sea land breeze development during a summer bora event along the north eastern adriatic coast the interaction of a summer frontal bora and the sea land breeze along the north eastern adriatic coast was investigated by means of numerical simulations and available observations available measurements in situ radiosonde satellite images provided model validation the modelled wind field revealed several regions where the summer bora weaker than 6 m s 1 allowed sea breeze development in the western parts of the istrian peninsula and rijeka bay and along the north western coast of the island of rab along the western istrian coast the position of the narrow convergence zone that formed depended greatly on the balance between the bora jets northward and southward of istria in the case of a strong northern trieste bora jet the westerly istrian onshore flow presented the superposition of the dominant swirled bora flow and local weak thermal flow it collided then with the easterly bora flow within the zone with weakening of the trieste bora jet the convergence zone was a result of the pure westerly sea breeze and the easterly bora wind in general during a bora event sea breezes were somewhat later and shorter with limited horizontal extent the spatial position of the convergence zone caused by the bora and sea breeze collision was strongly curved the orientation of the head of the thermally induced flow was more in the vertical causing larger horizontal pressure gradients and stronger daytime maximum wind speed than in undisturbed conditions except for the island of rab other lee side islands in the area investigated did not provide favourable conditions for the sea breeze formation within a bora wake near the island of krk onshore flow occurred as well although not as a sea breeze flow but as the bottom branch of the lee rotor that was associated with the hydraulic jump like feature in the lee of the velika kapela mountain copyright 2010 royal meteorological society

mass movement and landform degradation on the icy galilean satellites results of the galileo nominal mission the galileo mission has revealed remarkable evidence of mass movement and landform degradation on the icy galilean satellites of jupiter weakening of surface materials coupled with mass movement reduces the topographic relief of landforms by moving surface materials down slope throughout the galileo orbiter nominal mission we have studied all known forms of mass movement and landform degradation of the icy galilean satellites of which callisto by far displays the most degraded surface callisto exhibits discrete mass movements that are larger and apparently more common than seen elsewhere most degradation on ganymede appears consistent with sliding or slumping impact erosion and regolith evolution sliding or slumping is also observed at very small 100 m scale on europa sputter ablation while probably playing some role in the evolution of ganymede s and callisto s debris layers appears to be less important than other processes sputter ablation might play a significant role on europa only if that satellite s surface is significantly older than 108 years far older than crater statistics indicate impact erosion and regolith formation on europa are probably minimal as implied by the low density of small craters there impact erosion and regolith formation may be important on the dark terrains of ganymede though some surfaces on this satellite may be modified by sublimation degradation while impact erosion and regolith formation are expected to operate with the same vigor on callisto as on ganymede most of the areas examined at high resolution on callisto have an appearance that implies that some additional process is at work most likely sublimation driven landform modification and mass wasting the extent of surface degradation ascribed to sublimation on the outer two galilean satellites implies that an ice more volatile than h2o is probably involved

sublimation as a landform shaping process on pluto fields of pits both large and small in tombaugh regio sputnik planitia and the pitted uplands to the east and along the scarp of piri rupes are examples of landscapes on pluto where we conclude that sublimation drives their formation and evolution our heuristic modeling closely mimics the form spacing and arrangement of a variety of tombaugh regio s pits pluto s sublimation modified landforms appear to require a significant role for diffusive mass wasting as suggested by our modeling in our models the temporal evolution of pitted surfaces is such that initially lots of time passes with little happening then eventually very rapid development of relief and rapid sublimation small pits on sputnik planitia are consistent with their formation in n2 dominated materials as n2 ice readily flows some other stiffer volatile ice may play a role in supporting the relief of sublimation degraded landforms that exhibit several hundred meters of relief a strong candidate is ch4 which is spectroscopically observed to be associated with these features but the current state of rheological knowledge for ch4 ice at pluto conditions is insufficient for a firm assessment

ice sublimation as a geomorphic process a planetary perspective abstract sublimation plays a role in the shaping of landforms of planetary surfaces where ice is present as frost as polar caps or in the subsurface this review is focused primarily on the geomorphologic consequences of sublimation a summary of the suite of landforms that have been observed on the surface of various planetary bodies and whose formation is attributed to sublimation is presented this includes the sublimation of a range of different ices that are found on planetary bodies water ice carbonic ice etc at least four groups of landforms are distinguishable independent of the planetary body i residual lags that are depleted in ice which form after sublimation loss such residual lags isolate deeper ice from sublimation and thus can have an important impact on planetary volatile cycles ii landforms due to differential sublimation resulting from enhanced sublimation in low albedo warmer areas of the planet and preservation of ice in the high albedo regions iii landforms due to differential sublimation initiated by fractures or ground heterogeneities for example sublimation enhanced polygonal cracks iv pitted terrains that occur in a relatively homogeneous ice bearing subsurface or as an effect of local ice enrichment or segregation in the ground

mass wasting and ground collapse in terrains of volatile rich deposits as a solar system wide geological process the pre galileo view the polar terrains of mars are covered in many places with irregular pits and retreating scarps as are some of the surfaces of the outer planet satellites these features are interpreted by us as diagnostic of exogenic degradation due to the loss of a volatile rock forming matrix or cement in this study we propose that sublimation degradation is a plausible solar system wide geological process candidate examples have been identified on mars io and triton and possibly europa and ganymede we envision this process as having two end member expressions pits and scarps for which we hypothesize two end member mechanisms massive localized lenses and areally extensive basal layers in this study we focus on the role this process may play on the surfaces of the galilean satellites our principle modeling results are that for these satellites h2s co2 and nh3are the only viable candidate volatiles for sublimation degradation of landforms in light of galilean satellite cosmochemistry for io s polar regions only h2s and then only from slopes that face the sun and have thin lags is volatile enough to cause the observed sublimation induced erosion at those latitudes so2is not a viable candidate as an agent of erosion especially for these polar landforms in the case of europa only co2and h2s are viable candidates given surface age constraints both species could be efficient eroders in nonpolar regions h2s could generate erosion within the polar regions if the deposition and erosion conditions were essentially identical as those we invoked for io s polar regions for ganymede and callisto nh3might be an agent of erosion in equatorial terrains of great age the sublimation of co2and h2s is much more robust than nh3 the much slower rate of sublimation degradation from nh3might be detectable by galileo and used as a compositional indicator

bayesian source tracking via focalization and marginalization in an uncertain mediterranean sea environment this paper applies bayesian source tracking in an uncertain environment to mediterranean sea data and investigates the resulting tracks and track uncertainties as a function of data information content number of data time segments number of frequencies and signal to noise ratio and of prior information environmental uncertainties and source velocity constraints to track low level sources acoustic data recorded for multiple time segments corresponding to multiple source positions along the track are inverted simultaneously environmental uncertainty is addressed by including unknown water column and seabed properties as nuisance parameters in an augmented inversion two approaches are considered focalization tracking maximizes the posterior probability density ppd over the unknown source and environmental parameters marginalization tracking integrates the ppd over environmental parameters to obtain a sequence of joint marginal probability distributions over source coordinates from which the

modeling the development of martian sublimation thermokarst landforms abstract sublimation thermokarst landforms result from collapse of the surface when ice is lost from the subsurface on mars scalloped landforms with scales of decameters to kilometers are observed in the mid latitudes and considered likely thermokarst features we describe a landscape evolution model that couples diffusive mass movement and subsurface ice loss due to sublimation over periods of tens of thousands of mars years under conditions similar to the present the model produces scallop like features similar to those on the martian surface starting from much smaller initial disturbances the model also indicates crater expansion when impacts occur in surfaces underlain by excess ice to some depth with morphologies similar to observed landforms on the martian northern plains in order to produce these landforms by sublimation substantial quantities of excess ice are required at least comparable to the vertical extent of the landform and such ice must remain in adjacent terrain to support the non deflated surface we suggest that martian thermokarst features are consistent with formation by sublimation without melting and that significant thicknesses of very clean excess ice up to many tens of meters the depth of some scalloped depressions are locally present in the martian mid latitudes climate conditions leading to melting at significant depth are not required

hillslope evolution by nonlinear creep and landsliding an experimental study landscape evolution models are widely used to explore links between tectonics climate and hillslope morphology yet mecha nisms of hillslope erosion remain poorly understood here we use a laboratory hillslope of granular material to experimentally test how creep and landsliding contribute to hillslope erosion in our experimental hillslope disturbance driven sediment transport rates increase nonlinearly with slope due to dilation driven gran ular creep and become increasingly episodic at steep slope angles as creep gives way to periodic landsliding we use spectral analysis to quantify the variability of sediment flux and estimate the slope dependent transition from creep to landsliding the power spec trum of sediment flux steepens with hillslope gradient exhibiting fractal 1 f scaling just below the creep landsliding transition by evolving the experimental hillslope under fixed base level boundary conditions we demonstrate how disturbance driven transport gen erates hillslope convexity the transient evolution is consistent with numerical predictions derived from a recently proposed nonlinear transport model as initially steep hillslopes are lowered rapidly by landsliding before slopes decay slowly by creep dominated transport

geology before pluto pre encounter considerations the cameras of new horizons will provide robust data sets that should be imminently amenable to geological analysis of the pluto system s landscapes in this paper we begin with a brief discussion of the planned observations by the new horizons cameras that will bear most directly on geological interpretability then we broadly review the major geological processes that could potentially operate on the surfaces of pluto and its major moon charon we first survey exogenic processes i e those for which energy for surface modification is supplied externally to the planetary surface impact cratering sedimentary processes including volatile migration and the work of wind we conclude with an assessment of the prospects for endogenic activity in the form of tectonics and cryovolcanism

cold jets in the martian polar caps 1 mars seasonal polar caps display dark ice local darker spots aligned elongate patches and radially dendritic forms that reverse albedo contrast the unexpected variety and sequence of these features are explained on the basis of processes involving co2 dust sand and h2o these processes are largely related to the atmosphere being near its saturation temperature and they have few terrestrial analogies in the simplest case the 1 m thick seasonal cap initially dusty cleans itself and becomes translucent after sunrise and is impermeable over extensive regions except for local vents the slab ice sublimates at the base and is levitated on high pressure gas causing humidity exchange with deeper layers subslab gas converging toward the vents erodes channels in the soil and ejects this material in high velocity jets recent spectral observations indicate great variety in the details

growth and fluctuations of suncups on alpine snowpacks 1 a mathematical model for suncups on glacier and alpine snow during the summer melting season is compared with time lapse field observations the model consists of a nonlinear partial differential equation whose solution spontaneously forms quasi periodic patterns similar to suncups when started from a random initial condition the suncup patterns are found to fully develop in 5 days in the field under full sun the patterns fluctuate chaotically in time both in the observations and in the model the fluctuations can be described mathematically in terms of diffusion of individual suncups according to the model the rate at which the suncups diffuse contains information about the effect of the suncups on the albedo of the snow

the geology of pluto and charon through the eyes of new horizons nasa s new horizons spacecraft has revealed the complex geology of pluto and charon pluto s encounter hemisphere shows ongoing surface geological activity centered on a vast basin containing a thick layer of volatile ices that appears to be involved in convection and advection with a crater retention age no greater than 10 million years surrounding terrains show active glacial flow apparent transport and rotation of large buoyant water ice crustal blocks and pitting the latter likely caused by sublimation erosion and or collapse more enigmatic features include tall mounds with central depressions that are conceivably cryovolcanic and ridges with complex bladed textures pluto also has ancient cratered terrains up to 4 billion years old that are extensionally faulted and extensively mantled and perhaps eroded by glacial or other processes charon does not appear to be currently active but experienced major extensional tectonism and resurfacing probably cryovolcanic nearly 4 billion years ago impact crater populations on pluto and charon are not consistent with the steepest impactor size frequency distributions proposed for the kuiper belt

sublimation driven erosion on hyperion topographic analysis and landform simulation model tests abstract the unique appearance of hyperion can be explained in part by the loss to space of ballistic ejecta during impact events as was proposed by thomas et al thomas p c et al 2007a icarus 190 573 584 we conclude that such loss is a partial explanation accounting for the lack of appreciable intercrater plains on a saturation cratered surface in order to create the smooth surfaces and the reticulate honeycomb pattern of narrow divides between old craters appreciable subsequent modification of crater morphology must occur through mass wasting processes accompanied by sublimation probably facilitated by the loss of co 2 as a component of the relief supporting matrix of the bedrock during early stages of crater degradation steep crenulate bedrock slopes occupy the upper crater walls with abrupt transitions downslope onto smooth slopes near the angle of repose mantled by mass wasting debris as can be seen within young craters long continued mass wasting eventually results in slopes totally mantled with particulate debris this mass wasting effectively destroys small craters at least in part accounting for the paucity of sub kilometer craters on hyperion surface temperatures measured by cassini cirs range from 58 k to 127 k and imply a surface thermal inertia of 11 2 j m 2 k 1 s 1 2 and bolometric albedo ranging from 0 05 to 0 33 resulting h 2 o sublimation rates are only tens of cm per billion years for most of the surface so the evolution of the observed landforms is likely to require sublimation of more volatile species such as co 2

finite element models of non newtonian crater relaxation models of viscous crater relaxation proposed to date for the icy satellites of the outer solar system assume the behavior of a newtonian medium with viscosity independent of effective stress while this is reasonable if both effective stresses and temperatures are very low laboratory data on ice indicate that at effective shear stresses 0 1 mpa and temperatures 173 k likely to occur in regions underlying craters non newtonian behavior is probable such material would have a viscosity effective stress relation given by 1 n where n 4 it is likely due to the low activation energy of ice at these temperatures that stress differences may affect the profile of relaxing craters to a greater extent than temperature differences to investigate the effects of a non newtonian rheology on the profiles of relaxing craters two dimensional finite element simulations have been performed initially effective stresses are highest in the region below the crater center producing a zone of relatively low viscosity relaxation flow forces this region into a convex bulge as the crater relaxes at later stages the low viscosity region moves to beneath the crater rim leading to enhanced relaxation of crater rims compared to a newtonian rheology the reduction of effective stress as the crater relaxes increases viscosity in the region beneath the crater as a result relaxation rates are quite rapid compared to those in later stages this is in marked contrast to the exponential behavior of depth with time associated with newtonian relaxation the short relaxation times observed for the craters modeled indicate that a silicate component may be required in the crusts of icy satellites to account for the observed crater populations

triton s streaks as windblown dust the encounter of the voyager 2 spacecraft with neptune s satellite triton revealed many dark about 10 20 darker than the adjacent frost surface streaks in triton s southern hemisphere1 resembling the streaks that are due to windblown dust on mars2 it seems therefore that dust transport by winds in triton s tenuous atmosphere is required the main question being the mechanism for raising dust from the surface or sub surface the two obvious candidates are geyser like eruptions and direct lofting by surface winds1 here we show that despite triton s tenuous 16 3 bar atmosphere3 low cohesion grains with diameters of 5 m may be carried into suspension by aeolian surface shear stress given expected geostrophic wind speeds4 of l0ms 1 the wind velocities needed to lift grains as cohesive as those found on earth however are implausibly high for erupting plumes we show that dust settling timescales and expected wind velocities yield streak length scales in good agreement with those observed both candidate mechanisms therefore seem to be consistent with present observations of triton

power law rheology of ice and the relaxation style and retention of craters on ganymede numerical models of viscous relaxation of craters in ice using rheological laws determined from laboratory data previously indicated excessively short relaxation times te the time required for crater depth to become 1 e of its initial value for craters on the icy satellites a typical value of te was 104 years for a 100 km diameter crater these time scales are totally incompatible with the large regions of heavily cratered terrain on the icy satellites we discuss the application of a numerical unite element model incorporating the most recent rheological data for ice at temperatures and pressures appropriate to the near surface regions of ganymede the model permits a full representation of a temperature and stress dependent power law viscosity for ice for temperature gradients in reasonable agreement with those obtained from thermal and structural models of ganymede we obtain relaxation times te 10 years for craters with diameters less than 100 km for all craters with diameters greater than 10 km the strong dependence of viscosity on stress was found to significantly shorten the relaxation time an attempt was also made to determine whether newtonian or non newtonian rheological laws dominated relaxation for craters of various sizes newtonian rheologies appear to dominate crater relaxation only for situations where the effective temperature is several tens of degrees warmer than the surface is observed to be perhaps because of the effect of an insulating regolith and where temperature gradients are small in this case viscous relaxation of craters with diameters smaller than 25 km is expected to be dominated by newtonian flow laws provided that the currently accepted parameters gross extrapolations from near melting temperature measurements are valid for the low temperatures of the icy satellites on the other hand larger diameter craters undergo at least initially viscous relaxation determined by a strongly non newtonian rheological law and have geologically short relaxation times te 107 years for a 300 km crater although these times may be extended by silicate suspensions and by dispersion hardening this presumably accounts for the absence of such craters in unmodified form on ganymede finally the large stress exponent n 4 7 of the current rheological data for ice indicates a strong role for non newtonian flow in determining the topography of viscously relaxing craterforms of this size in principle a threshold crater diameter and hence stress for the onset of non newtonian viscous behavior could be obtained from galileo images allowing estimates to be made of near surface temperatures and thermal gradients in ganymede s past in practice however any morphological variability is almost certainly too subtle to be detected from imagery the calculated relaxation times from this work are still much shorter than those indicated by the topographic relief of ganymede s surface this remains an unresolved problem possible ways in which the observations can be resolved with current laboratory data on ice deformation are discussed

modeling surface roughness solar ablation feedback application to small scale surface channels and crevasses of the greenland ice sheet surface roughness enhances the net ablation rate associated with direct solar radiation relative to smooth surfaces because roughness allows solar energy reflected from one part of the surface to be absorbed by another part in this study we examine the feedback between solar radiation driven ablation and growth of surface roughness on the greenland ice sheet using a numerical model of radiative transfer our experiments extend previous work by examining 1 the effects of diurnal and seasonal variation of solar zenith angle and azimuth relative to incipient roughness features 2 the evolution of roughness geometry in response to radiatively driven ablation and 3 the relative solar energy collection efficiencies of various roughness geometries and geographic locations and orientations a notable result of this examination is that the time evolution of the aspect ratio of surface features under solar driven ablation collapses onto a roughly universal curve that depends only on latitude not the detailed shape of the feature the total enhancement of surface melt relative to a smooth surface over a full ablation season varies with this ratio and this dependence suggests a way to parameterize roughness effects in large scale models that cannot treat individual roughness features overall our model results suggest that surface roughness at the latitudes spanned by the greenland ice sheet tends to dissipate as the ablation season progresses

north and south subice gas flow and venting of the seasonal caps of mars a major geomorphological agent 1 dark polygons associated with fans and spots appear during the spring on the southern seasonal cap the basal sublimation of the translucent cap and the venting of the co2 gas are responsible for their formation as previously proposed for the spots and fans dark polygons appear when dark material emerges from elongated vents whereas spots and fans form from point sources a class of erosive features etched polygons is associated with depressions a few meters to tens of meters in diameters connected to a network of radiating troughs spiders spiders are shaped by the scouring action of the confined gas converging toward point sources whereas the etched polygons result from the forced migration of the co2 gas over longer distances the minimum age of the spiders is 104 years they result from one of the most efficient erosive processes on mars displacing 2 orders of magnitude more dust per year than a typical dust storm or than all the dust devils during the same time period in the north parts of the seasonal cap are translucent between ls 355 and ls 60 and are associated with spots fans dark polygons and possibly spiders suggesting that the basal sublimation and venting of the cap triggers a subice gas and dust flow that is modifying the morphology of the surface layer however perennial features are extremely uncommon on the north regolith indicating that the conditions for their formation or conservation are not met the reduced basal energy budget of the north cap compared to the south and the shorter seasonal life time of the north translucent ice may explain the relative scarcity of features in the north the polar layered deposits contain the stratigraphic record of climatic changes and catastrophic events both polar deposits may have been locally disrupted by the seasonal subice gas flow and the stratigraphic record may have been partially lost

relaxation of impact basins on icy satellites the extent and style of viscous relaxation of the largest crater basins on the icy satellites of saturn can be used as a probe of the viscosity of the deep interiors of these bodies in particular some constraints on the size of a silicate core and the magnitude of the internal viscosity gradient can be determined if the relaxation process is sufficiently well understood we discuss the application of a unite element model incorporating spherical symmetry to the general problem of relaxation of large craters on spherical bodies we examine the influence of core size geothermal gradient and rheologic law on relaxation flow and consider the implications for the internal structures of mimas and tethys our model results show that relaxation of crater topography on a spherical satellite is qualitatively and quantitatively different from relaxation on a planar surface once the crater diameter becomes a significant fraction of the satellite radius for small to moderate sized basins relaxation flow is bidirectional with flow both from rim to bowl and rim to surrounds this is the same style of flow observed for craters on planar surfaces for large enough basins however the spherical geometry of the problem leads to flow that is unidirectional toward the crater bowl throughout the satellite the transition from bidirectional to unidirectional flow appears to be very sensitive to the basin diameter the critical basin diameter for transition increases with core size thermal gradient rim height and rheologie law stress exponent unidirectional and bidirectional flow produce fundamentally different stress fields in the regions surrounding the relaxing crater relaxation velocities for large craters on spherical bodies can be appreciably more rapid than those for equivalent craters on planar surfaces again because of the geometric effects of relaxation on a sphere the difference in degree of relaxation between the large basins odysseus on tethys which has undergone significant modification and herschel on mimas which appears essentially unmodified can be explained by different thermal histories for tethys and mimas by the effects of stress dependent rheology or by a combination of the two the influence of a core at sizes consistent with the observed densities of the satellites on relaxation time scales is unimportant if the ithaca chasma graben system on tethys is the result of stresses generated by relaxation of the odysseus basin then tethys s core must be small enough that it allows unidirectional relaxation flow for a basin of odysseus s size if this assumption it correct we estimate an upper limit of roughly 20 of tethys s radius for the radius of the satellite s core

the pluto system initial results from its exploration by new horizons the pluto system was recently explored by nasa s new horizons spacecraft making closest approach on 14 july 2015 pluto s surface displays diverse landforms terrain ages albedos colors and composition gradients evidence is found for a water ice crust geologically young surface units surface ice convection wind streaks volatile transport and glacial flow pluto s atmosphere is highly extended with trace hydrocarbons a global haze layer and a surface pressure near 10 microbars pluto s diverse surface geology and long term activity raise fundamental questions about how small planets remain active many billions of years after formation pluto s large moon charon displays tectonics and evidence for a heterogeneous crustal composition its north pole displays puzzling dark terrain small satellites hydra and nix have higher albedos than expected

formation of gravel pavements during fluvial erosion as an explanation for persistence of ancient cratered terrain on titan and mars abstract in many terrestrial channels the gravel bed is only transported during rare floods threshold channels and rates of erosion are very slow in this paper we explore how coarse debris delivered to channels on mars and titan from erosion may inhibit further erosion once a coarse gravel channel bed develops portions of the equatorial region of titan are fluvially eroded into banded crenulated terrain some of which contains numerous circular structures that are likely highly degraded large impact craters surviving from the late heavy bombardment no mechanism that can chemically or physically break down ice likely the most important component of titans crust has been unambiguously identified this paper examines a scenario in which fluvial erosion on titan has largely involved erosion into an impact generated megaregolith that contains a modest component of gravel sized debris as the megaregolith is eroded coarse gravel gradually accumulates as a lag pavement on channel beds limiting further erosion and creating a dissected but largely inactive or senescent landscape similar development of gravel pavements occur in ancient mountain belts on earth and partially explain the persistence of appreciable relief after hundreds of millions of years likewise coarse gravel beds may have limited the degree to which erosion could modify the heavily cratered terrains on mars particularly if weathering were largely due to physical rather than chemical weathering processes in a relatively cold and or arid environment

modeling of ice pinnacle formation on callisto callisto s pinnacle terrain has been interpreted to form through sublimation weathering of bedrock and subsequent deposition of the sublimated ice in local cold traps on peaks and crater rims to investigate how these processes are affected by environmental parameters including solar illumination and the composition and concentration of ices in the crust we employ the marssim landform evolution model and advance its treatment of the physics that underlies the relevant processes both ice sublimation and deposition are controlled by surface temperature which we calculate based on energy contributions from both insolation and thermal reradiation from the surrounding landscape we perform 4 5 gyr duration simulations whereby we separately consider and model co2 and h2o as the crustal ice species we find that sublimating a crustal content of 10 co2 ice a reasonable but arbitrarily selected value yields present day landform degradation and regolith coverage that is comparable to what is observed on callisto in our h2o ice simulations we reproduce the essential features of pinnacle ice distribution at both the equator and midlatitudes our present nominal crustal h2o ice content is 33 which produces a maximum pinnacle ice thickness of 64 m pinnacle height is likely limited by collapse or mass wasting of the ice once it reaches a certain thickness

sublimation driven erosion on callisto a landform simulation model test 1 callisto s landscape exhibits widespread erosion from some non impact induced process which is characterized by smooth undulating dark albedo surfaces with isolated high albedo knobs that are remnants of crater rims we develop a landform simulation model that incorporates sublimation erosion of exposed bedrock on crater walls composed of ice cemented dust with non linear mass wasting of the released dust and redeposition of the ice on convex summits the model reproduces the essential elements of landscapes on callisto and lends strong support to the 1999 hypothesis of moore and his colleagues that volatile sublimation causes slope forming bedrock disaggregation and subsequent mass wasting while reprecipitation caps and armors local crests with frost

the role of eolian processes in forming surface features of the martian polar layered deposits abstract the major topographic features of the martian polar layered deposits include the conspicuous spiral troughs subtle undulations broad reentrants chasma steep arcuate scarps and dune fields a prominent role for eolian processes in the formation of all of these features is proposed strong katabatic winds occur on the north polar cap producing widespread frost streaks these cold drainage winds are analogous to those on the terrestrial antarctic cap in the chasmae convergent katabatic winds create yardangs and erode arcuate scarps in the layered deposits that are also the source for local dune fields migrating outward from the polar cap the chasmae are postulated to originate by long term erosion by katabatic wind wind plays a role in formation of the troughs and scarps primarily through removal of dust freed from exposed layered deposits by ablation of ice on defrosted equator facing slopes the undulations are created by interaction between surface erosion or deposition of perennial ice and standing waves in the shallow katabatic windflow the south polar layered deposits exhibit topographic features similar to those at the north polar cap but erosion and depositional processes creating these features may be inactive during the current epoch because of the lack of an extensive perennial ice cover and associated katabatic wind

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

intra surface radiative transfer limits the geographic extent of snow penitents on horizontal snowfields penitents are broad snow spikes and ridges that range in height between centimeters and meters two key features of penitents remain unexplained 1 they generally form at low latitudes and 2 their ridges and troughs have an east west orientation here we show that surface to surface exchange of shortwave radiation and the local geometry of the sun s daily arc across the sky are the key processes that in the absence of other effects determine the geographic extent of where surface roughness features can grow or dissipate on snowfields and ice surfaces as an application of our analysis we examine the question of the geographic extent of snow penitents on horizontal surfaces the results show that surface to surface radiative transfer can explain why penitents do not form on horizontal surfaces more than 558 off the equator we further show on the basis of the sun s path across the sky that penitents that are corrugated i e occur in long ridges or rows must align their ridge axis within 308 of the east west transect

evidence for nonlinear diffusive sediment transport on hillslopes and implications for landscape morphology steep soil mantled hillslopes evolve through the downslope movement of soil driven largely by slope dependent transport processes most landscape evolution models represent hillslope transport by linear diffusion in which rates of sediment transport are proportional to slope such that equilibrium hillslopes should have constant curvature between divides and channels on many soil mantled hillslopes however curvature appears to vary systematically such that slopes are typically convex near the divide and become increasingly planar downslope this suggests that linear diffusion is not an adequate model to describe the entire morphology of soil mantled hillslopes here we show that the interaction between local disturbances such as rainsplash and biogenic activity and frictional and gravitational forces results in a diffusive transport law that depends nonlinearly on hillslope gradient our proposed transport law 1 approximates linear diffusion at low gradients and 2 indicates that sediment flux increases rapidly as gradient approaches a critical value we calibrated and tested this transport law using high resolution topographic data from the oregon coast range these data obtained by airborne laser altimetry allow us to characterize hillslope morphology at 2 m scale at five small basins in our study area hillslope curvature approaches zero with increasing gradient consistent with our proposed nonlinear diffusive transport law hillslope gradients tend to cluster near values for which sediment flux increases rapidly with slope such that large changes in erosion rate will correspond to small changes in gradient therefore average hillslope gradient is unlikely to be a reliable indicator of rates of tectonic forcing or baselevel lowering where hillslope erosion is dominated by nonlinear diffusion rates of tectonic forcing will be more reliably reflected in hillslope curvature near the divide rather than average hillslope gradient