are the viking lander sites representative of the surface of mars abstract global remote sensing observations of mars are compared with remote sensing observations of the two viking lander site regions and with orbiter and lander imaging of the sites the lander sites do not fit most of the global trends of remote sensing data the presence of a duricrust in the top meter of the surface is inferred for most regions of high thermal inertia although the duricrust is thinner at the lander sites than elsewhere regions of low thermal inertia are covered by greater than several centimeters of unconsolidated dust a thin microns thick layer of bright dust appears at the surface at the lander sites and these locations may be regions of incipient formation of low thermal inertia the lander sites are intermediate in structure between classical bright and dark regions and are distinctive from most of the rest of the planet

the geology of the terrestrial planets during the last four years our knowledge of the geology of the terrestrial planets has advanced rapidly the advances are particularly noticeable for venus and mars improved understanding of venus has come largely from the pioneer venus mission colin 1980 which has given us our first global view of the planet albeit at fairly low resolution the period was also one of almost continuous data gathering for mars as the viking orbiters and landers emplaced at the planet in 1976 continued to function

ice lubricated gravity spreading of the olympus mons aureole deposits abstract gravity sliding and spreading at low strain rates can account for the general morphology and structure of the aureoles and basal scarp of olympus mons detachment sliding could have occurred around the volcano if either pore fluid pressures were exceptionally high greater than 90 or the rocks had very low resistance to shear about 1 105 pa or 1 bar because of the vast areal extent and probable shallow depth of the detachment zone development of ubiquitous high pore fluid pressures beneath aureole forming material was unlikely however a zone of sufficiently weak material consisting of about 10 interstitial or interbedded ice could have been present if so a simple rheologic model for the aureole deposits can be applied that consists of a thin ductile layer overlain by a thicker brittle layer according to this model extensional deformation would have occurred near the shield and compressional deformation in its distal parts proximal grabens and distal corrugations on aureole surfaces support this model a submarine slide at kitimat arm british columbia is a valid qualitative analogy for the observed features and inferred emplacement style of the aureole deposits ground ice processes have been considered the cause of many geologic features on mars a 3 average concentration of ground ice in the regolith is predicted by theoretical models for the ice budget and cryosphere ice may have been deposited in higher concentrations below the aureole forming material the source of the ice could have been juvenile water circulated hydrothermally by olympus mons volcanism the basal scarp of olympus mons apparently demarcates the transition between the upper stable part of the shield and its lower part that decoupled and formed the aureole deposits this transition may reflect a change in the bulk shear strength of the shield caused either by a radial dependence in the abundance of ice or fluid in the shield materials or by the concentration of intrusive dikes within the volcano other martian volcanoes exhibit virtually no evidence of similar large scale gravity spreading and basal scarps perhaps such evidence if it existed has been buried by lava flows or perhaps the smaller size of other volcanoes did not permit the development of these features

the shape of mars before global surveyor results from reanalysis of the viking control point network three dimensional coordinates of 3739 globally distributed control points derived from photogrammetric analysis of viking orbiter image data are studied with respect to the shape and large scale morphology of mars spheres spheroids spherical functions and a digital terrain model dtm of 50 km grid spacing are fitted to the data prominent topographic features in the terrain model include the tharsis volcanoes olympus mons alba patera and prominent mare and highland regions as well as the major impact basins while the global dichotomy is clearly visible in our data our model does not reveal any distinct signature associated with the presumed dichotomy boundary at this global scale rather it suggests a smooth topographic transition from southern to northern hemisphere this model is unique among existing topographic data sets for mars as it combines global coverage a spatial resolution sufficient to resolve regional topography and absolute elevation data more accurate than in previous control point network analyses formal errors and a comparison with the first released topographic profiles obtained by mars global surveyor s laser altimeter mola suggest that 70 and 90 of the dtm grid elements represent the topography of the planet to better than 1000 m and 2000 m respectively

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

ice and debris in the fretted terrain mars viking moderate and high resolution images along the northern highland margin were studied monoscopically and stereoscopically to contribute to an understanding of the development of fretted terrain results suport the hypothesis that the fretting process involved flow facilitated by interstitial ice the process apparently continued for a long period of time and debris apron formation shaped the fretted terrain in the past as well as the present interstitial ice in debris aprons is most likely derived from ground ice obtained by sapping or scarp collapse debris aprons could have been removed by sublimation if they consisted mostly of ice or by deflation if they consisted mostly of debris to remove the debris wind erosion was either very intense early in martian history or was intermittent perhaps owing to climatic cycles the location of debris aprons in two midlatitudinal belts can be attributed to atmospheric conditions that permit ice to remain in the ground at moderate depth in those latitudes and climatic factors that permit temperatures to be warm enough for ice to flow channels have minimum gradients of 5 8 m km which permits flowing ice to deform by dislocation creep at exceedingly low strain rates alternately ice charged debris may have been buoyed by brines by analogy with the fretted channels ice could have flowed through the outflow channels if the atmospheric pressure was somewhat higher in the past and permitted ice to exist in the equatorial area

a 500 year long record of tephra falls from redoubt volcano and other volcanoes in upper cook inlet alaska abstract volcanic ash layers preserved in glacial lacustrine sediments at skilak lake on the kenai peninsula of southcentral alaska constitute a record of eruptions at redoubt volcano and other alaskan volcanoes which affected the upper cook inlet area during the last 500 years high resolution magnetic susceptibility profiling delineates similar sequences of tephra layers in several 1 m long lake sediment cores electron microprobe analyses of glass shards from the tephras indicate correlation of some ash layers with known reference tephras from the source volcanoes while other ash layers record previously unknown prehistoric eruptions skilak lake cores contain ash from the historic 1912 katmai eruption the 1902 redoubt eruption and the 1883 mount st augustine eruption as well as prehistoric ash layers erupted from crater peak at mt spurr ca 250 350 years ago from redoubt volcano at ca 300 400 years ago and again at ca 350 450 years ago and a 500 year old ash from mount st augustine still older tephras from redoubt volcano and crater peak at mt spurr are found lower in the cores the cores indicate that volcanoes in the cook inlet area have erupted every 10 35 years during the 20th century and ash falls have occurred at skilak lake at least once every 50 100 years for the last 500 years with redoubt spurr and augustine volcanoes being the most important sources of tephra

mars near infrared comparative spectroscopy during the 1986 opposition abstract near infrared 0 7 2 5 m spectral observations of mars during the 1986 opposition were carried out at the mauna kea observatory utilizing the university of hawaii 2 2 m telescope spectra were obtained of several martian locations using a continuously variable filter cvf spectrometer with a resolution of 1 25 during two separate runs in june and august approximately 60 distinct spots between 354 w and 163 w and 32 n and 53 s were observed at an angular resolution of 0 5 to 1 5 arcsec corresponding to a spatial resolution on mars of 200 to 460 km varying with nightly seeing conditions these different spots fall roughly into a set of eight distinct geologic regions volcanic regions ridged plains ridged volcanic plains scoured plains impact basins channels and canyons densely cratered regions and layered terrain and ice the spectra exhibit typical noise related or weather induced errors of less than 4 of the full scale signal to analyze these spectral data spot to spot ratios or relative reflectance spectra were produced between spectra taken in different geologic regions spectral features observed in these ratios can act as indicators of mineralogic differences between areas under consideration perhaps the most striking result obtained from the many ratios taken close in time and under similar viewing geometries was the consistent lack of noticeable differences between spectra taken of areas which in geologic maps and viking orbiter images appear to have very different morphologies this observation leads to several possible conclusions a the spectral feature differences are below the detection limit of these measurements b the spatial resolution of spots observed on mars was not high enough to merit comparison with medium to high resolution viking orbiter images and geologic maps i e the local morphology varies significantly within the aperture region and a mixing or averaging effect operates to reduce the spectral feature differences c all of these regions are the same spectrally in the near infrared it is likely that all three of these effects operate to some degree to prevent spectral features from being observed among the areas measured possibility c may best explain these results as it is consistent with several previous studies indicating a grossly uniform mantle of global dust over much of the observed surface the message to mars orbiting spectroscopy experiments such as mars observer vims is that the spectral differences are small only a few percent of the continuum or nonexistent among many areas on mars on the scale of several hundred kilometers

viking landing sites remote sensing observations and physical properties of martian surface materials abstract important problems that confront future scientific exploration of mars include the physical properties of martian surface materials and the geologic processes that formed the materials the design of landing spacecraft roving vehicles and sampling devices and the selection of landing sites vehicle traverses and sample sites will be in part guided by the physical properties of the materials four materials occur in the sample fields of the viking landers 1 drift 2 crusty to cloddy 3 blocky and 4 rock the first three are soillike drift materials is weak loose and porous we estimate that it has a dielectric constant near 2 4 and a thermal inertia near 1 10 3 to 3 10 3 cal cm 2 sec 1 2 k 1 because of its low bulk density fine grain size and small cohesion crusty to cloddy material is expected to have a dielectric constant near 2 8 and a thermal inertia near 4 10 3 to 7 10 3 because of its moderate bulk density and cementation of grains blocky material should have a dielectric constant near 3 3 and a thermal inertia near 7 10 3 to 9 10 3 because of its moderate bulk density and cementation common basaltic rocks have dielectric constans near 8 and thermal inertias near 30 10 3 to 60 10 3 comparisons of estimated dielectric constants and thermal inertias of the materials at the landing sites with those obtained remotely by earth based radars and viking orbiter thermal sensors suggest that the materials at the landing sites are good analogs for materials elsewhere on mars correlation of remotely estimated dielectric constant and thermal inertias indicates two modal values for paired values of dielectric constants and thermal inertias near a 2 and 2 10 3 and b 3 and 6 10 3 respectively these two modes are comparable to the dielectric constants and thermal inertias for drift and crusty to cloddy material respectively dielectric constants and thermal inertias for blocky material are larger but conistent with values in the northern plains our interprertations are compatible with an aeolian origin for drift and similar materials elsewhere on mars the postulate that moderate dielectric constants and thermal inertias larger than 3 or 4 10 3 are produced by cementation of soillike materials is partly consistent with the data the average dielectric constant and thermal inertia and their correlation with one another suggest that most of the surface of mars should present few difficulties to future surface exploration but some surfaces may present difficulties for spacecraft that are not suitably designed

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

varve counting vs tephrochronology and 137cs and 210pb dating a comparative test at skilak lake alaska the age of recently deposited sediments in skilak lake has previously been estimated only by counting open quotes varves close quotes we measured the sedimentation rate of skilak lake using two radionuclides sup 137 cs and sup 210 pb and found it to be about an order of magnitude lower than previous estimates based on varve counts we also identified several tephras through a combination of visual inspection core x radiographs observation of variations of the magnetic susceptibility intensity of magnetization of the unconsolidated sediments and microprobe analyses of volcanic glass shards tephrochronologic dates using matches with the katmai 1912 tephra and an augustine tephra from 500 550 yr b p are in good agreement with the sedimentation rate estimates based on the radioisotope data and indicate that the rhythmite layers at skilak lake are not annual varves these new estimates of sedimentation rate reaffirm that care is needed in varve dating and require that earlier work on sunspot and climate changes thought to have been recorded in the skilak lake sediments be reevaluated 16 refs 6 figs 1 tab

thermokarst landforms and processes in ares vallis mars abstract with a length of 1500 km ares vallis is one of the largest martian outflow channels and is inferred to have been formed by cataclysmic floods of water conveyed from source areas which are marked by chaotic terrain to chryse planitia near its downstream outlet 14 n 28 w the floor of ares widens to 100 km from its average 25 km width this area of widened channel floor is marked by a complex of irregular terraces elongated depressions linear ridges sinuous ridges and other indicators of highly irregular dissection of a formerly continuous surface thermokarst processes following either glacial or alluvial histories seem best to explain these relationships various indicators of fluctuating discharge for water and sediment ponding of debris and prolonged flow suggest the emplacement of ice rich debris in the anomalous reach of ares vallis post flood or post glacial thawing of the ice rich sediments would then generate the thermokarst landscape these processes which are consistent with other indicators of anomalously warm climatic conditions imply a profound change from the modern martian environment

thermophysical properties of the isidis basin mars 1 we investigated the thermal properties of the isidis basin in order to understand the high values 450 j m 2 k 1 s 1 2 located in the southern region of the basin thermal inertia data were compared to a variety of complementary data sets including radar visible and results from mesoscale atmospheric simulations we considered four mechanisms for creating the high thermal inertia including 1 the thinning of a dust mantle 2 the presence of unconsolidated coarse grained material 3 high rock abundance and 4 a high degree of induration induration is the scenario most consistent with the data although we cannot rule out unconsolidated materials and it is likely that rocks contribute to values of thermal inertia to a lesser degree we also investigated three mechanisms for controlling the geographical distribution of the high thermal inertia values including 1 the influence of topography 2 the role of surface morphology and 3 present aeolian processes topography plays a significant role along the southern boundary of the basin but not within the basin itself themis data show a complex relationship between the thermal inertia and morphology the wind patterns modeled by the mars regional atmospheric modeling system mrams are not fully consistent with the wind directions implied by streaks in the thermal data but are consistent with a second group of streaks observed in the visible data this suggests that small scale tens of kilometers streaks observed in the thermal data did not form under present day nominal winds

erosion by flowing martian lava new insights for hecates tholus from mars express and mer data 1 we have used new compositional information on martian basaltic rocks from the mars exploration rover spirit and data from new stereo imaging by the high resolution stereo camera hrsc on the mars express orbiter to constrain an existing analytical numerical computer model to assess the potential of martian lavas to form lava channels by erosion of substrate the basaltic rocks studied in gusev crater by spirit have compositions consistent with lavas of higher liquidus temperature and lower dynamic viscosity than terrestrial tholeiitic basalts suggesting that they had a greater potential for turbulent flow and erosion of substrate during flow emplacement than terrestrial basalts more similar to lunar mare basalts we modeled a specific case to determine whether these lavas could have formed part of a 66 km long channel on the martian shield volcano hecates tholus this channel formed on relatively steep slopes 2 8 based on measurements from the hrsc digital terrain model our results suggest that erosion rates were of the order of tens to hundreds of centimeters day depending on flow rate and ice content of the substrate eruption durations required to erode the hecates channel 100 30 m deep over the first 20 km depth decreasing downstream range from weeks to months which are consistent with the known eruption durations of terrestrial basaltic lavas and the previous modeling of wilson and mouginis mark 2004 any hecates lava channels formed from erosion by lava could have served as conduits for later fluvial activity as recently described by fassett and head 2004 2005

effect of the greenhouse gases co2 h2o so2 on martian paleoclimate there is general agreement that certain surface features on mars are indicative of the presence of liquid water at various times in the geologic past in particular the valley networks are difficult to explain by a mechanism other than the flow of liquid water it has been suggested in several studies that a thick co2 atmosphere on mars early in its history could have provided a greenhouse warming that would have allowed the flow of water either on the surface or just below the surface however we have examined this effect with a detailed radiation model and have found that if reduced solar luminosity early in the history of the solar system is taken into account even three bars of co2 will not provide sufficient greenhouse warming the addition of water vapor and sulfur dioxide both plausible gases that may have been emitted by martian volcanoes to the atmosphere also fail to warm the surface above 273k for reduced solar luminosity conditions the increase in temperature may be large enough however for the formation of these features by brines

sedimentology and progressive tectonic unconformities of the sheetflood dominated hell s gate alluvial fan death valley california abstract the hell s gate alluvial fan of northern death valley has an area of 49 5 km2 a radius of 11 8 km and a smooth 5 3 sloping surface interrupted by shallow

using dendrogeomorphology and 137cs and 210pb radiochronology to estimate recent changes in sedimentation rates in kushiro mire northern japan resulting from land use change and river channelization abstract the purpose of this study is to describe the history of sediment deposition that has been occurring for several decades along the margins of the kushiro mire into which the kuchoro river drains the dendrogeomorphic technique was used to examine an even aged forest and adventitious roots to assess short term 20 years deposition rates and the frequency of heavy rainfall events for medium 40 years and long term 100 years deposition rates radiochronological analyses using 137 cs and 210 pb were also conducted several instances of high deposition rates caused by flooding events during the last 20 years were identified from the analysis of adventitious roots the average sedimentation rate from 1963 to the present estimated from the 137 cs study is over 1 3 cm year using the 210 pb dating method based on a cfcs model which considered the organic matter content appropriate to wetland sediment three deposition rates in the last 60 years were estimated 2 0 cm year from 1981 to 2000 8 9 cm year from 1975 to 1981 and 0 14 cm year from 1939 to 1975 the analysis of environmental radionuclides indicated that the greatest sedimentation rates occurred in the years 1975 to 1981 when the kuchoro river was extensively channelized and flood and or precipitation events occurred this suggests that land use development and channelization introduced a large amount of sediment into the marginal areas of wetland through the drainage system and this was deposited on top of the peat soil

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

martian gases in an antarctic meteorite significant abundances of trapped argon krypton and xenon have been measured in shock altered phases of the achondritic meteorite elephant moraine 79001 from antarctica the relative elemental abundances the high ratios of argon 40 to argon 36 2000 and the high ratios of xenon 129 to xenon 132 2 0 of the trapped gas more closely resemble viking data for the martian atmosphere than data for noble gas components typically found in meteorites these findings support earlier suggestions made on the basis of geochemical evidence that shergottites and related rare meteorites may have originated from the planet mars

coastal geomorphology of the martian northern plains the paper considers the question of the formation of the outflow channels and valley networks discovered on the martian northern plains during the mariner 9 mission parker and saunders 1987 and parker et al 1987 1989 data are used to describe key features common both in the lower reaches of the outflow channels and within and along the margins of the entire northern plains it is suggested that of the geological processes capable of producing similar morphologies on earth lacustrine or marine deposition and subsequent periglacial modification offer the simplest and most consistent explanation for the suit of features found on mars

assessing the formation of valley networks on a cold early mars predictions for erosion rates and channel morphology abstract the ancient noachian highlands of mars host an extensive population of valley networks which formed predominantly during the early geologic history of the planet morphologic characteristics of the valley networks have been interpreted to indicate the formation of these features through precipitation derived fluvial activity and therefore as evidence for a relatively warm and wet noachian mars climate however these interpretations conflict with the results of sophisticated global climate modeling studies which suggest that early mars was dominated by a cold and icy climate with conditions characterized by adiabatic cooling and regional ice sheets within the highlands difficulties in replicating the warm and wet early climate conditions interpreted from the valley networks has served as the basis for alternative suggestions for the formation of valley networks by transient heating and snowmelt in an otherwise cold and icy climate here we test a conceptual model for valley network formation and incision under cold and icy conditions with a substrate characterized by the presence of an ice free desiccated surface regolith and subjacent ice cemented regolith similar to that found in the antarctic mcmurdo dry valleys on earth we implement numerical thermal models quantitative erosion and transport estimates and morphometric analyses in order to outline and test predictions for 1 the nature and structure of the cold and icy noachian substrate 2 valley network fluvial erosion and incision rates and 3 resulting channel valley morphology morphologic predictions are compared against observational data to determine if the valley networks characteristics are consistent with formation in a cold and icy climate through this approach we present and develop the underlying conceptual model identify and generate the fundamental data inputs required to evaluate it and perform a preliminary first order assessment to serve as a basis for further investigation while these analyses have been performed over a broad parameter space to address relative uncertainties we report findings with a specific emphasis on the nominal results we find that under cold conditions the substrate is characterized by a kilometers thick globally continuous cryosphere with a 50 100 m thick ice free surface layer in diffusive equilibrium with the atmosphere and underlying ice cemented regolith the top of which forms the ice table estimates of the potential infiltration capacity of the ice free surface regolith layer indicate that surface runoff generation does not require excessively large precipitation rates and thus does not preclude fluvial activity sourced by rainfall additionally due to the predicted thicknesses of the ice free surface regolith any transient period of warming would need to be sustained in duration 2 kyr to induce melting of ground ice to initiate solifluction gelifluction activity the predicted range of ice table depths is exceeded by the incised depths of a majority of the valley network population therefore suggesting interactions were possible evaluation of the rates of mechanical substrate erosion and thermal ice cement erosion by valley network fluvial activity are subject to large uncertainties due to several poorly constrained parameters i e the substrate erodibility factor and the valley network fluvial water temperature but generally indicate that at low water temperatures consistent with a cold and icy surface environment thermal erosion of the ice cement can be outpaced by mechanical erosion of the substrate in this scenario the relative efficiency of lateral erosion is predicted to be enhanced during incision below the ice table causing preferential channel valley widening and increased width to depth ratios assessment of this prediction through a morphometric analysis of valley network width to depth ratios and occurrence of u shaped cross sections indicates no significant correlation to ice table depths this result suggests that either 1 permafrost was not present in the noachian mars substrate indicating a warmer climate 2 the permafrost ice table did not significantly influence valley network width to depth ratios possibly owing to more rapid thermal erosion rates than mechanical or 3 additional factors not accounted for in this analysis are involved potential additional factors which could influence the results of this analysis include variable surface geothermal heat flux substrate thermal conductivity substrate composition and physical state as well as valley network preservation state and morphometric sampling biases due to data availability constraints these factors represent areas for future investigation to refine assessments of valley network formation under cold early mars conditions

the stability of ground ice in the equatorial region of mars consideration of the partial pressure of h2o in the martian atmosphere and the range of mean annual temperatures at the martian surface suggests that the occurrence of ground ice in equilibrium with the atmosphere is restricted to latitudes poleward of 40 however there is a growing body of morphologic evidence that indicates that substantial quantities of ground ice may have been present in the equatorial regolith throughout martian geologic time the accepted explanation for this apparent contradiction has been that the h2o found near the equator is a relic emplaced very early in martian geologic history 3 5 b y ago and under substantially different climatic conditions it is generally believed that this fossil ground ice layer has been preserved to the present day by the diffusion limiting properties of a relatively shallow layer 10 m of fine grained regolith to evaluate this hypothesis the lifetime of a 200 m layer of ground ice buried below 100 m of ice free regolith has been examined for the latitudes between 30 on mars twelve model pore size distributions representative of silt and clay type soils found on earth were selected to simulate the pore structure of the martian regolith the parallel pore model of gaseous diffusion was then used to calculate the flux of escaping h2o molecules from the buried ground ice layer the potential effects of such factors as depth of burial the martian geothermal gradient regolith porosity adsorption surface diffusion and climatic change were also considered based on our analysis the most important factors affecting the stability of equatorial ground ice appear to be 1 soil structure 2 the magnitude of the geothermal gradient and 3 the climatic desorption of co2 from the regolith we conclude that while the conditions necessary for the long term survival of ground ice may exist in isolated regions within the equatorial regolith on the global scale it appears unlikely that a fossil ground ice layer has been preserved throughout martian geologic history if massive ground ice does presently exist in the equatorial regolith then its presence may imply the existence of some continuous or periodic process of replenishment

an overview of distal tephrochronology in northern europe during the last 1000 years several tephra layers from the last millennium have been identified in distal peat and lake sediment sequences in northern europe forming a framework of volcanic events of great value for palaeoenvironmental investigations most of the tephras within this framework have an origin in iceland but distal layers from jan mayen have also been identified the predominant transport pathway in an easterly southeasterly direction has led to the deposition of these tephras in a number of terrestrial deposits in northern europe ash from silicic eruptions 63 sio2 dominate at these sites even though many of the documentary records in distal areas report tephra fall from several basaltic eruptions here we provide an overview of the distribution shard concentration and geochemistry of these tephras to highlight the most important isochrones for addressing key dating issues in particular three horizons hekla 1 ad 1104 oraefajokull ad 1362 and askja ad 1875 are found at a number of different locations in northern europe and as such are valuable tie points for improving and validating chronological models and for synchronisation of records spanning the last 1000 years in addition we present new data identifying tephra from the grimsvotn volcanic system within the lomonosovfonna ice cap on svalbard demonstrating that some tephras have been transported 2000 km to as far north as 798 n along a northeasterly trajectory this discovery highlights the potential for utilising tephrochronology as a correlation tool for palaeoarchives located in more northerly areas and the complex nature of fall out from different eruptions copyright 2009 john wiley sons ltd

mars dual polarization radar observations with extended coverage abstract thirteen centimeter wavelength radar observations of mars made in 1982 at arecibo observatory yield accurate measurements of the full backscatter spectrum in two orthogonal polarizations the data which were obtained for several widely separated subradar longitudes at 24 n latitude provide the first global view of the distribution of small scale surface roughness on mars the diffuse component of the echo exhibits strong spatial variations areas of maximum depolarization correlate well with volcanic regions tharsis and elysium while the heavily cratered upland terrain yields relatively low depolarization parts of tharsis give near complete depolarization polaziation ratio c 1 when viewed at oblique angles of incidence northern martian plains regions tharsis elysium and amazonis may comprise the most extensive area of severe decimeter scale surface roughness in the inner solar system on the average the northern martian tropics yield higher diffuse radar cross sections d 0 05 0 12 and a higher of degree disk integrated depolarization c 0 1 0 4 than is found for the moon mercury and venus comparisons between the moon and mars using radar data ground truth and simple scattering models suggest that mars possesses a relatively high average coverage by decimeter scale rocks also discussed are several of the more interesting quasispecular scattering results the most unsual of which were obtained over the olympus mons aureole region

the 1883 and late prehistoric eruptions of augustine volcano alaska abstract the eruptive history of augustine volcano has been characterized by cycles of growth and destruction of the volcano repeated failure of 5 10 of the edifice has produced mobile debris avalanches that reached the sea on all sides high lava extrusion rates rapidly restore the volcano to its pre failure configuration this equilibrium between constructive and destructive processes has resulted in a relatively low lava dome complex surrounded by an apron of volcaniclastic debris three times the volume of the dome complex the most recent edifice collapse occurred in 1883 producing the 0 3 km3 burr point debris avalanche deposit three major slide blocks extended the shoreline up to 2 km and produced a tsunami that swept across cook inlet hummock morphologies change from a proximal radial orientation to a dominantly transverse alignment reflecting deceleration and compression of the avalanches as they enter the sea the breached crater formed by collapse was then largely filled by a 0 09 km3 lava dome and a 0 04 km3 lava flow travelled down the north flank lithic block and ash flows and pyroclastic surges reached the coast the burr point avalanche deposit partially overlaps the rocky point debris avalanche deposit to the west that was probably emplaced 200 400 years b p a major collapse event at ca 1540 110 a d produced the west island debris avalanche ending a period of expansion of the western side of the island an accompanying lateral blast overtopped the avalanche covering a 40 sector of the west flank the plinian tephra layer b may also have been erupted at the time of the west island eruption today augustine volcano has rebuilt itself to a size similar to that which preceded the last edifice failure in 1883 the frequency of past collapses three in the last 500 years suggests that summit collapse is a possibility during any future eruption the next major collapse is expected to involve 0 1 0 5 km3 of the summit the ensuing debris avalanche would likely reach the coast producing a tsunami that could impact populated areas of the kenai peninsula the largest tsunami would result from collapse in directions other than to the north or west tsunami magnitude is contingent on failure volume direction and timing with respect to tides

mars mapping with delay doppler radar mars radar imaging results from arecibo 12 6 cm observations are presented the images were derived from delay doppler mapping using a coded long pulse technique to mitigate the effects of echo overspreading images of the depolarized echo are used to identify regions of high decimeter scale roughness some of the strongest echo features are located on the major shield volcanoes or on relatively young off shield flows such as the olympus and pavonis lava aprons the shields themselves have highly irregular radar signatures suggesting complex volcanic histories some mars radar features have twice the depolarized brightness of the roughest terrestrial lava flows apparently due to higher levels of multiple scattering from surfaces of spectacular roughness or from volume scattering low brightness smooth areas are associated with older surfaces such as fractured and highland terra as well as with terrain interpreted to be debris lobes ash flows and aureoles in particular a close connection was found between the 12 6 cm counterpart of the stealth feature and the medusae fossae formation postulated to be deep ignimbrite deposits marte valus is anomalous in being the only outflow channel showing strongly enhanced echoes which supports the idea that this channel and the elysium basin that it drained are filled with lava flows a weak radar feature was found for the south polar residual ice cap comparisons with goldstone 3 5 cm data show that the south polar enhancement is much weaker at 12 6 cm than at 3 5 cm indicating that the southern ice cap becomes optically thin at the longer wavelength a north polar enhancement has also been found which is comparable in strength to the 12 6 cm south polar feature

global duricrust on mars analysis of remote sensing data global remote sensing data for mars are analyzed to obtain a simple self consistent model for the surface layer the data sets discussed include radar cross section measurements at several wavelengths radio whole disk thermal emission observations at two wavelengths the global distribution of thermal inertia deviations of diurnal temperatures from those of a homogeneous model and thermal spectral estimates of surface rock abundance and of the thermal inertia of the nonrocky component of the surface the data sets which most constrain the interpretation are the rock abundance map and the correlation of thermal inertia with radar cross section these require the rock abundance to not vary significantly from place to place and simultaneously require the density and thermal inertia of the fines to vary in a consistent manner the simplest model which can explain all of the data involves a global case hardened crust duricrust which varies spatially in its degree of formation in general low thermal inertia regions have a poorly developed crust and highinertia regions have a well developed crust there are however regions that consist of coarse particles and which do not fit this model e g chryse this model is consistent with the ages of low inertia regions and with aeolian mechanisms for their development the duricrust is thought to form via the mobilization of salt ions within a layer of water adsorbed within the regolith and its formation may be associated with the exchange of water between the regolith and atmosphere which occurs on the 105 and 106 year time scale

a radar study of the chryse region mars arecibo 12 6 cm delay doppler measurements are used to study the topography and radar scattering properties of the chryse region including the viking 1 and mars pathfinder lander sites and environs the viking 1 lander lies on a gentle 0 13 east facing slope at a 6 1 mbar altitude of 1 35 km the mars pathfinder lander site lies slightly lower 1 7 km on a flat low relief plain quasi specular roughness across chryse is considerably higher than the martian average and shows some strong spatial variation not apparent from older cw observations some of the rougher regions coincide with the distal ends of the tiu and ares vallis channels while another is located just to the northeast of the viking 1 lander chryse shows asymmetric scattering skew similar to that seen in mars southern hemisphere and in recent magellan radar observations of venus comparison of 12 6 cm and 3 5 cm data indicates that chryse s quasi specular reflectivity is strongly wavelength dependent being higher at the longer wavelength suggesting a rapid density increase within the top decimeter of the regolith depolarized reflectivity images of the general chryse area show modest enhancements from decimeter scale roughness or rocks associated with maja and kasei valles and the plateau bordering simud vallis these images indicate that the rock abundance at the proposed mars pathfinder lander site is similar to that at the viking lander sites

calendar year ages of three mid holocene tephra layers identified in varved lake sediments in west central sweden three intermediate to rhyolitic icelandic holocene tephra horizons hekla 3 kebister and hekla 4 have been identified in annually laminated varved lake sediments in the province of varmland west central sweden calendar year ages were obtained from varve counts and are supported by additional c 14 dating based on terrestrial plant macrofossils the varve ages of the three tephras are 3295 95 cal bp hekla 3 4030 103 cal bp kebister and 4390 107 cal bp hekla 4 the varve age of hekla 3 refines the former calibrated 14 c age based on studies in the british isles and germany considering the age error estimates associated with the varve chronology and calibrated c 14 ages the ages of kebister and hekla 4 are in agreement with former studies thus the age difference between kebister and hekla 4 is estimated to be ca 400 40 varve years formally estimated to ca 200 c 14 years between hekla 3 and hekla 4 to ca 1135 55 varve years formally estimated to ca 1100 calibrated c 14 years and between hekla 3 and kebister 708 20 varve years less

thermophysical properties of the mer and beagle ii landing site regions on mars 1 we analyzed remote sensing observations of the isidis basin gusev crater and meridiani planum landing sites for beagle ii mer a spirit and mer b opportunity spacecraft respectively we emphasized the thermophysical properties using daytime and nighttime radiance measurements from the mars global surveyor mgs thermal emission spectrometer and mars odyssey thermal emission imaging system themis and thermal inertias derived from nighttime data sets themis visible images mgs mars orbiter camera moc narrow angle images and mgs mars orbiter laser altimeter mola data are incorporated as well additionally the remote sensing data were compared with ground truth at the mer sites the isidis basin surface layer has been shaped by aeolian processes and erosion by slope winds coming off of the southern highlands and funneling through notches between massifs in the gusev region surface materials of contrasting thermophysical properties have been interpreted as rocks or bedrock duricrust and dust deposits these are consistent with a complex geological history dominated by volcanic and aeolian processes at meridiani planum the many layers having different thermophysical and erosional properties suggest periodic deposition of differing sedimentological facies possibly related to clast size grain orientation and packing or mineralogy

the case for a martian origin of the shergottites nitrogen and noble gases in eeta 79001 abstract nitrogen and noble gases were measured in samples of a glass inclusion and the surrounding basaltic matrix from the antarctic shergottite eeta 79001 a nitrogen component trapped in the glass but not present in the matrix has a 15n value at least as high as 190 ratios of40ar 14n and15n 14n in the glass are consistent with dilution of a martian atmospheric component 15n 620 160 40ar 14n 0 33 0 03 by either terrestrial atmosphere adsorbed on the samples or by indigenous nitrogen from the minerals of the rock trapped noble gases in the glass reproduce within error the elemental and isotopic compositions measured in mars atmosphere by viking and are in general agreement with previous measurements except for much lower abundances of neutron generated krypton and xenon isotopes the most reasonable explanation at the present time for the noble gas pattern and the isotopically heavy nitrogen is that a sample of martian atmosphere has been trapped in the eeta 79001 glass and that this meteorite and thus the shergottites and probably the nakhlites and chassignites as well originated on mars nitrogen in the non glassy matrix of eeta 79001 amounts to less than 0 5 ppm and has a spallation corrected 15n value in the range 0 to 20 it may reflect indigenous nitrogen in the basalt or a mixture of indigenous and adsorbed terrestrial nitrogen spallogenic noble gases yield single stage exposure ages between 400 000 and 900 000 years depending on irradiation geometry trapped argon may have an unusually low36ar 38ar ratio trapped krypton except for a small excess at80kr is smoothly mass fractionated with respect to either terrestrial or chondritic kr the trapped xenon composition is consistent with addition of neutron capture radiogenic and fissiogenic isotopes to a base composition resembling terrestrial atmospheric xe the elemental84kr 132xe ratio of 25 is close to the terrestrial value and very different from the chondritic ratio

thermal inertia mapping of mars from 60 s to 60 n twenty micrometer brightness temperatures are used to derive the thermal inertia for 81 of the martian surface between latitudes 60 these data were acquired by the two viking infrared thermal mappers in 1977 and 1978 following the two global dust storms of 1977 the spatial resolution used is 2 in latitude by 2 in longitude and the total range in derived inertia is 1 to 15 10 3 cal cm 2 sec 12 k 1 the distribution of thermal inertia is strongly bimodal with all values of thermal inertia less than 4 10 3 cal cm 2 sec 12 k 1 being associated with three disjoint bright regions mostly in the northern hemisphere sufficient dust is raised in global storms to provide fine material adequate to produce these low inertia areas but the specific deposition mechanism has not been defined at the low resolution used no complete exposures of clean rock were found there is some tendency for darker material to be associated with higher thermal inertia although the trend is far from one to one the distribution of high and low inertia areas is sufficiently nonrandom to produce a variation in whole disk brightness temperature with central meridian longitude this variation and the change in surface kinetic temperature associated with dust storms are factors in establishing the whole disk brightness temperature at radio and infrared wavelengths and will be important for those who use mars as a calibration source

growth of a tectonic ridge during the landers earthquake the formation of tectonic ridges by localized vertical uplift along strike slip faults has long been suspected but the actual growth of a tectonic ridge during an earthquake has never been documented during the 1992 landers california earthquake sequence an awl shaped dome like topographic ridge along the emerson fault zone increased its height at least 1 m concurrently with 3 m of right lateral shift across the fault zone containing the ridge five deformation vectors within the ridge reveal dilatant behavior in addition to the uplift and shift on boundary faults 10 refs 5 figs

contribution to the study of thermal erosion on mars similar to the coldest terrestrial periglacial regions like yakutia siberia the planet mars exhibits wide outflow channels this analogy and the presence of permanent ground ice suggest that thermal erosion have existed during martian fluvial outbursts 3000 m y ago thermal erosion here is considered to be the result of ground thawing produced by heat transfer between the water flow and the frozen ground followed by a transport of unfrozen sediments this paper proposes a qualitative explanation of thermal erosion with the help of some physical models from the quantitative point of view two thermal mathematical models are proposed and discussed the zones undergoing the most efficient erosion are river banks the first model studied here describes extreme thermomechanical actions a constant thermal flux on the ground surface produces ground thaw and the unfrozen sediments are immediately removed by water flow it is an ablation model it allows a theoretical evaluation of the river bank recession validity of theoretical estimations is acquired by comparing the calculations to the observed backwearing of the banks of some siberian rivers which can reach 25 m yr 1 thermal erosion acting upon the bottom of wide rivers on mars or in siberia as well is a very complex mechanism indeed the mathematical modeling requires the study of interaction between thermal processes and transport of sediments laws these laws are not yet well defined and are very difficult to establish thus another model presented in this paper concerns only one dimensional thermal actions of water flow upon the bottom of wide rivers it considers fluvial flow at positive celsius temperature producing a thermal flux from the bottom to the initially frozen semi infinite ground this model considers a constant convective heat transfer coefficient and allows an estimation of the thickness of the thawed ground beneath the river talik calculated thickness of the melted ground is given in the paper for different periods of time

selective concentration and enumeration of tephra shards from lake sediment cores this paper describes a technique for the enumeration of tephra shards from lake sediment cores whereby approximately 85 of unwanted sediment fractions organic matter biogenic silica carbonates are removed by selective stepwise chemical attack the order of 100 samples can be prepared simultaneously in a modest sized water bath and the recovery rate of the technique is greater than 90 the procedure is appli cable to all lake sediment types

planetary radar astronomy planetary radar research reported during 1979 1982 was highlighted by radar observations of venus by the pioneer venus spacecraft earth based high resolution imaging of venus and the moon construction of accurate topographic profiles for martian tropical regions observational and theoretical advances in relating the radar signatures of mars and the moon to surface characteristics and the initial radar detections of echoes from a comet and a mainbelt asteroid this review begins with a brief synopsis of radar definitions and technical terminology and then summarizes recent results for individual targets readers interested in radar astronomy prior to the current quadrennium are directed to excellent reviews by jurgens 1982a pettengill 1978 evans 1969 muhleman 1966 and pettengill and shapiro 1965 detailed descriptions of planetary radar techniques include pettengill 1970 and evans and hagfors 1968

regional dust deposits on mars physical properties age and history major dust storms on mars play an important role in the deposition and removal of fine dust material thermal radar and visual remote sensing observations provide important constraints on the martian regolith which have been used to determine the location and physical properties of regional dust deposits these deposits are located in three northern equatorial regions tharsis 20 s to 50 n 60 to 190 w arabia 5 s to 30 n 300 to 360 w and elysium 10 to 30 n 210 to 225 w they are covered by fine 2 40 m bright albedo 0 27 particles with fewer exposed rocks and coarse deposits than found elsewhere dust is currently deposited uniformly throughout the equatorial region at a rate of 40 m global storm over geologic time the rate of accumulation may vary from 0 to 250 m yr due to changes in atmospheric conditions produced by orbital variations dust deposited during global storms is subsequently removed only from dark regions resulting in a net accumulation in the low inertia bright regions the thickness of these current dust deposits is 0 1 2 m the thermal inertia places a lower limit of 0 1 m on the thickness of these deposits while the sparse but ubiquitous presence of exposed rocks and the degree of visible mantling indicate that the thickness is less than 5 m dual polarization radar observations of a very rough texture in tharsis are consistent with this model with a 2 m thick dust layer burying most of the surface rocks but permitting radar sampling of the rough subsurface based on their thickness and rate of accumulation the age of these deposits is 105 106 years suggesting a cyclic process of deposition and removal one possible cause may be cyclic variations in the magnitude and location of maximum wind velocities related to variations in mars orbit at present perihelion and maximum wind velocities occur in the south whereas regional dust deposits occur in the north suggesting net transport from south to north orbital parameters oscillate with periods ranging from 5 104 to 106 years the agreement between these periods and the dust deposit age suggests a possible link at different stages in orbit evolution maximum wind velocities will occur in the north with subsequent erosion and redistribution of the accumulated fines based on this model much of the uppermost martian surface is very young and is being continually reworked

a comparison of the thermal and radar characteristics of mars abstract there is a correlation between martian thermal inertia and radar cross section data centered on 22 latitude the correlation is strongest with 70 cm radar except between longitudes 10 and 90 where there is a slight anticorrelation and gets progressively weaker at 12 5 and 3 8 cm wavelengths respectively a correlation is expected because of the dependence of both properties on density but an increase in the average particle size of the surface with increasing dielectric constant is also required in order to explain the data this may take the form of an increased number of small rocks the anticorrelation may result from either the effects of atmospheric dust on the surface temperature or from the effects on radar of local variations in large scale roughness or scattering by rocks the relative behavior between the wavelengths can be understood in terms of appropriately sized rocks which act as radar scatterers the trend of the correlation agrees with the dichotomy of the planet into two types of terrain as noted in other remote sensing data and is consistent with an erosional versus depositional surface nature variations in the surface dielectric constant inferred from the 3 8 cm radar data can explain discrepancies between 2 8 cm radio emission observations and a simple model based on the global distribution of thermal inertia and albedo

high resolution thermal inertia mapping of mars sites of exobiological interest we have mapped thermal inertia at high resolution for selected regions of mars that are of potential biological relevance using observations made by the mars global surveyor thermal emission spectrometer thermal inertia is a direct indicator of physical properties of the surface at the decimeter to meter scale our goal is to understand the geological processes by which the sites formed and their subsequent evolution their current state and their safety and science potential as landing sites for future lander rover and sample return spacecraft missions the thermal inertia values at 3 km scale for the sites considered span the entire range of values measured at mars thermal inertias range from low values indicative of substantial aeolian mantling up to high values suggesting surfaces covered predominantly with bedrock exposed rocks or blocks or well indurated crusts the highest thermal inertias correlate strongly with local morphology while areas with intermediate and low thermal inertias generally show no such correlation this suggests that selection of future landing sites will be plagued by a choice of a well mantled site that is safe but less interesting scientifically versus an unmantled site that is more interesting scientifically but less safe

generation of martian chaos and channels by debris flows abstract a debris flow mechanism is proposed to account for the formation of chaos and the large channels debouching into chryse planitia from the adjacent southern uplands of mars the debris is thought to have originated through a mechanism of collapse in the chaotic terrains which exist at the head of these channels as well as locally along the channels this proposition is based on the detailed morphologic similarities between martian channel source areas and the heads of both subaerial and subaqueous terrestrial debris flows the downslope movement of the debris produced the channels through a modification of earlier collapse areas b active bed erosion and c loading induced collapse the large scale channel geometry and the assemblage of related morphologic features on mars correspond tto that observed in subaqueous debris flow chutes on the mississippi delta front through various mechanisms of strain dependent viscosity decrease the debris flow gained mobility downstream turned into a debris avalanche and moved onto chryse planitia at very high velocities this high velocity avalanche eroded a series of streamlined remnants near the channel mouths and deposited its load as a thin blanket over a large area of the basin creating virtually no depositional relief

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

granite a planetary point of view the telluric planets and the asteroid belt display the same internal structure with a metallic inner core and a silicate outer shell experimental data and petrological evidence in silicate systems show that granite can be produced through all types of magmatic processes on moon 4 4 3 9 ga granite clasts displaying dry mineral assemblages correspond to discrete intrusive events large k ca enrichment and low ree abundances in granite relative to kreep are consistent with silicate liquid immiscibility a process observed in melt inclusions within olivine of lunar basalts on mars black and white rhythmic layers observed on the tharsis rise along the flanks of valles marineris and the peripheral scarps of the tharsis montes giant volcanoes suggest the eruption of possibly felsic pyroclastites samples analysed in the mars pathfinder landing site yield basic to intermediate 45 to 62 wt sio2 compositions though no granites were found so far in the martian snc meteorites a component close to terrestrial continental granitic crust is inferred from trace element and isotope systematics like the martian northern hemisphere venus has suffered extensive volcanic resurfacing whereas folded and faulted areas resemble terrestrial continents the hypothesis of a granitic component is again tantalizing finally extra terrestrial granite is also found as enclaves within iron meteorites and ordinary chondrites granite a major component of the earth s crust can be generated in all geodynamic settings the low density of granite favours continental accretion thus the occurrence or absence of granite and of associated silicic volcanism within the other telluric planets is not a trivial question granite is generally thought to be produced through wet processes lunar evidence shows that dry conditions may apply as well in venus a large planet with high rates of magma production it is speculated that significant volumes of granite can develop

mars northern hemisphere slopes and slope distributions we investigate slope distributions in the northern hemisphere of mars from topographic profiles collected by the mars orbiter laser altimeter analysis of the region from about 12 s to 82 n over diverse geologic units indicates that the range of regional scale slopes is small generally 3 surface smoothness is most distinctive in the vast northern hemisphere plains where slopes are typically 1 amazonis planitia is particularly remarkable in its smoothness exhibiting an rms variation in topography of 2 m over a 100 km baseline this relative smoothness is still present when compared with other sampled areas of the martian northern hemisphere and with volcanically resurfaced terrains elsewhere in the solar system planetary surfaces of large areal extent that are most comparable to amazonis in terms of rms elevation variation over long baselines are depositional in origin and include terrestrial oceanic abyssal plains and certain sedimentary basins slopes across the valles marineris canyon system show that the upper portion of the walls are significantly and consistently steeper than the lower walls characteristic of extensive mass wasting the observed long runout is consistent with a high energy collapsed flow in the neighboring noctis labyrinthus canyons the duality between the upper and lower walls is reduced and indicates a lower energy modificational history and or greater cohesion of wall rock

quantitative description and analysis of earthquake induced deformation zones along strike slip and dip slip faults 1 deformation zones are belts of high strains that can occur at the ground surface centered or asymmetrical relative to the trace of an earthquake fault and can range in width from a meter or two up to hundreds of meters in order to minimize damage to engineering structures within deformation zones one needs to be able to determine the characteristics of the deformation zones we develop an elastic plastic model of fault slip propagation to explain formation of deformation zones and estimate certain parameters to characterize deformation zones our theory suggests the ratio of widths of deformation zones in hanging wall and footwall of dipping faults should be controlled by fault dip angle and the kind of fault the relations are different for strike slip and dip slip faults also the total width of the deformation zone normalized with fault slip during the earthquake should be determined by the dip angle the exponent of the yield condition and the kind of fault the theoretical parameters measured for deformation zones along the strike slip duzce bolu fault at kaynasli turkey and two deformation zones along the chi chi thrust fault taiwan agree well with parameters determined from geophysical and geological sources the theoretical model also indicates that the winnetka strain belts related to the 1994 northridge earthquake could have formed above a previously unknown blind fault at winnetka the analysis suggests that the winnetka fault is a normal dip slip fault dipping 54 s with a fault tip depth of 360 m

mid holocene glacier peak and mount st helens we tephra layers detected in lake sediments from southern british columbia using high resolution techniques abstract a glacier peak tephra has been found in the mid holocene sediment records of two subalpine lakes frozen lake in the southern coast mountains and mount barr cirque lake in the north cascade mountains of british columbia canada the age depth relationship for each lake suggests an age of 5000 5080 14 c yr b p 5500 5900 cal yr b p for the eruption which closely approximates the estimated age 5100 5500 14 c yr b p of the dusty creek tephra assemblage found near glacier peak the tephra layer which has not been reported previously from distal sites and was not readily visible in the sediments was located using contiguous sampling magnetic susceptibility measurements wet sieving and light microscopy the composition of the glass in pumice fragments was determined by electron microprobe analysis and used to confirm the probable source of this mid holocene tephra layer using the same methods the a d 1481 1482 mount st helens we tephra layer was identified in sediments from dog lake in southeastern british columbia suggesting the plume drifted further north than previously thought this high resolution method for identifying tephra layers in lake sediments which has worldwide application in tephrachronologic paleoenvironmental studies has furthered our knowledge of the timing and airfall distribution of holocene tephras from two important cascade volcanoes

volcanic tsunamis and prehistoric cultural transitions in cook inlet alaska abstract the 1883 eruption of augustine volcano produced a tsunami when a debris avalanche traveled into the waters of cook inlet older debris avalanches and coeval paleotsunami deposits from sites around cook inlet record several older volcanic tsunamis a debris avalanche into the sea on the west side of augustine island ca 450 years ago produced a wave that affected areas 17 m above high tide on augustine island a large volcanic tsunami was generated by a debris avalanche on the east side of augustine island ca 1600 yr bp and affected areas more than 7 m above high tide at distances of 80 km from the volcano on the kenai peninsula a tsunami deposit dated to ca 3600 yr bp is tentatively correlated with a southward directed collapse of the summit of redoubt volcano although little is known about the magnitude of the tsunami the 1600 yr bp tsunami from augustine volcano occurred about the same time as the collapse of the well developed kachemak culture in the southern cook inlet area suggesting a link between volcanic tsunamis and prehistoric cultural changes in this region of alaska

the spatial distribution of rocks on mars abstract the spatial distribution of rocks exposed at the surface of mars has been mapped using viking infrared thermal mapper irtm observations overall there are no regions on the surface of mars at a scale of 1 1 in latitude and longitude that are rock free the modal value of rock abundance is 6 areal coverage with no areas having more than 30 35 rock cover the model developed to determine rock abundance relates the thermal emission in each of the four surface sensing irtm bands to temperature contrasts within the field of view non unit thermal emissivity due to absorption bands in the surface materials and the absorption and scattering of the outgoing energy by atmospheric dust and water ice each of these effects produce characteristic spectral and diurnal signatures allowing them to be separated the temperature contrasts provide a means to determine both the abundance of exposed rocks and the fine component thermal intertia rock abundance alone does not produce the observed variation in bulk thermal inertia of the surface low inertia fine bright surfaces have fewer rocks exposed than do high inertia coarse dark surfaces rock abundance does not correlate well with the rms slope nor reflectivity determined from delay doppler radar measurements there is however a possible correlation between rms slope determined from continuous wave radar observations dual polarization radar measurements which provide the best radar measure of small scale roughness indicate that the tharsis volcanic region is very rough whereas thermal measurements indicate very few rocks and a covering of dust together these observations suggest an approximately 1 m thick mantle of fines covering a very rough subsurface this fine material may be an aeolian deposit of dust storm fallout valles marineris together with several major channels and chaotic terrains have high rock abundances as does the acidalia planitia basin this observed distribution may reflect the initial deposition of coarse material associated with channel formation syrtis major is unique in having a high inertia but a very low rock abundance together with low radar roughness these observations are consistent with mantling of rocks by sand the observed distribution of rocks and fines indicates that aeolian processes both erosional and depositional play a dominant role in shaping the present martian surface

global distribution and migration of subsurface ice on mars a thermal diffusive model of h2o kinetics and equilibrium was developed to investigate the long term evolution and depth distribution of subsurface ice on mars the model quantitatively takes into account 1 obliquity variations 2 eccentricity variations 3 long term changes in the solar luminosity 4 variations in the argument of subsolar meridian in planetocentric equatorial coordinates 5 albedo changes at higher latitudes due to seasonal phase changes of co2 and the varying extent of co2 ice cover 6 planetary internal heat flow 7 temperature variations in the regolith as a function of depth time and latitude due to the above factors 8 atmospheric pressure variations over a 104 year time scale 9 the effects of factors 1 through 5 on seasonal polar cap temperatures and 10 knudsen and molecular diffusion of h2o through the regolith the migration of h2o into or out of the regolith is determined by two boundary conditions the h2o vapor pressure at the subsurface ice boundary and the annual average h2o concentration at the base of the atmosphere these are controlled respectively by the annual average regolith temperature at the given depth and seasonal temperatures at the polar cap starting from an arbitrary initial uniform depth distribution of subsurface ice h2o fluxes into or out of the regolith are calculated for 100 selected obliquity cycles each representing a different epoch in mars history the h2o fluxes are translated into ice thicknesses and extrapolated over time to give the subsurface ice depth as a function of latitude and time the results show that obliquity variations influence annual average regolith temperatures in varying degrees depending on latitude with the greatest effect at the poles and almost no effect at 40 lat insolation changes at the pole due to obliquity argument of subsolar meridian and eccentricity variations can produce enormous atmospheric h2o concentration variations of 6 orders of magnitude over an obliquity cycle superimposed on these cyclic variations is a slow monotonic change due to the increasing solar luminosity albedo changes at the polar cap due to seasonal phase changes of co2 and the varying thickness of the co2 ice cover are critically important in determining annual average atmospheric h2o concentrations despite the strongly oscillating character of the boundary conditions only small amounts of h2o are exchanged between the regolith and the atmosphere per obliquity cycle 10 g cm2 the net result of h2o migration is that the regolith below 30 40 lat is depleted of subsurface ice while the regolith above 30 40 lat contains permanent ice due to the depth of penetration of the annual thermal wave this result is supported by recent morphological studies the rate of migration of h2o is strongly dependent on average pore capillary radius for which we have assumed values of 1 and 10 m we estimate that the h2o ice removed from the regolith would produce a permanent ice cap with a volume between 2 106 and 6 106 km3 this generally agrees with estimates deduced from deflationary features at lower latitudes depositional features at higher latitudes and the mass of the polar caps

a 1500 year record of temperature and glacial response inferred from varved iceberg lake southcentral alaska we present a varve thickness chronology from glacier dammed iceberg lake in the southern alaska icefields radiogenic evidence confirms that laminations are annual and record continuous sediment deposition from a d 442 to a d 1998 varve thickness is positively correlated with northern hemisphere temperature trends and more strongly with a local 600 yr long tree ring width chronology varve thickness increases in warm summers because of higher melt runoff and sediment transport as expected but also because shrinkage of the glacier dam allows shoreline regression that concentrates sediment in the smaller lake varve thickness provides a sensitive record of relative changes in warm season temperatures relative to the entire record temperatures implied by this chronology were lowest around a d 600 warm between a d 1000 and a d 1300 cooler between a d 1500 and a d 1850 and have increased dramatically since then combined with stratigraphic evidence that contemporary jokulhlaups which began in 1999 are unprecedented since at least a d 442 this record suggests that 20th century warming is more intense and accompanied by more extensive glacier retreat than the medieval warm period or any other time in the last 1500 yr

interactions between the landers and hector mine california earthquakes from space geodesy boundary element modeling and time dependent friction the m w 7 1 hector mine earthquake happened 7 years after the 1992 m w 7 3 landers earthquake within a system of right lateral strike slip faults comprising the eastern california shear zone because estimates of recurrence intervals of m 7 earthquakes on these faults range anywhere from 1500 to 50 000 years the close temporal spacing of these two earthquakes suggests that there is some interaction between the two current models of simple coulomb static stress interactions between the earthquake ruptures do not predict an obvious cause and effect relationship the interaction between the computed normal and right lateral shear stress reductions induced by the landers earthquake at the hector mine hypocenter is unclear we use a combination of space geodesy boundary element modeling and computer modeling of time dependent fault friction to investigate the interaction between the two earthquakes we compare stress changes on the hector mine rupture plane induced by the landers earthquake with the detailed slip distribution inferred using a combination of gps and insar data the slip distributions of both earthquakes are also used to infer the magnitude of the shear stress drop on each earthquake rupture and the orientation of the remote background stress consistent with these two recent events for each earthquake the azimuth of the remote maximum compressive stress was approximately 17 6 and the magnitude of the shear stress drop was 8 1 mpa on the landers rupture and 10 2 mpa on the hector mine rupture using a simple spring and slider model as a proxy for the rate and state frictional response of the hector mine faults to landers earthquake imposed stress steps we find that while a decrease in normal stress at the hector mine hypocenter would by itself have caused the hector mine earthquake to nucleate immediately the simultaneous decrease in shear stress may have caused a delay in the peak shear loading consideration of an acceptable range of rate and state friction parameters secular strain rates and crustal stiffnesses leads us to conclude that this delay could have been 0 to 40 years

volcano ground ice interactions in elysium planitia mars abstract the occurence within elysium planitia of meltwater deposits possible pseudocraters collapse features within troughs and outflow channels indicates that a layer of subsurface volatiles existed at the time of volcanic activity within this area the pseudocraters are interpreted to be indicators of near surface volatiles while meltwater deposits and the degree of preservation of trough walls and floors are thought to signify greater volatile depths a latitudinal variation in the distribution of these features indicates either that the depth to the volatile layer increased from less than about 50 m at 35 n to greater than 600 m at 24 n or that an ice wedge that existed at 35 n thinned to nonexistence at 24 n braided distributary channel systems within the chaotic terrain north of elysium planitia show that ephemeral lakes were repeatedly created and drained at this locality the existence of volatiles contemporaneous with volcanic activity permits a search to be made for explosively generated landforms predicted to exist by previous theoretical models morphological evidence for strombolian vulcanian and plinian eruptions is lacking within western elysium planitia there are no identifiable cinder cones pyroclastic flow deposits or mantled areas indicative of large airfall deposits at an image resolution of 50 150 m pixel however the pseudocraters indicate that small scale phreatomagmatic activity may have taken place

recent holocene changes in sedimentation in a landslide dammed lake in the cascade mountains southwestern british columbia canada landslide damming of silver lake in the cascade mountains took place about 1000bp delta growth favoured the faulted west valley side at the commencement of logging activity in ad 1946 the course

ice sculpture in the martian outflow channels many landforms in martian outflow channels have characteristics that suggest sculpture by glaciers ice streams or ice sheets viking orbiter and terrestrial satellite images were examined at similar resolution to compare features of the martian outflow channels to features produced by the movement of ice on earth many resemblances were found they include the anastomoses sinuosities and u shaped cross profiles of valleys hanging valleys and linear scour marks on valley walls grooves and ridges on valley floors and streamlining of bedrock highs the question of whether ice could have moved in the martian environment is investigated since gradients on martian channel floors are extremely low or even reversed a certain thickness of ice is required to initiate glacial motion if ice filled the martian channels to the level of interior plateaus flow could have occurred even under present climatic conditions although warmer climates in the past would have been more favorable additionally if the channel fluids were brines ice might have been wet based and would have moved readily by slipping over the ground it is envisioned that springs or small catastrophic outbursts discharged fluids from structural outlets or chaotic terrains the fluids built icings that may have grown into substantial masses and eventually flowed like glaciers down preexisting valleys alternatively the fluids may have formed rivers or floods that formed ice jams and consolidated into icy masses in places where obstacles blocked their flow these masses of ice or slush were probably episodic and temporary but where they occurred within the channels they may have produced landforms that are characteristic of glacial sculpture on earth

paleoseismological evidence of recent earthquakes on the 1967 mudurnu valley earthquake segment of the north anatolian fault zone this study contributes paleoseismological data on the recent history of surface rupturing earthquakes on the southern main branch of the north anatolian fault zone nafz turkey west of the bolu basin we focused on the fault segment that ruptured during the 1967 mudurnu valley earthquake m s 7 1 which preceded the devastating earthquakes of 1999 in the sequence of westward migrating nafz earthquakes since 1939 geomorphological mapping was carried out in a search for trenching sites on the central part of the 22 july 1967 earthquake segment in the absence of locations in sedimentary environments best suited for paleoseismological interpretation of faulted holocene deposits we trenched fluvial channel deposits at a terrace of the gravel dominated mudurnu river the most conservative interpretation of the trench stratigraphy and faulting evidence suggests that at least one paleoearthquake most probably two occurred after a d 1693 the 1967 earthquake segment has ruptured at least once since the historical earthquake of a d 1668 which was previously considered to be a likely candidate for the penultimate event and before 1967 it is not possible to confidently assign the penultimate event to one of the post a d 1693 historical earthquakes in the broader area around the mudurnu valley e g the earthquake of a d 1719 because the historical data published so far do not provide conclusive information about when past ruptures of the mudurnu valley branch of the nafz a secluded area did or did not take place

thermal behavior of horizontally mixed surfaces on mars abstract current methods for deriving thermal inertia from spacecraft observations of planetary brightness temperature generally assume that surface properties are uniform for any given observation or co located set of observations as a result of this assumption and the nonlinear relationship between temperature and thermal inertia sub pixel horizontal heterogeneity may yield different apparent thermal inertia at different times of day or seasons we examine the effects of horizontal heterogeneity on mars by modeling the thermal behavior of various idealized mixed surfaces containing differing proportions of either dust sand duricrust and rock or slope facets at different angles and azimuths latitudinal effects on mixed surface thermal behavior are also investigated we find large several 100 j m 2 k 1 s 1 2 diurnal and seasonal variations in apparent thermal inertia even for small 10 admixtures of materials with moderately contrasting thermal properties or slope angles together with similar results for layered surfaces mellon m t putzig n e 2007 lunar planet sci xxxviii abstract 2184 this work shows that the effects of heterogeneity on the thermal behavior of the martian surface are substantial and may be expected to result in large variations in apparent thermal inertia as derived from spacecraft instruments while our results caution against the over interpretation of thermal inertia taken from median or average maps or derived from single temperature measurements they also suggest the possibility of using a suite of apparent thermal inertia values derived from single observations over a range of times of day and seasons to constrain the heterogeneity of the martian surface

varve formation during the past three centuries in three large proglacial lakes in south central alaska the sediments stored in the large deep proglacial lakes of south central alaska are largely unstudied we analyzed sediments in 20 cores up to 160 cm long from eklutna kenai and skilak lakes using a combination of repeated lamination counting radionuclide dating event stratigraphy and tephrochronology we show that the characteristically rhythmic layers were deposited annually most of these glacial varves consist of one coarse grained base and a fine grained top but varves composed of multiple coarse grained turbidite pulses are common too they are likely related to successive episodes of high sediment discharge during flooding and they become more frequent in all three lakes along with increased sedimentation rates during the nineteenth century late phase of the little ice age these flood turbidites were generated by rain events and intense melting of snow and ice other mega turbidites are a result of earthquake triggered slope collapses e g a d 1964 some event layers are present in all three lakes in addition the annual time series of varve thickness normalized annual sedimentation rate are significantly correlated among the three lakes p 0 27 p 0 001 differences between the varve thickness records can be attributed partly to the dam construction at eklutna lake and outbursts from an ice dammed lake at skilak lake geomorphologic differences among the catchments result in further differences in sedimentation patterns in the three lakes

mars a water rich planet abstract mars had outgassed at least 0 5 to 1 km of water 10 to 20 bar of co2 and 0 1 to 0 3 bar of n2 the volatiles that have been retained are mostly in the cratered uplands terrain softening fretted channels debris flows and closed depressions indicate that at least the upper 2 km of the cratered uplands at high latitudes 30 contain ice in amounts that exceed the porosity estimated to be 10 20 theoretical studies and lack of these features in the cratered uplands at low latitudes suggest that the upper 1 km of the uplands at low latitudes is ice poor however valley networks indicate that water was present near the surface early in the planet s history although in amounts smaller than at high latitudes the entire upper 1 km planetwide is estimated to have contained 75 125 m of water at the end of heavy bombardment the largest sink for water is the megaregolith below 1 km episodic eruption of water from the deep megaregolith cut many of the large outflow channels from the volume of water needed to cut the circum chryse channels and assuming uniform planetwide distribution of water the deep megaregolith is estimated to have contained at least 350 m of water at the end of heavy bombardment thereby giving a total minimum inventory of 424 475 m planetwide most of the water lost from the low latitude uplands by diffusion and in cutting the valley networks is now believed to be in the polar layered terrains most of the water involved in cutting the outflow channels is in the low lying northern plains where a variety of features that have been attributed to ground ice is present a large fraction of the planet s surface has been overplated with water poor volcanics of which we have samples in the snc meteorites the younger volcanics have reacted extensively with the old volatile rich basement some of the co2 and n2 outgassed was lost during heavy bombardment by impact erosion of the atmosphere and other processes the remaining was fixed carbonates and folded deep into the megaregolith during heavy bombardment

wind streaks in tharsis and elysium implications for sediment transport by slope winds detailed maps of wind streaks in tharsis and elysium have been compiled from viking orbiter observations spanning one complete martian year the streak pattern is controlled by slope winds on the central volcanoes and on the flanks of the tharsis bulge while the global circulation dominates in elysium dust erosion by downslope winds occurs over much of tharsis and in the vicinity of elysium mons this process is effective even at the low atmospheric pressures found near the summits of the large volcanoes erosional streaks are largely absent in elysium planitia net deposition of dust might have occurred during the period of our observations surface properties such as slope thermal inertia and roughness may influence the efficiency of slope wind production sufficiently to account for the pronounced differences in streak types and patterns present in these two regions

explosive volcanism on hecates tholus mars investigation of eruption conditions evidence is presented supporting the identification of a discrete well preserved air fall deposit generated by explosive volcanism on mars the deposit is located immediately to the west of the summit caldera of hecates tholus 32on 209ow the northernmost of the three volcanic constructs in the elysium planitia region the absence of superposed impact craters larger than the resolution limit of the viking images 40 m per pixel indicates a very young age for this eruption which evidently postdates even the most recent collapse episode of the olympus mons caldera 300 m y b p neukum and hiller 1981 from the distribution of craters smaller than 2 km in diameter it appears that the air fall material mantles an area about 50 x 75 km in extent to an estimated thickness of about 100 m by adapting numerical models for terrestrial volcanic eruptions to the martian environment these dimensions imply an eruption cloud height of about 70 km in order to attain such an altitude the mass eruption rate must have been 107 kg s and the volatile content either 1 wt for h20 or 2 wt for co2 although it is not possible to distinguish between silicic and basaltic volcanism on hecates were the volatile species co2 the depth of most recent storage prior to eruption of the magma would have to be 50 100 km due to the solubility of co2 in the melt if h20 were the driving volatile a minimum depth of storage would be 0 2 4 km thereby permitting the possibility of ground water assimilation by the magma

holocene fluctuations of a meromictic lake in southern british columbia abstract holocene deposits of mahoney lake a meromictic saline lake located in a closed basin in the semi arid okanagan valley contain evidence of frequent and marked changes in lake depth up to 12 m 10014c yr probably caused by short term changes in effective precipitation we studied a 5 45 m long core comprising a basal layer of inorganic mud overlain by a succession of layers of calcareous laminated and nonlaminated organic mud marl and sand we used mazama tephra to adjust nine radiocarbon ages for the hardwater effect meromixis developed ca 900014c yr b p and the lake has been episodically meromictic for about half the time since because of close linkages between sediments and depositional environments in meromictic and saline lakes we infer that laminated sediments indicate meromictic conditions and high lake levels ca 12 m water depth whereas thick marl layers and nonlaminated sediments indicate nonmeromictic conditions and thus low lake levels

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

surficial geologic surveys of gale crater and melas chasma mars integration of remote sensing data abstract remote sensing observations of gale crater and melas chasma are synthesized to better understand the present surface layer in these two scientifically interesting regions data sets analyzed include geologic maps mars orbiter laser altimeter mola elevation thermal emission spectrometer tes albedo tes thermal inertia mola residual pulse width tes rock abundance and viking and mars orbiter camera images using these data sets we constrain the properties of and processes acting on the present surface and create self consistent models for the surface layer surface properties within gale crater are variable and complex and interpreting the surface layer is not straightforward observations indicate that aeolian processes have shaped some of the intracrater surface but other areas do not comply with this model and have counterintuitive surface characteristics in contrast aeolian activity appears to have played a large role in shaping the present day physical structure of all surfaces in melas chasma and is reflected in the remote sensing data sets here we summarize our analysis and discuss the surface attributes as determined from these data sets

ground ice on mars inventory distribution and resulting landforms abstract most 90 of the estimated original volume of outgassed water on mars cannot be satisfactorily accounted for by exospheric escape or storage in the atmosphere as frost or in the permanent north polar ice cap the balance may be stored as ground ice in the martian cryosphere a zone of permanently frozen ground that is protected from the atmosphere by a debris cover ground ice can exist throughout the entire cryosphere but it need not fill it if the ground ice does fill the cryosphere then excess water can exist in a confined aquifer the theoretical distribution of ground ice can be tested by identification of forms on the martian surface that may be related to the presence of subsurface ice the observed features that are most likely to reflect ground ice are thermokarst like pits and debris flows landforms with ambivalent origins include polygonally patterned ground lobate ejecta blankets craters with central pits and curvilinear features the most persuasive morphologic evidence for ground ice is thermokarst pits and debris flows the thermokarst pits are primarily located in the volcanic regions of tharsis and elysium the association of ice related features with these volcanic areas suggests that these forms are not directly latitude dependent activation by orbital variations could produce periodic multiple episodes of melting that are dependent upon latitude the presence of ice related features in both hemispheres and the equatorial region of mars indicates that ground ice may be or have been present over the entire planet as predicted by the cryosphere model

dual polarization radar observations of mars tharsis and environs abstract observations of the tharsis region of mars with the 12 6 cm radar at arecibo observatory have yielded radar echoes which are highly depolarizes and which are in terms of total echo power dominated by diffuse rather than quasi specular backscattering the observations were made on february 7 8 and 9 1980 and the subradar track extended from 77 to 126 w longitude at 22 n latitude dual polarized reception was employed i e the echo was received in the same sense of circular polarization as transmitted depolarized sense as well as in the opposite polarized sense the disk integrated ratio of depolarized power to polarized power averages 0 37 and the ratio of diffuse power to quasi specular power averages 3 2 the depolarized spectra are dominated by a broad enhancement identified primarily with echoes from the tharsis ridge implying that extensive areas of tharsis are rough on decimeter scales the major tharsis shield volcanoes are candidates for sources of strong depolarization although they alone cannot account for the entire depolarization enhancement

mars the regolith atmosphere cap system and climate change abstract a new model for predicting the behavior of the martian regolith atmosphere cap co 2 regime and describing its role in climate change is derived the model describes the time temperature histories of 90 regolith chunks on a latitude depth grid accounting for co 2 exchange by means of laboratory derived expressions relating temperature co 2 pressure p co 2 and adsorbed co 2 mass co 2 polar cap formation and sublimation is accounted for subject to the constraint of constant total co 2 in the atmosphere regolith cap system the influence of differences in regolith adsorption laws for basalt and clay and the influence of variations in regolith depth with latitude regolith thermal diffusivity and total exchangeable co 2 inventory on predicted variations in atmospheric pressure and cap mass are examined the following results are indicated 1 the atmosphere acts as a low capacity conduit through which flows between 10 and 100 times the current atmospheric mass of co 2 between two reservoirs a regolith ocean of adsorbed co 2 and a polar cap cryosphere 2 exchange between these reservoirs is driven by variations of obliquity with the polar cap the dominant co 2 sink at low and the regolith dominating at high atmospheric pressure ranges between 0 1 low and 15 mbar high pressures of up to 25 mbar could result from pre tharsis variations pressure up to 40 mbarare achieved only in models which also call for a huge quasi permanent present co 2 cap which is not apparent 3 at high the atmospheric pressure is buffered by the regolith and satisfies adsorption equilibrium for the 90 chunks as well as conservation of co 2 mass at low a potetially large co 2 cap appears and the atmospheric pressure is buffered by the cap not the regolith 4 the periodic reservoir flushing can account for the observation of simultaneous nonenrichment of 18 o and enrichment of 13 n 5 mars climate history may be divided into three parts a post tharsis formation history as described above b pre tharsis formation with qualitatively similar processes but larger oscillations between reservoirs and larger atmospheric pressure and cap mass variation and c the very early period of channel formation 6 the nature of the response of the three part regolith atmosphere polar cap martian climate system to surface insolation variations may be analogous to that of earth s ocean atmosphere cryosphere system

martian fluvial thermal erosion laboratory simulation wide outflow channels occur both in siberia and on the planet mars in siberia thermal erosion results from ground thawing produced by the heat transfer from the flow of water to the frozen ground we suggest that relatively warm floods on mars could enlarge outflow channels by a combination of thermal and mechanical erosion along frozen river banks a one dimensional model is proposed to estimate the thermal erosion efficiency a first test of this model is a comparison of results with experiments carried out in a cold chamber a hydraulic channel allows measurements of the thawing line propagation as well as the thermal erosion rate in simulated ground ice that is subjected to warm water flow various laboratory simulations demonstrate the validity of the mathematical model for the range of laboratory conditions this model is then applied to a range of possible current and ancient martian conditions

geological evolution of ares vallis on mars formation by multiple events of catastrophic flooding glacial and periglacial processes abstract ares vallis is one of the greatest outflow channels of mars using high resolution images of recent missions to mars mgs 2001 odyssey and mars express we investigated ares vallis and its valley arms taking advantage of 3 dimensional analysis performed using the high resolution stereo capability of the mars express high resolution stereo camera hrsc in our view ares vallis is characterized by catastrophic flood landscapes partially superimposed by ice related morphologies catastrophic flood landforms include erosional terraces grooved terrains streamlined uplands giant bars pendant bars and cataract like features ice related morphologies include probable kame features thermokarstic depressions and patterned grounds our investigations outline that throughout the hesperian age ares vallis and its valley arms had been sculpted by several time scattered catastrophic floods originating from iani hydaspis and aram chaos geomorphological evidence suggests that catastrophic floods were ice covered and that climatic conditions of mars at this time were similar to those of the present day at the end of each catastrophic flood ice masses grounded forming a thick stagnant dead ice body each catastrophic flood was followed by a relatively brief period of warmer wetter climatic conditions originated as a consequence of catastrophic flooding during such periods thermokarstic depressions originated liquid water formed meandering channels and ice contact deposits were emplaced by ice walled streams finally the climate turned into cold dry conditions similar to the present day ones and ice masses sublimated