impacts into non polar ice rich paleodeposits on mars excess ejecta craters perched craters and pedestal craters as clues to amazonian climate history we compare three previously independently studied crater morphologies excess ejecta craters perched craters and pedestal craters each of which has been proposed to form from impacts into an ice rich surface layer our analysis identifies the specific similarities and differences between the crater types the commonalities provide significant evidence for a genetic relationship among the morphologies we use new surveys of excess ejecta and perched craters in the southern hemisphere in conjunction with prior studies of all of the morphologies to create a comprehensive overview of their geographic distributions and physical characteristics from these analyses we conclude that excess ejecta craters and perched craters are likely to have formed from the same mechanism with excess ejecta craters appearing fresh while perched craters have experienced post impact modification and infilling impacts that led to these two morphologies overwhelmed the ice rich layer penetrating into the underlying martian regolith resulting in the excavation of rock that formed the blocky ejecta necessary to armor the surface and preserve the ice rich deposits pedestal craters which tend to be smaller in diameter have the same average deposit thickness as excess ejecta and perched craters and form in the same geographic regions they rarely have ejecta around their crater rims instead exhibiting a smooth pedestal surface we interpret this to mean that they form from impacts into the same type of ice rich paleodeposit but that they do not penetrate through the icy surface layer and thus do not generate a blocky ejecta covering instead a process related to the impact event appears to produce a thin indurated surface lag deposit that serves to preserve the ice rich material these results provide a new basis to identify the presence of amazonian non polar ice rich deposits to map their distribution in space and time and to assess amazonian climate history specifically the ages distribution and physical attributes of the crater types suggest that tens to hundreds of meters of ice rich material has been episodically emplaced at mid latitudes in both hemispheres throughout the amazonian due to obliquity driven climate variations these deposits likely accumulated more frequently in the northern lowlands resulting in a larger population of all three crater morphologies in the northern hemisphere

pitted rock surfaces on mars a mechanism of formation by transient melting of snow and ice 1 pits in rocks on the surface of mars have been observed at several locations similar pits are observed in rocks in the mars like hyperarid hypothermal stable upland zone of the antarctic dry valleys these form by very localized chemical weathering due to transient melting of small amounts of snow on dark dolerite boulders preferentially heated above the melting point of water by sunlight we examine the conditions under which a similar process might explain the pitted rocks seen on the surface of mars rock surface temperatures above the melting point atmospheric pressure exceeding the triple point pressure of h2o an available source of solid water to melt we find that on mars today each of these conditions is met locally and regionally but that they do not occur together in such a way as to meet the stringent requirements for this process to operate in the geological past however conditions favoring this process are highly likely to have been met for example increases in atmospheric water vapor content due for example to the loss of the south perennial polar co2 cap could favor the deposition of snow which if collected on rocks heated to above the melting temperature during favorable conditions e g perihelion could cause melting and the type of locally enhanced chemical weathering that can cause pits even when these conditions are met however the variation in heating of different rock facets under martian conditions means that different parts of the rock may weather at different times consistent with the very low weathering rates observed on mars furthermore as is the case in the stable upland zone of the antarctic dry valleys pit formation by transient melting of small amounts of snow readily occurs in the absence of subsurface active layer cryoturbation

complex evolution of paleolacustrine systems on mars an example from the holden crater 1 the 150 km wide holden crater lies in an area characterized by high density of valley networks implying conditions conducive to forming of water related environments we undertook geological mapping and a stratigraphic survey in order to probe the evolution of water related landforms and their paleoenvironmental implications our investigations lead us to propose that the holden area was subjected to a wet lacustrine phase of hesperian age and an icy phase during the amazonian deltaic coastal and lacustrine environments occurred during the wet phase some displaying a cyclic depositional pattern presumably related to autogenic processes water was delivered to the basin by the uzboi vallis and by surface runoff channels from a series of drainage basins along the crater walls fan delta geometries and coastal onlap enabled estimation of major water levels two levels of major stand of the water have been recognized possibly reflecting allogenic controls geologic units related to this wet lacustrine phase were subsequently eroded by glacial abrasion and plucking and were disconformably overlain by glacial deposits of amazonian age defining an icy phase these features are consistent with a warm based glacier entering the holden crater through the wide uzboi vallis to form a proglacial lake in the central part of the crater changes in sedimentary units reflect changes of depositional environments probably connected with climatic variation

formation of patterned ground and sublimation till over miocene glacier ice in beacon valley southern victoria land antarctica a thin glacial diamicton informally termed granite drift occupies the floor of central beacon valley in southern victoria land antarctica this drift is 40 ar 39 ar analyses of presumed in situ ash fall deposits that occur within granite drift at odds with the great age of this ice are high centered polygons that cut granite drift if polygon development has reworked and retransported ash fall deposits then they are untenable as chronostratigraphic markers and cannot be used to place a minimum age on the underlying glacier ice our results show that the surface of granite drift is stable at polygon centers and that enclosed ash fall deposits can be used to define the age of underlying glacier ice in our model for patterned ground development active regions lie only above polygon troughs where enhanced sublimation of underlying ice outlines high centered polygons the rate of sublimation is influenced by the development of porous gravel and cobble lag deposits that form above thermal contraction cracks in the underlying ice a negative feedback associated with the development of secondary ice lenses at the base of polygon troughs prevents runaway ice loss secondary ice lenses contrast markedly with glacial ice by lying on a d versus 18 o slope of 5 rather than a precipitation slope of 8 and by possessing a strongly negative deuterium excess the latter indicates that secondary ice lenses likely formed by melting downward percolation and subsequent refreezing of snow trapped preferentially in deep polygon troughs the internal stratigraphy of granite drift is related to the formation of surface polygons and surrounding troughs the drift is composed of two facies a nonweathered matrix supported diamicton that contains 25 striated clasts in the 16 mm fraction and a weathered clast supported diamicton with varnished and wind faceted gravels and cobbles the weathered facies is a coarse grained lag of granite drift that occurs at the base of polygon troughs and in lenses within the nonweathered facies the concentration of cosmogenic 3 he in dolerite cobbles from two profiles through the nonweathered drift facies exhibits steadily decreasing values and shows the drift to have formed by sublimation of underlying ice these profile patterns and the 3 he surface exposure ages of 1 18 0 08 ma and 0 18 0 01 ma atop these profiles indicate that churning of clasts by cryoturbation has not occurred at these sites in at least the past 10 5 and 10 6 yr although granite drift is stable at polygon centers low frequency slump events occur at the margin of active polygons slumping together with weathering of surface clasts creates the large range of cosmogenic nuclide surface exposure ages observed for granite drift maximum rates of sublimation near active thermal contraction cracks calculated by using the two 3 he depth profiles range from 5 m m y to 90 m m y sublimation rates are likely highest immediately following major slump events and decrease thereafter to values well below our maximum estimates nevertheless these rates are orders of magnitude lower than those computed on theoretical grounds during eruptions of the nearby mcmurdo group volcanic centers ash fall debris collects at the surface of granite drift either in open thermal contraction cracks or in deep troughs that lie above contraction cracks these deposits subsequently lower passively as the underlying glacier ice sublimes the fact that some regions of granite drift have escaped modification by patterned ground for at least 8 1 ma indicates long term geomorphic stability of individual polygons once established polygon toughs likely persist for as long as 10 5 10 6 yr our model of patterned ground formation which applies to the hyperarid cold desert polar climate of antarctica may also apply to similar sized polygons on mars that occur over buried ice in utopia planitia

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

preservation of miocene glacier ice in east antarctica antarctic climate during the pliocene has been the subject of considerable debate one view holds that during part of the pliocene east antarctica was largely free of glacier ice and that vegetation survived on the coastal mountains1a 4 an alternative viewpoint argues for the development of a stable polar ice sheet by the middle miocene which has persisted since then5a 10 here we report the discovery of buried glacier ice in beacon valley east antarctica which appears to have survived for at least 8 1 million years we have dated the ice by 40ar 39ar analysis of volcanic ash in the thin overlying glacial till which we argue has undergone little if any reworking isotope and crystal fabric analyses of the ice show that it was derived from an ice sheet we suggest that stable polar conditions must have persisted in this region for at least 8 1 million years for this ice to have avoided sublimation

mars and earth comparison of cold climate features abstract on earth glacial and periglacial features are common in areas of cold climate on mars the temperature of the present day surface is appropriate for permafrost and the presence of water is suspected from data relating to the outgassing of the planet from remote sensing measurements over the polar caps and elsewhere on the martian surface and from recognition of fluvial morphological features such as channels these observations and the possibility that ice could be in equilibrium with the atmosphere in the high latitudes north and south of 40 latitude suggest that glacial and periglacial features should exist on the planet morphological studies based mainly on viking pictures indicate many features that can be attributed to the action of ice among these features are extensive talus aprons debris avalanches flows that resemble glaciers or rock glaciers ridges that look like moraines various types of patterned ground scalloped scarps and chaotically collapsed terrain that could be attributed to thermokarst processes and landforms that may reflect the interaction of volcanism and ice

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

normal fault inversion by orthogonal compression sandbox experiments with weak faults abstract linear frictional failure criteria predict that normal faults form dipping around 60 and reverse faults around 30 depending on dry rock properties therefore it is unlikely that normal faults be reactivated as reverse faults unless the stress conditions are favourable or the intrinsic properties of the intact rock or of the precursor fault pf are modified in the present study we focused on friction strength of the pf we used sandbox experiments with an initially embedded weak pf dipping 60 or 70 filled with a thin film of silicone putty that lubricated the weak fault to investigate inversion of high angle pf by orthogonal compression the results show that 1 the pf can be inverted if it is weak during compression even if the angle of dip is as great as 70 2 after inversion initiation the reverse movement on the pf can last for as much as 30 model shortening leading to great amounts of reverse displacement along the pf before the formation of a thrust ahead 3 in models with more than one pf the weakness of the reactivated fault closer to piston was not enough to prevent reactivation of the pf further ahead after an amount of shortening that depended on distance between pfs the viscous material used to weaken the fault is scalable to salt in nature however the great decrease in friction due to lubrication with a viscous material can simulate many other weakening mechanisms observed in nature

origin and evolution of a cold based tropical mountain glacier on mars the pavonis mons fan shaped deposit 1 each of the large tharsis montes volcanoes in the equatorial region of mars has an unusual amazonian aged fan shaped deposit on its west northwestern flank on the basis of viking orbiter data the origin of these deposits has been variously ascribed to volcanic mass wasting tectonic and glacial processes using new mgs and odyssey data combined with recent developments in the study of cold based glaciers we reassess the geology and mode of origin for these deposits with particular emphasis on pavonis mons the deposits share three characteristic facies including 1 a ridged facies consisting of tens to 100 parallel concentric ridges around the margins of the deposits 2 a knobby facies composed of irregular hills and hummocks and 3 a smooth facies of broad lobate plains that superposes all other units within the deposits on the basis of morphology topography superposition relationships and close terrestrial analogs in the dry valleys of antarctica we interpret the pavonis fan shaped deposit as the depositional remains of a cold based glacier that formed on the northwestern flank in recent martian history we interpret the ridged facies as drop moraines formed around the margins of a retreating cold based glacier the knobby facies as a sublimation till derived from in situ down wasting of cold based glacial ice and the smooth facies as extant debris covered glacial ice in addition to the three main facies the fan shaped deposit at pavonis mons contains several unique features including arcuate scarps high relief flow like features and radial ridges which suggest that volcanism played a role during its formation using recent results from mars general circulation model simulations we outline a model of glacier formation involving atmospheric deposition of water ice on the northwestern flanks of the tharsis montes during periods of high mean obliquity reconstructed ice sheet profiles for each of the tharsis montes glaciers suggest that the ice sheets attained average thicknesses of 1 6 2 4 km values that are consistent with a cold based glacial origin analysis of crater size frequency distributions using new data indicates that the age of the glaciation lies within the late amazonian 10 200 ma thus our results suggest that multiple phases of tropical mountain glaciation occurred on mars within the past few hundred myr and that significant amounts of near surface equatorial ice may remain within the deposit today

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

the olympus mons aureole formation by gravitational spreading new observations of the aureole deposits of olympus mons are in agreement with previous suggestions that the aureole lobes could have been formed by movement under gravity away from the observed scarps the characteristic corrugated morphology of the aureole is probably secondary formed by erosion along structural inhomogeneities geometries of the corrugations and translational faults in the aureole deposits favor a mechanism of emplacement that involves material with substantial shear strength rather than viscous flow estimates of the aspect ratios of terrestrial landslides nappes and ash flows suggest that the aureole deposits are more similar in overall shape to slide emplaced bodies than to pyroclastic flows although martian physical conditions permit the formation of ash flows there is no positive evidence for their existence a gravitational spreading mechanism is proposed that involves imbricate thrusting in distal regions analogous with terrestrial thrust sheets corrugations in the aureole developed by erosion along imbricate or listric faults basal shear stresses on the decoupling surface may have been of the order of 106 pa 10 bars the nature of the decoupling surfaces in the proximal regions is uncertain but is likely to have been the topographic surface in distal parts the aureole deposits were probably emplaced as a series of sheets by spreading under gravity from an ancestral olympus mons which extended farther to the northwest than does the present volcano as a result of the accumulation of lavas under the then prevailing stress conditions recent lava eruptions from the volcano have been concentrated in northeast and southwest sectors indicating a changed stress regime since aureole emplacement

the oldest ice on earth in beacon valley antarctica new evidence from surface exposure dating abstract beacon valley antarctica contains unique remnants of glacier ice underneath a till layer covering the valley floor to constrain the age and evolution of this important indicator of antarctic paleoclimate we analyzed two dolerite erratics from the till surface and one from within the ice for cosmogenic helium and neon a conservative minimum exposure age of the older surface sample is 2 3 ma but taking into account erosion the true exposure age of this boulder is likely to be considerably higher the buried sample contains more than 20 times less cosmogenic noble gases than the old surface sample although its current shielding would imply only a three times lower production rate this indicates that the ice level has slowly been lowered by sublimation at the rate of a few m ma the high exposure age of the surface sample as well as the very low sublimation rate of the relict ice both support the conclusion that the remnant ice in beacon valley was deposited many million years ago sugden et al nature 376 1995 412 414 and has never been thinner than at present in addition we found that cosmogenic helium and neon are released quantitatively from pyroxene at temperatures of 1000 c respectively

minimal pliocene pleistocene uplift of the dry valleys sector of the transantarctic mountains a key parameter in ice sheet reconstructions we propose that there has been little or no pliocene pleistocene uplift of the dry valleys sector of the transantarctic mountains on the basis of isotopic dating and mapping of in situ cinder cone deposits on the walls of taylor valley twenty seven 40ar 39ar incremental heating analyses on whole rock samples from subaerially erupted olivine basanite volcanic outcrops of known elevations define 14 eruptions ranging in age from 3 89 to 1 50 ma because taylor valley opens directly onto the ross sea these results show that any surface uplift during the past 2 57 m y was 300 m our conclusion of minimal uplift contradicts previous models of dramatic uplift up to 3000 m since 3 ma and associated hypotheses that uplift caused climatic cooling and growth of a polar east antarctic ice sheet

landform assemblage in isidis planitia mars evidence for a 3 ga old polythermal ice sheet abstract the floor of isidis planitia a giant impact basin located close to the martian equator exhibits a landform assemblage nicknamed thumbprint terrain made of arcuate ridges aligned cones isolated cones cone fields associated with a peripheral network of sinuous ridges linear depressions and mounds from a new comprehensive mapping initiative of these landforms and from comparisons with terrestrial analogues ribbed moraines dirt cones kettle holes eskers tunnel valleys and moraine plateaux we demonstrate that this distinctive assemblage is a glacial landsystem inherited from the presence of a massive polythermal ice sheet over the basin during the hesperian the flow of the ice sheet was controlled by its basal thermal regime wet based conditions led to the formation of arcuate ridges and aligned cones in most parts of the basin while a negative geothermal anomaly due to impact related crustal thinning was responsible for cold based conditions in its central part where only isolated cones and cones fields are present sinuous ridges linear depressions and mounds at the basin margins are interpreted as relicts of a radial network of subglacial channels which drained the glacial meltwater produced within the interior of the ice sheet across its cold based periphery

geomorphological evidence of cold based glacier activity in south victoria land antarctica cold based glaciers have long been recognized as capable of covering and protecting landscapes however recent studies of modern cold based glaciers in antarctica show that in some situations erosion deformation and deposition can occur recognizing the dual ability of cold based glaciers to protect and preserve surfaces on the one hand and erode and modify on the other is important for correctly interpreting the often subtle imprint of cold based glaciers on landscapes a range of geomorphological features related to cold based glacier activity has now been documented along with an improved understanding of cold based glacier structure processes and interaction with various substrates collectively this provides an enhanced ability to understand the impact of cold based glaciers on landscapes and reappraise the geomorphological record such insight allows recognition of previously unknown glacial events and better interpretations of the landscape exposure record this is particularly important at the margins of the antarctic ice sheets where past fluctuations in ice sheet volume and its contributions to post glacial sea level rise are poorly constrained this paper reviews the known geomorphological evidence associated with cold based glaciers in the south victoria land region of the transantarctic mountains it aims to provide progress towards a set of criteria for recognizing cold based glacier activity in other regions and to highlight the implications of cold based glacial activity for surface exposure studies and interpreting glacial history cold based glaciers are below pressure melting point throughout and are therefore frozen to the substrate and move primarily by internal deformation drewry 1986 this led to the long standing view that cold based glaciers cannot slide and are thus incapable of erosion and deposition and therefore protect the underlying surface while numerous studies have shown this to be true in many situations recent investigations of modern cold based glaciers have revealed that in some circumstances complex processes operate at subfreezing temperatures in the basal zone and that cold based glaciers can generate a variety of geomorphological features these studies have forced a reappraisal of the geomorphic effectiveness of cold based glaciers and have confirmed that they can both protect and modify landscapes e g fitzsimons 1996 atkins et al 2002 fitzsimons 2003 waller et al 2012 thus the debate has moved on and the challenge now is to understand the full range of processes and products associated with cold based glaciers and the implications for landscape development hambrey fitzsimons 2010 waller et al 2012 recognizing the often subtle features indicative of cold based glacial activity offers the potential to delineate and date previously unknown or poorly constrained glacial events this is particularly relevant for interpreting glacial history and modelling ice sheet reconstructions for example numerous surface exposure dating studies have been carried out on ice marginal landforms with the aim of constraining past variations in the ice sheet volume however many of these studies have produced inconsistent contradictory results including evidence of complex exposure histories suggesting episodes of burial and reworking by cold based ice e g strasky et al 2008 di nicola et al 2009 compared with warm based glaciers there are still relatively few studies of cold based glaciers and significant gaps in our understanding of the processes and products remains in addition lingering misconceptions regarding the geomorphic effectiveness of cold based glaciers and historic use of ambiguous terminology to describe cold based sediments and landforms mean that the evidence and implications of past cold based glacial events have yet to be fully appreciated by the wider geomorphological community this review provides a summary of known geomorphological features associated with cold based glaciers in the south victoria land region of antarctica it aims to provide a basis for recognizing similar features elsewhere and attempts to draw attention to the implications of cold based glacial geomorphology for the correct application of surface exposure dating studies and interpretation of cold based glacial history

mechanisms and timescales of fluvial activity at mojave and other young martian craters mojave crater and five other relatively young late hesperian to amazonian age martian craters exhibit channelized alluvial fans that are sourced from bedrock eroded catchments these catchments emerge from the crests of sloping surfaces suggesting a formation mechanism that involved precipitation the evidence for fluvial activity at all six craters is restricted to their interiors and the immediate surrounding regions detailed mapping at mojave reveals the highest density of channels catchments and fans interior to the crater similar landforms are identified outside of the crater but not beyond 200 km from the rim irregular pits on the floor of mojave interpreted as degassing structures from hot impact melt directly superpose several fan surfaces and partly destroy the fan toes this suggests that sediment was mobilized immediately after crater formation while the crater was still hot based on the patterns and timing of channel fan development at all six craters we favor several hypotheses for the precipitation mechanism 1 snowfall and melt on young hot impact craters 2 impact plume precipitation and 3 degassing of volatiles from impact melt terrain scenario 1 suggests a different global or regional climate relative to modern conditions requiring equatorial and midlatitude snowfall accumulation scenarios 2 and 3 do not necessarily require unique climate conditions as water may have been mobilized from the target or the impactor

cold glaciers erode and deposit evidence from allan hills antarctica here we report previously undescribed features of erosion and deposition by a cold polar glacier a recent study challenged the assumption that cold glaciers neither slide nor abrade their beds but no geological evidence was offered the features we describe include abrasion marks subglacial deposits glaciotectonically deformed substrate isolated blocks ice cored debris mounds and boulder trains all products of a recent cold ice advance and retreat mapping these features elsewhere in antarctica will document recent shifts in the east antarctic ice sheet margin providing new insight on regional mass balance changes

formation of olympus mons and the aureole escarpment problem on mars based on morphologic interpretation of viking orbiter images it is postulated that on the summit area of arsia mons mars there is a several kilometer thick ice cover in addition numerous linear striae on the flanks of arsia mons resemble terrestrial washboard moraines behind which there may be substantial dead ice deposits this implies that glacier phenomena are active in the tharsis region these features may have bearing on the formation of the aureole deposits of olympus mons olympus mons has been the cause of dispute among geologists for years and several contrasting models have been proposed to explain the up to 10 km high distal escarpment and broad lobate aureole deposits below one model by hodges and moore 1979 assumed 2 3 km thick ice under which volcanism proceeded at an early stage to build olympus mons thereby leading to the growth of the high cliff section it has been argued that the origin of the aureole has not been satisfactorily explained modifications of the hodges and moore hypothesis are proposed to explain some aspects of both the aureole formation and the escarpment at the lava aureole boundary the assumption is made that volcanism that persisted was mostly localized on the olympus mons massif throughout the aureole development and that a blanket of ice and wind blown dust covered the lower flanks of the volcano deposition of volcanic products on the flank blanket led to faulting and sliding of material away from the summit area thereby creating the aureole deposits and scarp further eruptions of lavas in the summit area substantially elevated the cliff segment and additions of lavas off the cliffs into the wing area led to further creeping of the lower flank region thus generating the vast aureoles therefore the aureole formation succeeded and resulted from olympus mons volcanic activity and is one of the youngest features of olympus mons and not older as has been postulated

reconciling channel formation processes with the nature of elevated outflow systems at ophir and aurorae plana mars 1 many hesperian outflow channels head at elevations compatible with aquifer recharge beneath the martian south polar cap and such channels are widely interpreted as the products of this recharge some outflow channels head at greater elevations that are inconsistent with southern recharge including three systems located in aurorae planum and eastern ophir planum these three systems have previously been interpreted as having formed through aqueous outbursts from local aquifers recharged by the meltwaters of ancient upland glaciers to the west however the viability of this interpretation is weakened by the lack of a geomorphic record supportive of past meltwater flow from western uplands inconsistencies between hypothesized processes and the nature of regional topography and mineralogy and the absence of satisfactory analog processes for catastrophic aqueous flow from the subsurface in contrast a volcanic origin for the ophir and aurorae systems appears to be in accord with the basic characteristics of constituent channels and associated landforms the volcanotectonic nature of the valles marineris system and adjacent upland plains and the nature of available analog landforms and processes though numerous uncertainties remain a volcanic interpretation of these outflow systems can more simply account for the existence of component channels the attributes of other elevated outflow systems on mars similarly appear to be most consistent with volcanic origins if the ophir and aurorae systems formed volcanically thermal considerations imply minimum erupted lava volumes of 6 4 103 km3 for allegheny vallis and 6 2 104 km3 for elaver vallis

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

forward modeling of ice topography on mars to infer basal shear stress conditions 1 understanding the history of ice caps on mars could reveal important information about martian geologic and climatic history to do this an ice reconstruction model is needed that operates over complex topography and can be constrained with a limited number of free parameters in this study we developed a threshold sliding model for ice cap morphology based on the classic model of nye later incorporated into the models of reeh and colleagues we have updated the nye reeh model with a new numerical algorithm although the model was originally developed to model perfectly plastic deformation it is applicable to any ice body that deforms when a threshold basal shear stress is exceeded the model requires three inputs a digital elevation model of bed topography a mask grid that defines the position of the ice terminus and a function defining the threshold basal shear stress to test the robustness of the model the morphology of the greenland ice sheet is reconstructed using an empirical equation between threshold basal shear stress and ice surface slope the model is then used to reconstruct the morphology of ice draping impact craters on the margins of the south polar layered deposits using an inferred constant basal shear stress of 0 6 bar for the majority of the examples this inferred basal shear stress value is almost 1 3 of the average basal shear stress calculated for the greenland ice sheet what causes this lower basal shear stress value on mars is unclear but could involve the strain weakening behavior of ice

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

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

development of sediment landform associations at cold glacier margins dry valleys antarctica hambrey m j fitzsimons s j 2010 development of sediment landform associations at cold glacier margins dry valleys antarctica sedimentology 57 3 857 882 michael hambrey is corresponding author sponsorship marsden fund of new zealand university of otago research committee nerc grant no ner a s 2000 01256

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

dating martian climate change abstract geological evidence indicates that low latitude polygonally patterned grounds on mars generally thought to be the product of flood volcanism are periglacial in nature and record a complex signal of changing climate by studying the martian surface stratigraphically in terms of the geometrical relations between surface landforms and the substrate rather than genetically by form analogy with earth we have identified dynamic surfaces across one fifth of martian longitude new stratigraphical observations in the elysium amazonis plains have revealed a progressive surface polygonisation that is destructive of impact craters across the region this activity is comparable to the climatically driven degradation of periglacial landscapes on earth but because it affects impact craters the martian chronometer it can be dated here we show that it is possible to directly date this activity based on the fraction of impact craters affected by polygon formation nearly 100 of craters of all diameters are superposed by polygonal sculpture considering the few 100 ma age of the substrate this suggests that the process of polygon formation was active within the last few million years surface polygonisation in this region often considered to be one of the signs of young plains forming volcanism on mars is instead shown to postdate the majority of impact craters seen we therefore conclude that it is post depositional in origin and an artefact of thermal cycling of near surface ground ice stratigraphically controlled crater counts present the first way of dating climate change on a planet other than earth a record that may tell us something about climate change on our own planet parallel climate change on these two worlds an ice age mars coincident with earth s glacial quaternary period might suggest a coupled system linking both we have previously been unable to generalise about the causes of long term climate change based on a single terrestrial example with the beginnings of a chronology for climate change on our nearest planetary neighbour we can

measurement of accessible reactive surface area in a sandstone with application to co2 mineralization measurement of accessible reactive surface area in a sandstone with application to co 2 mineralization gautier landrot 1 jonathan b ajo franklin li yang stefano cabrini and carl i steefel glandrot gmail com jbajo franklin lbl gov lyang lbl gov scabrini lbl gov cisteefel lbl gov lawrence berkeley national laboratory 1 cyclotron rd berkeley ca 94720 8099 usa corresponding author glandrot gmail com tel 66 90 79 77 922 fax 66 29 42 81 06 1 present address department of environmental engineering kasetsart university 10 th floor building 14 50 ngamwongwan road jatujak bangkok 10900 thailand

high outflow channels on mars indicate hesperian recharge at low latitudes and the presence of canyon lakes abstract a number of martian outflow channels were carved by discharges from large dilational fault zones these channels were sourced by groundwater not surface water and when observed on high standing plateaus they provide indicators of elevated paleo groundwater levels we identify three outflow channels of hesperian age that issued from a 750 km long fault zone extending from candor chasma to ganges chasma two of these channels allegheny vallis and walla walla vallis have sources 2500 m above the topographic datum too high to be explained by discharge from a global aquifer that was recharged solely in the south polar region the indicated groundwater levels likely required regional sources of recharge at low latitudes the floodwaters that erupted from ophir cavus to form allegheny vallis encountered two ridges that restricted the flow forming temporary lakes the flow probably breached or overtopped these obstructions quickly catastrophically draining the lakes and carving several scablands after the last obstacle had been breached a single main channel formed that captured all subsequent flow we performed hydrologic analyses of this intermediate phase of the flooding prior to incision of the channel to its present depth using floodwater depths of 30 60 m we calculated flow velocities of 6 15 m s 1 and discharges in the range of 0 7 3 10 6 m 3 s 1 locally higher flow velocities and discharges likely occurred when the transient lakes were drained variable erosion at the channel and scabland crossing of mola pass 10644 suggests that the upper 25 30 m may consist of poorly consolidated surface materials underlain by more cohesive bedrock we infer that an ice covered lake with a surface elevation 2500 m probably existed in eastern candor chasma because this canyon is intersected by the ophir catenae fault system from which allegheny vallis and walla walla vallis originated we introduce a new hydrology concept for mars in which the groundwater system was augmented by recharge from canyon lakes that were formed when water was released by catastrophic melting of former ice sheets in tharsis by effusions of flood basalts this model could help to reconcile the expected presence of a thick cryosphere during the hesperian with the abundant evidence for groundwater as a source for some of the circum chryse outflow channels

the dielectric permittivity of terrestrial ground ice formations considerations for planetary exploration using ground penetrating radar 1 exploration of the polar ice caps and apparent glacial and periglacial landforms on mars will aid our understanding of its ancient climate conditions and the history of water on the planet given that ground penetrating radar gpr is likely to be used to understand these features we investigated the real component of the complex dielectric permittivity of stratified segregation ice non stratified segregation ice and polygonal ice wedge deposits in the canadian arctic we acquired moveout profiles with a 450 mhz gpr on ground ice formations that had active layer sediments excavated prior to surveying using ice core data collected from these sites we found that the volumetric fraction of ice plays the greatest role in defining the dielectric permittivity of the deposit and that it can be described using a modified complex refractive index method crim dielectric mixing model using the modified crim model we estimate the dielectric permittivity of several ground ice deposits on earth and present further estimates for similar features on mars using permittivity values for martian sediments derived from both theory and laboratory methods

extensive amazonian aged fluvial channels on mars evaluating the role of lyot crater in their formation widespread amazonian aged fluvial channels have been mapped proximal to lyot crater a 225 km diameter impact basin in the northern lowlands of mars comparable in area to some noachian hesperian fluvial systems their morphology differs being dominated by broad shallow braided channels using new developments in the study of cratering water inventory and climate history we assess eight different models for their origin dewatering of excavated ice rich lyot ejecta and contact melting from hot lyot ejecta superposed on surface ice deposits are the most plausible channel origins the existence of this extensive amazonian fluvial system is attributed to 1 the large size of lyot and its consequent hot ejecta and 2 the presence of surface ice at the time of impact attributed to obliquity changes redistributing polar ice to the mid latitudes a relatively common occurrence in martian geologic history

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

roughness and near surface density of mars from sharad radar echoes 1 we present a technique for estimating mars topographic roughness on horizontal scales from about 10 m to 100 m using shallow radar sharad sounding data our results offer a view of surface properties complementary to mars orbiter laser altimeter mola pulse width or baseline roughness maps and can be compared to sharad peak echo properties to infer deviations from the average near surface density latitudinal averaging of sharad derived roughness over arabia and noachis terrae shows good agreement with mola derived roughness and provides clear evidence for latitude dependent mantling deposits previously inferred from image data in northwestern gordii dorsum we find that bulk density in at least the upper few meters is significantly lower than in other units of the medusae fossae formation we observe the same behavior indicative of low near surface density in wind eroded crater fill in the southern highlands combining surface properties analysis subsurface sounding and high resolution optical images we show that the pavonis mons fan shaped deposit differs significantly from lobate debris aprons which sharad has shown to be ice cored there are no internal radar reflections from the smooth facies portion of the pavonis mons fan shaped deposit and we suggest that these deposits are either quite thin or have little dielectric i e density contrast with the underlying terrain future application of these techniques can identify other low density units across mars assist in the mapping of regional volatile rich mantling units and provide new constraints on the physical properties of the polar layered terrain

formation of lobate debris aprons on mars assessment of regional ice sheet collapse and debris cover armoring abstract lobate debris aprons lda are lobate shaped aprons surrounding scarps and isolated massifs that are concentrated in the vicinity of the northern dichotomy boundary on mars ldas have been interpreted as 1 ice cemented talus aprons undergoing viscous flow 2 local debris covered alpine like glaciers or 3 remnants of the collapse of a regional retreating ice sheet we investigate the plausibility that ldas are remnants of a more extensive regional ice sheet by modeling this process we find that as a regional ice sheet collapses the surface drops below cliff and massif bedrock margins exposing bedrock and regolith and initiating debris deposition on the surface of a cold based glacier reduced sublimation due to debris cover armoring of the proto lda surface produces a surface slope and consequent ice flow that carries the armoring debris away from the rock outcrops as collapse and ice retreat continue the debris train eventually reaches the substrate surface at the front of the glacier leaving the entire lda armored by debris cover using a simplified ice flow model we are able to characterize the temperature and sublimation rate that would be necessary to produce ldas with a wide range of specified lateral extents and thicknesses we then apply this method to a database of documented lda parameters height lateral extent from the dichotomy boundary region and assess the implications for predicted climate conditions during their formation and the range of formation times implied by the model we find that for the population examined here typical temperatures are in the range of 85 to 40 c and typical sublimation rates lie in the range of 6 14 mm a lobate debris apron formation times from the point of bedrock exposure to complete debris cover cluster near 400 500 ka these results show that lda length and thickness characteristics are consistent with climate conditions and a formation scenario typical of the collapse of a regional retreating ice sheet and exposure of bedrock cliffs this scenario helps resolve many of the unusual characteristics of lobate debris aprons lda and lineated valley fill lvf for example the distribution of lvf is very consistent with extensive flow of glacial ice from plateau icefields and the acquisition of a debris cover in the waning stages of retreat of the regional cover as the bedrock scarps are exposed the typical concentric development of lda around massifs is much more consistent with ice sheet retreat than insolation related local accumulation and flow we thus conclude that the retreating ice sheet model is robust and should be investigated and tested in more detail in addition these results clearly show that the lobate debris aprons in the vicinity of the dichotomy boundary could not have attained temperatures near or above the ice melting point and retained their current shape a finding that supports subzero temperatures for the last several hundred million years the age of the lda surfaces a further implication is that the lda ice has been preserved for at least several hundred million years and could potentially contain the record of the climate of mars preserved since that time below a sublimation lag deposit

northern mid latitude glaciation in the late amazonian period of mars criteria for the recognition of debris covered glacier and valley glacier landsystem deposits lobate debris aprons lda and lineated valley fill lvf have been known to characterize the mid latitude regions of mars since documented by viking their flow like character suggested that deposition of ice in talus pile pore space caused lubrication and flow during an earlier climatic regime a number of factors have remained uncertain however including the detailed structure and texture of lda lvf the relationships between them their direction of flow the origin and abundance of the lubricating agent and their exact mode of origin e g ice assisted rock creep ice rich landslides rock glaciers debris covered glaciers we use new high resolution stereo camera hrsc image and topography data in conjunction with a range of other post viking data sets and new insights provided by cold based terrestrial glacial analogs to assess the characteristics of lda lvf in the northern mid latitudes of mars we find evidence that the characteristics and flow patterns of the lda and lvf are most consistent with late amazonian debris covered glacial valley landsystems the broad distribution and integrated characteristics of the lda lvf systems suggest that earlier in the amazonian climatic conditions were such that significant snow and ice accumulated on mid latitude plateaus and in valleys producing integrated glacial landsystems the remnants of which are preserved today beneath residual sublimation till derived from adjacent valley walls atmospheric general circulation models suggest that these climatic conditions occurred when mars was at a spin axis obliquity of 35 and the atmosphere was relatively dusty glacial flow modeling under these conditions produces patterns similar to those documented in the lda lvf and sharad radar data suggests that significant amounts of ice remain sequestered below the sublimation lag today

young lava flows on the eastern flank of ascraeus mons rheological properties derived from high resolution stereo camera hrsc images and mars orbiter laser altimeter mola data 1 we report on estimates of the rheological properties of late stage lava flows on the eastern flank of ascraeus mons mars from previous studies it is known that the dimensions of flows reflect rheological properties such as yield strength effusion rates and viscosity our estimates are based on new high resolution images obtained by the high resolution stereo camera hrsc on board the european space agency s mars express spacecraft in combination with mars orbiter laser altimeter mola data compared to earlier studies the high spatial resolution of the hrsc and mola data allowed us to map 25 late stage lava flows and to measure their dimensions as well as their morphological characteristics in greater detail our estimates of the yield strengths for these flows range from 2 0 102 pa to 1 3 105 pa with an average of 2 1 104 pa these values are in good agreement with estimates for terrestrial basaltic lava flows and are comparable to previous estimates derived for a small number of lava flows on ascraeus mons our investigation indicates that the effusion rates for the studied ascraeus mons flows are on average 185 m3 s 1 ranging from 23 m3 s 1 to 404 m3 s 1 these results are higher than earlier findings that indicate effusion rates of 18 60 m3 s 1 with an average of 35 m3 s 1 however our effusion rates are similar to terrestrial effusion rates of kilauea and mauna loa and other martian volcanoes on the basis of our estimates of the effusion rates and the measured dimensions of the flows we calculated that the time necessary to emplace the flows is on average 26 days viscosities were estimated on the basis of yield strengths and effusion rates yielding average values of 4 1 106 pa s and ranging from 1 8 104 pa s to 4 2 107 pa s on the basis of newly available data sets e g hrsc mola we are now able not only to identify possible differences in eruptive behavior between ascraeus mons and elysium mons but also to study such differences over time

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

high resolution imaging science experiment hirise observations of glacial and periglacial morphologies in the circum argyre planitia highlands mars 1 the landscape of the argyre planitia and adjoining charitum and nereidum montes in the southern hemisphere of mars has been heavily modified since formation of the argyre impact basin this study examines morphologies in the argyre region revealed in images acquired by the high resolution imaging science experiment hirise camera and discusses the implications for glacial and periglacial processes distinctive features such as large grooves semicircular embayments in high topography and streamlined hills are interpreted as glacially eroded grooves cirques and whalebacks or roche moutonnee respectively large boulders scattered across the floor of a valley may be ground moraine deposited by ice ablation glacial interpretations are supported by the association of these features with other landforms typical of glaciated landscapes such as broad valleys with parabolic cross sections and stepped longitudinal profiles lobate debris aprons interpreted as remnant debris covered glaciers or rock glaciers and possible hanging valleys aligned boulders observed on slopes may also indicate glacial processes such as fluting alternatively boulders aligned on slopes and organized in clumps and polygonal patterns on flatter surfaces may indicate periglacial processes perhaps postglaciation that form patterned ground at least portions of the argyre region appear to have been modified by processes of ice accumulation glacial flow erosion sediment deposition ice stagnation and ablation and perhaps subsequent periglacial processes the type of bedrock erosion apparent in images suggests that glaciers were at times wet based the number of superposed craters is consistent with geologically recent glacial activity but may be due to subsequent modification

cold based mountain glaciers on mars western arsia mons surface environmental conditions on mars are currently extremely cold and hyperarid most equivalent to polar deserts on earth coupling newly acquired mars data with fieldbased observations regarding the flow surface morphology and depositional history of polar glaciers in antarctica we show that the multiple facies of an extensive fan shaped deposit on the western flanks of arsia mons volcano are consistent with deposition from cold based mountain glaciers an outer ridged facies that consists of multiple laterally extensive arcuate and parallel ridges resting without disturbance on both well preserved lava flows and an impact crater is interpreted as drop moraines formed at the margin of an ablating and predominantly receding cold based glacier a knobby facies that consists of equidimensional knobs each to several kilometers in diameter is inward of the ridges this facies is interpreted as a sublimation till derived from in situ downwasting of ashrich glacier ice a third facies comprising distinctive convex outward lobes with concentric parallel ridges and aspect ratios elongated downslope likely represents rock glacier deposits some of which may still be underlain by a core of glacier ice taken together these surficial deposits show that the western flank of arsia mons was occupied by an extensive mountain glacial system accumulating on and emerging from the upper slopes of the volcano and spreading downslope to form a piedmont like fan

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

recent formation and evolution of northern martian polar layered deposits as inferred from a global climate model 1 we present a time marching model which simulates the exchange of water ice between the martian northern cap the tropics and a high latitude surface reservoir net annual exchange rates of water and their sensitivity to variations in orbital rotational parameters are examined using the martian water cycle modeled by the lmd three dimensional global climate model these rates are propagated over the last 10 myr to follow the thickness of the reservoirs the effect of a sublimation dust lag is taken account to test simple models of layer formation periods of high mean polar summer insolation 5 10 ma ago lead to a rapid exhaustion of a northern polar cap and a prolonged formation of tropical glaciers the formation of a northern cap and of a high latitude icy mantle may have started 4 ma ago with the average decrease of polar insolation tropical ice may have disappeared around 2 7 ma ago but small glaciers could have formed during the last peaks of polar summer insolation over the last 4 myr most of the present cap may have formed at the expense of tropical and high latitude reservoirs forming distinct layers at almost each 51 kyr 120 kyr insolation cycle layers thickness ranges from 10 to 80 m variations being produced by the modulation of the obliquity with 2 4 and 1 3 myr periods because only 30 insolation cycles have occurred since 4 ma ago we found an inconsistency between the recent astronomical forcing the observed number of layers and simple astronomically based scenarios of layers formation

an extended period of episodic northern mid latitude glaciation on mars during the middle to late amazonian implications for long term obliquity history mars is the only planet other than earth in the solar system that has a preserved nonpolar geological record of glaciation on its surface nonpolar ice deposits on mars have been linked to variations in spin axis obliquity that cause mobilization of polar ice and redeposition at lower latitudes forming ice rich and glacial deposits remnant nonpolar glacial deposits are found across the northern mid latitudes where surface ice is not currently stable implying that different climatic conditions existed on mars in the past individual glacial deposits are often too small to date reliably using impact crater size frequency data we describe a novel approach that allows us to derive new information about when glaciation occurred in broad areas of the northern mid latitudes in this region we have classified 1 craters that superpose preexisting glacial deposits and were modified by later accumulation and therefore formed during an epoch when glaciation was occurring and 2 craters that are superposed on glacial deposits but are themselves unmodified by ice accumulation and thus post date significant glaciation the sparse population of post glacial craters reveals that the last period of extensive ice deposition of this type in this latitude band was recent late amazonian the substantial number of craters formed during the recurring glacial periods implies that northern mid latitude glaciation was a long lived recurring process occurring over a period of at least 600 m y on the basis of mars atmospheric general circulation models these results are consistent with higher obliquity being common in the past with recurring periods of obliquity exceeding the 25 axial tilt of mars today these observations support the statistical prediction of j laskar and colleagues that the median obliquity during the amazonian was 35 40

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

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

entrainment at cold glacier beds here we present measurements of the gas content and isotopic composition of debris rich basal layers of a polar glacier meserve glacier antarctica which has a basal temperature of 17 c these measurements show that debris entrainment has occurred without alteration of the glacial ice and provide the most direct evidence to date that active entrainment occurs at the beds of cold glaciers without bulk freezing of water entrainment at subfreezing temperatures may have formed the u shaped trough containing meserve glacier in addition to possibly allowing some cold based glaciers to be important geomorphic agents entrainment at subfreezing temperatures provides a general mechanism for formation of the dirty basal layers of polar glaciers and ice sheets which are rheologically distinct and can limit the time span of ice core analyses furthermore accumulating evidence suggests that geomorphologists should abandon the assumption that cold based glaciers do not slide and abrade their beds