permittivity estimation over mars by using sharad data the cerberus palus area 1 cerberus palus is a thoroughly studied region of mars characterized by evident platy textures that were interpreted either as evidence for a frozen sea close to mars equator or as being resultant of lava mud or ice flows coming from cerberus fossae through athabasca valles radargrams provided by radar sounder sharad clearly show the presence of subsurface layers in the area by exploiting the great amount of available data authors have performed an accurate quantitative analysis aimed to estimate electromagnetic properties of surface and subsurface layers in terms of permittivity and attenuation to this aim a simplified electromagnetic approach has been used but taking into account effects of scattering due to surface roughness for avoiding overestimated results this has been done by using theory of electromagnetic scattering from fractal surfaces and by estimating needed parameters from topographic data provided by mola three distinct geologic formations have been analyzed namely a part of zephyria planum the cerberus plains and the bedrock beneath the plains the retrieved electromagnetic parameters have been also modeled as a mixture of volcanic rocks with either ice or air the zephyria planum material was found to be significantly porous 50 60 with an attenuation more likely compatible with empty pores ambiguous results were obtained for the plains material being the resulting porosity high in both the cases of empty 40 50 and of ice filled 80 pores the obtained results do not allow for evidence of a frozen sea on cerberus palus area

origins of the reversed flow over the windward alpine foothills during map iop3 and iop8 the synoptic scale situations during the two intensive observing periods iops of the mesoscale alpine programme map characterized by persisting precipitation and down valley flow as observed by the doppler on the wheel radar dow over the two alpine valleys toce and ticino were investigated the first period iop3 24 27 september 1999 was characterized by a south westerly flow and convective precipitation whereas the second period iop8 20 21 october 1999 by a down valley flow and stratiform precipitation during iop3 the down valley northerly flow over the north western part of the po valley was confined within a thin layer of 200 300 m depth during iop8 the northerly flow extended from the alps foothills to the ligurian sea in a deep layer of 1 2 km height the meso nh numerical model with a 2 5 km horizontal mesh grid reproduced the characteristics of both cases from the valley scale to the meso scale sensitivity experiments were furthermore performed in order to highlight the relationships between wet or dry drainage flow channelled by the alpine orography mesoscale upstream flow blocked by the alps and a regional cold pool at the foothills inside the po valley during iop8 the diabatic processes were dominant at local scales in confirmation of steiner results based on the dow observations and they were significant at regional scales upstream of the alps by maintaining a cold pool over the po valley the iop3 low level flow reversal occurred as the flow began to cross over the alps instead of turning around a downslope flow is associated with the blocked regime period upstream of the alps copyright 2006 royal meteorological society

very recent and wide spread basaltic volcanism on mars new spacecraft data provide increasing evidence for a dynamic environment on presenta day mars exogenic processes such as impact cratering mass wasting processes and active dune migration have all been observed to modify the surface no traces of current endogenic activity have been found yet but some studies point to very localized volcanism in the last few millions of years however no systematic study of young volcanic surfaces had been performed so far we present absolute model age determinations of plains volcanism on mars as derived from impact crater sizefrequency distributions extended areas in tharsis the largest volcanoa tectonic region on mars have been resurfaced by lava flows in the last few tens of millions of years we also present results on the rheologic properties of these lava flows inferred from morphometric measurements yield strengths are in the range of 100a 300 pa and viscosities reach values of 10 2 to 10 3 pa s indicating basaltic compositions the results imply that mars retained until recently and probably still retains enough internal heat to produce widea spread plaina style volcanism producing lowa viscosity lava flows throughout large parts of tharsis

early views of the martian surface from the mars orbiter camera of mars global surveyor high resolution images of the martian surface at scales of a few meters show ubiquitous erosional and depositional eolian landforms dunes sandsheets and drifts are prevalent and exhibit a range of morphology composition inferred from albedo and age as seen in occurrences of different dune orientations at the same location steep walls of topographic depressions such as canyons valleys and impact craters show the martian crust to be stratified at scales of a few tens of meters the south polar layered terrain and superposed permanent ice cap display diverse surface textures that may reflect the complex interplay of volatile and non volatile components low resolution regional views of the planet provide synoptic observations of polar cap retreat condensate clouds and the lifecycle of local and regional dust storms

origin of martian northern hemisphere mid latitude lobate debris aprons lobate debris aprons in the martian mid to high latitudes northern and southern hemispheres have been interpreted as ice related features that indicate periglacial climate conditions as recently as late amazonian using mola topographic profiles perpendicular to apron flow fronts we surveyed 36 debris aprons in the northern hemisphere found in the regions of mareotis protonilus and deuteronilus mensae and acheron fossae the profiles of these aprons were compared with idealized simple plastic and viscous power law models for ice rock mixtures all aprons studied exhibit convex profiles similar to a simple plastic model this confirms previous interpretations that debris aprons are ice rich mixtures with rheologies similar to stagnant ice sheets thus indicating high ice concentrations 40 by volume about 60 of the surveyed debris apron population significantly deviates from the idealized simple plastic model profile this may be due to locally reduced ice content which primarily controls apron topography although post emplacement modification due to near surface ice sublimation plays a secondary role in defining the overall shape of aprons it causes conspicuous surface textures degradation by ice sublimation probably results in pitted and ridge and furrow surface textures revealed by high resolution moc images such textures may indicate decreased near surface ice stability since the formation of the aprons possibly due to mars current low obliquity after their emplacement high ice content inferred from topography suggests some debris aprons have ice cores potentially exploitable water resources for future robotic human operations that could prove invaluable for missions remote from polar regions

stratigraphical and morphological evidence for pingo genesis in the cerberus plains rootless debris cones or pseudocraters occur in platy patterned ground throughout the cerberus plains of mars and are thought to represent the products of explosive magma ice interaction lanagan et al 2001 geophys res lett 28 2365 2368 fagents et al 2002 in smellie j l chapman m g eds volcano ice interaction on earth and mars in geol soc spec publ vol 202 pp 295 317 requiring lava and water interspersed they are central to theories of multiple magmatic and aqueous flood events burr et al 2002 icarus 159 53 73 berman d c hartmann w k 2002 icarus 159 1 17 and widespread sheet volcanism keszthelyi et al 2000 j geophys res 105 15027 15049 in the region during the late amazonian a region reported to have been occupied by water bodies ranging from lakes to oceans scott et al 1995 map of mars showing channels and possible paleolake basins usgs miscellaneous investigations series map i 2461 1 30 000 000 the nature of the platy substrate is the subject of debate with evidence given for lava keszthelyi et al 2000 j geophys res 105 15027 15049 plescia j b 2003 icarus 164 79 95 and ice brakenridge g r 1993 lunar planet sci xxiv part 1 175 176 rice et al 2002 lunar planet sci xxxiii abstract 2026 murray et al 2005 nature 434 352 355 the superposition relationships of cones and platy deposits in the channels of the athabasca valles precludes a magmatic origin indicating later formation as permafrost mounds or pingos with implications for geologically recent flood volcanism age constraints on young surfaces and recent climate change on mars

martian hillside gullies and icelandic analogs abstract we report observations of icelandic hillside gully systems that are near duplicates of gullies observed on high latitude martian hillsides the best icelandic analogs involve basaltic talus slopes at the angle of repose with gully formation by debris flows initiated by ground water saturation and or by drainage of water from upslope cliffs we report not only the existence of mars analog gullies but also an erosional sequence of morphologic forms found both on mars and in iceland the observations support hypotheses calling for creation of martian gullies by aqueous processes issues remain whether the water in each case comes only from surficial sources such as melting of ground ice or snow or from underground sources such as aquifers that gain surface access in hillsides iceland has many examples of the former but the latter mechanism is not ruled out our observations are consistent with the martian debris flow mechanism of f costard et al 2001c science 295 110 113 except that classic debris flows begin at midslope more frequently than on mars from morphologic observations we suggest that some martian hillside gully systems not only involve significant evolution by extended erosive activity but gully formation may occur in episodes and the time interval since the last episode is considerably less than the time interval needed to erase the gully through normal martian obliteration processes

mesoscale linear streaks on mars environments of dust entrainment abstract variable surface albedo features on mars are likely caused by the entrainment and deposition of dust by the wind most discrete markings are associated with topographic forms or with regional slopes that serve to alter the effective wind shear stress on the surface some of the largest variable features here termed mesoscale linear streaks are up to 400 km in length and repeatedly occur in one of the smoothest regions of mars amazonis planitia their orientations and apparent season of variability as observed by viking and mars orbiter cameras indicate linear streak formation by enhanced surface wind stresses during regional or local dust storms and during the initial stages of global dust storms they provide an example of the ability of large scale winds without significant local enhancement to initiate dust motion on mars the sizes and spacing of the linear streaks may be controlled by boundary layer rolls the repetitive formation of these streaks over a span of more than 11 mars years gives one measure of the stability of mars eolian processes

searching for the source regions of martian meteorites using mgs tes integrating martian meteorites into the global distribution of igneous materials on mars the objective of this study was to identify and map possible source regions for all 5 known martian meteorite lithologies basalt lherzolite clinopyroxenite orthopyroxenite and dunite using data from the mars global surveyor thermal emission spectrometer mgs tes we deconvolved the tes data set using laboratory spectra of 6 martian meteorites los angeles zagami alh a77005 nakhla alh 84001 and chassigny as end members along with atmospheric and surface spectra previously derived from tes data global maps 16 pixels degree of the distribution of each meteorite end member show that meteorite like compositions are not present at or above tes detectability limits over most of the planet s dust free regions however we have confidently identified local scale 100s1000s km2 concentrations of olivine and orthopyroxene bearing materials similar to alh a77005 chassigny and alh 84001 in nili fossae in and near ganges chasma in the argyre and hellas basin rims and in eos chasma nakhla like materials are identified near the detection limit throughout the eastern valles marineris region and portions of syrtis major basaltic shergottites were not detected in any spatially coherent areas at the scale of this study martian meteorite like lithologies represent only a minor portion of the dust free surface and thus are not representative of the bulk composition of the ancient crust meteorite like spectral signatures identified above tes detectability limits in more spatially restricted areas tens of km are targets of ongoing analysis

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

elysium planitia lava flows crater count chronology and geological implications mars global surveyor mgs and viking images allow analysis of chronological and geological relations among lava flows in southern elysium planitia based on crater populations mgs and viking images clearly show morphological features of lava flows with some extremely sparsely cratered young flow units atop somewhat older surfaces there is no evidence of substantial dust mantling on the young flows and hence we infer that the crater populations date not sediment accumulation but the lava flows themselves the youngest flows have some of the lowest crater densities that we have seen on mars some 1 of lunar mare values at crater diameters below about 180 to 500 m we infer that thin scattered volcanic flows some tens of meters thick have been emplaced atop stratigraphic units within the last 100 myr and possibly within the last 10 myr volcanism is thus a continuing process in the recent geologic history of mars and this must constrain geophysical models of the planet

recent flood lavas in the elysium region of mars abstract a vast area of smooth plains in southeastern elysium here referred to as the cerberus formation is interpreted to be of volcanic origin surface morphology lobate edges of the unit the identification of vents low shields and the embayment relation of the unit with adjacent older units all suggest a volcanic origin the plains were formed by the eruption of low viscosity lavas that filled a topographic depression in southeast elysium and then flowed into western amazonis planitia flow into western amazonis was facilitated by a series of channels carved by an earlier fluvial episode which were exploited by lavas as they moved down slope crater frequencies and stratigraphic relations indicate that the unit is very young upper amazonian the presence of such young flood lavas indicates 1 late in martian history large scale eruptions of low viscosity lava was still possible b sufficient heat remained in the mantle to mobilize large quantities of magma and c flood volcanism either continued or resumed in elysium after activity of the large central volcanoes had ceased each of these points are important considerations in understanding the martian thermal and volcanic history

context camera investigation on board the mars reconnaissance orbiter 1 the context camera ctx on the mars reconnaissance orbiter mro is a facility instrument i e government furnished equipment operated by a science team not responsible for design and fabrication designed built and operated by malin space science systems and the mro mars color imager team marci ctx will 1 provide context images for data acquired by other mro instruments 2 observe features of interest to nasa s mars exploration program e g candidate landing sites and 3 conduct a scientific investigation led by the marci team of geologic geomorphic and meteorological processes on mars ctx consists of a digital electronics assembly a 350 mm f 3 25 schmidt type telescope of catadioptric optical design with a 5 7 field of view providing a 30 km wide swath from 290 km altitude and a 5000 element ccd with a band pass of 500 700 nm and 7 m pixels giving 6 m pixel spatial resolution from mro s nearly circular nearly polar mapping orbit raw data are transferred to the mro spacecraft flight computer for processing e g data compression before transmission to earth the ground data system and operations are based on 9 years of mars global surveyor mars orbiter camera on orbit experience ctx has been allocated 12 of the total mro data return or about 3 terabits for the nominal mission this data volume would cover 9 of mars at 6 m pixel but overlapping images for stereo mosaics and observation of changes and meteorological events will reduce this area ctx acquired its first instrument checkout images of mars on 24 march 2006

implications of large elastic thicknesses for the composition and current thermal state of mars abstract the martian elastic lithosphere thickness t e has recently been constrained by modeling the geodynamical response to loading at the martian polar caps and t e was found to exceed 300 km at the north pole today geological evidence suggests that mars has been volcanically active in the recent past and we have reinvestigated the martian thermal evolution identifying models which are consistent with t e 300 km and the observed recent magmatic activity we find that although models satisfying both constraints can be constructed special assumptions regarding the concentration and distribution of radioactive elements the style of mantle convection and or the mantle s volatile content need to be made if a dry mantle rheology is assumed strong plumes caused by e g a strongly pressure dependent mantle viscosity or endothermic phase transitions near the core mantle boundary are required to allow for decompression melting in the heads of mantle plumes for a wet mantle large mantle water contents of the order of 1000 ppm are required to allow for partial mantle melting also for a moderate crustal enrichment of heat producing elements the planet s bulk composition needs to be 25 and 50 sub chondritic for dry and wet mantle rheologies respectively even then models resulting in a globally averaged elastic thicknesses of t e 300 km are difficult to reconcile with most elastic thickness estimates available for the hesperian and amazonian periods it therefore seems likely that large elastic thicknesses in excess of 300 km are not representative for the bulk of the planet and that t e possibly shows a large degree of spatial heterogeneity

late holocene lake levels of the dead sea this work presents a high resolution lake level record of the late holocene dead sea a hypersaline terminal lake whose drainage basin encompasses both mediterranean and hyperarid climatic zones the lake level curve reflects the regional hydrologic variations in the drainage basin which in turn represent the levant paleoclimates the curve is based on 46 radiocarbon ages of organic remains from well exposed sedimentary sequences along the dead sea shores these sequences record fluvial and lacustrine depositional environments the paleolakeshores are marked by shore ridges coarse sand units and aragonite crusts in the modern dead sea such features indicate the exact elevation of the shore the late holocene dead sea level fluctuated within the range of 390 to 415 m below sea level mbsl for most of the time the lake was below the topographic sill 402 mbsl separating the northern and southern basins of the dead sea and was confined to the deep northern basin nevertheless short term rises in the late holocene dead sea level caused the flooding of the shallow and flat southern basin highstands occurred in the second and first centuries b c and the fourth century a d during the roman and early byzan tine periods respectively in the eleventh and twelfth centuries a d during the crusader period and at the end of the nineteenth century a d the rises mark a significant change in the annual rainfall in the region which likely exceeded the instrumentally measured modern average the curve also indicates drastic drops that exposed the sedimentary sequences to erosion the oldest and probably deepest drop in the lake level culminated during the fifteenth and fourteenth centuries b c after a retreat from a higher lake stand the longest lowstand occurred after the byzantine period and continued at least until the ninth century a d this arid period coincided with the invasion of moslem arab tribes into the area during the seventh century a d the dramatic fall of the dead sea level during the twentieth century is primarily artificial and has been caused by the diversion of runoff water for the drainage basin but the magnitude is not considered exceptional for the late holocene although the past drops in the lake never exceeded the modern artificial drop rates they do represent extreme arid conditions that occurred frequently over the past several thousand years

mineralogy of recent volcanic plains in the tharsis region mars and implications for platy ridged flow composition volcanism on mars occurred until recently but the mineralogy of recent lava plains is poorly known because few regions display fresh outcrops devoid of dust using visible and near infrared data of the mars express probe two new volcanic plains in noctis labyrinthus have been identified and the existence of a volcanic plain on the floor of echus chasma has been confirmed crater retention ages estimated for these three plains range between 50 and 100 my corresponding to the late amazonian these plains represent an excellent opportunity to constrain the mineralogy of recent volcanic rocks results show that basaltic compositions with plagioclase and high calcium pyroxene are predominant the low olivine proportion suggests that the apparent fluidity of these flat plains is not related to magmas being ultramafic in addition a platy ridged texture is observed in two of the studied regions our study shows for the first time that this texture is associated with volcanic rocks and that these rocks are of typical basaltic mineralogy finally these volcanic plains are located more than 1000 km east of previously known late amazonian volcanic centers of the tharsis region an observation to be taken into account when considering models of recent volcanism on mars c 2009 elsevier bm all rights reserved

explosive volcanism in the tharsis region global evidence in the martian geologic record 1 a global equatorial set of layered deposits on mars has been reexamined with mars global surveyor data the stratigraphy morphology and erosional characteristics of units separated by thousands of kilometers are remarkably similar to each other and consistent with a widespread episodic subaerial source of fine grained material this study is the first to propose a genetic link between many units that have traditionally been considered on a local or regional level including the medusae fossae formation valles marineris interior deposits chaotic terrain terra meridiani and arabia materials mapping relationships suggest that all of these units are post noachian in age and formation may have continued until the recent past thinning of deposits with increasing distance from the tharsis rise suggests that much of these materials may be volcanic ash flows and air fall from explosive eruptions in the tharsis region analogous to those produced by terrestrial plinian eruptions contemporary martian winds would preferentially transport ash from an eruption plume near tharsis east or west along the equator depending on the season erosion has removed much of the original volcanic ash and only isolated layered stacks remain sometimes in topographic depressions that inhibit erosion modeling indicates that widespread dispersion of ash after an eruption is easily attainable in present or past atmospheric conditions consistent with the hypothesis that the far reaching deposits may be composed of ash from past explosive eruptions in the vicinity of tharsis

evidence for recent volcanism on mars from crater counts impact craters help characterize the age of a planetary surface because they accumulate with time they also provide useful constraints on the importance of surface erosion as such processes will preferentially remove the smaller craters earlier studies of martian crater populations revealed that erosion and dust deposition are important processes on mars they disagreed however on the age of the youngest volcanism these earlier studies were limited by image resolution to craters larger than a few hundred metres in diameter here we report an analysis using new images obtained by the mars global surveyor spacecraft of crater populations that extend the size distribution down to about 16 m our results indicate a wide range of surface ages with one region lava flows within the arsia mons caldera that we estimate to be no older than 40 100 million years we suggest that volcanism is a continuing process on mars

elysium utopia flows as mega lahars a model of dike intrusion cryosphere cracking and water sediment release 1 high resolution altimetry from the mars orbiter laser altimeter mola provides new data to test the interpretation that unusual flow like deposits in elysium utopia were emplaced as lahars mass flows fluidized by water that are induced by volcanism using several data products derived from mola altimetry we confirm that two major types of terrain dominate the region 1 lava flows and 2 deposits consistent with emplacement by debris flows along medial channels supporting the lahar hypothesis of previous workers associated terrain types are interpreted to be the result of modification of lavas by water and or ice associated with the debris outflows and by later climatically controlled deposition and removal of a volatile rich dust layer at high latitudes both lava flows and debris flows originate from northwest trending radial fossae on the flanks of the elysium rise the fossae are interpreted here to have been formed by laterally propagating dikes from elysium mons that have intersected or approached the surface fossae that are sources for only lava flows lie at higher elevations 3400 m and above than those that are the sources of lahars and channels 3100 m to 4300 m this discrepancy in source location suggests that the availability of groundwater responsible for lahar formation is elevation dependent and reflects a hydrostatic equilibrium distribution of water in the subsurface these observations at elysium allow a geologic test of the prevailing hypothesis on the configuration of the subsurface martian hydrosphere that an interconnected groundwater system at hydrostatic equilibrium may exist below a confining cryosphere if water at a certain elevation is under hydrostatic pressure and this cryosphere is disrupted the potential arises for groundwater to flow to the surface we propose the following flow emplacement model in which geologic activity in northwest elysium is consistent with the preceding hydrological model laterally propagating dikes from elysium approached or intersected the surface on the flanks of the rise resulting in effusion of lava flows and possibly pyroclastics disruption of the cryosphere by the dikes allowed groundwater to escape to the surface and form lahars by interaction with erupted and existing material at elevations at and below the maximum level of subsurface saturated ground this model provides a consistent explanation for the major structures and units both lava flows and lahars and their elevation and spatial relationships in the elysium utopia region this type of mega lahar with groundwater as its primary water source is rare on earth and occurs on mars due to martian climatic and hydrologic conditions and the presence of a global confining cryosphere this study supports the idea that groundwater outflow resulting from disruption of a confining cryosphere may be an important phenomenon in martian geology in particular general association of major outflow with major volcanic areas on mars is highly consistent with a model of disruption of a groundwater confining cryosphere by dikes expected to be intruded in these areas further geologic analyses of features and processes related to groundwater outflow will help constrain the degree and causes of variability within the martian hydrologic system

u pb isotopic systematics of shock loaded and annealed baddeleyite implications for crystallization ages of martian meteorite shergottites abstract shock recovery and annealing experiments on basalt baddeleyite mixtures were undertaken to evaluate shock effects on u pb isotopic systematics of baddeleyite shock pressures up to 57 gpa caused fracturing of constituent phases mosaicism of olivine maskelynitization of plagioclase and melting but the phase transition from monoclinic baddeleyite structure to high pressure temperature polymorphs of zro 2 was not confirmed the u pb isotopic systems of the shock loaded baddeleyite did not show a large scale isotopic disturbance the samples shock recovered from 47 gpa were then employed for annealing experiments at 1000 or 1300 c indicating that the basalt baddeleyite mixture was almost totally melted except olivine and baddeleyite fine grained euhedral zircon crystallized from the melt was observed around the relict baddeleyite in the sample annealed at 1300 c for 1 h the u pb isotopic systems of baddeleyite showed isotopic disturbances many data points for the samples annealed at 1000 c plotted above the concordia both radiogenic lead loss uranium gain and radiogenic lead gain uranium loss were observed in the baddeleyite annealed at 1300 c complete radiogenic lead loss due to shock metamorphism and subsequent annealing was not observed in the shock loaded annealed baddeleyites studied here these results confirm that the u pb isotopic systematics of baddeleyite are durable for shock metamorphism since shergottites still preserve fe mg and or ca zonings in major constituent phases i e pyroxene and olivine the shock effects observed in martian baddeleyites seem to be less intense compared to that under the present experimental conditions an implication is that the u pb systems of baddeleyite in shergottites will provide crystallization ages of martian magmatic rocks

planetary cratering 2 studies of saturation equilibrium a realistic computer model has been developed to display images of imaginary cratered surfaces taking into account empirically measured input size distributions of primary and secondary craters ejecta blanket morphology including feathering with distance obliteration due to ejecta from outside the imaged area lighting effects etc the model allows us to track surface evolution of morphology as new craters are added using the model as well as lunar photos we have studied the approach to saturation equilibrium defined as a condition when no further proportionate increase in crater density occurs as input cratering increases we find that an identifiable saturation equilibrium occurs close to a level previously identified for this state hartmann 1984 typically fluctuating around a crater density from 0 4 to 2 times that level this result is fairly robust vis a vis the range of model parameters we have chosen flooding basin ejecta blankets and other obliterative effects can introduce structure and oscillations within this range even after saturation equilibrium is achieved these findings may constrain or revise certain earlier interpretations of satellite and planet surface evolution and impactor populations which were predicated on the assumed absence of saturation equilibrium in our fourth experimental run we found that suppression of sandblasting by subresolution impacts allows the smallest secondaries to rise above the saturation equilibrium line a result that might be relevant to a similar situation on gaspra and perhaps some other asteroids

airflow within major alpine river valleys under heavy rainfall summary this study documents the aire ow within major alpine river valleys in the presence of precipitation the analysis seeks a conceptual understanding of the effect of rain on the valley e ow ground based and airborne doppler radar and surface data from the mesoscale alpine programme show that during persistent rainy periods the subsidence caused by melting and evaporation of precipitation particles contributes to the formation of a down valley e ow this down valley eow opposes moist southerly e ow aloft which is lifted over the topographic barrier and in which precipitation particles are formed

amazonis planitia the role of geologically recent volcanism and sedimentation in the formation of the smoothest plains on mars 1 amazonis planitia located between the two main volcanic provinces on mars tharsis and elysium is characterized by extremely smooth topography at several scale lengths as smooth as oceanic abyssal plains topography on earth we use mars global surveyor mgs data primarily very high resolution mars orbiter laser altimeter mola topography and derivative slope maps gradient maps and detrended maps to examine the surface morphology of amazonis planitia and the stratigraphic relationships among previously mapped and newly defined units these new data reveal the presence of a 1300 km diameter noachian impact basin in northwest amazonis planitia and an extensive late hesperian lava flow unit that appears to have originated from the olympus mons source area prior to aureole formation the presence of this previously unrecognized flow unit strongly suggests that olympus mons activity dates back to at least the hesperian as did activity on the tharsis montes emplacement of this 100 meter thick flow unit formed a barrier along the northern margin of amazonis planitia which had a profound influence on the subsequent geologic history of the region formation of olympus mons aureole deposits created an eastern topographic barrier and subsequent tharsis montes lava flows entered the basin from the south flowing around the aureole these three barriers degraded noachian crater rim protoolympus mons flow unit and olympus mons aureole caused subsequent lava flows and outflow channel effluents primarily from the elysium region to the west to pond on the floor of amazonis planitia preferentially smoothing the terrain there mars orbiter camera moc images substantiate that at least two very fluid lava flows alternated with fluvial episodes from elysium planitia flowing through marte valles onto the floor of the amazonis planitia basin within amazonis planitia moc images show flow like textures heavily mantled by sediments and radar data reveal the presence of rough lava flow surfaces underlying the sedimentary debris these data thus suggest that the unique smoothness of amazonis planitia is the result of deposition of thin fluid lava flows and fluvial sediments in an enclosed basin crater counts suggest that the most recent resurfacing may have occurred in the latest amazonian period in the last 1 of the history of mars in light of its unique history it is somewhat ironic to note that amazonis planitia was originally thought to be a typical young martian surface and therefore used to name the amazonian era index terms 6225 planetology solar system objects mars 5415 planetology solid surface planets erosion and weathering 5470 planetology solid surface planets surface materials and properties 5480 planetology solid surface planets volcanism 8450 4267 oceanography general paleoceanography keywords mars water amazonis planitia marte vallis volcanism amazonian citation fuller e r and j w head iii amazonis planitia the role of geologically recent volcanism and sedimentation in the formation of the smoothest plains on mars j geophys res 107 e10 5081 doi 10 1029 2002je001842 2002

cloud water in windward and leeward mountain forests the stable isotope signature of orographic cloud water 1 cloud water can be a significant hydrologic input to mountain forests because it is a precipitation source that is vulnerable to climate change it is important to quantify amounts of cloud water input at watershed and regional scales during this study cloud water and rain samples were collected monthly for 2 years at sites on windward and leeward east maui the difference in isotopic composition between volume weighted average cloud water and rain samples was 1 4 18o and 12 2h for the windward site and 2 8 18o and 25 2h for the leeward site with the cloud water samples enriched in 18o and 2h relative to the rain samples a summary of previous literature shows that fog and or cloud water is enriched in 18o and 2h compared to rain at many locations around the world this study documents cloud water and rain isotopic composition resulting from weather patterns common to montane environments in the trade wind latitudes an end member isotopic composition for cloud water was identified for each site and was used in an isotopic mixing model to estimate the proportion of precipitation input from orographic clouds orographic cloud water input was 37 of the total precipitation at the windward site and 46 at the leeward site this represents an estimate of water input to the forest that could be altered by changes in cloud base altitude resulting from global climate change or deforestation

a candidate methane clathrate destabilisation event on mars a model for sub millennial scale climatic change on earth abstract methanogenic explosion of siberian permafrost mounds over the last three years questions whether this new phenomenon is the first sign of cascading release under climatic warming identical mounds occur in their millions on mars but are uniformly interpreted as ancient volcanic structures a geomorphic paradigm whose geological basis continues to escape objective observation here i show that thousands of mars mounds have recently exploded onto overlying aeolian dunes and are thus active and climatogenic the time lag between formation and synchronous explosion naturally explained by a trigger of climatic origin time transgressive mass explosion of a multi billion year aged source has no parallel in rock forming processes and points to regional scale mobilisation of volatiles this abrupt destabilisation event having immediate implications for hypothesised cascading releases from terrestrial clathrate reservoirs whether the siberian explosions are new or simply newly discovered is uncertain but their spatial density is 20 000 times lower than on mars inconsistent with ongoing multi millennial scale process we should therefore consider the possibility that they are just beginning and irrespective of volatile involved we now have a scaleable example of how they might end were the clathrates of the east siberian arctic shelf to degas on the density and frequency of mars then the entire reservoir would be depleted and unstoppable runaway warming initiated

rift zone volcanism and associated cinder cone field in utopia planitia mars 1 we analyzed a small cone field in sw utopia planitia that shows striking similarities to volcanic rift zones on earth this is of particular interest as the study area lies off any of the volcanic centers of mars in the northern hemisphere lowlands and is surrounded by material of the amazonian aged vastitas borealis formation vbf we believe that the study area could be the first direct evidence for volcanic activity in utopia planitia prior to the resurfacing by vbf material the most striking characteristics that we observed are 1 a set of broad eruptive fissures showing signs of ongoing extension during cone formation 2 parallel dike swarms 3 magmatic intrusions and 4 a number of lava flows that have erupted from the fissures and pitted cones that surround a larger cone in the center of the study area and that are often associated with or aligned along the fissures and dikes cratering model ages indicate that the study area is of late noachian to early hesperian age and is thus distinctly older than the surrounding vbf falling into the time frame of the main phases of activity in the volcanic centers of syrtis major elysium planitia and the southern highlands

cloud top entrainment instability mixing processes at cloud boundaries are thought to play a critical role in determining cloud lifetime spatial extent and cloud microphysical structure high fidelity direct numerical simulations by mellado j fluid mech 2010 this issue vol 660 pp 5 36 show for the first time the character and potency of a curious instability that may arise as a result of molecular mixing processes at cloud boundaries an instability which until now has been thought by many to control the distribution of climatologically important cloud regimes

special climatological conditions in the deserts of sinai and the negev during the latest pleistocene abstract results of hydrological and geological investigations carried out during the last ten years in the deserts of the sinai and the negev indicate that unique climatological and hydrological conditions prevailed between ca 100 000 and ca 10 000 yr b p the uniqueness was expressed by the following characteristics 1 1 higher precipitation and recharge rates caused the nubian sandstone aquifers to be filled up through the outcrops in central sinai and to overflow through big springs emerging along the faults of the syrian african rift system this water is of special isotopic composition namely depleted in 18o and deuterium and with a lower excess of the latter 2 2 dust laden rainstorms prevailed probably mainly during the autumn season causing the deposition of thick layers of loess the quantity of rain during the humid periods was double that of the present 3 3 the drainage system of many western and northern wadis of sinai as well as the negev could not drain out all the silt loaded water during the rainy season and shallow lakes and marshes extended in many wadis during this season 4 4 the floods and the springs flowing into the dead sea rift valley contributed to the lisan lake which was 200 m above the level of the contemporary dead sea

cerberus fossae elysium mars a source for lava and water cerberus fossae a long fracture system in the southeastern part of elysium has acted as a conduit for the release of both lava and water onto the surface the southeastern portion of the fracture system localized volcanic vents having varying morphology in addition low shields occur elsewhere on the cerberus plains three locations where the release of water has occurred have been identified along the northwest athabasca and grjota vallis and southeast rahway vallis portions of the fossae water was released both catastrophically and noncatastrophically from these locations a fluvial system that extends more than 2500 km has formed beginning at the lower flank of the elysium rise across the cerberus plains and out through marte vallis into amazonis planitia the timing of the events is late amazonian

on the dynamics of hawaiian cloud bands island forcing abstract this study focuses on basic island scale forcing mechanisms for the formation and evolution of a band cloud typically present upwind of the island of hawaii by means of numerical experiments and verification of our results against observations and laboratory experiments reported in the literature we show that the band cloud is a complex three dimensional phenomenon which is inseparable from the airflow around the island in particular we demonstrate that the event needs to be analyzed in terms of the basic fluid dynamics of strongly stratified flow past a three dimensional obstacle the band cloud is found to arise primarily from the dynamic interaction of the trade winds with the island the upwind surface flow forms a separation line with an associated stagnation point a low level convergence zone forms along this line resulting in an updraft line if the updrafts are strong enough a band cloud forms formation and characteristics of such a system are mostly controlled by the environmenta

observations of martian gullies and constraints on potential formation mechanisms ii the northern hemisphere abstract the formation process es responsible for creating the observed geologically recent gully features on mars has remained the subject of intense debate since their discovery we present new data and analysis of northern hemisphere gullies from mars global surveyor data which is used to test the various proposed mechanisms of gully formation we located 137 mars orbiter camera moc images in the northern hemisphere that contain clear evidence of gully landforms and analyzed these images in combination with mars orbiter laser altimeter mola and thermal emission spectrometer tes data to provide quantitative measurements of numerous gully characteristics parameters we measured include apparent source depth and distribution vertical and horizontal dimensions slopes orientations and present day characteristics that affect local ground temperatures northern hemisphere gullies are clustered in arcadia planitia tempe terra acidalia planitia and utopia planitia these gullies form in craters 84 knobby terrain 4 valleys 3 other unknown terrains 9 and are found on all slope orientations although the majority of gullies are equator facing most gullies 63 are associated with competent rock strata 26 are not associated with strata and 11 are ambiguous assuming thermal conductivities derived from tes measurements as well as modeled surface temperatures we find that 95 of the gully alcove bases with adequate data coverage lie at depths where subsurface temperatures are greater than 273 k and 5 of the alcove bases lie within the solid water regime the average alcove length is 470 m and the average channel length is 690 m based on a comparison of measured gully features with predictions from the various models of gully formation we find that models involving carbon dioxide melting ground ice in the upper few meters of the soil dry landslide and surface snowmelt are the least likely to describe the formation of the martian gullies although some discrepancies still exist between prediction and observation the shallow and deep aquifer models remain as the most plausible theories interior processes involving subsurface fluid sources are generally favored over exogenic processes such as wind and snowfall for explaining the origin of the martian gullies these findings gleaned from the northern hemisphere data are in general agreement with analyses of gullies in the southern hemisphere heldmann j l mellon m t 2004 icarus 168 285 304

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

on the dynamics of hawaiian cloud bands comparison of model results with observations and island climatology abstract this paper presents a detailed comparison study of three dimensional model results with an aircraft wind field mapping for the island of hawaii model runs were initialized using an aircraft sounding from 1 august 1985 and detailed predictions from the model are compared with observations from that day the strength and location of the upwind convergence zone were well simulated as well as the strong deflection and deceleration of the flow around the island and the geometry and location of the upstream cloud bands the good agreement between the model results and observations supports the results of our previous study in which we show that the flow pattern and associated cloud processes around the island of hawaii can be understood by considering the flow of a stably stratified fluid around a large three dimensional obstacle model runs with different wind directions showed that increasing northerly tradewind flow resulted in the band clouds moving closer to the shore line and the large scale

mid mountain clouds at whistler during the vancouver 2010 winter olympics and paralympics a comprehensive study of mid mountain clouds and their impacts on the vancouver 2010 winter olympics and paralympics is presented mid mountain clouds were frequently present on the whistler alpine venue as identified in an extensive archive of webcam images over a 45 day period from february 5 to march 21 2010 these clouds posed serious forecast challenges and had significant impacts on some olympic and paralympic alpine skiing competitions under fair weather conditions a diurnal upslope anabatic flow can work in concert with a diurnal temperature inversion aloft to produce a localized phenomenon known as harvey s cloud at whistler two detailed case studies in this paper suggest that mid mountain clouds can also develop in the area as a result of a moist valley flow interacting with a downslope flow descending from the mountaintop a southerly inflow through the sea to sky corridor can be channeled by the local topography into a westerly upslope flow toward whistler mountain resulting in orographic clouds on the alpine venue under favorable circumstances these clouds are trapped to the mid mountain zone by the leeward subsidence of an elevated southerly flow the presence of the downslope subsidence was manifested by a distinguished dry layer observed on the top of the mid mountain clouds in both cases it is the subsidence induced adiabatic warming that imposes a strong buoyant suppression to trap the mid mountain cloud on the other hand the subsidence induced dry layer has the potential to trigger evaporative instability to periodically breakup the mid mountain cloud

the age of snc meteorites and the antiquity of the martian surface we report new sm nd lu hf and pb pb mineral and whole rock isotope data for the basaltic shergottite zagami as well as pb pb whole rock isotope data for the basaltic shergottite los angeles the lherzolitic shergottite dar al gani 476 dag 476 and the clinopyroxenite nakhla in agreement with previous findings our new sm nd and lu hf mineral ages on the martian meteorite zagami are young 155 and 185 ma respectively the 207pb 206pb 204pb 206pb compositions of the insoluble fractions of shergottites zagami los angeles and literature data for shergotty and eeta79001 form an excellent alignment indicative of a 4 0 ga crystallization age the range of pb isotope compositions observed in the leachates of these samples attests to negligible contamination of the shergottites by terrestrial pb and argues against mixing relationships the age of 4 048 0 017 ga mswd 1 5 provided by the pb isotope compositions of the zagami whole rock and residues is therefore taken to date the crystallization of this rock which so far was believed to be only not vert similar 180 ma old based on this result we argue that the lithosphere of mars is extremely old and that most mineral ages were reset recently by acidic aqueous solutions percolating through the martian surface this interpretation is consistent with photographic interpretations of erosional features on mars it also relieves the constraint imposed by the presence of anomalies of 142nd and 182w both products of extinct radioactive nuclides that the martian mantle should have preserved primordial isotopic heterogeneities thus allowing for the planet interior to be actively convecting

the influences of inversion height on precipitation and airflow over the island of hawaii abstract both the daily rainfall on the windward side of the island of hawaii and the early morning 0200 hst hawaiian standard time trade wind inversion height at hilo varied substantially during the hawaiian rainband project harp in general the inversion was higher during the passage of a cold front to the north or during the approach of tropical disturbances from the east to the south the daily rainfall on the windward side is highly correlated with the 0200 hst inversion height at hilo with a maximum correlation greater than 0 7 in the hilo area the daily daytime 1100 1900 hst rainfall on the windward slopes nocturnal 1900 0300 rst showers an the windward lowland and coastal precipitation in the predawn and early morning hours 0300 1100 hst are also highly correlated with the inversion height with a maximum correlation greater than 0 7 0 7 and 0 5 respectively for the low high inversion days the median daily rainfall on the windward side is about one half more than twice of t

sar mapping of burfellshraun a terrestrial analog for recent volcanism on mars 1 images of the northern plain on mars have revealed up to 1500 km long lava flows the low density of impact craters on the lava flows implies that these lava flows were formed during the most recent volcanic activity on mars estimates of the ages of the flows are controversial but generally between 10 and 100 myr parts of the lava flows show smooth kilometer sized plates that appear to have rafted on the moving lava flow we have found a terrestrial analogue with similar features the burfellshraun lava flow in northern iceland this is the only known lava flow on earth where kilometer sized rafting plates are observed and constitute the dominating feature using a combination of airborne remote sensing data and field observations we have studied the emplacement and physical properties of the flow on the basis of our observations we have reconstructed the sequence of events that led to the disruption of the lava surface our observations show that a 45 km2 lava lake holding about 0 7 km3 of lava catastrophically collapsed releasing a flood of lava during the collapse the crust of the lava lake was broken into plates up to a kilometer in width and a few meters thick that floated downstream for almost 10 km

emplacement and inflation of pahoehoe sheet flows observations and measurements of active lava flows on kilauea volcano hawaii inflated pahoehoe sheet flows have a distinctive horizontal upper surface which can be several hundred meters across and are bounded by steep monoclinal uplifts the inflated sheet flows we studied ranged from 1 to 5 m in thickness but initially propagated as thin sheets of fluid pahoehoe lava generally 20 30 cm thick individual lobes originated at outbreaks from the inflated front of a prior sheet flow lobe and initially moved rapidly away from their source velocities slowed greatly within hours due to radial spreading and to depletion of lava stored within the source flow as the outward flow velocity decreases cooling promotes rapid crustal growth at first the crust behaves plastically as pahoehoe toes form after the crust attains a thickness of 2 5 cm it behaves more rigidly and develops enough strength to retain incoming lava thus increasing the hydrostatic head at the flow front the increased hydrostatic pressure is distributed evenly through the liquid lava core of the flow resulting in uniform uplift of the entire sheet flow lobe initial uplift rates are rapid flows thicken to 1 m in 1 2 hours but rates decline sharply as crustal thickness increases and as outbreaks occur from the margins of the inflating lobe one flow reached a final thickness of nearly 4 m after 350 hr inflation data define power law curves whereas crustal cooling follows square root of time relationships the combination of data can be used to construct simple models of inflated sheet flows as the flow advances preferred pathways develop in the older portions of the liquid cored flow these pathways can evolve into lavatube systems within a few weeks formation of lava tubes results in highly efficient delivery of lava at velocities of several kilometers per hour to a flow front that may be moving 1 2 orders of magnitude slower if advance of the sheet flow is terminated the tube remains filled with lava that crystallizes in situ rather than draining to form the cave like lava tubes commonly associated with pahoehoe flows inflated sheet flows from kilauea and mauna loa are morphologically similar to some thick icelandic and submarine sheet flows suggesting a similar mechanism of emplacement the planar sheet like geometry of flood basalt flows may also result from inflation of sequentially emplaced flow lobes rather than nearly instantaneous emplacement as literal floods of lava

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

geomorphic analysis of small rayed craters on mars examining primary versus secondary impacts 1 twenty confirmed impacts over a 7 year time period on mars were qualitatively and statistically compared to 287 secondary craters believed to originate from zunil an 500 ka 10 km diameter primary crater our goal was to establish criteria to distinguish secondaries from primaries in the general crater population on the basis of their horizontal planforms recent primary impacts have extensive air blast zones distal ray systems 100 crater radii r and ephemeral ejecta recent primaries formed clusters of craters from atmospheric fragmentation of the meteoroid body secondary craters have ejecta blankets with shorter rays that are consistent with emplacement by low impact velocities near 1 km s the mean extent of the continuous ejecta blankets was less distal for secondaries 5 38 1 57r versus primaries 18 07 7 01r though primary ejecta were less fractal fractal dimension index fdi 1 30 and more circular on average circularity ratio cr 0 55 0 25 versus 0 27 0 13 for secondaries crater rims were remarkably circular primaries cr 0 97 0 02 secondaries at 0 94 0 05 though secondaries have the lowest values cr 0 9 secondary crater rims were elongated toward or orthogonal to their primary of origin uprange source directions for most secondaries determined by ejecta planform and crater rim ellipticity point toward zunil although contamination from other primaries is considered in some areas ejecta blanket discrepancies between recent primaries and zunil secondaries are attributable to differences in impact velocity and retention age after removal of the ejecta blanket crater rims are generally not diagnostic for determining crater origin fragmentation of primaries may play some role in steepening the size frequency distribution of crater diameters in the 5 m d 30 m range

structure and origin by injection of lava under surface crust of tumuli lava rises lava rise pits and lava inflation clefts in hawaii tumuli are positive topographic features that are common on hawaiian pahoehoe lava flow fields particularly on shallow slopes and 75 measured examples are presented here to document the size range tumuli form by up tilting of crustal plates without any crustal shortening and are thus distinguished from pressure ridges which are up buckled by laterally directed pressure the axial or star like systems of deep clefts that characterize tumuli are defined here as lava inflation clefts their tips advanced into red hot lava and they widened as uplift proceeded and while the lava crust was thickening flat surfaced uplifts formed like tumuli by injection of lava under a surface crust were previously called pressure plateaus but lava rise is proposed instead the pits that abound among lava rises previously attributed to collapse or subsidence are generally formed because the lava around them rose and the name lava rise pit is proposed unique examples of tumuli and lava rises from which lava drained out under a surface crust 1 5 to 2 5 m thick are described from kilauea caldera these examples show that in tumuli and lava rises the crust floats on considerable bodies of fluid lava and is able to do so because of its higher vesicle content the fluid lava loses many of its gas bubbles during residence beneath the crust the bulk densities of samples from tumuli show a general downward increase the form of the density profile is consistent with the relationship that for any given crustal thickness the density of fluid lava closely matched the average density of that crust suggesting that the lava was stably density stratified it is inferred that stable stratification was regulated by out flows of the more vesicular lava fractions loss of bubbles through the lava inflation clefts and entry of injected lava at its level of neutral buoyancy below the uppermost meter the downward decrease in vesicularity closely conforms with that expected by compression of a uniform mass of gas per unit mass of lava

orographic effects on precipitating clouds 1 precipitation over and near mountains is not caused by topography but rather occurs when storms of a type that can occur anywhere deep convection fronts tropical cyclones form near or move over complex terrain deep convective systems occurring near mountains are affected by channeling of airflow near mountains capping of moist boundary layers by flow subsiding from higher terrain and triggering to break the cap when low level flow encounters hills near the bases of major mountain ranges mesoscale convective systems are triggered by nocturnal downslope flows and by diurnally triggered disturbances propagating away from mountain ranges the stratiform regions of mesoscale convective systems are enhanced by upslope flow when they move over mountains in frontal cloud systems the poleward flow of warm sector air ahead of the system may rise easily over terrain and a maximum of precipitating cloud occurs over the first rise of terrain and rainfall is maximum on ridges and minimum in valleys if the low level air ahead of the system is stable blocking or damming occurs shear between a blocked layer and unblocked moist air above favors turbulent overturning which can accelerate precipitation fallout in tropical cyclones the tangential winds encountering a mountain range produce a gravity wave response and greatly enhanced upslope flow depending on the height of the mountain the maximum rain may occur on either the windward or leeward side when the capped boundary layer of the eye of a tropical cyclone passes over a mountain the cap may be broken with intense convection resulting

lava flows at arsia mons mars insights from a graben imaged by hirise abstract hirise has imaged a graben wall on the western flank of arsia mons volcano mars this graben is 3 16 km in plan view size and is oriented almost perpendicular to the general volcano slope we have identified 1318 individual sub horizontal layers which we interpret to be lava flows in the 885 m high nearly vertical eastern wall of this graben the average and median outcrop widths of each layer are 149 and 85 m respectively no layers extend 1 72 km across the width of the section arguing against these being either areally extensive ash or paleo glacial deposits which has implications for the reoccurrence interval of glacial events and or the long term magma production rate of the volcano measurements n 118 made at a 100 m spacing across the width of the section reveal that there are on average 17 3 layers at each location this implies an average layer thickness of 51 m locally however as many as 7 layers can be counted within a 70 m high part of the section implying if these layers are indeed lava flows that arsia mons occasionally erupted flows that were only 10 m thick

isotopic and petrographic evidence for young martian basalts radiometric age data for shergottites yield ages of 4 0 ga and 180 575 ma the interpretation of these ages has been and remains a subject of debate here we present new 39 ar 40 ar laser probe data on lherzolitic shergottites allan hills alh 77005 and northwest africa nwa 1950 these two meteorites are genetically related but display very different degrees of shock damage on a plot of 40 ar 36 ar versus 39 ar 36 ar the more strongly shocked alh 77005 45 55 gpa does not yield an array of values indicating an isochron but the data are highly scattered with the shock melts yielding 40 ar 36 ar ratios of 1600 2026 apparent ages calculated from these extractions range from 374 8183 ma with 50 of the data particularly from the shock melts yielding impossibly old ages 4 567 ga on the same plot extractions from igneous minerals in the less shocked nwa 1950 30 44 gpa yield a fitted age of 382 36 ma argon extractions from the shock melts are well distinguished from minerals with the melts exhibiting the highest 40 ar 36 ar ratios 1260 1488 and the oldest apparent ages laser step heating was also performed on maskelynite separates from nwa 1950 yielding ages of 1000 ma at the lowest release temperatures and ages of 360 and 362 ma at higher temperature steps stepped heating data from previous studies have yielded ages of 500 and 700 ma to 1 7 ga for alh 77005 maskelynite separates if the ages obtained from igneous minerals represent undegassed argon from an ancient 4 0 ga rock then the ages are expected to anticorrelate with the degree of shock heating the data do not support this inference our data support young crystallization ages for minerals and martian atmosphere as the origin of excess 40 ar in the shock melts the shock features of shergottites are also reviewed in the context of what is known of the geologic history of the martian surface through remote observation the oldest most heavily cratered surfaces of mars are thought to be 4 0 ga we contend that ancient rocks from mars noachian 3 5 ga are likely to record multiple impact events reflecting megaregolith formation and the cumulative effects of erosion and aqueous alteration occurring during or since that era young rocks late amazonian 0 6 ga should record a relatively simple history of emplacement and ejection from the near surface we show that although shergottites are strongly shocked they are relatively pristine crystalline igneous rocks and not pervasively altered breccias the petrography of shergottites is at odds with an ancient age interpretation a model in which young coherent rocks are preferentially sampled by hypervelocity impact because of material strength is considered highly plausible

the holocene climatic record of the salt caves of mount sedom israel mount sedom is a salt diapir on the southwestern shore of the dead sea which has been rising above the local base level throughout the holocene karst development within the salt body has kept pace with the rise forming subhorizontal cave passages with vertical shafts wood fragments found embedded in flood sediments that were deposited in the cave passages yielded 14c ages ranging from c 7100 to 200 bp a palaeoclimatic sequence was constructed based on parameters that include relative abundance of plant types or floral communities the elevations of the corresponding cave passages and the ratio of their width to present passage width the results were correlated to the holocene sedimentary sequence of the dead sea basin and other features associated with shifting lake levels moister climatic stages are indicated by relatively abundant wood remains by wide cave passages and by elevated outlets indicating high dead sea level arid periods are marked by a scarcity of wood remains by narrow cave pa

investigating the volcanic versus aqueous origin of the surficial deposits in eastern elysium planitia mars abstract the elysium volcanic province consists of numerous overlapping flow units and may include the youngest lava flows on mars however it is possible that these volcanic units have been modified or overprinted by aqueous processes understanding the timing of the igneous and aqueous events in this region is therefore essential for constraining the geological and environmental history of mars during the amazonian period we investigate the geologic evolution of eastern elysium planitia to determine the relationship between major units with the support of a geological map and chronological constraints from crater size frequency distributions we also evaluate the hypothesized origin of these units via volcanic fluvial and or fluvioglacial processes using a detailed facies mapping approach the study area includes the eastern cerberus fossae rahway valles and marte vallis the surficial deposits in rahway valles were formerly interpreted to be modified by fluvial and fluvioglacial processes however our facies map reveals that the surface of eastern elysium planitia includes nineteen morphologically distinct regions i e facies which are interpreted to be the products of flood lava volcanism including a p hoehoe and transitional lava flow types in contrast to previous studies which determined that rahway valles and marte vallis consist of two distinct geologic units with middle to late amazonian ages the results of this work show that the region was resurfaced by at least two volcanic flows with much younger ages of 20 0 ma and 8 8 ma furthermore by coupling results of our geologic and facies mapping with chronological constraints as well as subsurface information provided by shallow radar reflectors we show that there is an erosional unconformity located between the two youngest lava flow units in marte vallis we interpret that this unconformity was generated by a catastrophic aqueous flooding event that occurred only 8 8 20 0 ma ago this implies alternating episodes of volcanism and aqueous flooding that have continued into the geologically recent past on mars and may again occur within elysium planitia

the mode of emplacement of neogene flood basalts in eastern iceland facies architecture and structure of simple aphyric basalt groups simple flows tabular in the neogene flood basalt sections of iceland are described and their mode of emplacement assessed the flows belong to three aphyric basalt groups the kumlafell group the holmatindur group and the hjalmadalur group the groups can be traced over 50 km and originate in the brei dalur thingmuli volcanic zone the groups have flow fields that display mixed volcanic facies architecture and can be classified after dominating type morphology the kumlafell and the holmatindur groups have predominantly simple flows of p hoehoe and rubbly p hoehoe morphologies with minor compound or lobate p hoehoe flows the hjalmadalur group has simple flows of rubbly p hoehoe but also includes minor compound or lobate flows of rubble and a simple flows are most common in the distal and medial areas from the vents while more lobate flows in proximal areas the simple flows are formed by extensive sheet lobes that are several kilometers long with plane parallel contacts some reaching thicknesses of 40 m aspect ratios 0 01 they have overlapping contacts and are free of tubes and inflation structures their internal structure consists generally of a simple upper vesicular crust a dense core and a thin basal vesicular zone the brecciated flow top is formed by clinker and crustal rubble the clinker often welded or agglutinated the simple flows erupted from seemingly short lived fissures and have the characteristics of cooling limited flows we estimate the effusion rates to be 105 m3 s for the simple flows of the kumlafell and holmatindur groups and 104 m3 s for the hjalmadalur group the longest flows advanced 15 20 km from the fissures with lava streams of fast propagating flows inducing tearing and brecciation of the chilled crust compound or lobate areas appear to reflect areas of low effusion rates or the interaction of the lava with topographic barriers or wetlands resulting in chaotic flowage slowing lobes with brecciated flow tops developed into a flows the groups interdigitated with lava groups from the rey arfjor ur volcanic zone to the east and the exhumed brei dalur thingmuli volcanic zone which appear to have formed as a flank lineament parallel the main rift zone flood basalt volcanism in flank areas may support a mantle anomaly more pronounced and or perhaps more widespread in the neogene of iceland than today eruptions of simple flows have not been observed in modern times and are significant for models of crustal accretion in iceland and other large igneous provinces

the search for active marsquakes using subpixel coregistration and correlation best practice and first results the state of seismic activity on mars is currently unknown on earth coseismic displacement has been observed using visible wavelength images and subpixel coregistration and correlation techniques we apply this method to mars with the cosi corr co registration of optically sensed images and correlation software package using high resolution imaging science experiment hirise images focusing on part of the cerberus fossae fault system we derive best practices for applying this method to the study of coseismic displacements on mars using a time series of eight overlapping hirise images we achieve pixel coregistration with a mean accuracy of about 1 50 of a pixel we see no clear evidence for coseismic displacement in this region during a time period of over 8 years one possible displacement signal 1 2 m of west east displacement over a length scale of about 50 m that has similarities to terrestrial coseismic deformation was dismissed as the result of incomplete correction of steep topography during the coregistration stage ancillary observations of recurring slope lineae rsl activity in the surrounding fault system offer no supporting evidence for the occurrence of coseismic displacement but do seem to suggest rsl activity that does not fit into previous seasonal timescales although it is unlikely that we have observed coseismic displacement in our study area during this time period the best practice method and the accuracy of our results offer encouragement for future studies hirise context camera and color and stereo surface imaging system images can be used to complement and independently verify in situ seismic observations by the insight interior exploration using seismic investigations geodesy and heat transport lander or source location changes from the exomars trace gas orbiter spacecraft

the geologic evolution of mars episodicity of resurfacing events and ages from cratering analysis of image data and correlation with radiometric ages of martian meteorites we have investigated 12 prominent regions on mars in detail with respect to their geologic evolution through time on the basis of detailed geologic mapping exercises and determining age relationships through crater counting techniques using imagery new data in combination with previously obtained data have been analyzed by way of a refined method of cratering age extraction that also gives fine details of periods of resurfacing we have found that there has been volcanic and fluvial glacial geologic activity on the martian surface at all times from 4 ga ago until today this activity shows episodic pulses in intensity of both volcanic and fluvial glacial processes at 3 8 3 3 ga 2 0 1 8 ga 1 6 to 1 2 ga 800 to 300 m y 200 m y and 100 m y and a possible weaker phase around 2 5 2 2 ga ago in between these episodes there was relative quiescence of volcanic and or fluvial glacial activity the episodes we find on the martian surface in the crater frequency analyses of hrsc moc and themis data coincide with some age groups of the martian meteorites 1 3 ga 600 300 m y 170 m y it appears that the surface activity expressions and their episodicity are related to the interior evolution of the planet when convection in the asymptotic stationary state changes from the so called stagnant lid regime to an episodic behavior similarities in episodic behavior are found for the other terrestrial planets venus the earth s moon and the earth itself suggesting a common general relationship in the evolutionary tracks

widespread inflation and drainage of a pāhoehoe flow field the nesjahraun þingvellir iceland this study describes the emplacement of the nesjahraun a basaltic lava flow that entered the lake ingvallavatn sw iceland high resolution remotely sensed data were combined with fieldwork to map the flow field onshore the nesjahraun exhibits a variety of textures related to the widespread inflation and collapse of a p hoehoe flow field its emplacement is interpreted as follows initially the eruption produced sheet p hoehoe in the central part of the flow field the lava has a platy ridged surface which is similar to some other lava flows in iceland and on mars here the texture is interpreted to have formed by unsteady inflation of the brittle crust of stationary sheet p hoehoe causing it to break into separate plates the ridges of broken p hoehoe slabs formed as the plates of crust moved vertically past each other in a process similar to the formation of shatter rings upstream fresh lava overflowed repeatedly from channels and tubes covering the surface with shelly p hoehoe formation of a 250 m wide open channel through the flow field allowed the inflated central part of the flow to drain rapidly this phase produced a lava which eroded the channel walls carrying broken p hoehoe slabs lava balls and detaching large 200 m long rafts of compound shelly p hoehoe lava much of this channelized lava flowed into the lake leaving a network of drained channels and tubes in the upstream part of the flow as in other locations the platy ridged texture is associated with a low underlying slope and high eruption rate here its formation was possibly enhanced by lateral confinement hindered entry into the lake and an elevated vent location we suggest that formation of this type of platy ridged lava where the plates are smooth and the ridges are slabs of broken p hoehoe can occur without significant horizontal transport as the surface crust is broken into plates in situ this reconstruction of the emplacement of the nesjahraun also demonstrates that high resolution aerial survey data are extremely useful in the mapping and measurement of lithofacies distributions in large flow fields but that fieldwork is still necessary to obtain the detailed textural information necessary to interpret them

rootless cones on mars a consequence of lava ground ice interaction fields of small cratered cones on mars are interpreted to have formed by rootless eruptions due to explosive interaction of lava with ground ice contained within the regolith beneath the flow melting and vaporization of the ice and subsequent explosive expansion of the vapour act to excavate the lava and construct a rootless cone around the explosion site similar features are found in iceland where flowing lava encountered water saturated substrates the martian cones have basal diameters of c 30 1000 m and are located predominantly in the northern volcanic plains high resolution mars orbiter camera images offer significant improvements over viking data for interpretation of cone origins a new model of the dynamics of cone formation indicates that very modest amounts of water ice are required to initiate and sustain the explosive interactions that produced the observed features this is consistent with the likely low availability of water ice in the martian regolith the scarcity of impact craters on many of the host lava flows indicates very young ages suggesting that ground ice was present as recently as less than 10 l00 ma and may persist today rootless cones therefore act as a spatial and temporal probe of the distribution of ground ice on mars which is of key significance in understanding the evolution of the martian climate the location of water in liquid or solid form is of great importance to future robotic and human exploration strategies and to the search for extraterrestrial life

martian cratering vi crater count isochrons and evidence for recent volcanism from mars global surveyor this paper develops a methodology to establish absolute martian ages by deriving isochrons on a plot of martian impact crater density vs crater diameter calibrated by lunar crater age data the isochrons illustrated here are based on a mars moon cratering ratio of 1 6 at constant size but there is a factor of 2 to 4 uncertainty in this ratio and the consequent model ages martian crater diameter distributions are determined in several areas down to diameter d 16 45 m the shapes of the curves in young areas are found to be close to that of the predicted isochrons and close to the standard production function found by neukum the youngest areas studied here display the lunar like production function down to d 30 m where saturation equilibrium sets in model crater retention ages of several volcanic units are found to be a few hundred million years or less with estimated uncertainties ranging from a factor of 2 lower to a factor of 4 higher the results are consistent with martian meteorite ages volcanism on mars has probably persisted into the last 10 to 15 of the planet s history and is likely ongoing because surfaces as young as a few hundred million years have reached crater saturation equilibrium at d 60 to 100 m mars is likely to have widespread impact produced regoliths at least a few meters deep and this may contribute to the widespread mobile dust and boulder fields of mars

the morphology and formation of flow lobe tumuli on icelandic shield volcanoes three types of tumuli are recognized on monogenetic shield volcanoes in iceland namely 1 lava coated tumuli 2 upper slope tumuli and 3 flow lobe tumuli flow lobe tumuli grade into lava rises which are larger inflation structures but both structures have a similar mode of emplacement the areal distribution of flow lobe tumuli in the flow field differs from that of lava coated tumuli and upper slope tumuli flow lobe tumuli are frequent in the medial and distal parts of pahoehoe flow fields whereas the other two tumulus types are more frequent in the proximal parts of the flow fields the flow lobe tumuli also differ from the two other tumulus types as regards their morphology they are significantly larger have shallower flanks and do not have extensive outflows from the cracks the vesicle distribution within the flow lobe tumuli is similar to that of p type flow lobes a fairly dense zone is situated between the upper and lower vesicular zones each flow lobe tumulus is an individual lobe that inflates and forms tension cracks in the lava crust major lava tubes are mostly absent from the areas where flow lobe tumuli form and therefore the emplacement of flow lobe tumuli must be related to secondary short lived pathways of lava the flow lobe tumuli inside the flow fields of icelandic shield volcanoes are morphologically identical to those flow lobe tumuli that are found in the margins of flow fields of other icelandic volcanoes these observations allow us to model the flow lobe tumuli as morphological variants of p type flow lobes forming along terminating secondary lava paths flow lobe tumuli form at low lava supply rates of the order of 10 2 10 5 m3 s and are generated by inflation of the lava crust as a result of magmatic overpressure in the associated lava core we model the tumulus as a circular elastic plate that becomes uplifted inflated and fractured by a uniform magmatic overpressure at its bottom we conclude that 1 the effective thickness of the lava crust that is subject to bending is 0 2 0 4 m and remains essentially constant during the formation of the tumulus and 2 for flow lobe tumuli that are supplied with magma from tubes that originate in overflow from the lava lake of a shield volcano the elevation difference between the tumuli and the surface of the source lava lake is commonly around 100 m this elevation difference can give rise to a static magmatic overpressure of 2 5 mpa in the tumulus whereas the overpressure needed to form a typical flow lobe tumulus is only 0 2 1 mpa

observations of martian gullies and constraints on potential formation mechanisms abstract the discovery of presumably geologically recent gully features on mars malin and edgett 2000 science 288 2330 2335 has spawned a wide variety of proposed theories of their origin including hypotheses of the type of erosive material to test the validity of gully formation mechanisms data from the mars global surveyor spacecraft has been analyzed to uncover trends in the dimensional and physical properties of the gullies and their surrounding terrain we located 106 mars orbiter camera moc images that contain clear evidence of gully landforms distributed in the southern mid and high latitudes and analyzed these images in combination with mars orbiter laser altimeter mola and thermal emission spectrometer tes data to provide quantitative measurements of numerous gully characteristics parameters we measured include apparent source depth and distribution vertical and horizontal dimensions slopes orientations and present day characteristics that affect local ground temperatures we find that the number of gully systems normalized to the number of moc images steadily declines as one moves poleward of 30 s reaches a minimum value between 60 63 s and then again rises poleward of 63 s all gully alcove heads occur within the upper one third of the slope encompassing the gully and the alcove bases occur within the upper two thirds of the slope also the gully alcove heads occur typically within the first 200 meters of the overlying ridge with the exception of gullies equatorward of 40 s where some alcove heads reach a maximum depth of 1000 meters while gullies exhibit complex slope orientation trends gullies are found on all slope orientations at all the latitudes studied assuming thermal conductivities derived from tes measurements as well as modeled surface temperatures we find that 79 of the gully alcove bases lie at depths where subsurface temperatures are greater than 273 k and 21 of the alcove bases lie within the solid water regime most of the gully alcoves lie outside the temperature pressure phase stability of liquid co2 based on a comparison of measured gully features with predictions from the various models of gully formation we find that models involving carbon dioxide melting ground ice in the upper few meters of the soil dry landslide and surface snowmelt are the least likely to describe the formation of the martian gullies although some discrepancies still exist between prediction and observation the shallow and deep aquifer models remain as the most plausible theories interior processes involving subsurface fluid sources are generally favored over exogenic processes such as wind and snowfall for explaining the origin of the martian gullies

resurfacing of the martian highlands in the amenthes and tyrrhena region the southern cratered highlands of mars contain a large population of flat floored rimless craters which have previously been interpreted to have formed by aeolian mantling or flood volcanism neither of these geologic processes accurately explains the observed morphology or the crater statistics geologic mapping in the amenthes and tyrrhena region indicates that craters with this morphology occur on undulating intercrater materials near the dichotomy boundary and on more rugged materials farther into the highlands containing numerous ancient valley networks cumulative size frequency distribution curves indicate ages of n 5 790 early to middle noachian and n 5 540 middle noachian for the cratered plateau and cratered highland materials respectively opposite the observed stratigraphic relations for crater diameters 16 km the population of impact craters is consistent with stratigraphy but the population of smaller craters in the region indicates the importance of resultacing superposed fresh craters indicate a resultacing event that ceased at n 5 200 250 late noachian to early hesperian crater counts divided into 5 o latitudinal bins show an increase in the number of craters between the 8 and 50 km diameter range with increasing northerly latitudes suggesting that the resurfacing was not a single event statistical modelling of an erosive event capable of removing the continuous ejecta deposits from the craters eroding them to reduce the apparent diameter and simultaneously burying smaller eroded craters explains both the morphology of the flat floored rimless craters and their population distribution matching the slope of the modelled curves with that of the cratered highland materials suggests that up to 1400 m of erosion may have taken place in the highlands some of this eroded material probably remained locally burying the smaller craters later stripping of this material indicated by exposed layering and inverted topography has exhumed the smaller craters in the cratered plateau material resulting in the apparent age discrepancy determined from crater counts up to 1 0 km of material may have been removed by this later erosive event to explain the low density of ancient valley networks in the cratered plateau materials

structural evolution of the northern cerberus fossae graben system elysium planitia mars to determine whether the structural evolution of the northern cerberus fossae ncf was dominated by cryospheric melting and collapse or fault related subsidence we used moc themis and hirise images and mola data to document spatial variations in vertical offset along strike the fossae are a series of fractures on the martian surface that cross cut noachian hesperian and in places very young late amazonian terrain serial cross sections across the fracture related topography from mola data show that vertical offsets are not greater where fractures traverse older terrain showing that offsets have accumulated since the formation of the amazonian terrain vertical offsets are greater in the central portions of the fracture system with the profile resembling that for a single fault system topographic features that pre date deformation are preserved on the graben floors suggesting little sediment infill so the mola elevation measurements constrain total vertical offsets since the fractures formed deficits in vertical offset occur where fractures have not linked and remain en echelon across relay zones or have linked leaving palaeo graben tips this indicates that the traces of the fractures propagate along strike at the surface and intersect over time periods that are likely to be in the range of 105 106 years rather than in a single collapse event deficits are also in places associated with collapse pits suggesting such collapse is the early stage of graben subsidence at propagating lateral graben tips we use these observations to argue that the primary mechanism causing subsidence is not cryospheric melting and collapse but faulting