products of subglacial volcanic eruptions under different ice thicknesses two examples from antarctica late cenozoic subglacially erupted volcanic sequences are scattered throughout the antarctic peninsula two of the best preserved examples at mount pinafore alexander island c 5 5 6 ma and brown bluff graham land c 1 ma are complete enough to be regarded as sequence holotypes for this uncommonly preserved eruptive depositional setting despite a common glacial association the sedimentary lithofacies in the two outcrops suggest flowing and ponded water conditions respectively indicating significant differences in the depositional palaeoenvironments the original ice thicknesses exerted a major control on the lithofacies which resulted from each eruptive phase at mount pinafore the lithofacies were confined within a steep sided valley during successive eruptions beneath thin 100 150 m wet based ice the much thicker succession at brown bluff is a tindar tuya edifice which formed within a small basin probably 15 km across confined by ice 400 m thick

the early environment and its evolution on mars implication for life there is considerable evidence that the early climate of mars was very different from the inhospitable conditions there today this early climate was characterized by liquid water on the surface and a dense atmosphere composed predominantly of co2 the duration of these warm initial conditions on the surface of mars is uncertain but theoretical models suggest that they could have persisted for hundreds of millions up to a billion years from studies of the earth s earliest biosphere we know that by 3 5 gyr ago life had originated on earth and reached a fair degree of biological sophistication surface activity and erosion on earth make it difficult to trace the history of life before the 3 5 gyr time frame if mars did maintain a clement environment for longer than it took for life to originate on earth then the question of the origin of life on mars follows naturally the fossil evidence of early life on earth provides clues as to what form fossils on mars might take of particular interest are stromatolites macroscopic layered structures that result from the anchoring of sediments by microorganisms living in the photic zone since over two thirds of the martian surface is more than 3 5 gyr old the possibility exists that mars may hold the best record of the events that led to the origin of life even though there may be no life there today

morphometry of glaciovolcanic edifices from iceland types and evolution abstract the morphology of many glaciovolcanoes is considered one of the distinctive characteristics of their ice confining eruption environment however a thorough morphometric analysis of a large number of glaciovolcanic edifices has never been performed based on a semi automatic geomorphometric mapping of glaciovolcanic edifices of the icelandic neovolcanic zones we present a morphometric database of 155 glaciovolcanic edifices formed during the last 0 78 ma this database enables a comprehensive analysis of the morphometric diversity of a large suite of glaciovolcanic edifices sheet like formations however are not considered due to lack of data using three planimetric measurements basal length average basal width and average summit plateau width and their ratios three main morphometric groups can be distinguished in a ternary diagram 1 conical edifices with no or small summit plateaus 2 linear ridges and 3 flat topped edifices subdivided into equidimensional and elongated all three groups contain edifices with and without lava caps these morphometric groups can be fitted to the commonly accepted terminology for cone mound tindar and tuya however since lava caps occur in all morphometric groups a grouping based on its existence is not practical this suggests that by adding the descriptor lava capped to any of the three classes may be a useful way to refine the classification based on the ternary diagram ridges are the most morphometrically distinct glaciovolcanic edifice because of their very extreme elongation followed by flat topped edifices and finally conical edifices however morphometric parameters cannot be used singlehanded to identify glaciovolcanic edifices from other types of volcanic edifices such as composite volcanoes shields or submarine volcanoes and should always be complemented with other observations the glaciovolcanic edifice volumes range from 0 15 10 2km3 to 32 km3 conical edifices are the smallest 1 km3 overall with growth three morphological evolutions can be considered a an initial eruptive fissure concentrates into one vent generating an equidimensional edifice that either can be a conical or a flat topped edifice b the edifice maintains its elongation suggesting that a fissure is the dominating vent structure and during continued eruption develops significant summit plateaus generating elongated flat topped edifices and c the edifice increases in elongation because the fissure lengthens during the eruption and a plateau building stage does not occur producing increasingly elongated ridges

heat transfer in volcano ice interactions on mars synthesis of environments and implications for processes and landforms we review new advances in volcano ice interactions on mars and focus additional attention on 1 recent analyses of the mechanisms of penetration of the cryosphere by dikes and sills 2 documentation of the glacial origin of huge fan shaped deposits on the northwest margins of the tharis montes and evidence for abundant volcano ice interactions during the later amazonian period of volcanic edifice construction and 3 the circumpolar hesperian aged dorsa argentea formation interpreted as an ice sheet and displaying marginal features channels lakes and eskers indicative of significant melting and interior features interpreted to be due to volcano ice interactions e g sub glacial volcanic edifices pits basins channels and eskers in this context we describe and analyse several stages and types of volcano ice interactions 1 magmatic interactions with ice rich parts of the cryosphere 2 subglacial volcanism represented by intrusion under and into the ice and formation of dikes and moberg like ridges intrusion of sills at the glacier volcano substrate interface and their evolution into subglacial lava flows formation of subglacial edifices marginal melting and channels 3 synglacial ice contact volcanism represented by flows banking up against glacier margins chilling and forming remnant ridges and 4 post glacial volcanism and interactions with ice deposits

subkilometer martian volcanoes properties and possible terrestrial analogs kilometer to subkilometer cones with large central craters are the most numerous volcanic structures in the northern plains of mars based on examination of more than 12 000 high resolution viking orbiter images most of these very small cones are located in parts of eastern acidalia and utopia isidis elysium planitia measurements of base and pit diameter for some 2000 well resolved features show small variations in the histogram of base diameters between and within regions but remarkable similarity in the distribution of crater cone diameter ratios this suggests that the small cones had a similar origin with only minor variations in local conditions the acidalia cones are generally larger more widely distributed and occur on a greater variety of terrains than those in utopia isidis elysium based on morphology distribution and the crater cone ratio histograms the smallest martian cones may be similar to icelandic pseudocraters somewhat larger steeper cones with smaller crater cone ratios which also occur in eastern acidalia may be analogs of terrestrial cinder cones

new bioclimatic models for the quaternary palaearctic based on insectivore and rodent communities mammal remains preserved in archaeological and palaeontological deposits are commonly used to reconstruct past terrestrial climates and environments here we propose new species specific models for bioclimatic analysis a palaeoclimatic method based on a climatic restriction index for each mammal species discriminant analysis and multiple linear regressions our new models are based on small mammal associations particularly insectivores and rodents from quaternary paleoarctic contexts a dataset including new localities and an updated taxonomy was constructed in order to develop two approaches the first using only rodentia the second based on associations including both rodentia and eulipotyphla both approaches proved to be reliable for inferring both climate zone and quantifying temperature precipitation and seasonality rarefaction analysis revealed these new models to be reliable even when a substantial percentage of species from the original palaeocommunity was absent from the fossil site application of these new models to small mammal associations from two sequences balma de l abeurador france and el miron spain spanning from the last glacial maximum to the holocene are consistent with the primary climatic changes recorded by regional pyrenean proxies and showed an increase in mean annual temperature of between 3 and 5 c

meltback of hesperian aged ice rich deposits near the south pole of mars evidence for drainage channels and lakes ponding minimum volumes 10 12 m 3 overtopping downcutting and further drainage of material through a series of craters and into the prometheus basin near the edge of the current cap topography data show that water filled some craters to depths of at least 200 m and possibly as much as 600 m materials derived from melting of this lobe of the daf drained over a lateral distance of 600 km and a vertical height of 800 m partially emptying into the prometheus basin these combined observations imply that meltback of the older volatile rich deposit was a widespread event occurring on both sides of the deposit over a distance of at least 1800 km and in an area possibly as much as 2 9 10 6 km 2 candidate top down and bottom up melting scenarios are examined the presence of associated hesperian aged volcanic deposits and possible subglacial edifices suggests that local and regional basal heating was a major factor in generating the meltwater that formed the drainage features index terms 6225 planetology solar system objects mars 5416 planetology solid surface planets glaciation 5470 planetology solid surface planets surface materials and properties 3309 meteorology and atmospheric dynamics climatology 1620 5418 planetology solid surface planets heat flow keywords mars polar glaciers hesperian channels water

variations in the thermal output of the subglacial grimsvotn caldera iceland a 69 year record 1922 1991 of heat release has been obtained from the subglacial geothermal system of the grimsvotn caldera within the vatnajokull ice cap the data were derived from in situ measurements of the volume of meltwater accumulated in the caldera lake subtracting climatically induced melting the overall fluctuations in the heat flux are closely related to volcanic activity and are dominated by a main pulse of 11 600 mw caused by a major eruption in 1938 gradually declining to 1600 mw in 1976 1982 heat extracted from the roof of a magma chamber with the aid of hydrothermal convection may have given a basic contribution to the heat flux of 1500 to 2000 mw an upper bound the variable part of the heat flux from 0 to 10 000 mw was released from magma erupted at the base of the glacier and from shallow intrusions the total heat released over the period 1922 to 1991 was 8 1 1 6 1018j equivalent to the energy released by the solidification and cooling of 2 1 0 4 km of basaltic magma the contribution to the total heat flux was 45 max from a magma chamber 35 min from shallow intrusions and 20 from eruptions this implies that magma at the roof of a chamber solidified and cooled at the rate of 1 2 1 6 107 m a 1 or about 1 km over the last 69 years heat release at grimsvotn was probably more intense in the 19th century when volcanic eruptions were more frequent

ice volcano interaction of the 1996 gjalp subglacial eruption vatnajokull iceland volcanic eruptions under glaciers can cause dangerous floods and lahars1 2 3 and create hyaloclastite fragmented glassy rock mountains4 5 6 7 8 but processes such as the rate of heat transfer between ice and magma edifice formation and the response of the surrounding glacier are poorly understood because of the lack of data here we present observations from the fissure eruption at vatnajokull ice cap iceland in october 1996 in the 13 days of the eruption 3 km3 of ice were melted and the erupted magma fragmented into glass forming a hyaloclastite ridge 6 7 km long and 200 300 m high under 500 750 m of ice meltwater of temperatures of 15 20 c flowed along a narrow channel at the glacier bed into the grimsvotn subglacial lake for five weeks before draining in a sudden flood or jokulhlaup subsidence and crevassing of the ice cap occurred over the eruptive fissure and the meltwater path whereas elsewhere the glacier surface remained intact suggesting that subglacial eruptions do not trigger widespread basal sliding in warm based glaciers

convection in a catastrophic flood deposit as the mechanism for the giant polygons on mars a formational mechanism for the large scale polygons that are defined by intersecting fractures in the northern plains of mars is proposed in this work the presented model is based on rayleigh convection of interstitial water driven by an unstable density temperature gradient within a saturated porous medium catastrophic emplacement of water rich sediments into the martian northern plain basins could have provided a thick sedimentary layer in which rayleigh convection could have occurred convection within this active layer is proposed to have differentially thawed an underlying ice rich permafrost layer that had been at the planet s surface before being rapidly buried the resulting morphology of the permafrost subsurface is thought to have resembled the scalloped solid liquid interface morphology produced in terrestrial convective flow visualization studies the exact size and shape of the scallops on the frozen subsurface would have been controlled by the dimensions of the convection cells which are estimated to have had width to depth ratios of between 3 4 and 4 5 subsequent stresses e g gravity and bending stresses would have produced maximum tensile stresses in the overlying sediments preferentially above the subsurface topographic highs as described previously by mcgill and hills 1992 additional desiccation of the sediments would have required contraction of the sediment cover and would have produced large scale polygonal fractures along the preexisting weaknesses located above the raised subsurface topography thus the underlying subsurface geometric morphology would have been translated to the surface and would be represented by the large scale polygonal fractures visible in the viking orbiter and mars global surveyor images of the martian northern plains

present day seasonal gully activity in a south polar pit sisyphi cavi on mars abstract the large amount of multi temporal high resolution images acquired in the last few years offers the opportunity to identify morphological changes associated with recent geologic activity on the surface of mars in this study we focus on a single gully in sisyphi cavi located in the south polar region at 1 44 e and 68 54 s the gully incises the gullied equator facing slope of an isolated polar pit within an infilled impact crater it is important to notice that the following investigations describe the activity and modifications of an existing gully and not the formation of the gully itself high resolution image data analyses show new deposits at the terminus of the gully channel and on the gully apron within spring after solar longitudes of 236 of martian years my 29 and 31 our morphological investigations show that the identified new deposits were formed by dark flows through the entire gully deposited on top of the apron between solar longitudes l s 218 and 226 thermal data show a temperature increase between l s 218 and 226 near infrared spectral data show relatively constant band strengths of co 2 ice and h 2 o ice in this time range after the formation of the dark flows after l s 226 temperatures increase rapidly from 180 k to 270 k at l s 250 at this time spectral data indicate that all volatiles on the surface sublimated however an earlier beginning of sublimation when the dark flows were observed between l s 218 and 226 is likely due to the fact that the instruments can only show the last phase of sublimation decrease of volatile band strengths spectral modeling shows that from winter to mid spring the surface of the studied area is covered by translucent co 2 slab ice contaminated by minor amounts of h 2 o ice and dust furthermore our spectral modeling indicates that the dark material most likely flows on top of the co 2 slab ice cover three different scenarios were proposed to explain the identified dark flows including 1 flows supported by liquid h 2 o 2 flows supported by co 2 gas and 3 dry flows on the basis of our study we find that scenario 1 is unlikely because of the very low temperatures while scenario 2 is consistent with the observed beginning of co 2 ice sublimation in the study area it is unlikely because of the limitation of the activity to only one gully compared to surrounding gullies that share the same morphologies slope angles and volatile contents also with scenario 3 dry flows the activity of only one gully is difficult to explain thus we propose a mixture of scenario 2 and 3 dry flows supported by the ongoing sublimation of co 2 ice within the gully to be the most plausible scenario when the observed active gully comprises different source material than the surrounding gullies i e a higher content of probably sand sized material from outcrops located in the alcove

tuyas a descriptive genetic classification we present a descriptive genetic classification scheme and accompanying nomenclature for glaciovolcanic edifices herein defined as tuyas positive relief volcanoes having a morphology resulting from ice confinement during eruption and comprising a set of lithofacies reflecting direct interaction between magma and ice melt water the combinations of lithofacies within tuyas record the interplay between volcanic eruption and the attending glaciohydraulic conditions although tuyas can range in composition from basaltic to rhyolitic many of the characteristics diagnostic of glaciovolcanic environments are largely independent of lava composition e g edifice morphology columnar jointing patterns glass distributions pyroclast shapes our classification consolidates the diverse nomenclature resulting from early isolated contributions of geoscientists working mainly in iceland and canada and the nomenclature that has developed subsequently over the past 30 years tuya subtypes are first recognized on the basis of variations in edifice scale morphologies e g flat topped tuya then on the proportions of the essential lithofacies e g lava dominated flat topped tuya and lastly on magma composition e g basaltic lava dominated flat topped tuya these descriptive modifiers potentially supply additional genetic information and we show how the combination of edifice morphologies and lithofacies can be directly linked to general glaciohydraulic conditions we identify nine distinct glaciovolcanic model edifices that potentially result from the interplay between volcanism and glaciohydrology detailed studies of tuya types are critical for recovering paleo environmental information through geological time including ice sheet locations extents thicknesses and glaciohydraulics such paleo environmental information represents a new innovative underutilized resource for constraining global paleoclimate models

evidence age and thickness of a frozen paleolake in utopia planitia mars abstract recent mapping studies west of elysium mons mars have pinpointed subice features that suggest the existence of a frozen paleolake in utopia planitia as recently as 1 8 billion years ago the subice features are interpreted to be hyaloclastic ridges and hills table mountains associated jokulhlaup deposits and fluvial channels photoclinometric studies of these features and of a basal scarp around the northwest flank of elysium mons interpreted to have been an ice sheet boundary indicate that the maximum thickness of ice within the basin may have been about 180 m this thickness of ice during a relatively late stage of martian geologic history would have important implications concerning the atmospheric the climatic and possibly the exobiologic history of the planet

interior trough deposits on mars subice volcanoes widespread several kilometer thick successions of layered deposits occur as mounds that partly fill the troughs or chasmata that compose the valles marineris on mars like terrestrial subice volcanoes the layered deposits occur in a volcano tectonic setting within basins that may have held ponded water or ice on the basis of their dimensions morphologies and associated catastrophic floods and other geologic events as shown in viking and new mars global surveyor mgs data sets we suggest that the interior deposits are volcanic in origin and possibly generated by subice eruptions a tuya origin for the mounds can explain the lack of external sediment mound heights that can rival the plateau local flat topped mesas morphologically distinct mounds of different ages horizontal to steep dips fine grained materials indications of rare volcanic vents and lava flows and spectral composition the extremely diverse layering of west candor chasma and possible volcanic cones in melas may have formed by related subaerial eruptions consistent with the suggestion that interior deposits are eroding out of the wall rock some deposits could have been erupted from sites along the walls

physical controls and resulting morphological forms of quaternary ice contact volcanoes in western canada abstract volcanism in association with large quantities of ice manifests itself in a variety of morphological forms developed under differing physical conditions these physical conditions include the location amount thickness and type of confining ice the location and quantity of trapped water and the surrounding topography ice in the form of thick continental ice sheets thinner alpine glaciers or even perennial accumulations of snow can influence the resulting morphological form of the volcano the chemical composition of the erupting magma effusion rate and total erupted volume will also affect the shape of the resulting edifice quaternary volcanoes influenced by many of these factors are found in western canada the morphological forms range from tuyas to subglacial mounds to stratovolcanoes this paper provides a review of ice contact volcanism and volcanic products formed in these environments using canadian examples for illustration

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

icelandic pseudocraters as analogs to some volcanic cones on mars pseudocraters are rootless vents formed by the interaction of lava flows with surface or near surface water this interaction can produce mild explosions and the accumulation of scoria and spatter into small constructs pseudocraters in several localities in iceland were examined in the field and compared to similar appearing features observed on mars the icelandic pseudocrater cones in this study range in size from 6 to 70 m in diameter have summit craters which range from 2 to 28 m in diameter many cones lack craters entirely and have flanks that are either concave up or convex up the size and spacing of icelandic pseudocraters might be a function of the availability of water in which larger closely spaced features result from efficient lava water interaction as suggested by the environments in which the features formed possible martian pseudocrater cones in amazonis planitia range in diameter from 30 to 180 m and have craters 12 to 80 m in diameter a numerical model for volcanic explosions was adapted to study the formation of pseudocraters under terrestrial and martian conditions the results suggest that explosions forming martian cones require significantly less water calculated masses are less by a factor of 4 to 16 than those forming icelandic pseudocraters despite their larger sizes this is attributed to the low gravity and atmospheric pressure in the mars environment and is consistent with the likely lower abundance of water which might be present as interstitial ice at shallow depths in the regolith locations of potential pseudocraters on mars at latitudes as low as 8 n imply the presence of crustal ice stores at the time of their formation

the meteorology of gale crater as determined from rover environmental monitoring station observations and numerical modeling part ii interpretation abstract numerical modeling results from the mars regional atmospheric modeling system are used to interpret the landed meteorological data from the rover environmental monitoring station onboard the mars science laboratory rover curiosity in order to characterize seasonal changes throughout the martian year simulations are conducted at ls 0 90 180 and 270 two additional simulations at ls 225 and 315 are explored to better understand the unique meteorological setting centered on ls 270 the synergistic combination of model and observations reveals a complex meteorological environment within the crater seasonal planetary circulations the thermal tide slope flows along the topographic dichotomy mesoscale waves slope flows along the crater slopes and mt sharp and turbulent motions all interact in nonlinear ways to produce the observed weather ls 270 is shown to be an anomalous season when air within and outside the crater is well mixed by strong flushing northerly flow and large amplitude breaking mountain waves at other seasons the air in the crater is more isolated from the surrounding environment the potential impact of the partially isolated crater air mass on the dust water noncondensable and methane cycles is also considered in contrast to previous studies the large amplitude diurnal pressure signal is attributed primarily to necessary hydrostatic adjustments associated with topography of different elevations with contributions of less than 25 to the diurnal amplitude from the crater circulation itself the crater circulation is shown to induce a suppressed boundary layer

17 000 years of vegetation fire and climate change in the eastern foothills of the andes lat 44 s abstract paleoenvironmental records from patagonia reveal the importance of latitude longitude and elevation in shaping the response of vegetation to climate change we examined the vegetation fire and watershed history from two sites at lat 44 s as inferred from pollen charcoal and lithologic data these reconstructions were compared with independent paleoenvironmental records to better understand ecosystem dynamics along the southeastern andes lat 41 50 s our results show that at lat 44 s late glacial heath steppe was colonized by trees at 14 200 cal yr bp and forests became more closed at 11 500 cal yr bp differences in forest cover between the two sites were likely due to elevation dependent disparities in humidity and fire north of lat 44 s increasing precipitation favored initial forest development at 16 500 cal yr bp while dry conditions restricted tree expansion in the south until 7000 cal yr bp the time transgressive pattern is attributed to a gradual southward shift in the southern westerlies resulting from deglaciation and increasing annual insoltion present day vegetation developed at all latitudes during the middle to late holocene when the core of the southern westerlies reached its modern position 50 s asynchronous forest expansions north and south of lat 45 s between 5000 and 3000 cal yr bp are ascribed to centennial cycles of contraction and expansion of the southern westerlies which led to seasonal variations in precipitation at the core and northern border of the wind belt synchronous oscillations in tree abundance along the eastern andes prevailed during the last 3000 years decreased forest cover at all latitudes between 2500 and 1500 cal yr bp is concurrent with la nina like conditions and high solar irradiance these climate drivers likely decreased effective moisture and favored fires at all latitudes

density variations within the south polar layered deposits of mars 1 the south polar layered deposits spld constitute the largest known reservoir of water on mars previous studies solved for the best fit uniform density of the deposits using a forward approach here we invert for the lateral density variations in the layered deposit using gravity data from radio tracking of mars reconnaissance orbiter topography from mola on board mars global surveyor and radar sounding data from marsis on board mars express we use the gravity anomalies outside the spld to construct a wiener filter which is applied to the gravitational signature of the spld to remove the short wavelength anomalies over the spld that are spectrally consistent with an origin in the crust or mantle we then use a constrained inversion for the vertically averaged density within the spld as a function of position the results suggest significant density variations within the spld an inverse relationship between the density and thickness of the spld suggests that thicker portions of the cap contain less dust alternatively the dorsa argentea formation may extend beneath the spld and result in the observed high gravity anomaly in the marginal area of the spld we find these conclusions to be robust against the choice of inversion constraint and perturbations to the applied filter a synthetic test is also performed to verify the recoverability of the density variation in our approach

polar basal melting on mars if ice is present throughout the cryosphere anywhere on mars thermodynamic considerations suggest that it is most likely at the poles given this condition the deposition of dust and h2o at the polar surface will ultimately result in a situation where the equilibrium depth to the melting isotherm has been exceeded melting ice at the base of the cryosphere until thermal equilibrium is once again established should deposition persist the polar deposits will ultimately reach a thickness where melting will occur at their actual base at this point the cap may reach a state of equilibrium where the deposition of any additional ice is balanced by geothermal melting thermal calculations yield basal melting thicknesses that are consistent with the inferred 4 6 km thickness of the present north polar cap however in the south the deposits appear sufficiently thin 1 2 km that geothermal melting is likely to be relegated to a depth that lies well below the regolith polar cap interface similar conclusions are reached from consideration of the polar caps theoretical equilibrium profiles in the north a basal yield stress characteristic of ice at or near the melting point is indicated while in the south it appears the cap has yet to achieve the necessary height for significant deformation to occur at its base the potential importance of basal melting is illustrated through the discussion of four examples 1 the origin of the major polar reentrants 2 the removal and storage of an ancient martian ice sheet 3 the mass balance of the polar terrains and 4 the possibility of basal melting at temperate latitudes this analysis suggests that the process of basal melting may play a key role in understanding the evolution of the martian polar terrains and the long term climatic behavior of water on mars

changes in jokulhlaup sizes in grimsvotn vatnajokull iceland 1934 91 deduced from in situ measurements of subglacial lake volume a record of volumes of jokulhlaups from the subglacial grimsvotn lake vatnajokull iceland has been derived for the period 1934 91 the change in lake volume during jokulhlaups is estimated from the lake area ice cover thickness and the drop in lake level the jokulhlaup volumes have decreased gradually during this period of low volcanic activity and declining geothermal power the two jokulhlaups in the 1930s each discharged about 4 5 km peak discharge 25 30 10 3 m 3 s 1 in the 1980s jokulhlaup volumes were 0 6 1 2 km 3 peak discharge 2 10 3 m 3 s 1 the lake level required to trigger a jokulhlaup has risen as an ice dam east of the lake has thickened water flow in a jokulhlaup ceases when the base of a floating ice shelf covering grimsvotn settles to about 1160 m a s l apparently the jokulhlaups are cut off when the base of the ice shelf collapses on to a subglacial ridge bordering the lake on its eastern side the decline in melting rates has resulted in a positive mass balance of the 160 170 km grimsvotn ice drainage basin comparison of maps shows that the average positive mass balance rate was 0 12 km 3 a 1 25 of the total accumulation in the period 1946 87 a gradually increasing positive mass balance has prevailed since 1954 reaching 0 23 km 3 a 1 in 1976 86 48 of total accumulation

rootless cones on mars indicating the presence of shallow equatorial ground ice in recent times high resolution mars orbiter camera moc images have revealed the existence of clusters of small cones in the cerberus plains marte valles and amazonis planitia mars these cones are similar in both morphology and planar dimensions to the larger of icelandic rootless cones which form due to explosive interactions between surficial lavas and near surface groundwater impact crater size frequency relationships indicate that surfaces upon which the cones sit are no older than 10 ma if martian cones form in the same manner as terrestrial rootless cones then equatorial ground ice or ground water must have been present near the surface in geologically recent times

geomorphology of subglacial volcanoes in the azas plateau the tuva republic russia abstract the azas plateau volcanic field is located in the tuva republic of the russian federation the compositions of the azas plateau volcanics include low viscosity trachybasalt and basanite volcanic edifices of middle late pleistocene age are widely distributed in the southeastern part of the volcanic field there are subglacial volcanoes among the volcanic edifices and their formation coincided with extensive ancient glaciations in the region the dominant subglacial volcanoes in the area are tuyas the general shapes of the tuyas flat tops with steep sides are due to eruptions into meltwater lakes and confinement of ice walls and effusive subaerial eruptions of basaltic lavas there are also non flat topped subglacial volcanoes and at least one subaerial volcanic edifice in the area degradation appears to have modified the primary shapes of the tuya edifices and such processes seem to include failures of over steepened slopes gully formation due to stream runoff and debris flows cirque valley glaciation and modification by rock glaciers the estimated thicknesses of the ice sheets covering the subglacial volcanoes during their eruptions range 300 600 m on average

mineralogic evidence for subglacial volcanism in the sisyphi montes region of mars abstract here we examine the mineral assemblages detected on possible glaciovolcanic edifices in the sisyphi planum region of mars a high latitude region in the southern highlands nestled between the argyre and hellas impact basins minerals were identified utilizing visible near infrared spectra from the compact reconnaissance imaging spectrometer for mars crism analysis of eleven crism images located on the volcanic edifices revealed three distinct spectral classes in the region which are interpreted to be gypsum dominated smectite zeolite iron oxide dominated possibly palagonite and polyhydrated sulfate dominated material while sulfates can form under a variety of alteration conditions palagonite like mineral assemblages require low temperature and high water to rock hydrothermal conditions typically found in subglacial or subaqueous volcanic eruptions the possible palagonite detections on the volcanic edifices the geomorphology of the region and the analogous terrestrial mineralogy of subglacial eruptions strongly suggests the formation of these minerals during subglacial eruptions or associated hydrothermal systems this implies that thick water ice sheets were present in this region in the late noachian or early hesperian and that the subglacial hydrothermal systems could have supported habitable environments with excellent biosignature preservation potential

evidence of volcanic and glacial activity in chryse and acidalia planitiae mars abstract chryse and acidalia planitiae show numerous examples of enigmatic landforms previously interpreted to have been influenced by a water ice rich geologic history these landforms include giant polygons bounded by kilometer scale arcuate troughs bright pitted mounds and mesa like features to investigate the significance of the last we have analyzed in detail the region between 60 n 290 e and 10 n 360 e utilizing hirise high resolution imaging science experiment images as well as regional scale data for context the mesas may be analogous to terrestrial tuyas emergent sub ice volcanoes although definitive proof has not been identified we also report on a blocky unit and associated landforms drumlins eskers inverted valleys kettle holes consistent with ice emplaced volcanic or volcano sedimentary flows the spatial association between tuya like mesas ice emplaced flows and further possible evidence of volcanism deflated flow fronts volcanic vents columnar jointing rootless cones and an extensive fluid rich substratum giant polygons bright mounds rampart craters allows for the possibility of glaciovolcanic activity in the region landforms indicative of glacial activity on chryse acidalia suggest a paleoclimatic environment remarkably different from today s climate changes on mars driven by orbital obliquity changes or giant outflow channel activity could have resulted in ice sheet related landforms far from the current polar caps

candidate subglacial volcanoes in the south polar region of mars morphology morphometry and eruption conditions 1 a number of isolated mountains mapped in the south polar region of mars are documented using mars global surveyor mgs mars orbiter laser altimeter mola and mars orbiter camera moc data these mountains have average separation distances of 175 km they are typically 30 40 km in diameter and 1000 1500 m high and their bases fall near an elevation of 1200 m a significant number of the population are located on or very close to a 660 km long line extending toward the south pole the summits of a number of these mountains have unusual shapes flat topped flat topped with a cone and large summit craters relative to the summit diameter sinuous channels are found in association with the margins of several of the mountains several modes of origin are considered for these mountains including impact tectonic and volcanic these mountains occur in intimate association with the hesperian aged dorsa argentea formation a unit containing features and structures interpreted to be related to a thick areally extensive ice sheet on the basis of these observations and analyses it is concluded that the most plausible origin for these mountains is volcanic and that they represent extrusion of lava from vents many of which lay underneath an ice sheet the unusual shape of many of the mountains is consistent with construction of a volcanic edifice underneath an ice sheet and melting of adjacent ice rich material sometimes forming drainage channels the topography of these mountains suggests that the ice sheet averaged at least 1 4 km thick at the time of eruption these features appear to be associated with early hesperian aged ridged plains hr

extensive hesperian aged south polar ice sheet on mars evidence for massive melting and retreat and lateral flow and ponding of meltwater local and regional mars orbiter laser altimeter mola topographic data support the presence of an extensive hesperian aged volatile rich south polar deposit the dorsa argentea formation hd and related units underlying the present amazonian aged polar cap api residual ice and apl layered terrain and covering a surface area that could be as large as 2 94 106 km2 about 2 of the surface of mars over twice the area of the present amazonian aged south polar deposits the deposit characteristics indicate that it contained significant quantities of water ice in amounts comparable to present day polar deposits several lines of evidence for melting indicate that the ice sheet deposits underwent melt back and liquid water drainage into surrounding lows including a large valley near the crater schmidt and the argyre basin narrow sinuous ridges lie in a broad linear depression extending from a high near the present polar cap continuously downslope to near the distal portion of hd the new topographic data support the interpretation of these ridges as eskers representing meltwater distribution networks at the base of the receding deposit extensive development of large pits and depressions cavi have previously been interpreted as eolian etching or basal melting of ice rich deposits analysis of mola topography supports the interpretation that they represent basal melting of ice rich deposits and shows that they have links to the esker systems volumetric considerations and topographic lineations suggest that some of the basal melting occurred beneath regions presently occupied by apl and that some of the liquid water formed ponds and lakes in the distal parts of hd the presence of pedestal craters is further evidence of the removal of extensive volatile rich deposits and contributes to the quantitative measure of the former deposit thickness where did the melt products go inspection of the margins of the dorsa argentea formation reveals several large channels that begin there and drain downslope for distances between 900 and 1600 km onto the floor of the argyre basin some 3 5 4 0 km below their origin these channels do not exhibit tributaries their broad lateral distribution supports other evidence that deposit melting was areally very widespread and volumetrically significant and that a large part of the meltwater entered the surface distribution system and was deposited on the floor of the argyre basin over 1000 km away estimates of the present deposit thicknesses together with amounts of the deposit removed by meltback suggest that the original volume could have been as much as 5 9 106 km3 equivalent to a global layer of water 20 m deep if the deposit consisted of 50 volatiles a portion of these volatiles migrated across the surface to pond in adjacent valleys and basins and into the groundwater system a significant portion of the volatiles remain in the deposit representing a net removal from the atmosphere and from the active hydrologic system in early to middle mars history and forming an accessible record of aqueous conditions and possible biological environments dating from that time

ice confined construction of a large basaltic volcano austurfjoll massif askja iceland austurfjoll is the largest basaltic glaciovolcanic massif at askja volcano central iceland and through detailed studies of its volcanological and geochemical characteristics we provide a detailed account of the sequence and structure of the ice confined construction of a large icelandic basaltic volcano in particular austurfjoll represents a geometry of vents and resulting glaciovolcanic morphology not previously documented in ice confined basaltic volcanoes austurfjoll was constructed during two major phases of basaltic volcanism via seven eruptive episodes through disperse fissure dominated eruptions the earliest episode involved a rare and poorly exposed example of subaerial activity and this was succeeded by six episodes involving the eruption of ice confined pillow lavas and numerous overlapping fissure eruptions of phreatomagmatic tephra evidence of local subaerial lavas and tephras indicates the local growth of eruptive centers above englacial lake levels and subsequent flooding but no prolonged subaerial activity localized ice contact facies paleowater levels and diamictons indicate the position and thickness of the ice was variable during the construction of austurfjoll and eruptive activity likely occurred in multiple and variable level meltwater lakes during the last glacial period lithofacies evidence including gradational transitions from effusive to explosive deposits superposition of fragmental facies above coherent facies and drainage channels suggest that changes in eruptive style were driven largely by external factors such as drainage and the increasing elevation of the massif this study emphasizes the unique character of austurfjoll being composed of large pillow lava sheets numerous 40 overlapping glaciovolcanic tindars and only localized emergent deposits as a product of its prolonged ice confined eruptive history contrasts with previous descriptions of tuyas and tindars

martian impact craters correlations of ejecta and interior morphologies with diameter latitude and terrain abstract the premise of this study is that global analysis of crater morphologies can discriminate between the effects of impact energy atmosphere and subsurface volatiles based on the correlation between morphology and latitude diameter and terrain this study focuses on seven ejecta and nine interior morphologies associated with 3819 craters 8 km in diameter distributed across the entire martian surface this data set is sufficiently large to provide statistically viable results on a global scale the results of the analyses indicate that changes in ejecta and interior morphology correlate with increases in crater diameter excavation depths corresponding to these diameters are calculated from depth diameter relationships and are compared to the theoretical distribution of subsurface volatiles the different ejecta morphologies can be described by impact into material with varying proportions of volatiles and the latidudinal variations seen for rampart crater morphologies correlate well with the proposed latitude depth relationship for ice and brines across the planet many of the interior structres show distributions indicative of terrain dependent influences for example the concentrations of central pit craters around ancient impact basins and on alba patera suggest that volatiles preferentially collect in these areas however central peak and peak ring interior morphologies show little relationship to planetary properties and probably result from changes in impact energy thus many of the unique morphologies associated with martian impact craters result from the presence of subsurface volatiles

constraints on the history of open basin lakes on mars from the composition and timing of volcanic resurfacing 1 abundant evidence exists for valley network related fluvial activity near the noachian hesperian transition on mars and areally significant quantities of volcanic ridged plains were emplaced during this period as well thus it is worthwhile to explore the hypothesis that lava water interaction occurred on the surface of mars at this time we analyzed the morphology physical properties composition and surface ages of thirty open basin lakes topographic lows with both an inlet valley and an outlet valley that were also resurfaced by volcanic flows hyperspectral imaging data from the compact reconnaissance imaging spectrometer for mars crism and observatoire pour la mineralogie l eau les glaces et l activite omega instruments indicate that of the 30 basins 12 exhibit the spectral properties of basaltic lithologies with diagnostic absorptions of olivine high calcium pyroxene and low calcium pyroxene an olivine high calcium pyroxene mixture is the most commonly identified mineral assemblage consistent with other hesperian aged volcanic units therefore our mineralogical results for over a third of the open basin lake floors analyzed support prior interpretations that the basins were resurfaced by volcanic flows supporting evidence for resurfacing by volcanic flows is also given by the observed morphology and physical properties e g surface roughness thermal inertia of the resurfaced open basin lake floors in these 30 examples however no evidence was found for lava water interaction the ages of emplacement derived through counts of superposed craters of all 30 of the open basin lake volcanic resurfacing units show that resurfacing began in the late noachian near the noachian hesperian boundary was concentrated in the hesperian and continued into the early amazonian the lack of geologic features indicative of lava water interaction suggests that the basins were likely to have been mostly devoid of water at the time of the latest phase of volcanic resurfacing we conclude that there is no geologic evidence that suggests the fluvial activity associated with the studied paleolakes was coeval with the emplacement of the observed volcanic resurfacing units several of which date to the late noachian early hesperian

crater size frequency distributions and a revised martian relative chronology a revised martian relative chronology is determined which dates geologic units with respect to the end of the period of heavy bombardment this analysis differs from previous studies by using viking 1 2m photomosaics to map all 25 826 craters 8km diameter which postdate the lithologic units making up the martian surface the relative plotting technique is used because it shows changes in the shape and density of the crater size frequency distribution curves more clearly than cumulative plots the changes in shapes of the distribution curves are interpreted to be due to two different impacting populations one dominating during the heavy bombardment period and the other emplaced during the post heavy bombardment period the 8 km diameter limit was chosen to exclude the majority of secondary craters and to minimize obliteration effects acting over the age of the planet the results obtained are average ages valid for units with typical thicknesses between about 1 and 3 km and extending over an area of about 105 km2 the shapes and densities of the crater distribution curves indicate that approximately 60 of the martian lithologic units in which these craters occur formed during the period of heavy bombardment many of the small volcanoes those generally less than 200 km diameter including most in the tharsis and elysium regions date from this period the hellas and argyre impacts bracket the average age of the intercrater plains in the highlands the ridged plains distribution curves indicate formation during the period of heavy bombardment but their lower crater density indicates that they are the last geologic unit to retain the scars from this population of impactors they therefore likely formed near the end of heavy bombardment the remaining 40 of martian terrain units show distribution curves indicative of emplacement since the end of heavy bombardment the wide range in crater densities among different regions of plains indicate a range in formation ages although the general view of martian geologic evolution does not differ significantly from previous studies the present analysis explicitly states the relationship of numerous geologic units to the period of heavy bombardment and has revised the relative ages of localized regions across mars

ancient martian volcanoes in the aeolis region new evidence from mola data mars orbiter laser altimeter mola altimetric data confirm the volcanic origin of a noachian aged hilly feature zephyria tholus in the aeolis area of mars similar characteristics shared by at least one nearby topographic high suggest that volcanic activity represented by such features may have been more widespread than previously thought morphological structures and morphometric data for zephyria are consistent with a stratovolcano origin in which the edifice formed by mixed explosive and effusive eruptions and was altered by subsequent flank erosion to produce a distinctive truncated cone with concave upward flanks criteria are outlined to help detect and distinguish the origin of such features in other ancient regions of mars

present day gully activity in sisyphi cavi mars flow like features and block movements abstract the continuously increasing number of multi temporal high resolution images from the surface of mars offers the possibility for detailed studies of present day surface activity in this study we investigated all gullies in the sisyphi cavi region 355 e 71 s of the south polar region of mars this region is influenced by the seasonal deposition of a decimeters thick translucent slab ice in late autumn winter and its subsequent sublimation in spring we mapped all gullies n 17 760 and measured their orientations we also identified gullies with contemporary activity n 35 using multi temporal hirise images for martian years my 28 to 34 we observed two different kinds of activity 1 dark flow like features and 2 movement of blocks for both sediment was transported from the source region alcove and or flanks of channels down the gully using image data from hrsc ctx and hirise we monitored the general defrosting of the study region we also analyzed the maximum daytime surface temperatures of the complete study region based on tes data from mys 24 to 26 to identify the origin and triggering mechanism of the observed activity we used 1 detailed topographic investigations e g slope angles of two extensively gullied slopes based on two hirise dtms 2 identification of small scale displacements with digital image correlation dic and 3 orientation measurements of active gullies and comparison to non active gullies we found that for the active gullies studied activity happens at the end of spring between ls 225 and 250 this is consistent with the timing of final stages of defrosting in the region at this time some surfaces are already defrosted while others still host the seasonal slab ice cover for the surfaces with slab ice dark defrosting spots and flows if the surface is inclined are observed on dark dunes as well as on gully aprons and in gully channels these spots form when triggered by basal sublimation generated overpressure sediment entrained in co2 gas is transported through cracks within the ice and redeposited onto the frosted surface we compared and linked both morphologic features dark dune spots and dark flow like features and concluded that these features have comparable or even the same triggering mechanisms based on this extensive study the most plausible mechanism for ongoing gully activity can be divided into two steps 1 accumulation of material within gully channels via small dry flows on top of the slab ice comparable to dark dune spots flows 2 when a critical mass is reached the sediment flows down the still frosted gully on top of the sublimating ice or as a mixture of dry material and ice in a catastrophic flow the triggering factor for the movement of blocks remains unclear as their timing could not be constrained with the available data we identified headwall erosion in one gully in the study region whereas a discrete source could not be identified for the other sites suggesting multiple failure mechanisms could be active in such gullies finally through volume balance calculations we show that active gullies in sisyphi cavi could have been formed within decades to several tens of thousands of my but gully morphology indicates a much longer period for formation of the entire gully landform

formation constraints on martian north polar volcanic edifices 1 this study focuses on probable volcanic features in the north polar region of mars in an effort to constrain their formation mechanisms and to estimate the thickness of a possible former ice sheet using mars orbiter laser altimeter mola high resolution imaging science experiment hirise thermal emission imaging system themis and context camera ctx data we conduct topographic analyses of 108 putative volcanic edifices in the borealis volcanic field within 69 n 81 n and 197 e 330 e as it is rarely possible to identify rock types on mars such as hyaloclastite or palagonite we are limited to the use of topographic data and images alone in our study therefore we use available data for volcanic features in iceland to predict the formational mechanisms of similar features on mars we examined 21 icelandic volcanoes of subglacial and postglacial origin using digital elevation models dems as well as limited differential gps data and suggest by analogy that many of the features in the borealis volcanic field were likely formed subglacially we use these data to estimate a minimum ice sheet thickness for the area and suggest a range of minimum ice sheet thickness that varies between 57 and 610m with an average value of 283 m

topography of the northern hemisphere of mars from the mars orbiter laser altimeter the first 18 tracks of laser altimeter data across the northern hemisphere of mars from the mars global surveyor spacecraft show that the planet at latitudes north of 50 is exceptionally flat slopes and surface roughness increase toward the equator the polar layered terrain appears to be a thick ice rich formation with a non equilibrium planform indicative of ablation near the periphery slope relations suggest that the northern tharsis province was uplifted in the past a profile across ares vallis channel suggests that the discharge through the channel was much greater than previously estimated the martian atmosphere shows significant 1 micrometer atmospheric opacities particularly in low lying areas such as valles marineris

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

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

recent volcano ice interaction and outburst flooding in a mars polar cap re entrant abstract formation of chasms in the polar ice caps of mars has been attributed to meltwater outburst floods but the cause of melting has remained uncertain in a cap re entrant enveloping abalos colles west of casma boreale in the north polar cap we have found possible evidence of recent volcano ice interaction and outburst flooding in this paper we demonstrate that these two mechanisms can have acted together to form or expand the abalos re entrant flat topped ridges and circular rims protruding above the ice cap surface in the re entrant apex may be lava ridges and volcano craters and can have caused melting of 3 3 to 7 7 10 3 km 3 of ice the surrounding cap surface appears to have subsided and the likely volume of missing ice matches the melt estimate outburst flooding from this area may have reached peak discharges of 0 3 to 1 5 10 8 m 3 s 1 according to scour patterns in one of the re entrant channels this required ponding of melt water during lava eruption and catastrophic release through a sub or englacial melt water tunnel the collapse of which has left a chasm in the ice cap margin the flood features are geologically recent and volcano ice interaction may have occurred within the last 20 000 years

a network of lava tubes as the origin of labyrinthus noctis and valles marineris on mars abstract the role of lava tube networks and lava channels is reassessed as the primordial stage of the volcano erosional processes that formed the labyrinthus noctis valles marineris system instead of a tectonic origin the combined use of ctx crism hirise imagery and mola profiles has provided valuable insight in the evolution of pit chains into fossae first and then chasmata later due to mass wasting processes caused by the erosional effect of the lava flows that draped valles marineris and other outflow channels although a quantitative evaluation of eruption rates is difficult even with digital terrain models dtms because of the mixing between new flows and paleoflows a comparison with elysium and other tharsis outflow channels suggests that the availability of lava supply is correlated to their widths the images of ubiquitous lava flows rather than sporadic light toned deposits strengthen the role of lava over that of water in the erosional processes that formed labyrinthus noctis and carved valles marineris like many other outflow channel on mars the erosional evolution of the outflow channels shows an increasing trend of age and a decreasing trend of depth from the sources on tharsis to the mouths at chryse planitia this finding coupled with the observation of lava flows mantling chryse planitia may have profound implications for the water inventories thought to have filled the lowlands with an ocean

cavi angusti mars characterization and assessment of possible formation mechanisms received 26 august 2002 revised 5 february 2003 accepted 20 february 2003 published 24 may 2003 1 cavi angusti represent a series of large irregular depressions localized in part of the south circumpolar area previously mapped as the hesperian aged dorsa argentea formation their origin has primarily been interpreted to be due to eolian deflation or subglacial melting we use mgs mola and moc data to analyze the largest of these features 100 50 km and up to about 1500 m deep these data reveal terraced interiors centrally located equidimensional and elongated edifices and lava flow like structures that strongly suggest that this basin formed as a result of magmatic intrusion and extrusion causing heating and melting of a volatile rich substrate and drainage and loss of the liquid water volume estimates and heat transfer calculations are consistent with a mechanism involving a combination of intrusion and extrusion very similar to that observed to be responsible for icelandic subglacial eruptions and meltwater generation mounds and ridges in the floors of other depressions suggest that this mechanism may have operated in at least several other features of the cavi eolian activity sublimation and solution are also likely to have played a role in further modification of these features meltwater from basin formation appears to have drained laterally and may also have reentered the regional subsurface groundwater system index terms 6225 planetology solar system objects mars 5480 planetology solid surface planets volcanism 8450 5462 planetology solid surface planets polar regions 5416 planetology solid surface planets glaciation keywords mars cavi angusti dorsa argentea formation