rare earth element enrichment in post variscan polymetallic vein systems of the harz mountains germany carbonate gangue in historically important post variscan polymetallic pb zn cu ag vein systems in the upper harz mountains has elevated rare earth element contents ree y 1500 340 ppm n 16 in bulk samples this enrichment is due to the occurrence of abundant micrometer sized synchysite inclusions in calcite identified via raman spectroscopy calcite bulk analyses have roof shaped paas normalized ree patterns with a eu peak but without ce or y anomalies and with a steeply dipping hree pattern microbeam analysis electron microprobe and la icpms identifies these patterns as dominated by synchysite ce nd with strong eu enrichment in the weight percent range and lree hree fractionation la lu 100 paas normalized the synchysite component in calcite gangue is detected in polymetallic veins all over the harz mountains which seems to be a diagnostic feature of the region and suggests a large scale mesozoic fluid system however the upper western harz systems with no fluorite have more elevated ree content compared with the lower eastern harz fluorite rich systems with less ree content carbonate gangue in the upper harz systems has homogeneous 87sr 86sri around 0 714 and endi of 9 while carbonate gangue in the lower harz systems has 87sr 86sri around 0 716 and endi of 2 to 5 fluorite in the lower harz mountains has strong positive y anomalies and variable eu anomalies at generally low ree abundances and no ree mineral inclusions both sr and nd isotope compositions in the fluorite are very variable and indicate an open system 87sr 86sri 0 710 0 718 endi 3 to 17 the synchysite mree enrichment in calcite gangue in the upper harz mountains compares favorably with carbonatite related lree dominated bastnasite from china and elsewhere and allows an interesting perspective as a by product of pb zn mining

usability of small impact craters on small surface areas in crater count dating analysing examples from the harmakhis vallis outflow channel mars abstract the availability of very high resolution images has made it possible to extend crater size frequency distribution studies to small deca hectometer scale craters this has enabled the dating of small and young surface units as well as recent short time and small scale geologic processes that have occurred on the units usually however the higher the spatial resolution of space images is the smaller area is covered by the images thus the use of single very high resolution images in crater count age determination may be debatable if the images do not cover the studied region entirely here we compare the crater count results for the floor of the harmakhis vallis outflow channel obtained from the images of the context camera ctx and high resolution imaging science experiment hirise aboard the mars reconnaissance orbiter mro the ctx images enable crater counts for entire units on the harmakhis vallis main valley whereas the coverage of the higher resolution hirise images is limited and thus the images can only be used to date small parts of the units our case study shows that the crater count data based on small impact craters and small surface areas mainly correspond with the crater count data based on larger craters and more extensive counting areas on the same unit if differences between the results were founded they could usually be explained by the regional geology usually these differences appeared when at least one cratering model age is missing from either of the crater datasets on the other hand we found only a few cases in which the cratering model ages were completely different we conclude that the crater counts using small impact craters on small counting areas provide useful information about the geological processes which have modified the surface however it is important to remember that all the crater counts results obtained from a specific counting area always primarily represent the results from the counting area not the whole unit on the other hand together with crater count results from extensive counting areas and lower resolution images crater counts on small counting areas but by using very high resolution images is a very valuable tool for obtaining unique additional information about the local processes on the surface units

possible pingo fields in the utopia basin mars geological and climatical implications abstract the presence of pingos on mars has been hypothesized since the period of the viking mission in fact a diverse range of pingo like features has been found at various martian sites including elysium chryse and utopia planitiae in the northern lowlands due to the morphology and the geological setting some of those features were interpreted in different ways creating some controversies as happened in athabasca valles this reflects the complexity of interpreting these features by remote sensing and multiple plausible interpretations of the same feature with the objective of identifying new possible pingos or rootless cones on mars we selected a study area in utopia planitia 10 55 n 210 260 w where the presence of both features is possible due to its geological history volcanic and hydrological we analyzed more than 2100 mars orbiter camera moc narrow angle images in addition to viking thermal emission imaging system themis and high resolution stereo camera hrsc images together with mars orbiter laser altimeter mola derived digital elevation models dems with a geographic information system gis we found in 94 moc narrow angle images dome cone and ring shaped features we analyzed them from morphological and morphometrical points of view in order to compare them with relevant features on mars and earth we tested different possible origins for those features following the approach of multiple working hypotheses we conclude that the dome cone and ring shaped features could be pingos which is in agreement with their geological settings regarding the driving heat source for the formation of the purported pingos we propose the existence of a heat source possibly a magma chamber underneath the surface of the utopia basin together with possible climatic shifts the past activities of the heat source may have caused melting of ground ice the pingo growth due to freezing of the water would have occurred during the following cold climatic conditions

chaos formation by sublimation of volatile rich substrate evidence from galaxias chaos mars abstract galaxias chaos deviates significantly from other chaotic regions due to the lack of associated outflow channels lack of big elevation differences between the chaos and the surrounding terrain and due to gradual trough formation a sequence of troughs in different stages is observed and examples of closed troughs within blocks suggest that the trough formation is governed by a local stress field rather than a regional stress field moreover geomorphic evidence suggests that galaxias chaos is capped by elysium lavas which superpose an unstable subsurface layer that causes chaotic tilting of blocks and trough formation based on regional mapping we suggest a formation model where vastitas borealis formation embedded between elysium lavas is the unstable subsurface material because gradual volatile loss causes shrinkage and differential substrate movement this process undermines the lava cap depressions form and gradually troughs develop producing a jigsaw puzzle of blocks due to trough coalescence observations of chaos west of elysium rise indicate that this process might have been widespread along the contact between vastitas borealis formation and elysium lavas however the chaotic regions have probably been superposed by elysium utopia flows to the nw of elysium rise and partly submerged with younger lavas to the west

possible sub glacial eruptions in the galaxias quadrangle mars we have identified several landforms in the galaxias quadrangle of mars mtm 35217 33 0 35 5 n 216 0 218 0 w which are consistent with this area having been covered by an ancient ice sheet concurrent with volcanic eruptions volcanic activity was initiated by the intrusion of several large dikes measuring 50 100 m wide and protruding up to 35 m above the present day surface these dikes appear to have originated from elysium planitia 600 km to the se in one instance a dike at an elevation of 3750 m appears to have produced a subglacial mound referred to here as galaxias mons 2 that evolved into an extrusive eruption and produced copious volumes of melt water that carved an outflow channel that extends almost 300 km to the north at a lower elevation 3980 m a second putative dike may have failed to break the surface of the ice sheet and formed galaxias mons as a laccolithic intrusion we numerically model the formation of galaxias mons and find that at least 200 m of ice may once have existed at this latitude at the time of the dike intrusions such a conclusion supports the idea that enigmatic small domes in the area may be pingoes collectively these observations suggest that the previous interpretations for the origin of near by hrad vallis as a sub aerial eruption may need to be revised

thermally distinct ejecta blankets from martian craters utilizing the termoskan data set of the phobos 88 mission we have recognized a new feature on mars ejecta blanket distinct in the thermal infrared edith virtually all of the more than 100 features discovered in the termoskan data are located on the plains near valles marineris ediths have a startlingly clear dependence upon terrains of hesperian age implying a spatial or temporal dependence on hesperian terrains almost no thermally distinct ejecta blankets are associated with any of the thousands of craters within the data set that occur on the older noachian units ediths also do not appear on the portions of the younger tharsis amazonian units seen in the data the hesperian terrain dependence cannot be explained by either atmospheric or impactor variations noachian and hesperian terrains must have experienced identical atmospheric and impactor conditions during hesperian times thermally distinct ejecta blankets therefore reflect target material differences and or secondary modification processes not all lobate ejecta blankets are thermally distinct but all ediths correlated with visibly discernible ejecta blankets are associated with lobate ejecta blankets the boundaries of the thermally distinct areas usually follow closely the termini of the fluidized lobate ejecta blankets even when the ejecta blankets show a high degree of sinuosity thus the thermally distinct nature of ediths must be due to the primary ejecta formation process the coupling of these thermal anomalies to morphology is unlike most sharp martian inertia variations which are decoupled from observed surface morphology some thermally distinct ejecta blankets occur near otherwise similar craters that do not have thermally distinct ejecta blankets thus wind patterns or locally available aeolian material cannot provide a single overall explanation for the observed variations we compiled a data base of 110 edith and non edith craters ranging in diameter from 4 2 km to 90 6 km there are almost no correlations within the data base other than occurrence on hesperian terrains we postulate that most of the observed ediths are due to excavation of thermally distinctive noachian age material from beneath a relatively thin layer of younger more consolidated hesperian volcanic material the plausibility of this theory is supported by much geological evidence for relatively thin near surface hesperian deposits overlying massive noachian megabreccias on the edith rich plains units we suggest that absence of thermally distinct ejecta blankets on noachian and amazonian terrains is due to absences of distinctive near surface layering thermally distinct ejecta blankets are excellent locations for future landers and remote sensing because of relatively dust free surface exposures of material excavated from depth

morphology and composition of the surface of mars mars odyssey themis results the thermal emission imaging system themis on mars odyssey has produced infrared to visible wavelength images of the martian surface that show lithologically distinct layers with variable thickness implying temporal changes in the processes or environments during or after their formation kilometer scale exposures of bedrock are observed elsewhere airfall dust completely mantles the surface over thousands of square kilometers mars has compositional variations at 100 meter scales for example an exposure of olivine rich basalt in the walls of ganges chasma thermally distinct ejecta facies occur around some craters with variations associated with crater age polar observations have identified temporal patches of water frost in the north polar cap no thermal signatures associated with endogenic heat sources have been identified

thermally distinct craters near hrad vallis elysium planitia mars abstract evidence of volcano ground ice interactions on mars can provide important constraints on the timing and distribution of martian volcanic processes and climate characteristics northwest of the elysium rise is hrad vallis a 370 m deep 800 km long sinuous valley that begins in a source region at 34 n 218 w flanking both sides of the source region is a lobate deposit that extends 50 km perpendicular from the source and is an average of 40 m thick previous studies have suggested the formation of the hrad vallis source region was the result of explosive magma ice interaction and that the lobate deposit is a mudflow here we use newly available mola moc and themis data to investigate the evidence supporting this hypothesis within the lobate deposit we have identified 12 craters with thermal infrared signatures and morphologies that are distinct from any other craters or depressions in the region the thermally distinct craters are distinguished by their cool interiors surrounded by warm ejecta in the nighttime themis ir data and warm interiors surrounded by cool ejecta in the daytime themis ir data the craters are typically 1100 1800 m in diameter one crater is 2300 m across and 30 40 m deep but may be up to 70 m the craters are typically circular and have central depressions several with interior dune fill surrounded by 1 to 6 concentric fracture sets the distribution of the craters and their morphology suggests that they are likely the result of the interaction between a hot mudflow and ground ice

episodes of aqueous flooding and effusive volcanism associated with hrad vallis mars nasa planetary geology and geophysics program nasa planetary science division nnx13ar14g 80nssc17k0307 nasa earth and space sciences fellowship nessf program nnx16ap09h

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

lahars in the elysium region of mars photogeological studies of the elysium volcanic province mars show that its sinuous channels are part of a large deposit that was probably emplaced as a series of huge lahars some flows extend 1000 km from their sources the deposits are thought to be lahars on the basis of evidence that they were 1 gravity driven mass flow deposits lobate outlines steep snouts smooth medial channels and rough lateral deposits deposits narrow and widen in accord with topography and extend downslope 2 wet channeled surfaces draining features and 3 associated with volcanism the deposits and channels extend from a system of fractures which also fed lava flows heat associated with magmatism probably melted ground ice below the elysium volcanoes and formed a muddy slurry that issued out of regional fractures and spread over the adjoining plain the identification of these lahars adds to the evidence that mars has a substantial volatile element endowment

phreatomagmatic explosive origin of hrad vallis mars 1 hrad vallis is a 370 m deep 800 km long depression located at 34 n 218 w in elysium planitia mars a distinctive deposit present on both sides of the source area of hrad vallis has a maximum width of 70 km along the strike of the depression a lower unit extends for nearly 100 km away from the depression on either side and an upper unit extends for 50 km viking and mars orbiter camera moc images show lobate deposit boundaries rheomorphic deformation and numerous craters 270 580 m in diameter within the deposit the deposit coincides with a broad topographic rise 30 km wide and 100 150 m high extending along the sides of the valley for at least 100 km along strike we propose that these features formed when a dike underlying the axis of the valley generated a shallow sill which in turn is partly responsible for the rise topography the remainder of the rise consists of a mud like deposit of ejecta from a large scale phreatomagmatic explosion due to violent mechanical and thermal mixing between the central part of the sill and ice rich rock layers in the upper few hundred meters of the crust in a fuel coolant type interaction the observed range and thickness of ejecta and the depth of the hrad depression imply explosion steam pressures up to 360 mpa ejecta speeds of 400 m s 1 and a sill at least 150 m thick intruded at a depth of 350 400 m below the original surface

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

widespread crater related pitted materials on mars further evidence for the role of target volatiles during the impact process abstract recently acquired high resolution images of martian impact craters provide further evidence for the interaction between subsurface volatiles and the impact cratering process a densely pitted crater related unit has been identified in images of 204 craters from the mars reconnaissance orbiter this sample of craters are nearly equally distributed between the two hemispheres spanning from 53 s to 62 n latitude they range in diameter from 1 to 150 km and are found at elevations between 5 5 to 5 2 km relative to the martian datum the pits are polygonal to quasi circular depressions that often occur in dense clusters and range in size from 10 m to as large as 3 km pit sizes scale with both the host crater s diameter and the host deposit size these pits have subtle raised rims and unlike primary and secondary impact craters they lack well defined ejecta deposits and overlapping stratigraphic relationships they also lack any sign of any preferential alignment expected of volcanic or tectonic collapse features morphologic and stratigraphic evidence in support of an impact origin includes the observation that pitted materials primarily occur as ponded and flow like deposits on crater floors behind terraces and infilling the lowest local topographic depressions atop the ejecta blanket similar to the distribution of impact melt bearing bodies on the moon based on the observations and comparisons to terrestrial and lunar analogs we conclude that the pit bearing materials are impactite deposits the presence of these deposits in older craters where preserved suggests that they have formed on mars throughout most of its geologic history thus understanding their origin may help to constrain the hydrological and climate history of mars

formation erosion and exposure of early amazonian dikes dike swarms and possible subglacial eruptions in the elysium rise utopia basin region mars hundreds of narrow linear ridge segments are found in the transition zone between the elysium rise and the utopia basin occurring as both single and multiple ridges the ridges are distinctive because of their very linear steep sided nature their often sharp ridge crest which sometimes is fractured their association with stubby flows their continuity over long distances and their cross cutting of different terrain the linear ridges are interpreted to be single dikes and dike swarms either emplaced as normal dikes or as dikes emplaced subglacially feeding an explosive or effusive eruption five dike swarms are identified having lengths ranging from 10 45 km and being between 1 7 km wide while single ridges are up to 20 km long and 100 500 m wide in the areas of dike swarms crustal dilatation is estimated to vary from 15 60 dikes emplaced en echelon suggest that variations in the local stress field caused rotation during dike emplacement and dikes crosscutting flow units imply that dike emplacement can account for some of the observed linear fractures in the area the ridges both modify and constrain early amazonian flows and flood plain deposits suggesting intense dike emplacement in the early amazonian the association with different stages of inverted craters as well as some features of ice related origin possible ice cauldron and tindar like features indicate that the dikes may have been exposed due to eolian erosion and loss of volatile rich units subsequent to their emplacement

geological geomechanical and geostatistical assessment of rockfall hazard in san quirico village abruzzo italy abstract this paper describes the results of a rockfall hazard assessment for the village of san quirico abruzzo region italy based on an engineering geological model after the collection of geological geomechanical and geomorphological data the rockfall hazard assessment was performed based on two separate approaches i simulation of detachment of rock blocks and their downhill movement using a gis and ii application of geostatistical techniques to the analysis of georeferenced observations of previously fallen blocks in order to assess the probability of arrival of blocks due to potential future collapses the results show that the trajectographic analysis is significantly influenced by the input parameters with particular reference to the coefficients of restitution values in order to solve this problem the model was calibrated based on repeated field observations the geostatistical approach is useful because it gives the best estimation of point source phenomena such as rockfalls however the sensitivity of results to basic assumptions e g assessment of variograms and choice of a threshold value may be problematic consequently interpolations derived from different variograms have been used and compared among them hence those showing the lowest errors were adopted the data sets which were statistically analysed are relevant to both kinetic energy and surveyed rock blocks in the accumulation area the obtained maps highlight areas susceptible to rock block arrivals and show that the area accommodating the new settlement of s quirico village has the highest level of hazard according to both probabilistic and deterministic methods

modification history of the harmakhis vallis outflow channel mars based on ctx scale photogeologic mapping and crater count dating abstract harmakhis vallis is one of the four major outflow channel systems dao niger harmakhis and reull valles that cut the eastern rim region of the hellas basin the largest well preserved impact structure on mars the structure of harmakhis vallis and the volume of its head depression as well as earlier dating studies of the region suggest that the outflow channel formed in the hesperian period by collapsing when a large amount of subsurface fluid was released thus harmakhis vallis as well as the other nearby outflow channels represents a significant stage of the fluvial activity in the regional history on the other hand the outflow channel lies in the martian mid latitude zone where there are several geomorphologic indicators of past and possibly also contemporary ground ice the floor of harmakhis also displays evidence of a later stage ice related activity as the outflow channel has been covered by lineated valley fill deposits and debris apron material the eastern rim region of the hellas impact basin has been the subject of numerous geologic mapping studies at various scales and based on different imaging data sets however harmakhis vallis itself has received less attention and the studies on the outflow channel have focused only on limited parts of the outflow channel or on separated different geologic events in this work the harmakhis vallis floor is mapped and dated from the head depression to the beginning of the terminus based on the mars reconnaissance orbiter s context camera images ctx 6 m pixel our results show that harmakhis vallis has been modified by several processes after its formation age determinations on the small uncovered parts of the outflow channel which possibly represent the original floor of harmakhis imply that harmakhis may have experienced fluvial activity only 780 850 400 600 ma ago the discovered terrace structure instead shows that the on surface activity of the outflow channel has been periodic the most significant of the modification processes on harmakhis vallis has been the formation of lineated valley fill units the lineated valley fills now cover the outflow channel almost entirely they formed not later than 400 ma ago based on stratigraphic analyses and crater counts all the floor units have also been resurfaced several usually two or three times the resurfacing ages of the dated units show that the later modification processes have occurred at least on a local scale in the harmakhis vallis region not only inside the outflow channel this in turn may indicate that the processes resulted from a larger scale change for example in the local climate or endogenic conditions

lava rise plateaus and inflation pits in the mccartys lava flow field new mexico an analog for pāhoehoe like lava flows on planetary surfaces

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

formation of hrad vallis mars by low viscosity lava flows abstract hrad vallis is a martian outflow channel previously interpreted as a product of aqueous outbursts from the subsurface possibly involving mudflows associated with lahar like events however an alternative volcanic hypothesis for the development of the system is worthy of consideration on the basis of 1 the nature of landforms preserved along component channels and adjacent uplands and 2 similarities between the basic properties of this system and large volcanic channels of the inner solar system hrad vallis commences on the distal flanks of the elysium mons shield volcano terminates within extensive volcanic plains is associated with landforms typical of large volcanic channels and shows evidence for having been a conduit for large volumes of lava the properties of this system are consistent with incision by low viscosity lava crude thermal estimates suggest that this system could have formed through effusion of as little as 10 900 km 3 of magma to the surface or 6 of the volume of the terrestrial columbia river basalt group incision rates of up to several meters per day are estimated for mechanical and thermal processes involving lava flows with depths of 5 20 m and dynamic viscosities of 1 pa s flow of lava within the hrad vallis system is predicted to have been fully turbulent and characterized by discharges as great as 865 000 m 3 s predicted flow conditions are consistent with those previously determined for athabasca valles which also formed as a result of the expulsion of flows from structures associated with elysium mons

hydrovolcanic features on mars preliminary observations from the first mars year of hirise imaging abstract we provide an overview of features indicative of the interaction between water and lava and or magma on mars as seen by the high resolution imaging science experiment hirise camera during the primary science phase of the mars reconnaissance orbiter mro mission the ability to confidently resolve meter scale features from orbit has been extremely useful in the study of the most pristine examples in particular hirise has allowed the documentation of previously undescribed features associated with phreatovolcanic cones formed by the interaction of lava and groundwater on rapidly emplaced flood lavas these include moats and wakes that indicate that the lava crust was thin and mobile respectively jaeger w l keszthelyi l p mcewen a s dundas c m russel p s 2007 science 317 1709 1711 hirise has also discovered entablature style jointing in lavas that is indicative of water cooling milazzo m p keszthelyi l p jaeger w l rosiek m mattson s verba c beyer r a geissler p e mcewen a s and the hirise team 2009 geology 37 171 174 other observations strongly support the idea of extensive volcanic mudflows lahars evidence for other forms of hydrovolcanism including glaciovolcanic interactions is more equivocal this is largely because most older and high latitude terrains have been extensively modified masking any earlier 1 10 m scale features much like terrestrial fieldwork the prerequisite for making full use of hirise s capabilities is finding good outcrops