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

age dates of valley network drainage basins and subbasins within sabae and arabia terrae mars the precise timing of valley network drainage basin formation is critical to understanding the history of water and climate on mars to determine whether there are any variations in ages within separate drainage basins and subbasins that may reflect local or regional variations in climate or resetting from resurfacing e g impact ejecta or lava flows we dated 27 basins and subbasins in sabaea and arabia terrae the age dating basin technique we employed allowed sufficient precision to give accurate ages and shows that fluvial activity within the basins and subbasins ceased at approximately the same time around the early hesperian late hesperian transition our results support the hypothesis that valley networks formed during a unique fluvial optimum that may have shut off gradually because of a global climate change that affected all areas simultaneously on mars

quantification of the ice cored moraines short term dynamics in the high arctic glaciers ebbabreen and ragnarbreen petuniabukta svalbard abstract extensive ice cored moraine complexes are common elements marking the last advance of many svalbard glaciers sediment gravity flows are among the most dynamic processes transforming these landforms the short term yearly and weekly dynamics of mass wasting processes were studied in a cm scale using repetitive topographic scanning we monitored several active sites on the forelands of two glaciers ebbabreen and ragnarbreen both of which are located near petuniabukta at the northern end of billefjorden in spitsbergen the surveys indicate high dynamic rates of landforms transformation the mean annual volume loss of sediments and dead ice for the most active parts of the moraines was up to 1 8 m a 1 however most of the transformation occurred during summer with the short term values of mean elevation changes as high as 104 mm day 1 in comparison the dynamics of the other i e non active parts of the ice cored moraines were much lower namely the mean annual lowering attributed mainly to dead ice downwasting was up to 0 3 m a 1 whereas lowering during summer was up to 8 mm day 1 our results indicate that in the case of the studied glaciers backwasting was much more effective than downwasting in terms of landscape transformation in the glacier forelands however despite the high activity of localised mass movement processes the overall short term dynamics of ice cored moraines for the studied glaciers were relatively low we suggest that as long as debris cover is sufficiently thick thicker than the permafrost s active layer depths the mass movement activity would occur only under specific topographic conditions and or due to occurrence of external meltwater sources and slope undercutting in other areas ice cored moraines remain a stable landsystem component in a yearly to decadal time scale

conductive heat flux in vc 1 and the thermal regime of valles caldera jemez mountains new mexico over 5 of heat in the western united states is lost through quaternary silicic volcanic centers including the valles caldera in north central new mexico these centers are the sites of major hydrothermal activity and upper crustal metamorphism metasomatism and mineralization producing associated geothermal resources we present new heat flow data from valles caldera core hole 1 vc 1 drilled in the southwestern margin of the valles caldera thermal conductivities were measured on 55 segments of core from vc 1 waxed and wrapped to preserve fluids these values were combined with temperature gradient data to calculate heat flow above 335 m which is probably unsaturated heat flow is 247 16 mw m 2 the only deep temperature information available is from an uncalibrated commercial log made 19 months after drilling gradients derived from uncalibrated temperature logs and conductivities are inversely correlated between 335 and 737 m indicating a conductive thermal regime and component heat fluxes over three depth intervals 335 539 m 549 628 m and 628 737 m are in excellent agreement with each other with an average of 504 15 mw m 2 temperature logs to 518 m depth with well calibrated temperature sensors result in a revised heat flow of 463 15 mw m we use shallow thermal gradient data from 75 other sites in and around the caldera to interpret the thermal regime at the vc 1 site a critical review of published thermal conductivity data from the valles caldera yields an average thermal conductivity of 1 w m 1 k 1 for the near surface tuffaceous material and we assume that shallow gradient values c km 1 are approximately numerically equal to heat flow mw m 2 heat loss from the caldera is asymmetrically distributed with higher values 400 mw m 2 or higher concentrated in the west southwestern quadrant of the caldera this quadrant also contains the main drainage from the caldera and the youngest volcanism associated with the caldera we interpret the shallow thermal gradient data and the thermal regime at vc 1 to indicate a long lived hydrothermal and magmatic system in the southwestern valles caldera that has been maintained through the generation of shallow magma bodies during the long postcollapse history of the caldera high heat flow at the vc 1 site is interpreted to result from hot water circulating below the base of the core hole and we attribute the lower heat flow in the unsaturated zone to hydrologic recharge

radar interferometry for measuring tidal strains across cracks on europa 1 a major uncertainty in understanding the interaction between the surface of europa and its ocean below is the present day activity of fractures using well constrained models for tidal strain and a force balance in a cracked shell we estimate the shear and normal displacement of cracks that penetrate upward from the base of the shell if more than half of the plate is fractured then surface displacements having amplitudes of 3 to 30 cm will be localized in a band 1 to 100 km from the crack plate spreading will occur if more than 85 of the plate is fractured the pattern of deformation is sensitive to both the percentage of plate that is cracked and the total thickness of the shell repeat pass radar interferometry could easily detect and map the activity of the cracks during a short experiment from a variety of suitable orbits with repeating ground tracks

the timing of martian valley network activity constraints from buffered crater counting abstract valley networks concentrations of dendritic channels that often suggest widespread pluvial and fluvial activity have been cited as indicators that the climate of mars differed significantly in the past from the present hyperarid cold desert conditions some researchers suggest that the change in climate was abrupt while others favor a much more gradual transition thus the precise timing of valley network formation is critical to understanding the climate history on mars we examine thirty valley network incised regions on mars including both cratered upland valley networks and those outside the uplands and apply a buffered crater counting technique to directly constrain when valley network formation occurred the crater populations that we derive using this approach allow assessment of the timing of the last activity in a valley network independent of the mapping of specific geological units from these measurements we find that valley networks cluster into two subdivisions in terms characteristics and age 1 valley network activity in the cratered highlands has an average cessation age at the noachian hesperian boundary and all valleys that we crater counted are early hesperian or older no evidence is found for valley networks in the cratered uplands of late hesperian or amazonian age the timing of the cessation of cratered upland valley network activity at the noachian hesperian boundary also corresponds to a decline in the intensity of large crater formation and degradation and to the apparent end of phyllosilicate type weathering 2 a few valley network incised regions formed outside of the cratered uplands on volcanic edifices in association with younger impact craters and on the rim of valles marineris we applied our buffered crater counting technique to four such valleys on the volcanoes ceraunius tholus hecates tholus and alba patera and on the rim of echus chasma and find that each has distinctive and different late hesperian or early amazonian ages indicating that valley networks formed from time to time in the post noachian period unlike the cratered upland valley networks these isolated occurrences are very local and have been interpreted to represent local conditions e g snowpack melted during periods of intrusive volcanic activity in contrast to a gradual cessation in the formation of valley networks proposed by some workers our new buffered crater counting results indicate a relatively abrupt cessation in the formation of the widespread cratered upland valley networks at approximately the end of the noachian followed only by episodic and very localized valley network formation in later mars history very likely due to specific conditions e g local magmatic heating these valley network ages and correlations are thus consistent with a major change in the near surface aqueous environment on mars at approximately the noachian hesperian boundary the noachian environment supported surface running water and fluvial erosion across mars in the cratered uplands enhanced crater degradation and a weathering environment favoring the formation of phyllosilicates the hesperian amazonian environment was more similar to the hyperarid cold desert of today with valley networks forming only extremely rarely and confined to localized special conditions sources of water for these latter occurrences are likely to be related to periodic mobilization and equatorward migration of polar volatiles due to variations in spin axis orbital parameters and to periodic catastrophic emergence of groundwater

valley formation by fluvial and glacial erosion cross valley profiles from the west slope of the olympic peninsula washington are used to investigate the relative effects of fluvial and glacial erosion on valley formation unlike most ranges where glaciers and rivers sequentially occupied the same valleys neighboring valleys in the olympic mountains developed in similar lithologies but were subject to different degrees of glaciation allowing comparison of the net effect of glacial and fluvial processes integrated over many glacial cycles upslope drainage area was used to normalize comparisons of valley width ridge crest to valley bottom relief and valley cross sectional area as measures of net differences in the mass of rock excavated from below ridgelines for 131 valley spanning transects valley width relief and cross sectional areas are similar for glaciated partly glaciated and unglaciated fluvial valleys with drainage areas of 10 km 2 but diverge downslope glaciated valleys draining 50 km 2 reach two to four times the cross sectional area and have to 500 m greater relief than comparable fluvial valleys partly glaciated valleys have intermediate dimensions at distances of 5 km from valley heads the cumulative upstream volume of rock removed to form valleys is two to four times greater in glacially incised valleys than in fluvial valleys the finding of strong differences in the net result of valley excavation by fluvial and glacial erosion supports the interpretation that alpine glaciers are more effective erosional agents than are rivers and implies that large alpine valleys deepened and enlarged in response to pleistocene glaciation

an evaluation of stream characteristics in glacial versus fluvial process domains in the colorado front range abstract many of the conceptual models developed for river networks emphasize progressive downstream trends in morphology and processes such models can fall short in describing the longitudinal variability associated with low order streams a more thorough understanding of the influence of local variability of process and form in low order stream channels is required to remotely and accurately predict channel geometry characteristics for management purposes and in this context designating process domains is useful we define process domains with respect to glacial versus fluvial valleys and lateral confinement of valley segments we evaluated local variability of process domains in the colorado front range by systematically following streams categorizing them into stream morphologic type and process domain and evaluating a number of channel geometry characteristics we evaluated 111 stream reaches for significant differences in channel geometry among stream types and process domains location and clustering of stream types on a slope drainage area s a plot and downstream hydraulic geometry relationships although individual channel geometry variables differed significantly between individual stream types in glacial and fluvial process domains no single channel geometry variable consistently differentiated all stream types between process domains hypothetical s a boundaries between bedrock and alluvial bed channels proposed in previous studies did not reliably divide bedrock and alluvial reaches for our study sites although downstream hydraulic geometry relationships are well defined using all reaches in the study area reaches in glacial valleys display much more variability in channel geometry characteristics than reaches in fluvial valleys less pronounced downstream hydraulic geometry relationships and greater scatter of reaches on an s a plot local spatial variability associated with process domains at the reach scale 10 1 10 3 m overrides progressive downstream relationships in low order mountain streams of the colorado front range

estimation of runoff critical shear stress for soil erosion from soil shear strength abstract critical shear stress is an important soil parameter governing detachment by runoff which appears in numerous erosion models soil shear strength has been often presented as the best soil property to predict critical shear stress however only a few studies have documented the relationship between soil shear strength and critical shear stress and the results obtained have sometimes seemed contradictory this is why we have put together all available data about the relationship between critical shear stress and soil shear strength in order to analyse and discuss its significance and its generality results showed that contradictions between different studies mainly arise because total shear stress is a poor predictor of detachment on rough soils when grain shear stress is used rather than total shear stress a significant relationship between saturated soil shear strength and critical shear stress does exist soil shear strength may thus be used to predict critical grain shear stress however it is recalled that in general only total shear stress is predicted by erosion models which makes detachment predictions difficult on rough natural soils

eskers in a complete wet based glacial system in the phlegra montes region mars although glacial landsystems produced under warm wet based conditions are very common on earth even here observations of subglacial landforms such as eskers emerging from extant glaciers are rare this paper describes a system of sinuous ridges emerging from the in situ but now degraded piedmont terminus of a late amazonian aged 150 ma glacier like form in the southern phlegra montes region of mars we believe this to be the first identification of martian eskers that can be directly linked to their parent glacier together with their contextual landform assemblage the eskers are indicative of significant glacial meltwater production and subglacial routing however although the eskers are evidence of a wet based regime the confinement of the glacial system to a well defined regionally significant graben and the absence of eskers elsewhere in the region is interpreted as evidence of sub glacial melting as a response to locally enhanced geothermal heat flux rather than climate induced warming these observations offer important new insights to the forcing of glacial dynamic and melting behaviour on mars by factors other than climate

relative size of fluvial and glaciated valleys in central idaho quantitative comparisons of the morphometry of glaciated and fluvial valleys in central idaho were used to investigate the differences in valley relief and width in otherwise similar geologic and geomorphic settings the local relief width and cross sectional area of valleys were measured using gis software to extract information from usgs digital elevation models hillslope gradients were also measured using gis software power law relationships for local valley relief width and cross sectional area as a function of drainage area were developed local valley relief in glaciated valleys relates to drainage area with a power law exponent similar to fluvial valleys but glaciated valleys are deeper for a given drainage area local valley width in glaciated valleys is greater than in fluvial valleys but the exponent of the power law relationship to drainage area is similar in both valley types local valley cross sectional area in glaciated valleys increases with drainage area with a power law exponent similar to fluvial valleys however glacial valleys have roughly 80 greater cross sectional area steep valley walls in glaciated basins increase the potential for bedrock landsliding relative to fluvial basins both the olympic mountains of washington and valleys in central idaho show relationships in which glaciated valleys are up to 30 deeper than fluvial valleys despite differences in lithology tectonic setting and climate

allometry and cirque evolution a deductive analysis of the processes responsible for cirque formation leads to a model that describes cirque development through time in this model cirque volumes increase as the third power of time although observed variations in cirque size also reflect pre glacial erosion as well as the average rate of surface recession lowering the deductive findings are extended via analysis of 23 cirques from a part of the sangre de cristo mountains south central colorado the assumption that glacier occupance times are proportionately adjusted to topoclimatic situation leads to the conclusion that average rates of cirque erosion exhibit at least a fourfold possibly as much as an order of magnitude range within a given massif the notion that cirque development rates depend on bed rock resistance is supported by a statistically significant inverse relationship between estimated erosion coefficients and average bed rock joint spacing allometric analysis of a 15 cirque subsample the cirques were chosen because they exhibit similar erosion susceptibility lends credence to the hypothesis that headwall recession has been more rapid than cirque floor lowering within the study area however allometric enlargement cannot by itself account for observed values for the ratio cirque length cirque depth the results imply that pre glacial topography strongly influences observed variability in glacial morphometry

soil formation in kettle holes from high altitudes in central apennines italy abstract kettle holes are relatively common features of glaciated landscapes and have been widely reported in the literature the work reported here documents the presence of kettle holes at high altitude and low latitude in the central apennines italy and describes the geomorphic and pedogenic processes that originated the soils infilling these depressions the areas selected for this study were located on three of the main massifs of the central apennines italy gran sasso majella and sibillini the kettle holes on these massifs formed at the end of the wurm glaciation appear smaller and shallower than those reported from elsewhere in the northern hemisphere are roughly circular in form and do not contain bogs or lakes in each area the dimensions of 40 kettle holes were measured and three kettle holes were excavated to examine the soils developed inside them the size of the kettle holes was highest in the sibillini massif where the glaciers reached altitudes as low as 1700 m in the very narrow low lying valleys it is hypothesised that at lower elevations the glacier receded more rapidly generating larger blocks of ice and consequently larger kettle holes once formed the kettle hole depressions were very effective as sediment traps and acted as sink for materials washed in from the surrounding slopes or from more distant wind blown sources in the kettle holes from gran sasso and majella massifs small fragments of woody charcoal were found the material filling the kettle holes accumulated inside them in the form of layers soils formed inside the kettle holes showed horizons whose thickness and properties appeared mostly inherited from the amassed layers the only pedogenic process common to the kettle holes of the three massifs was the incorporation of organic matter that as expected from the rather cold climatic conditions was subjected to slow dynamics in the kettle holes of the majella massif the horizons developed from layers rich of materials of volcanic origin and the formation of short range order minerals occurred we conclude that the soils inside the kettle holes are a repository of geomorphic pedogenic and in reference to the source of the charcoal paleo environmental information

supraglacial eskers in antarctica abstract this paper describes eskers that form at the edge of the ice sheet in the vestfold hills antarctica eskers are linear ridges that are deposited by streams constrained by glacier ice their formation requires a sediment source and the presence of meltwater capable of thermal erosion and penetration of glacier ice these requirements mean that eskers are generally associated with temperate glaciers and are not usually associated with cold polar glaciers the eskers described in this paper form small ridges of gravel adjacent to ice cored moraines the form orientation sedimentary properties together with consideration of the field relationships suggests they were formed by supraglacial streams that drain moraine dammed lakes and recycle sediment deposited on ice cored moraines the small size of the eskers combined with the active nature of ice marginal processes in the area means the eskers have a low preservation potential and do not occur beyond the ice margin in the vestfold hills

large alluvial fans on mars 1 several dozen distinct alluvial fans 10 to 40 km long downslope have been observed in highlands craters within a search region between 0 and 30 s alluvial fan containing craters were found only between 18 and 29 s and they all occur at around 1 km of the mola defined martian datum within the study area they are not randomly distributed but instead form three distinct clusters fans typically descend 1 km from where they disgorge from their alcoves longitudinal profiles show that their surfaces are very slightly concave with a mean slope of 2 many fans exhibit very long narrow low relief ridges radially oriented downslope often branching at their distal ends suggestive of distributaries morphometric data for 31 fans were derived from mola data and compared with terrestrial fans with high relief source areas terrestrial low gradient alluvial ramps in inactive tectonic settings and older martian alluvial ramps along crater floors the martian alluvial fans generally fall on the same trends as the terrestrial alluvial fans whereas the gentler martian crater floor ramps are similar in gradient to the low relief terrestrial alluvial surfaces for a given fan gradient martian alluvial fans generally have greater source basin relief than terrestrial fans in active tectonic settings this suggests that the terrestrial source basins either yield coarser debris or have higher sediment concentrations than their martian counterpoints martian fans and terrestrial basin and range fans have steeper gradients than the older martian alluvial ramps and terrestrial low relief alluvial surfaces which is consistent with the construction of martian fans from dominantly gravel sized sediment rather than sand and silt martian fans are relatively large and of low gradient similar to terrestrial fluvial fans rather than debris flow fans although gravity scaling uncertainties make the flow regime forming martian fans uncertain however evidence of bedforms accentuated by differential erosion such as scroll bars supports the contention that these are fluvially formed fans martian fans at least those in holden crater apparently formed around the time of the noachian hesperian boundary we infer that these fans formed during an episode of enhanced precipitation probably snow and runoff which exhibited both sudden onset and termination

a critical appraisal of allometric growth among alpine cirques based on multivariate statistics and spatial analysis when considering the morphometric attributes of a glacial cirque imbalances between length width and amplitude have been deemed relevant tools for discriminating between two possible pathways of cirque growth downwearing by glaciers or backwearing by freeze thaw processes based on a sample of 1071 cirques in the french pyrenees we reframe the concern for climatic variables by also granting systematic consideration to cirque lithology insight into the factors that control cirque shape is gained from principal component analysis where maps of eigenvalues assigned to six classes of bedrock display spatial patterns of cirque form as a function of position along the regional climatic gradient among crystalline rocks granite gneiss migmatite cirque form is predominantly determined by climatic controls this is highlighted in the contrast between the elevated core of the pleistocene icefield where cirque isometry prevails and the more peripheral areas external sierras of the atlantic precipitation zone and high sierras of the drier mediterranean zone where the lighter imprint of glaciation on the landscape has failed to erase through glacial deepening the allometric signature of pre pleistocene topographic features such as shallow valley heads and etch basins as a result wide and shallow cirques occur in these settings among schist outcrops in contrast cirque form appears randomly distributed suggesting that bedrock characteristics e g structure rather than climate are the key controls on cirque growth patterns given the importance of geological structure and preglacial topographic inheritance cirques are complex landforms for which assumptions of allometric growth may be spurious it follows that form is not always a reliable guide to process

tropical to mid latitude snow and ice accumulation flow and glaciation on mars images from the mars express hrsc high resolution stereo camera of debris aprons at the base of massifs in eastern hellas reveal numerous concentrically ridged lobate and pitted features and related evidence of extremely ice rich glacier like viscous flow and sublimation together with new evidence for recent ice rich rock glaciers at the base of the olympus mons scarp superposed on larger late amazonian debris covered piedmont glaciers we interpret these deposits as evidence for geologically recent and recurring glacial activity in tropical and mid latitude regions of mars during periods of increased spin axis obliquity when polar ice was mobilized and redeposited in microenvironments at lower latitudes the data indicate that abundant residual ice probably remains in these deposits and that these records of geologically recent climate changes are accessible to future automated and human surface exploration

geomorphological characterisation and interpretation of a mid latitude glacier like form hellas planitia mars we describe and interpret the surface terrain types associated with a widely reported 4 km long midlatitude martian viscous flow feature vff the feature is located in the southern hemisphere on the poleward facing rim of a 60 km diameter crater in eastern hellas planitia high resolution imaging science experiment hirise images analysed in both 2d and 3d reveal that the upper margin of the feature is bounded by steep 30 headwalls typically some tens of metres high that are formed from unconsolidated material and characterised by a series of slope parallel linear incisions below these incised headwalls the feature flows at a general angle of 10 from a broad upper basin to a confined lower tongue that is bounded by a nested sequence of elongate raised ridges these characteristics are typical of several vffs in the region and are strikingly similar to moraine bounded valley glaciers on earth and we sub classify this feature as a glacier like form glf 1 the glf comprises five distinctive surface terrain types that contrast sharply with surface characteristics outside its bounding moraines four of these terrains scaly terrain polygonized terrain linear terrain and mound and tail terrain are located within the glf s innermost bounding moraine while the fifth rectilinear ridge terrain is located between its frontal moraines these terrains are mapped characterised and associated with possible mechanisms of formation to draw inferences about the glf s glaciology and glacial history this analysis suggests that the glf reached its maximal extent in the geologically recent past and that it may have been partially wetbased at that time subsequent to this phase the glf experienced an extended period of general recession that has been punctuated by several episodes of still stand or advance currently the glf s basin appears to be composed of a lower zone that is dominated by an exposed former glacier bed and an upper zone that may still contain a now degraded and dust mantled viscous mass similar to many partially glacierized basins on earth

origin of the valley networks on mars a hydrological perspective abstract the geomorphology of the martian valley networks is examined from a hydrological perspective for the compatibility with an origin by rainfall globally higher heat flow and localized hydrothermal systems comparison of morphology and spatial distribution of valleys on geologic surfaces with terrestrial fluvial valleys suggests that most martian valleys are probably not indicative of a rainfall origin nor are they indicative of formation by an early global uniformly higher heat flow in general valleys are not uniformly distributed within geologic surface materials as are terrestrial fluvial valleys valleys tend to form either as isolated systems or in clusters on a geologic surface unit leaving large expanses of the unit virtually untouched by erosion with the exception of fluvial valleys on some volcanoes most martian valleys exhibit a sapping morphology and do not appear to have formed along with those that exhibit runoff morphology in contrast terrestrial sapping valleys form from and along with runoff valleys the isolated or clustered distribution of valleys suggests localized water sources were important in drainage development persistent groundwater outflow driven by localized but vigorous hydrothermal circulation associated with magmatism volcanism impacts or tectonism is however consistent with valley morphology and distribution snowfall from sublimating ice covered lakes or seas may have provided an atmospheric source of water for the formation of some valleys in regions where the surface is easily eroded and where localized geothermal hydrothermal activity is sufficient to melt accumulated snowpacks

updated global map of martian valley networks and implications for climate and hydrologic processes 1 martian valley networks have long been viewed as some of the best evidence of prolonged surface water on mars analysis from viking data showed that valleys were primarily contained on the ancient crust drainage networks were immature and large undissected regions occurred in between individual systems these observations led many to propose that they formed primarily by groundwater processes and limited or no climate change from the present state was required using more recent and higher resolution data sets including visible infrared and topographic data we have manually remapped valleys on a global scale more than eight times as many valleys have been identified on the surface and calculated drainage densities are on average higher by a factor of 2 further regions previously thought to be undissected have significant incision by fluvial processes most of these systems seem to have formed around the noachian hesperian boundary 3 8 3 6 ga minor valley formation continued through the hesperian and into the early amazonian epoch approximately 2 8 ga ago the new data reveal characteristics of sustained precipitation and surface runoff including inner braided channels terraces multiple periods of formation complex network morphology and correlation with other fluviosedimentary features and chloride salts on mars groundwater processes or a transient steam atmosphere generated by impacts played at most a minor role these new results imply that mars had a long lived period or periods of clement conditions toward the end of the noachian epoch that supported a hydrologic cycle and potentially a biosphere

outlet glacier trough size drainage area relationships fiordland new zealand abstract this paper examines relationships between the area supplying ice to fiord troughs and various measures of fiord size such as depth width and length in fiordland new zealand the size of the outlet troughs was found to be adjusted to the discharge of ice following a similar relationship to that encountered with fiords developed under essentially cold based ice sheets in british columbia however the fiordland outlet troughs were substantially shorter and shallower than their counterparts in british columbia this difference may reflect contrast in mode of erosion in each case although the major dimensions of the fiords undoubtedly reflect the controlling influence of the pre glacial lanscape upon which ice caps were superimposed with their rediating outlet glaciers

features of glacial valley profiles simply explained 1 glacial occupation of alpine valleys results in a distinct signature in the long valley profile including steepening of the profile in the headwaters flattening at lower elevations and a step in the profile at the convergence of headwater tributaries we present analytic results for glacial erosion patterns by making the following assumptions 1 the initial profile is linear 2 the width of the valley is uniform 3 the annual mass balance varies linearly with elevation 4 the glacier at any time is quasi steady 5 the erosion rate is proportional to ice discharge per unit valley width and 6 glacial erosion rates far exceed fluvial erosion rates a steady glacier under these conditions would erode a parabolic divot in the longitudinal valley profile with its maximum depth coinciding with the down valley position of the equilibrium line altitude ela the calculated flattening of the valley floor down valley of the ela and the steepening of it up valley captures the essence of the glacial signature when a reasonable probability distribution of elas is allowed the predicted erosion peaks at 30 40 of the down valley distance to the glacial limit and the pattern merges smoothly with the steeper fluvial profile downstream of the glacial limit profiles of mass balance that are capped at a maximum value produce shorter glaciers and a slight asymmetry in the expected erosion pattern only when we mimic the tributaries of glacial headwaters by specifying a valley width distribution do we obtain the upper step observed in many valley profiles

equatorial glaciations on mars revealed by gravitational collapse of valles marineris wallslopes abstract martian global climate models that account for evidence of past glaciations reported in tropical to mid latitude regions of mars predict accumulation of water ice in valles marineris during past periods of high obliquity observational evidence for such glaciations is given here topographic basement ridges of tectonic origin are common in valles marineris and display sackung features an assemblage of tectonic patterns that are diagnostic of deep seated gravitational slope deformation this deformation is most easily explained by paraglacial ridge failure subsequent to ridge wall debuttressing and decohesion following the retreat of glaciers this interpretation is supported by extensive bibliographic analysis of sackung triggers on earth by morphological evidence of subglacial erosion of the lower parts of valles marineris wallslopes of periglacial erosion of their upper parts and by the presence of various types of glacial landforms on the floors of valles marineris troughs the age of these equatorial glaciations is found to be older than 1 4 gy and younger than 3 5 gy

morphometric evidence of 3 6 ga glacial valleys and glacial cirques in martian highlands south of terra sabaea abstract the climate of early mars remains unclear and the debate is topical recently climatic models have suggested a cold climate during the noachian early hesperian on mars which goes against the wet and warm climate often put forward the purpose of this study is to seek geomorphologic evidence of this early cold climate to achieve this a step by step study of the geometry and morphology of several martian valleys has been done in the southern highlands the analysis highlights the morphometric properties which enable the identification of martian glacial landscapes we identified 100 cirques and 83 glacial valleys in two craters and on one mountain in the southern part of terra sabaea the studied morphologies have the same morphometric characteristics and trends as terrestrial and martian glacial valleys and glacial cirques in contrary these trends are very different from those observed in fluvial valleys on earth and on mars 1 the martian glacial valleys are u shaped with a large flat floor and a v index 0 20 while martian and terrestrial fluvial valleys are v shaped with a v index 1 while for fluvial valleys this ratio is 1 3 finally the cross sectional area and the elevation are higher for the glacial valleys compared to the fluvial ones these glacial valleys often originate with a topographic hollow which have the same properties than terrestrial glacial cirque the glacial landscapes identified in southern terra sabaea are restricted to elevations 1000 m and are dated by crater counting to be 3 6 ga this study strongly supports glacial processes as the origin of these valleys and cirques and is the first morphometric evidence of glacial valleys associated with glacial cirques in the southern highlands in agreement with the climatic models we propose that the martian climate during the late noachian early hesperian was characterized by glaciated highlands at elevations 1500 m and at lower elevations where fluvial valley network has been identified

radar evidence for ice in lobate debris aprons in the mid northern latitudes of mars 1 subsurface radar sounding data indicate that lobate debris aprons found in deuteronilus mensae in the mid northern latitudes of mars are composed predominantly of water ice the position in time delay and the relatively low amount of signal loss of the apparent basal reflectors below the debris aprons indicate that aprons contain only a minor component of lithic material the current presence of large ice masses at these latitudes has important implications for the climate evolution of mars and for future targets for in situ exploration

martian cratering 8 isochron refinement and the chronology of mars abstract this paper reviews and refines the technique of dating martian surfaces by using impact crater isochrons defined as size distributions of impact craters on undisturbed martian surfaces of specified ages in the 1970s this system identified not only abundant ancient martian volcanic surfaces but also extensive lava plains with ages of a few 108 y old this dating was initially controversial but confirmed in the 1980s and 90s by martian meteorites the present update utilizes updated estimates of the mars moon cratering ratio the most important calibration factor improves treatment of gravity and impact velocity scaling effects combines aspects of the crater size distribution data from earlier work by both neukum and hartmann and for the first time applies a correction for loss of small meteoroids in the martian atmosphere from popova et al 2003 meteorit planet sci 38 905 925 the updated isochrons are not radically different from the previous 2002 iteration but fit observed data better and give somewhat older model ages for features dated from small craters diameter d 100 m crater counts from young lava flows in various areas give good fits to the new isochrons over as much as 3 orders of magnitude in d confirming the general isochron shape and giving crater retention ages in the range of some 106 to some 108 y interpreted as lava flow ages more complex older units are also discussed uncertainties are greatest if only small craters d 100 m are used suggestions by other workers of gross uncertainties due to local secondary craters and deposition exhumation are discussed they do not refute our conclusions of significant volcanic fluvial and other geologic activity in the last few percent of martian geologic time or the importance of cratering as a tool for studying processes such as exhumation indeed crater count data suggest certain very recent episodes of deposition exhumation and ice flow possibly associated with obliquity cycles of 10 7 y timescale evidence from ancient surfaces suggests higher rates of volcanism fluvial activity glaciation and other processes in noachian hesperian time than in amazonian time

amazonian northern mid latitude glaciation on mars a proposed climate scenario recent geological observations in the northern mid latitudes of mars show evidence for past glacial activity during the late amazonian similar to the integrated glacial landsystems in the dry valleys of antarctica the large accumulation of ice many hundreds of meters required to create the observed glacial deposits points to significant atmospheric precipitation snow and ice accumulation and glacial flow in order to understand the climate scenario required for these conditions we used the lmd laboratoire de meteorologie dynamique mars gcm general circulation model which is able to reproduce the present day water cycle and to predict past deposition of ice consistent with geological observations in many cases prior to this analysis however significant mid latitude glaciation had not been simulated by the model run under a range of parameters in this analysis we studied the response of the gcm to a wider range of orbital configurations and water ice reservoirs and show that during periods of moderate obliquity 25 35 and high dust opacity sdust 1 5 2 5 broad scale glaciation in the northern mid latitudes occurs if water ice deposited on the flanks of the tharsis volcanoes at higher obliquity is available for sublimation we find that high dust contents of the atmosphere increase its water vapor holding capacity thereby moving the saturation region to the northern mid latitudes precipitation events are then controlled by topographic forcing of stationary planetary waves and transient weather systems producing surface ice distribution and amounts that are consistent with the geological record ice accumulation rates of 10 mm yr

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

one million cubic kilometers of fossil ice in valles marineris relicts of a 3 5 gy old glacial landsystem along the martian equator abstract self consistent landform assemblages suggest that valles marineris the giant valley system that stretches along the martian equator was entirely glaciated during late noachian to early hesperian times and still contains huge volumes of fossil ice some of these glacial landform assemblages are illustrated here with representative examples selected in three regions ius chasma central candor chasma and the junction between coprates chasma and capri chasma a morphological boundary separating an upper spur and gully morphology from a smooth basal escarpment has been spectacularly preserved along valley walls throughout valles marineris the boundary winds around topographic obstacles and displays long wavelength variations in elevation it is associated with lateral benches hanging valleys and truncated spurs comparisons with terrestrial analogs indicate that it is most reasonably interpreted as a glacial trimline chasma floors are covered by various kinds of terrains including hummocky terrains platy terrains lateral banks layered benches and a draping mantle landforms in these terrains and their spatial relationship with the interpreted trimline suggest that they correspond to various disintegration stages of an ancient glacial fill currently protected by a superficial cover of ablation till altogether these landforms and terrains compose a full glacial landsystem with wet based glaciers that were able to flow and slide over their beds it was most probably fed by ice accumulating at low elevations directly from the atmosphere onto valley floors and walls with only minor contributions from tributary glaciers flowing down from higher elevations similar fossil glacial landsystems dating back from the early martian history are to be expected in many other low latitude troughs such as chasmata chaos valleys impact craters and other basins

deglacial meltwater drainage and glaciodynamics inferences from laurentide eskers canada abstract this paper evaluates current knowledge of laurentide eskers in canada in the light of developments in glacier hydrology and glacial sedimentology questions regarding the morpho sedimentary relations of eskers the synchroneity and operation of r channel systems the role of supraglacial meltwater input and proglacial water bodies the controls on esker pattern and the glaciodynamic condition of the ice sheet at the time of esker formation are discussed a morphologic classification of eskers is proposed five types of eskers are identified and investigated type i eskers likely formed in extensive synchronous dendritic r channel networks under regionally stagnant ice that terminated in standing water type ii eskers likely formed in short subaqueously terminating r channels or reentrants close to an ice front or grounding line that may have actively retreated during esker sedimentation type iii eskers plausibly formed in short r channels that drained either to interior lakes in or tunnel channels under regionally stagnant ice type iv eskers may have formed as time transgressive segments in short subaerially terminating r channels or reentrants that developed close to the ice margin as the ice front underwent stagnation zone retreat or downwasted and backwasted regionally stagnant ice however formation in synchronous r channels cannot be discounted on the basis of reported observations type v eskers may have formed in h channels that terminated subaerially the spatial distribution of these esker types is discussed the factors that determined laurentide r channel pattern and operation were likely a complex combination of i supraglacial meltwater discharge ii the number and location of sink holes iii the ice surface slope thickness and velocity and iv the permeability topography and rigidity of the bed these factors cause and respond to changes in ice dynamics and thermal regime over the glacial cycle

early mars climate near the noachian hesperian boundary independent evidence for cold conditions from basal melting of the south polar ice sheet dorsa argentea formation and implications for valley network formation currently and throughout much of the amazonian the mean annual surface temperatures of mars are so cold that basal melting does not occur in ice sheets and glaciers and they are cold based the documented evidence for extensive and well developed eskers sediment filled former sub glacial meltwater channels in the south circumpolar dorsa argentea formation is an indication that basal melting and wet based glaciation occurred at the south pole near the noachian hesperian boundary we employ glacial accumulation and ice flow models to distinguish between basal melting from bottom up heat sources elevated geothermal fluxes and top down induced basal melting elevated atmospheric temperatures warming the ice we show that under mean annual south polar atmospheric temperatures 100 c simulated in typical amazonian climate experiments and typical noachian hesperian geothermal heat fluxes 45 65mw m 2 south polar ice accumulations remain cold based in order to produce significant basal melting with these typical geothermal heat fluxes the mean annual south polar atmospheric temperatures must be raised from today s temperature at the surface 100 c to the range of 50 to 75 c this mean annual polar surface atmospheric temperature range implies lower latitude mean annual temperatures that are likely to be below the melting point of water and thus does not favor a warm and wet early mars seasonal temperatures at lower latitudes however could range above the melting point of water perhaps explaining the concurrent development of valley networks and open basin lakes in these areas this treatment provides an independent estimate of the polar and non polar surface temperatures near the noachian hesperian boundary of mars history and implies a cold and relatively dry mars climate similar to the antarctic dry valleys where seasonal melting forms transient streams and permanent ice covered lakes in an otherwise hyperarid hypothermal climate 2012 elsevier inc

ancient glaciation on mars a large number of anomalous landforms on mars can be attributed to glaciation including the action of ice and meltwater glacial landscapes are concentrated south of lat 33 and in the northern plains suggesting vast austral and boreal ice sheets crater densities on the glaciated terrains indicate that the final glacial epoch occurred late in martian history thus mars may have had a relatively warm moist climate and dense atmosphere much later than previously believed

radar sounding evidence for buried glaciers in the southern mid latitudes of mars lobate features abutting massifs and escarpments in the middle latitudes of mars have been recognized in images for decades but their true nature has been controversial with hypotheses of origin such as ice lubricated debris flows or glaciers covered by a layer of surface debris these models imply an ice content ranging from minor and interstitial to massive and relatively pure soundings of these deposits in the eastern hellas region by the shallow radar on the mars reconnaissance orbiter reveal radar properties entirely consistent with massive water ice supporting the debris covered glacier hypothesis the results imply that these glaciers formed in a previous climate conducive to glaciation at middle latitudes such features may collectively represent the most extensive nonpolar ice yet recognized on mars

martian flow features moraine like ridges and gullies terrestrial analogs and interrelationships ridges that resemble terrestrial moraines are commonly visible at the foot of many mid latitude crater walls in mars global surveyor mars orbiter camera images these moraine like ridges are often associated with hillside gullies mantling material and glacier like flows and are usually in contact with crater fill suggesting possible interrelationships we consider terrestrial glacier systems that may be analogs of martian moraine like ridges and glacier like flows and suggest that the formation of some gullies and crater fill is intimately tied to ice deposition ice flow and rock glacier processes upper limits on age suggest the possibility that many of these features formed during the last or last few high obliquity cycles