visible albedo of mars south polar cap 2003 hst observations abstract the martian south polar cap was observed with the high resolution camera on hubble space telescope near the very favorable 2003 opposition well calibrated images taken at a number of wavelengths in visible and uv were used to measure the apparent lambert albedos of two bright polar areas these were corrected for the effects of atmospheric dust to obtain wavelength dependent surface albedos which are diagnostic for the purity and grain size of the co 2 deposits the bolometric albedo estimated from these data may be sufficiently large to be consistent with stability of the perennial co 2 in the residual cap

material ejection by the cold jets and temperature evolution of the south seasonal polar cap of mars from themis crism observations and implications for surface properties as the seasonal co 2 ice polar caps of mars retreat during spring dark spots appear on the ice in some specific regions these features are thought to result from basal sublimation of the transparent co 2 ice followed by ejection of regolith type material which then covers the ice we have used compact reconnaissance imaging spectrometer for mars crism reflectance data thermal emission imaging system themis visible images and themis derived temperature retrievals along with a thermal numerical model to constrain the physical and compositional characteristics of the seasonal cap for several areas exhibiting dark spots at both high spatial and temporal resolutions data analysis suggests an active period of material ejection before solar longitude ls 200 accumulation around the ejection points and spreading of part of the ejected material over the whole area followed by a period where no significant amount of material is ejected followed by complete defrosting ls 245 dark material thickness on top of the co 2 ice is estimated to range from a few hundreds of microns to a few millimeters in the warmest spots based on numerical modeling combined with the observed temperature evolution the nature of the venting process and the amount of material that is moved lead to the conclusion that it could have an important impact on the surface physical properties

theoretical regime equations for mobile gravel bed rivers with stable banks a system of rational regime equations is developed for gravel bed rivers with stable banks using the optimality theory ot the optimality theory is based on the premise that equilibrium river geometry is characterised by an optimum configuration defined here as maximum sediment transport efficiency theoretical dimensionless equations are derived for width depth slope width depth ratio and meandering braiding transition independent dimensionless variables comprise discharge sediment concentration and relative bank strength which is defined as the ratio of the critical shear stresses for the bank and bed sediments discharge exponents and general form of the equations agree well with previously developed empirical relations relative bank strength is used to parameterise the influence of riparian vegetation on bank strength and is evaluated by calibrating against observed width depth ratio once calibrated the hydraulic geometry of natural gravel rivers is well described by the theoretical equations including discrimination between meandering and braiding channels the results provide strong support for the assumption that equilibrium or regime river behavior is equivalent to an optimal state and underline the importance of bank strength and sediment load as controls on hydraulic geometry

models of climate cycles recorded in martian polar layered deposits abstract layered strata observed in orbital images of polar sedimentary terrains on mars have been hypothesized to contain information about recent variations in the martian climate celestial mechanicians have determined that mars has experienced large amplitude quasi periodic variations in obliquity and eccentricity planetary meteorologists have inferred that the resulting changing patterns of solar heating must have had dramatic effects on martian climate accordingly it might be possible to link the known recent history of orbit axial variations with the physical characteristics of the most recently deposited strate determined from orbital imagery our paper explores that possibility quantitatively for various models of the formation of the polar layered deposits and the layering developed within them we modeled the formation of polar layered deposits during the past 10 my for two general classes of model uniform deposition rate udr models assume that the major constituent of the layered deposits is deposited at a uniform rate and that layering is established by climate induced variations in the concentration of a minor constituent climate modulated deposition rate cmdr models assume that the deposition rate of the major constituent is controlled by climate and that layer boundaries correspond to intervals of nondeposition in both models abrupt changes in deposition regime occur when a function of the orbit axial parameters crosses a threshold value detailed physical mechanisms for the control of sedimentation by orbit axial variations were developed for two specific models of the cmdr type in one model the deposits are assumed to be primarily composed of dust in the other they are assumed to be predominantly water ice we calculated the times at which abrupt changes in deposition regime occur and determined the relative thicknesses of successive layers which can be compared against layer thicknesses made from orbital imagery in all these models obliquity variations exert the dominant influence on the sequential variations in layer thickness although eccentricity and precession index longitude of perihelion may take recognizable contributions as well the layer patterns for the north and south polar deposits are identical for the dust model and only slightly different for the ice model but this is at least partly a consequence of simplifying assumptions the sequential variation in layer thickness is also very sensitive to those model parameters which control the fraction of time for which deposition occurs when the climate threshold for deposition is low deposition occurs a large fraction of the total time and characteristic patterns form with one thick layer and a number of much thinner ones such patterns would be easily recognized in photogeological measurements of layer thickness when the threshold for deposition lies in the mid range with respect to excursions of the climate function deposition occurs approximately half of the time and there is only slight modulation of layer thickness when the threshold for deposition is high deposition occurs only a small fraction of the total time and groups of layers form which are separated form other groups by long periods of nondeposition the stratigraphic unconformities that separate groupings of five to ten layers in the polar deposits may indicate that the martian polar region has experienced such a depositional history the feasibility of using these model results to verify the theory of climate control of polar stratigraphy on mars and to gain additional insights into the significant processes is considered the stratigraphy issues raised here are also explored in the context of recent work on the interpretation of stratigraphy of ocean margins from this comparison there emerge some valuable insights into the stratigraphic effects of periods of nondeposition and the uncertaintiesin interpreting images of exposed polar strata on mars

stability of composite river banks the stability of a river bank depends on the balance of forces motive and resistive associated with the most critical mechanism of failure many mechanisms are possible and the likelihood of failure occurring by any particular one depends on the size geometry and structure of the bank the engineering properties of the bank material the hydraulics of flow in the adjacent channel and climatic conditions rivers flowing through alluvial deposits often have a composite structure of cohesionless sand and gravel overlain by cohesive silt clay bank erosion occurs by fluvial entrainment of material from the lower cohesionless bank at a much higher rate than material from the upper cohesive bank this leads to undermining that produces cantilevers of cohesive material upper bank retreat takes place predominantly by the failure of these cantilevers three mechanisms of failure have been identified shear beam and tensile failure the stability of a cantilever may be analysed using static equilibrium and beam theory and dimensionless charts for cantilever stability constructed application of the charts requires only a few simple measurements of cantilever geometry and soil properties in this analysis the effects of cracks and fissures in the soil must be taken into account these cracks seriously weaken the soil and can invalidate a stability analysis by affecting the shape of the failure surface following mechanical failure blocks of soil must be removed from the basal area by fluvial entrainment if rapid undermining and cantilever generation are to continue hence the rate of bank retreat is fluvially controlled even though the mechanism of failure of the upper bank is not directly fluvial in nature this cycle of bank erosion undermining cantilever failure and fluvial scour of the toe operates over several flood events and has important implications for river engineering channel changes and the movement of sediment through fluvial systems

absorption and scattering properties of the martian dust in the solar wavelengths a new wavelength dependent model of the single scattering properties of the martian dust is presented the model encompasses the solar wavelengths 0 3 to 4 3 m at 0 02 m resolution and does not assume a particular mineralogical composition of the particles we use the particle size distribution shape and single scattering properties at viking lander wavelengths presented by pollack et al 1995 we expand the wavelength range of the aerosol model by assuming that the atmospheric dust complex index of refraction is the same as that of dust particles in the bright surface geologic units the new wavelength dependent model is compared to observations taken by the viking orbiter infrared thermal mapper solar channel instrument during two dust storms the model accurately matches afternoon observations and some morning observations some of the early morning observations are much brighter than the model results the increased reflectance can be ascribed to the formation of a water ice shell around the dust particles thus creating the water ice clouds which colburn et al 1989 among others have predicted

results from the mars global surveyor thermal emission spectrometer the thermal emission spectrometer spectra of low albedo surface materials suggests that a four to one mixture of pyroxene to plagioclase together with about a 35 percent dust component provides the best fit to the spectrum qualitative upper limits can be placed on the concentration of carbonates 10 percent olivine 10 percent clay minerals 20 percent and quartz 5 percent in the limited regions observed limb observations in the northern hemisphere reveal low lying dust hazes and detached water ice clouds at altitudes up to 55 kilometers at an aerocentric longitude of 224 degrees a major dust storm developed in the noachis terra region the south polar cap retreat was similar to that observed by viking

early views of the martian surface from the mars orbiter camera of mars global surveyor high resolution images of the martian surface at scales of a few meters show ubiquitous erosional and depositional eolian landforms dunes sandsheets and drifts are prevalent and exhibit a range of morphology composition inferred from albedo and age as seen in occurrences of different dune orientations at the same location steep walls of topographic depressions such as canyons valleys and impact craters show the martian crust to be stratified at scales of a few tens of meters the south polar layered terrain and superposed permanent ice cap display diverse surface textures that may reflect the complex interplay of volatile and non volatile components low resolution regional views of the planet provide synoptic observations of polar cap retreat condensate clouds and the lifecycle of local and regional dust storms

interannual observations and quantification of summertime h2o ice deposition on the martian co2 ice south polar cap abstract the spectral signature of water ice was observed on martian south polar cap in 2004 by the observatoire pour l mineralogie l eau les glaces et l activite omega bibring et al 2004 three years later the omega instrument was used to discover water ice deposited during southern summer on the polar cap langevin et al 2007 however temporal and spatial variations of these water ice signatures have remained unexplored and the origins of these water deposits remains an important scientific question to investigate this question we have used observations from the compact reconnaissance imaging spectrometer for mars crism instrument on the mars reconnaissance orbiter mro spacecraft of the southern cap during austral summer over four martian years to search for variations in the amount of water ice we report below that for each year we have observed the cap the magnitude of the h2o ice signature on the southern cap has risen steadily throughout summer particularly on the west end of the cap the spatial extent of deposition is in disagreement with the current best simulations of deposition of water ice on the south polar cap montmessin et al 2007 this increase in water ice signatures is most likely caused by deposition of atmospheric h2o ice and a set of unusual conditions makes the quantification of this transport flux using crism close to ideal we calculate a minimum apparent amount of deposition corresponding to a thin h2o ice layer of 0 2 mm with 70 porosity this amount of h2o ice deposition is 0 6 6 of the total martian atmospheric water budget we compare our minimum apparent quantification with previous estimates this deposition process may also have implications for the formation and stability of the southern co2 ice cap and therefore play a significant role in the climate budget of modern day mars

spatial and temporal distributions of martian north polar cold spots before during and after the global dust storm of 2001 1 in the 1970s mariner and viking observed features in the mars northern polar region that were a few hundred kilometers in diameter with 20 m brightness temperatures as low as 130 k considerably below co2 ice sublimation temperatures over the past decade studies have shown that these areas commonly called cold spots are usually due to emissivity effects of frost deposits and occasionally to active co2 snowstorms three mars years of mars global surveyor thermal emission spectrometer data were used to observe autumn and wintertime cold spot activity within the polar regions many cold spots formed on or near scarps of the perennial cap probably induced by adiabatic cooling due to orographic lifting these topographically associated cold spots were often smaller than those that were not associated with topography we determined that initial grain sizes within the cold spots were on the order of a few millimeters assuming the snow was uncontaminated by dust or water ice on average the half life of the cold spots was 5 julian days the mars global dust storm in 2001 significantly affected cold spot activity in the north polar region though overall perennial cap cold spot activity seemed unaffected the distribution of cold spots did change by a decrease in the number of topographically associated cold spots and an increase in those not associated with topography we propose that the global dust storm affected the processes that form cold spots and discuss how the global dust storm may have affected these processes

moc observations of four mars year variations in the south polar residual cap of mars abstract the residual south polar cap of mars rspc is distinct from the residual north polar cap both in composition and in morphology co 2 frost in the rspc is stabilized by its high albedo during southern spring and summer despite the relatively large insolation during that period the morphology of the rspc in summer displays a bewildering variety of depressions that are formed in relatively thin layers of co 2 the increase of the size of these depressions between each of the first three years of mars global surveyor mgs observations may possibly signal some sort of climate change on the planet for example the erosion of the bright plateaus might reduce the rspc albedo and affect the energy balance the mars orbiter cameras moc on mgs observed mars for four consecutive martian years before contact with the spacecraft was lost in late 2006 during this period coverage of the polar regions was particularly dense because mgs flew over them on every orbit in this paper we report on the four year behavior of the morphological features in the rspc and on the large scale variability in rspc albedo over the period the changes in the size of the surface features in the rspc due to backwasting that were first observed between mars years my 24 and 25 and subsequently between my25 and m26 was observed to continue at the same rate through my 27 the results indicate that on average thicker layers in the rspc retreat faster than thinner ones roughly in proportion to their thickness we argue that a simple difference in porosity between the a and b layers can explain this difference although other factors could be involved the large scale albedo of the rspc decreases as the depressions are uncovered by sublimation of seasonal co 2 however any interannual differences in albedo due to the backwasting process are masked by interannual differences in the summer dust opacity in the rspc region

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

hydraulic geometry of cohesive channels undergoing base level drop abstract this study extends earlier contributions on dynamic adjustments of fluvial channels to base level changes we have investigated an in situ response of self formed cohesive channels to a base level drop conditions analogous to a gradual change in uplift and or climate empirical hydraulic geometry equations for clayey cohesive natural streams are presented using data from eight channels draining perennial brackish springs and discharge into the dead sea investigation of downstream variations in gradient and stream power relations suggests existence of three distinct reaches in which channel adjustment to base level drop is shared inequitably among hydraulic geometry variables values of the flow velocity exponent m are low 0 11 m 0 24 the mid channel reach having the lowest exponent the depth exponent f has the lowest value f 0 3 for the uppermost channel reaches the rest having higher values f 0 4 the smallest width exponent b 0 35 characterizes the upper reaches these values and their spatial distribution exhibit a regular pattern we show that the lowermost channel reach adjusts by profile steepening and channel narrowing f b the prevailing mechanism in the mid channel reaches is lateral width adjustment cross sections transiently transforming toward equilibrium the uppermost reaches have wide and shallow channel cross sections because of series of bank collapses and resultant sediment aggradation bringing rise to decreased local gradient forcing further channel widening the results of this study not only allow inference about how cohesive channels regulate their geometry but also reveal the means by which hydraulic forces overcome substrate resistance adjusting slope and channel dimensions and as such have implication for reach scale channel morphology and models of stream power

predicting downstream hydraulic geometry a test of rational regime theory 1 the classical equations of hydraulic geometry are purely empirical but the widespread similarity of the scaling downstream form of them suggests that they express some important underlying regularities in the morphology of stream channels through the drainage network a successful physical theory of river regime must be able to reproduce and explain this regularity in this paper we test the regime theory of eaton et al 2004 using selected data of hydraulic geometry we first use data from environments in which bank strength presumably does not vary greatly such as in anabranched channel systems and deltas regime models parameterized by assuming uniform relative bank strength plausibly describe the observed bankfull channel geometries in these systems we then test a modified bank strength formulation for vegetated gravel bed rivers against downstream hydraulic geometry data sets in which relative bank strength is supposed to vary with channel scale assuming a uniform effective cohesion due to riparian vegetation the regime model is again able to reproduce details of the channel geometry both analyses show that the classical hydraulic geometry represents only an approximation of the variation of channel form if we have confidence in the theory we may infer information about bank strength and bed material transport the pattern of variation in these quantities as well as discharge through the drainage system lends approximate regularity to stream channel scaling that is summarized in the empirical relations

seasonal h2o and co2 ice cycles at the mars phoenix landing site 1 prelanding crism and hirise observations 1 the condensation evolution and sublimation of seasonal water and carbon dioxide ices were characterized at the mars phoenix landing site from martian northern midsummer to midspring ls 142 ls 60 for the year prior to the phoenix landing on 25 may 2008 ice relative abundances and grain sizes were estimated using data from the compact reconnaissance imaging spectrometer for mars and high resolution imaging science experiment aboard mars reconnaissance orbiter and a nonlinear mixing model water ice first appeared at the phoenix landing site during the afternoon in late summer ls 167 as an optically thin layer on top of soil co2 ice appeared after the fall equinox by late winter ls 344 the site was covered by relatively pure co2 ice 30 cm thick with a small amount of 100 m diameter water ice and soil as spring progressed co2 ice grain sizes gradually decreased a change interpreted to result from granulation during sublimation losses the combined effect of co2 sublimation and decreasing h2o ice grain sizes allowed h2o ice to dominate spectra during the spring and significantly brightened the surface co2 ice disappeared by early spring ls 34 and h2o ice by midspring ls 59 spring defrosting was not uniform and occurred more rapidly over the centers of polygons and geomorphic units with relatively higher thermal inertia values

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

scale free distribution of dead sea sinkholes observations and modeling there are currently more than 5500 sinkholes along the dead sea in israel these were formed due to the dissolution of subsurface salt layers as a result of the replacement of hypersaline groundwater by fresh brackish groundwater this process has been associated with a sharp decline in the dead sea water level currently more than one meter per year resulting in a lower water table that has allowed the intrusion of fresher brackish water we studied the distribution of the sinkhole sizes and found that it is scale free with a power law exponent close to 2 we constructed a stochastic cellular automata model to understand the observed scale free behavior and the growth of the sinkhole area in time the model consists of a lower salt layer and an upper soil layer in which cavities that develop in the lower layer lead to collapses in the upper layer the model reproduces the observed power law distribution without involving the threshold behavior commonly associated with criticality

hirise observations of gas sublimation driven activity in mars southern polar regions iii models of processes involving translucent ice abstract enigmatic surface features known as spiders found at high southern martian latitudes are probably caused by sublimation driven erosion under the seasonal carbon dioxide ice cap the mars reconnaissance orbiter mro high resolution imaging science experiment hirise has imaged this terrain in unprecedented details throughout southern spring it has been postulated kieffer h h titus t n mullins k f christensen p r 2000 j geophys res 105 9653 9700 that translucent co 2 slab ice traps gas sublimating at the ice surface boundary wherever the pressure is released the escaping gas jet entrains loose surface material and carries it to the top of the ice where it is carried downslope and or downwind and deposited in a fan shape here we model two stages of this scenario first the cleaning of co 2 slab ice from dust and then the breaking of the slab ice plate under the pressure built below it by subliming ice our modeling results and analysis of hirise images support the gas jet hypothesis and show that outbursts happen very early in spring

on the mystery of the perennial carbon dioxide cap at the south pole of mars a perennial ice cap has long been observed near the south pole of mars the surface of this cap is predominantly composed of carbon dioxide ice the retention of a co 2 ice cap results from the surface energy balance of the latent heat solar radiation surface emission subsurface conduction and atmospheric sensible heat while models conventionally treat surface co 2 ice using constant ice albedos and emissivities such an approach fails to predict the existence of a perennial cap here we explore the role of the insolation dependent ice albedo which agrees well with viking mars global surveyor and mars express albedo observations using a simple parameterization within a general circulation model in which the albedo of co 2 ice responds linearly to the incident solar insolation we are able to predict the existence of a perennial co 2 cap at the observed latitude and only in the southern hemisphere further experiments with different total co 2 inventories planetary obliquities and surface boundary conditions suggest that the location of the residual cap may exchange hemispheres favoring the pole with the highest peak insolation

influence of alluvial cover and lithology on the adjustment characteristics of semi alluvial bedrock channels abstract a growing body of research has focused on evaluating the adjustment characteristics of semi alluvial channels containing proximate bedrock mixed and alluvial sections active orogens have been the focus of most empirical field based studies with comparatively less focus on semi alluvial bedrock channels located in other regions in this study we present an inventory of channel geometry data collected from semi alluvial bedrock channels in ontario and quebec canada which are not subject to tectonic uplift data were sourced from a variety of physiographic settings permitting evaluation of the influence of alluvial cover lithology and gradient on cross sectional channel form our results show no substantial difference in channel width or scaling behaviour amongst bedrock mixed and alluvial channels included in our study except for sedimentary bedrock channels virtually bare of alluvial cover that represent a uniquely wide distinct subgroup channel gradient does not appear to exhibit any observable control on channel width amongst our study rivers suggesting that sedimentary bedrock channels form a distinct subgroup because of lithology comparatively the widths of our bedrock channels formed in igneous metamorphic bedrock are comparable to the widths of mixed channels and alluvial channels for a given discharge and drainage area our findings also suggest that cross sectional adjustment of sedimentary bedrock channels is achieved through lateral erosion of the channel banks and downward erosion of the channel bed whereas cross sectional adjustment of igneous metamorphic bedrock is primarily achieved through downward erosion of the bed with limited lateral erosion of the banks

erosivity of natural intact structured clay evaluation previous studies on erodibility of cohesive soil are briefly reviewed and it is concluded that experimental observations have been mainly concerned with remolded and reconsolidated or weathered cla

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

color and albedo of the south polar layered deposits on mars five color albedo units including polar frost have been recognized and mapped in the southern layered deposits on mars atmospheric dust scattering was measured in shadows and modeled in order to remove the component of brightness in mars images due to the atmosphere and quantify the albedo and color of the surface the layered deposits appear to be mantled by red dust except where eolian stripping has exposed the underlying bedrock frost and bare ground are mixed below the resolution of the images in many areas adjacent to the polar cap some of which appear to be younger than the surrounding layered terrain dark material has been deposited in topographic depressions in much of the south polar region including the layered deposits the available observational data suggest that the layered deposits are composed of bright dust ice and a small amount of dark material if the dark material is sand a periodic change in polar winds seems required in order to transport the sand poleward into the layered terrain in any case the observations are not consistent with the layered deposits being composed only of bright dust and ice the mars observer camera and infrared instruments should be particularly useful in this investigation

limits of downstream hydraulic geometry adjustments to flow width depth and velocity in response to changes in discharge are commonly characterized by using downstream hydraulic geometry relationships the spatial limits of these relationships within a drainage basin have not been systematically quantified where the erosional resistance of the channel substrate is sufficiently large hydraulic driving forces presumably will be unable to adjust channel form data sets from 10 mountain rivers in the united states panama nepal and new zealand are used in this study to explore the limits of downstream hydraulic geometry relationships where the ratio of stream power to sediment size d 84 exceeds 10 000 kg s3 downstream hydraulic geometry is well developed where the ratio falls below 10 000 kg s3 downstream hydraulic geometry relationships are poorly developed these limitations on downstream hydraulic geometry have important implications for channel engineering and simulations of landscape change

discovery of a widespread low latitude diurnal co2 frost cycle on mars while the detection of co2 ice has only been reported outside the martian polar regions at very high elevation i e elysium olympus mons and the tharsis montes nighttime surface observations by the mars climate sounder on board the mars reconnaissance orbiter document the widespread occurrence of atmospherically corrected ground temperatures consistent with the presence of extensive carbon dioxide frost deposits in the dusty low thermal inertia units at middle low latitudes thermal infrared emissivities interpreted in conjunction with mass balance modeling suggest micrometer size co2 ice crystals forming optically thin layers never exceeding a few hundreds of microns in thickness i e 10 2 kg m 2 locally which is insufficient to generate a measurable diurnal pressure cycle 0 1 of the martian atmosphere atmospheric temperatures at middle low latitudes are not consistent with precipitation of co2 ice suggesting that condensation occurs on the surface the recurring growth and sublimation of co2 ice on martian dusty terrains may be an important process preventing soil induration and promoting dynamic phenomena soil avalanching and fluidization and regolith gardening maintaining a reservoir of micrometer size dust particles that are mobile and available for lifting the discovery of this diurnal co2 cycle represents an important step forward in our understanding of the way the martian atmosphere interacts with the surface

quasi periodic dust events in the summertime south polar region of mars abstract a hovmoller diagram analysis of the dust optical depth measured by the mars global surveyor thermal emission spectrometer shows the occurrence of quasi periodic westwardly propagating disturbances with timescales of 10 20 sols during summer in the south polar region of mars dust clouds emerge repeatedly around the region with a latitude of around 70 80 s and a longitude of 240 300 e move westward at speeds of 3 6 m s 1 reach the region with a longitude of 60 120 e and finally disappear this longitude range coincides with elevated terrains in the south polar region and in this region an increase of dust optical depth encircling the south pole is also observed this implies that the quasi periodic dust events will contribute to the enhancement of the atmospheric dust loading in this region these dust events might be related to baroclinic instability caused by the thermal contrast across the co2 cap edge or the horizontal advection or vertical convection with radiative dynamical feedback the westward movement of the dust clouds suggests steady westward winds blowing in the near surface layer where the quasi periodic dust lifting is expected to occur such a westward cap edge flow will be created by the coriolis force acting on the flow from the ice side to the regolith side

debris accumulations of co2 ice in the south polar residual cap of mars longevity and processes abstract the residual south polar cap rspc of mars is a thin covering of co2 ice resting on water ice rich deposits as such it is a likely indicator of the net effects of recent polar climate this covering has had minor changes in outline for the period of spacecraft observation piqueux and christensen 2008a and estimates of its recent mass balance suggest fractionally small changes in its volume thomas et al 2016 pit growth by scarp retreat malin et al 2001 byrne and ingersoll 2003a thomas et al 2005 2013 is a major relatively easily measured component of the cap s mass balance this scarp retreat is only the beginning of a process fracturing slumping and sublimation byrne et al 2008 thomas et al 2009 lead to production of a trail of debris this study focuses on that debris using spacecraft imaging data the rough relatively dark debris forms ubiquitous ramps typically tens of m wide around scarps within pits or on perimeters of mesas much wider accumulations of debris debris fields mimic distinctive scalloped outlines of mesas and are observed to originate by merging of expanding pits within a mesa the subsequent evolution of debris fields includes repeated year to year local relief inversions that involve trapping and retention of seasonal ice in low areas that effectively reduce the vertical loss rates complete loss of the co2 debris from a surface of water ice rich polar layered deposits pld can initiate new net accumulation of co2 ice the longevity of some debris fields essentially instances of slow downwasting appear to facilitate relief inversion on large scales by allowing the surrounding areas to accumulate new co2 ice and to thicken relative to the debris fields

no signature of clear co2 ice from the cryptic regions in mars south seasonal polar cap the seasonal polar ice caps of mars are composed mainly of co2 ice a region of low 30 albedo has been observed within the south seasonal cap during early to mid spring the low temperature of this cryptic region has been attributed to a clear slab of nearly pure co2 ice with the low albedo resulting from absorption by the underlying surface here we report near infrared imaging spectroscopy of the south seasonal cap the deep and broad co2 absorption bands that are expected in the near infrared with a thick transparent slab of co2 ice are not observed models of the observed spectra indicate that the low albedo results from extensive dust contamination close to the surface of a co2 ice layer which could be linked to atmospheric circulation patterns the strength of the co2 absorption increases after mid spring so part of the dust is either carried away or buried more deeply in the ice layer during the co2 ice sublimation process

concentrated perchlorate at the mars phoenix landing site evidence for thin film liquid water on mars 1 nasa s phoenix mission which landed on the northern plains of mars in 2008 returned evidence of the perchlorate anion distributed evenly throughout the soil column at the landing site here we use spectral data from phoenix s surface stereo imager to map the distribution of perchlorate salts at the phoenix landing site and find that perchlorate salt has been locally concentrated into subsurface patches similar to salt patches that result from aqueous dissolution and redistribution on earth we propose that thin films of liquid water are responsible for translocating perchlorate from the surface to the subsurface and for concentrating it in patches the thin films are interpreted to result from melting of minor ice covers related to seasonal and long term obliquity cycles

thermal and albedo mapping of the polar regions of mars using viking thermal mapper observations 1 north polar region we present the first maps of the apparent thermal inertia and albedo of the south polar region of mars the observations used to create these maps were acquired by the infrared thermal mapper irtm instruments on the two viking orbiters over a 30 day period in 1977 during the martian late southern summer season the maps cover the region from 60 s to the south pole at a spatial resolution of 1 of latitude thus completing the initial thermal mapping of the entire planet the analysis and interpretation of these maps is aided by the results of a one dimensional radiative convective model which is used to calculate diurnal variations in surface and atmospheric temperatures and brightness temperatures at the top of the atmosphere for a range of assumptions concerning dust optical properties and dust optical depths the maps show that apparent thermal inertias of bare ground regions decrease systematically from 60 s to the south pole in unfrosted regions close to the south pole apparent thermal inertias are among the lowest observed anywhere on the planet on the south residual cap apparent thermal inertias are very high due to the presence of co2 frost in most other regions of mars best fit apparent albedos based on thermal emission measurements are generally in good agreement with actual surface albedos based on broadband solar reflectance measurements however in the frost free region poleward of 75 s best fit apparent albedos are significantly higher than measured lambert albedos implying that measured brightness temperatures in this area are up to 15 k colder than would be expected for surfaces with the same measured albedos during this season the one dimensional atmospheric model calculations also predict anomalously cold brightness temperatures close to the pole during late summer and after considering a number of alternatives it is concluded that the net surface cooling due to atmospheric dust is the best explanation for this phenomenon the observed systematic decrease in apparent thermal inertia from 60 s to the south pole during this season is also consistent with the predictions of atmospheric model calculations the region of lowest apparent thermal inertia close to the pole which includes the south polar layered deposits is interpreted to be mantled by a continuous layer of aeolian material that must be at least a few millimeters thick the low thermal inertias mapped in the south polar region imply an absence of surface water ice deposits which is consistent with viking mars atmospheric water detector mawd measurements which show low atmospheric water vapor abundances throughout the summer season however these observations do not necessarily imply a complete absence of water thermal model calculations that can reproduce observed diurnal temperature variations in the south polar region show that annual maximum subsurface temperatures at depths ranging from 4 to 20 cm are cold enough to permit the stability of ground ice deposits even if they are in excellent diffusive contact with the atmosphere therefore the presence of near surface ground ice in the south polar region is not inconsistent with the viking irtm and mawd observations

defrosting dark flow features and dune activity on mars example in russell crater 1 defrosting processes observed on mars are among the most unusual features described on high resolution images a defrosting sequence has been observed near the crest of the megadune located in the russell crater on new high resolution images obtained from the hirise instrument and on hyperspectral cubes obtained from crism instrument both on board mro hyperspectral images show that frost overlaps the entire megadune in middle winter this frost is composed mainly of co2 and of a small amount of water ice the deepest ice signatures are mainly located near the crest of the megadune the defrosting sequence monitored by crism reveals spatial heterogeneity and refrosting processes on the morphological counterpart the defrosting sequence starts with the development of dark spots similar to those described in the cryptic regions after few sols we observe the emplacement of dark linear flow features that start from the dark spots downward of the main slope of the dune these linear flow features are 1 to 2 m wide and 50 to 100 m long they settle on the small rills visible on the frost cover they are interpreted as avalanches of a mixing of sand dust and unstable co2 gas released under pressure the avalanches would be triggered by the eruption of the dark spots the flux of material transported by the flow features has been estimated to 0 25 to 0 5 m3 by meter width each year on the megadune this flux is larger than flux transported by wind these dark flow features are thus very efficient to transport material on slopes located in frosted areas

deflation erosion rates for the parva member dorsa argentea formation and implications for the south polar region of mars 1 the origins of the surficial materials in the geologic units surrounding the martian southern polar region have been poorly constrained on the basis of pre mars global surveyor mgs data and studies mgs studies suggest that these units are the remnant of volatile loss from an originally massive volatile rich debris blanket or the result of fluidized slurries resulting from magma volatile interactions or impact shaking we use mars orbiter laser altimeter data to examine a region adjacent to the south polar layered terrain at 72 79 s and 230 275 e generally equivalent to the mapped parva member of the dorsa argentea formation daf the pedestal and ghost impact crater morphologies in this area suggest that extensive deposits of loosely consolidated materials have been removed from this region the parva member is thus likely to be the remaining debris blanket from the deflated remnant of an unprotected deposit that was originally similar to the buried daf deposits in the adjacent cavi member crater counts indicate that the parva member is of hesperian age and overlies an older noachian surface likely the highland cratered terrain npl1 if regional deflation began in the hesperian and continues through today the region has been exposed to erosion rates of 1 3 1 6 10 7 m yr however if deflation started later than the assumed times or ceased in the amazonian when deposition of the polar layered deposits began erosion rates as high as 2 5 2 10 7 m yr might have existed these erosion rates are within the range of published martian nonbedrock erosion rates of 10 8 10 5 m yr

the influence of bank strength on channel geometry an integrated analysis of some observations bank strength exerts a significant influence on river channel geometry but quantification of this relationship has been limited to only a few specific circumstances this is due to both the complex nature of bank strength and the difficulty in incorporating its influence in river channel geometry relations in order to undertake an integrated analysis of wide ranging field observations this study applies a recently developed multivariate model of channel geometry when the banks of a number of laterally stable streams are categorized on the basis of the bank sediment and vegetation the multivariate model yields numerical indices of bank strength within the range of the data analysed bank strength can produce a three fold change in channel width and a two fold change in depth corresponding to about a 1 6 fold change in cross sectional area 1998 john wiley sons ltd

phase equilibrium in the system co2 h2o application to mars 1 thermodynamic analysis of the system co2 h2o shows that although co2 clathrate and liquid co2 are stable over most of the pressure and temperature range expected for the martian regolith hydraulic equilibrium of the regolith pore gas with the overlying atmosphere a condition most likely in equatorial regions will destabilize both phases condensation on mars comes in four predictable assemblages pure h2o ice co2 clathrate hydrate a eutectic mixture of solid co2 and either clathrate or h2o ice if the clathrate fails to nucleate and under limited conditions pure solid co2 seasonal frosts are likely to consist of thin layers of water ice and or clathrate overlain by the eutectic assemblage growing ice caps are also likely to be layered with sets of ice lower and eutectic upper layers interspersed with pure solid co2 layers the saturated water content of a 1 bar co2 atmosphere with surface temperatures 273 k would have reached 20 precipitable millimeters basal melting triggered by trapped heat flow from the interior limits the thickness and composition of the polar ice caps and is to be expected during periods of low obliquity when there is extensive cooling and condensation at the poles introduction of liquid co2 into the martian regolith by basal melting at the poles may be a major mechanism for loss of the ancient greenhouse atmosphere and its long term sequestration explosive release of co2 fluid coexisting with groundwater may trigger outflow channel floods and reset atmospheric isotope ratios

stable channels with mobile gravel beds regime type equations for mobile gravel bed rivers are presented based on data obtained from 62 stable gravel bed river reaches in the united kingdom multiple regression techniques are applied to derive equations relating reach average and riffle values of width mean and maximum depth slope velocity sinuosity and riffle spacing to bankfull discharge bed and bank material characteristics valley slope bank vegetation type and an independent estimate of bankfull bed load transport rates although discharge has a dominant control on channel geometry these equations indicate that bed load discharge also has a significant influence particularly with regard to channel slope bank vegetation has a major control on width and velocity while depth velocity and slope are storngly affected by bed material size reasons for these results are considered in terms of the physical processes controlling channel adjustment the application of these regime equations is discussed and particular consideration is given to the design of sinuous channels with a pool riffle bed topograph

spatial variability in the seasonal south polar cap of mars we present the first comprehensive discussion of the south seasonal polar cap spectra obtained by the mariner 7 infrared spectrometer in the short wavelength region 2 4 m in addition we correlate the infrared spectra with images acquired by the wide angle camera significant spectral variation is noted in the cap interior and regions of varying water frost abundance co2 ice frost cover and co2 ice path length can be distinguished many of these spectral variations correlate with heterogeneity noted in the camera images but certain significant infrared spectral variations are not discernible in the visible we use simple reflectance models to classify the observed spectral variations into four regions region i is at the cap edge where there is enhanced absorption beyond 3 m inferred to be caused by an increased abundance of water frost the increase in water abundance over that in the interior is on the level of a few parts per thousand or less region ii is the typical cap interior characterized by spectral features of co2 ice at grain sizes of several millimeters to centimeters these spectra also indicate the presence of water frost at the parts per thousand level a third unusual region iii is defined by three spectra in which weak co2 absorption features are as much as twice as strong as in the average cap spectra and are assumed to be caused by an increased path length in the co2 such large paths are inconsistent with the high reflectance in the visible and at 2 2 m and suggest layered structures or deposition conditions that are not accounted for in current reflectance models the final region iv is an area of thinning frost coverage or transparent ice well in the interior of the seasonal cap these spectra are a combination of co2 and ground signatures

seasonal recession of martian south polar cap 1992 hst observations the seasonal recession of the south polar cap of mars has been studied using the wide field planetary camera images from hubble space telescope obtained during the summer of 1992 when the angular size of mars was between 5 and 6 arc sec the observations cover the interesting period betweenls 259 and 284 when the recession is rapid and the asymmetry in the cap is large these will be the only hst observations of this season during the 1990s because of the solar elongation constraint on telescope pointing the well known mountains of mitchel outlier which has been observed by viking and by many ground based observers nearls 260 is clearly present in the first set of hubble images the latitude of the cap edge the displacement of the center of the cap from the geographical pole and the albedo of the polar deposits determined from these images are consistent with observations of these quantities by viking in 1977 the data are not compatible with a recession as advanced as that deduced from the 1956 telescopic observations

stability analysis of semicohesive streambanks with concepts coupling field and laboratory investigations to quantify the onset of fluvial erosion and mass failure abstractthe overarching goal of this study is to perform a comprehensive bank stability analysis that is phenomenologically sound by considering both mass failure and fluvial erosion the nature of this study is twofold first field and experimental analyses are conducted to generate data for channel cross section properties soil index properties and mechanical and erosional strengths at two sites in a representative midsize midwestern stream in southeastern iowa that is subjected to frequent flash floods and characterized by active fluvial erosion and cantilever failure second the channel surveys and data obtained from the field and laboratory analyses are used as input parameters for an established one dimensional channel evolution model namely the conservational channel evolution and pollutant transport system concepts version 2 0 langendoen and alonso 2008 to estimate the factor of safety for mass failure fsm and fluvial erosion fsf and simulate the bank retreat as a result of eithe

mariner 9 observations of the south polar cap of mars evidence for residual co2 frost the first spacecraft observations of the south residual polar cap of mars were obtained by the mariner 9 orbiter during the martian southern summer season 1971 1972 analyses of viking orbiter observations obtained 3 mars years later have shown that residual carbon dioxide frost was present at the south polar cap in 1977 in this study mariner 9 infrared interferometer spectrometer spectra and television camera images are used in conjunction with multispectral thermal emission models to constrain the temperatures of dark bare ground and bright frost regions within the south residual cap the results provide strong evidence that carbon dioxide frost was present throughout the summer season despite the fact that the residual frost deposits observed by mariner 9 were less extensive than those observed by viking

hirise observations of gas sublimation driven activity in mars southern polar regions ii surficial deposits and their origins abstract the high resolution imaging science experiment hirise onboard mars reconnaissance orbiter mro has been used to monitor the seasonal evolution of several regions at high southern latitudes and in particular the jet like activity which may result from the process described by kieffer jgr 112 e08005 doi 10 1029 2006je002816 2007 involving translucent co 2 ice in this work we mostly concentrate on observations of the inca city 81 s 296 e and manhattan 86 s 99 e regions in the southern spring of 2007 two companion papers hansen et al this issue and portyankina et al this issue discuss the surface features in these regions and specific models of the behaviour of co 2 slab ice respectively the observations indicate rapid on set of activity in late winter initiating before hirise can obtain adequately illuminated images ls 2 titus et al 2007 agu abstract p41a 0188 these deposits originate from araneiform structures spiders boulders on ridges cracks on slopes and along linear cracks in the slab ice on flatter surfaces the type of activity observed can often be explained qualitatively by considering the local topography some dark fans are observed to shorten enormously in length on a timescale of 18 days we consider this to be strong evidence that outgassing was in progress at the time of hirise image acquisition and estimate a total particulate emission rate of 30 g s 1 from a single typical jet feature brighter deposits at inca city become increasingly hard to detect after ls 210 in the inca city region the orientations of surficial deposits are topographically controlled the deposition of dark material also appears to be influenced by local topography suggesting that the ejection from the vents is at low velocity 1 and that a ground hugging flow process a sort of cryo fumarole may be occurring the failure up to this point to obtain a clear detection of outgassing though stereo imaging is consistent with low level transport the downslope orientation of the deposits may result from the geometry of the vent or from catabatic winds at many sites more than one ejection event appears to have occurred suggesting re charging of the sources around ls 230 the brightness of the surface begins to drop rapidly on north facing slopes and the contrast between the dark deposits and the surrounding surface reduces this indicates that the co 2 ice slab is being lost completely in some areas at around this time by ls 280 at inca city the ice slab has effectively gone crism band ratios and themis brightness temperature measurements are consistent with this interpretation

evolution of mars northern polar seasonal co2 deposits variations in surface brightness and bulk density small scale variations of seasonal ice are explored at different geomorphic units on the northern polar seasonal cap npsc we use seasonal rock shadow measurements combined with visible and thermal observations to calculate density over time the coupling of volume density and albedo allows us to determine the microphysical state of the seasonal co2 ice we find two distinct end members across the npsc 1 snow deposits may anneal to form an overlying slab layer that fractures these low density deposits maintain relatively constant densities over springtime 2 porous slab deposits likely anneal rapidly in early spring and fracture in late spring these high density deposits dramatically increase in density over time the end members appear to be correlated with latitude

mars global surveyor bistatic radar probing of the mpl ds2 target area abstract mars global surveyor bistatic radar was used to probe the mars polar lander and deep space 2 target areas 76 s 195 w in may 2000 the behavior of quasi specular echoes at wavelength 3 6 cm indicates that the top few centimeters of regolith are similar in their reflecting properties everywhere along a track of approximately 1000 km which crosses the mpl ds2 area our provisional estimate of surface dielectric constant e 2 25 is consistent with loose soil moderately packed h 2 o snow solid co 2 or a mixture of at least two but other data rule out both h 2 o and co 2 near the surface in late southern summer l s 351 leaving dry soil with density 1 4 g cm 3 as the most likely material

mosaicking of global planetary image datasets 1 techniques and data processing for thermal emission imaging system themis multi spectral data 1 the mosaicking of global planetary data sets allows for the examination of local regional and global scale processes on all planetary bodies processing techniques that allow us and other users to crate mosaics of tens of thousands of images are documented along with the associated errors introduced by each image processing algorithm these techniques e g non uniformity correction running contrast stretches line and row correlated noise removal and random noise removal were originally developed for the 2001 mars odyssey thermal emission imaging system themis infrared multispectral imager data but can be adapted and applied to other data sets by the alteration of input parameters the techniques for mosaicking planetary image data sets e g image registration blending and normalization are also presented along with the generation of qualitative and quantitative products these techniques are then applied to generate themis daytime and nighttime infrared viking context imager ctx and mars orbiter camera moc visible mosaics using a variety of input and output types at a variety of scales by creating mosaics of the same area using different data sets such as those that illustrate compositional diversity thermophysical properties or small scale morphology it is possible to view the surface of the planet and geologic problems through many different perspectives in addition to the techniques used to create large scale seamless mosaics we also present the themis daytime and nighttime relative temperature global mosaics which are the highest resolution 100m pixel global scale data sets available for mars to date

accumulation of sedimentary debris in the south polar region of mars and implications for climate history abstract stratigraphic units of the south polar region of mars were mapped relative chronology determined and detailed modeling of the observed crater populations was used to set absolute constraints on the age of emplacement of materials significant secular variation in the net debris accumulation rate over history is evident an episode of enhanced crater obliteration at about 3 7 ga ago lasting a few hundred ma is inferred for south polar cratered terrains a similar peak in low latitude obliteration rates suggests that the event may have been global in scale whether the debris is volcanic or aeolian in origin the event suggests a possible enhancement in atmospheric density at the time modeling results imply that cratered terrains poleward of 65 south latitude have subsequently experienced steady state net accumulation of material at a rate of about 0 1 km ga while equatorial cratered terrains have been retained in relatively pristine form fifteen craters of impact origin were discovered on the south polar layered terrain formerly thought to be almost devoid of craters their presence implies that the surface is at least a few 100 ma old and that the net accumulation rate is no more than 10 km ga if layer formation is modulated by periodic climatic effects either the period of oscillation is a few ma or longer or the layer deposition mechanism ceased operating at least several 100 ma ago

consistency of scaling relations among bedrock and alluvial channels 1 this paper presents field data on channel geometry and potential control variables from 47 field settings representing a diverse range of environments these data are used to evaluate existing scaling relationships used in models of the evolution of bedrock channel geometry and to test the hypothesis that channel width w increases more slowly and depth d more rapidly in relation to discharge q or drainage area a as substrate resistance increases for this data set w a0 3 w q0 5 d a0 2 and d q0 3 the w a and w q relations are close to those found by previous investigators the d a and d q relations have not previously been reported for bedrock channels examination of trends within the data does not support the hypothesis and instead suggests that the erosional resistance of channel boundaries is not the primary control on scaling relations for channel geometry

martian south polar cap boundary 1971 and 1973 data abstract international planetary patrol photographs of mars obtained during the 1971 and 1973 apparitions have been used to produce regression curves for the martian south polar cap for those years useful data span the range in areocentric longitude l s 186 261 in 1971 and l s 255 301 in 1973 these regression curves are compared to the 1977 regression curve obtained from viking observations and to the results of 1956 observations there is remarkable consistency between the 1971 ipp and 1977 viking data points and the 1973 regression does not appear to have differed significantly from those of 1971 or 1977

use of local soil and vegetation classifications to improve regional downstream hydraulic geometry relations abstractregional downstream hydraulic geometry equations are developed using flow with a 1 5 year recurrence interval and corresponding widths depths and velocities the study includes 634 gauge stations located across canada and are grouped by characteristics that affect or are correlated with bank and bed stability jack knife analysis was done to test the predictive capabilities of each grouping for width prediction grouping the data by geology and vegetative characteristics improved predictions in 14 of the 15 categories with drainage characteristics and mode of deposition groupings showing the best results grouping the data by vegetative characteristics showed the best improvement among noncontiguous categories when considering all of the hydraulic geometry variables width depth and velocity these groupings are investigated further the study demonstrates that classifying downstream hydraulic geometry equations by local geology and vegetation improves the predictive capabilities of the eq

downstream variations in the width of bedrock channels field surveys of channel width w and drainage area a in bedrock channel reaches reveal relationships where w 5 ca b similar to the classic hydraulic geometry of alluvial channels data from five mountain channel networks support the assumption used in many landscape evolution models that an alluvial hydraulic geometry relationship where b 5 0 3 0 5 holds for bedrock channel systems although there is substantial local variability in channel width in bedrock channel systems there is no systematic difference in width versus drainage area relations for the surveyed bedrock and alluvial reaches in sedimentary lithologies in coastal oregon and washington in contrast bedrock channels were narrower and therefore had deeper flow than alluvial channels with equal drainage areas in the granite and limestone terrain of the yuba river california in addition data from the mokelumne river show that bedrock channel width decreases substantially downstream at the contact between relatively weak limestone and more erosion resistant granite but that channel slope does not change appreciably across contacts between these two lithologies data from coastal oregon drainage basins further show systematic channel widening after flood flows and debris flow impacts we conclude that downstream variations in the width of bedrock channels generally follow traditional hydraulic geometry relations but also reflect the local influence of longitudinal patterns of bedrock erosivity and disturbance history

h2o grain size and the amount of dust in mars residual north polar cap in mars north polar cap the probable composition of material residual from the annual condensation cycle is a mixture of fine dust and h2o grains of comparable size and abundance however metamorphism of such material will gradually lower its albedo by increasing the size of the h2o grains only if the cap is undergoing net annual sublimation as inferred from water vapor observations late summer observations should be of old ice with h2o grain sizes of 100 microns or more ice of this granularity containing 30 percent fine dust has a reflectivity similar to that of dust alone the observed albedo and computed ice grain size imply dust concentrations of 1 part per 1000 or less the brightness of the icy areas conflicts with what would be expected for a residual cap deposited by an annual cycle similar to that observed by viking and aged for thousands of years the residual cap surface cannot be old dirty ice it could be old coarse and clean or it could be young fine and dirty this brings into question both the source of the late summer water vapor and the formation rate of laminated terrain

experimental investigation of insolation driven dust ejection from mars co2 ice caps mars polar caps are depending on hemisphere and season partially or totally covered with co2 ice icy surfaces such as the polar caps of mars behave differently from surfaces covered with rock and soil when they are irradiated by solar light the latter absorb and reflect incoming solar radiation within a thin layer beneath the surface in contrast ices are partially transparent in the visible spectral range and opaque in the infrared due to this fact the solar radiation can penetrate to a certain depth and raise the temperature of the ice or dust below the surface this may play an important role in the energy balance of icy surfaces in the solar system as already noted in previous investigations we investigated the temperature profiles inside co2 ice samples including a dust layer under martian conditions we have been able to trigger dust eruptions but also demonstrated that these require a very narrow range of temperature and ambient pressure we discuss possible implications for the understanding of phenomena such as arachneiform patterns or fan shaped deposits as observed in mars southern polar region

downstream hydraulic geometry of clay dominated cohesive bed rivers empirical downstream hydraulic geometry equations for consolidated clay dominated cohesive bed nonalluvial natural streams are presented using data from six rivers in eastern ontario canada and four rivers from other regions the width exponent 0 57 was comparable to the exponents reported for previous studies however the depth exponent 0 52 was greater for clay dominated cohesive bed than for typical alluvial gravel bed and sand bed rivers the width to depth ratio of smaller channels qbf 20 m3 s was greater for consolidated clay bed than for either sand bed or gravel bed channels this study suggests that the concept of hydraulic geometry and bankfull channel forming discharge can be extended to nonalluvial consolidated clay bed channels

the global topography of mars and implications for surface evolution elevations measured by the mars orbiter laser altimeter have yielded a high accuracy global map of the topography of mars dominant features include the low northern hemisphere the tharsis province and the hellas impact basin the northern hemisphere depression is primarily a long wavelength effect that has been shaped by an internal mechanism the topography of tharsis consists of two broad rises material excavated from hellas contributes to the high elevation of the southern hemisphere and to the scarp along the hemispheric boundary the present topography has three major drainage centers with the northern lowlands being the largest the two polar cap volumes yield an upper limit of the present surface water inventory of 3 2 to 4 7 million cubic kilometers

sand dune materials and polar layered deposits on mars abstract the relationship of dark sand dunes to the polar layered deposits of mars is investigated by mapping the colors and morphologic settings of the dunes in and near the polar deposits in the north polar region the dunes have restricted sources in the layered deposits that are associated with are arcuate scarps 10 50 km in length and