicted at latitudes and for slope orientations corresponding to where the gullies have been observed on mars

the 3d microscopic signature of strain within glacial sediments revealed using x ray computed microtomography abstract x ray computed microtomography ct a non destructive analytical technique was used to create volumetric three dimensional 3d models representing the internal composition and structure of undisturbed pro and subglacial soft sediment sample plugs for the purposes of identifying and analysing kinematic indicators the technique is introduced and a methodology is presented addressing specific issues relating to the investigation of unlithified polymineralic sediments six samples were selected based on their proximity to type brittle and ductile deformation structures or because of their perceived suitability for successful application of the technique analysis of a proglacial ideal specimen permitted the 3d geometry of a suite of micro faults and folds to be investigated and the strain history of the sample reconstructed the poor contrast achieved in scanning a diamicton of glaciomarine origin is attributable to overconsolidation under normal loading the sediment demonstrated to have undergone subsequent subglacial deformation another overconsolidated diamicton contains an extensive small scale the subglacial sample evidence indicates that complex polyphase brittle ductile deformation histories are common in such diamictic soft sediments and that the local micro scale environment composition structure shear forces and effective pressure controls rheology the sediment void ratio is a key indicator of strain three of the samples are tentatively placed at different points on the strain cycle for subglacially deforming soft sediment based on their void ratio characteristics and distribution it has been demonstrated that ct offers significant potential for elucidating glacial soft sediment kinematics the ability of the technique to both test a variety of hypotheses pertaining to mechanisms operating within the subglacial environment and evaluate efforts to replicate those processes under controlled laboratory conditions is therefore discussed along with solutions to the problems encountered within this project ct also permits the seamless linking of analytical techniques applied at the hand specimen mm micromorphological m mm scanning electron microscopy and x ray diffraction fluorescence nm m scales and the archiving duplication and dissemination of sample volumetric 3d data

recognition classification and mechanical description of debris flows abstract various types of flow or mass movement involving water and sediments occur on steep slopes in mountainous areas among them debris flows are peculiar events during which a large volume of a highly concentrated viscous water debris mixture flows through a stream channel throughout the world these phenomena cause considerable damage but remain poorly understood although a basic knowledge is already available concerning their recognition and propagation firstly a synthesis of the useful practical criteria of recognition is proposed debris flows must be seen as intermediate phenomena between hyperconcentrated flows intense bed load transport and landslides separated from them by sharp transitions of some characteristics celerity deposit nature and flow type two parameters solid fraction and material type thought to be appropriate for a sound and practical classification are brought out and the corresponding complete classification of flow and mass movements in mountain areas is presented two extreme debris flow types are thus distinguished muddy debris flows and granular debris flows a critical review of recent advances in debris flow dynamic is then proposed it is pointed out that adequate work must be carried out in the field of non newtonian fluid mechanics in particular one fundamental rheological property of debris flow materials is the yield stress which explains thick deposits on steep slopes and can be inferred from field measurements furthermore it can be used to estimate viscous dissipation within the bulk during flow relevant models predicting muddy debris flow dynamics are already available whereas further progress is needed concerning granular flows

liquid co2 breakout and the formation of recent small gullies on mars we show that the action of a co2 suspended flow could have produced the recent small gullies on mars and hence that liquid water is not required the model involves the build up of a liquid co2 aquifer behind and below a dry ice barrier dam cap rock in the pore spaces a few meters into the rock from the cliff face and on order of a hundred meters below the top of the cliff brink surface seasonal or obliquity cycle seasonal heating causes pinching out of the dry ice barrier and rapid release of the liquid co2 erosion of the gullies occurs as the rapid vaporization of the liquid co2 with entrainment of rock and clathrate hydrate ice produces a density flow analogous to a terrestrial nue ardente

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

orientation and distribution of recent gullies in the southern hemisphere of mars observations from high resolution stereo camera mars express hrsc mex and mars orbiter camera mars global surveyor moc mgs data 1 geologically recent small gullies on mars display morphologies consistent with erosion by water or by debris flows suggested formation models are divided into two main categories 1 groundwater or 2 melting of near surface ice snow sourced from the atmosphere we have measured location and orientation and recorded the local contexts of gullies to constrain the likely models of gully formation more than 22 000 mars orbiter camera narrow angle moc na and 120 mars express high resolution stereo camera hrsc images in the southern hemisphere were searched for gullies discrete gullied slope sections with consistent orientation were recorded rather than individual gullies slope setting impact crater valley wall etc location and orientation were recorded for each slope section more than 750 moc images with gullies 900 distinct gullied slope sections and more than 40 hrsc images 380 distinct gullied slope sections were identified from both moc and hrsc gullies were found to be most common between 30 and 50 degrees latitude and to have an overall pole facing preference the preferred gully orientation for hrsc is southeast rather than south in moc owing to illumination effects that make gullies difficult to detect on south to southwest facing slopes in hrsc in both moc and hrsc surveys higher latitude gullies show less preference for pole facing than those at mid latitudes both data sets produced similar results demonstrating that our data are reliable we suggest that the observed latitudinal and orientation distributions of gullies show that insolation and atmospheric conditions play a key role in gully formation

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

high resolution bathymetry reveals contrasting landslide activity shaping the walls of the mid atlantic ridge axial valley 1 axial valleys are found along most slow spreading mid ocean ridges and are one of the most prominent topographic features on earth in this paper we present the first deep tow swath bathymetry for the axial valley walls of the mid atlantic ridge these data allow us to analyze axial valley wall morphology with a very high resolution 0 5 to 1 m compared to 50 m for shipboard multibeam bathymetry revealing the role played by landslides slow spreading ridge axial valleys also commonly expose mantle derived serpentinized peridotites in the footwalls of large offset normal faults detachments in our map of the ashadze area lat 13 n ultramafic outcrops have an average slope of 18 and behave as sliding deformable rock masses with little fragmentation by contrast the basaltic seafloor in the krasnov area lat 16 38 n has an average slope of 32 and the erosion of the steep basaltic rock faces leads to extensive fragmentation forming debris with morphologies consistent with noncohesive granular flow comparison with laboratory experiments suggests that the repose angle for this basaltic debris is 25 we discuss the interplay between the normal faults that bound the axial valley and the observed mass wasting processes we propose that along axial valley walls where serpentinized peridotites are exposed by detachment faults mass wasting results in average slopes 20 even in places where the emergence angle of the detachment is larger

present day development of gully channel sinuosity by carbon dioxide gas supported flows on mars martian gullies have been widely studied but their formation mechanism is still under debate their channels generally trend straight downslope but some display sinuosity seasonally active gullies are common on sand dunes and their channels have been reported to develop sinuosity here we perform a detailed analysis of a gully on a dune within matara crater 49 5 s 34 9 e where development of channel sinuosity has taken place over 5 martian years my29 33 of observation this study was performed using hirise images hirise elevation data spectroscopic crism data and a 1d gcm for surface temperature modelling the morphological evolution of the gully suggests a significant seasonal contribution of fluid each year we observed material collapse and accumulation in the alcove followed by transport events during which lateral migration and extension of the channel occur together with growth of the debris apron over one martian year the debris apron propagated by almost 140 m from an initial length of 800 m these transport events occur in the middle of winter when co2 frost is still present and are contemporaneous with the beginning of the defrosting we propose that the activity and the sinuosity development in the gully could be explained by 1 a flow composed of sand and co2 gas producing morphologies similar to those in hyper concentrated flows on earth and 2 contribution of material from alternating of the alcove source location

present day formation and seasonal evolution of linear dune gullies on mars linear dune gullies are a sub type of martian gullies as their name suggests they only occur on sandy substrates and comprise very long compared to their width straight or sinuous channels with relatively small source areas and almost non existent visible deposits linear dune gullies have never been observed on terrestrial dunes and their formation process on mars is unclear here we present the results of the first systematic survey of these features in mars southern hemisphere and an in depth study of six dunefields where repeat imaging allows us to monitor the changes in these gullies over time this study was undertaken with hirise images at 25 30 cm pix and 1 m pix elevation data derived from hirise stereo images we find the latitudinal distribution and orientation of linear dune gullies broadly consistent with the general population of martian gullies they occur predominantly between 36 3 s and 54 3 s and occasionally between 64 6 s and 70 4 s they are generally oriented toward ssw at bearings between 150 and 260 we find that these gullies are extremely active over the most recent 5 martian years of images activity comprises 1 appearance of new channels 2 lengthening of existing channels 3 complete or partial reactivation and 4 disappearance of gullies we find that gully channels lengthen by 100 m per year the intense activity and the progressive disappearance of linear dune gullies argues against the hypothesis that these are remnant morphologies left over from previous periods of high obliquity millions of years ago the activity of linear dune gullies reoccurs every year between the end of winter and the beginning of spring ls 167 4 216 6 and coincides with the final stages of the sublimation of annual co ice deposit this activity often coincides spatially and temporally with the appearance of recurrent diffusing flows rdfs digitate shaped dark patches with low relative albedo up to 48 lower than the adjacent dune that encompass the active site south and ssw facing dune slopes are those which preferentially host co2 frost deposits however it is only those with angles of 20 just below the crest which possess linear dune gullies suggesting a slope limited formation process these observations provide a wealth of temporal and morphometric data that can be used to undertake numerical modeling to direct future image monitoring and guide laboratory experiments that can be used to better constrain the formation process of these features

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

possible ice wedge polygons and recent landscape modification by wet periglacial processes in and around the argyre impact basin mars abstract the argyre basin and associated rim materials in the southern hemisphere of mars are ancient having been formed by the impact of a large body 4 gya this notwithstanding the regional landscape continues to be altered by a multiplicity of geological and geomorphological processes three landforms whose close spatial association is identified in a new geological map of the argyre region 290 360 e 30 72 s feature prominently in the list of very late amazonian epoch alterations a small sized 20 m in diameter and unsorted polygons that exhibit metre to sub metre elevated margins or shoulders giving them a low centred appearance in wet permafrost environments on earth low centred polygons lcps often are underlain by ice wedges b gullies seemingly formed by wet flow s and incised by the lcps c a putative possibly ice rich latitude dependent mantle ldm that underlies the lcps and spatially convergent wet gullies in all of our observations these landforms occur from the middle to the high near polar latitudes of the region and overlie geological units of all ages hitherto the presence of the lcps has been reported only fleetingly in the literature and only in as much as they have been observed on the walls of a few scalloped depressions in mid utopia planitia by contrast we report the ubiquitous occurrence of the lcps in and around the argyre impact basin on gully margins and adjacent slopes as well as on relatively flat inter crater terrain on the basis of three separate but related lines of reasoning we hypothesise that ice wedges could be present beneath lcp margins in our study region if we are correct then these lcp sites are geomorphological expressions of boundary conditions that were relatively warm and wet in the recent past first substantial ice wedging in permafrost environments on earth requires the availability of meltwater if as some researchers propose the formation of some wet gullies at the martian mid latitudes is induced by the localised slope side and crater wall thaw of the underlying ldm at the gully sites themselves then meltwater also should be available for ice wedging and the formation of lcps at these sites interestingly lcps are observed on gully channel walls as expected if meltwater is associated with gully formation however in some instances the lcps are also observed on the slope side terrain that extends for hundreds of metres beyond the channel walls and even above the gully alcoves this suggests that the distribution of icy terrain affected by thaw could be much more substantial than has been suggested hitherto second lcps that are identical in shape and scale to the slope side lcps are observed on relatively flat inter crater terrain also underlain by the ldm that is distal from the wet gullies by contrast here their distribution extends for kilometres this too could be indicative of meltwater being more extensive in the regional landscape than most workers have thought possible third on earth the dryness or the wetness of a permafrost environment determines whether lcp margins are underlain by sand or by ice when the observed lcps and major deposits of sand in the study region are plotted on our new map of the argyre impact basin we see that these deposits are rarely proximal on the other hand the ldm underlies the lcps in all instances and if modified by thaw seems to be a likelier source of margin fill for the lcps than sand

grain size segregation and levee formation in geophysical mass flows 1 data from large scale debris flow experiments are combined with modeling of particle size segregation to explain the formation of lateral levees enriched in coarse grains the experimental flows consisted of 10 m3 of water saturated sand and gravel which traveled 80 m down a steeply inclined flume before forming an elongated leveed deposit 10 m long on a nearly horizontal runout surface we measured the surface velocity field and observed the sequence of deposition by seeding tracers onto the flow surface and tracking them in video footage levees formed by progressive downslope accretion approximately 3 5 m behind the flow front which advanced steadily at 2 m s 1 during most of the runout segregation was measured by placing 600 coarse tracer pebbles on the bed which when entrained into the flow segregated upwards at 6 7 5 cm s 1 when excavated from the deposit these were distributed in a horseshoe shaped pattern that became increasingly elevated closer to the deposit termination although there was clear evidence for inverse grading during the flow transect sampling revealed that the resulting leveed deposit was strongly graded laterally with only weak vertical grading we construct an empirical three dimensional velocity field resembling the experimental observations and use this with a particle size segregation model to predict the segregation and transport of material through the flow we infer that coarse material segregates to the flow surface and is transported to the flow front by shear within the flow head coarse material is overridden then recirculates in spiral trajectories due to size segregation before being advected to the flow edges and deposited to form coarse particle enriched levees

experiments on deaerating granular flows and implications for pyroclastic flow mobility 1 granular flows were generated by the release of beds of particles in various fluidized states which then deaerated in a horizontal channel we describe characteristics of the flows and their deposits morphological similarities between deposits in experiments and in the field suggest that pyroclastic flow deposits form from a fluidized mixture the experiments show that slightly expanded fluidized flows are more mobile than non fluidized flows of equivalent volume and material composition they travel to a fixed distance from their source which depends only weakly on their initial degree of fluidization flows of fine particles 100 m deaerate slowly and are highly mobile pyroclastic flows commonly have large amounts of fine ash which may have a controlling influence on their high mobility

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

observations of martian gullies and constraints on potential formation mechanisms abstract the discovery of presumably geologically recent gully features on mars malin and edgett 2000 science 288 2330 2335 has spawned a wide variety of proposed theories of their origin including hypotheses of the type of erosive material to test the validity of gully formation mechanisms data from the mars global surveyor spacecraft has been analyzed to uncover trends in the dimensional and physical properties of the gullies and their surrounding terrain we located 106 mars orbiter camera moc images that contain clear evidence of gully landforms distributed in the southern mid and high latitudes and analyzed these images in combination with mars orbiter laser altimeter mola and thermal emission spectrometer tes data to provide quantitative measurements of numerous gully characteristics parameters we measured include apparent source depth and distribution vertical and horizontal dimensions slopes orientations and present day characteristics that affect local ground temperatures we find that the number of gully systems normalized to the number of moc images steadily declines as one moves poleward of 30 s reaches a minimum value between 60 63 s and then again rises poleward of 63 s all gully alcove heads occur within the upper one third of the slope encompassing the gully and the alcove bases occur within the upper two thirds of the slope also the gully alcove heads occur typically within the first 200 meters of the overlying ridge with the exception of gullies equatorward of 40 s where some alcove heads reach a maximum depth of 1000 meters while gullies exhibit complex slope orientation trends gullies are found on all slope orientations at all the latitudes studied assuming thermal conductivities derived from tes measurements as well as modeled surface temperatures we find that 79 of the gully alcove bases lie at depths where subsurface temperatures are greater than 273 k and 21 of the alcove bases lie within the solid water regime most of the gully alcoves lie outside the temperature pressure phase stability of liquid co2 based on a comparison of measured gully features with predictions from the various models of gully formation we find that models involving carbon dioxide melting ground ice in the upper few meters of the soil dry landslide and surface snowmelt are the least likely to describe the formation of the martian gullies although some discrepancies still exist between prediction and observation the shallow and deep aquifer models remain as the most plausible theories interior processes involving subsurface fluid sources are generally favored over exogenic processes such as wind and snowfall for explaining the origin of the martian gullies

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

relation between dry granular flow regimes and morphology of deposits formation of levees in pyroclastic deposits experiments on dry granular matter flowing down an inclined plane are performed in order to study the dynamics of dense pyroclastic flows the plane is rough and always wider than the flow focusing this study on the case of laterally unconfined free boundary flows we found that several flow regimes exist depending on the input flux and on the inclination of the plane each flow regime corresponds to a particular morphology of the associated deposit in one of these regimes the flow reaches a steady state and the deposit exhibits a levee channel morphology similar to those observed on small pyroclastic flow deposits the levees result from the combination between lateral static zones on each border of the flow and the drainage of the central part of the flow after the supply stops particle segregation features are created during the flow corresponding to those observed on the deposits of pyroclastic flows moreover the measurements of the deposit morphology thickness of the channel height of the levees width of the deposit are quantitatively related to parameters of the dynamics of the flow flux velocity height of the flow leading to a way of studying the flow dynamics from only measurements of the deposit some attempts to make extensions to natural cases are discussed through experiments introducing the polydispersity of the particle sizes and the particle segregation process

geologic settings of martian gullies implications for their origins 1 martian gullies are found on steep slopes of all origins on all sorts of terrains of all ages scattered across nearly all of mars gullies are observed on all manner of substrates layered massive shattered rubble with or without nearby mantling deposits gullies are most common in the southern midlatitudes but also occur in the northern hemisphere in near polar terrain on equatorial volcanoes and on northern plains most gullies in the southern hemisphere are on south facing slopes but they occur on slopes of all orientations gullies are among the youngest features on mars but locally are overlain by eolian deposits and cut by faults old or eroded gullies are rare and those found have been partially stripped from slopes leaving no rock debris behind most gully deposits contain no detectable rocks these data are inconsistent with published hypotheses of gully formation including seeps and breakouts of water or brine hydrothermal activity cryovolcanism and breakouts from liquid carbon dioxide the data are consistent with gullies being dry flows of eolian material dust and silt comparable to climax snow avalanches on earth eolian sedimentation should be correlated little with underlying geology cause of slope age of terrain type of terrain or the nature of the rocks eolian sedimentation should be correlated with wind deceleration which will cause suspended sediment to drop and areas with common gullies are those with strong wind deceleration predicted by global circulation model in such areas sediment will be deposited preferentially in the lee of obstacles for the gully rich areas of the southern midlatitudes winds blow from the nnw so that sediment is deposited on sse facing slopes i e poleward these predictions are in accord with observations