viscous flow features on the surface of mars observations from high resolution mars orbiter camera moc images 10 5 10 7 years of the material our shear stress estimates of 10 1 5 10 2 5 mpa yield strain rates on the order of 10 11 10 16 s 1 which are within the superplastic flow regime of ice mean annual surface temperatures age constraints and strain estimates show that it is possible for a meters thick ice dust mixture to undergo viscous deformation under past or present surface conditions for ice grain sizes 10 mm the meters thick layer in which the viscous flow features formed is morphologically similar to a degraded meters thick ice dust surface deposit dissected mantle terrain locations of the viscous flow features dissected mantle terrain and recent gullies are concentrated in the midlatitude regions and all three show identical distributions as a function of latitude with the maximum frequency of occurrence at 40 n and s the strong association between these small scale flow features and the dissected mantle terrain large scale viscous flow features and recent gullies imply that deposition deformation and removal of ice rich materials has played an important role in the modification of the surface in the midlatitudes of mars during the amazonian and possibly longer index terms 5470 planetology solid surface planets surface materials and properties 5416 planetology solid surface planets glaciation 1863 hydrology snow and ice 1827 1823 hydrology frozen ground 8168 tectonophysics stresses general keywords viscous flow viscous creep dissected mantle terrain ice rich deposits mars climate recent gullies

a closer look at water related geologic activity on mars water has supposedly marked the surface of mars and produced characteristic landforms to understand the history of water on mars we take a close look at key locations with the high resolution imaging science experiment on board the mars reconnaissance orbiter reaching fine spatial scales of 25 to 32 centimeters per pixel boulders ranging up to approximately 2 meters in diameter are ubiquitous in the middle to high latitudes which include deposits previously interpreted as finegrained ocean sediments or dusty snow bright gully deposits identify six locations with very recent activity but these lie on steep 20 degrees to 35 degrees slopes where dry mass wasting could occur thus we cannot confirm the reality of ancient oceans or water in active gullies but do see evidence of fluvial modification of geologically recent mid latitude gullies and equatorial impact craters

postorogenic denudation along the late paleozoic ouachita trend south central united states of america magnitude and timing constraints from apatite fission track data the magnitude and timing of synorogenic and postorogenic denudation along fold and thrust belts and their associated foreland basins of interest because of both tectonic and economic implications is generally poorly constrained along the late paleozoic ouachita trend a thin veneer of cretaceous strata is preserved above a low relief erosional surface that beveled the ouachita orogen and adjacent foreland areas this regional erosion surface provides a valuable constraint for interpreting new and previously published apatite fission track aft data obtained from exposed structural highs along the ouachita trend marathon llano arbuckle and benton uplifts aft data from sampled localities within the deformation belt marathon and benton uplifts exhibit younger ages and generally longer mean lengths than data from localities on the foreland side of the deformation front llano and arbuckle uplifts this observation suggests that erosion of the orogen rather than its extensional collapse was the primary mechanism responsible for flexural isostatic unloading of the foreland crust in addition all samples show evidence for mild reheating following their pre cretaceous cooling history specifically the lack of a significant population of 14 5 m tracks in all samples appears to require residence at temperatures of 55 5 c after development of the sub cretaceous erosional surface this implies that 1000 m of cretaceous paleogene strata were deposited across the entire ouachita frontal trend and subsequently removed during later tertiary time this tertiary denudation is interpreted to reflect the interplay between regional denudation and isostatic compensation in response to slow 10 m m y epeirogenic uplift of the southern midcontinent and a long term drop 200 m in eustatic sealevel during this time

a tale of 10 plutonsurevisited age of granitic rocks in the white mountains california and nevada 40 ar 39 ar incremental heating analysis and conventional k ar age determinations on plutonic rocks of the white mountains define two stages of magmatic emplacement late cretaceous between ca 90 ma and 75 ma and middle late jurassic between ca 180 and 140 ma the jurassic stage can be divided into two substages 180 165 ma and 150 140 ma thermal effects of the younger plutons on the older granitoids partially to completely reset ages making it difficult to determine the age of emplacement and cooling of several of the plutons even by 40 ar 39 ar incremental heating analyses new data together with published ages and regional geochronological synthesis of the sierra nevada batholith indicate that regions within the batholith have coherent periods or episodes of magmatic activity in the white mountains and sierra nevada directly to the west there was little or no activity in early jurassic and early cretaceous time magmatism took place during relatively short intervals of 15 m y or less in the middle and late jurassic and late cretaceous periods the new k ar and 40 ar 39 ar analyses of granitoids from the white mountains help but do not completely clarify the complex history of emplacement cooling and reheating of the batholith

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

heat flow and thermal history of the anadarko basin and the western oklahoma platform abstract the average geothermal gradient in the anadarko basin and the oklahoma platform estimated from 856 corrected bottom hole temperatures bhts is 21 c km analysis of previously published thermal maturation data indicates that the anadarko basin has undergone from 1 to 3 km of erosion starting about 40 to 50 ma the average thermal gradient at the time of maximum burial was in the range of 22 to 25 c km there is no evidence that the thermal state of the anadarko basin has changed significantly since the late paleozoic 250 ma to estimate heat flow in the anadarko basin and the oklahoma platform we made 652 thermal conductivity measurements on drill cuttings from 9 oil and gas wells all measurements were corrected for the effects of anisotropy temperature and porosity matrix conductivities perpendicular to bedding at 22 c range from 1 7 w m 1 k 1 for permian age sandstone and shale to 2 6 w m 1 k 1 for devonian silurian age limestone and shale in situ thermal conductivities vary from 1 3 w m 1 k 1 to 1 9 w m 1 k 1 estimated heat flow 20 ranges from 30 mw m2 to 42 mw m2 with a mean of 36 mw m2 we found no evidence for heat flow to increase significantly from the anadarko basin in the south to the oklahoma platform to the north these results contradict a previous study which found heat flow increases from south to north with heat flow in the oklahoma platform as much as 50 greater than heat flow in the anadarko basin at the present time we do not know if these differences are related to spatial variations or reflect methodological errors if our results are averaged with those reported in previous work mean heat flows in the anadarko basin and oklahoma platform are 39 mw m2 and 51 mw m2 respectively

modification of the dichotomy boundary on mars by amazonian mid latitude regional glaciation 1 restoration of the dichotomy boundary to its original position to assess its origin requires a thorough knowledge of processes responsible for its degradation and retreat the unique fretted terrain located along the deuteronilus protonilus mensae northern mid latitude portion of the boundary has been long held to provide clues to dichotomy degradation processes we use new spacecraft data to show that fretted valleys display a multitude of characteristics typical of integrated valley glacial systems on earth multiple theater headed alcove like accumulation areas sharp arete like ridges typical of glacial erosion converging patterns of downslope valley flow valley lineation patterns typical of folding and shear wrap around features indicative of flow around obstacles and broad piedmont like lobes as the valley fill extends out into the northern lowlands the single integrated system containing these features covers about 30 000 km2 and is one of dozens of fretted valleys along the dichotomy boundary in this region these relationships suggest that the boundary area was subjected to very large scale regional glaciation during the amazonian recognition and documentation of this important late stage process provides information critical to reconstructing the original dichotomy boundary

the rate of pressure dissipation from abnormally pressured compartments an improved analytic solution is presented that describes the dissipation of abnormal pressures via darcy flow out of a compartment formed of high permeability rock capped top and bottom by lower permeability rock the solution tends to the solutions presented by previous workers in the limit of 1 a thick compartment and thin barrier and 2 a thick barrier and a thin compartment the importance of including fluid compressibility when analyzing hydrocarbon reservoirs is demonstrated previous workers in this field have only included the effect of bulk rock compressibility and have neglected fluid compressibility the solution is applied to pressure compartments on the scale of a typical hydrocarbon reservoir and overpressured regions on the basin scale it is shown that the pressure gradient in a typical hydrocarbon reservoir compartment will return to the hydrostatic gradient over timescales of the order of hours or days but that abnormal pressures are likely to dissipate over periods of tens of thousands to hundreds of thousands of years thus any reservoir compartment with a different pressure from its neighbors at discovery can be considered as an independent unit during production however abnormal pressures on the basin scale may take tens or hundreds of millions of years to dissipate there is thus no need to invoke zero permeability seals or capillary pressure seals in order to explain the existence of abnormal pressures over geological time

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

antarctic dry valleys microclimate zonation variable geomorphic processes and implications for assessing climate change on mars the antarctic dry valleys adv are generally classified as a hyper arid cold polar desert the region has long been considered an important terrestrial analog for mars because of its generally cold and dry climate and because it contains a suite of landforms at macro meso and microscales that closely resemble those occurring on the martian surface the extreme hyperaridity of both mars and the adv has focused attention on the importance of salts and brines on soil development phase transitions from liquid water to water ice and ultimately on process geomorphology and landscape evolution at a range of scales on both planets the adv can be subdivided into three microclimate zones a coastal thaw zone an inland mixed zone and a stable upland zone zones are defined on the basis of summertime measurements of atmospheric temperature soil moisture and relative humidity subtle variations in these climate parameters result in considerable differences in the distribution and morphology of 1 macroscale features e g slopes and gullies 2 mesoscale features e g polygons including ice wedge sand wedge and sublimation type polygons as well as viscous flow features including solifluction lobes gelifluction lobes and debris covered glaciers and 3 microscale features e g rock weathering processes features including salt weathering wind erosion and surface pitting equilibrium landforms are those features that formed in balance with environmental conditions within fixed microclimate zones some equilibrium landforms such as sublimation polygons indicate the presence of extensive near surface ice identification of similar landforms on mars may also provide a basis for detecting the location of shallow ice landforms that today appear in disequilibrium with local microclimate conditions in the adv signify past and or ongoing shifts in climate zonation understanding these shifts is assisting in the documentation of the climate record for the adv a similar type of landform analysis can be applied to the surface of mars where analogous microclimates and equilibrium landforms occur 1 in a variety of local environments 2 in different latitudinal bands and 3 in units of different ages documenting the nature and evolution of the adv microclimate zones and their associated geomorphic processes is helping to provide a quantitative framework for assessing the evolution of climate on mars

formation of martian gullies by the action of liquid water flowing under current martian environmental conditions 1 geomorphic evidence suggests that recent gullies on mars were formed by fluvial activity the martian gully features are significant because their existence implies the presence of liquid water near the surface on mars in geologically recent times irrespective of the ultimate source of the fluid carving the gullies we seek to understand the behavior of this fluid after it reaches the martian surface we find that contrary to popular belief the fluvially carved martian gullies are consistent with formation conditions such as now occur on mars outside of the temperature pressure stability regime of liquid water our model of the action of flowing pure liquid water produces the observed gully length distribution only at surface pressures and temperatures below the triple point where liquid water simultaneously boils and freezes and thus suggests that gullies were formed under conditions similar to present day mars our results suggest a typical flow rate of 30 m 3 s to carve the gully channels at least 0 15 km 3 has flowed across the surface of mars to carvethegullysystemsobservedtoday andthiswouldrequireanaquifer recharge rate of 10 13 10 12 m yr the absence of gullies on mars that are long enough to have been created above the triple point pressure argues that the atmospheric pressure has not been significantly larger than it is now since the origin of the gullies this result may imply that mars does not possess a significant reservoir of condensed co2

identification of sublimation type thermal contraction crack polygons at the proposed nasa phoenix landing site implications for substrate properties and climate driven morphological evolution 1 we identify a surface within the nasa phoenix landing site area d characterized by boulder topped polygonally patterned mounds comparable in radius and cross sectional morphology to terrestrial sublimation polygons found in antarctica both martian and antarctic polygons display topographic asymmetry with shallow equator facing slopes and steep pole facing slopes interpreted to indicate insolation dependent differential sublimation of buried ice on the basis of morphological similarities we classify the phoenix box 1 polygons as sublimation polygons terrestrial sublimation polygons form where ice volumes exceeding available pore space occur in the shallow subsurface and where near surface conditions are too cold and dry to permit the development of saturated active layers conditions comparable to those recently modeled for mars in the phoenix landing site area d box 1 the identification of sublimation polygons on mars would provide direct evidence for shallow ground ice exceeding pore ice volumes and shed light on the emplacement mechanism of this ice

identification of gully debris flow deposits in protonilus mensae mars characterization of a water bearing energetic gully forming process gullies are a class of geologically recent landform on mars that show evidence of downslope transport of sedimentary material from recessed alcoves through incised channels to distributary fans or aprons the mechanisms invoked to account for the formation of gullies on mars range from completely dry granular flows or landslides to debris flows that incorporate some component of liquid water to fluvial erosion and alluvial fan like deposition each of these processes requires different amounts of liquid water and produces different characteristic morphologies we report on the identification of unusual lobate structures present in proximity to gullies in protonilus mensae the lobes are up to 3 m thick and terminate in rounded snouts these lobate structures are present mostly downslope of gullies and can be traced upslope through channels to gully fan termini and in places onto gully fan surfaces crater dating indicates that the deposits formed recently potentially within the past 500 ka we use hrsc digital elevation models to constrain mechanical properties of the lobate deposits and to compare their formation environment to that of typical martian gullies the protonilus mensae lobate deposits are interpreted to indicate local dominance of wet debris flows in the formation of the observed gullies and lobes these observations are consistent with 1 top down melting of the ice component of the latitude dependent mantle terrain in which the gullies form and 2 initiation of debris flows by mobilization of the dusty lithic component of the mantle the suite of morphological observations diagnostic of wet debris flow processes suggests the identification of an unusual environment in which the wet debris flow formational end member is locally the dominant gully forming process elsewhere on mars gully morphology may be more consistent with a range of other water related sediment transport mechanisms including fluvial erosion hyperconcentrated flow and low strength mudflows that deposit as fans rather than lobes these results suggest that 1 gully forming processes involve liquid water 2 that the water source is associated with the martian latitude dependent mantle and 3 that a range of water related sediment transport processes is involved in gully formation

apatite fission track analysis of oligocene strata in south texas u s a testing annealing models analysis of apatite fission track data from forty seven surface and subsurface samples of fine grained sandstone to pebbly conglomerate from the oligocene catahoula gueydan frio and vicksburg formations documents the response of fission track ages and track length distributions to simple post depositional thermal histories characterized by monotonic heating data from outcrop samples document that the apatite component was derived from source areas characterized by rapid cooling through the temperature range from 120 to 50 c during the early tertiary the apatite population is characterized by a log normal chlorine distribution mean 0 3 wt 0 3 wt consisting predominantly of low cl apatites 80 is 0 5 wt mean track lengths from core samples decrease systematically with increasing depth and temperature the decrease in apatite fission track ages with increasing depth and temperature is less systematic due to the scatter in inherited ages at the time of deposition no tracks were observed in apatite from samples at temperatures above 130 c mean track lengths for the south texas data agree well with those for a similar data set from the otway basin southeastern australia for present day temperatures of 70 c at higher temperatures mean lengths are 1 to 9 m longer than those observed from the otway basin this discrepancy is interpreted to reflect up to 40 ma longer residence times at maximum burial temperatures for the otway basin samples standard deviations about mean lengths are also lower than observed in the otway basin study consistent with the wider variation of cl contents mean 0 8 wt 0 7 wt that characterize apatite from the otway basin recently published apatite fission track annealing models predict significantly different mean track length vs present day temperature profiles for thermal histories believed to be representative of those experienced by sampled south texas strata because of the large uncertainties attributed to present day temperatures 10 c the predicted mean length vs temperature trends for these models essentially fall within or on the uncertainty envelope for the observed trend residuals of predicted minus observed mean lengths suggest that the previously published carlson composite parameter model using an initial mean length of 15 8 m instead of 16 5 m or the crowley et al model for track length reduction down to 11 m provide the best estimates of mean track length reduction over geologic time scales for near end member f apatite populations

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

the summit hydrothermal system of stromboli new insights from self potential temperature co2 and fumarolic fluid measurements with structural and monitoring implications accurate and precisely located self potential sp temperature t and co2 measurements were carried out in the summit area of stromboli along 72 straight profiles sp data were acquired every metre and t data every 2 5 m co2 concentrations were acquired with the same density as t but only along seven profiles the high density of data and the diversity of the measured parameters allows us to study structures and phenomena at a scale rarely investigated the shallow summit hydrothermal activity pizzo fossa area is indicated by large positive sp t and co2 anomalies these anomalies are focused on crater faults suggesting that the fracture zones are more permeable than surrounding rocks at stromboli the analysis of the distribution of these linear anomalies coupled with the examination of the geologic photographic and topographic data has led us to propose a new structural interpretation of the summit of stromboli this newly defined structural framework comprises 1 a large pizzo circular crater about 350 m in diameter 2 a complex of two concealed craters nested within the pizzo crater the large and the small fossa craters thought to have formed during the eruption of the pizzo pyroclastites unit the small fossa crater is filled with highly impermeable material that totally impedes the upward flow of hydrothermal fluids and 3 the present complex of active craters on the floor of the fossa short wavelength sp lows are organized in drainage like networks diverging from the main thermal anomalies and converging toward the topographic low in the fossa area inside the small fossa crater they are interpreted as the subsurface downhill flow of water condensed above the thermal anomalies we suspect that water accumulates below the small fossa crater as a perched water body representing a high threat of strong phreatic and phreatomagmatic paroxysms t and co2 anomalies are highly correlated the two types of anomalies have very similar shapes but the sensitivity of co2 measurements seems higher for lowest hydrothermal flux above t anomalies a pronounced high frequency sp signal is observed isotopic analyses of the fluids show similar compositions between the gases rising through the faults of the pizzo and large fossa craters this suggests a common origin for gases emerging along different structural paths within the summit of stromboli a site was found along the large fossa crater fault where high gas flux and low air contamination made gas monitoring possible near the active vents using the alkaline bottle sampling technique

overpressures in the anadarko basin southwestern oklahoma static or dynamic fluid pressures were estimated from mud weights and wellhead shut in pressures along a north south linear trend through the anadarko basin in southwest oklahoma fluid pressures above hydrostatic start at a depth of about 2 5 km on a normalized scale where hydrostatic pressure equals 0 and lithostatic pressure equals 1 estimates of fluid pressures were found to range from 0 4 to 0 8 over a depth range of 4 7 km using scale analyses and a simple numerical model we evaluated two end member hypotheses compaction disequilibrium and hydrocarbon generation as possible causes of overpressuring in the anadarko basin if compaction disequilibrium is the primary cause of present day overpressures in the anadarko basin the anadarko basin is required to have an average permeability of 10 23 m2 10 8 md or lower if geopressures in the anadarko basin result from hydrocarbon generation average basin permeabilities can be as high as 10 21 m2 10 6 md scaling these average permeabilities down to thicknesses of 100 m or less implies permeabilities lower than 10 25 m2 10 10 md are required in the most optimistic scenario the lowest permeabilities ever measured on sedimentary rocks are in the neighborhood of 10 22 10 23 m2 10 7 10 8 md thus it is not possible to reconcile the existence of overpressures in the anadarko basin with classic hydrodynamic theories that maintain that aquicludes do not exist either some unknown process is generating excess fluid pressures or the anadarko basin contains pressure seals geopressure models that invoke compaction disequilibrium and are commonly applied to cenozoic basins undergoing rapid sedimentation e g the gulf coast basin of the southeastern united states do not appear to apply to the anadarko basin the anadarko basin belongs to a group of cratonic basins that are tectonically quiescent and characterized by the association of abnormal pressures with natural gas begin page 146

late cenozoic uplift in southern asia and the american west rationale for general circulation modeling experiments geologic evidence suggests significant increases in uplift rates and absolute elevation in several areas during the late cenozoic especially in the last 10 m y regions of major uplift include the tibetan plateau and himalayan mountains of southern asia and the sierra nevada colorado plateau basin and range rocky mountains and high plains of the american west uplift occurred at a scale large enough to affect regional and global climate in a number of ways several of which we evaluate by general circulation model experiments in accompanying papers

formation of recent martian gullies through melting of extensive water rich snow deposits the observation of gullies on mars indicates the presence of liquid water near the surface in recent times1 2 which is difficult to reconcile with the current cold climate gullies have been proposed to form through surface runoff from subsurface aquifers1 3 or through melting of near surface ice under warmer conditions4 but these gullies are observed to occur preferentially in cold mid latitudes2 where the presence of liquid water is less likely and on isolated surfaces where groundwater seepage would not be expected making both potential explanations unsatisfactory here i show that gullies can form by the melting of water rich snow that has been transported from the poles to mid latitudes during periods of high obliquity within the past 105 to 106 years refs 5 6 melting within this snow7 can generate sufficient water to erode gullies in about 5 000 years my proposed model for gully formation is consistent with the age and location of the gullies and it explains the occurrence of liquid water in the cold mid latitudes as well as on isolated surfaces remnants of the snowpacks are still present on mid latitude pole facing slopes and the recent or current occurrence of liquid water within them provides a potential abode for life

martian cratering 9 toward resolution of the controversy about small craters abstract the malin et al malin m c edgett k posiolova l mccolley s noe dobrea e 2006 science 314 1573 1577 report of ongoing production of decameter scale primary craters matches within an order of magnitude the crater production curves of hartmann hartmann w k 2005 icarus 174 294 320 and appears to contradict models that say our curves grossly overpredict primary production nonetheless such models may still predict correct order of magnitude secondary production the new observations if correct require geologically recent martian surface modification in some areas on timescales comparable to the cycles of obliquity changes suggesting episodic martian climatic environmental change driven by the obliquity cycles

fracturing associated with the 1977 1978 eruption of usu volcano north japan as revealed by geophysical measurements abstract none of the ground temperature measurements inside the somma caldera of usu volcano in southwestern hokkaido japan show patterns that correlate with the development of surface faults and the hypocenter distribution of earthquake swarms observed during the 1977 1978 eruptions audiomagnetotelluric a m t soundings on the surface of the somma caldera display well defined high resistivity zones h r z within the low resistivity edifice h r z are explained as being due to rising dry steam and low resistivity zones are attributed to ionized water in the volcanic edifice inversion of data shows that elongated h r z have a shallow roof and are some hundred meters wide steam rising along narrow vertical fractures generates widely distributed vapor dominated geothermal systems because rising steam condenses near the surface the condensed steam creates a water filled zone which inhibits the free escape of succeeding steam distribution of elongated h r z correlates well with the high ground temperature zones a self potential survey reveals a positive anomaly developed over the usu edifice about 350 mv in magnitude electrokinetic coupling effect due to intensive hydrothermal convection is a probable interpretation of the anomaly because the high potential zone is closely related to a high ground temperature zone hydraulic fracturing of the upper crust at the time of eruption allowed release of elastic strain energy due to magma pressure at depths with the spectacular consequence that one side of the major fracture was uplifted about 180 m the geometry of such a process may be drawn from seismological results the roof of the edifice is pushed up by expanding magma accompanying intensive seismic activities we suggest that earthquake free zones are proof of magma filled fractures and that eruption took place when one of these fractures opened to the surface

formation of gullies on mars link to recent climate history and insolation microenvironments implicate surface water flow origin features seen in portions of a typical midlatitude martian impact crater show that gully formation follows a geologically recent period of midlatitude glaciation geological evidence indicates that in the relatively recent past sufficient snow and ice accumulated on the pole facing crater wall to cause glacial flow and filling of the crater floor with debris covered glaciers as glaciation waned debris covered glaciers ceased flowing accumulation zones lost ice and newly exposed wall alcoves continued as the location for limited snow frost deposition entrapment and preservation analysis of the insolation geometry of this pole facing crater wall and similar occurrences in other craters at these latitudes on mars shows that they are uniquely favored for accumulation of snow and ice and a relatively more rapid exposure to warmer summer temperatures we show that after the last glaciation melting of residual snow and ice in alcoves could have formed the fluvial channels and sedimentary fans of the gullies recent modeling shows that top down melting can occur in these microenvironments under conditions similar to those currently observed on mars if small amounts of snow or frost accumulate in alcoves and channels accumulation and melting is even more favored in the somewhat wetter relatively recent geological past of mars after the period of active glaciation

dynamics of unusual debris flows on martian sand dunes 1 gullies that dissect sand dunes in russell impact crater often display debris flow like deposits in their distal reaches the possible range of both the rheological properties and the flow rates are estimated using a numerical simulation code of a bingham plastic flow to help explain the formation of these features our simulated results are best explained by a rapid debris flow for example a debris flow with the viscosity of 102 pa s and the yield strength of 102 pa can form the observed deposits with a flow rate of 0 5 m3 s sustained over several minutes and total discharged water volume on the order of hundreds of cubic meters which may be produced by melting a surface layer of interstitial ice within the dune deposits to several centimeters depth

thermal uplift and erosion across the continent ocean transform boundary of the southern exmouth plateau thermal evolution of the continental lithosphere at a continent ocean transform margin is examined using a two dimensional heat conduction model all heating is assumed to result from the emplacement of new oceanic ridge against the continent the assumed initial continental temperature gradient is probably best applied to regions having experienced finite duration periods of rifting lasting tens of millions of years a deep seismic reflection profile across the southern paleo transform margin of the exmouth plateau northwest australia tests the predictions of the model using this reflection profile it is estimated that up to 3 5 km of sediments have been eroded from the continental rim diminishing to almost no erosion at 60 km from the continent ocean transform boundary this trend and these values for erosion can be matched approximately using the model under the condition of local isostasy a finite difference scheme is employed where the surface elevation is the result of the competing 1 thermal uplift up 2 surficial erosion down and 3 local isostatic rebound up in response to the erosion the model predicts that most of the erosion ceases by 40 ma after ridge emplacement and that of the order of 1000 km3 eroded sediments are shed for every 10 km of transform length

evidence for differential unroofing in the adirondack mountains new york state determined by apatite fission track thermochronology abstract apatite fission track ages of 168 83 ma for 39 samples of proterozoic crystalline rocks three samples of cambrian potsdam sandstone and one cretaceous lamprophyre dike from the adirondack mountains in new york state indicate that unroofing in this region occurred from late jurassic through early cretaceous samples from the high peaks section of the adirondack massif yielded the oldest apatite fission track ages 168 135 ma indicating that it was exhumed first unroofing along the northern northwestern and southwestern margins of the adirondacks began slightly later as shown by younger apatite fission track ages 146 114 ma determined for these rocks this delay in exhumation may have resulted from burial of the peripheral regions by sediment shed from the high peaks apatite fission track ages for samples from the southeastern adirondacks are distinctly younger 112 83 ma than those determined for the rest of the adirondack region these younger apatite fission track ages are from a sec

low temperature thermal history and landscape development of the eastern adirondack mountains new york constraints from apatite fission track thermochronology and apatite u th he dating the adirondack mountains in northern new york state form an elongate domal exposure of mainly high grade metamor phic tectonites in a mountainous setting with topographic relief of 1 km the origin of the adirondack mountains and this relief has long been enigmatic since the adirondacks presently lie within an intracratonic setting inboard of the north american passive mar gin and far from any active plate boundaries through the application of apatite fi ssion track aft thermochronology and apatite u th he ahe dating within the eastern adirondack mountains this study provides constraints on both the thermal and ero sional effects of mesozoic passage near a hot spot and the timing of relief development aft thermochronology and ahe dating record relatively stable thermal conditions within the eastern adirondacks from the middle jurassic into the early cretaceous during the early cretaceous ca 130 120 ma the region underwent heating as sociated with progressive movement near the great meteor hotspot resulting in the temporary establishment of an elevated geo thermal gradient following regional heat ing cooling rates increased considerably ca 105 95 ma likely due to both thermal doming producing an increase in erosion rate and the relaxation of isotherms after passage near the hotspot the regional distribution of aft ages across the eastern adirondacks reveals no systematic age gradient from core to periph ery which would be expected under con ditions of persistent high relief during the decay of a crustal root over many tens to hun dreds of millions of years instead thermo chronological data suggest that the present relief developed during the late cretaceous cenozoic through plateau dissection during periodic base level changes

northern hemisphere martian gullies and mantled terrain implications for near surface water migration in mars recent past 1 we report on a systematic study of gullies and mantled terrain in the northern hemisphere of mars consistent with previous work the mantled terrain is generally located on poleward facing slopes and gullies are found at all orientations new results are as follows 1 the range of orientations of mantled terrain increases toward the pole 2 near polar gullies are commonly less morphologically developed compared to ones in the temperate latitudes 3 gullies toward the pole are better preserved than those closer to the equator and 4 these studies are conducted in the northern hemisphere whereas most previous work investigated the south no gully model in the literature cleanly fits all these observations nor any other gully observations reported in other papers however the likely effects of obliquity and precession variations on snow formation preservation and melting are consistent with many of the results

self potential survey near the craters of stromboli volcano italy inference for internal structure and eruption mechanism the presence of self potentials on the upper part of stromboli volcano is associated with the existence of convection cells of gases and condensed liquids whose rising parts are situated above the hot zones a model of a convection cell fed by a hot fluids through its lower middle part was calculated and applied to the various structures of the upper part of the volcano this model which takes account of a process which is probably fairly common in volcanic system gives a clear explanation of the various potential zones

the relationship between track shortening and fission track age reduction in apatite combined influences of inherent instability annealing anisotropy length bias and system calibration abstract the relationship between reduced track density 0 and reduced mean confined track length l l 0 during annealing has been studied for both spontaneous and induced tracks in four apatite samples with different chemical composition compositional range and origin and with spontaneous tracks giving mean confined track lengths varying from 14 5 m down to 12 3 m in all four apatites induced tracks show a relationship between l l 0 and 0 composed of two regions at higher values the two appear to be equal while at lower values l l 0 is greater than 0 this can be understood qualitatively in terms of the anisotropy of annealing and the bias against revelation of short tracks data from three apatites of uniform composition show near identical relationships in a sample showing a range of apatite compositions the point of divergence from the 1 1 relationship is somewhat higher than in the uniform composition apatites because individual grains anneal at different rates and the presence of highly annealed grains affects the track density more strongly than the mean track length spontaneous tracks show similar relationships to those observed for induced tracks in each sample when the data are renormalised to allow for the natural annealing present in the spontaneous tracks previous studies which led to the idea of length reduction without density reduction for spontaneous tracks did not renormalise density data as well as length data thereby distorting the apparent relationship data for the multi compositional apatite sample where annealing has taken place in geological conditions also agrees with the laboratory annealing data for both spontaneous and induced tracks this consistency suggests that a single process is responsible in all three cases implying that a laboratory based description of annealing can be applied to geological conditions with confidence recognition that spontaneous tracks in apatite are commonly annealed suggests that in general the fission track age should be interpreted as a reflection of both the time over which tracks have been retained and the distribution of etchable track lengths since the latter is a manifestation of the thermal history the fission track age should be interpreted in similar terms

rapid cooling and exhumation in the western part of the mesoproterozoic albany fraser orogen western australia abstract the albany fraser orogen of southwestern australia is an understudied orogenic belt which is interpreted to record the mesoproterozoic suturing of the yilgarn craton of western australia to the mawson craton of east antarctica during rodinia assembly previous u pb geochronology has dated peak amphibolite to granulite facies metamorphism in the orogen at ca 1180 ma here we report the first 40ar 39ar thermochronology of hornblende biotite and muscovite grains from a 360 km transect across the western albany fraser orogen and uncover a record of strikingly fast syn orogenic cooling and exhumation to the north muscovites from the northern foreland record cooling at ca 1159 ma in the central and southern domains of the orogen the biranup and nornalup zones hornblende yields ca 1169 ma cooling ages and biotite yields ca 1172 1144 ma cooling ages the new cooling ages imply that the three domains were exhumed rapidly following peak metamorphism at ca 1180 ma attained a similar structural level by ca 1159 ma and have experienced a uniform exhumation history since that time to constrain mineral closure temperatures and post peak metamorphic cooling rates we conducted a monte carlo simulation which fully propagates uncertainty and minimises error correlations modelling of cooling from hornblende to biotite closure temperatures ca 585 c and 365 c respectively in the nornalup and biranup zones yields fast cooling rates of 33 9 17 c ma and 22 5 7 c ma respectively these fast cooling rates imply rapid exhumation in an active tectonic setting undergoing peak metamorphism although the structural evolution of the albany fraser orogen remains poorly constrained the transpressional tectonic activity associated with deformation in the western part of the albany fraser orogen may have been an active driver of this fast exhumation this is distinctly different from exhumation models for granulite facies domains in other mesoproterozoic orogens which typically experience post orogenic slow 1 5 c ma cooling driven by mechanisms such as orogenic collapse and erosion we consider that the observed differences reflect the interpreted syn tectonic transpressional exhumation history of the albany fraser orogen which is an underrepresented tectonic regime in the mesoproterozoic cooling record

k ca ages of authigenic sediments examples from paleozoic glauconite and applications to low temperature thermochronometry k ca ages of cambrian glauconites from the llano uplift central texas were determined in order to re evaluate the ability of the k ca system to constrain the timing of deposition of sedimentary packages all of the k ca ages presented here were found to be younger than their stratigraphic ages in addition to being too young the k ca ages are also highly variable ranging in age from silurian to permian the oldest subset of glauconite ages are in agreement with previously published rb sr ages from the same outcrop and provide further evidence for there having been a post depositional thermal or recrystallization event that reset both the rb sr and k ca systems the range of younger glauconite k ca ages is similar to the distribution of available apatite fission track ages for the llano basement k ca ages are interpreted as thermochronologic data reflecting partial retention of ca in thermally fluctuating basin conditions estimates of the closure temperature of ca in glauconite are found to be 60 90 c for cooling rates of 0 5 1 c my the k ca system is potentially useful as a low temperature thermochronometer with closure temperatures 100 c for glauconite

geologically recent gully polygon relationships on mars insights from the antarctic dry valleys on the roles of permafrost microclimates and water sources for surface flow we describe the morphology and spatial relationships between composite wedge polygons and mars like gullies consisting of alcoves channels and fans in the hyper arid antarctic dry valleys adv as a basis for understanding possible origins for martian gullies that also occur in association with polygonally patterned ground gullies in the adv arise in part from the melting of atmospherically derived wind blown snow trapped in polygon troughs snowmelt that yields surface flow can occur during peak southern hemisphere summer daytime insolation conditions ice cemented permafrost provides an impermeable substrate over which meltwater flows but does not significantly contribute to meltwater generation relationships between contraction crack polygons and sedimentary fans at the distal ends of gullies show deposition of fan material in polygon troughs and dissection of fans by expanding polygon troughs these observations suggest the continuous presence of meters thick ice cemented permafrost beneath adv gullies we document strong morphological similarities between gullies and polygons on mars and those observed in the adv inland mixed microclimate zone on the basis of this morphological comparison we propose an analogous top down melting model for the initiation and evolution of martian gullies that occur on polygonally patterned mantled surfaces

lineated valley fill and lobate debris apron stratigraphy in nilosyrtis mensae mars evidence for phases of glacial modification of the dichotomy boundary 1 the nilosyrtis mensae region is important among dichotomy boundary fretted terrain outcrops as it provides evidence of overprinting of ancient landscapes by a suite of glacial features providing a composite view of the variety of midlatitude glacial modification processes that can occur during recent martian ice ages on the basis of a series of criteria developed for the identification of a glacial origin for lineated valley fill and lobate debris aprons we interpret stratigraphic topographic and textural relationships between lineated valley fill and lobate debris apron morphological units as evidence of local and regional glacial overprinting of the landscape during the recent amazonian we document 1 stratigraphic relationships between lineated valley fill subunits including the presence of apparently superposed and small scale lobate features 2 the regional integration and flow of lineated valley fill material 3 lineated valley fill degradation and 4 the nature and stratigraphic position of lobate debris aprons these observations suggest multiple phases or episodes of midlatitude valley glacier activity these observations together with those of surface units elsewhere in northern arabia terra interpreted as glacially modified landforms suggest the possibility of midlatitude glacial deposits extending over broad portions of the martian dichotomy boundary within the past several hundred million years

orogeny and metamorphism a model for deformation and pressure temperature time paths with applications to the central and southern appalachians a model is presented for deformation uplift and exhumation in convergent orogens based on the following premises 1 foreland basin subsidence monitors the distribution in time and space of overthrust loads added to an orogen 2 the presence of an inherited rifted margin plays an important role in the subsequent history of an orogen by forming a basement ramp or buttress that must be surmounted in order for thrusts to advance on the craton on the seaward side of this transition up to 20 km of overthrusts can be accumulated without creating topography 3 critical shape theory can be applied to orogens as a whole allowing predictions to be made concerning dynamic balance between mass addition and loss uplift exhumation and growth of topography and 4 pressure temperature time p t t data can be used to reconstruct particle paths within the deforming orogen three states of overthrust orogens can be defined based on the relative rates of mass loss and mass addition as monitored by the foreland rapid exhumation of metamorphic terranes is most likely in the steady state where erosion balances accretion a constructive state where mass addition is greater than mass loss results in crustal thickening and initially little exhumation a destructive state where mass loss outweighs mass addition results in slow exhumation or subsidence of metamorphic rocks in the orogen depending on whether mass is removed by erosion or by extension p t t data on peak metamorphism pluton emplacement uplift exhumation and cooling can be used in conjunction with data from the foreland to distinguish among these various states the topography and strength of the inherited rifted margin play an important role in localizing zones of exhumation and uplift within the orogen application of this model to the central and southern appalachians suggests that during the constructive phases of the taconian and acadian orogenies overthrust loads accumulated mainly on the seaward side of the ocean continent transition as marked by the bouguer gravity gradient between the acadian and alleghanian orogenies the appalachian orogen was probably in a steady state with uplift and exhumation of rocks in the orogen but little subsidence of the foreland or advance of thrusts toward the craton the constructive stage of the alleghanian orogeny achieved the critical topography necessary to drive crystalline thrust sheets over the craton this resulted in widespread uplift and westward transport of older metamorphic rocks post orogenic unroofing of the southern appalachians is compatible with the predictions of flexural models the post orogenic unroofing history of the central appalachians and ouachitas probably reflects mesozoic extension in these areas

debris flows over sand dunes on mars evidence for liquid water 1 this study focuses on the formation and physical properties of the gullies observed over large martian dunes especially those of the russell crater 54 s 347 w geomorphic features like sinuosities and connections of the channels show that gullies over dunes involve flows with a significant proportion of liquid the occurrence of levees implies that these flows are debris flows with a yield strength characteristics of bingham plastic materials we apply terrestrial methods to estimate viscosity and velocity of these flows from levee size and sinuosities we obtain average velocities in the range of 1 to 7 m s 1 and apparent viscosities of 2 8 to 46 000 pa s with an average at 740 pa s compared with the 0 001 pa s of pure water these viscosities and velocities are in the range of terrestrial debris flows with a proportion of 10 to 40 of h2o these properties are typical of water holding debris flows but not of pure water surface runoff or co2 driven flows the debris flows over dunes are oriented on south facing slopes like other recent gullies meltwater from ground ice formed during a recent period of high obliquity is the more likely explanation for the formation of such flows over dunes

tip to midpoint observations on syntectonic veins ouachita orogen arkansas trading space for time abstract by examining a vein from its tip to center we have established the transition from a single filled fracture at the vein tip to typical crack seal textures observed in fibered laminated veins the vein is contained in the boudin neck of a sandstone layer within the lower ordovician mazarn formation benton uplift ouachita orogen the tip of the vein is composed of one or more isolated veinlets defined as quartz filled narrow 5 25 m fractures parallel to the larger vein s long dimension scanned sem based cathodoluminescence shows that quartz laminae of the same orientation and thickness are found throughout the vein wall normal fibers first appear in the vein where detrital grains are cut by multiple veinlets each veinlet mimicking the crystallographic orientation of the detrital grain whereas later veinlets reflect the established crystallographic orientation of the fiber fibers throughout the vein retain evidence of having been formed by repeated fracturing and filling of a pre existing grain at the vein walls or fiber however recrystallization later modified the fibers by obliterating some evidence of the veinlets and moving fiber walls boudin formation provided the extension site that localized fracturing and vein filling the vein grows by the repeated addition of veinlets in the neck region recrystallization altered the shape of previously formed fibers

the role of arcuate ridges and gullies in the degradation of craters in the newton basin region of mars abstract a survey of craters in the vicinity of newton basin using high resolution images from mars global surveyor and mars odyssey was conducted to find and analyze examples of gullies and arcuate ridges and assess their implications for impact crater degradation processes in the phaethontis quadrangle mc 24 we identified 225 craters that contain these features of these 188 had gullies on some portion of their walls 118 had arcuate ridges at the bases of the crater walls and 104 contained both features typically on the same crater wall a major result is that the pole facing or equator facing orientation of these features is latitude dependent at latitudes 44 s equator facing orientations for both ridges and gullies are prevalent but at latitudes

role of aquicludes in formation of martian gullies liquid water is not currently stable on the surface of mars but images provided by the mars orbiter camera aboard the mars global surveyor spacecraft reveal erosional landforms previously interpreted to be geologically young gullies formed by groundwater seepage we test the basic hypothesis that as on earth the location of these gullies is controlled in part by the presence of an impermeable rock layer aquiclude and that the depths of the gully heads below the surface should thus be correlated to subsurface geology we show that 1 gullies emanate from a specific cliff forming layer even if the layer is faulted and 2 the depth of gullies below the local surface ranges from 70 to 800 m and 3 is positively correlated to mapped geologic units gully formation is therefore dependent upon both favorable climatic conditions to produce and sustain liquid water and the presence of impermeable subsurface layers to collect the groundwater gullies may mark the distribution of subsurface impermeable layers globally and are prime targets for the search for present water and life on mars

on the orbital forcing of martian water and co2 cycles a general circulation model study with simplified volatile schemes 1 variations in the martian water and co2 cycles with changes in orbital and rotational parameters are examined using the geophysical fluid dynamics laboratory mars general circulation model the model allows for arbitrary specification of obliquity eccentricity and argument of perihelion as well as the position and thickness of surface ice exchange of co2 between the surface and atmosphere is modeled generating seasonal cycles of surface ice and surface pressure water is allowed to exchange between the surface and atmosphere cloud formation is treated and both cloud and vapor are transported by modeled winds and diffusion exchange of water and co2 with the subsurface is not allowed and radiative effects of water vapor and clouds are not treated the seasonal cycle of co2 is found to become more extreme at high obliquity as suggested by simple heat balance models maximum pressures remain largely the same but the minima decrease substantially as more co2 condenses in the more extensive polar night vapor and cloud abundances increase dramatically with obliquity the stable location for surface ice moves equatorward with increasing obliquity such that by 45 obliquity water ice is stable in the tropics only ice is not spatially uniform but rather found preferentially in regions of high thermal inertia or high topography eccentricity and argument of perihelion can provide a second order modification to the distribution of surface ice by altering the temporal distribution of insolation at the poles further model simulations reveal the robustness of these distributions for a variety of initial conditions our findings shed light on the nature of near surface ice rich deposits at midlatitudes and low latitudes on mars

the potential of crinoids as u th sm he thermochronometers abstract u th sm he dating of crinoid fossils from late paleozoic rocks from a variety of sites in north america suggest that this material can be used as a useful low t thermochronometer under certain conditions available data suggest that common he is present in crinoids and at the low production rates typical of calcite this common he will be sufficient to produce spurious ages in crinoid samples of any age heating of samples to temperatures in excess of the opening temperature will expel all he common and radiogenic with all subsequent he accumulation being exclusively radiogenic such samples have potential for being robust thermochronometers sensitive to temperatures in the range of 60 110 c without common he analysts can take advantage of the large size of crinoid columnals and produce reliable ages even when young miocene or with low production rates eu 0 1 ppm samples not subjected to post depositional heating above the opening temperature burial to depths of 2 to 4 km depending on geothermal gradient sedimentation rate and residence time at peak t will likely retain common he and be unsuitable for thermochronologic studies

the magnetic fabric of the wolfcamp shale midland basin west texas understanding petrofabric variability hydrocarbon associations and iron enrichment rock fabrics have long been recognized as a key variable influencing unconventional reservoir properties and yet petrofabric analysis is rarely incorporated in reservoir characterization in a quantitative and scalable manner this work introduces anisotropy of magnetic susceptibility ams coupled with handheld x ray fluorescence to define the origin of petrofabrics in the wolfcamp shale and examine their relationship with total organic carbon toc and oil saturation indices osi standard paleomagnetic plugs were drilled from three vertical cores spanning the entire wolfcamp shale in the midland basin west texas low temperature magnetic experiments suggest paramagnetic minerals contribute between 93 4 and 98 6 to the low field bulk magnetic susceptibility klf across all lithotypes scanning electron microscopy revealed frequent occurrences of paramagnetic minerals such as chlorite illite ferroan dolomite marcasite and pyrite the fe rich clays such as chlorite carry the ams signal in mudrocks with a minor contribution from ferroan dolomite conversely ferroan dolomite carries the ams signal in most carbonate facies with a minor influence from fe rich clays the degree of magnetic anisotropy pj and shape factor t in mudrocks are compositionally dependent and respond to changes in both clay and framework grain concentration for carbonate facies pj and t vary widely because of changes in depositional facies and the concentration of ferroan dolomite the toc correlates well with pj and strongly oblate magnetic fabrics this relationship likely stems from the adsorption of organic matter om to clays during deposition and may indicate that organoclay composites were responsible for delivering om to the midland basin elevated osi are fabric selective favoring low pj and t fabrics suggesting that such fabrics facilitate hydrocarbon migration more so than high pj and t fabrics fuzzy c means clustering provides a framework to describe ams and geochemical transitions at the core scale and could serve as a tool to map barriers and pathways to hydrocarbon migration finally ti nb and klf data point to a mafic provenance lithotype and suggest layered intrusive complexes in the central basin uplift were exposed and eroded during deposition of the wolfcamp shale mafic source rocks probably increased supply of micronutrients such as dissolved iron and may have enhanced productivity in the midland basin

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

use of spacecraft data to derive regions on mars where liquid water would be stable combining viking pressure and temperature data with mars orbital laser altimeter topography data we have computed the fraction of the martian year during which pressure and temperature allow for liquid water to be stable on the martian surface we find that liquid water would be stable within the hellas and argyre basin and over the northern lowlands equatorward of about 40 the location with the maximum period of stable conditions for liquid water is in the southeastern portion of utopia planitia where 34 of the year liquid water would be stable if it were present locations of stability appear to correlate with the distribution of valley networks

intermediate tectonic pattern and hydrodynamic process deduced from audiomagnetotelluric investigations on the volcanic island of mayotte comores archipelago abstract audiomagnetotelluric soundings were carried out on the volcanic island of mayotte comores archipelago the field method and data are described and discussed all the sounding cross sections show coherent curves with a high conductive layer between 100 and 200 m depth this layer is considered to be a fluctuating water table zone correlated to yearly climatic changes under tropical weathering processes dipping and sudden level variations are linked to tectonic volcanic features and are the visualization of a block faulting system of the primitive basaltic shield a consequence of a distensive phase possibly connected with the collapse of the western flank of the volcano piano key panels are the typical sub surface style and the guide line for any water prospection on the volcano and the activity of the island water transfer system

confirmation and utilization of the production function size frequency distributions of martian impact craters 1 on any planetary surface impacts of interplanetary bodies create an initial or production function size frequency distribution sfd of impact craters recent questions have been raised about whether this size distribution can be reliably detected especially at small sizes in a test area we confirm an excellent fit to the distribution we have used previously at diameters 11 m d 1 km at d 1 km images with the high resolution stereo camera hrsc allow us to confirm earlier proposals on how the burial of old small craters by lava flows can distort the sfd curve in some areas as a product of this analysis we present a new tool for quantitative analysis of geologic processes on mars namely use of crater statistics to interpret subsurface structure

evidence from apatite fission track analysis for regional cretaceous cooling in the ouachita mountain fold belt and arkoma basin of arkansas geologic note 1 a reconnaissance study involving apatite fission track analysis of surface paleozoic sedimentary and cretaceous intrusive rocks was undertaken to evaluate the low temperature thermal history of the ouachita mountain fold belt and arkoma basin of arkansas paleozoic rocks have apparent apatite fission track ages ranging from 184 or 12 ma to 95 or 11 ma with mean track lengths in the range of 12 95 or 0 17 micrometers to 13 51 or 0 13 micrometers indicating that these samples have undergone significant postdepositional annealing cretaceous samples have apatite fission track ages between 104 or 4 and 88 or 6 ma that are concordant with rb sr and k ar ages and mean track lengths in the range 14 69 or 0 16 micrometers to 15 36 or 0 10 microme ers indicating that these rocks cooled rapidly to paleotemperatures below 50 60 degrees c following their emplacement and have subsequently remained cool paleozoic strata of the ouachita mountain fold belt and arkoma basin in arkansas are inferred to have undergone regional cooling from paleotemperatures greater than 110 degrees c beginning in the early cretaceous to paleotemperatures generally less than 80 90 degrees c prior to the intrusion of alkaline plutons along the western margin of the mississippi embayment during the middle cretaceous whether regional cooling during the cretaceous was caused by uplift and erosion or whether a dramatic reduction in the paleogeothermal gradient was involved remains uncertain although a significant component of uplift and erosion is inferred from independent geological observations the results of this study indicate that paleozoic rocks of the ouachita mountain fold belt and arkoma basin of ar ansas were exposed to maximum paleotemperatures during late paleozoic burial prior to the emplacement of cretaceous plutons in the region

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

dissipation of anomalous pressures in the subsurface 1 zones of anomalous pressure higher and lower than hydrostatic pressure have been observed in many sedimentary basins around the world these normally consist of groups of pressure compartments volumes of higher permeability rock surrounded on all sides by lower permeability barriers knowledge of the timescales over which these abnormal pressures are maintained and the mechanisms by which they dissipate is critical for understanding how fluids such as oil and gas move in the subsurface existing analytic solutions investigate pressure dissipation through low permeability barriers on top of or underneath an isolated pressure compartment there are no analytic solutions describing pressure dissipation through lateral barriers such as faults or investigating the impact of groups of pressure compartments on the rate of pressure dissipation this paper presents simple analytic models to investigate pressure dissipation through barriers such as faults forming the sides of pressure compartments the timescales are compared with a solution for pressure dissipation through barriers on top of and underneath the compartment it also investigates analytically the rate of pressure dissipation from groups of pressure compartments lateral seal permeabilities of 10 19 m2 may delay pressure equilibration for millions of years provided the compartment has a sufficiently high fluid storage capacity factors contributing toward a high fluid storage capacity include a high fluid compressibility as is the case in hydrocarbon reservoirs and a high porosity the grouping of abnormally pressured compartments into megacompartment complexes may delay pressure dissipation for hundreds of millions of years

epeirogeny and eustatic sea level changes as inferred from cretaceous shoreline deposits applications to the central and western united states uplift and subsidence histories of continental margins are by now reasonably well understood in the context of plate tectonics but the epeirogenic movements of continental interiors have been neither well documented nor properly understood epeirogenic movements are important to recognize when reconstructing paleogeography and may yield information regarding mantle dynamics and the amplitudes wavelengths and rates of lithospheric flexure sediments deposited at or near sea level can be used as a worldwide datum against which to measure postdepositional epeirogenic movements the present elevations of shoreline sediments of epicontinental seas deposited during sea level highstands at particular times in the past define a warped surface documenting subsequent epeirogeny of continental interiors when the amplitude of sea level rise during transgression is small relative to the observed epeirogenic motions the diachronous shoreline deposits represented in the entire transgressive surface can be used as a datum in the analysis thus greatly augmenting the available data and areal coverage if a stable frame of reference can be defined a eustatic sea level correction can be applied to every continent the elevation of the upper cenomanian mid cretaceous shoreline gives little evidence of warping tilting or uplift in central cratonic north america but indicates that a large area of the western united states including the colorado plateau has undergone more than 2 km of post cenomanian epeirogenic uplift

ancient melting of mid latitude snowpacks on mars as a water source for gullies abstract we hypothesize that during past epochs of high obliquity seasonal snowfields at mid latitudes melted to produce springtime sediment rich surface flows resulting in gully formation significant seasonal mid latitude snowfall does not occur on mars today general circulation model gcm results however suggest that under past climate conditions there may have been centimeters of seasonal mid latitude snowfall mischna m a richardson m i wilson r j mccleese d j 2003 j geophys res planets 108 doi 10 1029 2003je002051 5062 gully locations have been tabulated by several researchers e g heldmann j l mellon m t 2004 icarus 168 285 304 heldmann j l carlsson e johansson h mellon m t toon o b 2007 icarus 188 324 344 malin m c edgett k s 2000 science 288 2330 2335 and found to correspond to mid latitude bands a natural question is whether the latitudinal bands where the gullies are located correspond to areas where the ancient snowfalls may have melted producing runoff which may have incised gullies in this study we model thin snowpacks with thicknesses similar to those predicted by mischna m a richardson m i wilson r j mccleese d j 2003 j geophys res planets 108 doi 10 1029 2003je002051 5062 we model these snowpacks under past climate regimes in order to determine whether snowmelt runoff could have occurred and whether significant amounts of warm soil t 273 k existed on both poleward and equatorward slopes in the regions where gullies exist both warm soil and water amounts are modeled because soil and water may have mixed to form a sediment rich flow we begin by applying the snowpack model of williams et al williams k e toon o b heldmann j e mellon m 2008 icarus 196 565 577 to past climate regimes characterized by obliquities of 35 600 ka before present and 45 5 5 ma before present and to all latitudes between 70 n and 70 s we find that the regions containing significant snowmelt runoff correspond to the regions identified by heldmann and mellon heldmann j l mellon m t 2004 icarus 168 285 304 heldmann et al heldmann j l carlsson e johansson h mellon m t toon o b 2007 icarus 188 324 344 and malin and edgett malin m c edgett k s 2000 science 288 2330 2335 as containing large numbers of gullies we find that the snowmelt runoff 1 mm with equivalent rainfall rates of 0 25 mm h and warm soil 1 cm depth would have occurred on slopes within the gullied latitudinal bands the snowfall amounts modeled are predicted to be seasonal mischna m a richardson m i wilson r j mccleese d j 2003 j geophys res planets 108 doi 10 1029 2003je002051 5062 and our modeling finds that under the previous climate regimes there would have been meltwater present on the slopes in question for brief periods of time on the order of days each year our model provides a simple explanation for the latitudinal distribution of the gullies and also suggests that the gullies date to times when water migrated away from the present poles to the mid latitudes

formation of recent martian debris flows by melting of near surface ground ice at high obliquity the observation of small gullies associated with recent surface runoff on mars has renewed the question of liquid water stability at the surface of mars the gullies could be formed by groundwater seepage from underground aquifers however observations of gullies originating from isolated peaks and dune crests question this scenario we show that these landforms may result from the melting of water ice in the top few meters of the martian subsurface at high obliquity our conclusions are based on the analogy between the martian gullies and terrestrial debris flows observed in greenland and numerical simulations that show that above freezing temperatures can occur at high obliquities in the near surface of mars and that such temperatures are only predicted at latitudes and for slope orientations corresponding to where the gullies have been observed on mars

absolute dune ages and implications for the time of formation of gullies in nirgal vallis mars 1 transverse dunes cover the valley floor of nirgal vallis a 670 km long valley network at 318 e and 29 s the dunes are superposed by small undeformed impact craters which implies that the dunes are inactive under present atmospheric conditions the last active phase of dune movement absolute age can be determined by crater size frequency distributions the derived absolute ages from high resolution mars global surveyor mars orbiter camera imagery range from approximately 300 000 years to 1 4 myr b p error of factor of 2 the dunes are also superposed by gully deposits aprons which implies a younger age of the gullies these superposition relationships show that the gullies in this midlatitude region are at the most 3 myr old but might be even younger than 300 000 years

internal structure of mount merapi indonesia derived from long offset transient electromagnetic data 1 a long offset transient electromagnetic lotem survey was carried out on merapi volcano indonesia in 1998 lotem data have been recorded at 41 receiver locations which cover a 10 km w e and a 15 km s n profile the signals were transmitted at four locations on the south west and north sides of merapi the data were interpreted with one dimensional 1 d inversions in addition two particular features were investigated with 3 d modeling on the south flank the magnetic field data show strong 3 d distortions consistently over the profile which can only be explained by a conductive near surface structure like a fracture filled with conductive fluids the simulation of topographic effects shows that the interpretation is not significantly affected on both profiles the most striking feature is a conductive layer of 20 m at depths of 500 1000 m below the surface and a thickness of 1 2 km the cause of the increased conductivity may be different for the summit area the intermediate zone and at the flanks below the summit in vicinity of the conduit the decrease in resistivity is produced either by hydrothermal fluids by partial melts or rocks altered by the hydrothermal system or by a combination in the intermediate zone between the conduit and the flanks either alteration or hydrothermal fluids may be the source of the conductivity increase fluids seem to be the most likely cause for the conductive layer at the flanks and the west east striking anomaly from the resistivity of the conductive layer and the typical porosity of volcanic rock we estimate fluid resistivities of 0 2 1 m

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

liquid co2 breakout and the formation of recent small gullies on mars we show that the action of a co2 suspended flow could have produced the recent small gullies on mars and hence that liquid water is not required the model involves the build up of a liquid co2 aquifer behind and below a dry ice barrier dam cap rock in the pore spaces a few meters into the rock from the cliff face and on order of a hundred meters below the top of the cliff brink surface seasonal or obliquity cycle seasonal heating causes pinching out of the dry ice barrier and rapid release of the liquid co2 erosion of the gullies occurs as the rapid vaporization of the liquid co2 with entrainment of rock and clathrate hydrate ice produces a density flow analogous to a terrestrial nue ardente

the effect of sea level changes on the morphology of mountain belts we have examined quantitatively the effect of large 200 m long period 50 m y sea level changes on the development of the landscape of old mountain belts on the basis of the available data we have assumed that the rate of denudation of these old landscapes is proportional to the average regional elevation y by a constant k 10 4 1000 years the results are as follows 1 in the absence of large sea level changes it will take in excess of 300 m y and more likely more than 450 m y to degrade a himalayan size mountain belt y 5000 m to a peneplain y 10 m for an old mountain belt that has been eroded to a regional elevation of 500 m it will take an additional 220 m y and more likely 390 m y to degrade to a peneplain 2 in a system in which the river valleys are graded with respect to base level the rate of downcutting is enhanced by the rate of uplift caused by the isostatic response to regional denudation with sea level base level rising the rate of downcutting is decreased by the rate of rise however transgression of the river valleys cannot take place until the rate of river valley uplift caused by isostatic response to the denudation is equal to the rate of sea level rise under usual conditions of sea level rise nonglacial this will not occur until the landscape has been degraded to a regional elevation of 60 m or less however under these conditions the decrease in the rate of downcutting in the river valleys greatly enhances the rate of degradation as a consequence older mountain bells already eroded to a regional elevation of 500 m or less may be further degraded to a peneplain y 10 m during an episode of persistent sea level rise at rates of several tenths of a centimeter per 1000 years for several tens of millions of years with sea level falling the landscapes evolve toward an equilibrium surface at which point the rate of degradation is equal to the rate of sea level fall 3 we have applied these concepts to the post triassic evolution of the ridge and valley province of the appalachians sea level probably rose 300 m during the interval from 205 to 95 ma which was sufficient to degrade those areas with a regional elevation of 500 m or less to a peneplain subsequent to this time from 80 to 10 ma sea level has fallen approximately 300 m sufficient to cause emergence of the former peneplain to a regional elevation y of 215 m which is approximately equal to the present day regional elevation of the appalachians since the ridge and valley province near harrisburg we have made a further test of this by attempting to restore the remanent peneplain surface i e the schooley mountain surface to its former elevation in the upper cretaceous and thus estimate the height that sea level had to be at that time by infilling the valleys with country rock up to 457 m which is the present elevation of the presumed former peneplain remanent surface and making the appropriate isostatic adjustments we may conclude that at a minimum sea level was 277 m above present in the upper cretaceous finally we conclude that large scale peneplanation can only take place during episodes of significant sea level rise 250 m over long periods of time 50 m y thus episodes of extensive peneplanation are indicative of sea level changes of this magnitude

the formation and evolution of youthful gullies on mars gullies as the late stage phase of mars most recent ice age gullies are extremely young erosional depositional systems on mars that have been carved by an agent that was likely to have been comprised in part by liquid water malin m c edgett k s 2000 evidence for recent groundwater seepage and surface runoff on mars science 288 2330 2335 mcewen a s et al 2007 a closer look at water related geologic activity on mars science 317 1706 1709 the strong latitude and orientation dependencies that have been documented for gullies require 1 a volatile near the surface and 2 that insolation is an important factor for forming gullies these constraints have led to two categories of interpretations for the source of the volatiles 1 liquid water at depth beneath the melting isotherm that erupts suddenly groundwater and 2 ice at the surface or within the uppermost layer of soil that melts during optimal insolation conditions surface near surface melting in this contribution we synthesize global hemispheric regional and local studies of gullies across mars and outline the criteria that must be met by any successful explanation for the formation of gullies we further document trends in both hemispheres that emphasize the importance of top down melting of recent ice rich deposits and the cold trapping of atmospherically derived h 2o frost snow as important components in the formation of gullies this provides context for the incorporation of high resolution multi spectral and hyper spectral data from the mars reconnaissance orbiter that show that 1 cold trapping of seasonal h 2o frost occurs at the alcove channel level on contemporary mars 2 gullies are episodically active systems 3 gullies preferentially form in the presence of deposits plausibly interpreted as remnants of the late amazonian emplacement of ice rich material and 4 gully channels frequently emanate from the crest of alcoves instead of the base showing that alcove generation is not necessarily a product of undermining and collapse at these locations a prediction of the groundwater model we interpret these various lines of evidence to mean that the majority of gullies on mars are explained by the episodic melting of atmospherically emplaced snow ice under spin axis orbital conditions characteristic of the last several myr

present day impact cratering rate and contemporary gully activity on mars the mars global surveyor mars orbiter camera has acquired data that establish the present day impact cratering rate and document new deposits formed by downslope movement of material in mid latitude gullies on mars twenty impacts created craters 2 to 150 meters in diameter within an area of 21 5 106 square kilometers between may 1999 and march 2006 the values predicted by models that scale the lunar cratering rate to mars are close to the observed rate implying that surfaces devoid of craters are truly young and that as yet unrecognized processes of denudation must be operating the new gully deposits formed since august 1999 are light toned and exhibit attributes expected from emplacement aided by a fluid with the properties of liquid water relatively long extended digitate distal and marginal branches diversion around obstacles and low relief the observations suggest that liquid water flowed on the surface of mars during the past decade

orientation and distribution of recent gullies in the southern hemisphere of mars observations from high resolution stereo camera mars express hrsc mex and mars orbiter camera mars global surveyor moc mgs data 1 geologically recent small gullies on mars display morphologies consistent with erosion by water or by debris flows suggested formation models are divided into two main categories 1 groundwater or 2 melting of near surface ice snow sourced from the atmosphere we have measured location and orientation and recorded the local contexts of gullies to constrain the likely models of gully formation more than 22 000 mars orbiter camera narrow angle moc na and 120 mars express high resolution stereo camera hrsc images in the southern hemisphere were searched for gullies discrete gullied slope sections with consistent orientation were recorded rather than individual gullies slope setting impact crater valley wall etc location and orientation were recorded for each slope section more than 750 moc images with gullies 900 distinct gullied slope sections and more than 40 hrsc images 380 distinct gullied slope sections were identified from both moc and hrsc gullies were found to be most common between 30 and 50 degrees latitude and to have an overall pole facing preference the preferred gully orientation for hrsc is southeast rather than south in moc owing to illumination effects that make gullies difficult to detect on south to southwest facing slopes in hrsc in both moc and hrsc surveys higher latitude gullies show less preference for pole facing than those at mid latitudes both data sets produced similar results demonstrating that our data are reliable we suggest that the observed latitudinal and orientation distributions of gullies show that insolation and atmospheric conditions play a key role in gully formation

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

thermal contraction crack polygons on mars classification distribution and climate implications from hirise observations morphology is shown to be consistent with thermal contraction cracking of an ice rich mantling unit consistent with observations of sediment wedge thermal contraction crack polygons forming in ice cemented sediment at the phoenix landing site polygon groups are distributed symmetrically in both northern and southern hemispheres suggesting strong climate controls on polygon morphology northern hemisphere polygonally patterned surfaces are found to decrease in age from low to high latitude spanning surface ages from 1 to 0 1 ma suggesting more recent deposition of ice rich material at high latitudes than at low latitudes six of the seven classes of polygons are interpreted to be capable of forming because of the combined effects of thermal contraction cracking and differential sublimation suggesting that sublimation and sand wedge polygons dominate martian high latitudes gully polygon systems present at midlatitudes suggest that small amounts of liquid water may have been involved in thermal contraction crack polygon processes producing composite wedge polygons no evidence is found for the presence of pervasive small scale ice wedge polygons

recent ice rich deposits formed at high latitudes on mars by sublimation of unstable equatorial ice during low obliquity observations from the gamma ray spectrometer instrument suite on the mars odyssey spacecraft have been interpreted as indicating the presence of vast reservoirs of near surface ice in high latitudes of both martian hemispheres1 2 3 4 5 ice concentrations are estimated to range from 70 per cent at 60 latitude to 100 per cent near the poles possibly overlain by a few centimetres of ice free material in most places4 this result is supported by morphological evidence of metres thick layered deposits that are rich in water ice6 7 8 9 and periglacial like features10 11 found only at high latitudes diffusive exchange of water between the pore space of the regolith and the atmosphere has been proposed to explain this distribution12 but such a degree of concentration is difficult to accommodate with such processes9 13 14 alternatively there are suggestions that ice rich deposits form by transport of ice from polar reservoirs and direct redeposition in high latitudes during periods of higher obliquity9 13 but these results have been difficult to reproduce with other models here we propose instead that during periods of low obliquity less than 25 high latitude ice deposits form in both hemispheres by direct deposition of ice as a result of sublimation from an equatorial ice reservoir that formed earlier during a prolonged high obliquity excursion using the ice accumulation rates estimated from global climate model simulations we show that over the past ten million years large variations of mars obliquity have allowed the formation of such metres thick sedimentary layered deposits in high latitude and polar regions

kilometer scale roughness of mars results from mola data analysis the mars orbiter laser altimeter mola data are used to characterize the kilometer scale surface roughness of mars the median absolute value of the differential slope at a given baseline is proposed as a data derived measure of the surface roughness at this scale study of the scale dependence of roughness for the smoothest terrains gives an independent estimate of 20 cm for mola ranging accuracy the baseline lengths from 0 6 to 20 km are used and kilometer scale roughness is mapped for the entire surface the maps show that different geological units have distinctive roughness characteristics scale dependence of roughness for a number of geological units is presented and discussed the southern polar cap is rougher than the northern at kilometer and subkilometer scale which suggests differences in the sublimation condensation balance the vastitas borealis formation has a distinctive 3 km scale background surface topography which suggests a nonvolcanic origin for its upper layer young volcanic plains in amazonis planitia and the eastern part of elysium planitia are very similar to each other in their roughness characteristics and differ from other volcanic plains on mars which suggests a distinctive eruption style there are systematic latitudinal variations of roughness in both the southern highlands and the northern lowlands terrains at high latitude are smoother at short baselines the characteristic vertical scale related to this difference is several meters processes that could be responsible for formation of this trend include creep of ice rich near surface material at high latitudes treatment of the surface with repetitive deposition and sublimation of seasonal frost climate controlled deposition and or cementation of dust at high latitudes and repetitive sublimation and accumulation of subsurface ice at low latitudes with climate variations all mechanisms of origin could operate more effectively under different climate conditions relevant morphological observations favor mechanisms involving deposition of smooth blankets at high latitudes

recent debris flows on mars seasonal observations of the russell crater dune field 1 debris flows occur on slopes in the russell crater dune field the morphology of the erosion features resembles terrestrial viscous slurry flows mudflows and suggests that a flow of fine grained material mixed with liquid water might have been responsible for their formation seasonal mgs tes and moc imagery based observations of the dune field show 1 an annual frosting and defrosting cycle and 2 that liquid h2o could be stable within a limited time period in the summer of the southern hemisphere these observations lead to the conclusion that debris flows in the russell crater dune field may form under current climatic conditions by episodic or seasonal melting of small amounts of autumn winter condensed water ice

evidence for recent climate change on mars from the identification of youthful near surface ground ice ground ice in the crust and soil may be one of the largest reservoirs of water on mars1 2 3 near surface ground ice is predicted to be stable at latitudes higher than 40 ref 4 where a number of geomorphologic features indicative of viscous creep and hence ground ice have been observed5 mid latitude soils have also been implicated as a water ice reservoir6 the capacity of which is predicted to vary on a 100 000 year timescale owing to orbitally driven variations in climate7 it is uncertain however whether near surface ground ice currently exists at these latitudes and how it is changing with time here we report observational evidence for a mid latitude reservoir of near surface water ice occupying the pore space of soils the thickness of the ice occupied soil reservoir 1 10 m and its distribution in the 30 to 60 latitude bands indicate a reservoir of 1 5 6 0 104 km3 equivalent to a global layer of water 10 40 cm thick we infer that the reservoir was created during the last phase of high orbital obliquity less than 100 000 years ago and is now being diminished

inversion of apatite fission track data for thermal history information apatite fission track length distributions and ages provide an integrated record of the low temperature 20 150 c thermal history of the host rock over geologic time scales the information content of these data is quantified by applying a stochastic optimization technique simulated annealing to determine the range of thermal histories compatible with synthetic apatite fission track data given a mathematical description of fission track annealing the goodness of fit between the observed and predicted data parameters and a slowly decreasing control parameter are treated as analogous to the free energy and temperature respectively of a thermodynamic system on this basis a boltzmann type probability distribution is defined and used to accept or reject random thermal history perturbations a priori information used to constrain the model space may include the temperature range in which the solutions are sought present day temperature the complexity of the thermal history and the maximum duration of the data sensitive thermal history this approach allows determination of the range of thermal histories compatible with an observed confined track length distribution and associated fission track age and it provides an estimate of the probability distribution of temperatures at a specific time results for synthetic data sets for diverse model thermal histories suggest that the resolution of thermal history is generally poor parts of the thermal history to which the data are most sensitive can be resolved to no better than about 10 c for ideal data bounds on acceptable time temperature space are sensitive to the assumed complexity of the thermal history but are relatively insensitive to typical uncertainties associated with the data application of this approach to real data is fundamentally limited by the uncertainty associated with extrapolating annealing models to geologic conditions

thermal maturity of carboniferous strata ouachita mountains the ouachita mountains a relatively untested potential hydrocarbon province contain a thick paleozoic section of apparently favorable source beds reservoir beds and trap configurations to estimate the thermal maturity of these strata vitrinite reflectance was measured on 89 samples collected mostly from carboniferous rocks from throughout the ouachita outcrop area thermal maturity contours generally parallel structural grain in the western two thirds of the ouachitas reflectance values in oil range from 3 0 in the core area in oklahoma and from about 1 0 to 3 0 in analogous positions in arkansas older strata on upthrown sides of thrust faults are more thermally mature than younger strata on downthrown sides in the eastern one third of the outcrop belt thermal maturities are significantly higher 2 0 5 0 ro and thermal maturity contours cut obliquely across structural grain strata on either side of thrust faults display identical levels of maturity in the western two thirds of the ouachitas sedimentary and tectonic burial have been the major influences of thermal maturation although a mesozoic thermal overprint has increased levels of maturity in arkansas throughout this area strata are within the oil and wet gas windows the anomalous levels and patterns of thermal maturity in the eastern third of the ouachitas are probably the result of a thermal overprint related to mesozoic rifting and intrusive activity in the mississippi embayment this thermal overprint has elevated the maturity of strata in most of this area above the level of hydrocarbon preservation although maturities within the dry gas window are retained locally

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

recent bright gully deposits on mars wet or dry flow bright gully sediments attributed to liquid water flow have been deposited on mars within the past several years to test the liquid water flow hypothesis we constructed a high resolution 1 m pixel photogrammetric digital elevation model of a crater in the centauri montes region where a bright gully deposit formed between 2001 and 2005 we conducted one dimensional 1 d and 2 d numerical flow modeling to test whether the deposit morphology is most consistent with liquid water or dry granular flow liquid water flow models that incorporate freezing can match the runout distance of the flow for certain freezing rates but fail to reconstruct the distributary lobe morphology of the distal end of the deposit dry granular flow models can match both the observed runout distance and the distal morphology wet debris flows with high sediment concentrations are also consistent with the observed morphology because their rheologies are often similar to that of dry granular flows as such the presence of liquid water in this flow event cannot be ruled out but the available evidence is consistent with dry landsliding

metastability of liquid water on mars abstract a simple model of local heat transport on mars demonstrates that transient melting of ice may occur in depressions and gullies nearly anywhere on the planet where thin ice is illuminated by normal incidence insolation an experiment has been performed to confirm the model of evaporation rate at low pressure reduction of radiative cooling due to gully geometry is shown to be important since appropriate meteorological topographic and optical conditions may occur on slopes nearly anywhere on the planet hydrological features such as gullies would likely form only where such ice might accumulate notably in sheltered locations at high latitudes it is suggested that cold trapping of winter condensation could concentrate a sufficient amount of ice to allow seasonal melting in gullies

audiomagnetotelluric profiling on the volcano stromboli internal structure and mechanism of the strombolian activity abstract the audiomagnetotelluric profiling method has found exceptional utility in detecting anomalies of shallow resistivities associated with intrusive dikes and active lava channels on stromboli volcano using a computerized finite element method it has been shown that the important lateral contrast of the measured apparent resistivity along different profiles represents realistic situations of vertical conductive structures buried in the volcanic grounds self potential measurements and field observations have suggested that the conductive bodies are present at shallow depth a good knowledge of the lateral extent of these hot active zones has provided insights into the upper internal structure of the volcano the elongated zones between two large low resistivity structures in the south and the craters in the northwest deepen from the southeast to the northwest this geometrical layout strongly suggests an explanation of the strombolian eruptions in which the flow of lava temporarily blocks part of the path of the gases the plug of lava cools and the increase in pressure of the gases once it becomes greater than the resistance of viscosity ejects the mass of lava which shatters on leaving the vent and gives rise to the well known effect of well collimated jets of gases loaded with hot spatter and scoria which is characteristic of strombolian activity

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

geologic settings of martian gullies implications for their origins 1 martian gullies are found on steep slopes of all origins on all sorts of terrains of all ages scattered across nearly all of mars gullies are observed on all manner of substrates layered massive shattered rubble with or without nearby mantling deposits gullies are most common in the southern midlatitudes but also occur in the northern hemisphere in near polar terrain on equatorial volcanoes and on northern plains most gullies in the southern hemisphere are on south facing slopes but they occur on slopes of all orientations gullies are among the youngest features on mars but locally are overlain by eolian deposits and cut by faults old or eroded gullies are rare and those found have been partially stripped from slopes leaving no rock debris behind most gully deposits contain no detectable rocks these data are inconsistent with published hypotheses of gully formation including seeps and breakouts of water or brine hydrothermal activity cryovolcanism and breakouts from liquid carbon dioxide the data are consistent with gullies being dry flows of eolian material dust and silt comparable to climax snow avalanches on earth eolian sedimentation should be correlated little with underlying geology cause of slope age of terrain type of terrain or the nature of the rocks eolian sedimentation should be correlated with wind deceleration which will cause suspended sediment to drop and areas with common gullies are those with strong wind deceleration predicted by global circulation model in such areas sediment will be deposited preferentially in the lee of obstacles for the gully rich areas of the southern midlatitudes winds blow from the nnw so that sediment is deposited on sse facing slopes i e poleward these predictions are in accord with observations