planetary surface dating from crater size frequency distribution measurements partial resurfacing events and statistical age uncertainty abstract we describe the procedure to fit a cumulative production function polynomial to a partial crater size frequency distribution the technique is of particular use in deriving ages for surfaces which have undergone partial resurfacing events namely erosional or depositional events which have affected a limited diameter range of the crater population we demonstrate its use in obtaining times for both the surface formation and the resurfacing event we give a practical outline of the method for making age measurements from crater counts and how to identify resurfacing effects in the results we discuss the conversion of production function polynomials between common presentations and the statistical uncertainty of the determined ages with respect to the non linear chronology function and a minor refinement of data binning

ascent velocity and dynamics of the fiumicino mud eruption rome italy author s vona a giordano g de benedetti aa d ambrosio r romano c manga m abstract 2015 american geophysical union all rights reserved in august 2013 drilling triggered the eruption of mud near the international airport of fiumicino rome italy we monitored the evolution of the eruption and collected samples for laboratory characterization of physicochemical and rheological properties over time muds show a progressive dilution with water the rheology is typical of pseudoplastic fluids with a small yield stress that decreases as mud density decreases the eruption while not naturally triggered shares several similarities with natural mud volcanoes including mud componentry grain size distribution gas discharge and mud rheology we use the size of large ballistic fragments ejected from the vent along with mud rheology to compute a minimum ascent velocity of the mud computed values are consistent with in situ measurements of gas phase velocities confirming that the stratigraphic record of mud eruptions can be quantitatively used to infer eruption history and ascent rates and hence to assess or reassess mud eruption hazards

deflection of dykes into sills at discontinuities and magma chamber formation abstract many rift zones contain composite volcanoes central volcanoes most of which are supplied with magma from shallow crustal magma chambers volcanotectonic studies of eroded rift zones such as in iceland as well as geophysical studies indicate that many shallow magma chambers evolve from sills here i provide field description of sills and extinct magma chambers in the quaternary and tertiary palaeorift zones of iceland focusing on the felsic pluton of slaufrudalur southeast iceland as a fine example of a magma chamber developed through the injection of sills in this paper i review analyse and develop further two related mechanisms for the deflection of dykes into sills and thus the potential initiation of a magma chamber namely a cook gordon debounding delamination and b stress barriers and propose a third mechanism c favourable material toughness ratios due to elastic mismatch difference in young s moduli or stiffnesses of layers in contact in the cook gordon mechanism a weak contact opens up as a result of dyke induced tensile stress this mechanism is likely to operate primarily at shallow depths as is supported by field observations and numerical models a stress barrier is a layer where the local stress is unfavourable to a particular type of rock fracture here a dyke field observations and numerical models show that on meeting a stress barrier a dyke either changes into a sill or becomes arrested the material toughness mechanism indicates that when the upper layer at a contact has the same or less stiffness than the lower layer hosting the dyke there is little tendency for the dyke to become deflected into the contact however when the upper layer is stiffer such as when a stiff basaltic lava flow is on the top of a soft pyroclastic layer the dyke tends to become deflected into the contact to form a sill field results suggest that all these mechanisms may cause dyke deflection into sills and may operate together particularly where the rock consists of alternating soft and stiff layers since the quaternary lava pile in iceland has many more soft hyaloclastite layers than the tertiary lava pile these mechanisms were probably very efficient in generating sills and by implication shallow magma chambers during the quaternary this may be one reason why in comparison with the tertiary lava pile the quaternary lava pile contains so many sills and extinct plutons and active shallow magma chambers

estimation of shape factor and depth from gravity anomalies due to some simple sources the gravity anomalies over some simple geometry sources have been inverted to compute the shape factor and depth using a hybrid algorithm involving simulated annealing followed by non linear curve fitting the shape factors for a point an infinite horizontal line and a semi infinite vertical line source are 1 5 1 0 and 0 5 respectively a procedure to determine the depth and the horizontal or vertical extent of a line source has been developed a ribbon of finite vertical extent is characterized by a shape factor varying between 0 1 and 1 0 a symmetrical syncline can be distinguished from an anticline on the basis of the shape factor as this assumes values greater than 1 0 for a syncline and less than 1 0 for an anticline interpretation schemes are presented to compute the depth to the horizontal base and its radius for models of a 2d dome and a 2d depression the efficiency and potential of the proposed technique has been evaluated by applying it to three published field examples a chromite anomaly in cuba the mobrun orebody and the louga anomaly

a new concept in euler deconvolution of isolated gravity anomalies euler s homogeneity equation has been used to develop a new technique to interpret the gravity anomalies over some simple geometrical sources namely a finite horizontal line vertical line a finite vertical ribbon a semicircular dome basin and an isosceles triangle approximating an anticline syncline a linear over determined system of equations has been solved to compute the depth the horizontal location and the structural index all treated as free parameters the concept of a variable structural index provides better depth estimates and helps to identify the source geometry nomograms have been prepared to compute an additional model parameter namely the horizontal vertical extent of a line the vertical extent of a ribbon and the radius of a dome basin the efficacy of the proposed method has been evaluated using two real field examples

evidence for and implications of sedimentary diapirism and mud volcanism in the southern utopia highland lowland boundary plain mars abstract several types of spatially associated landforms in the southern utopia planitia highland lowland boundary hlb plain appear to have resulted from localized geologic activity including 1 fractured rises 2 elliptical mounds 3 pitted cones with emanating lobate materials and 4 isolated and coalesced cavi depressions stratigraphic analysis indicates these features are hesperian or younger and may be associated with resurfacing that preferentially destroyed smaller 8 km diameter impact craters based on landform geomorphologies and spatial distributions the documented features do not appear to be specifically related to igneous or periglacial processes or the back wasting and erosion of the hlb scarp we propose that these features are genetically related to and formed by sedimentary mud diapirs that ascended from zones of regionally confined poorly consolidated and mechanically weak material we note morphologic similarities between the mounds and pitted cones of the southern utopia boundary plain and terrestrial mud volcanoes in the absheron peninsula azerbaijan these analogs provide a context for understanding the geological environments and processes that supported mud diapir related modification of the hlb in southern utopia mud diapirs near the elysium volcanic edifice may have resulted in laccolith like intrusions that produced the fractured rises while in the central boundary plain mud diapirs could have extruded to form pitted cones mounds and lobate flows perhaps related to compressional stresses that account for wrinkle ridges the removal of material a few kilometers deep by diapiric processes may have resulted in subsidence and deformation of surface materials to form widespread cavi collectively these inferences suggest that sedimentary diapirism and mud volcanism as well as related surface deformations could have been the dominant hesperian mechanisms that altered the regional boundary plain we discuss a model in which detritus would have accumulated thickly in the annular spaces between impact generated structural rings of utopia basin we envision that these materials and perhaps buried ejecta of utopia basin contained volatile rich low density material that could provide the source material for the postulated sedimentary diapirs thick water rich low density sediments buried elsewhere along the hlb and within the lowland plains may account for similar landforms and resurfacing histories

localization of volcanic activity topographic effects on dike propagation eruption and conduit formation magma flow in a dike rising in a crack whose strike runs from a highland or a ridge to an adjacent lowland has been modeled to determine the effect of topography on the flow it is found that there is a distinct tendency for the flow to be diverted away from the highland end of the strike toward the lowland separation of the geometric effect of the topography from its effect on lateral confining stresses on the crack indicates that both contribute to the effect but that the effect of stress is less important although this analysis explains a tendency for volcanic eruptions to occur in low lands it does not preclude eruptions on highlands the particular configuration modeled mimics topography around the proposed nuclear waste repository at yucca mountain nevada so that the results may indicate some reduction in the volcanic hazard to the site

a numerical model of dyke propagation in layered elastic media summary we develop a mathematical model describing dyke propagation in proximity of an elastic discontinuity of the embedding medium the dyke is modelled as a fluid filled crack in plane strain configuration employing the boundary element method the pressure gradient along the crack is assumed proportional to the difference between the densities of the host rock and the fluid mass conservation is imposed during propagation and fluid compressibility is taken into account the path followed by the crack is found by maximizing the total energy release given by the sum of the elastic and gravitational contributions the mathematical simulations provide a sort of refraction phenomenon that is a sudden change in the direction of propagation when the crack crosses the boundary separating different rigidities if the dyke enters a softer medium its path deviates towards the vertical if the dyke enters a harder medium its path deviates away from the vertical and may even become arrested as a horizontal sill along the interface if the rigidity contrast is large gravitational energy plays a major role during propagation in particular in proximity of layer boundaries this role is enhanced by the shift of the centre of mass due to changes of dyke shape mathematical results were validated by laboratory experiments performed injecting tilted air filled cracks through gelatin layers with different rigidities

catastrophic flood sediments in chryse basin mars and quincy basin washington application of sandar facies model viking visible and thermal infrared observations and terrestrial catastrophic flood deposits provide clues to identify the outflow channel sediments that went into chryse basin on mars on earth sandar outwash plains formed by coalescence of many jokulhlaup floods are described in terms of three laterally adjacent facies proximal midfan and distal the missoula flood sediments deposited in quincy basin washington comprise a miniature analog of chryse basin the terminology and general characteristics of the sandar facies model are applied to quincy basin although the depositional environment and clast sizes are somewhat different higher energy flood larger clasts subaqueous rather than subaerial deposition for example the ephrata fan a deposit of boulders cobbles and pebbles forms the midfan facies analog a downfan sandy deposit reworked into a dune field comprises the distal facies analog in chryse basin the midfan is defined by a heterogeneous rocky 0 25 intermediate albedo 0 21 0 26 intermediate thermal inertia 260 460 j m 2 s 0 5 k 1 surface while the distal facies has a low albedo 0 14 0 16 and higher thermal inertia 340 700 j m 2 s 0 5 k 1 the chryse midfan unit has rocks and windblown dust exposed at the surface the sand of the distal facies in chryse acidalia is reworked by the wind as in quincy basin the viking 1 and mars pathfinder landing sites are located on the midfan unit observations that can be made at the mars pathfinder site might help in reevaluating whether or not viking 1 landed on outflow channel sediments

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

submersible study of mud volcanoes seaward of the barbados accretionary wedge sedimentology structure and rheology abstract in 1992 the nautile went to a mud volcano field located east of the barbados accretionary wedge near 13 50n using nannofossil analysis on cores we determined the sedimentation rate and provided a new estimation of the age of the mud volcanoes 750 000 years for the oldest one six structures have been explored with the submersible nautile and manifestations of fluid venting chimneys carbonate cementation and chemosynthetic communities were observed on all sedimentological analysis identifies two sources of diapiric mud most mud volcanoes expel mud containing late miocene to quaternary faunae that have the same composition as sediments drilled above the barbados wedge decollement one volcano also contains older oligocene taxa with a mud composition corresponding to the sedimentary sequence below the decollement we use diving observations to map the fine scale morphology the distribution of chemosynthetic fauna and define two end member types of structures mud pies flat topped mud volcanoes and conical mounds mud pies atalante and cyclops are characterised by the presence of a lake of highporosity mud 70 to 75 in their central parts chemosynthetic benthic communities calyptogena colonies and sponge bushes are concentrated in the outer parts contrasting morphologies of the two mud pies indicate different stages of activity cyclops is growing whereas atalante is collapsing expulsion of water and methane occurs mostly through the mud lake and may be stronger during the collapse phase on conical mounds there are no mud lakes fluid venting concentrates near the summit and occurs through carbonate cemented chimneys which form within the sediment viscosity measurements have been carried out on mud samples from the two mud pies and one conical mound all mud samples have a plastic fluid behaviour the plastic threshold decreases with porosity and thixotropy is observed for a porosity of more than 70 an analogue experiment shows that for this thixotropic mud shearing in the feeding conduit liquefies the mud which then spreads to form a mud pie conical mounds form when the mud remains plastic we show that the dissociation of methane hydrate is the cause of the high porosity in mud pies and confirm that these structures are a consequence of large scale dissociation of methane hydrate at the base of its stability field dissociation of hydrates before and during ascent is only slightly contributing to the pore fluid in conical mounds but solid hydrates still present in the mud may contribute to its buoyancy

flexure and faulting of sedimentary host rocks during growth of igneous domes henry mountains utah abstract a sequence of sedimentary rocks about 4 km thick was bent stretched and uplifted during the growth of three igneous domes in the southern henry mountains mount holmes mount ellsworth and mount hillers are all about 12 km in diameter but the amplitudes of their domes are about 1 2 1 85 and 3 0 km respectively these mountains record successive stages in the inflation of near surface diorite intrusions that are probably laccolithic in origin the host rocks deformed along networks of outcrop scale faults or deformation bands marked by crushed grains consolidation of the porous sandstone and small displacements of sedimentary beds zones of deformation bands oriented parallel to the beds and formation contacts subdivided the overburden into thin mechanical layers that slipped over one another during doming measurements of outcrop scale fault populations at the three mountains reveal a network of faults that strikes at high angles to sedimentary beds which themselves strike tangentially about the domes these faults have normal and reverse components of slip that accommodated bending and stretching strains within the strata an early stage of this deformation is displayed at mount holmes where states of stress computed from three fault samples correlate with the theoretical distribution of stresses resulting from bending of thin circular elastic plates field observations and analysis of frictional driving stresses acting on horizontal planes above an opening mode dislocation as well as the paleostress analysis of faulting indicate that bedding plane slip and layer flexure were important components of the early deformation as the amplitude of doming increased radial and circumferential stretching of the strata and rotation of the older faults in the steepening limbs of the domes increased the complexity of the fault patterns steeply dipping map scale faults with dip slip displacements indicate a late stage jostling of major blocks over the central magma chamber radial dikes pierced the dome and accommodated some of the circumferential stretching

volcanic rilles streamlined islands and the origin of outflow channels on mars 1 the widely accepted view that catastrophic flow of liquid water was the dominant process involved in formation of outflow channels on mars has as part of its foundation the assumption that the flow of lava could not have formed martian features such as streamlined islands and anastamosing channels however lunar and venusian channels believed to have formed through volcanic processes in the absence of water are indeed associated with such features additionally many lunar and venusian rilles head at topographic depressions a common characteristic of martian outflow channels lunar rilles typically lack positive relief accumulations of volcanic deposits at their mouths suggesting that contrary to previous assertions absence of such accumulations at the mouths of martian outflow channels is not incompatible with a common mode of formation consistent with an igneous origin for outflow channels and certain valley systems on mars volcanic processes can produce a wide range of landforms that are similar to those normally associated with the flow of water including channel terraces and complex channel networks the simplest interpretation of martian channels that extend from volcanic source regions onto volcanic plains is as conduits formed by the flow of lava channel formation hypotheses requiring major changes in martian atmospheric properties or repeated catastrophic flow of water from volcanic features appear needlessly exotic alongside the igneous hypothesis for channel formation in light of these points future investigations of martian outflow channels should more actively consider volcanic processes as candidate mechanisms for channel formation

morphologies of rocks within and near the rock garden at the mars pathfinder landing site this paper considers the morphology of several rocks and rock fragments within and near the rock garden at the mars pathfinder landing site we have analyzed stereo images taken both by the lander imp camera and by the rover forward cameras the rocks were found to differ in their roundness angularity and in their densities of millimeter to centimter sized pits and flute like features on the rock facets no correlation between rock roundness and the degree of rock pitting was found indicating that rounding and pitting formed by different processes pits are either gas bubbles implying the rocks are volcanic or resulted from eolian abrasion deflation putting no constraints on the nature of the rocks or both if pits are of eolian origin variations in the density of pits on different rocks imply that either the rock surfaces have been exposed for different times or the susceptibility of different rocks to pitting varies significantly from rock to rock implying differences in composition and or lithology the densities of pits and flutes on the rocks show anti correlation this may be connected to their formation but probably is mostly related to issues of observation and definition of what is a pit and what is a flute flute like features may be a result of eolian abrasion but in this case the spatial closeness of fluted rocks and those having delicately pitted textures requires explanation other mechanisms producing flute like features such as collisions in the deposit forming flows and the breaking of rock in impact cratering should not be ignored our observations agree with the conclusion of golombek et al this issue that deflational exhumation in this area was minor the observed relatively large rocks typically do not show a concentration of small rock fragments at their feet this implies diurnal thermal cycles are very ineffective at destructing rocks the rock half dome may be a conglomerate as suggested by smith et al 1997a for this and several other rocks but this hypothesis remains to be proven impact craters of a few meters to a few tens meters in diameter may have played a role in the local geology

hydrovolcanic tuff rings and cones as indicators for phreatomagmatic explosive eruptions on mars hydrovolcanism is a common natural phenomenon on earth and should be common on mars too since its surface shows widespread evidence for volcanism and near surface water we investigate fields of pitted cones in the nephentes amenthes region at the southernmargin of the ancient impact basin utopia which were previously interpreted as mud volcanoes the cone fields contain pitted and breached cones with associated outgoing flow like landforms based on stratigraphic relations we determined ahesperian or youngermodel age we test the hypothesis of a hydro volcanic origin based on a detailed morphological and morphometrical analysis and an analysis of the regional context an igneous volcanic origin of these cones as hydrovolcanic edifices produced by phreatomagmatic eruptions is plausible several lines of evidence suggest the existence of subsurface water ice the pitted cones display well developed wide central craters with floor elevations below the preeruptive surface their morphometry and the overall appearance are analogous to terrestrial tuff cones and tuff rings mounds that are also observed in the same region resemble terrestrial lava domes the hydrovolcanic interaction between ascending magma and subsurface water and or water ice may explain the formation of the pitted cones although other scenarios such as mud volcanism cannot be ruled out together with the mounds the cones might represent effusive and explosive edifices of amonogenetic volcanic field composed of lava domes tuff rings tuff cones and possibly maars

short note source geometry identification by simultaneous use of structural index and shape factor a cross plot of the shape factors and the structural indices determined from gravity anomalies over various idealized sources namely horizontal vertical lines and vertical ribbons with various strike lengths and depth extents forms a closed loop different segments of this loop termed the source geometry identification loop sgil correspond to different source geometries combined use of the structural index and the shape factor determined from an isolated gravity anomaly reduces the ambiguity in characterizing the source geometry a simulated example and three field examples namely a cuban chromite anomaly an indian example over manganese ore and a sulphide ore from quebec have been analysed by the proposed method in order to identify their respective source geometries

composition and flux of explosive gas release at lusi mud volcano east java indonesia the lusi mud volcano has been erupting since may 2006 in the densely populated sidoarjo regency east java indonesia forcing the evacuation of 40 000 people and destroying industry farmland and over 10 000 homes mud extrusion rates of 180 000 m 3 d 1 were measured in the first few months of the eruption decreasing to a loosely documented 4000 m for methane and approximately 600 m for carbon dioxide however the mass fractions of these gases are insufficient to explain the observed dynamics rather the primary driver of the cyclic bubble bursting activity is decompressional boiling of water which initiates a few tens of meters below the surface setting up slug flow in the upper conduit our measured gas flux and conceptual model lead to a corresponding upper bound estimate for the mud water mass flux of 10 5 m 3 d 1

formation of ice layers by infiltration and refreezing of meltwater melt layer frequency and magnitude in polar and sub polar ice cores have been interpreted as measures of past summer temperature and calibrations have been proposed relating frequency of occurrence of ice layers in ice cores to past summer temperatures but observations in the percolation facies in greenland and an analysis of the combined processes of meltwater infiltration and refreezing of water in snow indicate that in addition to unusually high rates of meltwater input formation of ice layers will also be facilitated by unusually cold initial conditions or early onset of melt uniform warming of both summer and winter conditions has the opposite effect and suppresses ice layer formation in favor of uniform wetting and refreezing of the snowpack numerical modeling of infiltration and refreezing at a stratigraphic fine to coarse transition allows quantification of the effects of significant parameters initial temperature grain size and density contrast across the stratigraphic transition water input rate and minimum impermeable layer thickness calculations are made to distinguish threshold values of parameters at which infiltration progresses faster than refreezing resulting in a break through of water across the stratigraphic transition from values leading to the formation of an ice layer when refreezing progresses faster than infiltration

reconciling different equations for proton conduction using the meyer neldel compensation rule 1 proton conduction in nominally anhydrous minerals is the likely explanation for moderate values of electrical resistivity observed in the lithospheric and sublithospheric mantle however results from the various laboratories making the controlled measurements on mantle minerals predominantly olivine are not in agreement with one another importantly the groups use different formalisms to fit their experimental data in this paper we show that neither of the two formalisms employed by the various laboratories is consistent with the meyer neldel rule mnr or compensation law by which the preexponent term of the arrhenian equation is linearly related to the activation energy term we also demonstrate why the formalism of karato and colleagues can be used at low water contents 100 wt ppm and below whereas at higher water contents above 300 wt ppm the formalism of yoshino s and poe s labs needs to be employed a new mnr self consistent formalism is presented that is applicable over all water contents mnr consistency appears to operate for most processes that can be described by an arrhenius equation so its adoption through an mnr consistent formalism is highly recommended when fitting experimental observations

dynamics of a fluid flow on mars lava or mud a distinctive flow deposit southwest of cerberus fossae on mars is analyzed the flow source is a similar to 20 m deep similar to 12 x 1 5 km wide depression within a yardang associated with the medusae fossae formation the flow traveled for similar to 40 km following topographic lows to leave a deposit on average 3 4 km wide the surface morphology of the deposit suggests that it was produced by the emplacement of a fluid flowing in a laminar fashion and possessing a finite yield strength we use topographic data from a digital elevation model dem to model the dynamics of the motion and infer that the fluid had a bingham rheology with a plastic viscosity of similar to 1 pa s and a yield strength of similar to 185 pa although the low viscosity is consistent with the properties of komatiite like lava the combination of values of viscosity and yield strength as well as the surface morphology of the flow suggests that this was a mud flow comparison with published experimental data implies a solids content close to 60 by volume and a grain size dominated by silt size particles comparison of the similar to 1 5 km 3 deposit volume with the similar to 0 03 km 3 volume of the source depression implies that similar to 98 of the flow material was derived from depth in the crust there are similarities between the deposit studied here which we infer to be mud and other flow deposits on mars currently widely held to be lavas this suggests that a re appraisal of many of these deposits is now in order

the sieve lobe paradigm observations of active deposition sieve deposits were once considered to be one of the building blocks in alluvial fan stratigraphy later reinterpretation of sieve lobes as debris flow deposits favored because no visual records of active sieve deposition had been reported undermined their significance divided opinions and left this issue unresolved here i document active deposition of sieve lobes in natural settings in support of the original model sieve deposition can easily occur in natural settings such as proglacial outwash fans small arid alluvial fans or perennial streams when there is a scarcity of fine material significant bedload high slope permeable ground and discharges moderate enough to allow infiltration the only hydrodynamic requirement for sieve deposition is a high rate of water loss promoted by permeable bed sediments under some circumstances alluvial fans can be built almost entirely of sieve deposits as shown here one effect of the rapid extraction of water is the creation of sigmoidal fan profiles a gradation from sieve deposition to sheetflood occurs if sediment becomes progressively less permeable or if water flow increases overcoming bed permeability sieve deposition is a universal depositional process based simply on infiltration and it explains matrix poor clast supported gravels while alternative hypotheses such as matrix winnowing of debris flows used to dispute the sieve model still need to be proven by observations in nature

fluid expulsion in terrestrial sedimentary basins a process providing potential analogs for giant polygons and mounds in the martian lowlands abstract on earth burial of fine grained sediments in offshore passive margins e g underwater fans and deltas commonly results in fluid expulsion features including large scale polygonal fractures mud volcanoes and pockmarks comparison of resulting offshore polygons and mud volcanoes with giant polygons and high albedo mounds in the chryse acidalia region of mars shows the terrestrial and martian features to be similar in size morphology geologic context and general co occurrence within the same basin these similarities suggest that the process of terrestrial fluid expulsion may provide an analog that could link the giant polygons and mounds in chryse and acidalia to a single process moreover while the terrestrial offshore polygons and mud volcanoes commonly develop in the same basins these features do not necessarily occur in exactly the same locations within those basins as they are independent responses to compaction and dewatering thus the fluid expulsion analog does not require that the martian giant polygons and mounds have identical distributions this is the situation in chryse and acidalia where the giant polygons and mounds are extensively developed and generally have overlapping distributions but where each set of features may occur in places without the other this fluid expulsion analog is enhanced by the fact that giant polygons and mounds in chryse and acidalia co occur in a regional sense and in a geologic setting that is consistent with a fluid expulsion model of formation implications of this analog may impact our view of the role of water in the depositional history of the martian lowlands

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

a unique volcanic field in tharsis mars pyroclastic cones as evidence for explosive eruptions based on theoretical grounds explosive basaltic volcanism should be common on mars yet the available morphological evidence is sparse we test this hypothesis by investigating a unique unnamed volcanic field north of the shield volcanoes biblis patera and ulysses patera on mars where we observe several small conical edifices and associated lava flows twenty nine volcanic cones are identified and the morphometry of many of these edifices is determined using established morphometric parameters such as basal width crater width height slope and their respective ratios their morphology morphometry and a comparison to terrestrial analogues suggest that they are martian equivalents of terrestrial pyroclastic cones the most common volcanoes on earth the cones are tentatively interpreted as monogenetic volcanoes according to absolute model age determinations they formed in the amazonian period our results indicate that these pyroclastic cones were formed by explosive activity the cone field is superposed on an old elevated window of fractured crust which survived flooding by younger lava flows it seems possible that a more explosive eruption style was common in the past and that wide spread effusive plain style volcanism in the late amazonian has buried much of its morphological evidence in tharsis

sedimentary history and mass flow structures of chryse and acidalia planitiae mars geologic mapping and crater counting in chryse and acidalia planitiae cap reveal five major sedimentary deposits of hesperian to early amazonian age including 1 a mass flow deposited during the early hesperian near deuteronilus mensae northeast of the map region that may have resulted from the carving of kasei valles 3000 km southwest of the exposed part of the deposit 2 knobby plains material consisting of channel likely from simud and tiu valles and possibly ares and shalbatana valles and mass wasting deposits in central and eastern cap 3 material largely from maja and ares valles emplaced in at least western and southern cap outcrops in southern chryse planitia developed thermokarst 4 a thin mass flow covering much of southern chryse planitia that emanated from simud and tiu valles and 5 a thick extensive perhaps 3500 km across mass flow deposit in central and northern cap derived from accumulation and backflow of the preceding thin mass flow or perhaps melting of polar deposits other possible deposits may not be recognizable owing to burial by younger materials or a lack of morphologic signature various associated landforms appear to be consistent with the mass flow interpretations including lobate and linear scarps along deposit edges fractures related to desiccation of thick sediments troughs and ridges near the edges of the deposit indicative of secondary mass movement and deformation pitted domes and fissure fed flows possibly formed by sedimentary mud eruptions and longitudinal channel grooves perhaps formed by roller vortices no convincing evidence for paleoshorelines or stagnant ice sheets is found in cap these findings suggest that mass flow and hyperconcentrated flooding may have been the predominant processes of outflow channel dissection in cap elsewhere in the northern plains similar landforms are prevalent the mass flow interpretation does not require either multiple episodes of extraordinarily high water discharge rates achieved by freeing huge volumes of water from the crust repetitive recycling of immense volumes of water into highland aquifers at the heads of chryse channels or profound climate change mars pathfinder will most likely land on and inspect the surface of the thin mass flow that originated from the canyons of simud and tiu valles

debris flow origin for the simud tiu deposit on mars a late hesperian smooth plains deposit on mars interpreted as a debris flow extends more than 2000 km from hydraotes chaos through simud and tiu valles and into chryse planitia the simud tiu deposit widens out to 1000 km and embays streamlined landforms and knobs made up of sedimentary and perhaps volcanic deposits that were carved by earlier channeling activity morphologic features of the simud tiu deposit observed in viking and pathfinder images are generally consistent with a debris flow origin but some of the deposit s salient features are not readily explained by catastrophic flooding or ice flow internal depressions appear to be bounded by linear scarps along flow margins where differential shearing may have occurred and in areas where flow spreading may have produced zones of extensional breakup and thinning within the flow possible flow lobes within the deposit may have formed by successive flow surges within the flow unit the pathfinder landing site is on the simud tiu deposit and the observations there are consistent with debris flow the low longitudinal ridges at the site may have formed by clast interactions as the flow ground to a halt imbricated planar rocks on the ridges such as in the rock garden also may have been emplaced by debris or ice flow however stream energy calculations at ares vallis and channel geology indicate that flooding probably was incapable of emplacing the meter size boulders observed at the pathfinder site dewatering of pressurized zones in the debris flow or underlying material may be responsible for mud eruptions that formed a couple of patches of low pancakelike shields up to 5 km in diameter and for probable water flows that formed two small rille channels a few kilometers long local irregular grooves may be cracks that resulted from later desiccation and contraction of the flow material the debris flow unit apparently coalesced from outflows of water fluidized debris originating from beneath chaotic and hummocky terrains within and along the margins of simud and tiu valles the deposit is onlapped from the north by another flow deposit originating from acidalia planitia if the simud tiu debris flow had entered a standing body of water a turbidity current may have arisen from the debris flow and then backflowed over the debris flow to account for the acidalia deposit

minimum effective area for high resolution crater counting of martian terrains the acquisition of high resolution imagery for the surface of mars has enabled mapping of spatially limited order of 200 m on four type terrains using mars reconnaissance orbiter mro context camera ctx imagery that span the noachian hesperian and amazonian epochs the counts from each location include a region covering 10 000 km2 ten 1000 km2 subsets of that larger area and approximately one hundred 100 km2 samples the data demonstrate significant variation in the crater size frequency and derived model ages across a single terrain type for the 100 km2 samples the crater size frequency at this area scale varies across a single uniform geologic unit by up to a factor of 2 3 on the four different terrains at 1000 km2 the local pattern variations that are relevant at the 100 km2 scale become less important and the age variations are tighter in all four terrain cases the 10 000 km2 and 1000 km2 samples capture distinct crater populations km sized craters that formed before and after resurfacing event s however due to the relatively high mean distance between km sized craters the 100 km2 size area samples more commonly than not exclude a statistically significant sample at the kilometer size range masking important information about the pre resurfacing history of the terrain we therefore suggest that due to the effect of pattern variability in cratering over 100 km2 and the susceptibility of smaller craters to resurfacing crater counts derived from small area samples are suspect to major uncertainties

insights into volcanic conduit flow from an open source numerical model 1 numerical models that calculate the fluid dynamics of explosive volcanic eruptions have been used with increasing frequency to understand volcanic processes and evaluate volcanic hazards yet those who develop such models rarely make them publicly available so that they can be verified used and possibly improved by other scientists in this paper i present a visual interactive open source numerical model that calculates steady state flow of magma and gas in vertical eruptive conduits and contains user friendly utilities for quickly determining physical thermodynamic and transport properties of silicate melts h2o gases and melt gas crystal mixtures the model represents an advance over previously published conduit models by incorporating a non arrhenian viscosity relation for hydrous silicate melts a relation between viscosity and volume fraction of gas that depends on capillary number and adiabatic temperature changes in the mixture using established thermodynamic relations for melts and h2o gas respectively volcanologists who have not had access to conduit models have frequently approximated conduit flow using an analytical equation for incompressible laminar newtonian pipe flow which predicts that the mass flux is proportional to the fourth power of conduit radius and inversely proportional to mixture viscosity the model presented here which is not much more difficult to use than a back of the envelope calculation shows that the pipe flow approximation significantly overestimates the sensitivity of mass flux to both conduit radius and mixture viscosity results from the model also show that viscous heating in the lower conduit which is not considered in most other models may increase the mass flux of large silicic eruptions by several percent and decrease the viscosity of the mixture at the fragmentation depth by a few tens of percent

bubble mobility in mud and magmatic volcanoes the rheology of particle laden fluids with a yield stress such as mud or crystal rich magmas controls the mobility of bubbles both the size needed to overcome the yield stress and their rise speed we experimentally measured the velocities of bubbles and rigid spheres in mud sampled from the davis schrimpf mud volcanoes adjacent to the salton sea southern california combined with previous measurements in the polymer gel carbopol we obtained an empirical model for the drag coefficient and bounded the conditions under which bubbles overcome the yield stress yield stresses typical of mud and basaltic magmas with sub mm particles can immobilize millimeter to centimeter sized bubbles at stromboli volcano italy a vertical yield stress gradient in the shallow conduit may immobilize bubbles with diameter

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