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

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

the acidalia mensa region on mars a key element to test the mars ocean hypothesis abstract we present the results of a detailed photogeological study of a region surrounding acidalia mensa 43 50 n 15 35 w based on analysis of a mosaic of the ctx images nominal resolution 5 m px the main result of the study is the unfolding of the geologic history of the study region and determination of absolute model ages of its major episodes the documented history begins with the formation of a volcanic plateau of acidalia mensa 4 ga ago the surface of the acidalia plateau was strongly modified since its formation the crater size frequency distribution csfd on the plateau indicates that the resurfacing was likely consisted of multiple episodes the latest such episode recognizable by the crater statistics occurred 3 65 ga ago the vast majority of the surface around acidalia mensa is covered by materials of the background plains that correspond to the interior unit of the vastitas borealis formation vbf the csfd on the background plains corresponds to an absolute model age ama of 3 58 ga which is completely within the range of amas determined for the vbf along its boundary with the southern uplands small scale features such as bright cones mounds polygonal troughs and flow like mantling materials postdate the emplacement of the background plains and manifest the post formational evolution of the vbf the majority of crater ejecta in the study area have higher albedo in the ctx and hirise images but appear as dark spots in the themis ir nighttime images these wavelength dependent properties of the ejecta indicate the presence of light toned and fine grained material beneath the surface of the background plains this material was the source of numerous bright cones mounds we interpret the formation of this reservoir as the result of sorting of large amounts of water mud deposited in the study area and by implication within the northern lowlands the final episodes of the ancient geologic history of the study area were related to the emplacement of materials of the thick flows at topographically high levels within the acidalia plateau 3 47 ga ago the morphology of the flows is inconsistent with lava and we interpret the occurrences of the thick flows as the result of displacement of water saturated regolith in the form of either soli or gelifluction flows or ice cored rock glaciers

effects of dispersed particulates on the rheology of water ice at planetary conditions we have investigated the effects of initial grain size and hard particulate impurities on the transient and steady state flow of water ice i at laboratory conditions selected to provide more quantitative constraints on the thermomechanical evolution of the giant icy moons of the outer solar system our samples were molded with particulate volume fractions of 0 001 to 0 56 and particle sizes of 1 to 150 m deformation experiments were conducted at constant shortening rates of 4 4 10 7 to 4 9 10 4 s 1 at pressures of 50 and 100 mpa and temperatures 77 to 223 k for the pure ice samples initial grain sizes were 0 2 0 6 mm 0 75 1 75 mm and 1 25 2 5 mm stress strain curves of pure ice i under these conditions display a strength maximum u at plastic strains e 0 01 after initial yield followed by strain softening and achievement of steady state levels of stress ss at e 0 1 to 0 2 finer starting grain size in pure ice generally raises the level of u petrography indicates that the initial transient flow behavior is associated with the nucleation and growth of recrystallized ice grains and the approach to ss evidently corresponds to the development of a steady state grain texture effects of particulate concentrations 0 1 are slight at these concentrations a small but significant reduction in u with respect to that for pure water ice occurs mixed phase ice with 0 1 is significantly stronger than pure ice the strength of samples with 0 56 approaches that of dry confined sand the magnitude of the strengthening effect is far greater than expected from homogeneous strain rate enhancement in the ice fraction or from pinning of dislocations orowan hardening this result suggests viscous drag occurs in the ice as it flows around the hard particulates mixed phase ice is also tougher than pure ice extending the range of bulk plastic deformation versus faulting to lower temperatures and higher strain rates the high pressure phase ice ii formed in 0 56 mixed phase ice during deformation at high stresses bulk planetary compositions of ice rock 0 4 0 5 are roughly 2 orders of magnitude more viscous than pure ice promoting the likelihood of thermal instability inside giant icy moons and possibly explaining the retention of crater topography on icy planetary surfaces

on the icy edge at louth and korolev craters abstract the modern climate of mars has been well characterized from over a decade of orbiting spacecraft in situ measurements via landers rovers and theoretical advances in climate modeling nonetheless important questions remain unanswered including the present day mass balance of the north polar residual cap and its icy outliers exposed water ice mounds are found in craters and extend as far equatorward as 70 2 n due to their southerly location these ice mounds are likely more sensitive to ongoing changes in climate we analyze high resolution images of the louth crater ice mound and employ a coupled 1 d thermal and atmospheric model to estimate annual mass balance of both louth and korolev water ice we incorporate the effects of shallowly sloping surfaces and seasonally dependent water ice albedo no clear trend in the advance or retreat of louth crater water ice is observed in over 4 mars years of repeat high resolution images secular changes are either sufficiently small as to not be detected or the ice is in equilibrium modeled mass balance ranges from 6 to 2 mm of water ice per mars year at both sites with nominal cases being in near equilibrium

recent glaciation at high elevations on arsia mons mars implications for the formation and evolution of large tropical mountain glaciers 1 the 166 000 km2 fan shaped deposit at arsia mons contains three characteristic facies ridged knobby and smooth which are interpreted as the depositional remains of a cold based glacier that was present on the west northwestern flanks in the late amazonian period of mars history here we consider several high elevation graben on the western flank of arsia mons that are interpreted as the source regions for late stage cold based glaciers that overflowed graben walls advanced tens to hundreds of kilometers downslope experienced subsequent retreat and left distinctive depositional features similar to those associated with cold based glaciers in the dry valleys of antarctica these new observations provide additional support for a cold based glacial interpretation of the tharsis montes fan shaped deposits morphological evidence suggests that the largest of these graben was the primary source region for the most proximal smooth facies lobes at arsia mons and map plane ice sheet reconstructions are consistent with these observations this relationship has significant implications for the relative ages of the individual facies within the fan shaped deposit including the possibility that the smooth facies represents several distinct phases of glaciation the high relief and large elevation differences between the upslope and downslope walls of these graben appear to be critical factors for ice accumulation and the generation collection of rockfall within glacial accumulation zones we suggest that rockfall was the dominant process responsible for debris cover formation on the glaciers sourced within these graben and consider the implications for the entire arsia fan shaped deposit new crater count data suggest that the fill material in the large arsia graben formed within the past 100 myr model age of 65 ma taken together these new observations provide additional evidence for several periods of late amazonian climate change on mars within the past few 100 myr resulting in episodes of tropical mountain glaciation finally mola topography reveals that several lobate features interpreted as remnant debris covered ice from the most recent phase of glaciation are presently hundreds of meters thick suggesting the possibility of long term near surface water ice survival in the equatorial regions of mars

morphology stratigraphy and mineralogical composition of a layered formation covering the plateaus around valles marineris mars implications for its geological history an extensive layered formation covers the high plateaus around valles marineris mapping based on hirise ctx and hrsc images reveals these layered deposits lds crop out north of tithonium chasma south of ius chasma around west candor chasma and southwest of juventae chasma and ganges chasma the estimated area covered by lds is not vert similar42 300 km2 they consist of a series of alternating light and dark beds a 100 m in total thickness that is covered by a dark unconsolidated mantle possibly resulting from their erosion their stratigraphic relationships with the plateaus and the valles marineris chasmata indicate that the lds were deposited during the early to late hesperian and possibly later depending on the region before the end of the backwasting of the walls near juventae chasma and probably before louros valles sapping near ius chasma their large spatial coverage and their location mainly on highly elevated plateaus lead us to conclude that lds correspond to airfall dust and or volcanic ash the surface of lds is characterized by various morphological features including lobate ejecta and pedestal craters polygonal fractures valleys and sinuous ridges and a pitted surface which are all consistent with liquid water and or water ice filling the pores of lds lds were episodically eroded by fluvial processes and were possibly modified by sublimation processes considering that lds correspond to dust and or ash possibly mixed with ice particles in the past lds may be compared to dissected mantle terrains currently observed in mid to high latitudes on mars which correspond to a mantle of mixed dust and ice that is partially or totally dissected by sublimation the analysis of crism and omega hyperspectral data indicates that the basal layer of lds near ganges chasma exhibits spectra with absorption bands at not vert similar1 4 m and not vert similar1 9 m and a large deep band between not vert similar2 21 and not vert similar2 26 m that are consistent with previous spectral analysis in other regions of lds we interpret these spectral characteristics as an enrichment of lds in opaline silica or by al phyllosilicate rich layers being overlain by hydroxylated ferric sulfate rich layers these alteration minerals are consistent with the aqueous alteration of lds at low temperatures

validation of the rupture properties of the 2001 kunlun china ms 8 1 earthquake from seismological and geological observations summary we determine the finite fault slip distribution of the 2001 kunlun earthquake ms 8 1 by inverting teleseismic waveforms as constrained by geological and remote sensing field observations the spatial slip distribution along the 400 km long fault was divided into five segments in accordance with geological observations forward modelling of regional surface waves was performed to estimate the variation of the speed of rupture propagation during faulting for our modelling the regional 1 d velocity structure was carefully constructed for each of six regional seismic stations using three events with magnitudes of 5 1 5 4 distributed along the ruptured portion of the kunlun fault our result shows that the average rupture velocity is about 3 6 km s 1 consistent with teleseismic long period wave modelling the initial rupture was almost purely strike slip with a rupture velocity of 1 9 km s 1 increasing to 3 5 km s 1 in the second fault segment and reaching a rupture velocity of about 6 km s 1 in the third segment and the fourth segment where the maximum surface offset with a broad fault zone was observed the rupture velocity decelerated to a value of 3 3 km s 1 in the fifth and final segment coseismic slip on the fault was concentrated between the surface and a depth of about 10 km we infer that significant variations in rupture velocity and the observed fault segmentation are indicative of variations in strength along the interface of the kunlun fault as well as variations in fault geometry

softened impact craters on mars implications for ground ice and the structure of the martian megaregolith abstract terrain softening is a distinct style of landform degradation observed on mars the morphology and distribution of softened terrain have led to the hypothesis that it is the result of quasiviscous relaxation of topology due to the creep deformation of subsurface ice in order to test this hypothesis we use a finite element model to investigate the relaxation of impact craters on mars for the martian megaregolith we assume a non newtonian viscoelastic rheology derived from experiments on frozen soils our results indicate that impact craters in softened terrain at midlatitudes on mars have a morphology consistent with relaxation in a deforming layer no more than 1 km deep we therefore conclude that creep of ground ice is consistent with the morphology of terrain softening we also use our results to estimate the total quantity of subsurface ice on mars we find a quantity of ice equal to 17 m spread over the planet associated with the terrain softening observed to date this number increases to 55 m if we include locations for which terrain softening is likely but for which adequate imaging data do not exist and 125 m if the conditions required for terrain softening are assumed to exist everywhere poleward of 30 latitude

maps of subsurface hydrogen from the high energy neutron detector mars odyssey after 55 days of mapping by the high energy neutron detector onboard mars odyssey we found deficits of high energy neutrons in the southern highlands and northern lowlands of mars these deficits indicate that hydrogen is concentrated in the subsurface modeling suggests that water ice rich layers that are tens of centimeters in thickness provide one possible fit to the data

distribution and orientation of northern hemisphere gullies on mars from the evaluation of hrsc and moc na data abstract martian gullies show morphologic characteristics that indicate the presence of a flowing liquid during their formation process however the current climate in the northern hemisphere of mars does not allow the existence of substantial amounts of liquid water and therefore an assessment of the regional distribution and characteristics of gullies is required in order to understand the most recent climatic development of mars we examined high resolution stereo camera hrsc and mars orbiter camera narrow angle moc na data covering the northern hemisphere in order to determine the distribution geological setting and orientation of gullied slopes we used these results to test the consistency of formation models proposed in earlier works and to define the climate dependence gully orientations were analyzed only at impact crater walls because craters have an azimuthally uniform distribution of slopes this is ideal when investigating the influence of insolation on the distribution and development of landforms we examined 230 hrsc and 21 000 moc na images and identified more than 2200 gullies on hrsc and more than 3100 gullies in moc na data both surveys show the highest densities of gullies between 35 n and 55 n and a shift of gully orientation at 40 n from pole facing slopes to slopes facing the equator orientation trends as well as the latitudinal distribution of identified gullies strongly support the view of gully formation caused by insolation climatic conditions this result suggests that formation mechanisms based on the assumption of atmospheric water ice deposition proposed in earlier work are more likely than processes related to groundwater flow further support for a theory related to deposition is gained through observation of the high occurrence of gullies at isolated knobs and hills which cannot be associated with formation models based upon groundwater flow

degradation of mid latitude craters on mars abstract recent geomorphic remote sensing and atmospheric modeling studies have shown evidence for abundant ground ice deposits in the martian mid latitudes numerous potential water ice rich flow features have been identified in craters in these regions including arcuate ridges gullies and small flow lobes previous studies such as in newton basin have shown that arcuate ridges and gullies are mainly found in small craters 2 30 km in diameter these features are located on both pole facing and equator facing crater walls and their orientations have been found to be dependent on latitude we have conducted surveys of craters 20 km in diameter in two mid latitude regions one in the northern hemisphere in arabia terra and one in the southern hemisphere east of hellas basin in these regions prominent lobes potentially ice rich are commonly found on the walls of craters with diameters between 20 100 km additional water ice rich features such as channels valleys alcoves and debris aprons have also been found in association with crater walls in the eastern hellas study region channels were found to be located primarily on pole facing walls whereas valleys and alcoves were found primarily on equator facing walls in the arabia terra study region these preferences are less distinct in both study regions lobate flows gullies and arcuate ridges were found to have pole facing orientation preferences at latitudes below 45 and equator facing orientation preferences above 45 similar to preferences previously found for gullies and arcuate ridges in smaller craters interrelations between the features suggest they all formed from the mobilization of accumulated ice rich materials the dependencies of orientations on latitude suggest a relationship to differences in total solar insolation along the crater walls differences in slope of the crater wall differences in total solar insolation with respect to wall orientation and variations in topography along the crater rim can explain the variability in morphology of the features studied the formation and evolution of these landforms may best be explained by multiple cycles of deposition of ice rich material during periods of high obliquity and subsequent modification and transport of these materials down crater walls

global distribution of neutrons from mars results from mars odyssey global distributions of thermal epithermal and fast neutron fluxes have been mapped during late southern summer northern winter using the mars odyssey neutron spectrometer these fluxes are selectively sensitive to the vertical and lateral spatial distributions of h and co 2 in the uppermost meter of the martian surface poleward of 60 latitude is terrain rich in hydrogen probably h 2 o ice buried beneath tens of centimeter thick hydrogen poor soil the central portion of the north polar cap is covered by a thick co 2 layer as is the residual south polar cap portions of the low to middle latitudes indicate subsurface deposits of chemically and or physically bound h 2 o and or oh

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

mars global surveyor observations of martian fretted terrain the martian fretted terrain between latitudes 30 and 50 n and between 315 and 360 w has been reexamined in light of new mars orbiter camera moc and mars orbiter laser altimeter mola data from mars global surveyor much of the terrain in the 30 50 latitude belt in both hemispheres has a characteristic stippled or pitted texture at moc 1 5 m scale the texture appears to result from partial removal of a formerly smooth thin deposit as a result of sublimation and deflation a complex history of deposition and exhumation is indicated by remnants of a former thicker cover of layered deposits in some hollows and on some slopes particularly those facing the pole are smooth textured deposits outlined by an outward facing escarpment throughout the study area are numerous escarpments with debris flows at their base the escarpments typically have slopes in the 20 30 range at the base of the escarpment is commonly a deposit with striae oriented at right angles to the escarpment outside this deposit is the main debris apron with a surface that typically slopes 2 3 and complex surface textures suggestive of compression sublimation and deflation the presence of undeformed impact craters indicates that the debris flows are no longer forming fretted valleys contain lineated fill and are poorly graded they likely form from fluvial valleys that were initially like those elsewhere on the planet but were subsequently widened and filled by the same mass wasting processes that formed the debris aprons slope reversals indicate that downvalley flow of the lineated fill is minor the ubiquitous presence of breaks in slope formed by mass wasting and the complex surface textures that result from mass wasting deflation and sublimation decreases the recognizability of the shorelines formerly proposed for this area

identity and emplacement of domical structures in the western arcadia planitia mars 1 morphologic morphometric and thermophysical aspects of domical structures in a restricted part of the mars northern plains were characterized using mars odyssey and mars global surveyor data the majority of domical structures consist of relatively high thermal inertia subcircular to irregularly shaped core bodies surrounded by adjacent relatively low albedo low thermal inertia annuli and dispersed aureoles of apparently disaggregated material core profiles vary considerably from low to high aspect ratios elongate arms of material extend from the central summit regions in some of the structures core features include apparent blocky surface texture summit fissures and pits apparent summit and flank ruptures suggestive of eruption of material and concentric and straight summit ridges core heights range from 30 to 400 m mean 160 m diameters range from 620 to 3090 m mean 1550 m aspect ratios range from 0 02 to 0 36 mean 0 11 and volumes range from 0 1 to 1 8 km3 an additional morphologic type consists of subcircular domical mounds that are apparently covered by plains materials we propose that the majority of the structures are partially extrusive cryptodomes and lava domes whereas the mounds are entirely intrusive cryptodomes

combining multi scale geophysical techniques for robust hydro structural characterisation in catchments underlain by hard rock in post glacial regions summary accurate conceptual models of groundwater systems are essential for correct interpretation of monitoring data in catchment studies in surface water dominated hard rock regions modern ground and surface water monitoring programmes often have very high resolution chemical meteorological and hydrological observations but lack an equivalent emphasis on the subsurface environment the properties of which exert a strong control on flow pathways and interactions with surface waters the reasons for this disparity are the complexity of the system and the difficulty in accurately characterising the subsurface except locally at outcrops or in boreholes this is particularly the case in maritime north western europe where a legacy of glacial activity combined with large areas underlain by heterogeneous igneous and metamorphic bedrock make the structure and weathering of bedrock difficult to map or model traditional approaches which seek to extrapolate information from borehole to field scale are of limited application in these environments due to the high degree of spatial heterogeneity here we apply an integrative and multi scale approach optimising and combining standard geophysical techniques to generate a three dimensional geological conceptual model of the subsurface in a catchment in ne ireland available airborne lidar electromagnetic and magnetic data sets were analysed for the region at field scale surface geophysical methods including electrical resistivity tomography seismic refraction ground penetrating radar and magnetic surveys were used and combined with field mapping of outcrops and borehole testing the study demonstrates how combined interpretation of multiple methods at a range of scales produces robust three dimensional conceptual models and a stronger basis for interpreting groundwater and surface water monitoring data

groundwater in the celtic regions this book covers a diverse range of hydrogeological environments that occur in the celtic regions of britain and ireland these include hard rock aquifers of lower palaeozoic and precambrian age generally dominated by fracture flow within a shallow zone of weathering carboniferous limestone aquifers often characterized by conduit flows in karstic systems dual porosity permo triassic sandstone aquifers and quaternary deposits many of which form shallow granular aquifers the papers presented here address a number of current issues common to the celtic regions including groundwater protection policies groundwater management in karst aquifers groundwater development in quaternary aquifers groundwater evaluation in data scarce aquifers and groundwater supplies to small island communities

martian gullies a comprehensive review of observations mechanisms and insights from earth analogues upon their discovery in 2000 martian gullies were hailed as the first proof of recent i e less than a few million years flowing liquid water on the surface of a dry desert planet many processes have been proposed to have formed martian gullies ranging from liquid water seepage from aquifers melting of snow ice and frost to dry granular flows potentially lubricated by co2 terrestrial analogues have played a pivotal role in the conception and validation of gully formation mechanisms comparison with the terrestrial landscape argues for gully formation by liquid water debris flows originating from surface melting however limited knowledge of sediment transport by sublimation is a critical factor in impeding progress on the co2 sublimation hypothesis we propose avenues towards resolving the debate a laboratory simulations targeting variables that can be measured from orbit b applications of landscape evolution models c incorporation of the concept of sediment connectivity d using 3d fluid dynamic models to link deposit morphology and flow rheology and e a more intense exchange of techniques between terrestrial and planetary geomorphology including quantitative and temporal approaches finally we emphasize that the present may not accurately represent the past and that martian gullies likely formed by a combination of processes

evolution of periglacial landforms in the ancient mountain range of the thaumasia highlands mars possible periglacial and relict glacial landforms in the ancient mountain range of the thaumasia highlands mars are described the landforms include large scale mantling lineated crater and valley fill materials debris aprons protalus lobes and ramparts the most pristine icerelated landforms appear to be small scale protalus lobes and ramparts with no visible distinct impact craters at both medium high resolution stereo camera hrsc and high mars orbiter camera moc narrow angle na context camera ctx spatial resolution these small landforms are possibly active at present and post date more extensive features such as crater fills possibly formed during high obliquity climatic periods in contrast to the rock glacier like landforms with distribution preferentially occurring on southfacing slopes possibly controlled by enhanced exposure to the sun older less pristine lineated fill materials show a less systematic distribution of flow directions suggesting a more generalized periglacial and possibly glacial environment in the thaumasia highlands

major episodes of the hydrologic history in the region of hesperia planum mars 1 the high resolution stereo color camera hrsc data over hesperia planum and its surroundings reveal important details of geologic episodes and water related processes in this region 1 the noachian fluvial events of hesperia planum depression included accumulation of water and formation of a water ice reservoir there later the reservoir was depleted in several phases reflecting diminishing amounts of water climate changes and or volcanism were important in these volatile releases 2 the massive 0 45 1 5 106 km3 erosion from the hesperia depression before the main lava eruption possibly resulted in thick 0 5 1 5 km deposits in hellas planitia 3 measurements of the flooded craters within hesperia planum provide the estimates of the thickness of lavas there about 250 500 m the final volume of lavas within hesperia planum 0 4 0 7 106 km3 is comparable with the range of some terrestrial igneous provinces such as columbia river basalts 4 extended magmatism possibly triggered formation of the outflow channel in a few locations after the lava emplacement during this episode about 0 04 106 km3 of material about 4 5 8 9 of the volume eroded in the episode of massive erosion were removed the thickness of the composite lava layer exposed on the walls of the outflow channels a few hundreds of meters corresponds well to the thickness estimates made by the measurements of the flooded craters 5 dispersed viscous flows debris aprons flow like deposits reflect the final fluvial events viscous flows from the subsurface sources in the southwestern trough associate with dao niger and harmakhis valles these flows represent the final volatile discharge from the hesperia reservoir that mostly was depleted by the earlier events of massive erosion and formation of the outflow channels viscous surface flows are mostly associated with reull vallis and probably reflect redistribution of volatiles related to the late episodes of evolution of this outflow channel

surface characteristics and degradational history of debris aprons in the tempe terra mareotis fossae region of mars abstract we have documented the surface characteristics and degradational history of a population of 65 lobate debris aprons in the tempe terra mareotis fossae region of mars these aprons were compared to other martian debris aprons to evaluate similarities and differences among different populations which can provide insight into the dominant controls on apron development tempe mareotis debris aprons found at the bases of isolated or clustered massifs escarpments and crater interior walls were studied using viking orbiter mars global surveyor and mars odyssey datasets in a gis database six textures related to degradation of apron surfaces are identified in moc images and they are divided into two groups an upper surface group and a lower surface group degradation occurs within an inferred smooth upper surface mantle of ice and debris producing a sequence of pitted ridge and valley and knobby textures of the upper surface group where upper surface materials have been removed smooth and ridged textures of the lower surface group are exposed degradation to various depths may expose lower surface materials which may consist of the main apron mass remnants of mantling deposits or both a combination of geologic processes may have caused the degradation including ice sublimation ice melt and eolian activity apron surfaces have lower maximum thermal inertias and mean surface temperatures than adjacent plains surfaces which may be explained by the trapping of unconsolidated materials in low lying pits and valleys formed by surface degradation or from the disruption of crusts on degraded portions of apron surfaces one feature observed only on tempe mareotis debris aprons are broad ridges which mimic the shape of massif bases for tens of kilometers we propose these to be constructional features that could have formed during cycles of increased debris production apron morphometric parameters including area volume slope thickness relief and h l were compiled and the results show that tempe mareotis aprons have average surface areas volumes and frontal thicknesses that are 2 3 times smaller than eastern hellas aprons within the tempe mareotis population escarpment related aprons are larger than massif related aprons suggesting that aprons with larger source areas have potentially greater volatile accumulation translating into longer apron travel distances and lower h l values

sub kilometre intra crater mounds in utopia planitia mars character occurrence and possible formation hypotheses abstract at the middle latitudes of utopia planitia 35 45 n 65 101 e hundreds of small sized mounds located in sub kilometre impact craters dot the landscape their shape varies from circular to crescentic and their height ranges from 10 to 50 m often metre to decametre pitting is observed as is metres thick banding or stratification mound albedo is relatively high i e 0 16 the plain s terrain in the region previously linked to the latitude dependent mantle ldm of ice dust displays pitting and albedo similar to the small intra crater mounds some workers have suggested that the mounds and the plain s terrain share a common ice dust origin if so then scrutinising the mounds could provide analogical insight on the key geological characteristics and spatial distribution of the ldm itself other workers have hypothesised that the mounds are eroded sedimentary landforms or periglacial mounds underlain by a perennial ice core closed system pingos in this article we develop and then discuss each of the three mound hypotheses in a much more substantial manner than has been done hitherto towards this end we use high resolution images present a detailed regional map of mound distribution and establish a regional platform of topographical analysis using mola data superposed on a large scale ctx mosaic although the ice dust hypothesis is consistent with some observations and measurements we find that a loess based sedimentary hypothesis shows greater plausibility of the three hypotheses evaluated the pingo or periglacial one is the weakest

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

lineated valley fill and lobate debris apron stratigraphy in nilosyrtis mensae mars evidence for phases of glacial modification of the dichotomy boundary 1 the nilosyrtis mensae region is important among dichotomy boundary fretted terrain outcrops as it provides evidence of overprinting of ancient landscapes by a suite of glacial features providing a composite view of the variety of midlatitude glacial modification processes that can occur during recent martian ice ages on the basis of a series of criteria developed for the identification of a glacial origin for lineated valley fill and lobate debris aprons we interpret stratigraphic topographic and textural relationships between lineated valley fill and lobate debris apron morphological units as evidence of local and regional glacial overprinting of the landscape during the recent amazonian we document 1 stratigraphic relationships between lineated valley fill subunits including the presence of apparently superposed and small scale lobate features 2 the regional integration and flow of lineated valley fill material 3 lineated valley fill degradation and 4 the nature and stratigraphic position of lobate debris aprons these observations suggest multiple phases or episodes of midlatitude valley glacier activity these observations together with those of surface units elsewhere in northern arabia terra interpreted as glacially modified landforms suggest the possibility of midlatitude glacial deposits extending over broad portions of the martian dichotomy boundary within the past several hundred million years

stratigraphical evidence of late amazonian periglaciation and glaciation in the astapus colles region of mars abstract recent modeling of the meteorological conditions during and following times of high obliquity suggests that an icy mantle could have been emplaced in western utopia planitia by atmospheric deposition during the late amazonian period costard f m forget f madeleine j b soare r j kargel j s 2008 lunar planet sci 39 abstract 1274 madeleine b forget f head j w levrard b montmessin f 2007 lunar planet sci 38 abstract 1778 astapus colles aba is a late amazonian geological unit located in this hypothesized area of accumulation that comprises an icy mantle tens of meters thick tanaka k l skinner j a hare t m 2005 us geol surv sci invest map 2888 for the most part this unit drapes the early amazonian vastitas borealis interior unit abvi to a lesser degree it overlies the early amazonian vastitas borealis marginal unit abvm and the early to late hesperian up plains unit hbu2 tanaka k l skinner j a hare t m 2005 us geol surv sci invest map 2888 landscapes possibly modified by late amazonian periglacial processes costard f m kargel j s 1995 icarus 114 93 112 mcbride s a allen c c bell m s 2005 lunar planet sci 36 abstract 1090 morgenstern a hauber e reiss d van gasselt s grosse g schirrmeister l 2007 j geophys res 112 doi 10 1029 2006je002869 e06010 seibert n m kargel j s 2001 geophys res lett 28 899 902 soare r j kargel j s osinski g r costard f 2007 icarus 191 95 112 soare r j osinski g r roehm c l 2008 earth planet sci lett 272 382 393 and glacial processes milliken r e mustard j f goldsby d l 2003 j geophys res 108 e6 doi 10 1029 2002je002005 5057 mustard j f cooper c d rifkin m k 2001 nature 412 411 414 tanaka k l skinner j a hare t m 2005 us geol surv sci invest map 2888 have been reported within the region researchers have assumed that the periglacial and glacial landscapes occur within the same geological unit the aba i e morgenstern a hauber e reiss d van gasselt s grosse g schirrmeister l 2007 j geophys res 112 doi 10 1029 2006je002869 e06010 tanaka k l skinner j a hare t m 2005 us geol surv sci invest map 2888 in this study we use hirise high resolution image science experiment mars reconnaissance orbiter imagery to identify the stratigraphical separation of the two landscapes and show that periglacial landscape modification has occurred in the geological units that underlie the aba not in the aba itself moreover we suggest that the periglacial landscape extends well beyond the perimeter of the aba and could be the product of wet cold climate processes these processes involve freeze thaw cycles and intermittently stable liquid water at or near the surface by contrast we propose that the aba is a very recent late amazonian geological unit formed principally by dry cold climate processes these processes comprise accumulation by atmospheric deposition and ablation by sublimation

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

tropical mountain glaciers on mars altitude dependence of ice accumulation accumulation conditions formation times glacier dynamics and implications for planetary spin axis orbital history abstract fan shaped deposits up to 166 000 km 2 in area are found on the northwest flanks of the huge tharsis montes volcanoes in the tropics of mars recent spacecraft data have confirmed earlier hypotheses that these lobate deposits are glacial in origin increased knowledge of polar latitude terrestrial glacial analogs in the antarctic dry valleys has been used to show that the lobate deposits are the remnants of cold based glaciers that formed in the extremely cold hyper arid climate of mars mars atmospheric general circulation models gcm show that these glaciers could form during periods of high obliquity when upwelling and adiabatic cooling of moist air favor deposition of snow on the northwest flanks of the tharsis montes we present a simulation of the tharsis montes ice sheets produced by a static accumulation pattern based on the gcm results and compare this with the nature and extent of the geologic deposits we use the fundamental differences between the atmospheric snow accumulation environments mass balance on earth and mars geological observations and ice sheet models to show that two equilibrium lines should characterize ice sheet mass balance on mars and that glacial accumulation should be favored on the flanks of large volcanoes not on their summits as seen on earth predicted accumulation rates from such a parameterization together with sample spin axis obliquity histories are used to show that obliquity in excess of 45 and multiple 120 000 year obliquity cycles are necessary to produce the observed deposits our results indicate that the formation of these deposits required multiple successive stages of advance and retreat before their full extent could be reached and thus imply that spin axis obliquity remained at these high values for millions of years during the late amazonian period of mars history spin axis obliquity is one of the main factors in the distribution and intensity of solar insolation and thus in determining the climate history of mars unfortunately reconstruction of past climate history is inhibited by the fact that the chaotic nature of the solution makes the calculation of orbital histories unreliable prior to about 20 ma ago we show however that the geological record combined with glacial modeling can be used to provide insight into the nature of the spin axis orbital history of mars in the late amazonian and to begin to establish data points for the geologically based reconstruction of the climate and orbital history of mars

mars nature and evolution of young latitude dependent water ice rich mantle 1 high resolution altimetry and imaging have revealed the presence of a meters thick sedimentary layer at middle to high northern and southern latitudes presently covering at least 23 of the planet the layer is interpreted to be water ice rich and to undergone degradation recently its activity very likely coincided with the last major obliquity excursion a few hundred thousand years ago the majority of the layer at higher latitudes however persisted for a much longer time in the late amazonian stratigraphic analysis suggests a complex history of successive episodes of deposition and removal repeated deposition and removal of the mantles are interpreted to be responsible for the unusual statistical properties of kilometer scale topography in the transitional mid latitude zones

a recent ice age on mars evidence for climate oscillations from regional layering in mid latitude mantling deposits 1 two end member hypotheses have been proposed to account for the emplacement and distribution of ice in the near subsurface of mars at mid to high latitudes during recent spin axis orbital variation induced climate change in the first diffusion of atmospheric water vapor into and out of a porous regolith forms ice cemented soils whose latitudinal stability migrates as a function of orbitally controlled climatic conditions in the alternative hypothesis atmospheric deposition of ice snow and dust produces dusty ice rich layers during periods of higher obliquity new image data reveal meters thick layered deposits exposed on mid latitude pole facing slopes supporting the latter hypothesis these observations suggest that the near surface ice detected by the grs instrument suite and the phoenix lander at high latitudes is linked to thick buried ice that was atmospherically deposited during recent ice ages and that significant amounts of subsurface ice may remain today in the 30 50 mid latitude regions where fresh craters imaged by hirise expose abundant ice

fresh shallow valleys in the martian midlatitudes as features formed by meltwater flow beneath ice significant numbers of valleys have been identified in the martian midlatitudes 30 60 n s spatially associated with extant or recent ice accumulations many of these valleys date to the amazonian but their formation during these cold dry epochs is problematic in this study we look in detail at the form distribution and quantitative geomorphology of two suites of these valleys and their associated landforms in order to better constrain the processes of their formation since the valleys themselves are so young and thus well preserved uniquely we can constrain valley widths and courses and link these to the topography from the mars orbiter laser altimeter and high resolution stereo camera data we show that the valleys are both qualitatively and quantitatively very similar despite their being 5000 km apart in different hemispheres and around 7 km apart in elevation buffered crater counting indicates that the ages of these networks are statistically identical probably forming during the late amazonian 100 ma in both localities at least tens of valleys cross local drainage divides apparently flowing uphill we interpret these uphill reaches to be characteristic of flow occurring beneath a now absent relatively thin order 101 102 m regionally extensive ice cover ridges and mounds occasionally found at the foot of these valley systems are analogous to eskers and aufeis like refreezing features on the basis of their interaction with these aufeis like mounds we suggest that this suite of landforms may have formed in a single short episode perhaps order of days probably forced by global climate change

chemical composition of martian fines of the 21 samples acquired for the viking x ray fluorescence spectrometer 17 were analyzed to high precision compared to typical terrestrial continental soils and lunar mare fines the martian fines are lower in al higher in fe and much higher in s and cl concentrations protected fines at the two lander sites are almost indistinguishable but concentration of the element s is somewhat higher at utopia duricrust fragments successfully acquired only at the chryse site invariably contained about 50 higher s than fines no elements correlate positively with s except cl and possibly mg a sympathetic variation is found among the triad si al ca positive correlation occurs between ti and fe sample variabilities are as great within a few meters as between lander locations 4500 km apart implying the existence of a universal martian regolith component of constant average composition the nature of the source materials for the regolith fines must be mafic to ultramafic

temporal variability of phosphorus fractions in irish karst springs transfer pathways of phosphorus p from soil to surface waters are the subject of much current research because of concerns about eutrophication however p transfer via groundwater discharge has received little attention temporal p changes at eight carboniferous limestone karst springs from two catchments in western ireland are examined the eight springs were sampled fortnightly between june and october 1999 and thereafter monthly until february 2000 each sample was analysed for total p tp total dissolved p tdp and dissolved reactive p drp total p exhibited some hydrological response at all springs e g increase from 45 to 107 g l 1 reflecting significant changes in particulate p pp e g increase from 7 to 44 g l 1 and dissolved organic p dop e g increase from 0 to 27 g l 1 with drp displaying greatest temporal stability greatest response to rainfall events occurred after the first major autumnal rains in september 1999 when there appeared to be dislodging of loosely bound pp and dop which was transported to groundwater this response to the first autumnal rains probably reflects the hydrological switch where the catchments change from a soil moisture deficit to a soil moisture surplus situation daily autosampling demonstrated tp concentrations of up to 1 814 g l 1 due to local pollution highlighting the need to adopt storm event driven sampling rather than discrete sampling in karstic springs identification and management of springs in karst areas with associated point recharge via swallow holes presents an urgent and demanding challenge

introduction to the 4th mars polar science and exploration conference special issue five top questions in mars polar science abstract as an introduction to this icarus special issue for the 4th mars polar science and exploration conference we discuss five key questions in mars polar science gleaned from plenary discussions and presentations held at the conference these questions highlight major unknowns in the field 1 what are the physical characteristics of the polar layered deposits pld and how are the different geologic units within beneath and surrounding the pld related 2 how old are the pld and what are their glacial fluvial depositional and erosional histories 3 what are the mass and energy budgets of the pld and what processes control these budgets on seasonal and longer timescales 4 what chronology compositional variability and record of climatic change is expressed in the stratigraphy of the pld 5 how have volatiles and dust been exchanged between polar and non polar reservoirs and how has this exchange affected the past and present distribution of surface and subsurface ice

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

isidis basin site of ancient volatile rich debris layer abstract the interior plains of the isidis impact basin on mars contain landforms which have previously been interpreted as volcanic features these landforms can be classified into two broad units hillocky terrain and ridged terrain hillocky terrain the most central unit consists of isolated mounds commonly arranged in arcuate chains ridged terrain contains systems of parallel curvilinear ridges and occurs in a narrow band almost completely encircling the hillocky terrain ridges range from approximately 10 to 40 km long 0 5 to 1 0 km wide and 0 15 to 0 3 km high ridge properties and their distribution within isidis appear inconsistent with characteristics of typical volcanic fields on earth and mars alternatively we suggest that the isidis landforms reflect the deposition and subsequent removal of a thick layer of material within the basin crater statistics and the morphology of additional features within isidis provide further evidence that a major resurfacing event occurred within the basin although depositional and erosional processes are currently minimal terrestrial ice cover disintegration results in the development of landforms such as moraines kames and eskers and provides possible analogs for the features which occur in isidis the isidis cover however probably contained a vast amount of debris remained stationary throughout most of its existence and eventually sublimated thus differing from most terretrial glaciers a global survey of viking orbiter images reveals ridges elsewhere on mars with similar characteristics or spatial distribution thereby indicating that the isidis layer may have been part of a more widespread epoch of deposition this epoch possibly coincided with the period of major outflow channel formation when subsurface volatiles were released

landscape evolution in martian mid latitude regions insights from analogous periglacial landforms in svalbard periglacial landforms on spitsbergen svalbard norway are morphologically similar to landforms on mars that are probably related to the past and or present existence of ice at or near the surface many of these landforms such as gullies debris flow fans polygonal terrain fractured mounds and rock glacier like features are observed in close spatial proximity in mid latitude craters on mars on svalbard analogous landforms occur in strikingly similar proximity which makes them useful study cases to infer the spatial and chronological evolution of martian coldclimate surface processes the analysis of the morphological inventory of analogous landforms on svalbard and mars allows the processes operating on mars to be constrained different qualitative scenarios of landscape evolution on mars help to better understand the action of periglacial processes on mars in the recent past

effects of obliquity and water vapor trace gas greenhouses in the early martian climate 1 we explore possible mechanisms for the generation of warm wet climates on early mars as a result of greenhouse warming by both water vapor and periodic volcanic trace emissions the presence of both water vapor a strong greenhouse gas and other trace greenhouse gases such as so2 in a predominantly co2 atmosphere may act under certain conditions to elevate surface temperatures above the freezing point of liquid water at least episodically variations in obliquity are explored to investigate whether these periodic variations in insolation at mars can broaden the regions or seasons where warm temperatures can exist we use the mars weather research and forecasting general circulation model to perform several simulations of the conditions of the early martian atmosphere containing these gases and find global temperatures to be cooler than the elevated levels suggested by at least one recent study by johnson et al 2008 while achieving temperatures above 273 k globally remains challenging the additional warming by greenhouse gases under certain obliquity states can permit for widespread seasonally warm conditions which can help to explain the presence of fluvial surface features e g valley networks and hydrous minerals of post noachian age a period when alternate methods do not convincingly explain the sustainability of liquid water furthermore we find that global warming can be achieved with the presence of a darker surface globally which is consistent with both widespread exposure of unweathered basaltic bedrock or the presence of a large surface ocean or sea

former extent of glacier like forms on mars abstract mars mid latitude glacier like forms glfs have undergone substantial mass loss and recession since a hypothesised last martian glacial maximum lmgm stand to date there is a lack of knowledge of the nature and timing of the lmgm the subsequent mass loss and whether this mass loss has been spatially variable here we present the results of a population scale inventory of recessional glfs derived from analysis of 1293 glfs 3 identified within context camera ctx imagery to assess the distribution and controls on glf recession a total of 436 glfs were identified showing strong evidence of recession 197 in the northern hemisphere and 239 in the southern hemisphere relative to their parent populations recessional glfs are over represented in the low latitude belts between 25 and 40 and in areas of high relief suggesting that these zones exert some control over glf sensitivity and response to forcing this analysis is complemented by the reconstruction of the maximum extent and morphology of a specific glf for which high resolution imaging science experiment hirise derived digital elevation data are available using nye s nye j f 1951 proc roy soc lond ser a mat phys sci 207 554 572 perfect plastic approximation of ice flow applied to multiple flow lines under an optimum yield strength of 22 kpa we calculate that the reconstructed glf has lost an area of 6 86 km 2 with a corresponding volume loss of 0 31 km 3 since the lmgm assuming the loss reconstructed at this glf occurred at all mid latitude glfs yields a total planetary ice loss from mars glfs of 135 km 3 similar to the current ice volume in the european alps on earth

acheron fossae mars tectonic rifting volcanism and implications for lithospheric thickness 1 the acheron fossae region is an ancient crustal block exposed in the northwestern tharsis province on mars it is named after the acheron fossae a particularly well developed system of extensional tectonic grabens this study is the first to describe the tectonic inventory in detail using topographic and image data from the global surveyor and mars express missions we see the extensional tectonics along the east west trending topographic high of acheron fossae as a surface expression of upwelling asthenospheric material that initiated regional uplift crustal extension and breakup and associated volcanic activity in noachian time the tectonic architecture and the dimensions of the extensional structures are comparable to those of terrestrial continental rifts an area of elevated topography and strong erosion which constitutes a regional landmark in the eastern acheron fossae region is interpreted as a rift related center of volcanism caused by local magmatic uprise and involvement of the lithosphere the extension across the acheron fossae reaches values between 1 2 km and 8 7 km comparable to young continental rifts on earth crater statistics indicate an absolute cratering model age between 3 9 ga and 3 7 ga for the rifting the uplift observed on the flanks of the acheron fossae indicates a fairly thin and thus hot lithosphere using flexural analysis we have constrained the elastic lithosphere thickness at the time of rifting to 8 9 11 3 km corresponding to thermal gradients between 28 and 41 k km 1 these heat flows are substantially larger than noachian heat flow values previously reported but are consistent with the presence of rift related volcanism and a magmatically very active environment

scalloped terrains in the peneus and amphitrites paterae region of mars as observed by hirise abstract the peneus and amphitrites paterae region of mars displays large areas of smooth geologically young terrains overlying a rougher and older topography these terrains may be remnants of the mid latitude mantle deposit which is thought to be composed of ice rich material originating from airfall deposition during a high obliquity period less than 5 ma ago within these terrains there are several types of potentially periglacial features in particular there are networks of polygonal cracks and scalloped shaped depressions which are similar to features found in utopia planitia in the northern hemisphere this area also displays knobby terrain similar to the so called basketball terrains of the mid and high martian latitudes we use recent high resolution images from the high resolution imaging science experiment hirise along with data from previous mars missions to study the small scale morphology of the scalloped terrains and associated polygon network and knobby terrains we compare these with the features observed in utopia planitia and attempt to determine their formation process while the two sites share many general features scallops in peneus amphitrites paterae lack the diverse polygon network i e there is little variation in the polygon sizes and shapes and large curvilinear ridges observed in utopia planitia this points to a more homogeneous ice content within the substrate in the peneus amphitrites paterae region and implies that scallop formation is independent of polygon formation this work shows that as in utopia planitia sublimation of interstitial ice is a likely process explaining the formation of the scalloped depressions in the region of peneus amphitrites paterae therefore we provide a simplified scallop formation model based on sublimation of interstitial ice as proposed for utopia planitia we also show that the differences in scallop morphologies between the two regions may be explained by differences in near surface ice content sublimation rates and age of formation of the scalloped terrains

decameter scale pedestal craters in the tropics of mars evidence for the recent presence of very young regional ice deposits in tharsis abstract global climate models predict that ice will be deposited in tropical regions during obliquity excursions from the current mean obliquity of 25 to 35 but no geological evidence for such deposits has been reported we document the presence of very small decameter scale pedestal craters in the tropics of mars the daedalia planum tharsis region that are superposed on an impact crater dated to 12 5 ma ago the characteristics abundance and distribution of these small pedestal craters provide geological evidence that meters thick ice accumulations existed in the tropical tharsis region of mars in the last few million years when mean obliquity was 35 5 15 ma before it transitioned to a mean of 25 0 3 ma a reconnaissance survey reveals similar small pedestal crater examples superposed on the older amazonian arsia mons tropical mountain glacier deposit suggesting that ice can accumulate in these tropical regions without initiating large scale glacial conditions these results support the predictions of general circulation models that ice can migrate to the equatorial regions during periods of moderate obliquity and then serve as a source for mid latitude deposits

evidence for very recent melt water and debris flow activity in gullies in a young mid latitude crater on mars abstract terrestrial debris flows and their deposits are mainly studied and monitored because of their hazardous nature on mars they may serve as geomorphologic indicators of transient liquid water we compared the morphology of debris flow like deposits within a young 0 2 ma mid latitude crater on mars with debris flow fans on svalbard as possible terrestrial analogues it was our objective to constrain whether dry granular flow or processes related to water saturation at or close to the surface were responsible for the formation of the deposits within the crater we found that the morphological attributes of the deposits on mars are very similar to debris flows in svalbard and include overlapping terminal lobes debris tongues and snouts debris flow fans scoured channels with medial deposits debris plugs and clearly defined lateral deposits levees furthermore the interior crater walls display a range of landforms indicating aspect dependent degradation ranging from debris flow dominated pole facing slopes to east and west facing single channel gullies and north facing talus cones granular flow our findings suggest that the debris flows are not related to impact induced heating and release of meltwater we further suggest that degradation of a latitude dependent dust ice mantling unit may only have played a minor role in this youthful terrain instead we propose that the debris flows are mainly formed by melting of very recent snow deposits after the termination of the last martian ice age as such they may represent some of the most recent geomorphological indicators of transient liquid water in the martian mid latitudes the distinct north south asymmetry in degradation further demonstrates that insolation controlled slope processes are surprisingly efficient on mars during the last

statistics of mars topography from the mars orbiter laser altimeter slopes correlations and physical models data obtained recently by the mars orbiter laser altimeter mola were used to study the statistical properties of the topography and slopes on mars we find that the hemispheric dichotomy manifested as an elevation difference can be described by long baseline tilts but in places is expressed as steeper slopes the bimodal hypsometry of elevations on mars becomes unimodal when referenced to the center of figure contrary to the earth for which the bimodality is retained however ruling out a model in which the elevation difference is expressed in a narrow equatorial topographic step cannot be done by the hypsometry alone mars slope distribution is longer tailed than those of earth and venus indicating a lower efficiency of planation processes relative to relief building tectonics and volcanics we define and compute global maps of statistical estimators including the interquartile scale rms and median slope and characteristic decorrelation length of the surface a correspondence between these parameters and geologic units on mars is inferred surface smoothness is distinctive in the vast northern hemisphere plains where slopes are typically 0 5 amazonis planitia exhibits a variation in topography of 1 m over 35 km baselines the region of hematite mineralization in sinus meridiani is also smooth with median slopes lower than 0 4 but does not form a closed basin the shallower long wavelength portion of the lowlands topographic power spectrum relative to the highlands can be accounted for by a simple model of sedimentation such as might be expected at an ocean s floor the addition of another process such as cratering is necessary to explain the spectral slope in short wavelengths among their application these mola derived roughness measurements can help characterize sites for landing missions

sea water groundwater interactions along a small catchment of the european atlantic coast abstract the geochemistry and isotopic composition of a karstic coastal aquifer in western ireland has shed light on the effect of sea water groundwater interactions on the water quality of ireland s atlantic coastal zone the use of stable isotope data from the iaea precipitation station in valentia located in sw ireland has facilitated the characterization of groundwater recharge conditions in the western part of ireland and suggests that groundwater is mostly replenished by the isotopically light winter precipitation the dissolved so 4 2 in the karstic groundwater that was collected during baseflow conditions with 34s values between 4 6 and 18 may be composed of s stemming from three principal sources so 4 2 derived from precipitation which is composed of both sea spray s 34s 20 and an isotopically light anthropogenic source 34s 1 5 so 4 2 stemming from animal slurries 34s 5 and intruding sea water so 4 2 34s 20 2 the isotopic composition of 18o in dissolved groundwater so 4 2 collected during baseflow conditions is interpreted as reflecting sea water intrusion to the karstic coastal groundwater system the highest 18o values in dissolved groundwater so 4 2 were in samples collected near the coast 4 8 0 4 and the lowest 2 0 5 were collected further inland the 15n and 18o values of groundwater no 3 were between 3 4 and 11 4 and approximately 7 7 respectively and reflect geochemical conditions in the aquifer that do not promote attenuation of no 3 through denitrification as a result n loading to kinvara bay that is controlled by submarine groundwater discharge sgd was calculated as 5 tons day on average compared to an estimated n input that derives from precipitation of approximately 2 5 tons a sgd into the bay may result in near coastal sea water quality changes these results represent one of the first studies addressing the effect of groundwater quality in ireland on the european atlantic coastal zone

initiation and flow conditions of contemporary flows in martian gullies understanding the initial and flow conditions of contemporary flows in martian gullies generally believed to be triggered and fluidized by co2 sublimation is crucial for deciphering climate conditions needed to trigger and sustain them we employ the ramms rapid mass movement simulation debris flow and avalanche model to back calculate initial and flow conditions of recent flows in three gullies in hale crater we infer minimum release depths of 1 0 1 5 m and initial release volumes of 100 200 m3 entrainment leads to final flow volumes that are 2 5 5 5 times larger than initially released and entrainment is found necessary to match the observed flow deposits simulated mean cross channel flow velocities decrease from 3 4 m s 1 to 1 m s 1 from release area to flow terminus while flow depths generally decrease from 0 5 1 m to 0 1 0 2 m the mean cross channel erosion depth and deposition thicknesses are 0 1 0 3 m back calculated dry coulomb friction ranges from 0 1 to 0 25 and viscous turbulent friction between 100 200 m s 2 which are values similar to those of granular debris flows on earth these results suggest that recent flows in gullies are fluidized to a similar degree as are granular debris flows on earth using a novel model for mass flow fluidization by co2 sublimation we are able to show that under martian atmospheric conditions very small volumetric fractions of co2 of 1 within mass flows may indeed yield sufficiently large gas fluxes to cause fluidization and enhance flow mobility

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

the distribution and behavior of martian ground ice during past and present epochs mars undergoes significant oscillations in its orbit which will have a pronounced effect on its climate and in particular on the behavior of subsurface water ice we explore and map the behavior of ice in the martian near surface regolith over the past 1 m y using a diffusion and condensation model presented in an earlier paper with two primary modifications to include orbitally induced variations in insolation and atmospheric water abundance we find that the past behavior of ground ice differs significantly from that at the present epoch primarily the result of high amplitude oscillations in obliquity presently 25 in midlatitude and equatorial regions ground ice will condense from atmospheric water during times of higher obliquity filling the top few meters of the regolith with significant amounts of ice at an obliquity of 32 ground ice becomes stable globally during times of lower obliquity ground ice will sublime and diffuse back into the atmosphere dessicating the regolith to a depth of about 1 to 2 m equatorward of 60 to 70 latitude in the high latitude regions these oscillations are considerably subdued below this depth of cyclic saturation and dessication a long term stability of ice exists in some geographic regions we present a map of the distribution of ice expected at the present epoch cyclic exchange of water between the global regolith and polar regions will have significant implications for surface geology and the polar layered deposits

an assessment of evidence for pingos on mars using hirise pingos are small hills with cores of ice formed by injection and freezing of pressurized water the possibility of pingos on mars is of particular interest because of the associated implications for liquid water we have systematically searched for candidate pingos using images from the high resolution imaging science experiment hirise camera since pingos are expected to develop surface fractures due to extension of the frozen ground over the ice core we have searched for fractured features and identified a variety of mounds these features are confined to the martian mid latitudes in the bands where gullies are also most common the observed fractured mounds have a variety of morphologies and are likely of multiple origins isolated fractured mounds found on the floors of gullied craters in the southern hemisphere match the general morphologic characteristics of terrestrial pingos and are the best candidates for martian pingos but there is currently no direct evidence for presence of ice cores and it is difficult to produce the necessary water volumes so these features should still be interpreted with caution other fractured mounds appear more likely to be erosional remnants of an unusual mantling layer or possibly thermokarst structures flat topped mounds in utopia have some characteristics fracture pattern and latitudinal distribution consistent with pingos but differ in other aspects such as shape and setting while we do not rule out a pingo origin we prefer an erosional model for these enigmatic features

new slope normalized global gully density and orientation maps for mars we reanalyse the global distribution of gullies in order to provide a set of observational constraints that models of gully formation must explain we validate our results derived from the global data with four detailed case studies we show that the availability of steep slopes is an essential factor to consider when assessing the spatial distribution and abundance of gullies when the availability of steep slopes is taken into account it reveals with a few exceptions that gullies are found almost uniformly across the whole 30 90 latitude band our analysis also reveals that massive ice deposits are anti correlated with gullies and that the undulations in the equatorwards limits of the gully distribution could be explained by longitudinal variations in maximum surface temperatures controlled by variations in surface properties including thermal inertia and albedo we find a sharp transition in both hemispheres between pole facing gullies which extend from 30 to 40 to a more mixed but dominantly equator facing orientation of gullies polewards of 40 we have no definitive explanation for this transition but based on previous studies we suggest it could be linked to the availability of near surface ice deposits

constraints on the formation and properties of a martian lobate debris apron insights from high resolution topography sharad radar data and a numerical ice flow model

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

ice rich periglacial vs icy glacial depressions in the argyre region mars a proposed cold climate dichotomy of landforms on mars so called scalloped depressions are widely observed in utopia planitia up and malea planum mp typically they are rimless metres to decametres deep incised sharply tiered inwardly polygonised and sometimes pitted the depressions seemingly incise terrain that is icy and possibly thermokarstic i e produced by the thermal destabilisation of the icy terrain agewise the depressions are thought to be relatively youthful originating in the late amazonian epoch here we report the presence of similar depressions in the argyre region ar 30 60 s 290 355 e more importantly we separate and differentiate these landforms into two groups ice rich periglacial depressions type 1 and icy glacial depressions type 2a c this differentiation is presented to the mars community for the first time based on a suite of morphological and geological characteristics synonymous with ice complexes in the lena peninsula eastern russia and the tuktoyaktuk coastlands northwest territories canada we propose that the type 1 depressions are ice rich periglacial basins that have undergone volatile depletion largely by sublimation and as the result of thermal destabilisation in keeping with the terms and associated definitions derived of terrestrial periglacial geomorphology ice rich refers to permanently frozen ground in which ice lenses or segregation ice collectively referenced as excess ice have formed we suggest that the depressions are the product of a multi step cold climate geochronology 1 atmospheric precipitation and surface accumulation of an icy mantle during recent high obliquities 2 regional or local triple point conditions and thaw evaporation of the mantle either by exogenic forcing i e obliquity driven rises of aerial and sub aerial temperatures or endogenic forcing i e along argyre impact related basement structures 3 meltwater migration into the regolith at least to the full depth of the depressions 4 freeze thaw cycling and the formation of excess ice 5 sublimation of the excess ice and depression formation as high obliquity dissipates and near surface ice becomes unstable the type 2 depressions exhibit characteristics suggestive of supra glacial dead ice basins and snow ice suncups observed in high alpine landscapes on earth e g the swiss alps and the himalayas like the type 1 depressions the type 2 depressions could be the work of sublimation however the latter differ from the former in that they seem to develop within a glacial like icy mantle that blankets the surface rather than within an ice rich and periglacially revised regolith at near the surface interestingly the type 2 depressions overlie the type 1 depressions at some locations if the periglacial glacial morphological and stratigraphical dichotomy of depressions is valid then this points to recent glaciation at some locations within the ar being precursed by at least one episode of periglaciation this also suggests that periglaciation has a deeper history in the region than has been thought hitherto moreover if the hypothesised differences amongst the argyre based depressions are mirrored in utopia planitia and malea planum then perhaps this periglacial glacial dichotomy and its associated geochronology are as relevant to understanding late period landscape evolution in these two regions as it is in the ar

preservation of late amazonian mars ice and water related deposits in a unique crater environment in noachis terra age relationships between lobate debris tongues and gullies abstract the amazonian period of mars has been described as static cold and dry recent analysis of high resolution imagery of equatorial and mid latitude regions has revealed an array of young landforms produced in association with ice and liquid water because near surface ice in these regions is currently unstable these ice and water related landforms suggest one or more episodes of martian climate change during the amazonian here we report on the origin and evolution of valley systems within a degraded crater in noachis terra asimov crater the valleys have produced a unique environment in which to study the geomorphic signals of amazonian climate change new high resolution images reveal hesperian aged layered basalt with distinctive columnar jointing capping interior crater fill and providing debris via mass wasting for the surrounding annular valleys the occurrence of steep slopes 20 relatively narrow sheltered valleys and a source of debris have provided favorable conditions for the preservation of shallow ice deposits detailed mapping reveals morphological evidence for viscous ice flow in the form of several lobate debris tongues ldt superimposed on ldt are a series of fresh appearing gullies with typical alcove channel and fan morphologies the shift from ice rich viscous flow formation to gully erosion is best explained as a shift in martian climate from one compatible with excess snowfall and flow of ice rich deposits to one consistent with minor snow and gully formation available dating suggests that the climate transition occurred 8 ma prior to the formation of other small scale ice rich flow features identified elsewhere on mars that have been interpreted to have formed during the most recent phases of high obliquity taken together these older deposits suggest that multiple climatic shifts have occurred over the last tens of millions of years of martian history

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

patterns of accumulation and flow of ice in the mid latitudes of mars during the amazonian evidence has accumulated that non polar portions of mars have undergone significant periods of glaciation during the amazonian period this evidence includes tropical mountain glacial deposits lobate debris aprons lineated valley fill concentric crater fill pedestal craters and related landforms some of which suggest that ice thicknesses exceeded a kilometer in many places in some places several lines of evidence suggest that ice is still preserved today in the form of relict debris coved glaciers the vast majority of deposit morphologies are analogous to those seen in cold based glacial deposits on earth suggesting that little melting has taken place although these features have been broadly recognized and their modes of ice accumulation and flow analyzed at several scales they have not been analyzed and well characterized globally despite their significance for understanding the evolution of the martian climate a major outstanding question is the global extent of accumulation and flow of ice during periods of non polar glaciation as a mechanism to address this question we outline two end member scenarios to provide a framework for further discussion and analysis 1 ice accumulation was mainly focused within individual craters and valleys and flow was largely local to regional in scale and 2 ice accumulation was dominated by global latitudinal scale cold based ice sheets similar in scale to the laurentide continental ice sheets on earth in order to assess these end members we conducted a survey of ice related features seen in context camera ctx images in each hemisphere and mapped evidence for flow directions within well preserved craters in an effort to decipher orientation preferences that could help distinguish between these two hypotheses regional hemispheric glaciation or local accumulation and flow these new crater data reveal a latitudinal dependence on flow direction at low latitudes in each hemisphere 40 45 slopes of all orientations show signs of ice accumulation and ice related flow this latitudinal onset of concentric flow of ice within craters in each hemisphere correlates directly with the lowest latitudes at which typical pedestal craters have been mapped taken together these observations demarcate an important latitudinal boundary that partitions each hemisphere into two zones 1 poleward of 45 where net accumulation of ice is interpreted to have occurred on all surfaces and 2 equatorward of 45 where net accumulation of ice occurred predominantly on pole facing slopes these results provide important constraints for deciphering the climatic conditions that characterized mars during periods of extensive amazonian non polar glaciation

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