the global martian volcanic evolutionary history abstract viking mission image data revealed the total spatial extent of preserved volcanic surface on mars one of the dominating surface expressions is olympus mons and the surrounding volcanic province tharsis earlier studies of the global volcanic sequence of events based on stratigraphic relationships and crater count statistics were limited to the image resolution of the viking orbiter camera here a global investigation based on high resolution image data gathered by the high resolution stereo camera hrsc during the first years of mars express orbiting around mars is presented additionally mars orbiter camera moc and thermal emission imaging system themis images were used for more detailed and complementary information the results reveal global volcanism during the noachian period 3 7 ga followed by more focused vent volcanism in three tharsis elysium and circum hellas and later two tharsis and elysium volcanic provinces finally the volcanic activity became localized to the tharsis region about 1 6 ga ago where volcanism was active until very recently 200 100 ma these age results were expected from radiometric dating of martian meteorites but now verified for extended geological units mainly found in the tharsis montes surroundings showing prolonged volcanism for more than 3 5 billions years the volcanic activity on mars appears episodic but decaying in intensity and localizing in space the spatial and temporal extent of martian volcanism based on crater count statistics now provides a much better database for modelling the thermodynamic evolution of mars

petrogenesis of the elephant moraine a79001 meteorite multiple magma pulses on the shergottite parent body abstract the eeta 79001 achondrite consists of two distinct igneous lithologies joined along a planar non brecciated contact both are basaltic rocks composed primarily of pigeonite augite and maskelynite but one contains zoned megacrysts of olivine orthopyroxene and chromite that represent disaggregated xenoliths of harzburzite both lithologies probably formed from successive volcanic flows or multiple injections of magma into a small shallow chamber many similarities between the two virtually synchronous magmas suggest that they are related possible mechanisms to explain their differences involve varying degrees of assimilation fractionation from similar parental magmas or partial melting of a similar source peridotite of these assimilation of the observed megacryst assemblage seems most plausible however some isotopic contamination may be required in any of these petrogenetic models the meteorite has suffered extensive shock metamorphism and localized melting during a large impact event that probably excavated and liberated it from its parent body both basaltic lithologies and the inferred ultramafic protolith of the megacryst assemblage are petrologically similar to other members of the shergottite group and all may have been derived from a volcanic plutonic complex on a planetary body

calderas a planetary perspective caldera bearing volcanoes are the largest volcanic edifices on a planet and are expressions of long lived near surface magma chambers on earth only three morphological classes of calderas are common shield calderas e g mauna loa hawaii stratocone calderas e g crater lake oregon and ash flow calderas e g valles caldera new mexico each of these classes has a characteristic caldera size magma type and tectonic location no calderas have been recognized on the moon or mercury but mars has large shield calderas as well as the unique highland patera calderas the latter may represent an explosive ultramafic style of volcanism unlike any volcanic activity in modern earth history radar images suggest that venus has at least one large caldera bearing shield volcano and possible calderas of other types jupiter s satellite io has abundant large shieldlike calderas but no shield massifs the number and variety of calderas on a planet may be proportional to planet mass consistent with a previous suggestion that volcanic complexity increases with planet size io is an exception but heating in io is generated tidally rather than by the decay of radioactive elements so that its calderas are not related to its size the occurrence of shield volcanoes on four solar system bodies suggests that thermal and tectonic mechanisms i e hot spots giving rise to construction of shield mountains and associated collapsed summits are basic processes in planetary geology hot spot volcanism is expected to be most important on planets lacking plate tectonics on earth large shields have lifetimes of only a few million years but on mars large shields may have been active for 1 5 109 years shield calderas on earth are smaller than 20 km in diameter but known or suspected shield calderas on mars venus and io have considerably larger diameters assuming that caldera diameters are related to magma chamber diameters and depths magma chambers on other planets are significantly larger and or deeper than their counterparts on earth terrestrial magma chambers are small because terrestrial shield volcanoes are small in comparison to shields on mars and venus and terrestrial shields are small because the earth s mobile plates move growing shields away from their deep sources thus distributing magma along a narrow chain rather than piling it up around a central vent finally the long lava flows of mars are also explained if the volume of erupted magma has any simple relation to magma chamber volume

age and evolution of the lower nw flank of the hecates tholus volcano mars based on crater size frequency distribution on ctx images abstract we present results of crater size frequency distribution sfd analysis of the lower nw flank of the hecates tholus volcano elysium volcanic province of mars by the use of images acquired by the context ctx instrument on board of mars reconnaissance orbiter 6 m pixel in resolution previous similar works were focused on the caldera complex of the volcano and some sectors of the lower nw flank in this study we analyzed the complete crater population of the main geomorphological units characterizing this sector of the volcano de pablo m a centeno j d 2012 journal of maps 8 3 208 2014 discarding areas with possible clustering to avoid erroneous results in total 16 areas corresponding to 10 geomorphological units were measured and absolute model ages were derived for them the ages correspond to ages of origin as well as of the end of resurfacing events depending on the analyzed sector resulting in some cases in more than one age per area our results are in general in agreement with previous works and establish that the age of the origin of the hecates tholus volcano could be at least 3 8 ga with possible volcanic eruptions occurring until at least 335 ma glacial events were also dated at 90 ma 30 ma 16 ma and 6 ma although it is possible to recognize ages which could also be related to the recent ice ages of mars between 2 and 0 4 ma our results allowed us to determine that glacial processes could have been active as far back as 1 4 ga with possible events at intermediate ages we deduced from the resulting ages and our observations on ctx images and the available geomorphological map of the area that glacial related processes played an important role in sculpting this flank of the volcano and the possible level of the glacial sheet at the edge of the main depression of this flank was also deduced with altitudes ranging between 2035 m and 2490 m in agreement with the presence of smooth outcrops and roche moutonnees in the area finally a possible evolution of this region of the hecates tholus volcano is proposed and discussed establishing the sequence of the most important geological events which occurred in the area and their possible timings

numerical models of caldera scale volcanic eruptions on earth venus and mars volcanic eruptions of gassy magmas on earth venus and mars produce plumes with markedly different fluid dynamics regimes in large part the differences are caused by the differing atmospheric pressures and ratios of volcanic vent pressure to atmospheric pressure for each of these planets numerical simulations of an eruption of magma containing 4 weight percent gas were run on a workstation on venus the simulated eruption of a pressure balanced plume formed a dense fountain over the vent and continuous pyroclastic flows on earth and mars simulated pressure balanced plumes produced ash columns ash falls and possible small pyroclastic flows an overpressured plume illustrated for mars exhibited a complex supersonic velocity structure and internal shocks

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

scaling impact melting and crater dimensions implications for the lunar cratering record abstract the dimensions of large craters formed by impact are controlled to a large extent by gravity whereas the volume of impact melt created during the same event is essentially independent of gravity this differential scaling fosters size dependent changes in the dynamics of impact crater and basin formation as well as in the final morphologies of the resulting structures a variety of such effects can be observed in the lunar cratering record and some predictions can be made on the basis of calculations of impact melting and crater dimensions among them are the following 1 as event magnitude increases the volume of melt created relative to that of the crater will grow and more will be retained inside the rim of the crater or basin 2 the depth of melting will exceed the depth of excavation at diameters that essentially coincide with both the inflection in the depth diameter trend and the simple to complex transition 3 the volume of melt will exceed that of the transient cavity at a cavity diameter on the order of the diameter of the moon this would arguably correspond to a moon melting event 4 small lunar craters only rarely display exterior flows of impact melt because the relatively small volumes of melt created can become choked with clasts increasing the melt s viscosity and chilling it rapidly larger craters and basins should suffer little from such a process 5 deep melting near the projectile s axis of penetration during larger events will yield a progression in cen tral structure morphology with growing event magnitude this sequence should range from single peaks through multiple peaks to peak rings 6 the minimum depth of origin of central peak material should co incide with the maximum depth of melting the main central peak in a crater the size of tycho should have had a preimpact depth of close to 15 km

volcanism on mars more than 15 years of planetary exploration of mars have given insight into the geologic processes that have shaped its surface the newly acquired viking data have shown that volcanism is one of the most important geologic processes operating on mars throughout its history in situ chemical analyses of martian soil by the viking lander spacecraft indicate mafic to ultramafic source rocks this is consistent both with available remote sensing data which indicate the presence of mafic minerals such as pyroxene and olivine and with petrologic modeling based on available geophysical data which suggest that martian lavas are probably iron rich and ultramafic these data strongly suggest that basaltic volcanism is widespread on mars and much of the photogeological data may be studied in this context photogeological analysis of the martian surface has shown two main types of volcanic morphologies the first type is central volcanoes which are volcanic landforms developed by continued and prolonged eruption from a point source vent this category includes 1 shields the classic low profile volcanic mountains of which olympus mons is the most spectacular example 2 domes steep sided constructs such as tharsis tholus that may represent lower rates of eruption than the shields or possibly more silicic lava compositions 3 highland patera radially textured low profile volcanoes that occur in the cratered terrain and are interpreted as ash shields 4 alba patera an apparently unique volcanic landform consisting of a vast volcanic center over 1500 km across with flank slopes of less than a tenth of a degree and 5 various small features such as cinder cones the second major category is volcanic plains which are units recognized by several criteria of which the presence of mare ridges and flow lobes are the most useful volcanic plains are subdivided into four main groups 1 simple flows broad smooth to rolling plains that contain numerous mare type ridges but no flow lobes interpreted as being composed of thick single cooling units 2 complex flows displaying multiple overlapping flow lobes interpreted to be indicative of thin multiple cooling units 3 undifierentiated flows plains that typically lack any morphologic identifying feature but are considered to be volcanic partly on the basis of their association with large volcanic centers and 4 questionable plains volcanic units heavily modified by other processes erosion tectonism etc so that their origins are uncertain when these categories of volcanic morphologies are combined with relative age data provided by crater statistics a volcanic history for mars can be derived as follows early heavy bombardment of mars was accompanied and followed by small scale fluvial channeling extensive flood volcanism the plateau plains and ash shield volcanism in the cratered terrain shortly after this time less extensive flood volcanism continued to resurface the planet during formation of the northern southern hemisphere dichotomy central volcanism became more prominent with the development of the alba patera center as well as the older shields and domes of the northern hemisphere early tharsis and elysium regions the development of the tharsis and elysium uplifts may have triggered the release of large scale catastrophic floods producing large channels continued uplift and lithospheric thinning concentrated volcanic activity in the tharsis region producing large shield volcanoes and extensive lava plains both central vent and plains volcanism have been active throughout martian history but the volumes of extrusion have gradually decreased with time this is consistent with a moonlike thermal history involving a lithosphere of increasing thickness with time gradually turning off the volcanism although many questions remain regarding martian volcanism the viking data have provided a remarkable detailed overview of the probable nature of the volcanic history of mars

a comparison of volcanic eruption processes on earth moon mars io and venus the silicate planets and satellites display a wide range of physical chemical and atmospheric characteristics which may influence the nature of volcanism a major geological process common to the evolution of the surfaces of these bodies consideration of the process of magma ascent and eruption from first principles allows predictions to be made concerning volcanic eruption styles and expected landforms and deposits on each planetary body examination of actual land forms and deposits in light of these predictions leads to a better understanding of the nature of volcanic eruption processes and outlines outstanding problems

the dispersal of pyroclasts from ancient explosive volcanoes on mars implications for the friable layered deposits a number of voluminous fine grained friable deposits have been mapped on mars the modes of origin for these deposits are debated the feasibility for an origin by volcanic airfall for the friable deposits is tested using a global circulation model to simulate the dispersal of pyroclasts from candidate source volcanoes near each deposit it is concluded that the medusae fossae formation and electris deposits are easily formed through volcanic processes and that the hellas deposits and south polar pitted deposits could have some contribution from volcanic sources in specific atmospheric regimes the arabia and argyre deposits are not well replicated by modeled pyroclast dispersal suggesting that these deposits were most likely emplaced by other means

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

the tempe volcanic province of mars and comparisons with the snake river plains of idaho abstract the tempe volcanic province of mars is a broad region adjacent to and superimposed upon the western tempe mareotis plateau the volcanic region is a relatively low plain of probable basaltic flood lava affinity superimposed upon this plain are a variety of small constructional and nonconstructional volcanic features all of which appear structurally controlled along an orientation of approximately n60 e constructional features included low shields composite cones and low irregular hills which may be silicic domes the nonconstructional features include linear depressions which may be rift zones fissure flows and pit craters the tempe volcanic province appears comparable in many aspects to features of the snake river plains of idaho while the tempe region may cover a significantly larger area than the snake river plains the same type and scale of features are observed on both areas the tempe region includes three styles of volcanism flood basalts a capping of fissure and vent fed flows with scattered low shields and areas where low shields have coalesced into plains type volcanism the snake river plains are represented by one style plains volcanism this represents one of the few examples where direct comparison can be made between martian and terrestial geologic geomorphic features and where a scale problem is not encountered

recent and episodic volcanic and glacial activity on mars revealed by the high resolution stereo camera the large area coverage at a resolution of 10 20 metres per pixel in colour and three dimensions with the high resolution stereo camera experiment on the european space agency mars express mission has made it possible to study the time stratigraphic relationships of volcanic and glacial structures in unprecedented detail and give insight into the geological evolution of mars here we show that calderas on five major volcanoes on mars have undergone repeated activation and resurfacing during the last 20 per cent of martian history with phases of activity as young as two million years suggesting that the volcanoes are potentially still active today glacial deposits at the base of the olympus mons escarpment show evidence for repeated phases of activity as recently as about four million years ago morphological evidence is found that snow and ice deposition on the olympus construct at elevations of more than 7 000 metres led to episodes of glacial activity at this height even now water ice protected by an insulating layer of dust may be present at high altitudes on olympus mons

snc meteorites are they martian rocks snc shergottite nakhlite chassignite achondrites are similar in many respects to terrestrial basaltic and ultramafic rocks several independent geochemical and petrological characteristics suggest that they formed on mars these include young 1 3 b y crystallization ages evidence for a magmatic history too complex for an asteroid possibility of garnet in the source region calculations of the magnitude of the gravity field necessary for crystal accumulation by settling presence of trapped gases similar to the the martian atmosphere and other features consistent with what is known about mars however the dynamical difficulties of ejecting meteorites from planetary surfaces are formidable

chronology eruption duration and atmospheric contribution of the martian volcano apollinaris patera geologic mapping thermal inertia measurements and an analysis of the color visual wavelengths of the martian volcano apollinaris patera indicate the existence of two different surface materials comprising an early easily eroded edifice and a more recent competent fan on the southern flank a chronology of six major events that is consistent with the present morphology of the volcano has been identified we propose that large scale explosive activity occurred during the formation of the main edifice and that the distinctive fan on the southern flank appears to have been formed by lavas of low eruptive rate similar to those that form compound pahoehoe flow fields on earth a basal escarpment typically 500 m in relief and morphologically similar to the one surrounding olympus mons was produced between the formation of the main edifice and the fan indicating multistage eruptions over a protracted period of time contact relations between the volcanic units and the adjacent chaotic material indicate that formation of the chaotic material occurred over an extended period of time and may be related to the volcanic activity that formed apollinaris patera stereophotogrammetric measurements permit the volume of the volcano to be estimated at 105 km3 from this volume measurement and an inferred eruption rate 1 5 10 2 km3 yr 1 we estimate the total eruption duration for the main edifice to be 107 yrs plausible estimates of the exsolved volatile content of the parent magma imply that greater than 1015 kg of water vapor was released into the atmosphere as a consequence of this activity this large amount of water vapor as well as other exsolved gases must have had a significant impact on local and possibly global climatic conditions

geologic context of the mars radar stealth region in southwestern tharsis stealth is a region on mars that has no distinguishable radar return stealth was discovered in 1988 by muhleman et al 1991 in 3 5 cm earth based radar images and it was found to extend 2000 km along the martian equator west of arsia and pavonis montes stealth was proposed to be a deposit of unconsolidated granular material with a minimum thickness of several meters with the most likely explanation being that stealth is a volcanic tephra deposit muhleman et al 1991 1995 stealth overlies some of the youngest geologic units on mars including lava flows and a giant curvilinear ridged lobate unit on the west flank of arsia mons stealth also overlies part of a region of smooth and wind scoured materials called the medusae fossae formation examination of high resolution viking orbiter images suggests that stealth is the youngest of several discontinuous wind worked mantles of fine grained 1 cm sediment older deposits of fine sediment appear to be interbedded with lava flows and show evidence of aeolian deposition dunes and deposits in the lee of topographic obstacles and erosion yardangs and pedestal craters the geologic context supports a volcanic ash origin for stealth if stealth is composed of tephra then its extent and the nature of landforms in the region indicate that it resulted from multiple eruptions that occurred relatively late in martian history possible source vents include linear depressions flanked by constructive volcanic landforms that are located on the lower western slopes of arsia and pavonis montes

ejection of martian meteorites we investigated the transfer of meteorites from mars to earth with a combined mineralogical and numerical approach we used quantitative shock pressure barometry and thermodynamic calculations of post shock temperatures to constrain the pressure temperature conditions for the ejection of martian meteorites the results show that shock pressures allowing the ejection of martian meteorites range from 5 to 55 gpa with corresponding post shock temperature elevations of 10 to about 1000 c with respect to shock pressures and post shock temperatures an ejection of potentially viable organisms in martian surface rocks seems possible a calculation of the cooling time in space for the most highly shocked martian meteorite allan hills alh 77005 was performed and yielded a best fit for a post shock temperature of 1000 c and a meteoroid size of 0 4 to 0 6 m the final burial depths of the sub volcanic to volcanic martian rocks as indicated by textures and mineral compositions of meteorites are in good agreement with the postulated size of the potential source region for martian meteorites during the impact of a small projectile 200 m as defined by numerical modeling artemieva and ivanov 2004 a comparison of shock pressures and ejection and terrestrial ages indicates that on average highly shocked fragments reach earth crossing orbits faster than weakly shocked fragments if climatic changes on mars have a significant influence on the atmospheric pressure they could account for the increase of recorded ejection events of martian meteorites in the last 5 ma

structural record of an oblique impact abstract most impactors strike their target at an oblique angle the common criterion for identifying craters formed by an oblique impact is the pattern of the ejecta blanket on earth however ejecta blankets are rarely preserved and other morphological structural or geophysical criteria are needed here we present structural details from the central uplift of the upheaval dome impact structure that are diagnostic of the kinematics during crater collapse and central uplift formation a characteristic imbrication of thrust slices towards the se the pattern of strata orientation within the central uplift dominant radial faults that accommodated nw se shortening and an elliptical bedding outline indicate that the displacement field during crater collapse has not been axial symmetric instead an additional lateral component roughly towards the se is preserved in the internal structure of the central uplift the structural asymmetries are largest in the core of the central uplift and disappear outwards thereby preserving the large scale circular shape of the main structural elements rim monocline ring syncline comparison with numerical models of oblique impacts suggests that the additional lateral displacement component reflects a downrange material transport during the initial stages of central uplift formation similar patterns are identified in other impact structures and may serve as general criteria for identifying the impact direction of deeply eroded impact structures in sedimentary targets

oxygen and silicon isotopes in alha 81005 the antarctic meteorite alha 81005 has oxygen and silicon isotopic compositions identical with lunar highland rocks the oxygen is distinctly unlike that in calcium rich achondrites the isotopic data are entirely consistent with a lunar origin for the meteorite

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

polygenic eruptions on alba patera mars a combination of photogeologic mapping analysis of viking orbiter thermal inertia data and numerical modelling of eruption conditions has permitted us to construct a new model for the evolution of the martian volcano alba patera numerous digitate channel networks on the flanks of the volcano are interpreted to be carved by sapping due to the release of non juvenile water from unconsolidated flank deposits using the thermal inertia measurements we estimate the particle size of these deposits to be 3 10 m which together with theoretical modelling of the disperison of explosively derived volcanic materials leads us to conclude that the flank deposits on alba patera are low relief pyroclastic flows the recognition of numerous late stage summit and sub terminal lava flows thus makes alba patera a unique martian volcano that is transitional between the older pyroclastic dominated highland paterae and the more recent effusive central vent volcanoes such as the tharsis montes

rummaging through earth s attic for remains of ancient life abstract we explore the likelihood that early remains of earth mars and venus have been preserved on the moon in high enough concentrations to motivate a search mission during the late heavy bombardment the inner planets experienced frequent large impacts material ejected by these impacts near the escape velocity would have had the potential to land and be preserved on the surface of the moon such ejecta could yield information on the geochemical and biological state of early earth mars and venus to determine whether the moon has preserved enough ejecta to justify a search mission we calculate the amount of terran material incident on the moon over its history by considering the distribution of ejecta launched from the earth by large impacts in addition we make analogous estimates for mars and venus we find for a well mixed regolith that the median surface abundance of terran material is roughly 7 ppm corresponding to a mass of approximately 20 000 kg of terran material over a 10 10 square km area over the same area the amount of material transferred from venus is 1 30 kg and material from mars as much as 180 kg given that the amount of terran material is substantial we estimate the fraction of this material surviving impact with intact geochemical and biological tracers

theoretical modeling of eruption plumes on mars under current and past climates we have used a combined conduit transport eruption column model to explore the evolution of volcanic eruption plumes on mars under different atmospheric conditions in the calculations we consider a volatile phase composed of h2o co2 and so2 and take into account that the magmatic water erupted at the vent may condense as the eruption column rises into the martian atmosphere as two end member models we explore the eruption of rhyolitic and basaltic melt compositions containing different amounts of volatiles as well as having different eruption temperatures under current martian atmospheric conditions eruption plumes are found to rise as high as 100 km for a mass eruption rate of 5 107 kg s 1 which is consistent with model calculations by wilson and head 1994 in contrast under a dense atmosphere 105 pa on the martian surface which may have existed earlier in martian history the same eruption plume reaches only about 25 km height all magmatic water released during the eruption is found to freeze as it rises in the eruption column which means that fallout from the plume will contain water ice which can be subsequently deposited in near surface layers this ice may then suddenly melt due to higher surface heat flow or shallow intrusions leading to rapid release of water on the flanks of volcanoes only if the atmosphere were hotter in the past could the water in the eruption plume condense and produce rain rather than ice furthermore the calculations show that smaller micron size particles would be distributed globally from eruption plumes under current martian conditions but would not have been as widely dispersed from plumes erupted into an earlier dense atmosphere

aeolian dunes as evidence for explosive volcanism in the tharsis region of mars two transverse dune fields occur among late amazonian volcanic and aeolian landforms in southwestern tharsis mars the first is located 70 km northwest of biblis patera around 5 n 125 w the second is located about 500 km northwest of arsia mons at 2 s 130 w the latter is the largest dune field thus far documented to occur in the equatorial latitudes of mars unlike other dunes on the planet both dune fields in tharsis have low thermal inertias 2 7 10 3cal cm 2sec 0 5k 1 and high albedos 0 26 that are indistinct from their surrounding terrain both dune fields have superposed features such as impact craters lava flows smooth surfaced units and bright wind streaks the dune fields therefore appear to be inactive and mantled by fine grained material i e particles 60 m to form aeolian dunes require a supply of sand on earth most dune sands are supplied by fluvial and littoral processes but this is not the case in tharsis on mars because they are superposed on a late amazonian surface the climate is assumed to have been hyper arid throughout the time that the dunes have existed under these conditions the only plausible source for quantities of sediment sufficient to form transverse dune fields is explosive volcanism therefore the two dune fields in tharsis are evidence that explosive volcanism has occurred in this region in the late amazonian epoch

arecibo radar imagery of mars the major volcanic provinces abstract we present earth based radar images of mars obtained with the upgraded arecibo s band 12 6 cm radar during the 2005 2012 oppositions the imaging was done using the same long code delay doppler technique as for the earlier pre upgrade imaging but at a much higher resolution 3 km and for some regions a more favorable sub earth latitude this has enabled us to make a more detailed and complete mapping of depolarized radar reflectivity a proxy for small scale surface roughness over the major volcanic provinces of tharsis elysium and amazonis we find that vast portions of these regions are covered by radar bright lava flows exhibiting circular polarization ratios close to unity a characteristic that is uncommon for terrestrial lavas and that is a likely indicator of multiple scattering from extremely blocky or otherwise highly disrupted flow surfaces all of the major volcanoes have radar bright features on their shields although the brightness distribution on olympus mons is very patchy and the summit plateau of pavonis mons is entirely radar dark the older minor shields paterae and tholi are largely or entirely radar dark which is consistent with mantling by dust or pyroclastic material other prominent radar dark features include the fan shaped deposits possibly glacial associated with the three major tharsis montes shields various units of the medusae fossae formation a region south and west of biblis patera where stealth deposits appear to obscure tharsis flows and a number of dark halo craters with radar absorbing ejecta blankets deposited atop surrounding bright flows several major bright features in tharsis are associated with off shield lava flows these include the olympus mons basal plains volcanic fields east and south of pavonis mons the daedalia planum flows south of arsia mons and a broad expanse of flows extending east from the tharsis montes to echus chasma the radar bright lava plains in elysium are concentrated mainly in cerberus and include the fluvio volcanic channels of athabasca valles grjota valles and marte valles as well as an enigmatic region at the southern tip of the cerberus basin some of the cerberus bright features correspond to the distinctive platy ridged flows identified in orbiter images the radar bright terrain in amazonis planitia comprises two distinct but contiguous sections a northern section formed of lavas and sediments debouched from marte valles and a southern section whose volcanics may derive in part from local sources this south amazonis region shows perhaps the most complex radar bright structure on mars and includes features that correspond to platy ridged flows similar to those in cerberus

analysis of polygonal cracking patterns in chloride bearing terrains on mars indicators of ancient playa settings the ancient southern highlands on mars 3 5 gyr old contain 600 regions that display spectral evidence in the infrared for the presence of chloride bearing materials many of these locations were previously reported to display polygonal cracking patterns we studied more than 80 of the chloride bearing terrains using high resolution 0 25 0 5 m pixel images as well as near infrared spectral data to characterize the surface textures and the associated cracking patterns and mineralogies our study indicates that 75 of the studied locations display polygonal cracks that resemble desiccation cracks while some resemble salt expansion thrust polygons furthermore we detect spectrally the presence of smectites in association with 30 of the studied fractured terrains we note that smectites are a special class of swelling clay minerals that can induce formation of large desiccation cracks as such we suggest that the cracking patterns are indicative of the presence of smectite phyllosilicates even in the absence of spectral confirmation our results suggest that many chloride bearing terrains have a lacustrine origin and a geologic setting similar to playas on earth such locations would have contained ephemeral lakes that may have undergone repeated cycles of desiccation and recharging by a near surface fluctuating water table in order to account for the salt phyllosilicates associations these results have notable implications for the ancient hydrology of mars we propose that the morphologies and sizes of the polygonal cracks can be used as paleoenvironmental as well as lithological indicators that could be helpful in planning future missions

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

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

oblique impact a process for obtaining meteorite samples from other planets cratering flow calculations for a series of oblique to normal 10 to 90 impacts of silicate projectiles onto a silicate halfspace were carried out to determine whether or not the gas produced upon shock vaporizing both projectile and target material would form a downstream jet that could entrain and propel snc meteorites from the martian surface the difficult constraints that the impact origin hypothesis for snc meteorites has to satisfy are that these meteorites are lightly to moderately shocked and yet have been accelerated to speeds in excess of the martian escape velocity more than 5 kilometers per second two dimensional finite difference calculations were performed that show that at highly probable impact velocities 7 5 kilometers per second vapor plume jets are produced at oblique impact angles of 25 to 60 and have speeds as great as 20 kilometers per second these plumes flow nearly parallel to the planetary surface it is shown that upon impact of projectiles having radii of 0 1 to 1 kilometer the resulting vapor jets have densities of 0 1 to 1 gram per cubic centimeter these jets can entrain martian surface rocks and accelerate them to velocities greater than 5 kilometers per second this mechanism may launch snc meteorites to earth

absence of silicic volcanism on mars implications for crustal composition and volatile abundance on earth eruptions of silicic magmas with volumes of 1 100 km3 are generally associated with stratovolcanoes or composite cones whereas larger 100 1000 km3 ignimbrite deposits are erupted from resurgent calderas and related structures small volumes of silicic rocks are generated by differentiation within basic magma chambers associated with stratovolcanoes but large silicic deposits are largely confined to areas where the granitic crust is thicker than 25 km as mantle derived magmas rise through the thick granitic crust fractional crystallization and assimilation of hydrous crustal rocks concentrate volatiles and sio2 in the magma yielding explosive silicic eruptions on mars under similar chemical conditions ignimbrite eruptions could take place over a broader range of physical conditions than on earth but no large volume ignimbrite deposits can be identified positively explosive basic to ultrabasic eruptions may be responsible for small cinder conelike features on mars and perhaps for the ancient flank scoured paterae such eruptions may have been driven by near surface water ice magma interactions or volatile rich magmas the paterae represent a unique style of volcanism that stopped 2 b y ago we suggest that the volatiles associated with these features were derived from mantle sources and that the cessation of patera formation may coincide with the termination of the period of maximum planetary degassing volcanism since 2 b y ago has been dominantly effusive except for minor explosive ash events such as those which blanketed part of the summit of hecates tholus we propose that such eruptions were driven by volatiles generated by differentiation of a magma chamber similar to icelandic explosive eruptions the apparent lack of large scale silicic volcanism on mars is circumstantial evidence that mars is deficient in volatiles and lacks a granitic crust

origin of the valley networks on mars a hydrological perspective abstract the geomorphology of the martian valley networks is examined from a hydrological perspective for the compatibility with an origin by rainfall globally higher heat flow and localized hydrothermal systems comparison of morphology and spatial distribution of valleys on geologic surfaces with terrestrial fluvial valleys suggests that most martian valleys are probably not indicative of a rainfall origin nor are they indicative of formation by an early global uniformly higher heat flow in general valleys are not uniformly distributed within geologic surface materials as are terrestrial fluvial valleys valleys tend to form either as isolated systems or in clusters on a geologic surface unit leaving large expanses of the unit virtually untouched by erosion with the exception of fluvial valleys on some volcanoes most martian valleys exhibit a sapping morphology and do not appear to have formed along with those that exhibit runoff morphology in contrast terrestrial sapping valleys form from and along with runoff valleys the isolated or clustered distribution of valleys suggests localized water sources were important in drainage development persistent groundwater outflow driven by localized but vigorous hydrothermal circulation associated with magmatism volcanism impacts or tectonism is however consistent with valley morphology and distribution snowfall from sublimating ice covered lakes or seas may have provided an atmospheric source of water for the formation of some valleys in regions where the surface is easily eroded and where localized geothermal hydrothermal activity is sufficient to melt accumulated snowpacks

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

initiation of run out flows on venus by oblique impacts abstract a hypervelocity oblique impact results in a downrange moving vapor cloud a significant fraction of which is derived from the projectile since the vapor cloud expands to great extent and becomes very tenuous quickly on a planet with a thin or no atmosphere it does not leave a well defined geologic expression the thick atmosphere of venus however is sufficient to contain such a rapidly expanding vapor cloud as a result of atmospheric interactions impact vapor condenses and contributes to run out flows around craters on venus previous results of both laboratory experiments and simple semi analytical calculations indicate that an impact vapor origin can account for the morphology of run out flows on venus most consistently however the detailed dynamics and geologic record of downrange moving impact vapor clouds in venus s atmosphere are not understood quantitatively to approach these problems we carried out two dimensional hydrocode calculations parametric studies of these hydrocode calculations yield simple scaling laws for both the total downrange travel distance and the final temperature of impact vapor clouds under conditions on venus under typical impact conditions impact vapor clouds travel downrange more than a crater radius prior to the completion of crater formation furthermore the scaling law for the total travel distance is compared with observations for the downrange offset of the source regions of run out flows around oblique craters the results of this comparison suggest that energy momentum partitioning processes other than pure shock coupling may play important roles in hypervelocity impact at planetary scales the results of hydrocode calculations also indicate that the terminal temperature of the impact vapor is close to the condensation temperatures of silicates suggesting that two scenarios are possible for expected range of impact conditions 1 impact vapor condenses and forms run out flows 2 impact vapor fails to condense and leaves no run out flows consequently natural variation in impact angle velocity and projectile composition may account for partial occurrence of run out flows around impact craters on venus

evidence of active mantle flow beneath south china 1 the india eurasia collision is responsible for producing the himalayan mountains and tibetan plateau and has been hypothesized to have significant far field influences including driving the baikal rift and the eastward extrusion of south china however quantification of lithospheric buoyancy forces and integrated effect of tractions acting at base of the lithosphere are unable to explain the observed surface motions within south china we present 198 new sks shear wave splitting observations beneath south china and invert these data along with published gps data to solve for the subasthenospheric flow field beneath south china to assess the role of small scale convection here we find a 15 20 mm yr southwestward directed mantle flow toward the burma slab this flow is consistent with the mantle response of slab retreat over the past 25 ma and counter flow due to subduction of burma sunda slabs demonstrating the importance of localized mantle convection on present day plate motions

tephra deposition on glaciers and ice sheets on mars influence on ice survival debris content and flow behavior we examine the consequences of pyroclastic deposits being emplaced onto ice layers on mars both those in the polar caps and those forming glaciers on the flanks of some of the large shield volcanoes we show that layers of pyroclasts greater than a few meters in thickness whether emplaced cold as fall deposits or hot as pyroclastic density current deposits act almost exclusively to protect ice layers beneath them from sublimation irrespective of whether they are emplaced at high or low elevations or high or low latitudes layers less than about 2 m thick on the other hand can cause significant ice loss by raising the surface temperature due to their low albedo and then transmitting that increased temperature to the underlying ice especially on a diurnal time scale this can have a significant bearing on the emplacement history of polar water ice and on the survival time of glacial ice on shield volcano flanks a key factor in the latter case is the timing of the episodic volcanic activity relative to the cycles of climate change driven by mars obliquity and eccentricity variations

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

dark materials in valles marineris indications of the style of volcanism and magmatism on mars rifting on the equatorial canyon system of valles marineris provides a unique view of the interior of the martian crust to depths reaching 7 km exposing several in situ bedrock units which testify to past volcanic and magmatic processes on mars a thick regionally extensive deposit observed in coprates and juventae chasmata is interpreted on the basis of spectral reflectance erosional morphology and tendency for eolian mobilization to be composed of mafic glass possibly an ancient martian analogue of the lunar terra mantling deposits spectral mapping suggests that the dark floor covering materials in the lower canyons are derived from this unit a series of cliffs in the ophir chasma wall rock is interpreted to be exposures of resistant bedrock the spectral signature of this massive and uniform unit most closely resembles that of terrestrial mafic rocks altered to or coated by crystalline hematite application of computer mapping techniques to probable young volcanic materials in the central troughs yields an inferred distribution of volcanic activity consistent with the interpretation of extrusion along faults near the margins of the canyon floors this result supports the hypothesis that the valles originated through tectonic extension

climatic effects of an impact induced equatorial debris ring 1 several theoretical and laboratory studies suggest that some large impact events are capable of inserting material into space depending on mechanics of the impact this material would quickly coalesce to form a temporary debris ring in orbit around the equator which would cast its shadow on the winter hemisphere the results of an atmospheric general circulation model gcm simulation where an orbiting equatorial debris ring is applied as a boundary condition to the model show how the longer term effects of a major impact could affect the climate system the primary effect is a severe cooling in the tropics and the subtropics especially under the seasonally migrating ring shadow the globe cools and becomes drier with the exception of monsoonal regions that become wetter the hadley cell is weakened resulting in drier tropics and weaker subtropical high pressure cells in the winter hemisphere because the tropics cool more than middle latitude regions the equator to pole temperature gradient becomes shallower resulting in weaker tropospheric winds and less high latitude storminess we suggest that the late eocene impact s 35 5 ma could have generated a geologically temporary orbiting debris ring based on the global distribution of tektites associated with these events and patterns of climate change immediately above the iridium microtektite layer the cretaceous tertiary boundary event while larger did not produce a debris ring we also suggest that an opaque debris ring could have acted as the trigger to at least one episode of global glaciation during the neoproterozoic

explosive volcanic eruptions v observations of plume dynamics during the 1979 soufriere eruption st vincent summary during the 1979 eruption of the soufritre of st vincent west indies a 14min period of explosive activity occurred on april 22 the first three minutes of this activity were filmed five individual explosions formed distinct plumes which fed an eruption column which eventually ascended to a height of over 18 km the ascent velocities of the fronts of these plumes ranged from 8 5 to 61 7m s the half angle of spreading of the plume fronts ranged from 21 5 to 24 one of the plumes was observed to 8 km height and decelerated steadily from 5 1 5 to 23 m s l the main column fed by individual explosions was however observed to accelerate from 8 5 to 58 m s l in the same height interval a theoretical treatment of volcanic plume motion is presented measurements of dimensions velocities and spreading rates from the film are used to estimate plume parameters such as temperature particle content and volume discharge rate of magma from the theoretical relationships these calculations show that the individual plumes became hotter and richer in juvenile ash with time the acceleration of the main eruption column was the result of being fed by increasingly hotter and more ash rich explosions an average volume discharge rate of 12600m3s is estimated from the analysis of the plume motions this value agrees closely with an estimate of discharge rate based on the heat flux required to form an 18 km high column this agreement suggests that theories of convective motions in plumes can be successfully adapted to the volcanic case as long as the effect of hot entrained ash particles is considered

understanding oblique impacts from experiments observations and modeling natural impacts in which the projectile strikes the target vertically are virtually nonexistent nevertheless our inherent drive to simplify nature often causes us to suppose most impacts are nearly vertical recent theoretical observational and experimental work is improving this situation but even with the current wealth of studies on impact cratering the effect of impact angle on the final crater is not well understood although craters rims may appear circular down to low impact angles the distribution of ejecta around the crater is more sensitive to the angle of impact and currently serves as the best guide to obliquity of impacts experimental studies established that crater dimensions depend only on the vertical component of the impact velocity the shock wave generated by the impact weakens with decreasing impact angle as a result melting and vaporization depend on impact angle however these processes do not seem to depend on the vertical component of the velocity alone finally obliquity influences the fate of the projectile in particular the amount and velocity of ricochet are a strong function of impact angle

atmospheric effects on ejecta emplacement and crater formation on venus from magellan the venus cratering record provides a unique environment for assessing the effects of both gravity and an atmosphere on impact crater formation this contribution uses surface signatures of energy partitioning as a framework for testing extrapolations from laboratory experiments and other planetary settings seven general conclusions can be drawn first the dense lower atmosphere of venus takes on the role of a low density target for bodies smaller than about 4 km in diameter air blasts created by cratering in the atmosphere create distinctive surface signatures that allow the derivation of an independent assessment of impactor energy at the limit of break up second dynamic pressures during entry of larger bodies will exceed their strength limit but may not prevent penetration of the atmosphere due to aerodynamic reshaping that minimizes the drag coefficient such a process may account for the formation of unusually small craters 1 3 km third the dense atmosphere of venus preserves signatures of early time cratering processes on the surface that are typically lost on atmosphere free surfaces such signatures not only provide another estimate of impactor energy but also include a distinctive record of the impactor i e comet versus asteroid in distinctive run out flows created before the crater has finished formation strong winds and turbulence associated with the atmospheric disturbance at later times create wind streaks behind topographic barriers fourth ballistic ejection of excavated debris occurs from craters on venus just as it does on planets without an atmosphere thereby underscoring the fundamental mechanical transfer of energy from impactor to target fifth ejecta emplacement is nonballistic due to the large dynamic forces acting on the advancing curtain and its constituent ejecta the outward moving ejecta curtain induces strong response winds that entrain ejecta and drive a ground hugging debris flow outward without returning to the cavity flow separation creates an overriding run out ejecta flow further sustained by atmospheric turbulence and identified as radar dark lobate lobes sixth radar dark parabolas are proposed to be late time fallout deposits created as the downrange fireball evolves aloft perhaps analogous to terrestrial tektite strewn fields and seventh the response of crater formation to the atmosphere is conversely expressed by a reduction in cratering efficiency as revealed by the unusually large central peak complexes and the unexpected diameter depth relations of craters hence surface ages may be significantly underestimated

volcanism in the solar system the myriad bodies that occur in the solar system show a wide range of physical properties exploration by spacecraft during the past four decades has shown that volcanism a major mechanism by which internal heat is transported to the surface is common on many of these bodies

the change of eruption styles of martian volcanoes and estimates of the water content of the martian mantle abstract estimated water contents in the martian mantle range from 36 ppm to more than 1 these values are based on the chemical analyses such as hydrous minerals in snc meteorites and formation models of mars this study evaluates the water content of the martian mantle using the change with time of volcanic eruption style on mars as an observational constraint styles of volcanic activity depend on the volatile content of the magma and the atmospheric pressure because a low atmospheric pressure leads to a more explosive volcanic eruption it has been believed that the volcanism on the current martian environment would be very explosive our calculations however show that under the current martian atmospheric conditions erupted magma cannot entrain the ambient air effectively so the decrease in temperature of the magma during ascent is small consequently the erupted magma may form a lava like deposit when it falls back on the ground this effusive like style of eruption is a counterpart of clastogenic lava on mars on the other hand numerical calculations under a thick co 2 atmosphere which may correspond to an ancient martian atmosphere reveal a rather explosive eruption style geological features of earlier stages of martian history in the noachian and hesperian eras suggest that the volcanic eruptions on mars were explosive then effusive eruptions however became dominant in more recent times it has been widely accepted that mars experienced a major climate change in addition the release factor of volatiles on mars has been suggested to be as small as 0 017 0 112 this may imply that the volatile content has been almost constant throughout martian history consequently we assume that this change in eruption style was caused by the change in atmospheric pressure for a given water content of magma a major climatic change may lead to a transition in eruption style if we know the atmospheric pressure at the time of this transition we can calculate the possible range of the volatile content of the mantle using our numerical simulations if the atmospheric pressure on mars around late hesperian era is about 1 bar the estimated values for a typical martian magma are 0 05 0 25 wt which is within the range of the water content of typical terrestrial basaltic magmas

volcanic geology of hadriaca patera and the eastern hellas region of mars hadriaca patera is a low relief volcano in the southern highlands of mars northeast of the hellas basin layered friable deposits composing the extensive channeled flanks of the volcano surround a well defined summit caldera containing late stage eruptive products the morphologic characteristics of the channels suggest erosion by groundwater sapping and surface runoff the erosional morphology of the volcano the lack of lava flow features and the friable nature of the flank materials indicate that hadriaca patera consists predominantly of pyroclastic deposits gravity driven flow models demonstrate that the distribution of flank materials can be attributed to the emplacement of pyroclastic flows both magmatic and hydromagmatic eruption models are viable for the magmatic case the necessary mass eruption rates 107 108 kg s ejection velocities 400 m s and volatile contents 1 5 3 0 wt h2o are consistent with parameters derived for terrestrial plinian eruptions for the hydromagmatic case the required energy conversion efficiencies are comparable to those of laboratory experiments and the inferred permeability of the martian crust allows large amounts of groundwater to be transported rapidly at flow rates of 103 104 m3 s into the region models of cooling during emplacement indicate that welding of pyroclastic flows can occur at large distances hundreds of kilometers from a source vent on mars the layering within hadriaca patera could be attributed to welding of pyroclastic flows that would control its susceptibility to erosion morphologic similarities between hadriaca and tyrrhena paterae suggest a similar volcanic history with an early pyroclastic dominated shield building phase followed by effusive eruptions at their summit calderas and on the flank of tyrrhena patera the formation of the extensive ridged plains of hesperia planum following the formation of the highland paterae supports the interpretation of a transition from explosive to effusive volcanism in the eastern hellas region a progressive depletion of volatiles on mars is consistent with the morphologic properties of highland paterae and other central vent volcanoes a predominance of hydrovolcanic eruptions in the development of hadriaca and tyrrhena paterae would imply that the transition in volcanic eruption style can be attributed to a volatile depletion of the crust whereas magmatic eruptions at the paterae would be indicative of temporal changes in martian magmas

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

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

ancient martian volcanoes in the aeolis region new evidence from mola data mars orbiter laser altimeter mola altimetric data confirm the volcanic origin of a noachian aged hilly feature zephyria tholus in the aeolis area of mars similar characteristics shared by at least one nearby topographic high suggest that volcanic activity represented by such features may have been more widespread than previously thought morphological structures and morphometric data for zephyria are consistent with a stratovolcano origin in which the edifice formed by mixed explosive and effusive eruptions and was altered by subsequent flank erosion to produce a distinctive truncated cone with concave upward flanks criteria are outlined to help detect and distinguish the origin of such features in other ancient regions of mars

rheologies and ages of lava flows on elysium mons mars abstract we present results of our study of the rheologies and ages of lava flows in the elysium mons region of mars previous studies have shown that the geometric dimensions of lava flows reflect rheological properties such as yield strength effusion rate and viscosity in this study the rheological properties of lava flows in the elysium mons region were determined and compared to the rheologies of the ascraeus mons lava flows we also derived new crater size frequency distribution measurements csfds for the elysium lava flows to identify possible changes in the rheological properties with time in addition possible changes in the rheological properties with the distance from the caldera of elysium mons were analyzed in total 35 lava flows on and around elysium mons were mapped and divided into three groups lava flows on the flanks of elysium mons in the plains between the three volcanoes elysium mons hecates and albor tholus and lava flows south of albor tholus the rheological properties of 32 of these flows could be determined based on our morphometric measurements of each individual lava flow estimates for the yield strengths effusion rates viscosities and eruption duration of the studied lava flows were made the yield strengths of the investigated lava flows range from 3 8 102 pa to 1 5 104 pa with an average of 3 0 103 pa these yield strengths are in good agreement with estimates for terrestrial basaltic lava flows the effusion rates are on average 747 m3 s 1 ranging from 99 to 4450 m3 s 1 the viscosities are on average 4 1 106 pa s with a range of 1 2 105 pa s to 3 1 107 pa s the eruption durations of the flows were calculated to be between 6 and 183 days with an average of 51 days the determined rheological properties are generally very similar to those of other volcanic regions on mars such as on ascraeus mons in the tharsis region calculated yield strengths and viscosities point to a basaltic andesitic composition of the lava flows similar to basaltic or andesitic a a lava flows on earth absolute model ages of all 35 lava flows on elysium mons were derived from crater size frequency distribution measurements csfd the derived model ages show a wide variation from about 632 ma to 3460 ma crater size frequency distribution measurements of the elysium mons caldera show an age of 1640 ma which is consistent with the resurfacing age of werner 2009 significant changes of the rheologies with time could not be observed similarly we did not observe systematic changes in ages with increasing distances of lava flows from the elysium mons caldera

experimental constraints on impact induced winds abstract a new class of wind streaks on mars uniquely associated with impact craters is most clearly detected in nighttime thermal infrared imaging thermally bright streaks radiate from some well preserved impact craters and are related to the impact process using laboratory experiments performed at the nasa ames vertical gun range we test the hypothesis that these streaks are formed from either the winds within an air blast or winds set up by expanding impact vapor interacting with the atmosphere the experiments use a variety of tracers and instruments to document three interrelated processes occurring in the impact of a pyrex projectile into an easily vaporized powdered dolomite target 1 a surface roughening spreading outward from the impact point 2 an expanding vapor plume and 3 outward winds made visible by dust trails from vertically placed dusty pipe cleaners the clear connection between the surface roughening vapor expansion and outward winds implicate an expanding vapor interacting with the atmosphere as the controlling process

alha 81005 meteorite chemical evidence for lunar highland origin based on the well established characteristic lunar and meteoritic ratios of feo mno cr2o3 v and k la and ree patterns alha 81005 meteorite is undoubtedly of lunar highland origin the alha 81005 meteorite is an anorthositic gabbro 72 pl and matches closely in chemical composition to apollo 15 15418 and luna 16 21013 highland rocks the rock is a non kreepy and vlt type the siderophiles au ni and ir content is high 1 5 cl equivalent and similar to other lunar highland breccias the clast has a different ancient meteorite component than the bulk and matrix the meteorite has a young terrestrial age implying a recent lunar cratering event therefore during major lunar basins formation in early eons the earth must have received a significant amount of lunar material which is now mixed in the crust the finding of a lunar meteorite lends credibility to the suggestion that snc achondrites may come from mars

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

eruption transport and deposition of ignimbrite a case study from mexico abstract the acatlan ignimbrite covers 150 km 2 around a vent situated 40 km southwest of guadalajara mexico the upper and main ignimbrite flow unit is compositionally zoned and has white or pink rhyolitic pumice in its lower part and black andesite in its upper these parts are believed to have been erupted continuously from the same magma chamber this zonation has been important in correlating an extremely coarse lithic rich deposit a co ignimbrite lag fall deposit with this ignimbrite the co ignimbrite lag fall deposit indicates that the flow unit formed by continuous collapse of an explosive eruption column and enables the source vent to be located the vertical compositional grading of the flow unit also provides a means of testing the various proposed mechanisms of ignimbrite emplacement turbulent vs high concentration flow the preservation of compositional zonation and other features in the deposit indicate that flow was not turbulent details of the grain size distribution indicate that laminar flow was important early in the flow history when collapsing material from the eruption column was superimposed in stratigraphical sequence initial high gas flow rates associated with flow segregation and formation at the site of column collapse rapidly decayed away from vent and later in its history the flow degassed to a semi rigid plug overriding a sheared basal layer

origin and evolution of the layered deposits in the valles marineris mars abstract thick sequences of layered deposits are found in the martian valles marineris they exhibit fine nearly horizontal layering and are present as isolated plateaus of what may have once been more extensive deposits individual sequences of layered deposits are as thick as 5 km the greatest total thicknesses of deposits are found in candor ophir and melas chasmata individual layer thicknesses range from about 70 to 300 m some tilting of sequences is observed but at the best image resolutions no angular unconformities are detectable in the layers the sequences of events in the canyons as deduced from morphologic and stratigraphic evidence was 1 graben formation in response to the tharsis uplift 2 canyon wall retreat and canyon enlargement roughly contemporaneous with formation of the layered deposits 3 deep erosion of the layered deposits 4 landsliding of the canyon walls and 5 eolian erosion of the layered deposits perhaps continuing up to the present we consider four hypotheses for the origin of the layered deposits they are eolian deposits they are remnants of the material that makes up the canyon walls they are deposits of explosive volcanic eruptions or they were deposited in standing bodies of water the rhythmic nature of the layers and their lateral continuity horizontality great thickness and stratigraphic relationships with other units in the canyons all appear most consistent with deposition in an aqueous environment if standing bodies of water existed in the valles marineris they were almost certainly ice covered there are three ways in which sediment could have entered an ice covered lake down through the ice cover up from the lake bottom or in from the lake margins layers of sediment could have been transported downward through an ice cover by foundering or rayleigh taylor instabilities but it is not clear whether there was a viable mechanism for repeatedly accumulating thick sediment layers on top of the ice cover subaqueous volcanic eruption on the lake bottom does not suffer from many of the morphologic arguments that make origin by subaerial volcanism seem improbable while this mechanism is attractive there are no eruptive centers observed and there is no other direct evidence to support it because canyon enlargement took place at roughly the same time as layer deposition debris from the canyon walls is an obvious and likely source for some of the material in the layered deposits however the volume of material removed from the canyon walls may be insufficient to account for all of the presently observed material we conclude that there are several geologically feasible but as yet unproven mechanisms that could have led to formation of thick deposits in ice covered paleolakes in the valles marineris present data are insufficient to choose conclusively among the various possibilities several types of data from the mars observer mission will be useful in further characterizing the deposits and clarifying the process of their origin the deposits should be considered important targets for a future mars sample return mission

ejecta formation and crater development of the mjolnir impact crater ejecta correlation is an important element in the analysis of crater formation and its influence on the geological evolution in this study both the ejecta distribution and the internal crater development of the jurassic cretaceous mjolnir crater 40 km in diameter located in the barents sea are investigated through numerical simulations the simulations show a highly asymmetrical ejecta distribution and underscore the importance of a layer of surface water in ejecta distribution as expected the ejecta asymmetry increases as the angle of impact decreases the simulation also displays an uneven aerial distribution of ejecta the generation of the central high is a crucial part of crater formation in this study peak generation is shown to have a skewed development from approximately 50 90 sec after impact when the peak reaches its maximum height of 1 1 5 km during this stage the peak crest is moved about 5 km from an uprange to a downrange position ending with a final central position which has a symmetrical appearance that contrasts with its asymmetrical development

comparative planetology and the origin of continental crust abstract this paper summarizes crustal evolution in silicate planets the moon mercury mars venus and meteorite parent bodies and outlines a general theory for the origin of continental crust based on comparative planetology and terrestrial evidence silicate planets and some meteorite parent bodies have undergone early global differentiation nonplate tectonic followed by a late basin forming bombardment and a long basaltic second differentiation evidence for analogous stages except a late bombardment can be found in terrestrial geology modified by conditions of hydrous magma generation and persistent tectonism continental crust is inferred to have largely been formed in the early archean by andesitic volcanism accompanying catastrophic early degassing this global crust was disrupted by basin forming impacts that initiated mantle upwelling and sea floor spreading basaltic overplating and underplating from mantle plumes continued on the continents producing greenstone belts mafic dike swarms and by partial melting of underplated basalt and sialic crust the granitoids of archean granite greenstone terrane this process produced most of the present continental crust by 2 5 ga ago when the global tectonic style evolved into the present one of tectonism marginal to and within continents subsequent crustal evolution has largely been deformation metamorphism anatexis and rearrangement of previously formed crustal segments not separation of new sialic crust from the mantle the crustal growth that has occurred since the archean has primarily been crustal thickening resulting directly or indirectly from generation of basalt in the subcontinental tectosphere viewed in the light of evidence from comparative planetology the continents are interpreted as the greatly altered remnants of an originally global primordial crust the result of an evolutionary sequence shared by all the silicate planets to some degree depending on their mass volatile content and location in the solar system this theory can be tested by deep drilling in archean terranes to locate remnants of the original crust by determination of the composition of the highland crust of mars and by investigations of the crust of venus

snc meteorites clues to martian petrologic evolution the shergottites nakhlites and chassigny snc meteorites are apparently cumulate mafic and ultramafic rocks that crystallized at shallow levels in the crust of their parent body the mineralogy and chemistry of these meteorites are remarkably like equivalent terrestrial rocks although their ratios of fe fe mg and certain incompatible elements and their oxygen isotopic compositions are distinctive all have crystallization ages of 1 3 b y or younger and formed from magmas produced by partial melting of previously fractionated source regions isotope systematics suggest that the snc parent body had a complex and protracted thermal history spanning most of geologic time some meteorites have been severely shock metamorphosed and all were ejected from their parent body at relatively recent times possibly in several impact events late crystallization ages complex petrogenesis and possible evidence for a large gravitational field suggest that these meteorites are derived from a large planet trapped gases in shergottite shock melts have compositions similar to the composition measured in the martian atmosphere ejection of martian meteorites may have been accomplished by acceleration of near surface spalls or other mechanisms not fully understood if snc meteorites are of martian origin they provide important information on planetary composition and evolution the bulk composition and redox state of the martian mantle as constrained by shergottite phase equilibria must be more earthlike than most current models planetary thermal models should benefit from data on the abundances of radioactive heat sources the melting behavior of the mantle and the timing of planetary differentiation calculated depletion of chalcophile elements in source regions indicates a core dominated by sulfides and paleomagnetic measurements suggest the presence of a weak magnetic field within the last several hundred thousand years concentrations of volatile elements indicate that the snc parent body was not volatile depleted and trapped atmospheric components measured in shock melts may be useful in understanding planetary degassing by providing comparisons for spectral reflectance data and viking soil analyses these meteorites may also constrain surface mineralogy and weathering mechanisms

physical processes in volcanic eruptions mechanisms are modeled in terms of dynamic physico chemical processes in this respect volcanology shares with much of earth science in general the benefits that accrue from the application of the methods and concepts of other disciplines to its problems basic concepts from the fields of thermo dynamics fluid mechanics and rheology have been particularly impor tant in fostering new insights recent developments have been so numerous as to make it necessary to limit the scope of this review and thus we concentrate here on the basic physical processes involved in the rise of magma to the surface and the distribution of cruption products on thc ground or in the atmosphere the perspective of planetary volcanism wilson hcad 1983 underlines the fact that volcanoes can be regarded as probes of the composition and structure of a planetary interior as a function of position depth and time