ponding draining and tilting of the cerberus plains a cryolacustrine origin for the sinuous ridge and channel networks in rahway vallis mars rahway vallis sits within a shallow basin the rahway basin in the cerberus plains of mars containing a branching network of channels converging on the basin floor using topographic cross profiles of the channels we have found that they are set within broader subtly expressed valleys these valleys are shallow around 15 m vertically compared to several kilometres in the horizontal and have convex to rectilinear slope profiles that are consistent in form across the whole rahway basin both channels and valleys descend and deepen consistently from west to east the channels typically widen down slope and increase in width at confluences the morphology and topology of this channel system are consistent with formation by contributory fluid flow generated from many distributed sources the transition between the older heavily cratered terrain and the floor of the rahway basin is bounded by near horizontal continuous topographic terraces plotting the elevation of the terraces shows that they conform to a plane with a height difference of around 100 m east to west for the 300 km width of the rahway basin we calculate that the volume of material needed to fill the topography up to the level of the plane best fit by the terraces is 1500 km3 bordering the channels are sinuous ridges typically several kilometres long 20 m across with heights on the order of 10 m they sometimes form branching networks leading into the channels but also occur individually and parallel to the channels the multiple tilted terraces the channel valley network with many fluvial like characteristics and the distributed source regions suggest that the landforms within the rahway basin are unlikely to have formed through purely volcanic processes rather the channels within the rahway basin are consistent with a genesis requiring the flow of liquid water and the sinuous ridges with melting of a static ice body that occupied the basin we suggest a hypothesis of rapid basin filling by fluvial flooding followed by lake drainage drainage could have occurred as a consequence of an ice or debris dam failure within or during the formation of the large nearby fluvial flood channel marte vallis if the lake was partly or largely frozen prior to drainage this offers a possible explanation for the sinuous ridge systems hence although the sinuous ridges provide some of the most compelling morphological analogues of terrestrial eskers yet observed we conclude that the contextual evidence for this interpretation in rahway vallis is not strong and instead they are better explained in the context of a frozen or partially frozen lake or cryolacustrine model

the topography and morphology of low shields and associated landforms of plains volcanism in the tharsis region of mars abstract the morphology and topography of volcanic landforms provide critical information to the investigation of their tectonic setting and the physical characteristics e g rheology of their eruption products their investigation is also an important prerequisite for studies of comparative planetology e g the comparison between surface features of the earth and other planetary bodies numerous small and low shield volcanoes on mars and associated vents and lava flows have previously been compared to terrestrial plains style volcanism which is defined as being an intermediate style between flood basalts and the hawai ian shields this study investigates the topography and morphology of martian landforms associated with plains volcanism using mola moc themis hrsc and hirise data low shields and other landforms of plains volcanism on mars display similarities with terrestrial basaltic volcanic fields and we do not observe any features that do not have morphologic analogues on earth the most typical landforms of martian plains style volcanism are low shields defined as volcanic shields with diameters of typically less than 50 km heights of a few hundred meters only and extremely shallow flank slopes of less than 0 5 other surface features related to plains style volcanism on mars are craters fissure vents cinder and spatter cones lava flows that are commonly associated with lava channels and tubes lava inflation features and volcanic rift zones our results reconfirm the viking orbiter based conclusion that plains volcanism in the eastern snake river plains is perhaps the best terrestrial morphological analogue for these martian surface features icelandic shields distinct structures in hawai i and other basaltic landforms also show similarities to martian plains volcanism sinuous rilles previously not described in association with plains volcanism on mars are interpreted as evidence for high eruption rates the extremely shallow flank slopes of the low shields suggest the eruption of shield building lavas with low viscosity which might be the result of high eruption temperatures high effusion rates a low si and a high mg content along with a possible high fe content or a combination of these factors the spatial distribution of low shield clusters in tharsis does not show any obvious association with large scale tectonic features plains volcanism might represent a relatively recent type of volcanism on mars which is not related to mantle plumes but to a zone of partial melting in an anomalously warm mantle underneath a thickened crust schumacher and breuer geophys res lett 34 l14202 doi 10 1029 2007gl030083 2007

color imaging of mars by the high resolution imaging science experiment hirise hirise has been producing a large number of scientifically useful color products of mars and other planetary objects the three broad spectral bands coupled with the highly sensitive 14 bit detectors and time delay integration enable detection of subtle color differences the very high spatial resolution of hirise can augment the mineralogic interpretations based on multispectral themis and hyperspectral datasets tes omega and crism and thereby enable detailed geologic and stratigraphic interpretations at meter scales in addition to providing some examples of color images and their interpretation we describe the processing techniques used to produce them and note some of the minor artifacts in the output we also provide an example of how hirise color products can be effectively used to expand mineral and lithologic mapping provided by crism data products that are backed by other spectral datasets the utility of high quality color data for understanding geologic processes on mars has been one of the major successes of hirise

chemically striking regions on mars and stealth revisited 1 the mars odyssey gamma ray spectrometer suite has yielded global chemical information for mars in this work we establish regions of unusual chemical composition relative to average mars primarily on the basis of ca cl fe h k si and th using data from mars odyssey the mars exploration rovers the mars reconnaissance orbiter imaging and 3 5 cm and 1 35 cm radar observations from earth we examine a chemically striking 2 e6 km2 region and find it to overlap significantly with a radar stealth region on mars it is remarkably enriched in cl and depleted in fe and si along with minor variations in h k and th relative to average mars surface dust observed at the two rover sites mixed with and indurated by ca mg bearing sulfate salts would be a reasonable chemical and physical analog to meter scale depths we describe potential scenarios that may have contributed to the unique properties of this region the bulk dust component may be an air fall deposit of compositionally uniform dust as observed in situ hydrothermal acid fog reactions on the flanks of nearby volcanoes may have generated sulfates with subsequent deflation and transport alternatively sulfates may have been produced by low temperature regional scale activity of ground ice driven brine and or regional scale deposition of acidified h2o snowfall

morphologic stratigraphic and morphometric investigations of valley networks in eastern libya montes mars implications for the noachian hesperian climate change dendritic valley networks and broad longitudinal valleys are widespread within the eastern libya montes region the morphologic characteristics of the studied dendritic valleys especially their occurrence at local summits provide evidence for the initial formation by surface runoff due to atmospheric precipitation whereas the longitudinal valley systems are thought to have been formed and modified by groundwater induced processes our crater counts and model ages show that the dendritic valley networks average age 4 0 ga formed earlier than the longitudinal valley systems average age 3 7 ga both fluvial forms indicate a temporal change of the erosive environment at the noachian hesperian transition at 3 8 ga our results suggest that the fluvial activity within our investigation area lasted for 800 my from 4 1 ga to 3 3 ga the dendritic valleys show valley densities between 0 12 km 1 and 0 57 km 1 indicative of highly mature and integrated valley systems that we interpret to be characteristic of warmer and wetter conditions on mars

windy mars a dynamic planet as seen by the hirise camera 1 with a dynamic atmosphere and a large supply of particulate material the surface of mars is heavily influenced by wind driven or aeolian processes the high resolution imaging science experiment hirise camera on the mars reconnaissance orbiter mro provides a new view of martian geology with the ability to see decimeter size features current sand movement and evidence for recent bedform development is observed dunes and ripples generally exhibit complex surfaces down to the limits of resolution yardangs have diverse textures with some being massive at hirise scale others having horizontal and cross cutting layers of variable character and some exhibiting blocky and polygonal morphologies reticulate fine polygonal texture bedforms are ubiquitous in the thick mantle at the highest elevations

tumulus development on lava flows insights from observations of active tumuli and analysis of formation models here we use observations of active flows along with detailed morphometric field measurements of more than 70 tumuli on flows at mount etna italy kilauea and hualalai us volcanoes to constrain a previously published model that estimates the pressure needed to form tumuli in an attempt to discover the nature and magnitude of pressure variations within active lava flow interiors we then consider how tumuli differ from idealized circular plates we incorporate observations of active tumuli and find that they may grow asymmetrically yet produce a symmetrical tumulus and can form where the flow path significantly changes direction bending models of clamped edges provide the most reasonable head estimates for the tumuli in our study tumulus formation requires the proper combination of cooling and effusion rate if cooling is too extensive and effusion rate too low the crust will provide too much resistance to bending if cooling is too limited and effusion rates too high crusts will not develop or have insufficient strength to resist fracture and subsequent breakouts we do not find it surprising that tumuli are rarely found over well established lava tubes that typically have rigid walls overlying crusts that exceed 2 m in thickness and provide too much resistance to bending silicic flows lack tumuli because the viscosity gradients within the flow are insufficient to concentrate stress in a localized area

erosion by flowing martian lava new insights for hecates tholus from mars express and mer data 1 we have used new compositional information on martian basaltic rocks from the mars exploration rover spirit and data from new stereo imaging by the high resolution stereo camera hrsc on the mars express orbiter to constrain an existing analytical numerical computer model to assess the potential of martian lavas to form lava channels by erosion of substrate the basaltic rocks studied in gusev crater by spirit have compositions consistent with lavas of higher liquidus temperature and lower dynamic viscosity than terrestrial tholeiitic basalts suggesting that they had a greater potential for turbulent flow and erosion of substrate during flow emplacement than terrestrial basalts more similar to lunar mare basalts we modeled a specific case to determine whether these lavas could have formed part of a 66 km long channel on the martian shield volcano hecates tholus this channel formed on relatively steep slopes 2 8 based on measurements from the hrsc digital terrain model our results suggest that erosion rates were of the order of tens to hundreds of centimeters day depending on flow rate and ice content of the substrate eruption durations required to erode the hecates channel 100 30 m deep over the first 20 km depth decreasing downstream range from weeks to months which are consistent with the known eruption durations of terrestrial basaltic lavas and the previous modeling of wilson and mouginis mark 2004 any hecates lava channels formed from erosion by lava could have served as conduits for later fluvial activity as recently described by fassett and head 2004 2005

hirise views enigmatic deposits in the sirenum fossae region of mars hirise images together with other recent orbital data from mars define new characteristics of enigmatic hesperian aged deposits in sirenum fossae that are mostly 100 200 m thick drape kilometers of relief and often display generally low relief surfaces new characteristics of the deposits previously mapped as the electris deposits include local detection of meter scale beds that show truncating relationships a generally light toned nature and a variably blocky weakly indurated appearance boulders shed by erosion of the deposits are readily broken down and contribute little to talus thermal inertia values for the deposits are 200 j m 2 k 1 s 1 2 and they may incorporate hydrated minerals derived from weathering of basalt the deposits do not contain anomalous amounts of water or water ice deflation may dominate degradation of the deposits over time and points to an inventory of fine grained sediment together with constraints imposed by the regional setting on formation processes these newly resolved characteristics are most consistent with an eolian origin as a loess like deposit comprised of redistributed and somewhat altered volcanic ash constituent sediments may be derived from airfall ash deposits in the tharsis region an origin directly related to airfall ash or similar volcanic materials is less probable and emplacement by alluvial fluvial impact lacustrine or relict polar processes is even less likely

linear volcanic features at alba patera mars probable spatter ridges a number of extensive linear constructional features occur on the north and east flanks of alba patera they are found in a 150 km wide zone and comprise aligned ridge elements that are locally associated with short volcanic flows they are among the youngest volcanic features in the region and are believed to be martian analogs of terrestrial spatter ridges on the basis of measurements made on viking images it appears that active volcanic fissures on mars were larger than their terrestrial counterparts

ridge like lava tube systems in southeast tharsis mars abstract lava tubes are widely distributed in volcanic fields on a planetary surface and they are important means of lava transportation we have identified 38 sinuous ridges with a lava tube origin in southeast tharsis the lengths vary between 14 and 740 km and most of them occur in areas with slopes

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

tharsis sourced relatively dust free lavas and their possible relationship to martian meteorites abstract the launch sites for martian snc meteorites remain unknown but they must derive from young volcanic provinces we present the first geologic and spectroscopic characteristics of a suite of relatively dust free lava flows that extend from underneath the regional dust cover on the south flank of the tharsis volcanic province on mars the purpose of this work is to 1 characterize these flows geologically by using thermal emission imaging system themis data supplemented by mars orbital laser altimeter mola mars orbital camera moc and high resolution imaging science experiment hirise datasets and 2 use thermal emission spectrometer tes data in order to test the hypothesis that tharsis represents a source for the sncs these flows are morphologically similar to flood lavas in amazonis planitia with the flow surfaces being a complex mixture of surficial materials with limited exposure the spectrally derived mineral composition and geochemistry for three flows reveals basaltic compositions that have an affinity with sncs especially the basaltic shergottites however discrepancies between spectra and mineral percentages for the flows versus the shergottites together with the observation of surface deposits on the flow surfaces make any connection between these flows and the sncs tenuous although not impossible further testing of a tharsis snc relationship will require measurements at finer spatial resolutions perhaps even in situ

scoria cones on mars detailed investigation of morphometry based on high resolution digital elevation models we analyze the shapes of 28 hypothesized scoria cones in three regions on mars i e ulysses and hydraotes colles and coprates chasma using available high resolution imaging science experiment and context camera ctx digital elevation models we determine the basic morphometric characteristics of the cones and estimate from ballistic modeling the physical parameters of volcanic eruptions that could have formed them when compared to terrestrial scoria cones most of the studied cones show larger volumes up to 4 2 109m3 larger heights up to 573m and smaller average slopes the average slopes of the ulysses hydraotes and coprates cones range between 7 and 25 and the maximum slopes only rarely exceed 30 which suggests only a minor role of scoria redistribution by avalanching ballistic analysis indicates that all cones were formed in a similar way and their shapes are consistent with an ejection velocity about 2 times larger and a particle size about 20 times smaller than on earth our results support the hypothesis that the investigated edifices were formed by low energy strombolian volcanic eruptions and hence are equivalent to terrestrial scoria cones the cones in hydraotes colles and coprates chasma are on average smaller and steeper than the cones in ulysses colles which is likely due to the difference in topographic elevation and the associated difference in atmospheric pressure this study provides the expected morphometric characteristics of martian scoria cones which can be used to identify landforms consistent with this type of activity elsewhere on mars and distinguish them from other conical edifices

shape of scoria cones on mars insights from numerical modeling of ballistic pathways abstract morphological observations of scoria cones on mars show that their cross sectional shapes are different from those on earth due to lower gravity and atmospheric pressure on mars particles are spread over a larger area than on earth hence erupted volumes are typically not large enough for the flank slopes to attain the angle of repose in contrast to earth where this is common the distribution of ejected material forming scoria cones on mars therefore is ruled mainly by ballistic distribution and not by redistribution of flank material by avalanching after the static angle of repose is reached as a consequence the flank slopes of the martian scoria cones do not reach the critical angle of repose in spite of a large volume of ejected material therefore the topography of scoria cones on mars is governed mainly by ballistic distribution of ejected particles and is not influenced by redistribution of flank material by avalanching the growth of a scoria cone can be studied numerically by tracking the ballistic trajectories and tracing the cumulative deposition of repeatedly ejected particles we apply this approach to a specific volcanic field ulysses colles on mars and compare our numerical results with observations the scoria cones in this region are not significantly affected by erosion and their morphological shape still preserves a record of physical conditions at the time of eruption we demonstrate that the topography of these scoria cones can be rather well with accuracy of 10 m reproduced provided that the ejection velocities are a factor of 2 larger and the ejected particles are about ten times finer than typical on earth corresponding to a mean particle velocity of 92 m s and a real particle size of about 4 mm this finding is in agreement with previous theoretical works that argued for larger magma fragmentation and higher ejection velocities on mars than on earth due to lower gravity and different environmental conditions

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

erosion by flowing lava field evidence erosion of substrate materials by melting or mechanical means has been suggested in active lava flows on earth and other planets although there are many references to lava erosion on earth unambiguous evidence is rare geological relationships commonly cited as evidence of downcutting by lava can be explained without recourse to erosion in order to assess possible erosion by flowing lava we carried out field studies of tube fed basalt flows sheet flows of the columbia river basalt province crb and precambrian komatiites unequivocal evidence for thermal erosion melted dacite substrate was found at the cave basalt lava tube mount st helens for which fluid dynamic analysis indicates laminar flow although erosion was enhanced in areas of locally steep slopes possibly as a result of localized turbulence other lava tubes in our study display strong but inconclusive evidence for erosion komatiite flows display good evidence for erosion of their substrate possibly in a turbulent regime but assessment of the extent of erosion is hampered by limited and disrupted exposures no evidence for thermal erosion was found in the crb our findings suggest that an erosional origin for planetary sinuous rilles and canali would be favored by high reynolds number flows high mass flux low viscosity lava steep slopes and substrates having a lower melting temperature than the lava or low mechanical strength e g regolith

high frequency radiation from earthquake sources in laterally varying layered structures point sources situated in a 2 d model of the earth s crust are presented special attention is devoted to faulting sources of finite extent with arbitrary spatial variations of rupture velocity and slip velocity intensity factor over a curved fault inserting gaussian beams and or paraxial ray approximations into the representation theorem leads to expressions which may be evaluated in several ways for situations in which the involved parameters vary smoothly along the fault the narrow beam approach may be used within the region on the fault illuminated by a beam the variation of parameters may be substituted by their taylor expansion and the expressions resulting from the representation theorem may be evaluated easily if any of the involved parameters do not change smoothly along the fault the broadbeam approach may be used in which the slip function is expanded into gaussian envelope functions several other modifications and or combinations of these approaches are proposed none of the mentioned algorithms requires a two point ray tracing moreover synthetic ground motions generated by different faulting models may under certain circumstances be computed using the same system of rays without repeating the relatively timeconsuming ray tracing this makes proposed algorithms more effective

the flood lavas of kasei valles mars abstract both the northern and southern arms of kasei valles are occupied by platy ridged flood lavas we have mapped these flows and examined their morphology to better understand their emplacement the lavas were emplaced as high flux turbulent flows exceeding 106 m3 s 1 lava in southern kasei valles can be traced back up onto the tharsis rise which is also the likely source of lavas in the northern arm these eruptions were similar to but somewhat smaller than the athabasca valles flood lava in elysium planitia with estimated volumes of 1200 km3 here and 5000 km3 in athabasca valles the flood lavas in both kasei and athabasca valles have evidence for distal inflation as well as widespread drainage or volume loss in medial areas this may be an important characteristic of many large recent martian eruptions despite their great size and flux the kasei valles flood lavas are only a late modification to the valley system capable of only modest local erosion the more vigorous athabasca valles lava may have been capable of somewhat more erosion in its smaller valley system

gamma ray constraints on the chemical composition of the martian surface in the tharsis region a signature of partial melting of the mantle the gamma ray spectrometer grs on board mars odyssey is the first instrument to provide quantitative estimates of the composition of the martian surface at the global scale at the present time published concentration maps are available across a broad equatorial swath for ca cl fe h k si and th however it remains to be determined to what extent the observed chemical signatures are the result of primary magmatic processes or secondary alteration at the surface with this question in mind we have considered in detail the grs signature on the western part of the tharsis region including olympus mons this region was chosen as it is clearly of volcanic origin has had a prolonged magmatic history and is of spatial extent sufficiently large that potential contributions of surrounding regions to the grs signature are limited it also has a characteristic composition being notably low in silica relative to the average composition of the martian mid latitudes the major element chemistry of the surface in this region sio2 feo cao k2o is compared with predictions of thermodynamic calculations of liquids produced by partial melting of the martian mantle composition proposed by dreibus and wanke dreibus g wanke h 1985 mars a volatile rich planet meteoritics 20 no 2 267 381 over a range of pressures and temperatures for all four oxides the tharsis compositions are consistent with liquids produced at pressures from 15 to 20 kbar and degrees of partial melting between 3 and 10 this pressure of melting implies a magma source depth in the range 125 170 km consistent with current estimates of the thickness of the lithosphere in this region the idea that the surface chemistry in the tharsis region is dominated by the signature of primary magmatism would therefore appear to be a reasonable working hypothesis although as more data become available more stringent and detailed tests of this simple model will be possible

reconciling channel formation processes with the nature of elevated outflow systems at ophir and aurorae plana mars 1 many hesperian outflow channels head at elevations compatible with aquifer recharge beneath the martian south polar cap and such channels are widely interpreted as the products of this recharge some outflow channels head at greater elevations that are inconsistent with southern recharge including three systems located in aurorae planum and eastern ophir planum these three systems have previously been interpreted as having formed through aqueous outbursts from local aquifers recharged by the meltwaters of ancient upland glaciers to the west however the viability of this interpretation is weakened by the lack of a geomorphic record supportive of past meltwater flow from western uplands inconsistencies between hypothesized processes and the nature of regional topography and mineralogy and the absence of satisfactory analog processes for catastrophic aqueous flow from the subsurface in contrast a volcanic origin for the ophir and aurorae systems appears to be in accord with the basic characteristics of constituent channels and associated landforms the volcanotectonic nature of the valles marineris system and adjacent upland plains and the nature of available analog landforms and processes though numerous uncertainties remain a volcanic interpretation of these outflow systems can more simply account for the existence of component channels the attributes of other elevated outflow systems on mars similarly appear to be most consistent with volcanic origins if the ophir and aurorae systems formed volcanically thermal considerations imply minimum erupted lava volumes of 6 4 103 km3 for allegheny vallis and 6 2 104 km3 for elaver vallis

regional dust deposits on mars physical properties age and history major dust storms on mars play an important role in the deposition and removal of fine dust material thermal radar and visual remote sensing observations provide important constraints on the martian regolith which have been used to determine the location and physical properties of regional dust deposits these deposits are located in three northern equatorial regions tharsis 20 s to 50 n 60 to 190 w arabia 5 s to 30 n 300 to 360 w and elysium 10 to 30 n 210 to 225 w they are covered by fine 2 40 m bright albedo 0 27 particles with fewer exposed rocks and coarse deposits than found elsewhere dust is currently deposited uniformly throughout the equatorial region at a rate of 40 m global storm over geologic time the rate of accumulation may vary from 0 to 250 m yr due to changes in atmospheric conditions produced by orbital variations dust deposited during global storms is subsequently removed only from dark regions resulting in a net accumulation in the low inertia bright regions the thickness of these current dust deposits is 0 1 2 m the thermal inertia places a lower limit of 0 1 m on the thickness of these deposits while the sparse but ubiquitous presence of exposed rocks and the degree of visible mantling indicate that the thickness is less than 5 m dual polarization radar observations of a very rough texture in tharsis are consistent with this model with a 2 m thick dust layer burying most of the surface rocks but permitting radar sampling of the rough subsurface based on their thickness and rate of accumulation the age of these deposits is 105 106 years suggesting a cyclic process of deposition and removal one possible cause may be cyclic variations in the magnitude and location of maximum wind velocities related to variations in mars orbit at present perihelion and maximum wind velocities occur in the south whereas regional dust deposits occur in the north suggesting net transport from south to north orbital parameters oscillate with periods ranging from 5 104 to 106 years the agreement between these periods and the dust deposit age suggests a possible link at different stages in orbit evolution maximum wind velocities will occur in the north with subsequent erosion and redistribution of the accumulated fines based on this model much of the uppermost martian surface is very young and is being continually reworked

using satellite imagery to identify and analyze tumuli on earth and mars abstract tumuli are small dome like features that form when magmatic pressures build within a subsurface lava pathway causing the overlying crust to bulge upwards as the appearance of these features has been linked to lava flow structure e g underlying lava flow tubes and conditions there is interest in identifying such features in satellite images so they can be used to expand our understanding of lava flows within regions difficult to access such as on other planets here we define a methodology for identifying and measuring tumuli within satellite imagery and validate it by comparing our results with fieldwork results of terrestrial tumuli reported in the literature and with independent measurements we made within amboy field ca in addition we present aggregated results from the application of our methodology to satellite images of six terrestrial fields and seven martian fields with 2100 tumuli identified per planet comparisons of tumuli morphometrics on earth and mars yield similarities in size and overall shape which were surprising given the many differences in the environmental and planetary conditions within which these features have formed given our measurements we identify constraints for tumulus formation models and drivers that would yield similar shapes and sizes on two different planets furthermore we test a published hypothesis regarding the number of tumuli that form per a square kilometer and find it unlikely that a diagnostic tumuli density value exists

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

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

layered megablocks in the central uplifts of impact craters abstract a database of bedrock exposed in crater central uplifts has been compiled from multiple orbital datasets in this study we focus on uplifts which show decameter scale layers within the exposed megablocks derived from the bedrock of the preexisting target this distinctive morphology found in 41 craters globally occurs mostly in regions mapped as hesperian plains material generally interpreted as regions of extensive flood lavas the association with volcanic units coupled with morphology and mineralogy that is consistent with flood lava emplacement suggests that the layers are stacks of dense lava interbedded with weaker materials estimates for the uplift of stratigraphic sections coupled with morphologic and morphometric analyses lead to estimated thicknesses of the layered unit these estimates indicate hesperian flood lavas are 23 thicker than a previous minimum estimate with a volume of 5 5 10 7 km 3 this increases the known extrusive volcanic production for the history of mars and volatile release to past martian atmospheres

the character of long term eruptions inferences from episodes 50 53 of the pu u ō ō kūpaianaha eruption of kīlauea volcano the pu u k paianaha eruption on the east rift zone of k lauea began in january 1983 the first 9 years of the eruption were divided between the pu u 1983 1986 and k paianaha 1986 1992 vents each characterized by regular predictable patterns of activity that endured for years in 1990 a series of pauses in the activity disturbed the equilibrium of the eruption and in 1991 the output from k paianaha steadily declined and a short lived fissure eruption broke out between k paianaha and pu u in february 1992 the k paianaha vent died and 10 days later eruptive episode 50 began as a fissure opened on the uprift flank of the pu u cone for the next year the eruption was marked by instability as more vents opened on the flank of the cone and the activity was repeatedly interrupted by brief pauses in magma supply to the vents episodes 50 53 constructed a lava shield 60 m high and 1 3 km in diameter against the steep slope of the pu u cone by 1993 the shield was pockmarked by collapse pits as vents and lava tubes downcut as much as 29 m through the thick deposit of scoria and spatter that veneered the cone as the vents progressively lowered the level of the pu u pond also dropped demonstrating the hydraulic connection between the two the downcutting helped to undermine the prominent pu u cone which has diminished in size both by collapse as a large pit crater formed over the conduit and by burial of its flanks intervals of eruptive instability such as that of 1991 1993 accelerate lateral expansion of the subaerial flow field both by producing widely spaced vents and by promoting surface flow activity as lava tubes collapse and become blocked during pauses

aeolian bedforms yardangs and indurated surfaces in the tharsis montes as seen by the hirise camera evidence for dust aggregates abstract hirise images of mars with ground sampling down to 25 cm pixel show that the dust rich mantle covering the surfaces of the tharsis montes is organized into ridges whose form and distribution are consistent with formation by aeolian saltation other dusty areas near the volcanoes and elsewhere on the planet exhibit a similar morphology the material composing these reticulate bedforms is constrained by their remote sensing properties and the threshold curve combined with the saltation suspension boundary both of which vary as a function of elevation atmospheric pressure particle size and particle composition considering all of these factors dust aggregates are the most likely material composing these bedforms we propose that airfall dust on and near the volcanoes aggregates in situ over time maybe due to electrostatic charging followed by cementation by salts the aggregates eventually reach a particle size at which saltation is possible aggregates on the flanks are transported downslope by katabatic winds and form linear and accordion morphologies materials within the calderas and other depressions remain trapped and are subjected to multidirectional winds forming an interlinked honeycomb texture in many places on and near the volcanoes light toned low thermal inertia yardangs and indurated surfaces are present these may represent duststone formed when aggregates reach a particle size below the threshold curve such that they become stabilized and subsequently undergo cementation

high resolution imaging science experiment hirise images of volcanic terrains from the first 6 months of the mars reconnaissance orbiter primary science phase 1 in the first 6 months of the mars reconnaissance orbiter s primary science phase the high resolution imaging science experiment hirise camera has returned images sampling the diversity of volcanic terrains on mars while many of these features were noted in earlier imaging they are now seen with unprecedented clarity we find that some volcanic vents produced predominantly effusive products while others generated mostly pyroclastics flood lavas were emplaced in both turbulent and gentle eruptions producing roofed channels and inflation features however many areas on mars are too heavily mantled to allow meter scale volcanic features to be discerned in particular the major volcanic edifices are extensively mantled though it is possible that some of the mantle is pyroclastic material rather than atmospheric dust support imaging by the context imager ctx and topographic information derived from stereo imaging are both invaluable in interpreting the hirise data

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

athabasca valles mars a lava draped channel system athabasca valles is a young outflow channel system on mars that may have been carved by catastrophic water floods however images acquired by the high resolution imaging science experiment camera onboard the mars reconnaissance orbiter spacecraft reveal that athabasca valles is now entirely draped by a thin layer of solidified lava the remnant of a once swollen river of molten rock the lava erupted from a fissure inundated the channels and drained downstream in geologically recent times purported ice features in athabasca valles and its distal basin cerberus palus are actually composed of this lava similar volcanic processes may have operated in other ostensibly fluvial channels which could explain in part why the landers sent to investigate sites of ancient flooding on mars have predominantly found lava at the surface instead

lava water interaction and hydrothermal activity within the 2014 2015 holuhraun lava flow field iceland abstract lava that erupted during the 2014 2015 holuhraun eruption in iceland flowed into a proglacial river system resulting in aqueous cooling of the lava and an ephemeral hydrothermal system we carried out a monitoring study of this system from 2015 to 2018 to document the cooling of the lava over this time using thermocouple measurements and data logging sensors the heat loss rate from advection through this hydrothermal system in august 2015 was 5 5 108 w since eruption aqueous cooling likely accounted for 1 of the total heat loss from the lava this estimate excludes steam losses from fumaroles as well as any groundwater that was not released to the surface and thus is a lower bound near the terminus of the flow advection of heat by flowing water may have locally accounted for tens of percent of the total cooling of that part of the flow our data quantify the importance of water cooling for this lava flow and can be compared with models to better understand lava water interactions more generally we also provide detailed methods for simple low cost monitoring of similar instances in the future

ring moat dome structures rmdss in the lunar maria statistical compositional and morphological characterization and assessment of theories of origin ring moat dome structures rmdss are positive morphologic features found clustered across many mare regions on the moon of which only a few isolated examples have been previously reported our continuing survey has expanded the known locations of the rmdss from 2 600 to over 8 000 indicating that rmdss are more common geological features than previously thought this work presents a detailed geomorphological analysis of 532 rmdss identified in several mare basins the combination of detailed elemental mapping morphological and morphometric analyses spatial distribution relationships with other geologic structures and comparison with terrestrial analogs lead us to conclude that 1 rmdss represent low circular mounds with diameters of a few hundred meters average about 200 m and a mean height of 3 5 m the mounds are surrounded by moats ranging from tens to over 100 m in width and up to several meters in depth 2 there is a wide variation of titanium abundances although rmdss are more commonly found in mare regions of moderate to high titanium content 3 wt tio2 3 rmdss are found to occur on or around fractures graben and volcanic edifices small shields and cones 4 a spatial association between rmdss and irregular mare patches see braden et al 2014 https doi org 10 1038 ngeo2252 is observed suggesting that both may form from related lava flows 5 comparisons between rmdss and lava inflationary structures on earth support an inflation related extrusive nature and a genetic relationship with host lava flow processes and 6 rmds embayment relationships with craters of different degradation ages superposed on the host mare and regolith development models produces conflicting age relationships and divide theories of rmds origin into two categories 1 synchronous with the emplacement and cooling of the host lava flows 3 4 ga and 2 emplaced substantially after the host mare lava unit in the period 0 3 ga we outline the evidence supporting this age conundrum and implications for the different theories of origin and describe future research avenues to help resolve these outstanding questions 2020 american geophysical union all rights reserved

emplacement and erosive effects of lava in south kasei valles mars abstract although it has generally been accepted that the martian outflow channels were carved by floods of water observations of large channels on venus and mercury demonstrate that lava flows can cause substantial erosion recent observations of large lava flows within outflow channels on mars have revived discussion of the hypothesis that the martian channels are also produced by lava an excellent example is found in south kasei valles skv where the most recent major event was emplacement of a large lava flow calculations using high resolution digital terrain models dtms demonstrate that this flow was locally turbulent similar to a previously described flood lava flow in athabasca valles the modeled peak local flux of approximately 106 m3 s 1 was approximately an order of magnitude lower than that in athabasca which may be due to distance from the vent fluxes close to 107 m3 s 1 are estimated in some reaches but these values are probably records of local surges caused by a dam breach event within the flow the skv lava was locally erosive and likely caused significant kilometer scale headwall retreat at several cataracts with tens to hundreds of meters of relief however in other places the net effect of the flow was unambiguously aggradational and these are more representative of most of the flow the larger outflow channels have lengths of thousands of kilometers and incision of a kilometer or more therefore lava flows comparable to the skv flow did not carve the major martian outflow channels although the skv flow was among the largest and highest flux lava flows known in the solar system

statistical distribution of tumuli on pahoehoe flow surfaces analysis of examples in hawaii and iceland and potential applications to lava flows on mars 1 spatial distributions of tumuli on lava flow surfaces can be quantitatively linked to subsurface inflation processes three distinct styles of flow emplacement are studied 1 lava flows undergo inflation that changes as a function of space and time resulting in random spatial distributions of tumuli 2 lava flows with preferred pathways result in systematic clustering of inflation features and 3 established tubes or narrow pahoehoe flows produce chains of tumuli statistical analyses are required to distinguish between styles one and two comparison of the spatial distribution of tumuli on a portion of a lava flow at mauna ulu with the poisson distribution indicates that tumuli are randomly distributed on the flow surface typical of style one emplacement where small scale topographic variability and low slope influence development of preferred pathways that evolve over time at thrainsskjoldur direct statistical comparisons to the poisson spatial distribution are inconclusive but nearest neighbor analysis indicates significant clustering an initially random spatial distribution is inferred that developed preferred pathways and systematic clustering of inflation features as with style two at elysium planitia on mars the flow margin is significantly deficient in inflation features while away from the margin the flow exhibits a random spatial distribution of tumuli typical of style one emplacement the flow is interpreted as multiple units or a single flow that migrated in space during emplacement at the 1843 flow on mauna loa tumuli occur on a linear trend consistent with style three emplacement

the dynamics of star dunes an example from the gran desierto mexico observations of patterns of erosion and deposition and surface wind velocity and direction on a 40 m high star dune in the gran desierto sand sea indicate that interactions between dune form and airflow as winds change direction seasonally play a major role in the formation of this dune type such interactions lead to deposition of sand in the central parts of the dune giving rise to its pyramidal shape as well as to some extension of the linear arms the major arms of the dune studied are oriented ne sw or transverse to summer sse and winter nnw winds an avalanche face up to 10 m high develops during the course of each season flow separation at the main crestline gives rise to a wide zone of lee side secondary flow which moves sand along the base of the avalanche face towards the central part of the dune where it is deposited as wind ripples migrate into zones of locally reduced flow velocity reattachment of the separated flow occurs on the lower part of the n or s arms parallel to the flow spring westerly winds move sand obliquely up the s and n arms of the dune and outwards on the e arm large scale flow separation and diversion are replaced by the development of strong helical eddies in the immediate lee of the main crestline which move sand along avalanche faces and into zones of lower flow velocity at the end of dune arms formation of star dunes in the gran desierto follows a sequence in which crescentic dunes migrating into areas of opposed winds first develop a reversing crestal ridge convergent leeside secondary flows are developed which result in the formation of linear elements parallel to each major wind direction and the concentration of sand in the central part of the dune examples of star dunes at different stages of their development can be documented

discovery of columnar jointing on mars we report on the discovery of columnar jointing in marte valles mars these columnar lavas were discovered in the wall of a pristine 16 km diameter impact crater and exhibit the features of terrestrial columnar basalts there are discontinuous outcrops along the entire crater wall suggesting that the columnar rocks covered a surface area of at least 200 km 2 assuming that the rocks obliterated by the impact event were similarly jointed we also see columns in the walls of other fresh craters in the nearby volcanic plains of elysium planitia amazonis planitia which include marte vallis and in a well preserved crater in northeast hellas

composition and location of volatiles at loki patera io abstract volatiles play a critical role in determining the nature of volcanic activity on earth but their role in the volcanism on io is less clear to help determine that role we analyze voyager and galileo images of loki patera loki is the largest caldera in the solar system and io s most powerful volcano however its eruptive behavior is still not understood it appears to be relatively volatile poor in comparison to other sites like pele where volatiles drive a 350 km high plume a resurfacing wave either from spreading flows or from foundering of a lava lake crust periodically sweeps around loki patera photometry from voyager i and ii violet and blue images shows that most of the features in and around loki have colors well matched by macroscopic mixing of sulfur and basalt the dark western portion of the patera has the color of bare basalt assuming such a macroscopic sulfur basalt mix in the voyager i images most of the rest of the patera appears to be covered with a background of 13 38 sulfur we infer this background sulfur was deposited from the nearby plume observed by voyager i and ii the surface of the patera is also dotted by numerous small bright areas which have colloquially been called bergs we find that they are also composed of sulfur with coverage ranging up to 100 darker regions adjacent to the patera such as the southwest overflow are a mixture of intermediate amounts of sulfur and basalt the bathtub ring at the edge of the overflow is again roughly 100 sulfur perhaps with significant amounts of so 2 included colors seen during the voyager ii flyby are also consistent with this general pattern but most of the patera has a sulfur abundance higher than that seen in voyager i while the then dark southern portion is again close to the reflectance of bare basalt we have also analyzed the spatial distribution of the bergs they clearly avoid the inner and outer margins of the patera and they also avoid each other while a simple explanation of the above patterns could be that the bergs are fumarolic sulfur deposited on a periodically resurfaced lava lake crust other observations seem inconsistent with that simple model careful comparison of voyager i and galileo data shows that the largest bergs in the southern patera have survived the intervening 22 years this requires that at least those larger bergs represent some more permanent feature perhaps higher standing kipuka which avoid inundation by the lava resurfacing wave

the importance of pahoehoe abstract pahoehoe lava flows are common in every basaltic province and their submarine variants pillow lavas and sheet flows cover the bulk of the earth pahoehoe flows are emplaced by inflation the injection of molten lava underneath a solidified crust only in the past few years has an understanding of the inflation process and the ability to recognize ancient inflated lava flows been achieved all large terrestrial basaltic flow fields studied to date including flood basalts were emplaced as thermally efficient inflated compound pahoehoe sheet flows this leads us to propose that this is the standard way of emplacing large lavas the swell hypothesis the atmospheric impact of such flood basalt eruptions could have been protracted and severe providing a plausible link between flood basalt eruptions and mass extinctions

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

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

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

numerical modeling of ejecta dispersal from transient volcanic explosions on mars the dynamics of ejecta dispersal in transient volcanic eruptions on mars are distinct from those on earth and venus because of the low atmospheric pressure and gravitational acceleration numerical modeling of the physical mechanisms of such activity accounting for the different martian environmental conditions can help constrain the style of emplacement of the eruptive products the scenario envisaged is one of pressurized gas contributed from either a magmatic or meteoric source accumulating in the near surface crust beneath a retaining medium on failure of the confining material the gas expands rapidly out of the vent displacing both the caprock and a mass of atmospheric gas overlying the explosion site in a discrete transient event trajectories of large blocks of ejecta are computed subject to the complex aerodynamic interactions of atmospheric and volcanic gases which are set in motion by the initiation of the explosion reservoirs of crustal and surface water and carbon dioxide may have increased the chances of occurrence of transient explosive events on mars in two ways by supplying a source of volatiles for vaporization by the magma and by acting to slow the ascent of the magma by chilling it providing conditions favorable for gas accumulation results of the modeling indicate that ejection velocities ranging up to 580 m sec 1were possible in martian h2o driven explosions with co2 driven velocities typically a factor of 1 5 smaller travel distances of large blocks of ejecta lie within the range of a few kilometers to the order of 100 km from the vent the low martian atmospheric pressure and gravity would thus have conspired to produce more vigorous explosions and more widely dispersed deposits than are associated with analogous events on earth or venus other phenomena likely to be associated with transient explosions include ashfall deposits from associated convecting clouds of fine material pyroclastic flows and ejecta impact crater fields it is anticipated that the martian environment would have caused such features to be greater in size than would be the case in the terrestrial environment ash clouds associated with discrete explosions are expected to have risen to a maximum of 25 km on mars producing deposits having similar widths another indication of a volcanic explosion site might be found in areas of high regolith ice content such as fretted terrains where ice removal and mass wasting may have modified the vent s initial morphology the modeling results highlight the implications of the occurrence of transient explosive eruptions for the global crustal volatile distribution and provide some predictions of the likely manifestation of such activity for testing by upcoming spacecraft missions to mars

lava rise ridges of the toomba basalt flow north queensland australia unusually long lava rises occur in the distal portion of the toomba basalt flow up to 120 km from the source in the lolworth creek region three parallel lava rise ridges occur over a 6 km section two of these ridges are continuous for the entire 6 km the ridges average 7 m in height and range from 35 m to 300 m in width lava inflation clefts are numerous and lava rise pits also occur down flow a single lava rise ridge averaging 18 m high and up to 500 m wide extends for a further 10 km this ridge has a generally level surface with abrupt edges sloping between 45 and 90 accurate surveys across the ridges show that in some cases there has been some stretching of the surface presumably prior to the formation of the prominent clefts the ridges were formed from an initially thin flow that was inflated by a continuous layer of lava that underlay almost the entire width of each ridge rather than by a system of lava tubes of more limited dimensions inflated material represents over 90 of the volume of the distal parts of the flow estimates of the time required to inflate the lava rise ridges range from 60 days to a year

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

reexamining the relationship between apollinaris patera and the basalts of the gusev crater plains mars 1 a possible source of the gusev crater basalts analyzed by the spirit rover is apollinaris patera we test this hypothesis by identifying and analyzing potential lava flow paths using thermal emission imaging system mars orbiter camera high resolution imaging science experiment and mars orbiter laser altimeter data sets together with published geologic mapping image interpretation reveals three possible flow paths from apollinaris onto gusev crater floor via a breach in gusev s northwest rim an unnamed crater that must have postdated any potential flow along the paths currently blocks the breach after correcting for the unnamed crater topographic profiles constructed along possible flow paths demonstrate that elevation along each path increases from 80 to 430 m for two of the pathways this elevation change indicates that lavas could not have traversed through them the third profile though is less conclusive as the topography may reflect a broad flexural arch however on the basis of two of the topographic profiles together with the lack of obvious lava flow structures that indicate flow south through the breach we propose that apollinaris was not the direct source of the gusev basalts instead we argue that it seems more likely that the gusev basalts were sourced from below the crater itself the similar ages as derived from crater counts of apollinaris s south flank and the gusev plains lavas however suggest that the two volcanic regions may be part of a common magmatic feature

development of the 1990 kalapana flow field kilauea volcano hawaii the 1990 kalapana flow field is a complex patchwork of tube fed pahoehoe flows erupted from the kupaianaha vent at a low effusion rate approximately 3 5 m3 s these flows accumulated over an 11 month period on the coastal plain of kilauea volcano where the pre eruption slope angle was less than 2 the composite field thickened by the addition of new flows to its surface as well as by inflation of these flows and flows emplaced earlier two major flow types were identified during the development of the flow field large primary flows and smaller breakouts that extruded from inflated primary flows primary flows advanced more quickly and covered new land at a much higher rate than breakouts the cumulative area covered by breakouts exceeded that of primary flows although breakouts frequently covered areas already buried by recent flows lava tubes established within primary flows were longer lived than those formed within breakouts and were often reoccupied by lava after a brief hiatus in supply tubes within breakouts were never reoccupied once the supply was interrupted during intervals of steady supply from the vent the daily areal coverage by lava in kalapana was constant whereas the forward advance of the flows was sporadic this implies that planimetric area rather than flow length provides the best indicator of effusion rate for pahoehoe flow fields that form on lowangle slopes

the distribution and behavior of martian ground ice during past and present epochs mars undergoes significant oscillations in its orbit which will have a pronounced effect on its climate and in particular on the behavior of subsurface water ice we explore and map the behavior of ice in the martian near surface regolith over the past 1 m y using a diffusion and condensation model presented in an earlier paper with two primary modifications to include orbitally induced variations in insolation and atmospheric water abundance we find that the past behavior of ground ice differs significantly from that at the present epoch primarily the result of high amplitude oscillations in obliquity presently 25 in midlatitude and equatorial regions ground ice will condense from atmospheric water during times of higher obliquity filling the top few meters of the regolith with significant amounts of ice at an obliquity of 32 ground ice becomes stable globally during times of lower obliquity ground ice will sublime and diffuse back into the atmosphere dessicating the regolith to a depth of about 1 to 2 m equatorward of 60 to 70 latitude in the high latitude regions these oscillations are considerably subdued below this depth of cyclic saturation and dessication a long term stability of ice exists in some geographic regions we present a map of the distribution of ice expected at the present epoch cyclic exchange of water between the global regolith and polar regions will have significant implications for surface geology and the polar layered deposits

a sinuous tumulus over an active lava tube at klauea volcano evolution analogs and hazard forecasts abstract inflation of narrow tube fed basaltic lava flows tens of meters across such as those confined by topography can be focused predominantly along the roof of a lava tube this can lead to the development of an unusually long tumulus its shape matching the sinuosity of the underlying lava tube such a situation occurred during k lauea volcano s hawai i usa ongoing east rift zone eruption on a lava tube active from july through november 2010 short lived breakouts from the tube buried the flanks of the sinuous ridge like tumulus while the tumulus crest its surface composed of lava formed very early in the flow s emplacement history remained poised above the surrounding younger flows at least several of these breakouts resulted in irrecoverable uplift of the tube roof confined sections of the prehistoric carrizozo and mccartys flows new mexico usa display similar sinuous ridge like features with comparable surface age relationships we contend that these distinct features formed in a fashion equivalent to that of the sinuous tumulus that formed at k lauea in 2010 moreover these sinuous tumuli may be analogs for some sinuous ridges evident in orbital images of the tharsis volcanic province on mars the short lived breakouts from the sinuous tumulus at k lauea were caused by surges in discharge through the lava tube in response to cycles of deflation and inflation di events at k lauea s summit the correlation between di events and subsequent breakouts aided in lava flow forecasting breakouts from the sinuous tumulus advanced repeatedly toward the sparsely populated kalapana gardens subdivision destroying two homes and threatening others hazard assessments including flow occurrence and advance forecasts were relayed regularly to the hawai i county civil defense to aid their lava flow hazard mitigation efforts while this lava tube was active

new observations of volcanic features on mars from the themis instrument 1 images obtained by the themis instrument on mars odyssey permit the identification of many new volcanic features on mars several new types of vent systems including fissure vents within the tharsis region flank vents on olympus mons and ascraeus mons and lava shields on the floor of arsia mons have been found the valley networks on hecates tholus are seen to be more complex than previously believed extending from the caldera rim to the base of hecates tholus volcano individual valleys change width and depth in apparent response to local topography valley formation spanned the time period during which lava flows from elysium mons embayed the southern flank of hecates tholus as demonstrated by the burial of some valleys by the lava flows and the formation of sediment fans on top of adjacent parts of the flows themis images now allow new constraints to be placed on the dynamics of lava flow emplacement with the identification of flows with well defined lava channels on the northern flank of ascraeus mons as well as an enigmatic braided lava channel three previously unreported collapse events 3 7 to 4 3 km in diameter are identified within the caldera of ascraeus mons details of the mode of formation of parts of the olympus mons aureole can also be identified supporting the idea that the aureole had a landslide origin themis images show that parts of the aureole have been modified by water discharged to the east of olympus mons

volcanic and structural history of the rocks exposed at pickering crater daedalia planum mars abstract in the western hemisphere of mars amazonian volcanism from arsia mons produced the smooth surfaces of daedalia planum and masks older rocks close to the southern termination of daedalia planum basement rocks are exposed in which are preserved craters that escaped or were only partially filled by this most recent volcanism pickering crater is an approximately 130 km diameter crater the youngest lavas flowed into this crater from daedalia planum by way of a nw rim breach covering its western part east of a well defined flow front an older lava sequence with a distinctive platy surface and derived from a more proximal unestablished source to the northeast is exposed several units are identified within this sequence on the basis of surface texture which is more subdued in progressively older rocks only local mapping of the flow front boundaries of these units is possible because of incomplete coverage by high resolution imagery during emplacement of the older lavas a ne sw striking en echelon graben system and parallel smaller troughs and dikes formed under inferred regional nw se extension a much earlier strike slip regime pre dating the lavas exposed in the crater floor is postulated based on the highly fretted nature of the rim of pickering crater and an elongated smaller crater to its northeast approximately 40 km long in the ne sw direction the rims of these craters contrast with that of a smoother rimmed impact crater in the southeast that was excavated subsequent to strike slip deformation but prior to the emplacement of platy surfaced lavas

the volcanic history of syria planum mars abstract a field of small 10s of km in diameter volcanoes in the syria planum region of mars is mapped to determine abundance distribution and alignments of vents these data are used to assess possible variations in eruption style across space and time each eruption site is assigned a point location nearest neighbor and two point azimuth analyses are conducted to assess the spacing and orientations between vents across the study area two vent fields are identified as unique volcanic units along with the previously identified syria mons volcano superposition relationships and crater retention rates indicate that these three volcanic episodes span 900 ma beginning in the early hesperian and ending in the early amazonian no clear hiatus in eruptive activity is identified between these events although a progression from eruptions at syria mons to regionally distributed eruptions that form the bulk of the syria planum plains to a final migration of dispersed eruptions to syria s northwest is identified nearest neighbor analyses suggest a non random distribution among the entire population of syria planum which is interpreted as resulting from the interaction of independent magma bodies ascending through the crust during different stress regimes throughout the region s eruptive history two point azimuth results identify three orientations of enhanced alignments which match well with radial extensions of three major tectonic centers to the south east and northwest of the study area as such syria planum volcanism evolved from a central vent volcano to dispersed shield field development over several hundred million years during which the independent magma bodies related to each small volcano interacted to some extent with one or more of at least three buried tectonic patterns in the older crust these results show a strong relationship between independent mapping efforts of tectonic and volcanic features continued integration of volcano tectonic mapping should provide direct constraints for future geodynamic models of magma production and thermal evolution of the tharsis province

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

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

determination of eruption temperature of io s lavas using lava tube skylights determining the eruption temperature of io s dominant silicate lavas would constrain io s present interior state and composition we have examined how eruption temperature can be estimated at lava tube skylights through synthesis of thermal emission from the incandescent lava flowing within the lava tube lava tube skylights should be present along io s long lived lava flow fields and are attractive targets because of their temporal stability and the narrow range of near eruption temperatures revealed through them we conclude that these skylights are suitable and desirable targets perhaps the very best targets for the purposes of constraining eruption temperature with a 0 9 0 7 m radiant flux ratio 6 3 being diagnostic of ultramafic lava temperatures because the target skylights may be small perhaps only a few m or 10 s of m across such observations will require a future io dedicated mission that will obtain high spatial resolution 100 m pixel unsaturated observations of io s surface at multiple wavelengths in the visible and near infrared ideally at night in contrast to observations of lava fountains or roiling lava lakes where accurate determination of surface temperature distribution requires simultaneous or near simultaneous 0 1 s observations at different wavelengths skylight thermal emission data are superior for the purposes of temperature derivation as emission is stable on much longer time scales minutes or longer so long as viewing geometry does not greatly change during that time

a network of lava tubes as the origin of labyrinthus noctis and valles marineris on mars abstract the role of lava tube networks and lava channels is reassessed as the primordial stage of the volcano erosional processes that formed the labyrinthus noctis valles marineris system instead of a tectonic origin the combined use of ctx crism hirise imagery and mola profiles has provided valuable insight in the evolution of pit chains into fossae first and then chasmata later due to mass wasting processes caused by the erosional effect of the lava flows that draped valles marineris and other outflow channels although a quantitative evaluation of eruption rates is difficult even with digital terrain models dtms because of the mixing between new flows and paleoflows a comparison with elysium and other tharsis outflow channels suggests that the availability of lava supply is correlated to their widths the images of ubiquitous lava flows rather than sporadic light toned deposits strengthen the role of lava over that of water in the erosional processes that formed labyrinthus noctis and carved valles marineris like many other outflow channel on mars the erosional evolution of the outflow channels shows an increasing trend of age and a decreasing trend of depth from the sources on tharsis to the mouths at chryse planitia this finding coupled with the observation of lava flows mantling chryse planitia may have profound implications for the water inventories thought to have filled the lowlands with an ocean

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

the high resolution imaging science experiment hirise during mro s primary science phase psp the high resolution imaging science experiment hirise on the mars reconnaissance orbiter mro acquired 8 terapixels of data in 9137 images of mars between october 2006 and december 2008 covering 0 55 of the surface images are typically 5 6 km wide with 3 color coverage over the central 20 of the swath and their scales usually range from 25 to 60 cm pixel nine hundred and sixty stereo pairs were acquired and more than 50 digital terrain models dtms completed these data have led to some of the most significant science results new methods to measure and correct distortions due to pointing jitter facilitate topographic and change detection studies at sub meter scales recent results address noachian bedrock stratigraphy fluvially deposited fans in craters and in or near valles marineris groundwater flow in fractures and porous media quasi periodic layering in polar and non polar deposits tectonic history of west candor chasma geometry of clay rich deposits near and within mawrth vallis dynamics of flood lavas in the cerberus palus region evidence for pyroclastic deposits columnar jointing in lava flows recent collapse pits evidence for water in well preserved impact craters newly discovered large rayed craters and glacial and periglacial processes of particular interest are ongoing processes such as those driven by the wind impact cratering avalanches of dust and or frost relatively bright deposits on steep gullied slopes and the dynamic seasonal processes over polar regions hirise has acquired hundreds of large images of past present and potential future landing sites and has contributed to scientific and engineering studies of those sites warming the focal plane electronics prior to imaging has mitigated an instrument anomaly that produces bad data under cold operating conditions

layering stratigraphy of eastern coprates and northern capri chasmata mars abstract distinct competent layers are observed in the slopes of eastern coprates chasma part of the valles marineris system on mars our observations indicate that the stratigraphy of coprates chasma consists of alternating thin strong layers and thicker sequences of relatively weak layers the strong competent layers maintain steeper slopes and play a major role in controlling the overall shape and geomorphology of the chasmata slopes the topmost competent layer in this area is well preserved and easy to identify in outcrops on the northern rim of coprates chasma less than 100 m below the southern ophir planum surface the volume of the topmost emplaced layer is at least 70 km 3 and may be greater than 2100 km 3 if the unit underlies most of ophir planum the broad extent of this layer allows us to measure elevation offsets within the north rim of the chasma and in a freestanding massif within coprates chasma where the layer is also observed rim outcrop morphology and elevation differences between ophir and aurorae plana may be indicative of the easternmost extent of the topmost competent layer these observations allow an insight into the depositional processes that formed the stratigraphic stack into which this portion of the valles marineris is carved and they present a picture of some of the last volcanic activity in this area furthermore the elevation offsets within the layer are evidence of significant subsidence of the massif and surrounding material

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