combined flow processes and sedimentary structures on the shoreface of the wave dominated grande riviere de la baleine delta abstract shoreface sediments exposed in raised deltaic deposits along the hudson bay coast are characterized by a thick succession of predominantly parallel laminated and small scale cross laminated fine sand ripple forms where preserved include both combined flow and wave ripple geometries hummocky cross stratification is present in lower parts of the section similar facies have been found in cores from the present day shoreface measurements of waves currents and suspended sediment concentrations in 10 m water depth conducted over a 15 day period in the fall of 1999 captured four different meteorological periods these included an intense four day storm which sustained significant wave heights over 3 m for 15 hours and a storm surge of over 1 m height fair weather conditions produce weak alongshore tidal flows but oscillatory motions generated by small local waves predominate during storms orbital motions dominate the flow but a strong inertial flow generated by wind forcing is also present comparison with a published combined flow bedform stability diagram suggests that the predominant bedforms at 10 m depth would be small 2 d wave dominated ripples and small weakly asymmetrical 3 d ripples under fair weather conditions and large 3 d ripples and upper plane bed under storm wave conditions the predominantly interbedded parallel laminated and small scale cross laminated facies is therefore interpreted to be characteristic of the upper shoreface where the seabed experiences intense oscillatory motions under all storms and even some fair weather conditions combined flow ripples would form during storm events because of the stronger wind driven mean residual current hummocky cross stratification forms in deeper water during storms where the ratio of maximum orbital velocity to mean residual current velocity remains for longer periods in the large 3 d ripple field during the waning phase of storms a numerical bed predictor model using the 15 day data set as input also suggests bimodal conditions fluctuating between wave ripples and upper plane bed at 10 m water depth this model further indicates that combined flow ripples would form rarely but tends to underestimate the threshold of sediment suspension

venusian channel formation as a subsurface process 1 we constructed detailed geologic maps of channels within three widely separated regions using magellan synthetic aperture radar sar imagery and altimetry radar data in order to understand the operative processes involved in venusian channel formation channels in each region cut topographic highs including ridges and shield edifices with no deflection of the channel course by surface topography we argue that these relationships are difficult to reconcile with the widely held view that venusian channels represent surface processes whether constructional or erosional we conclude that the channels evolved through subsurface fluid flow which involved local stoping and transport of overlying material that is these channels were carved from below rather than from above we postulate that at least some venusian channels form because of subsurface fluid flow along a shallow crustal interface that forms the boundary between overlying low backscatter surface materials and underlying basal materials fluid movement along the interface may facilitate piecemeal stoping and erosion of the local surface materials from below eventually resulting in the formation of channel traces exposed at the surface the low backscatter material which hosts the channels in this study also hosts abundant coalescing shields and associated deposits which may represent shield terrain

erosional modification and gully formation at meteor crater arizona insights into crater degradation processes on mars hydrogeological modification of meteor crater produced a spectacular set of gullies throughout the interior wall in response to rainwater precipitation snow melting and possible groundwater discharge the crater wall has an exceptionally well developed centripetal drainage pattern consisting of individual alcoves channels and fans some of the gullies originate from the rim crest and others from the middle crater wall where a lithologic transition occurs broad gullies occur along the crater corner radial faults deeply incised alcoves are well developed on the soft coconino sandstone exposed on the middle crater wall beneath overlying dolomite in general the gully locations are along crater wall radial fractures and faults which are favorable locales of erosion due to preferential rock breakup from faulting and groundwater flow discharge these structural discontinuities are also the locales where the surface runoff from rain precipitation and snow melting can preferentially flow causing erosion and crater degradation channels are well developed on the talus deposits and alluvial fans on the periphery of the crater floor caves exposed on the lower crater level point to percolation of surface runoff and selective discharge through fractures on the crater wall in addition lake sediments on the crater floor provide significant evidence of a past pluvial climate when the water table was higher and groundwater may have seeped from springs on the crater wall although these hydrological processes continue at meteor crater today conditions at the crater are much more arid than they were soon after impact reflecting a climatic shift this climate shift and the hydrological modifications observed at meteor crater provide insights for landscape sculpturing on mars during various parts of its history

orbital forcing of the martian polar layered deposits since the first images of polar regions on mars revealed alternating bright and dark layers there has been speculation that their formation might be tied to the planet s orbital climate forcing1 2 3 4 but uncertainties in the deposition timescale exceed two orders of magnitude estimates based on assumptions of dust deposition ice formation and sublimation and their variations with orbital forcing suggest a deposition rate of 10 3 to 10 2 cm yr 1 refs 5 6 whereas estimates based on cratering rate result in values as high as 0 1 to 0 2 cm yr 1 ref 7 here we use a combination of high resolution images of the polar layered terrains8 high resolution topography9 and revised calculations of the orbital and rotational parameters of mars to show that a correlation exists between ice layer radiance as a function of depth obtained from photometric data of the images of the layered terrains and the insolation variations in summer at the martian north pole similar to what has been shown for palaeoclimate studies of the earth10 11 12 for the best fit between the radiance profile and the simulated insolation parameters we obtain an average deposition rate of 0 05 cm yr 1 for the top 250 m of deposits on the ice cap of the north pole of mars

rapid conversion of an oceanic spreading center to a subduction zone inferred from high precision geochronology where and how subduction zones initiate is a fundamental tectonic problem yet there are few well constrained geologic tests that address the tectonic settings and dynamics of the process numerical modeling has shown that oceanic spreading centers are some of the weakest parts of the plate tectonic system gurnis m hall c lavier l 2004 geochem geophys geosys 5 q07001 but previous studies have not favored them for subduction initiation because of the positive buoyancy of young lithosphere instead other weak zones such as fracture zones have been invoked because these models differ in terms of the ages of crust that are juxtaposed at the site of subduction initiation they can be tested by dating the protoliths of metamorphosed oceanic crust that is formed by underthrusting at the beginning of subduction and comparing that age with the age of the overlying lithosphere and the timing of subduction initiation itself in the western philippines we find that oceanic crust was less than 1 my old when it was underthrust and metamorphosed at the onset of subduction in palawan philippines implying forced subduction initiation at a spreading center this result shows that young and positively buoyant but weak lithosphere was the preferred site for subduction nucleation despite the proximity of other potential weak zones with older denser lithosphere and that plate motion rapidly changed from divergence to convergence

ophiolites in earth history introduction ophiolites record significant evidence for tectonic and magmatic processes from rift drift through accrefionary and collisional stages of continental margin evolution in various tectonic settings structural petrological and geochemical features of ophiolites and associated rock units provide essential information on mantle flow field effects including plume activities collision induced aesthenospheric extrusion crustal growth via magmatism and tectonic accretion in subductionaccretion cycles changes in the structure and composition of the crust and mantle reservoirs through time and evolution of global geochemical cycles and seawater compositions ophiolite studies over the years have played a major role in better understanding of mid ocean ridge and subduction zone processes mantle dynanlics and heterogeneity magma chamber processes fluid flow mechanisms and fluid rock interactions in oceanic lithosphere the evolution of deep biosphere the role of plate tectonics and plume tectonics in crustal evolution during the precambrian and the phanerozoic and mechanisms of continental growth in accretionary and coltisional mountain belts through multi disciplinary investigations and comparative studies of ophiolites and modern oceanic crust and using advanced instrumentation and computational facilities the international ophiolite community has gathered a wealth of new data and syntheses from ophiolites around the world during the last 10 years the purpose of this book is to present the most recent data observations and ideas on different aspects of ophiolite science through case studies and to document the mode and nature of igneous metamorphic tectonic sedimentological and or biological processes associated with the evolution of oceanic crust in different tectonic settings in earth s history it comprises 32 papers collected in six sections on temporal relations anaongst ophiolite genesis mantle plume events and orogeny in earth history tethyan ophiolites in the alpinehimalayan orogenic system magmatic metamorphic and tectonic processes in ophiolite genesis hydrothermal and biogenic alteration of oceanic crust mechanisms of ophiolite emplacement and regional occurrences of ophiolites and their geodynamic implications

niveo aeolian sand deposition in subarctic dunes eastern coast of hudson bay quebec canada aeolian sand transport during winter and the snow free season was assessed quantitatively by direct year round field measurements along transects on the lee side of parabolic dunes in subarctic quebec in 1987 1988 niveo aeolian deposition was more important than aeolian sedimentation in three of the four study sites and contributed 75 of the total annual accumulation in exposed sites and 25 in protected forest sites the maximum depth of interstratified snow and sand deposits 3 5 m was recorded in march semi permanent snow lenses may persist longer than 2 years in the aeolian sediments after dissipation of snow 22 cm of sand as a maximum accumulated on the slipface of the most active dunes whereas only minor sand accumulation occurred in distant areas from active sand erosion wind driven sand was dispersed over 7 4 km2 in the whapmagoostui kuujjuarapik area the acumulation of snow and sand during the snow season together with spring thaw and collapse of the niveo aeolian deposit caused different types of injuries to trees especially in 1985 and 1987 when a maximum of torn branches was recorded over the last 10 year period

wave beach and dune interactions in southeastern australia abstract a morphodynamic classification of surfzones beaches and dunes of the microtidal low to high energy southeast australian coast is presented the first section a waves and beaches briefly deals with the transformation of deep water wave energy as it crosses the shelf nearshore and surfzone depending on the deep water wave characteristics and shelf and inshore morphology resultant breaker wave energy may be high moderate or low and the accompanying beach surfzone morphodynamic state in fine to medium sand beaches either dissipative intermediate or reflective dissipative beaches have wide surfzones with shore parallel bar s and channel s and predominantly shore normal circulation intermediate beaches are characterised by rip circulation crescentic transverse bars and megacusps and reflective beaches by a barless surfzone and steep cusped or bermed beach each beach form has a characteristic level of beach stability zone of sediment storage and mode of beach and dune erosion landward aeolian sediment transport of swash deposited sand section b is dependent on the subaerial beach topography and the aerodynamic flow regime across that topography characteristic profile shapes are ascribed to each beach type dissipative intermediate and reflective aeolian sand transport rates are potentially highest on dissipative beaches moderate on intermediate beaches and lowest on reflective beaches these rates determine the potential size of foredunes which are correspondingly largest on dissipative beaches and smallest on reflective beaches the combination of mode and frequency of beach dune erosion rates of aeolian sand transport and foredune volume and morphology provide an explanation of the nature and morphology of landward occurring large scale dune systems dissipative beaches are frequently characterised by large scale transgressive dune sheets intermediate by a trend from large scale parabolic dune systems high wave energy to small scale blowouts low wave energy and reflective beaches by minimal dune development

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

seismic reflection evidence for a dangerous grounds miniplate no extrusion origin for the south china sea the collision of india and asia has caused large strike slip faults to form in east asia resulting in the extrusion of crustal blocks toward the southeast since the eocene as a result of the indentation of rigid india into asia it has been suggested that the south china sea opened as a result of relative motion between a rigid indochina sundaland block and china alternative models propose that rifting and seafloor spreading were driven by trench forces to the south we test these competing models by analysis of seismic reflection profiles across the boundary between sundaland and the southern rifted margin known as the dangerous grounds we show that the southern boundary of the dangerous grounds is a subduction zone that jammed in the middle miocene to the west the dangerous grounds are bounded by a strike slip zone also active until similar to 16 ma that becomes diffuse south of the now inactive south china sea seafloor spreading center we place the western edge of the dangerous grounds just to the east of the natuna arch lupar line the west baram line is confirmed as originating as a major strike slip fault within the dangerous grounds and is continuous with the red river fault zone because the dangerous grounds were independent of sundaland until similar to 6 ma its motion cannot have been constrained by motion of this block making extrusion impossible as a mechanism to rift the south china sea se motion by both the dangerous grounds and sundaland suggests subduction forces were the primary trigger for plate motions our reconstruction places a similar to 280 km upper limit on the motion on the red river fault and a similar to 1400 km width to the paleo south china sea

overthrust emplacement of new caledonia ophiolite geophysical evidence geophysical studies support inferences from outcrop geology that during the late eocene an ophiolite sheet exposed on new caledonia was thrust southward over a rock complex consisting of sedimentary volcanic and metamorphic rocks that range in age from pre permian to eocene the outcropping ultramafic complex consists of a layered sequence approximately 3000 m thick including harzburgite dunite wehrlite serpentinite and gabbro the absence of pillow basalts and sheeted dikes on land suggests that during or after overthrusting these units were removed either by thrust faulting or by erosion seismic refraction profiles collected over the adjacent loyalty basin show that the lower crust and upper mantle are characterized by velocities of 4 7 5 8 6 8 and 8 1 8 4 km s suggesting the presence of a complete oceanic section that includes sediment basalt gabbro and peridotite the lower crust is probably 6 5 km thick beneath the loyalty basin a seismic reflection profile that extends across the loyalty basin is interpreted to show the oceanic crust rising toward new caledonia we suggest that the ophiolite on new caledonia is continuous with this rising oceanic crust studies of gravity anomalies observed both on land and offshore indicate the presence of a short wavelength high amplitude 180 mgal asymmetrical free air gravity anomaly along the northeastern coast of new caledonia a gravity anomaly profile calculated for a geological model characterized by a 10 km thick slab of oceanic crust and mantle material extending continuously from the ophiolite on new caledonia to the oceanic crust of the loyalty basin successfully matches the observed gravity data we interpret the extension of the high gravity anomaly over the whole length of the eastern lagoon as evidence for the lateral extension of the root zone of the ultramafic complex a tentative geodynamic reconstruction suggests that the proto loyalty basin crust formed a marginal basin along the eastern margin of gondwanaland prior to upper cretaceous time after the opening of the new caledonia basin during upper cretaceous to early paleocene time a subduction zone developed along the western margin of new caledonia while this zone was active the loyalty basin lithosphere overthrust new caledonia in a southeasterly direction and locally rotated clockwise this compressional tectonic event was terminated by upper eocene time

decadal and seasonal development of embryo dunes on an accreting macrotidal beach north lincolnshire uk embryo dunes are often ephemeral but can develop to become established coastal foredunes in 2001 a patch of embryo dunes 13 11 m2 appeared on a beach in north lincolnshire uk and had expanded to over 3600 m2 by 2011 the rate of expansion is linked to storm occurrence where expansion is slowed during years with a higher incidence of storm surges from july 2009 october 2010 seasonal changes in dune field topography were determined using terrestrial laser scanning tls data vegetation is important in the development of embryo dunes but can cause errors in tls data tests evaluating the impact of vegetation on the tls data suggest the minimum elevation value from the tls point cloud within a 0 05 m grid cell gives a good approximation of the ground surface digital elevation models dems of the dunes constructed using filtered data showed the embryo dunes underwent a classic seasonal cycle of erosion during the winter and accretion during the summer for example from october 2009 to april 2010 over 375 m3 of sediment was eroded from the dunes whereas during spring and summer 2010 the dune field gained over 600 m3 of sand the overall magnitude of change in dune height and volume from season to season exceeded the errors associated with the construction of the dem from the tls data and the vegetation filtering process which suggests tls can be useful for documenting topographic change in vegetated dunes after 10 years the patch of embryo dunes is still expanding but has not yet merged with more established foredunes to landward aeolian process measurements indicate that at present the embryo dunes do not prevent sand from reaching the foredunes however the rate of foredune progradation has slowed concurrently with the expansion of the embryo dune field copyright 2013 john wiley sons ltd

sedimentary structures of cold climate coastal dunes eastern hudson bay canada a study of sedimentary structures of cold climate coastal dunes along eastern hudson bay canada showed that in areas of very sparsely vegetated surfaces tractional sedimentary processes are dominant while in partly and well vegetated areas grainfall deposition is the dominant sedimentary process alternating fine and coarse sand strata are characteristic of the vegetated foredune ridge coarse strata are interpreted to be mainly related to niveo aeolian deposition in poorly vegetated areas deformed strata associated with the melting of snow were preserved a vaguely stratified strata interpreted as a dimpled surface as well as coarse lenses with irregular basal contact were found such distinctive sedimentary structures may represent good indicators of cold climate conditions and could serve as criteria to identify aeolianites that may have been deposited in similar cold climate environments in palaeoenvironmental reconstructions

a novel topographic parameterization scheme indicates that martian gullies display the signature of liquid water martian gullies resemble gullies carved by water on earth yet are thought to have formed in an extremely cold 50 c and dry humidity 100 precipitable micrometers surface environment cf mellon et al 2004 despite more than a decade of observations no consensus has emerged as to whether liquid water is required to form martian gullies with some recent studies favouring dry co2 driven processes that this argument persists demonstrates the limitations of morphological interpretations made from 2d images especially when similar looking landforms can form by very different processes to overcome this we have devised a parameterization scheme based on statistical discriminant analysis and hydrological terrain analysis of meter scale digital topography data which can distinguish between dry and wet surface processes acting on a landscape applying this approach to new meter scale topographic datasets of earth the moon and mars we demonstrate that martian gullied slopes are dissimilar to dry gullied slopes on earth and the moon but are similar to both terrestrial debris flows and fluvial gullies we conclude that liquid water was integral to the process by which martian gullies formed finally our work shows that quantitative 3d analyses of landscape have great potential as a tool in planetary science enabling remote assessment of processes acting on planetary surfaces

coastal barriers fresh look at origins nomenclature and classification issues abstract based on numerous publications and field work on the northern gulf of mexico coast u s and other coastal areas the present objective is to meet the need for an improved system of the definition and classification of barriers and their components this topic includes morphological and functional interrelationships between beach ridges barriers and similar landforms the term beach ridge was applied to a plethora of sub and supratidal ridge types in contrast the presently proposed definition restricts the term to relict berm and foredune ridges composed of sand or gravel and stabilized after isolation from shore zone of active processes barriers sustain paralic hydrology sediment biotic and nutrient condition in the coastal realm in combination with adjacent lagoons and river deltas these landforms represent physical barriers that lessen marine and related influences in brackish paralic coastal environments benefiting from historic evolution of concepts and nomenclature the task also involves the correction of misattributions rooted in early publications island spit and mainland barriers thus maintain lower salinities reduce wave erosion protect nutrient rich paralic deposits and mitigate storm induced inundation fetch limited lagoonal barrier islands are considered valid barriers only in lagoons where they face inlet transmitted full marine conditions mainland barriers of several subcategories often are important sediment archives of past sea levels hydroclimate climate and tectonic isostatic changes they consist mostly of ridgeplains at the start firmly attached or later migrated and welded to the mainland shore in addition to local hydrodynamic and topographic influences formation conditions may reflect overall paleogeographic conditions including fluvial impact in progradational regressive island settings barriers consist mainly of strandplains that laterally may alternate with narrow spit like sectors they include only single marine respectively lagoon side shore ridges with secondary dune fields sandwiched between them field observations and drillcore studies of microfossil and sediment based depositional facies suggest that most barrier islands originated by the often underestimated shoal aggradation mode two additional genetic models are recognizable a fourth remains hypothetical remotely sensed images indicate that post hurricane regeneration of the largest deltaic barrier chain in the gulf of mexico stalled in recent years late pleistocene barriers significantly influenced present coastal landforms in two extensive regions dramatic changes in past decades indicate that sea level rise and stormier future hydroclimate may likely accelerate the degradation of deltaic and non deltaic barrier islands

martian hillside gullies and icelandic analogs abstract we report observations of icelandic hillside gully systems that are near duplicates of gullies observed on high latitude martian hillsides the best icelandic analogs involve basaltic talus slopes at the angle of repose with gully formation by debris flows initiated by ground water saturation and or by drainage of water from upslope cliffs we report not only the existence of mars analog gullies but also an erosional sequence of morphologic forms found both on mars and in iceland the observations support hypotheses calling for creation of martian gullies by aqueous processes issues remain whether the water in each case comes only from surficial sources such as melting of ground ice or snow or from underground sources such as aquifers that gain surface access in hillsides iceland has many examples of the former but the latter mechanism is not ruled out our observations are consistent with the martian debris flow mechanism of f costard et al 2001c science 295 110 113 except that classic debris flows begin at midslope more frequently than on mars from morphologic observations we suggest that some martian hillside gully systems not only involve significant evolution by extended erosive activity but gully formation may occur in episodes and the time interval since the last episode is considerably less than the time interval needed to erase the gully through normal martian obliteration processes

sediment transport dis continuity across a beach dune profile during an offshore wind event abstract flow dynamics and sediment transport responses over a large vegetated foredune at prince edward island canada during an offshore wind event are examined data were collected along an instrumented transect that extended from the dune crest down the lee side seaward slope of the dune across a wave cut scarp and on to the back beach when the wind direction at the dune crest was approximately crest normal less than about 15 deviation the mean near surface flow directions along the dune slope and on the back beach were generally onshore indicating reversed onshore flow relative to the regional offshore wind direction although flow patterns were consistent with a lee side recirculation eddy large excursions in flow direction were also prevalent suggesting that the eddy was unstable and alternated with highly turbulent wake flow as wind direction at the crest veered to greater than 20 from crest normal lee side winds shifted toward strongly alongshore flow with minimal directionally variability on the dune slope the wind vectors were slightly offshore whereas on the back beach they were slightly onshore wind speeds and sediment transport were greatest at the foredune crest and declined rapidly downslope due to flow expansion and deceleration in the wake zone as well as to the influence of a sparse vegetation layer mean particle counts averaged over a 15 min interval derived from laser sensors positioned at the crest were large 7 76 per second in comparison to those measured in the immediate lee of the crest 0 52 per second and farther down the dune slope these results demonstrate that sediment transport across the beach dune system was spatially discontinuous during this offshore wind event rebuilding of the dune ramp at the toe of the scarp occurred quite independently of and with a different sediment source than the broadening of the dune crest which was fed with sediment from the landward side of the foredune such process decoupling is an example of the complexity by which foredunes evolve or are maintained and as with previous research reinforces the importance of offshore and alongshore wind events to beach dune morphodynamics

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

thrust tectonics along the north western continental margin of sabah borneo widely accepted plate tectonic models suggest that an inactive subduction zone lies along the north west continental margin of sabah in contrast interpretation of reflection seismic data acquired by bgr shows an autochthonous continental terrane comprising an oligocene to early miocene carbonate platform being progressively overthrust by an allochthonous rock complex progressive compression resulted in the development of four structural zones imbricated thrust sheets zone iii two thrust sheet systems one on top of the other zone iv a complex zone with multiphase deformation zone v and piercement ridges zone vi

niveo aeolian deposits and denivation forms with special reference to the great kobuk sand dunes northwestern alaska the geomorphology lithology and chronostratigraphy of extensive late pleistocene inland and river dune sands aeolian sand sheets cover sands and loess deposits of periglacial origin in northwestern europe are well known however the idea that some of these aeolian sediments result from niveo aeolian processes is still an open question as no diagnostic sedimentary features have yet been reported moreover actual niveo aeolian sediments and related denivation forms reported from various cold climate regions are not suitable analogues recent observations in active dune fields in northwestern alaska indicate that interstratification of wind driven snow and sand preferentially occurs on slip faces of transverse barchanoid or parabolic dune ridges annual denivation forms develop e g snow ramparts sinkholes snow hummocks snow meltwater fans and tensional cracks the surface consists of a cracked wet sand layer with a dimpled surface and spongy structure although the preservation potential of these features is low in this specific case similar features may be observed in ancient sediments elsewhere and provide useful palaeoclimatic indicators the niveo aeolian concept should therefore not specifically be related to late pleistocene cover sand deposition in northwestern europe as previously assumed

landform hierarchy and evolution in gorgonum and atlantis basins mars abstract this paper describes the evolution of landforms in atlantis and gorgonum basins using a geomorphologic approach which interprets landform distribution and hierarchy rather than looking at the distribution of large area 10 6 km 2 geologic sequences this study focuses on interpreting the local scale 3 km 2 cratered terrains tectono structural basins and local manifestation of exogenic processes specifically the evolution of fluvio lacustrine landforms is interpreted as being functionally subordinated to the evolution of the cratered terrains and to the tectono structural modifications of the landscape results show that three major phases of landscape evolution in atlantis and gorgonum basins can be identified a major impact cratering during the heavy bombardment period b tectonic displacements in response to volcano emplacement in the tharsis region and simultaneous landform creation by fluvial and lacustrine processes and c exogenic modification of the older landforms through weathering and eolian processes our results show that the smaller morphological features which form on the older geological units are not necessarily old themselves and can in fact be relatively recent e g amazonian the main implication of these results is that martian morphology did not form only during a period immediately following the heavy bombardment as commonly postulated but rather that landform evolution continued throughout the entire martian history

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

thermochronological evidence for the movement of the ailao shan red river shear zone a perspective from vietnam in order to explore the timing of strike slip movement along the ailao shan red river shear zone an 40ar 39ar thermochronological study of the day nui con voi metamorphic massif in northern vietnam was undertaken the massif exposed in the southeastern segment of the ailao shan red river shear zone reveals a rapid cooling in the early miocene 25 21 ma after a very slow cooling ca 34 25 ma the slow cooling period most likely resulted from a geothermal perturbation in the lithosphere owing to the late paleogene 40 30 ma extension in eastern tibet and western yunnan china the rapid cooling consistent with evidence of a wider rapid cooling span from 27 to 17 ma compiled from the entire ailao shan red river shear zone constrains the duration of left lateral shearing which eventually offset indochina from south china by about 600 km the time constraints we have established reinforce the argument that the onset of the ailao shan red river shear zone postdates the opening of the south china sea that began ca 30 ma this result highlights the necessity for reevaluating the cenozoic tectonic models of southeast asia

onland signatures of the palawan microcontinental block and philippine mobile belt collision and crustal growth process a review abstract the collision of the palawan microcontinental block with the philippine mobile belt had significantly influenced the geological evolution of the philippines multiple collisions involving several fragments through space and time resulted into the collage of terranes of varying origin exposed in this part of central philippines cusping of the overriding plate volcanic arc gap ophiolite emplacement incipient back arc rifting island rotation and tilting raised coastal terraces metamorphism intrusion of igneous rocks and steepened subducted slab as seen in focal mechanism solutions are some of the manifestations of this collision a late early miocene to early middle miocene age 20 16 ma is proposed for the major collision between the palawan indenter and the philippine mobile belt the collision boundary is located from the northern part of mindoro through the central mountain range swinging east of sibuyan island in the romblon island group and finally threading along the buruanga peninsula and eastern side of the antique ophiolite complex before exiting and connecting with the negros trench the collision through accretion and crustal thickening has contributed to the crustal growth of the philippine archipelago

evidence of gully formation by regional groundwater flow in the gorgonum newton region mars abstract the discovery of gullies on mars suggests liquid water activity near the surface of the planet in recent times since liquid water is unstable under the present day p t martian conditions the formation mechanisms of the gullies and the source of the putative water have been a matter of debate for the last years to provide new insights into these matters we have approached the problem studying the gullies in relation to their regional setting a major point in our study relates to the geographic orientation of gullies an aspect that has been previously regarded as a crucial matter in different models and has profound implications regarding their origin we present a comprehensive and detailed survey of the gorgonum newton region and a study of the dao and nirgal vallis regions the survey was carried out with the aid of 965 high resolution moc images 752 for gorgonum newton 102 for nirgal vallis and 111 for dao vallis regions and mola derived dems we found that gullies display a clear regional pattern geographically and topographically consistent with a decreasing regional slope we interpret the results in terms of the existence of several groundwater flow systems operating at different scales which ultimately may have led to gully formation by seepage at the slopes of craters and canyons we suggest that aquifers discharging at gully systems may have recharged from the surface in response to the melting of young partially eroded ice rich deposits

the sedimentary and tectonic evolution of the yinggehai song hong basin and the southern hainan margin south china sea implications for tibetan uplift and monsoon intensification 1 the yinggehai song hong basin is one of the world s largest pull apart basins lying along the trace of the red river fault zone in the south china sea south of hainan island this basin crosscuts the rifted margin of the northern south china sea in this paper we present for the first time a regional compilation of multichannel seismic reflection data from both the strike slip and rifted margins the basins started to open after similar to 45 ma especially after similar to 34 ma the yinggehai basin was folded and inverted in the middle miocene after 21 ma in the north and 14 ma in the south before rapidly subsiding again after similar to 5 ma because of continued tectonism this subsidence has caused shale diapirism especially driven by associated sedimentation in the late pliocene 2 6 2 0 ma extension along the adjacent south hainan margin shows preferential lower crustal extension suggestive of lower crustal flow increasing toward the continent ocean transition during breakup sediment supply is reconstructed to peak in the middle miocene then falls between 14 and 10 3 ma to reach a low in the late miocene however rates rose again in the pliocene pleistocene the red river sediment budget is incompatible with climate models that propose stronger monsoon rains starting at 8 ma or with large scale river capture away from the red river after similar to 10 ma both lines of evidence point to major uplift in the red river drainage being middle miocene or older the recent preindustrial red river carried much more sediment than the average pleistocene accumulation rate indicating modest sediment buffering onshore at least in recent geologic time

eutectic brines on mars origin and possible relation to young seepage features abstract if the recently observed young gullies on mars represent seeps or outflows of aqueous fluid that fluid must be highly concentrated brine to be even moderately stable under current martian surface conditions such brines are to be expected in the megaregolith if an initial saline hydrosphere underwent evapoconcentration via water escape from the atmosphere evolved into subsurface cacl 2 enriched brines by chemical interaction with mafic rocks and then froze until eutectic compositions were reached although most such brines would tend to sink deep into the megaregolith they could be preserved locally at relatively high elevations as aquifers or frozen paleoaquifers perched between ground ice and crystalline salts

foredunes and blowouts initiation geomorphology and dynamics this paper reviews the initiation dynamics geomorphology and evolution of incipient foredunes established foredunes and blowouts incipient foredunes may be initiated in a variety of ways leading to the formation of ramps terraces or ridges depending on progradation rates vegetation type and cover sediment transport rates and scale of erosional processes vegetation cover morphology growth rates and types combine with aerodynamic processes to determine dune and swale morphology established foredunes are classified into five morpho ecological types and the flow behaviour over two types is detailed a new model of foredune evolutionary paths at various possible time scales is presented blowout initiation dynamics and sediment transport and evolution is examined throughout the review the gaps in present understanding of dune processes and a range of ideas for new research possibilities are provided

preservation of ice formed features in a subarctic sandy beach sequence geologic implications abstract the barrier beach shoreline near michael river labrador is ice bound for more than 6 months each year the contemporary beachface deposits record a complete yearly cycle as follows the lowermost unit d a well laminated fine to medium grained sand and the overlying unit a a graded sequence of well mixed sand and gravel near the bottom and medium grained laminated sand at the top represent foreshore accretion during summer and fall unit a is overlain by unit b a laminated fine to medium grained sand deposit containing contorted and disrupted laminae and intrabedded sand clasts features which characterize middle to upper foreshore deposits that have accreted under freezing conditions the cycle is completed by unit c a mixed gravel and sand deposit that resembles ice rafted and ice push deposits which form on cold climate beaches during spring break up of nearshore ice unit b is considered to be the freeze up deposit formed during early winter and unit c the subsequent break up deposit which accumulated during spring unit c is overlain by unit d a well laminated foreshore sand which marks the beginning of the next cycle the fact that freeze up and break up events are recorded in a yearly cycle of beachface accretion indicates that such deposits could have been preserved in the rock record if the cyclic sequence recorded in the beachface near michael river were encountered in ancient rocks it could be a good indicator of paleo climatic summer winter seasonal conditions

regional implications of u pb shrimp age constraints on the tectonic evolution of new caledonia abstract u pb shrimp ages for zircons from plagiogranites indicate a late carboniferous age of formation for ophiolitic basement of the koh terrane in the central chain mountains of new caledonia samples from ophiolites at koh and koua yielded ages of 302 7 ma and 290 5 ma respectively the similarity of these ages to those of plagiogranites in the dun mountain ophiolite belt maitai terrane of new zealand and the comparable structural positions of the two terranes potentially constrain reconstructions of the cretaceous sw pacific margin detrital zircons from late mesozoic sediments that overlap the koh terrane also provide potential constraints on the location of new caledonia prior to its break up and dispersal from eastern australia

subduction zone polarity in the oman mountains implications for ophiolite emplacement two end member models have been proposed to account for the structure and metamorphism of rocks beneath the semail ophiolite in the oman mountains model a involves a single continuous ne directed subduction away from the continental margin during the late cretaceous the ophiolite and underlying thrust sheets of distal to proximal oceanic sediments were emplaced a minimum of 250 km sw onto the continental margin subduction of triassic jurassic oceanic basalts to c 10 kbar c 39 km depth led to the accretion of amphibolite facies rocks to the base of the ophiolite thrusting propagated towards the continental margin and ended with subduction of the thinned continental crust to c 20 kbar c 78 km depth choking the subduction zone buoyancy forces caused the rapid exhumation of eclogites blueschists and carpholite grade hp rocks along the ne margin of the continental plate during the later phase of foreland propagating thin skinned thrusting in the sw ne facing backfolding and backthrusting occurred in the hinterland with the final exhumation of the hp rocks model b follows recent suggestions that a nascent sw dipping subduction zone dipping beneath the continental margin existed between 130 and 95 ma prior to formation and emplacement of the ophiolite a major ne facing fold nappe structure in the pre permian basement rocks of saih hatat is interpreted as reflecting subduction beneath the margin two high pressure metamorphic events have been suggested the first predating ophiolite emplacement the second caused by ophiolite loading this model is untenable being based on a misinterpretation of the ne facing structures in northern saih hatat and on some dubious older 40ar 39ar cooling ages from the eclogite facies rocks of as sifah we conclude that all structures in northern oman and all the reliable geochronology point to a single emplacement obduction event lasting from cenomanian turonian time c 95 ma when amphibolites were accreted along the metamorphic sole of the ophiolite to campanian time when the continental margin was subducted to the ne producing blueschists and eclogites to the final thin skinned emplacement of all thrust sheets which ended before the late maastrichtian at c 68 ma

recent dynamics of subarctic dunes as determined by tree ring analysis of white spruce hudson bay quebec the radial growth patterns of white spruce were studied on a number of trees growing in subarctic dunes along the eastern coast of hudson bay to calculate the rates of accumulation erosion and migration of cold climate sand dunes the average rate of sand accumulation in sheltered dunes forest sites was 2 5 to 3 3 cm yr which is two to three times lower than in highly exposed dunes with a rate of sedimentation of 7 65 cm yr the average erosion rate was 1 4 1 7 cm yr about two times lower than the accumulation rate the migration rate of sheltered dunes was 18 to 30 cm yr three to five times lower than for an exposed dune which advanced at a speed of 74 cm yr this migration rate established for highly exposed dunes in the subarctic with tree ring methods is about 10 times lower than that established for a barchan in the sahara with other methods

a relationship between dunes fire and climate recorded in the holocene deposits of quebec during the past 5 000 yr bp the tropics have experienced an increase in aridity and aeolian activity in both maritime and continental areas1 4 in contrast the onset and subsequent development of post hypsithermal climates in northern latitudes were primarily conducive to global cooling it is suggested here that aeolian activity in cold environments represents a direct response to this long term cooling trend that began after 6 000 5 000 yr bp at the end of the climatic optimum5 9 this study establishes the holocene chronology of sand dunes near the outer forest limit in northern quebec fig 1 i show here that fires initiate the aeolian activity and that the fire dune relationship is typical of cooling period on this basis a palaeoclimatic reconstruction since the climatic optimum is proposed

the gravity fields of palawan and new caledonia insights into the subsurface geometries of ophiolites abstract new gravity data from palawan in the western philippines emphasize resemblances to new caledonia on both islands ophiolites derived from root zones just offshore rest on basal surfaces that change abruptly in depth by as much as 5 km the subsurface geometries of these thrust sheets are as important to an understanding of their emplacement histories as are their exposure patterns

role of aquicludes in formation of martian gullies liquid water is not currently stable on the surface of mars but images provided by the mars orbiter camera aboard the mars global surveyor spacecraft reveal erosional landforms previously interpreted to be geologically young gullies formed by groundwater seepage we test the basic hypothesis that as on earth the location of these gullies is controlled in part by the presence of an impermeable rock layer aquiclude and that the depths of the gully heads below the surface should thus be correlated to subsurface geology we show that 1 gullies emanate from a specific cliff forming layer even if the layer is faulted and 2 the depth of gullies below the local surface ranges from 70 to 800 m and 3 is positively correlated to mapped geologic units gully formation is therefore dependent upon both favorable climatic conditions to produce and sustain liquid water and the presence of impermeable subsurface layers to collect the groundwater gullies may mark the distribution of subsurface impermeable layers globally and are prime targets for the search for present water and life on mars

eocene arc continent collision in new caledonia and implications for regional southwest pacific tectonic evolution new caledonia preserves evidence that constrains models for the tectonic evolution of the southwest pacific region onland geology reflects four main tectonic phases 1 early mesozoic development of subduction related terranes and their accretion to the gondwana margin 2 cretaceous passive margin development and sea floor spreading during the gondwana breakup 3 foundering of an oceanic basin and the eocene arrival of thinned gondwana margin crust at a southwest facing subduction zone resulting in collisional orogenesis and obduction of an ophiolitic nappe from the northeast and 4 detachment faulting during extensional collapse resulting in unroofing of metamorphic core complexes the last phase explains supposedly anomalous metamorphic gradients in the northeast of the island

coastal aeolian dune development solheimasandur southern iceland abstract a coastal aeolian dune field on the distal parts of solheimasandur southern iceland is currently undergoing active construction ongoing sand deflation in the foreshore is demonstrated by the preservation of sand ridges in the downwind lee of obstacles while a backshore sandsheet is characterised by actively accumulating long wavelength wind ripples the main region of aeolian accumulation is in the immediate backshore where sand has accumulated to a thickness of up to 8 m and is largely stabilized by vegetation surrounding interdune areas have undergone repeated flooding by fluvial incursions from the adjacent jokulsa river and are characterised by mud drapes which lap against the lower flanks of neighbouring dunes widespread sand adhesion structures testify to the often damp nature of the substrate over 1200 vegetated and stabilized dunes nebkhas occupy a 5 km 2 area of wind deflated gravel sandur plain downwind from the main site of aeolian accumulation the nebkhas show strong relationships between plan form shape and height indicating that they have attained equilibrium morphology for the prevailing climatic conditions within the nebkha field dunes demonstrate a predictable downwind decrease in height spatial concentration and degree of sand stabilization a time series of aerial photographs documents the temporal evolution of the dune field and demonstrates that aeolian accumulation commenced about 1940 and has been ongoing to the present day prior to 1940 repeated outburst floods associated with catastrophic lake drainage events from the solheimajokull glacier 8 km inland were of sufficient magnitude to repeatedly destroy any incipient aeolian bedforms that developed although strong onshore winds and high rates of sediment supply promote aeolian sediment transport dune field development is rare in humid boreal and sub arctic climates as encountered in southern iceland because the availability of sediment for aeolian transport is usually severely limited by damp substrate conditions thus the airflow tends to be undersaturated with respect to its potential sand transporting capacity and dune construction can only occur because of the stabilizing influence of vegetation

downward migration of coastal conifers as a response to recent land emergence in eastern hudson bay quebec abstract postglacial uplift in the eastern hudson bay area is among the most rapid in the world 300 m during the last 8000 yr although emergence curves based on 14 c dated raised shorelines give a consistent basis for modeling relative sea level changes such a low resolution dating method is inappropriate for estimating trends over recent decades a major downward displacement of white spruce picea glauca moench voss and tamarack larix laricina duroi k koch occurred on protected shores as a response to shoreline retreat during this century analysis of the age distribution of trees indicates a progradation of white spruce and tamarack on gently sloping terrain ranging from 1 3 and 2 6 cm yr respectively toward the sea improvement of climatic conditions during the 20th century favored such expansion which was probably faster than the real land emergence rates but recent episodes of high water levels caused regression of forest margins over the highly exposed shores nevertheless the downward trend of the treeline over this century substantiates the projections of 14c dated coastal emergence curves during the modern period 1 0 to 1 3 cm yr by providing an estimate of the maximum rates of shoreline retreat

freezing resistant liquid water in porous media a possible mechanism to account for the fluidized transport of sediments on mars an example from east gorgonum crater a mudflow like deposit resting on the bottom of the east gorgonum crater mars 37 4s 168 0w may provide new insight regarding the debate on the existence of water over the martian surface because water in a mudflow is confined to a porous medium we analyse this case from the perspective of non equilibrium systems fluids confined to porous media behave in a special way the system being ruled by kinetic restrictions which alter the expected thermodynamic equilibrium these non equilibrium conditions allow the existence of pure liquid water to temperatures as low as 40 c and even less if the system includes brines thus application of the triple point diagram of water on the martian surface may constitute a simplistic approach if we are dealing with confined and yet moving water in the form of a mudflow we further suggest that the v shaped channels excavated alongside the mudflow may have been caused by water rejected by syneresis from the moving sediment we finally indicate that the series of deeply entrenched channels and debris aprons that occur only in the northern half of the crater might be related to the regional slope which decreases in altitude to the south

annual to decadal morphodynamics of the foredune system at greenwich dunes prince edward island canada the purpose of this study was to quantify relationships between season sediment availability sediment transport pathways and beach foredune morphology at greenwich dunes pei this was done for periods ranging from a few days to multiple decades using erosion pins bedframe measurements annual surveys and digital photogrammetry using historical aerial photographs the relative significance of seasonal annual processes versus response of the foredune system to broader geomorphic controls e g relative sea level rise storms etc was also assessed the data show that there are clear seasonal differences in the patterns of sand supply from the beach to the foredune at greenwich and that there are differences in sediment supply to the foredune between the east and west reaches of the study area resulting in ongoing differences in foredune morphology they also demonstrate that models that incorporate wind climate alone or even models that include other factors like beach moisture would not be able to predict the amount of sediment movement from the beach to the foredune in this environment unless there were some way to parameterize system morphology especially the presence or absence of a dune ramp finally the data suggest that the foredune can migrate landward while maintaining its form via transfers of sediment from the stoss slope over the crest and onto the lee slope although the rate of foredune development or recovery after disturbance changes over time due to morphological feedback the overall decadal evolution of the foredune system at greenwich is consistent with and supports the davidson arnott 2005 conceptual model of dune transgression under rising sea level copyright 2012 john wiley sons ltd

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

a large paleolake basin at the head of ma adim vallis mars at 8 to 15 kilometers wide ma9adim vallis is one of the largest valleys in the martian highlands although a groundwater source was previously suggested the channel originates at a spillway in the divide of a 3 000 000 square kilometer closed drainage basin the interior morphology of this source basin including likely shoreline features following topographic contours suggests that ma9adim vallis was created through catastrophic overflow of a 1 100 000 square kilometer highland lake the size constant levels and interior morphology of three regional paleolake basins require a warmer paleoclimate and a long term recharged stable highland water table more than 3 5 billion years ago

kinetic energy transfer through impact and its role in entrainment by wind of particles from frozen surfaces while extensive aeolian deposits are associated with glaciation little is known of the mechanisms which produced them observation of glaciofluvial sediments in pangnirtung pass n w t indicates that peak deflation occurs in the fall and winter months so that the nature of sediment transport involving frozen surfaces greatly differs from warm environments laboratory experiments indicate that such surfaces are mobilized through abrasion and are most susceptible at low volumetric water content less than 20 and low temperature 20 c stable surfaces have volumetric water contents in excess of 30 and temperatures of 15 c surface stability also increases with decreasing particle size density and possibly transport load collisions with frozen surfaces are relatively elastic with significantly greater kinetic energy transfer to ejected surface grains than observed for loose dry surfaces saltation transport in cold environments could therefore be sustained at lower windspeeds than for dry surfaces provided that some loose particles are available initially but do not accumulate at the surface

geomorphology of high latitude coastal dunes a review the purpose of this review is to assess if there are any specific processes and morphologies distinguishing coastal dunes developed in cold climate conditions in order to illustrate how climate can exert a control on coastal dune morphologies in the arctic availability of sand supply and the duration of winter conditions are limiting factors for the development of large coastal dunes they are small in size and embryo dunes including nebkha are the dominant and often only coastal dune type in milder subarctic settings characterized by a longer surficial ice free season a greater variety of coastal dunes are found mainly foredunes blowouts and parabolic dunes in subarctic areas as along the se coast of hudson bay niveo aeolian processes actively affect coastal dune development these processes do not generally imprint permanent morphologies although some distinctive sedimentary structures owing to the melting of snow are observed the coastal dunes of the arctic regions differ from the dunes of subarctic and temperate regions mainly because of their limited spatial and morphological development extreme climatic conditions low precipitation extreme cold and very limited vegetation growing season combined with low sediment supply explain the fact that only embryo dunes develop in arctic environments

martian hydrogeology sustained by thermally insulating gas and salt hydrates numerical simulations and geologic studies suggest that high thermal anomalies beneath within and above thermally insulating layers of buried hydrated salts and gas hydrates could have triggered and sustained hydrologic processes on mars producing or modifying chaotic terrains debris flows gullies and ice creep features these simulations and geologic examples suggest that thick hydrate deposits may sustain such geothermal anomalies shallow ground water tables and hydrogeologic activity for eons the proposed mechanism may operate and be self reinforcing even in today9s cold martian climate without elevated heat flux

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

morphology and facies architecture of a falling sea level strandplain umiujaq hudson bay canada coastal strandplain deposits near umiujaq eastern hudson bay canada were formed under falling relative sea level conditions resulting from postglacial isostatic uplift ground probing radar profiles across the strandplain reveal a lower progradational unit lpu discordantly overlain by an upper progradational unit upu which were correlated with stratigraphic sections exposed in incised valley walls the discordance is a wave erosion surface wes that separates fine shoreface sands of the lpu from coarse sand and gravel of the upu major basal downlap surfaces can be traced updip into marine terraces and define downstepping wedges the downstepping is interpreted as representing autocyclic morphological reconfiguration rather than a response to changes in the rate of sea level fall the internal architecture is strongly dependent on the accommodation and thus on antecedent topography a conceptual model for strandplain deposition under falling sea level incorporates a bipartite shallowing upward sandy succession when sufficient accommodation is available where accommodation space is limited a sharp based bar and beach sandbody directly overlies muddy deeper water deposits and the wes resembles a regressive surface of erosion

comparison of small lunar landslides and martian gullies some lunar crater wall landslides strongly resemble martian gullies despite the lack of geologically active water on the moon today or in the past the lunar features indicate that alcove channel apron morphology attributed on mars to seepage of liquid water can also form via a dry landslide mechanism therefore a more stringent test than just an alcove channel apron morphology is necessary to differentiate dry landslides from water carved gullies

coastline orientation aeolian sediment transport and foredune and dunefield dynamics of mocambique beach southern brazil abstract this paper examines the role of coastline orientation on foredune and dunefield development at mocambique beach southern brazil the beach displays significant alongshore variations in exposure to the prevailing winds and waves grain size beach surfzone morphodynamic type foredune volume and type and dimensions of the holocene dune systems two wind analyses and calculation of aeolian drift potentials were carried out one based on 1 year of wind record and another based on a record of 34 years monthly topographic surveys of beach and foredunes on 5 profiles along mocambique beach were conducted over one year to obtain data on beach mobility and width aeolian sediment transport and foredune development southerly winds dominate and aeolian sediment supply is minimal in the south moderate in the central portion and high in the northern portion of the embayment the relationship between actual sediment supply foredune building and potential sediment supply is relatively poor over one year due to factors such as beach type and mobility beach moisture levels rainfall storm surge and wave scarping the intermediate term 34 year record indicates a strong relationship between foredune size and volume winds and shoreline orientation foredune volume is minimum in the southern part of the beach and greatest in the northern part of the beach the holocene barrier and dunefield development also reflects the long term control of shoreline orientation and increasing longshore gradient in exposure to southerly winds for the last 6000 7000 years a small foredune developed in the southern portion parabolics and small transgressive dunes in the central portion and a large scale transgressive dunefield in the northern portion

aeolian dynamics over a coastal foredune prince edward island canada near surface airflow over a morphologically simple vegetated 8 m high foredune with a small wave cut scarp was measured for onshore to oblique onshore conditions during a low moderate 5 6 m s 1 wind event and a high velocity 11 18 m s 1 sand transporting gale event flow across the foredune was characterized by significant flow compression and acceleration up and across the foredune during both events during the gale a pronounced jet speed bulge developed at the foredune crest which increased in magnitude with increasing wind speed the vertical w velocity component of the 3d flow field was positive upwards across the stoss slope under low wind conditions but negative downwards during gale wind conditions with upslope acceleration during the low velocity event there was speed down within the vegetation canopy as would be expected for a porous roughness cover during the strong wind event there was speed up in the lower portion of the vegetation canopy and this was found up the entire stoss slope sediment transport during the gale force event was substantial across the beach and foredune despite the moderate vegetation cover and minimum fetch aeolian suspension was evident in the lee of the dune crest the observations presented herein show that strong storm winds are an effective mechanism for translating sediment landwards across a high vegetated foredune contributing sediment to the stoss slope crest and leeward slopes of the foredune and backing dunes copyright 2013 john wiley sons ltd

identifying martian gully evolution martian gullies are small scale geologically recent features characterized by the alcove channel apron morphology associated with flows with a component of liquid water theories advanced to explain martian gully formation include groundwater processes and melting of near surface ice due to climate variation gullies are often associated with mantling terrain that drapes topography at mid to high latitudes and which has been proposed to be ice rich we have morphologically classified martian gullies into four groupings according to whether they form solely within the mantle type a erode into bedrock type b and by how well developed they appear 1 or 2 orientation length geological setting and latitude were also recorded as well as whether more than one generation of gullies formed on a given slope labelled reactivated about 25 of gullies form solely within the mantle these are generally shorter than gullies that erode bedrock and the morphologically simplest gullies a1 are the shortest we present latitude and orientation trends for the most recent episode of gully formation we suggest that this recent activity is probably controlled by either deposition of ice rich material or degradation of pre existing ice rich material

evolution of a foredune and backshore river complex on a high energy drift aligned beach abstract this paper examines the multi decadal evolution of a foredune and backshore river complex on a wave dominated drift aligned coast at wickaninnish bay on southwestern vancouver island british columbia canada local shoreline positions are generally prograding seaward as fast as 1 46 m a 1 in response to rapid regional tectonic uplift and positive onshore sediment budgets the northern end of the foredune system has extended rapidly alongshore in response to net northward littoral drift despite these net accretional responses the beach dune system experiences relatively frequent return interval 1 53 years erosive events when total water levels exceed a local erosional threshold elevation of 5 5 m above regional chart datum geomorphic recovery of the beach dune system from erosive events is usually rapid i e within a year by way of high onshore sand transport and aeolian delivery to the upper beach this response is complicated locally however by the influence of a backshore river that alters spatial temporal patterns of both intertidal and supratidal erosion and deposition historic landscape changes and rates of shoreline positional change are derived from several years of aerial photography 1973 1996 2007 2009 2012 using the usgs digital shoreline analysis system dsas significant volumetric changes are also estimated from aerial lidar derived dems in 2005 2009 and 2012 and related morphodynamics are interpreted using a statistically constrained geomorphic change detection method results suggest that supratidal bar development overwash deposition and aeolian deposition on a low lying supratidal platform combined with alongshore extension of the foredune complex is forcing sandhill creek to migrate northward in the direction of beach drift in response the river actively erodes 1 24 m a 1 a bluff system landward of the channel which generates substantial sediment volumes 0 137 m3 m 2 a 1 that feed a large intertidal braided channel and delta system these local responses provide context for a conceptual model of the evolution of a wave dominated drift aligned beach foredune system that interacts with a backshore river this model may provide useful information to local park managers as erosion and sedimentation hazards threaten visitor safety and park infrastructure

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

the late holocene record of aeolian and fire activity in northern quebec canada a set of 196 14c dates was used to reconstruct late holocene aeolian activity in the hudson bay area along a south north transect crossing the northern boreal forest the forest tundra and the shru

knob fields in the terra cimmeria terra sirenum region of mars stratigraphy mineralogy and morphology abstract we investigate the stratigraphy morphology and mineralogy of five major knob fields in the region between terra cimmeria and terra sirenum on mars based on hrsc ctx moc and hirise imagery together with hyperspectral data from crism the knob fields comprise ariadnes colles atlantis chaos and gorgonum chaos and further unnamed fields of mounds they have been mapped in previous studies as hesperian or amazonian units and are located within the shoreline of the proposed eridania lake the putative source of ma adim vallis the mounds contain mg fe bearing phyllosilicates and locally al rich phyllosilicates our geological mapping shows that the knob fields have a late noachian age which indicates later phyllosilicate formation than typically observed on mars the knob fields formed by alteration of the electris deposit an airfall deposit possibly rich in basaltic glass grant j a schultz p h 1990 icarus 84 166 195 in local depressions possibly in the eridania lake the spectroscopic detection of phyllosilicates here may indicate that liquid water persisted longer in this region than elsewhere on mars the knob fields are embayed by the hesperian ridged plains numerous valleys carve into the ridged plains and document that the aqueous history of this region continued into the hesperian and amazonian the study area is traversed by the sirenum fossae these graben appear to post date the aqueous activity in the study area except in the gorgonum basin where a lake developed after their formation

origin of the new caledonian ophiolites based on a french australian seismic transect abstract the origin age and nature of the new caledonian ophiolites are still debated recently as part of the joint french australian seismic transect faust program the australian research vessel rig seismic recorded a series of multichannel deep seismic profiles between the new hebrides arc and the australian margin these profiles which ran south of new caledonia image the southern prolongation of the overthrusted ophiolites and allow a new interpretation of the eocene compressive tectonism along the new caledonia norfolk ridge a model involving abduction of the whole oceanic lithosphere of the loyalty basin is consistent with the age and origin of the ophiolite variations in tectonic style along strike in the north south trending part of the norfolk ridge have produced ophiolite exposures related to uplifted and partially overthrust upper mantle slivers within the southern part of the loyalty basin

discussion of a miocene collisional belt in north borneo uplift mechanism and isostatic adjustment quantified by thermochronology scientific editing by alex maltman john milsom robert holt write knowledge of the gravity field is vital to any study of isostasy this was acknowledged by hutchison et al 2000 when they noted that the work of holt 1998 placed constraints on their geological model for sabah however they went on to ignore these constraints arguing that the depth of the crustal root beneath the western cordillera might have been overestimated due to the model assumption of an excessively thick ophiolitic basement and that the presence of thick crust beneath sabah was in conflict with the outcropping geology the hutchison et al interpretations of the deep structure of sabah were illustrated in a series of cross sections in which some features notably the topography were amplified for the sake of clarity there was however no suggestion that any features would be underemphasized and the depth scales although described as only rough guides indicated normal 5 10 km thicknesses for oceanic crust therefore and in the light of the comments quoted above the thin crust shown throughout sabah and the generally somewhat greater thickness of the extended continental crust of the dangerous grounds must be regarded as essential elements of the model the late miocene cross section fig 1 showing the end of orogeny in sabah is a guide to the hutchison et al view of the present day situation crust is less than 30 km thick beneath the western cordillera and less than 20 km thick elsewhere we contend that these values are incompatible with the gravity field and that it is no more acceptable to present a geological interpretation that ignores geophysical data than a geophysical interpretation that ignores geology some way must be found of reconciling the two fig 1 sabah in the late miocene from hutchison et al 2000 fig 6b

neogene arc continent collision in sabah northern borneo malaysia abstract the neogene evolution of sabah can be interpreted in terms of an arc continent collision initiated during early middle miocene time and followed by intraplate shortening the latter being active in this area at the present day the volcanic arc of late oligocene middle miocene age is imbricated with melanges and thrust northwestward on a polyphase deformed turbiditic sequence of late cretaceous middle miocene age crocker range intraplate shortening is seen in the thrusting and folding offshore sabah along the palawan north borneo trench and also by broad open folds and strike slip faulting in the previously sutured terranes this collision can either be interpreted as the final stage of southward subduction of the hypothetical proto south china sea or the result of back thrusting of the sulu volcanic arc resulting from the subduction of the celebes sea toward the north

morphology dynamics and internal stratification of some established foredunes in southeast australia abstract foredunes are shore parallel dunes formed by aeolian deposition within vegetation modern established foredunes are classified into five morphologic stages and the morphologies and processes of each is described stage 1 foredunes are well vegetated symmetric stable ridges characterised by stoss face and crest deposition stage 2 foredunes display minor erosional patches 75 90 vegetation cover and slight lateral variation in deposition and erosion stage 3 foredunes are hummocky have a 45 75 vegetation cover range and display various scales of blowouts concave stoss faces and steeper lee faces stage 4 foredunes are characterised by large scale erosional features such as blowouts sand sheets and high asymmetry stage 5 foredunes comprise poorly vegetated remnant knobs each stage is characterised by a set of erosional and depositional processes which produce generally distinctive sets of cross strata sedimentary structures within examples of each foredune stage are examined stage 1 and 2 foredunes are dominated by simple large scale convex continuous strata stage 3 and 4 foredunes display increasingly variable sets of cross strata and a greater degree of planar and trough cross stratification wave cut scarps blowout structures and very steep lee slope bedding may be preserved the internal sedimentary structures presented here form the basis of a facies model for foredunes

ancient and modern cold climate aeolian sand deposition a review although partly active aeolian sand sheets and dunes cover large areas in the zones of dis continuous permafrost little precise information is available about the influence of cold climate conditions on modern aeolian processes this means that palaeoenvironmental reconstructions in the stabilised mainly late pleistocene dune fields and cover sand regions in the sand belts of the european lowlands and the northern great plains of the usa and canada are necessarily still based on ancient evidence cold climate wind deposits are typically derived from areas of abundant sediment supply like unvegetated flood plains glacial outwash plains till plains and lake shores the common parabolic and transverse dune forms resemble those observed in temperate regions although a variety of periglacial features has been identified in late pleistocene dune and cover sands none of them indicate that permafrost is crucial to aeolian activity specific structures in aeolian strata permit tentative interpretation of the moisture content of depositional sand surfaces the nature of annual sedimentation cycles and the processes by which strata were deposited and or contorted but surprisingly little is known about the role of vegetation in the process of sand accumulation dunes are most informative with respect to reconstructions of past wind regimes which offer important data for verification of palaeoclimatic simulations

beach ridges definitions and significance abstract beach ridges frequent components of quaternary coastal plains and other coastal landforms have been cited as indicators of the positions of ancient seashores and associated sea levels numerous authors utilized the term beach ridge for active and relict usually wave built supratidal and or intertidal forms wind built ridges have been only occasionally included in the definition the term was applied also to submerged landward shifting eventually stranded bars a consistent redefinition of the term is highly desirable beach ridges should include all relict strandplain ridges whether dominated by wave swash built or by eolian lithosomes all active ridge like shore features regardless of dimensions morphology and origin are excluded because of the resistance of coarse clastic ridges to wave and wind erosion swash built gravel or coarse shell storm ridges may build several meters above the level of high tide swash built high berms even on pure sandy beaches exceed the highest tides during episodes of wind induced record water levels frequently but not always burying underlying low relief berm ridges of berm lithosomes sequences of relatively steep multiple foredunes are commonly named beach ridge plains the narrow subparallel relict foredunes that form these strandplains presently are designated as eolian beach ridges beach ridges thus are defined as relict semiparallel multiple wave and wind built landforms that originated in the inter and supratidal zones until separated from the shoreline by progradation sandy pebbly or shell enriched backshore berm ridges behind an active foreshore should not be considered beach ridges strandplain progradation is either continuous or with the inclusion of subtidal cat s eye ponds discontinuous contrary to claims transgressive cheniers do not represent true cheniers alone within their overall progradational context cheniers a special category of beach ridges bracketed by subtidal intertidal mudflats may be transgressive or regressive in character landward driven transgressive ridges should be designated beach ridges only after they are stabilized on intertidal flats when recognizable between clearly identifiable intertidal and overlying eolian intervals the horizontal interface between these lithosomes in beach ridges may help the reconstruction of ancient tide lake levels diagnostic sedimentary textures structures and fossils however often may be unavailable in the deposits along with various types of elevated terraces composed of raised marine deposits and certain coastal landforms of erosional origin that occur worldwide beach ridges of clearly proven wave built origin may also serve as indicators of ancient higher than present sea levels

foredune development along a subarctic emerging coastline eastern hudson bay canada abstract a study of sedimentary processes and evolution of subarctic foredunes along a rapidly emerging coastline in southeastern hudson bay showed that niveo eolian sedimentation is a significant process contributing to the formation of these foredunes the fall storm berm and the sand laden ice foot are the prime sedimentary sources for the niveoeolian deposits which are generally coarser grained than the eolian sand deposited during summer the annual sedimentation in the backshore zone is less than in typical mid latitude regions the development of established foredunes in this subarctic environment seems to require a longer period of time than in other climatic zones the short term backshore evolution 1954 1990 shows that sediment supply appears to be a major factor controlling foredune morphology and dynamics phases of sediment surplus seem to correspond to rapid seaward progradation and formation of low foredune terraces or low foredune ridges with a beach ridge like morphology conversely high foredunes probably develop during periods of lower sediment supply and slower beach progradation on a longer time scale the relative sea level fall controls coastline progradation and results in the formation of raised coast parallel relict foredune ridges

winter variability of aeolian sediment transport threshold on a cold climate dune abstract changes in surface conditions on cold climate aeolian dunes are pronounced during winter dunes are wet snow covered and or frozen for extended periods of time it is unknown how the critical wind speed for sediment transport threshold varies and how threshold may influence sediment transport predictions although the impact of surface conditions on threshold has been examined in synthetic experiments wind tunnels complicated feedbacks between threshold sand transport and surface conditions that occur in natural environments suggest that a ground based empirical approach may provide enhanced insight in this study we investigate threshold variability for 73 days during fall winter spring surface conditions from 18 november 2008 to 30 may 2009 in the bigstick sand hills of saskatchewan canada simultaneous measurements of threshold and atmospheric variables air temperature relative humidity solar radiation wind speed and direction were used to examine the extent to which surface erodibility was regulated by meteorology time lapse images of the surface from a co located camera were used for quality control and interpreting changes in the surface affecting threshold results reveal that threshold varied throughout the deployment 25 75 quartiles 6 92 8 28 m s 1 mean 7 79 m s 1 threshold variability was especially evident at two scales i event timescale and ii seasonal timescale event scale variability peaked during mid winter in one event the threshold varied by 6 m s 1 in 2 h with freezing and re freezing of the surface and relatively constant atmospheric conditions the causes of event scale variability are complex though qualitatively related to changes of wind direction antecedent meteorological conditions and vertical variations of grain scale bonding agents such as pore ice and moisture seasonal scale changes manifested as an increase in threshold during fall peaking in mid winter and decreasing in spring increased threshold in mid winter was linked to lower insolation and air temperature suggesting low erodibility due to the presence of pore ice correlation coefficients of threshold versus atmospheric variables yielded relatively weak correlations air temperature r 0 322 relative humidity r 0 388 solar radiation r 0 309 that also varied according to wind direction suggesting that the link between atmospheric conditions and surface erodibility on cold climate dunes is complex this contrasts with results from field based studies in warmer climates and controlled wind tunnel experiments which show a more direct link between atmospheric variables temperature and humidity and surface erodibility nevertheless our results do show a seasonal pattern of threshold that could be important for modeling cold climate aeolian sediment transport

evidence for recent climate change on mars from the identification of youthful near surface ground ice ground ice in the crust and soil may be one of the largest reservoirs of water on mars1 2 3 near surface ground ice is predicted to be stable at latitudes higher than 40 ref 4 where a number of geomorphologic features indicative of viscous creep and hence ground ice have been observed5 mid latitude soils have also been implicated as a water ice reservoir6 the capacity of which is predicted to vary on a 100 000 year timescale owing to orbitally driven variations in climate7 it is uncertain however whether near surface ground ice currently exists at these latitudes and how it is changing with time here we report observational evidence for a mid latitude reservoir of near surface water ice occupying the pore space of soils the thickness of the ice occupied soil reservoir 1 10 m and its distribution in the 30 to 60 latitude bands indicate a reservoir of 1 5 6 0 104 km3 equivalent to a global layer of water 10 40 cm thick we infer that the reservoir was created during the last phase of high orbital obliquity less than 100 000 years ago and is now being diminished

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

flow dynamics over a foredune at prince edward island canada time averaged windspeed profiles at eight locations over a relatively high 8 m vegetated topographically simple foredune were measured using cup and ultrasonic anemometry during an onshore wind event in may 2002 the experiment was part of a largerstudyonthesedimentarydynamicsofabeach dunecomplexinthegreenwichdunes princeedwardisland pei canada the foredune is vegetated with ammophila breviligulata and vegetation density ranged from 0 on the foredune ramp to upward of 70 at the dune crest topographic forcing and resulting flow acceleration was observed distinctly in windspeed profiles and linear speedup occurred for all elevations above the vegetation canopy a distinct inflection point is evident in normalized windspeed profiles over the dune indicating a net momentum sink below the vegetation canopy top and systematic speed down within the vegetation was observed up the foredune stoss slope wind speed profile structure was consistent for the range of incident wind speeds measured a comparison of normal and slightly oblique incident winds indicated that for similar approach winds wind speeds are consistently higher during oblique flow conditions the implications for foredune morphodynamics and sedimentation are discussed d 2004 elsevier b v all rights reserved

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