fast and accurate estimation of solar irradiance on martian slopes 1 a general parameterization is proposed in this study to calculate in a mars like dusty atmosphere the solar irradiance reaching an inclined surface assuming the value in the horizontal case is known complete monte carlo radiative transfer calculations using the ockert bell et al 1997 dust optical properties enable the validation of the method for mars the total shortwave flux reaching the surface is composed of three contributions direct incoming flux reflected flux by surrounding terrains and scattered flux by the atmospheric dust the main difficulty is the parameterization of the latter component we show that the scattered flux reaching the slope can be expressed by a physically based simple formula involving one empirical coupling matrix and two vectors accounting for the scattering properties and the geometrical settings the final result is a computationally efficient parameterization with an accuracy in most cases better than 5 w m 2 such a fast and accurate method to calculate solar irradiance on martian slopes should they be topographical surfaces or solar panels is of particular interest in a wide range of applications such as remote sensing measurements geological and meteorological models and mars exploration missions design

western boundary currents in the atmosphere of mars western boundary currents wbcs are an intensification of north south flow adjacent to an eastward facing meridional boundary although most familiar in the oceans where the gulf stream is the best known example wbcs also occur in the earth s troposphere the main example being the east african jet1 which is thought to play an important role in the asiatic monsoon here we identify boundary currents in a different geophysical context a numerical simulation of the atmosphere of mars in our simulation wbcs exist in association with significant cross equatorial flow and the presence of equatorial martian topography which has vertical scale far exceeding terrestrial relief2 the intensity and width of these currents depend on model parameters notably the surface drag from a comparison of our results with other martian models we suggest that wbcs have already been simulated although they were not previously identified as such3 the available observational evidence appears to be consistent with the presence of martian wbcs which may be important in the generation of global and great dust storms

dynamics of ice ages on mars mars experiences much greater fluctuations in exposure to sunlight than the earth does because of larger variations in astronomical factors such as the tilt of its axis relative to the orbital plane climate change is accordingly more intense on mars than on earth norbert schorghofer has now developed a climate model that accounts for the advance and retreat of the subsurface martian ice sheets over forty major ice ages and five million years this explains the present distribution of subsurface ice on mars in addition lessons learned from the long and relatively simple martian ice age stratigraphy should help when it comes to interpreting the more complicated events here on earth numerical simulation and modelling of the retreat and growth of ground ice on mars demonstrates how the subsurface ice sheets could have evolved and ended up in the state we see them today and also reveals that 40 major ice ages occurred on mars over the past 5 million years unlike earth where astronomical climate forcing is comparatively small mars experiences dramatic changes in incident sunlight that are capable of redistributing ice on a global scale1 2 3 4 5 6 the geographic extent of the subsurface ice found poleward of approximately 60 latitude on both hemispheres of mars7 8 9 coincides with the areas where ice is stable7 10 11 however the tilt of mars rotation axis obliquity changed considerably in the past several million years earlier work3 12 has shown that regions of ice stability which are defined by temperature and atmospheric humidity differed in the recent past from today s and subsurface ice is expected to retreat quickly when unstable11 12 13 here i explain how the subsurface ice sheets could have evolved to the state in which we see them today simulations of the retreat and growth of ground ice as a result of sublimation loss and recharge reveal forty major ice ages over the past five million years today this gives rise to pore ice at mid latitudes and a three layered depth distribution in the high latitudes of from top to bottom a dry layer pore ice and a massive ice sheet combined these layers provide enough ice to be compatible with existing neutron and gamma ray measurements7 8 9

martian seasonal co2 ice in polygonal troughs in southern polar region role of the distribution of subsurface h2o ice the mars orbiter camera onboard the mars global surveyor has obtained several images of polygonal features in the southern polar region in images taken during the end of the southern spring when the surrounding surface is free of the seasonal frost co2 ice still appears to be present within the polygonal troughs in earth s polar regions polygons such as these are indicative of water ice in the ground below we analyzed the seasonal evolution of the thermal state and the co2 content of these features our 2 d model includes condensation and sublimation of the co2 ice a self consistent treatment of the variations of the thermal properties of the regolith and the seasonal variations of the local atmospheric pressure which we take from the results of a general circulation model we find that the residence time of seasonal co2 ice in troughs depends not only on atmospheric opacity and albedo of the co2 ice but also and most significantly on the distribution of water ice in the regolith optical properties of the atmosphere and surface co2 ice can be independently obtained from observations to date this is not true about the distribution of water ice below the surface our analysis quantifies the dependence of the seasonal cycle of the co2 ice within the troughs on the assumed distribution of the water ice below the surface we show that presence of water ice in the ground at a depth smaller than the depth of the troughs reduces winter condensation rate of co2 ice this is due to higher heat flux conducted from the water ice rich regolith toward the facets of the troughs

observations of the south seasonal cap of mars during recession in 2004 2006 by the omega visible near infrared imaging spectrometer on board mars express 1 the omega visible near infrared imaging spectrometer on board mars express has observed the southern seasonal cap in late 2004 and 2005 and then in the summer of 2006 these observations extended from the period of maximum extension close to the southern winter solstice to the end of the recession at ls 325 the spectral range and spectral resolution of omega make it possible to monitor the extent and effective grain size of co2 ice and h2o ice on the ground the level of contamination of co2 ice and h2o ice by dust and the column density of m sized ice grains in the atmosphere the co2 seasonal cap is very clean and clear in early southern winter contamination by h2o ice spreads eastward from the hellas basin until the southern spring equinox during southern spring and summer there is a very complex evolution in terms of effective grain size of co2 ice and contamination by dust or h2o ice h2o ice does not play a significant role close to the southern summer solstice contamination of co2 ice by h2o ice is only observed close to the end of the recession as well as the few h2o ice patches already reported by bibring et al 2004a these observations have been compared to the results of a general circulation model with good qualitative agreement on the distribution of h2o ice on the surface and in the atmosphere resolving the remaining discrepancies will improve our understanding of the water cycle on mars

jet efflux deposits of a subaqueous ice contact fan glacial lake rinteln northwestern germany abstract the coarse grained ice contact porta subaqueous fan delta complex was deposited in glacial lake rinteln at the margin of the saalian ice sheet that advanced south of the weser chains nw germany the ice proximal depositional system was up to 15 km long and 10 km wide the present study deals with ice proximal subaqueous fan deposits which are interpreted as products of a subcritical plane wall outflow jet that periodically passed into a supercritical jet with hydraulic jump the proximal facies assemblage consists of the coarse clast supported gravelly deposits of a hyperconcentrated high density effluent and of related cohesionless debris flows attributed to the conduit or immediate proximal jet outflow zone of flow establishment the intermediate facies assemblage attributed to the outflow jet proximal zone of flow transition is dominated by normally graded and cross stratified gravels with scour structures at their bases these gravels were deposited by a high density effluent capable of forming mouthbar like features these deposits pass downcurrent into an assemblage of planar parallel stratified and planar and trough cross stratified sands and pebbly sands partially interpreted as antidunes with abundant scour structures and intercalated layers of fine sand silt and silty mud attributed to the jet distal zone of flow transition the distal facies assemblage consists of trough cross stratified sands and pebbly sands and is attributed to the outflow jet proximal zone of established flow the sedimentary succession as a whole has wedge shape geometry with a gentle fan shaped inclination of the bedding from the southeast to the southwest repeated vertical alternations of supercritical and subcritical deposits and muddy interlayers can be attributed to temporary fluctuations in the meltwater outflow whereas the overall upward fining of the succession indicates a net decline of meltwater discharges

predicting head cut erosion and migration in concentrated flows typical of upland areas 1 soil erosion due to head cut development and migration can devastate agricultural lands yet current prediction technology does not address this important erosion process here an analytical model of this erosional phenomenon is presented realistic physically based approximations to the laws governing mass momentum and energy transfer in the neighborhood of the scour hole result in closed form predictive algorithms for the magnitude of the plunge pool erosion and the rate of head cut migration the model introduces a special treatment of nonventilated overfall conditions is limited to homogeneous unbounded soil layers and is validated by available experimental measurements

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

are coarse grained sediment waves formed as downstream migrating antidunes insight from an early pleistocene submarine canyon on the boso peninsula japan abstract gently undulating waveforms were identified in conglomerates and pebbly sandstones of the lower pleistocene higashihigasa formation which represents an infill of a submarine canyon on the boso peninsula japan on the basis of dimension geometry and texture these waveforms are interpreted as bedforms that are analogous to coarse grained sediment waves in modern deep water environments the studied waveforms exhibit symmetrical or dune like asymmetrical forms in association with minor antidune like asymmetrical forms with the lee sides being longer than the stoss sides the waveforms are also characterized internally by bedding gently inclined in the downstream direction to the northeast laterally washout dune and humpback dune deposits are locally developed in association with planar bedding the coarse grained sediment wave deposits are interpreted to have developed as downstream migrating antidunes in the upper flow regime condition of turbidity currents on the basis of the empirical relationship between the wavelengths and mean flow depths of downstream migrating gravel antidunes the waveforms are interpreted to have been formed by waves at the interface between the denser bottom flow and the less dense upper flow within a turbidity current it is possible that some of the coarse grained sediment waves in modern deep water environments may have been formed as downstream migrating antidunes regardless of their plan view geometry

evidence for rapid sedimentation in a tunnel channel oak ridges moraine southern ontario canada abstract in south central ontario a late wisconsinan regional unconformity consisting of tunnel channels and drumlinized till crops out north of lake ontario the tunnel channels are locally infilled and the unconformity buried by sediment of the oak ridges moraine based on seismic reflection profiling and drillcore the tunnel channels are known to continue beneath the moraine detailed sedimentological analysis of 300 m of continuous core from two drillholes located 7 km apart in subparallel tunnel channels identified three facies the gravel facies is 17 m thick and occurs in only one of the cores it directly overlies the unconformity and may include a number of upward fining units seismic reflection data suggests the gravel forms stacked gravel mesoforms or quasi horizontal gravel layers bed load sheets deposited from fluidal flows along the deep channel axis the graded massive sand facies up to 37 m thick is the most common facies and consists of silty medium sand with minor coarse sand strata are reverse graded normal graded or massive with isolated silt intraclasts and evidence locally for dewatering this facies is interpreted to have been deposited from hyperconcentrated dispersions downflow of a hydraulic jump or major channel confluence the third facies consists of medium scale and small scale cross stratified sand medium scale cross stratification occurs predominantly in the lower 37 m of the core and is interbedded with the graded massive sand facies small scale cross stratified sand is progressively more common upward in core medium and small scale cross stratified sands was deposited respectively by subaqueous dunes and ripples formed in dilute fluid flows the complete succession is interpreted to have been deposited very rapidly within a subglacial tunnel channel before discharge ceased along the channel deposition followed closely and in part coincided with rapid expansion of the channel by erosion in a hydraulic jump or at a major channel confluence along the grounding line of a subglacial lake scour into unconsolidated sediment contributed to the sediment flux and quickly overloaded the flow with suspended sediment which in turn resulted in extremely high rates of sedimentation immediately downflow such depositional conditions support the notion that tunnel channels in the study area formed and or served as conduits for subglacial jokulhlaup discharges and that the laurentide ice sheet most probably did not generally drain by steady state processes but instead by short lived catastrophic events

variations in the architecture of hydraulic jump bar complexes on non eroding beds sediment accumulation downstream of hydraulic jumps can occur in many settings but the architectures of such deposits are poorly documented here three flume runs were used to examine the influence of sediment grain size and transport rate on the characteristics of hydraulic jump unit bars in one of these runs six hydraulic jump unit bars formed a hydraulic jump bar complex in another the same sediment was supplied more quickly and only two unit bars formed in the third run with the same sediment supply rate but different grain size only one large unit bar formed all unit bars developed in a similar way but their size and internal architecture differed they all resulted from a reduction in sediment transport capacity at the transition from supercritical flow to subcritical flow in the hydraulic jump after initial onset of sedimentation and unit bar formation generation of subsequent unit bars may be i related to small changes in sediment flux and ii independent of changes in the hydraulic jump continued sedimentation caused changes from oscillating to weak hydraulic jumps and hydraulic jump unit bars formed in both circumstances the flow of water and suspended sediment becomes shallower over the lee of the bar complex this leads to flow acceleration and a return to supercritical flow conditions in turn a chain of such features can form and generate a chute and pool bed morphology there is an inherent upper size limit to a hydraulic jump bar complex due to the changing flow conditions over the growing deposit as the water above it becomes shallower there is also an amplitude minimum for the development of foresets and subsequent unit bar growth hydraulic jump unit bars have architectures that should be recognizable in the rock record and because their size is constrained by the flow conditions their identification should be useful for interpreting palaeoenvironment

improved general circulation models of the martian atmosphere from the surface to above 80 km we describe a set of two new generation general circulation models of the martian atmosphere derived from the models we originally developed in the early 1990s the two new models share the same physical parameterizations but use two complementary numerical methods to solve the atmospheric dynamic equations the vertical resolution near the surface has been refined and the vertical domain has been extended to above 80 km these changes are accompanied by the inclusion of state of the art parameterizations to better simulate the dynamical and physical processes near the surface boundary layer scheme subgrid scale topography parameterization etc and at high altitude gravity wave drag in addition radiative transfer calculations and the representation of polar processes have been significantly improved we present some examples of zonal mean fields from simulations using the model at several seasons one relatively novel aspect previously introduced by wilson 1997 is that around northern winter solstice the strong pole to pole diabatic forcing creates a quasi global angular momentum conserving hadley cell which has no terrestrial equivalent within such a cell the coriolis forces accelerate the winter meridional flow toward the pole and induce a strong warming of the middle polar atmosphere down to 25 km this winter polar warming had been observed but not properly modeled until recently in fact thermal inversions are generally predicted above one and often both poles around 60 70 km however the mars middle atmosphere above 40 km is found to be very model sensitive and thus difficult to simulate accurately in the absence of observations

critical flow constrains flow hydraulics in mobile bed streams a new hypothesis a new hypothesis predicts that in mobile bed river channels interactions between the channel hydraulics and bed configuration prevent the froude number fr from exceeding 1 for more than short distances or periods of time flow conditions in many steep competent streams appear to be close to critical froude numbers of steep slope 0 01 sand bed streams with considerable freedom to adjust boundaries oscillate between 0 7 and 1 3 over 20 to 30 s cycles with an average of 1 0 at the channel thalweg criticalflow in these streams is maintained by the interaction between the mobile bed and free water surface at highfr which results in a cyclical pattern of creation and destruction of bed forms field observations support that a similar mechanism offlow bed form interaction constrains fr 1 in active bed braided gravel rivers step pool streams laboratory rills lahar runout channels and even some bedrock channels empirical and analytical results show that as slope increases competentflows tend to asymptotically approach criticalflow an assumption of criticalflow would dramatically simplify paleohydraulicflow reconstructions and modeling offlow hydraulics in high gradient streams

local amplification of seismic waves from the denali earthquake and damaging seiches in lake union seattle washington 1 the mw7 9 denali alaska earthquake of 3 november 2002 caused minor damage to at least 20 houseboats in seattle washington by initiating water waves in lake union these water waves were likely initiated during the large amplitude seismic surface waves from this earthquake maps of spectral amplification recorded during the denali earthquake on the pacific northwest seismic network pnsn strong motion instruments show substantially increased shear and surface wave amplitudes coincident with the seattle basin because lake union is situated on the seattle basin the size of the water waves may have been increased by local amplification of the seismic waves by the basin complete hazard assessments require understanding the causes of these water waves during future earthquakes

evolution of a carbonate delta generated by gateway funnelling of episodic currents cool water carbonate sedimentation has dominated mediterranean shelves since the early pliocene skeletal sand and gravel herein consist of remains of heterozoan organisms which are susceptible to reworking due to weak early cementation in non tropical waters this study documents the lower pleistocene carbonate wedge of favignana island italy which prograded from a 5 km wide passage between two palaeo islands into a perpendicular 10 to 15 km wide strait between the palaeo islands at one side and sicily at the other during the emilian highstand 1 6 ma to 1 1 ma the clinoformed carbonate wedge which is 50 m thick and 6 km long formed by east south east progradation of a platform on the submarine sill by currents that were funnelled between the two palaeo islands platform slope clinoforms evolved from initial aggradation thin and low angle into a progradation phase thick and high angle both clinoform types are characterized by a bimodal facies stacking pattern defined by sedimentary structures created by i subaqueous dunes associated with dilute subcritical currents and ii upper flow regime bedforms associated with sediment laden supercritical turbidity currents focusing of episodic currents on the platform by funnelling between the islands controlled the downstream formation of a sediment body here named carbonate delta the carbonate delta interfingers with subaqueous dune deposits formed in the perpendicular strait this study uses a reconstruction of bedform dynamics to unravel the evolution of this gateway related carbonate accumulation

western boundary currents in the martian atmosphere numerical simulations and observational evidence western boundary currents hereafter wbcs are an intensification of meridional fluid flow along the eastward facing flank of a boundary they occur in the earth s oceans the best known instance being the gulf stream and in the terrestrial atmosphere an example of which is the east african jet we have investigated wbcs in numerical simulations of the martian atmosphere where they occur in the presence of large longitudinal topographical gradients combined with the effect we suggest that wbcs have already been simulated by other martian atmospheric models although not identified as such the intensity of these currents is dependent on basic model parameters notably surface drag we show that for physically reasonable values of drag frictional forces dominate the wbcs behavior the requirement of zero net cross equatorial time mean mass flow produces a return flow in simulations with relatively low surface drag which acts in opposition to the tharsis wbc we also show that the intense flow associated with wbcs advects potential vorticity across the equator although the presence of strong radiative damping inhibits low level inertial instabilities that might result from this slope winds are found to have a profound effect on wbc structure especially where they have a component parallel to the jet in these cases slope winds can cancel out or reinforce wbcs depending on their direction enhanced low level winds associated with wbcs may be a factor that influences the locations of dust storm generation the high vertical shear associated with wbcs may also play a role in the maintenance and subsequent decay of these dust storms some observational evidence may exist for wbcs in the form of the alignment of bright depositional dust streaks wave clouds and in wind measurements taken during the parachute descent phase of viking lander 1 through the planetary boundary layer

is the martian water table hidden from radar view 1 mars may possess a global sub surface groundwater table as an integral part of its current hydrological system however the mars advanced radar for subsurface and ionospheric sounding marsis onboard the mars express mex spacecraft has yet to make a definitive detection of such a body of liquid water in this work we quantify the conditions that would allow a detection of a deep aquifer and demonstrate that the lack of radar detection does not uniquely rule out the presence of such a body specifically if the overlying crustal material has a conductivity above 10 5 s m equivalent to a loss tanget of 0 008 a radar echo from an aquifer could be sufficiently attenuated by the intervening medium to prevent its detection by marsis as such the lack of direct detection by marsis a null result does not rule out the possibility of the water table s existence

geomorphic evidence for the distribution of ground ice on mars high resolution viking orbiter images show evidence for quasi viscous relaxation of topography the relaxation is believed to be due to creep deformation of ice in near surface materials the global distribution of the inferred ground ice shows a pronounced latitudinal dependence the equatorial regions of mars appear to be ice poor while the heavily cratered terrain poleward of 30 latitude appears to be ice rich the style of creep poleward of 30 varies with latitude possibly due to variations in ice rheology with temperature the distribution suggests that ice at low latitudes which is not in equilibrium with the present atmosphere has been lost via sublimation and diffusion through the regolith thereby causing a net poleward transport of ice over martian history

water ice at low to midlatitudes on mars 1 in this paper we analyze water ice occurrences at the surface of mars using near infrared observations and we study their distribution with a climate model latitudes between 45 s and 50 n are considered data from the observatoire pour la mineralogie l eau les glaces et l actitite and the compact reconnaissance imaging spectrometer for mars are used to assess the presence of surface water ice as a function of location and season a modeling approach combining the 1 d and 3 d versions of the general circulation model of the laboratoire de meteorologie dynamique de jussieu is developed and successfully compared to observations ice deposits 2 200 m thick are observed during the day on pole facing slopes in local fall winter and early spring ice extends down to 13 latitude in the southern hemisphere but is restricted to latitudes higher than 32 in the north on a given slope the pattern of ice observations at the surface is mainly controlled by the global variability of atmospheric water precipitation and vapor with local ground properties playing a lower role only seasonal surface ice is observed no exposed patches of perennial ground ice have been detected surface seasonal ice is however sensitive to subsurface properties the results presented in this study are consistent with the recent discovery of low latitude subsurface ice obtained through the analysis of co 2 frost

paleohydraulics of chute and pool structures in a paleoproterozoic fluvial sandstone abstract chute and pool structures consist of an inclined surface leading into a pool where a hydraulic jump causes deposition of backset laminae structures fitting this description are present at the base of a very fine grained sandstone bed in the fluvial matinenda formation of northern ontario reconstruction of the paleohydraulic system indicates that a depth of approximately 1 cm and a velocity of approximately 65 cm s formed these bedforms during the initial stage of a flow with increasing depth and decreasing velocity this type of deposit should be most common at the base of sandy beds deposited as emergent bars are overtopped during increasing discharge events

effect of upward seepage on scour and flow downstream of an apron due to submerged jets the upward seepage through the bed sediment downstream of an apron of a sluice gate structure is a common occurrence due to afflux of the flow level between the upstream and downstream reaches of a sluice gate the result of an experimental investigation on the characteristics of the scour hole and the flow field downstream of an apron due to submerged jets under the influence of upward seepage through the bed sediment is presented experiments were run for the conditions of submerged jets having submergence factors from 0 99 to 1 72 and jet froude numbers from 3 15 to 4 87 over beds of sediments median sizes 0 8 1 86 and 3 mm downstream of an apron under upward seepage velocities the characteristic lengths of the scour hole determined from the scour profiles are the maximum equilibrium scour depth the horizontal distance of the location of maximum scour depth from the edge of the apron the horizontal extent of the scour hole from the edge of the apron the dune height and the horizontal dist

facies architecture and stratigraphic evolution of a river dominated delta front turonian ferron sandstone utah u s a abstract facies architectural analysis of a river dominated deltaic parasequence in the turonian ferron sandstone member near factory butte utah was conducted to determine the hierarchical spatial arrangement of mouth bars and their role in constructing the delta five architectural elements were identified using 21 measured sections paleocurrent measurements and bedding diagrams they are 1 prodelta pf 2 frontal splay fs 3 detached distal bars dbs 4 distributary mouth bars dmbs and 5 terminal distributary channels tdcs lower in the parasequence detached bars consist of proximally located cross bedded and quasi parallel laminated subaqueous bars that onlap the delta front slope and grade distally into finer grained distal delta front splays these bars translate downstream in a progradational aggradational degradational trajectory and are overlapped by adjacent bars forming a bar assemblage these bars are interpreted to have been deposited by descending hyperpycnal flows as a decelerating axial jet deposition of these bars occurs at the delta front to prodelta chokepoint presumably due to flow deceleration the distal bar assemblage is capped by an extensive but discontinuous shale drape suggesting local abandonment upper facies assemblages show a distinct switch to predominantly cross bedded distributary mouth bars corresponding to a decrease in water depth an increase in friction and a likely transition into planar versus axial jets this is indicated by aggrading cross bedded distributary mouth bars that overlie the distal bars laterally the mouth bar deposits are interstratified with terminal distributary channel deposits with prominent scour surfaces at the base separate distributary channels and their bars coalesce ultimately to build the entire delta lobe the detached distal bars prograde locally west to northwest and lack fair weather wave formed sedimentary structures suggesting a local embayment along the regionally northeast prograding shoreline low levels of ichnofaunal diversity indicate a stressed river dominated setting at the base of the section frontal splays and detached bars dominated by storm driven river flood deposits are deposited over muddy prodelta facies detached bars are likely initiated about 500 meters distal of the distributary channel in water depths of 10 30 meters based on the thickness of the parasequence once this subaqueous platform is constructed by the distal bar assemblage more proximal distributary mouth bars fill the remaining shallow water accommodation as the system continues to shallow distributary channels override and scour the bars reflecting reduced accommodation

long period effects of the denali earthquake on water bodies in the puget lowland observations and modeling analysis of strong motion instrument recordings in seattle washington resulting from the 2002 m w 7 9 denali alaska earthquake reveals that amplification in the 0 2 to 1 0 hz frequency band is largely governed by the shallow sediments both inside and outside the sedimentary basins beneath the puget lowland sites above the deep sedimentary strata show additional seismic wave amplification in the 0 04 to 0 2 hz frequency range surface waves generated by the m w 7 9 denali alaska earthquake of 3 november 2002 produced pronounced water waves across washington state the largest water waves coincided with the area of largest seismic wave amplification underlain by the seattle basin in the current work we present reports that show lakes union and washington both located on the seattle basin are susceptible to large water waves generated by large local earthquakes and teleseisms a simple model of a water body is adopted to explain the generation of waves in water basins this model provides reasonable estimates for the water wave amplitudes in swimming pools during the denali earthquake but appears to underestimate the waves observed in lake union

reconstruction of bedform dynamics controlled by supercritical flow in the channel lobe transition zone of a deep water delta sant llorenc del munt north east spain eocene

surface seiches in lakes of complex geometry in lakes of small to medium size the characteristic frequencies of free oscillations of the water surface seiches depend only on the basin geometry in irregularly shaped basins such as dendritic reservoirs and multibasin lakes these characteristic frequencies are not easily determined with simple formulas clear lake a multibasin lake in northern california is presented here as a case in point the signature of the seiches in clear lake were only revealed after solving the eigenvalue problem governing the structure and frequency of seiches derived from the linear and frictionless depth averaged shallow water equations in a nonrotating frame

ancient melting of mid latitude snowpacks on mars as a water source for gullies abstract we hypothesize that during past epochs of high obliquity seasonal snowfields at mid latitudes melted to produce springtime sediment rich surface flows resulting in gully formation significant seasonal mid latitude snowfall does not occur on mars today general circulation model gcm results however suggest that under past climate conditions there may have been centimeters of seasonal mid latitude snowfall mischna m a richardson m i wilson r j mccleese d j 2003 j geophys res planets 108 doi 10 1029 2003je002051 5062 gully locations have been tabulated by several researchers e g heldmann j l mellon m t 2004 icarus 168 285 304 heldmann j l carlsson e johansson h mellon m t toon o b 2007 icarus 188 324 344 malin m c edgett k s 2000 science 288 2330 2335 and found to correspond to mid latitude bands a natural question is whether the latitudinal bands where the gullies are located correspond to areas where the ancient snowfalls may have melted producing runoff which may have incised gullies in this study we model thin snowpacks with thicknesses similar to those predicted by mischna m a richardson m i wilson r j mccleese d j 2003 j geophys res planets 108 doi 10 1029 2003je002051 5062 we model these snowpacks under past climate regimes in order to determine whether snowmelt runoff could have occurred and whether significant amounts of warm soil t 273 k existed on both poleward and equatorward slopes in the regions where gullies exist both warm soil and water amounts are modeled because soil and water may have mixed to form a sediment rich flow we begin by applying the snowpack model of williams et al williams k e toon o b heldmann j e mellon m 2008 icarus 196 565 577 to past climate regimes characterized by obliquities of 35 600 ka before present and 45 5 5 ma before present and to all latitudes between 70 n and 70 s we find that the regions containing significant snowmelt runoff correspond to the regions identified by heldmann and mellon heldmann j l mellon m t 2004 icarus 168 285 304 heldmann et al heldmann j l carlsson e johansson h mellon m t toon o b 2007 icarus 188 324 344 and malin and edgett malin m c edgett k s 2000 science 288 2330 2335 as containing large numbers of gullies we find that the snowmelt runoff 1 mm with equivalent rainfall rates of 0 25 mm h and warm soil 1 cm depth would have occurred on slopes within the gullied latitudinal bands the snowfall amounts modeled are predicted to be seasonal mischna m a richardson m i wilson r j mccleese d j 2003 j geophys res planets 108 doi 10 1029 2003je002051 5062 and our modeling finds that under the previous climate regimes there would have been meltwater present on the slopes in question for brief periods of time on the order of days each year our model provides a simple explanation for the latitudinal distribution of the gullies and also suggests that the gullies date to times when water migrated away from the present poles to the mid latitudes

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

deposition in an esker bead and fan complex lanark ontario canada abstract a glaciofluvial landform complex comprising a single esker ridge proximally multiple ridges and beads in the middle section and a complex of ridges and fans distally is mapped and described we present detailed successions in the associated sediment showing sedimentary structure grain size and palaeocurrent estimates sediment in the esker is mainly coarse grained and varies from boulders with a fine sand matrix deposited at maximum discharges to diamicton interpreted as a product of ice pressing under low discharges early stage deposition in the esker at high flow was from suspension and bed load intermediate stage deposition was mainly from bed load and late stage deposition was from hyperconcentrated suspension the esker rests in a bedrock channel which functioned as a nye channel prior to esker formation the channel surface carries a variety of fluvial erosional marks short distributary ridges of the ridges and beads complex contain mainly cobbles and boulders but beads are mainly in sand with rapid down flow fining and change in sedimentary structure faulting and overfolding of bead sediment suggest a subglacial origin deposition of the esker fan complex was highly variable in space and time down fan sedimentary changes with transitions from gravel to cross laminated fine sand in a few tens of metres indicate rapid loss in competence fan location lateral to the esker indicates a broadening of the zone of subglacial meltwater with time deposition from suspension and steep sided scours are interpreted to result from deposition and erosion by hyperconcentrated flows a model of underflows with submerged hydraulic jumps spilling laterally from the esker tunnel into subglacial cavities explains the morphological and sedimentary characteristics of the fans detailed analysis of small scale fining upwards sequences in the fans and beads indicates deposition by a large number of flow events these events are explained by glacier hydraulics whereby periodic separation of the glacier from its bed caused water with a high suspended sediment concentration to spill out from the esker tunnel into adjacent subglacial cavities evolution of the subglacial drainage system indicates a complexity of subglacial sedimentation near to a grounding line which is not readily apparent from observations at modern glaciers terminating in relatively deep water

subsurface ice on mars with rough topography high latitude ground ice on mars discovered by the gamma ray spectrometer suite is thought to be thermally stable owing to the presence of vapor in the martian atmosphere however local slopes can alter surface and subsurface temperatures substantially and hence allow ground ice to persist at locations where it would otherwise be unstable global statistics of the topography of mars are computed processed and extrapolated to derive a description of surface roughness on spatial scales to which ground ice should be sensitive this slope distribution is convolved with a new thermal model for the dependence of subsurface ice on slope to produce a prediction of the global ice distribution that includes the effect of topographic roughness in the highest latitudes slopes reduce the amount of buried ice while in lower latitudes the ice fraction increases widening the geographic boundary of the ice table at the high latitudes where ice is stable beneath horizontal ground the estimated reduction of ice is small compared to the existing ice volume areas in the midlatitudes with high surface roughness that have previously been predicted to be ice free are predicted to contain quantities of ice that may be detectable at present and accessible in the future slopes cause ground ice to be stable to latitudes of about 25 degrees in both hemispheres including for example areas within the northern olympus mons aureole deposits hecates tholus and hellas basin ice is unstable at equatorial latitudes even when accounting for surface slopes

turbulent shear stresses in hydraulic jumps bores and decelerating surges in an open channel a sudden rise in water level induces a positive surge or bore that may develop as a hydraulic jump in translation when the surge propagates against an adverse slope it decelerates until it becomes a stationary hydraulic jump both hydraulic jumps and decelerating surges induce some intense turbulent mixing and have some major impact on the sediment transport in natural systems herein a physical investigation was conducted in a relatively large rectangular channel hydraulic jumps and surges were generated by the rapid closure of a gate at the channel downstream end the turbulent shear stresses were measured with high temporal and spatial resolution 200 hz sampling rate in the jump flow a comparison between the stationary hydraulic jump hydraulic jump in translation and decelerating surge measurements showed some marked differences in terms of turbulent mixing the results highlighted some intense mixing beneath the jump front and roller for all configurations the levels of turbulent stresses were one to two orders of magnitude larger than a critical threshold for sediment motion the findings provide some insights into the hydraulic jump migration processes in mobile bed channels and the complex transformation from a moving jump into a stationary jump copyright c 2010 john wiley sons ltd

present day impact cratering rate and contemporary gully activity on mars the mars global surveyor mars orbiter camera has acquired data that establish the present day impact cratering rate and document new deposits formed by downslope movement of material in mid latitude gullies on mars twenty impacts created craters 2 to 150 meters in diameter within an area of 21 5 106 square kilometers between may 1999 and march 2006 the values predicted by models that scale the lunar cratering rate to mars are close to the observed rate implying that surfaces devoid of craters are truly young and that as yet unrecognized processes of denudation must be operating the new gully deposits formed since august 1999 are light toned and exhibit attributes expected from emplacement aided by a fluid with the properties of liquid water relatively long extended digitate distal and marginal branches diversion around obstacles and low relief the observations suggest that liquid water flowed on the surface of mars during the past decade

slope streaks on mars a new wet mechanism slope steaks are one of the most intriguing modern phenomena observed on mars they have been mostly interpreted as some specific type of granular flow we propose another mechanism for slope streak formation on mars it involves natural seasonal formation of a modest amount of highly concentrated chloride brines within a seasonal thermal skin and runaway propagation of percolation fronts given the current state of knowledge of temperature regimes and the composition and structure of the surface layer in the slope streak regions this mechanism is consistent with the observational constraints it requires an assumption that a significant part of the observed chlorine to be in form of calcium and ferric chloride and a small part of the observed hydrogen to be in form of water ice this wet mechanism has a number of appealing advantages in comparison to the widely accepted dry granular flow mechanism potential tests for the wet mechanism include better modeling of the temperature regime and observations of the seasonality of streak formation

the formation and evolution of youthful gullies on mars gullies as the late stage phase of mars most recent ice age gullies are extremely young erosional depositional systems on mars that have been carved by an agent that was likely to have been comprised in part by liquid water malin m c edgett k s 2000 evidence for recent groundwater seepage and surface runoff on mars science 288 2330 2335 mcewen a s et al 2007 a closer look at water related geologic activity on mars science 317 1706 1709 the strong latitude and orientation dependencies that have been documented for gullies require 1 a volatile near the surface and 2 that insolation is an important factor for forming gullies these constraints have led to two categories of interpretations for the source of the volatiles 1 liquid water at depth beneath the melting isotherm that erupts suddenly groundwater and 2 ice at the surface or within the uppermost layer of soil that melts during optimal insolation conditions surface near surface melting in this contribution we synthesize global hemispheric regional and local studies of gullies across mars and outline the criteria that must be met by any successful explanation for the formation of gullies we further document trends in both hemispheres that emphasize the importance of top down melting of recent ice rich deposits and the cold trapping of atmospherically derived h 2o frost snow as important components in the formation of gullies this provides context for the incorporation of high resolution multi spectral and hyper spectral data from the mars reconnaissance orbiter that show that 1 cold trapping of seasonal h 2o frost occurs at the alcove channel level on contemporary mars 2 gullies are episodically active systems 3 gullies preferentially form in the presence of deposits plausibly interpreted as remnants of the late amazonian emplacement of ice rich material and 4 gully channels frequently emanate from the crest of alcoves instead of the base showing that alcove generation is not necessarily a product of undermining and collapse at these locations a prediction of the groundwater model we interpret these various lines of evidence to mean that the majority of gullies on mars are explained by the episodic melting of atmospherically emplaced snow ice under spin axis orbital conditions characteristic of the last several myr

fluid flow and sediment entrainment in the garonne river bore and tidal bore collision a detailed field study was carried out on a tidal bore to document the turbulent processes and sediment entrainment which occurred the measured bore within the arcins channel of the garonne river france was undular in nature and was followed by well defined secondary wave motion due to the local river geometry a collision between the arcins channel tidal bore and the bore which formed within the main garonne river channel was observed about 800m upstream of the sampling site this bore collision generated a transient standing wave with a black water mixing zone following this collision the bore from the main garonne river channel propagated backward to the downstream end of the arcins channel velocity measurements with a fine temporal resolution were complemented by measurements of the sediment concentration and river level the instantaneous velocity data indicated large and rapid fluctuations of all velocity components during the tidal bore large reynolds shear stresses were observed during and after the tidal bore passage including during the backward bore propagation large suspended sediment concentration estimates were recorded and the suspended sediment flux data showed some substantial sediment motion consistent with the murky appearance of the flood tide waters copyright c 2015 john wiley sons ltd

flow patterns sedimentation and deposit architecture under a hydraulic jump on a non eroding bed defining hydraulic jump unit bars this paper presents results from two flume runs of an ongoing series examining flow structure sediment transport and deposition in hydraulic jumps it concludes in the presentation of a model for the development of sedimentary architecture considered characteristic of a hydraulic jump over a non eroding bed in run 1 a hydraulic jump was formed in sediment free water over the solid plane sloping flume floor ultrasonic doppler velocity profilers recorded the flow structure within the hydraulic jump in fine detail run 2 had identical initial flow conditions and a near steady addition of sand which formed beds with two distinct characteristics a laterally extensive basal wedge shaped massive sand bed overlain by cross laminated sand beds each cross laminated bed recorded the initiation and growth of a single surface feature here defined as a hydraulic jump unit bar a small massive sand mound formed on the flume floor and grew upstream and downstream without migrating to form a unit bar in the upstream portion of the unit bar sand finer than the bulk load formed a set of laminae dipping upstream this set passed downstream through the small volume of massive sand into a foreset which was initially relatively coarse grained and became finer grained downstream this downstream fining coincided with cessation of the growth of the upstream dipping cross set at intervals a new bed feature developed above and upstream of the preceding hydraulic jump unit bar and grew in the same way with the foreset climbing the older unit bar the composite architecture of the superimposed unit bars formed a fanning climbing coset above the massive wedge defined as one unit a hydraulic jump bar complex

lateral and vertical facies relationships of bedforms deposited by aggrading supercritical flows from cyclic steps to humpback dunes abstract the preservation of bedforms related to supercritical flows and hydraulic jumps is commonly considered to be rare in the geologic record although these bedforms are known from a variety of depositional environments this field based study presents a detailed analysis of the sedimentary facies and stacking pattern of deposits of cyclic steps chutes and pools antidunes and humpback dunes from three dimensional outcrops the well exposed middle pleistocene successions from northern germany comprise glacilacustrine ice contact subaqueous fan and glacial lake outburst flood deposits the studied successions give new insights into the depositional architecture of bedforms related to supercritical flows and may serve as an analogue for other high energy depositional environments such as fluvial settings coarse grained deltas or turbidite systems deposits of cyclic steps occur within the glacial lake outburst flood succession and are characterised by lenticular scours infilled by gently to steeply dipping backsets cyclic steps formed due to acceleration and flow thinning when the glacial lake outburst flood spilled over a push moraine ridge these bedforms are commonly laterally and vertically truncated and alternate with deposits of chutes and pools and antidunes the subaqueous fan successions are dominated by laterally extensive sinusoidal waveforms which are interpreted as deposits of aggrading stationary antidunes which require quasi steady flows at the lower limit of the supercritical flow stage and high rates of sedimentation humpback dunes are characterised by downflow divergent cross stratification displaying differentiation into topsets foresets and bottomsets and are interpreted as deposited at the transition from subcritical to supercritical flow conditions or vice versa gradual lateral and vertical transitions between humpback dunes and antidune deposits are very common the absence of planar parallel stratification in all studied successions suggests that the formation of these bedforms is suppressed in flows characterised by hydraulic jumps under highly aggradational conditions the large scale lateral and vertical successions of bedforms are interpreted as representing the temporal and spatial evolution of the initial supercritical flows which was strongly affected by the occurrence of hydraulic jumps small scale facies changes and the formation of individual bedforms are interpreted as controlled by fluctuating discharge bed topography and pulsating unstable flows

near tropical subsurface ice on mars near surface perennial water ice on mars has been previously inferred down to latitudes of about 45 and could result from either water vapor diffusion through the regolith under current conditions or previous ice ages precipitations in this paper we show that at latitudes as low as 25 in the southern hemisphere buried water ice in the shallow 1 m subsurface is required to explain the observed surface distribution of seasonal co2 frost on pole facing slopes this result shows that possible remnants of the last ice age as well as water that will be needed for the future exploration of mars are accessible significantly closer to the equator than previously thought where mild conditions for both robotic and human exploration lie copyright 2010 by the american geophysical union

formation of glaciers on mars by atmospheric precipitation at high obliquity surface conditions on mars are currently cold and dry with water ice unstable on the surface except near the poles however geologically recent glacierlike landforms have been identified in the tropics and the midlatitudes of mars the ice has been proposed to originate from either a subsurface reservoir or the atmosphere we present high resolution climate simulations performed with a model designed to simulate the present day mars water cycle but assuming a 45 obliquity as experienced by mars a few million years ago the model predicts ice accumulation in regions where glacier landforms are observed on the western flanks of the great volcanoes and in the eastern hellas region this agreement points to an atmospheric origin for the ice and reveals how precipitation could have formed glaciers on mars

recent ice rich deposits formed at high latitudes on mars by sublimation of unstable equatorial ice during low obliquity observations from the gamma ray spectrometer instrument suite on the mars odyssey spacecraft have been interpreted as indicating the presence of vast reservoirs of near surface ice in high latitudes of both martian hemispheres1 2 3 4 5 ice concentrations are estimated to range from 70 per cent at 60 latitude to 100 per cent near the poles possibly overlain by a few centimetres of ice free material in most places4 this result is supported by morphological evidence of metres thick layered deposits that are rich in water ice6 7 8 9 and periglacial like features10 11 found only at high latitudes diffusive exchange of water between the pore space of the regolith and the atmosphere has been proposed to explain this distribution12 but such a degree of concentration is difficult to accommodate with such processes9 13 14 alternatively there are suggestions that ice rich deposits form by transport of ice from polar reservoirs and direct redeposition in high latitudes during periods of higher obliquity9 13 but these results have been difficult to reproduce with other models here we propose instead that during periods of low obliquity less than 25 high latitude ice deposits form in both hemispheres by direct deposition of ice as a result of sublimation from an equatorial ice reservoir that formed earlier during a prolonged high obliquity excursion using the ice accumulation rates estimated from global climate model simulations we show that over the past ten million years large variations of mars obliquity have allowed the formation of such metres thick sedimentary layered deposits in high latitude and polar regions

kilometer scale roughness of mars results from mola data analysis the mars orbiter laser altimeter mola data are used to characterize the kilometer scale surface roughness of mars the median absolute value of the differential slope at a given baseline is proposed as a data derived measure of the surface roughness at this scale study of the scale dependence of roughness for the smoothest terrains gives an independent estimate of 20 cm for mola ranging accuracy the baseline lengths from 0 6 to 20 km are used and kilometer scale roughness is mapped for the entire surface the maps show that different geological units have distinctive roughness characteristics scale dependence of roughness for a number of geological units is presented and discussed the southern polar cap is rougher than the northern at kilometer and subkilometer scale which suggests differences in the sublimation condensation balance the vastitas borealis formation has a distinctive 3 km scale background surface topography which suggests a nonvolcanic origin for its upper layer young volcanic plains in amazonis planitia and the eastern part of elysium planitia are very similar to each other in their roughness characteristics and differ from other volcanic plains on mars which suggests a distinctive eruption style there are systematic latitudinal variations of roughness in both the southern highlands and the northern lowlands terrains at high latitude are smoother at short baselines the characteristic vertical scale related to this difference is several meters processes that could be responsible for formation of this trend include creep of ice rich near surface material at high latitudes treatment of the surface with repetitive deposition and sublimation of seasonal frost climate controlled deposition and or cementation of dust at high latitudes and repetitive sublimation and accumulation of subsurface ice at low latitudes with climate variations all mechanisms of origin could operate more effectively under different climate conditions relevant morphological observations favor mechanisms involving deposition of smooth blankets at high latitudes

summer evolution of the north polar cap of mars as observed by omega mars express the observatoire pour la mineralogie l eau les glaces et l activite omega visible infrared imaging spectrometer extensively observed regions of mars with latitudes above 70 n in late 2004 heliocentric longitude from ls 93 to ls 127 the extent of water ice at the surface and the size of ice grains were monitored as a function of time bright small grained frost which initially covered a large fraction of the polar cap waned in favor of large grained ice in outlying regions dominated by large grained ice the albedo increased over the period evaluating the dust content was model dependent however contamination of ice by dust was low

seismically observed seiching in the panama canal 1 a large portion of the seismic noise spectrum is dominated by water wave energy coupled into the solid earth distinct mechanisms of water wave induced ground motions are distinguished by their spectral content for example cultural noise is generally 1 s period microseisms dominate the seismic spectrum from periods of 2 to 20 s and the earth s hum is in the range of 50 to 600 s we show that in a large lake in the panama canal there is an additional source of long period noise generated by standing water waves seiches induced by disturbances such as passing ships and wind pressure we compare seismic waveforms to water level records and relate these observations to changes in local tilt and gravity due to an oscillating seiche the methods and observations discussed in this paper provide a first step toward quantifying the impact of water inundation as recorded by seismometers this type of quantified understanding of water inundation will help in future estimates of similar phenomena such as the seismic observations of tsunami impact

backset lamination produced by supercritical backwash flows at the beachface shoreface transition of a storm dominated gravelly beach middle pleistocene central italy abstract bedforms and resulting sedimentary structures of interpreted upper flow regime origin are fairly common in various ancient and modern depositional settings yet outcrop examples of shallow water strata dominated by sedimentary structures arising from such flow conditions are rarely documented this outcrop based study presents the first detailed analysis of mid pleistocene beachface shoreface strata containing sedimentary structures interpreted to have been formed by storm generated backwash flows during the transition in flow regime from supercritical to subcritical here we propose that moving down the steep beachface backwash flows rapidly accelerated and became thinner experienced abrupt deceleration and flow thickening passing through an erosional hydraulic jump in the trough at the toe of the beachface and then waned to thicker and subcritical conditions just downflow of the hydraulic jump in this frame landward dipping backset laminae deposited on the downflow side of the trough evolved into thinner upper stage plane parallel laminae further downstream the transition from the proximal to the distal upper shoreface records a significant increase of preserved wave ripples and burrowed intervals in concert with a progressive decrease in thickness and grain size of individual sets of plane parallel laminae and increase of gravel filled gutter casts

new and recent gully activity on mars as seen by hirise 1 fresh appearing gully deposits are found at tens of sites in the southern hemisphere of mars these deposits have latitudinal and azimuthal dependences similar to the overall preferences of southern hemisphere gullies suggesting that most gullies can undergo such events definite changes are seen at ten sites including two previously reported these include visible modification of gully channels and aprons those formation intervals constrained to better than one mars year tend to include winter and exclude summer suggesting seasonal activity this seasonal activity is consistent with proposed models for gully formation driven by co2 frost although at least some of the new deposits are probably due to dry granular flow with no volatile involvement as these deposits are capable of effecting distinct topographic changes to gully aprons and channels they represent a significant component of recent gully evolution

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

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