seasonal activity and morphological changes in martian gullies abstract recent studies of martian dune and non dune gullies have suggested a seasonal control on present day gully activity the timing of current gully activity especially activity involving the formation or modification of channels which commonly have been taken as evidence of fluvial processes has important implications regarding likely gully formation processes and necessary environmental conditions in this study we describe the results of frequent meter scale monitoring of several active gully sites by the high resolution imaging science experiment hirise on the mars reconnaissance orbiter mro the aim is to better assess the scope and nature of current morphological changes and to provide improved constraints on timing of gully activity on both dune and non dune slopes our observations indicate that 1 gully formation on mars is ongoing today and 2 the most significant morphological changes are strongly associated with seasonal frost and defrosting activity observed changes include formation of all major components of typical gully landforms although we have not observed alcove formation in coherent bedrock these results reduce the need to invoke recent climate change or present day groundwater seepage to explain the many martian gullies with pristine appearance

complete dynamic modeling calibration for the thurwieser rock avalanche italian central alps abstract few rock avalanches have been witnessed and no exact real time description is available the 2 5 m m 3 punta thurwieser rock avalanche september 2004 italian central alps is a unique event for which many quantitative observations have been gathered this is the first case ever of a natural rock avalanche being recorded on video and for which an almost exact value of the total time duration from initial detachment to final deposition is available the landslide travelled over 2 9 km from its source partially in a glacial environment the initial failure and the time for the complete evacuation of the source area were studied and assessed by a series of photos the mean front velocities along the path have been estimated from the video the final geometry and the characteristics of the deposit have been obtained by gps measurements aerial photos field surveys and laboratory tests a quasi 3d continuum dynamic analysis of the landslide motion has been performed assuming both a voellmy and a frictional rheology in the model dan 3d for the first time the landslide front velocities have been used for back analyses and calibration of the rheological parameters together with the final shape and thickness of the deposit and its developing extension the dynamic flow resistance parameters initially calibrated with dan were adopted and validated in dan 3d showing good consistency they are consistent with the existing database for calibrated landslides of similar type and scale flow velocities on the path segment underlain by glacial deposits up to 55 65 m s 1 are more accurately predicted by adopting a frictional rheology up to 50 55 m s 1 with zero pore pressure and a 26 friction angle than by a voellmy rheology up to 40 45 m s 1 both observations and modelling show that glacial ice plays a substantial role in increasing the rock avalanche mobility

predicting incipient motion including the effect of turbulent pressure fluctuations in the bed 1 incipient motion of particles on a river bed can in principle be understood and predicted from a balance of the forces acting on the particles on a natural river bed the exposure of particles to the flow is variable the effect of exposure on the initiation of motion including the case of deep embedding is studied in this paper so far the turbulence induced lifting force has been derived exclusively from examinations of the surface flow the understanding of destabilization processes of the riverbed is improved when turbulence induced vertical pressure gradients in the upper sediment layer are included this is particularly important for particles that lie in the lee of larger ones an analytical solution for the critical shields parameter of spherical particles is found including the effects of pressure fluctuations in the bed macroscale flow structures average bed slope and shallow flow existing laboratory data designed to test the effect of exposure and roughness conditions are in excellent agreement with the new model

rapid deposition of sand and gravel mixtures downstream of a negative step the role of matrix infilling and particle overpassing in the process of bar front accretion an experimental flow channel was used to investigate the rapid deposition of sand and gravel mixtures downstream of a negative step hydraulic processes give rise to the quasi simultaneous accumulation of openwork gravels matrix filled contact framework and dilated framework gravels the resultant structure is analogous to a bar front in gravel bed streams flow conditions were non uniform but steady in time whereas open and closed gravel fabrics are usually interpreted as representing deposition from unsteady flows for example a varying discharge regime consideration of the percentage of sand in the deposits indicated that in terms of packing the sediments may be considered as a simple binary mixture with partial framework dilation occurring with sand percentages in excess of c 32 despite dilation for sand percentages less than 50 structural stability of the foreset gravels was maintained so that the bar front exhibited a distinct brinkpoint and a planar slip face at the angle of initial yield which made an angular contact with the base of the flume for sand percentages in excess of 80 individual gravel clasts were completely supported by sand the original structural stability was lost so that the bar front eroded by reverse currents assumed a tangential contact with the flume base below the angle of initial yield the brinkpoint was rounded and indistinct in addition to altering the bar front slope increasing the quantity of sand in the bed sediments had a major influence on the dip of gravel particles on the foresets in all experimental runs a surface sand seal with openwork gravels beneath developed upstream of the brinkpoint the mechanics of sand seal formation require further investigation however an overpassing mechanism was noted to be very important in sorting gravel particles rolling over the brinkpoint a published mathematical model describing the overpassing mechanism was found to be appropriate to the present experimental observations

controls on tungsten concentrations in groundwater flow systems the role of adsorption aquifer sediment fe iii oxide oxyhydroxide content and thiotungstate formation abstract groundwater samples were collected along flow paths within the carrizo sand aquifer southeastern texas and the aquia aquifer coastal maryland for analysis of dissolved tungsten w concentrations along with the major solutes ph and measures of in situ redox conditions e g dissolved fe ii fe iii and s ii concentrations in addition sediment samples were collected from both aquifers to evaluate the solid phase speciation of w tungsten concentrations in the carrizo sand aquifer range from 3 64 to 1297 pmol kg 1 mean sd 248 440 pmol kg 1 with the lowest concentrations reported from the recharge area tungsten concentrations progressively increase down gradient along the flow path within carrizo sand aquifer groundwaters reaching the highest levels in sulfidic groundwater roughly 50 60 km from the recharge zone tungsten is strongly correlated with ph and dissolved sulfide i e s ii concentrations in carrizo groundwaters r 0 78 and 0 95 respectively in aquia aquifer groundwaters w concentrations range between 14 3 and 184 4 pmol kg 1 mean sd 63 9 59 pmol kg 1 and exhibit no or at best weak relationships with other geochemical parameters measured along the flow path e g r 0 4 and 0 08 for w vs ph and s ii respectively the data suggest that the increase in w concentrations in carrizo groundwaters reflects in part ph related adsorption desorption which has been shown to be substantial for groundwaters and lake waters with ph 8 owing to the similar chemical properties of w and mo which form thiomolybdates in sulfidic waters the formation of thiotungstate complexes may also be important in the sulfidic waters of the carrizo aquifer the substantially lower w concentrations in aquia aquifer groundwaters reflect the fact that the maximum groundwater ph never exceeds 8 4 mean sd ph 7 97 0 23 dissolved low s ii concentrations remain low mean sd s ii 0 29 0 16 mol kg 1 and that aquia aquifer sediments have substantially higher fe iii oxide oxyhydroxide contents compared to the carrizo sand aquifer our data indicate that ph related adsorption desorption reactions and the fe iii oxide oxyhydroxide content of aquifer sediments are key controls affecting w concentrations in oxic suboxic and anoxic groundwaters and further that the formation of thiotungstate species may also be important in some anoxic i e sulfidic waters

co2 gas fluidization in the initiation and formation of martian polar gullies 1 martian gully landforms indicative of rapid flow of sediment down steep slopes have been cited as evidence of the action of near surface liquid water in mars recent past gullies in polar regions cannot involve pure liquid water because ambient temperatures are too low here we show that polar gullies could be initiated by fluidization of sediment over a subliming seasonal deposit of co2 frost as has been proposed previously for gullies in sand the gas speed and co2 sublimation rate required for fluidization is calculated with the semi empirical ergun relation as validated in industrial applications for gullies in dust the gas speed and sublimation rate required for fluidization are estimated from laboratory experiments with comparable materials to determine if those rates can be achieved we compute diurnal and seasonal surface and subsurface temperatures through a martian year including co2 condensation and sublimation using the marstherm one dimensional finite difference thermal model models were run without sediment and with layers of sand or dust 10 4 10 1 m thick deposited over a seasonal layer of co2 frost the simulations show that in the spring sufficient heat reaches the co2 frost underlying the surface sediment layer to fluidize them this result confirms that martian gullies may have diverse origins and that polar and mid latitude gullies can be initiated on steep slopes by the fluidization of loose sediment on a sublimating seasonal deposit of co2 gas

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

depth of emplacement fluid provenance and metallogeny in granitic terranes a comparison of western thailand with other tin belts the most important tin mineralization in thailand is associated with the late cretaceous to middle tertiary western thai granite belt a variety of deposit types are present in particular pegmatite vein and greisen styles of mineralization a feature common to most of the deposits is that they are associated with granites that were emplaced into the khang krachan group which consists of poorly sorted carbonaceous pelitic metasediments most of the deposits contain low to moderately saline aqueous fluid inclusions and aqueous carbonic inclusions with variable ch4 co2 ratios low salinity aqueous inclusions represent trapped magmatic fluid in at least one case the nong sua pegmatite based on their occurrence as primary inclusions in magmatic garnet aqueous carbonic inclusions are commonly secondary and neither the co2 nor nacl contents of these inclusions decrease in progressively younger inclusions implying that they are not magmatic in origin reduced carbon is depleted in the metasediments adjacent to granites and the d values greisen muscovites are variable but are as low as 134 per mil indicative of fluid interaction with organic graphitic material this suggests that the aqueous carbonic fluid inclusions represent fluids that were produced at least in part during contact metamorphism metasomatism by comparing the western thai belt with other sn w provinces it is evident that there is a strong correlation between fluid composition and pressure in general low to moderately saline aqueous inclusions and aqueous carbonic inclusions are characteristic of mineralization associated with relatively deep plutonic belts mineralized pegmatites are also typically of deeper plutonic belts and pegmatite hosted deposits may contain cassiterite that is magmatic crystallized from granitic melt or is orthomagmatic hydrothermal crystallized from aqueous or aqueous carbonic fluids in origin the magmatic aqueous fluids those that were exsolved from granitic melts are interpreted to have had low salinities as a consequence of the low salinities tin is partitioned in favour of the melt on vapour saturation thus with a high enough degree of fractionation the crystallization of a magmatic cassiterite or different sn phase such as wodginite is inevitable because tin is not partitioned in favour of the vapour phase upon water saturation of the granitic melts it is proposed that relatively deep vein and greisen systems tend to form by remobilization processes in addition many deeper greisen systems are hosted in part by carbonaceous pelitic metasediments and the reduced nature of the metasediments may play a key role in remobilizing tin sub volcanic systems by contrast are characterized by high temperature high salinity fluids owing to the high chlorinity tin is strongly partitioned in favour of the vapour and cassiterite mineralization can form by of orthomagmatic hydrothermal processes similar relationships between the depth of emplacement and fluid composition also appear to apply to other types of granite hosted deposits such as different types of molybdenum deposits

martian hillside gullies and icelandic analogs abstract we report observations of icelandic hillside gully systems that are near duplicates of gullies observed on high latitude martian hillsides the best icelandic analogs involve basaltic talus slopes at the angle of repose with gully formation by debris flows initiated by ground water saturation and or by drainage of water from upslope cliffs we report not only the existence of mars analog gullies but also an erosional sequence of morphologic forms found both on mars and in iceland the observations support hypotheses calling for creation of martian gullies by aqueous processes issues remain whether the water in each case comes only from surficial sources such as melting of ground ice or snow or from underground sources such as aquifers that gain surface access in hillsides iceland has many examples of the former but the latter mechanism is not ruled out our observations are consistent with the martian debris flow mechanism of f costard et al 2001c science 295 110 113 except that classic debris flows begin at midslope more frequently than on mars from morphologic observations we suggest that some martian hillside gully systems not only involve significant evolution by extended erosive activity but gully formation may occur in episodes and the time interval since the last episode is considerably less than the time interval needed to erase the gully through normal martian obliteration processes

avalanche slope angles in low gravity environments from active martian sand dunes 1 the properties of granular material have an important effect on surface landforms and processes recently it has been suggested that material properties called dynamic and static angle of repose vary with gravitational acceleration which would have a significant effect on many planetary surface processes such as crater collapse and gully formation in order to test that hypothesis we measured lee slopes of active aeolian sand dunes on mars using the high resolution imaging experiment hirise dtms digital terrain model we examined dune fields in nili patera herschel crater and gale crater our measurements showed that the dynamic angles of repose for the sands in these areas are 33 34 in the first region and 30 31 in the other two these results fall within the 30 to 35 window for the dynamic angles of repose for terrestrial dunes with similar flow depths and grain properties and thus show that this angle does not significantly vary with decreasing gravity

global documentation of gullies with the mars reconnaissance orbiter context camera and implications for their formation abstract hypotheses ranging from fluvial processes and debris flows to co 2 frost lubricated or entirely dry flows have been proposed for the formation of martian gullies in order to constrain these potential formation mechanisms we mapped the global distribution of gullies on mars using 54 000 images from the mars reconnaissance orbiter mro context camera ctx covering 85 of the martian surface at a resolution of 6 m pixel the results of this mapping effort confirm the results of studies using lower resolution and or less areally extensive datasets that gullies are confined to the martian mid to high latitudes 30 80 in both hemispheres we also find a clear transition in gully orientation with increasing latitude going from poleward facing to equator facing preference in general gullies are more developed on poleward facing walls and mid latitude gullies are more developed than those at higher latitudes gullies are also found to be strongly correlated with regions of distinct thermophysical properties of sand to pebble sized grains low albedo and higher thermal inertia these observations all point to climate insolation and thermal properties of the substrate playing key factors in gully formation on mars supporting either a melting ground ice or snowpack hypothesis as the source for water involved in gully formation

present day seasonal gully activity in a south polar pit sisyphi cavi on mars abstract the large amount of multi temporal high resolution images acquired in the last few years offers the opportunity to identify morphological changes associated with recent geologic activity on the surface of mars in this study we focus on a single gully in sisyphi cavi located in the south polar region at 1 44 e and 68 54 s the gully incises the gullied equator facing slope of an isolated polar pit within an infilled impact crater it is important to notice that the following investigations describe the activity and modifications of an existing gully and not the formation of the gully itself high resolution image data analyses show new deposits at the terminus of the gully channel and on the gully apron within spring after solar longitudes of 236 of martian years my 29 and 31 our morphological investigations show that the identified new deposits were formed by dark flows through the entire gully deposited on top of the apron between solar longitudes l s 218 and 226 thermal data show a temperature increase between l s 218 and 226 near infrared spectral data show relatively constant band strengths of co 2 ice and h 2 o ice in this time range after the formation of the dark flows after l s 226 temperatures increase rapidly from 180 k to 270 k at l s 250 at this time spectral data indicate that all volatiles on the surface sublimated however an earlier beginning of sublimation when the dark flows were observed between l s 218 and 226 is likely due to the fact that the instruments can only show the last phase of sublimation decrease of volatile band strengths spectral modeling shows that from winter to mid spring the surface of the studied area is covered by translucent co 2 slab ice contaminated by minor amounts of h 2 o ice and dust furthermore our spectral modeling indicates that the dark material most likely flows on top of the co 2 slab ice cover three different scenarios were proposed to explain the identified dark flows including 1 flows supported by liquid h 2 o 2 flows supported by co 2 gas and 3 dry flows on the basis of our study we find that scenario 1 is unlikely because of the very low temperatures while scenario 2 is consistent with the observed beginning of co 2 ice sublimation in the study area it is unlikely because of the limitation of the activity to only one gully compared to surrounding gullies that share the same morphologies slope angles and volatile contents also with scenario 3 dry flows the activity of only one gully is difficult to explain thus we propose a mixture of scenario 2 and 3 dry flows supported by the ongoing sublimation of co 2 ice within the gully to be the most plausible scenario when the observed active gully comprises different source material than the surrounding gullies i e a higher content of probably sand sized material from outcrops located in the alcove

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

frosted granular flow a new hypothesis for mass wasting in martian gullies abstract recent gully deposits on mars have been attributed to both wet and dry mass wasting processes in this paper frosted granular flow fgf is presented as a new hypothesis for recent mass wasting activity in martian gullies fgf is a rare type of granular flow observed on a talus slope in the province of quebec canada hetu b van steijn h vandelac p 1994 geogr phys quat 48 3 22 frost reduces dynamic inter particle friction enabling flows to mobilize onto relatively low slope gradients 25 30 compared to those involving dry granular flow of the same material 35 41 resulting erosional and depositional features include straight to sinuous channels levees and digitate to branching arrangements of terminal deposits similar features are commonly found in association with geologically young gully systems on mars based on terrestrial observations of fgf processes the minimum criteria required for their occurrence on mars include i readily mobilized unconsolidated sediment at the surface ii an upper slope gradient at or near the angle of repose iii frost accumulation at the surface and iv triggering by rock fall all four conditions appear to be met in many areas on present day mars though triggering mechanisms may vary compared to terrestrial fgfs which are lubricated by thin liquid films at inter particle contacts those occurring on mars are more likely lubricated by vaporization of co 2 and small amounts of h 2 o frost that becomes incorporated in the translating mass some recent mass wasting activity in martian gullies therefore could be interpreted as the product of fgf

tin bearing greisens of mount bischoff northwestern tasmania australia the large mount bischoff tin deposit occurs within an inlier of precambrian sedimentary rocks which are surrounded by lower paleozoic and tertiary sedimentary and volcanic rocks tin is contained within a network of altered devonian porphyry dikes endogreisens replaced dolomite exogreisen mineralized hydrobreccias thin veins and alluvials greisen style alteration of porphyry dikes is zoned inward and downward from nearly fresh beta form quartz k feldspar dike material through muscovite fluorite or tourmaline greisen and topaz quartz greisen to quartz greisen tin grades of up to 2 wt percent occur within endogreisen with higher grades occurring near the topaz quartz quartz greisen contact replacement of dolomite by greisen assemblages and greisen style alteration of porphyry dikes were cogenetic the mineral assemblages and the spatial distribution of greisen minerals such as mica topaz and tourmaline in endo and exogreisens are similar topaz quartz fluorides cassiterite and tourmaline occur in endo and exogreisen although the proportion of fluoride minerals sellaite and fluorite is high where dolomite is replaced within exogreisens the highest grades of sn occur at the contact between topaz bearing endo and exogreisens grades obtained from drill core range up to 22 wt percent 1 3 m intersection the greisens were overprinted by assemblages containing phyllosilicates chlorite talc phlogopite serpentine phengite carbonates magnesite siderite dolomite abundant sulfides pyrrhotite or pyrite sphalerite late fluorite and later argillic alteration only limited quantities of dolomite were replaced by these later postgreisen assemblages fluid inclusion temperatures range from 90 degrees to near 500 degrees c with the greisen being produced between approximately 340 degrees to 420 degrees c or higher and the later overprints at progressively lower temperatures salinities at the greisen stage of mineralization were high with measurements commonly between 30 to 40 percent total dissolved salts ca na k fe mn chlorides possible fluorides co 2 and hydrocarbons were deduced as components of the fluid phase lesser amounts of dissolved si al and b and rare ti ca la p sn cu and s were inferred from daughter mineral identifications the deposit was formed from acidic and relatively reduced hydrothermal solutions in subvolcanic conditions at a depth of approximately 1 km above a leucogranite pluton granite inclusions exist in the dikes high level brecciation was cogenetic with porphyry dike intrusion and both occurred in several separate intrusion mineralization cycles

the interplay of groundwater and magmatic fluids in the formation of the cassiterite sulfide deposits of western tasmania abstract the cassiterite sulfide deposits of western tasmania are spatially and temporally related to devonian granitoids the stable isotope and fluid inclusion data of these deposits are best explained by a genetic model in which sn is leached from the granites by reduced non magmatic fluids mixed with late stage magmatic fluids these fluids mineralize the overlying dolomite horizons and subjacent faults by a combination of wallrock and boiling induced reactions the model requires co incidental release of volatiles and ingress of groundwaters to sustain the leach mechanism this implies some specific structural deformational controls on the process and an intimate association between cassiterite sulfide deposits and volatile rich granites the sulfur isotope data show a wide range in values from about 2 to 20 per mil and are explained in terms of a near zero magmatic component and three heavier country rock sources the precambrian oonah formation the crimson creek formation and the mount read volcanics following this interpretation the heavy sulfur isotope values from the heemskirk granite hajitaheri 1985 and the federal bassett fault at renison kitto 1994 indicate ingress of groundwater into the granites salinities of fluid inclusions from the deposits show a restricted range around 5 to 15 weight percent nacl equivalent compared with the range shown by inclusions from alteration zones within the granites around 5 to 40 weight percent nacl equivalent it is suggested that the wide range of salinities in the granites is generated in the critical region of the nacl h 2 o system at temperatures around 400 to 500 c and pressures around 400 to 500 bars the limited range of salinities in the deposits reflects cooling to sub critical conditions cooling through the critical region promotes homogenization of groundwater and magmatic vapor and brine condensation of magmatic volatiles within this zone of mixing maintains acidity and promotes fluid rock reaction the geochemistry of the granites underlying the renison bell area bajwah et al 1995 is interpreted in terms of two granites the geological relationships indicate the more mafic phase the renison granite was intruded by the more fractionated pine hill granite fluids from the pine hill granite sericitised and tourmalinized both the renison granite and pine hill granite along their mutual contact generating a broad north east trending zone of alteration this contact may have been offset by the federal bassett fault before the renison deposit was formed it is suggested that groundwater flow was essentially constrained within this nw se trending structure and subsidiary structures magmatic volatiles emanating from deep within the pine hill granite acidified the reduced groundwater and promoted leaching of the granite the siting of the renison deposit on the margin of the pine hill granite is consistent with a strong up flow zone on the margin of a cooling pluton the very constant s isotope signature in the deposit is consistent with a large scale homogenization process operating over a sustained period the very large size of the renison deposit is accounted for by a long lived groundwater system maintained by the high heat flow from a fractionated granite

evidence for present day gully activity on the russell crater dune field mars 1 on the basis of high resolution imaging science experiment hirise images of two successive years we observed changes of a gully on the russell crater dune field within the first year the length of a 2 m wide incised gully channel grew about 50 m downslope and 120 m within in the second year gully activity occurred in early spring between ls 198 and 218 in the first year and between ls 192 and 221 in the second year based on the channel morphology spectral data and modeled surface temperatures the changes can be best explained with transient melting of small amounts of h2o ice triggering slurry flows consisting of sand mixed with liquid water

a novel method for measuring the timing of bed erosion during debris flows and floods 1 we describe a novel channel bed erosion sensor and the first results of its usage the sensor is based on a resistance chain built into a column of 5 cm tall cylindrical aluminum elements the timing and change in resistance as elements are removed from the column are logged outside of the channel five sensor columns were placed in the illgraben torrent bed prior to the start of the 2008 flow season before the first debris flow event 0 1 m of sediment was deposited by small flood events during the 16 june 2008 debris flow this layer was eroded and erosion was therefore first measured 44 min after front arrival and took place progressively over the next 12 min the results at the erosion sensors are consistent with measurements over the entire reach using traditional surveying methods and data from the adjacent debris flow monitoring station provide a basis for interpretation the main limitation is that this sensor records only the rate and timing of the maximum bed erosion and cannot be used to determine deposition and subsequent erosion within a given event

is the critical shields stress for incipient sediment motion dependent on channel bed slope data from laboratory flumes and natural streams show that the critical shields stress for initial sediment motion increases with channel slope which indicates that particles of the same size are more stable on steeper slopes this observation is contrary to standard models that predict reduced stability with increasing slope due to the added downstream gravitational force processes that might explain this discrepancy are explored using a simple force balance model including increased drag from channel walls and bed morphology variable friction angles grain emergence flow aeration and changes to the local flow velocity and turbulent fluctuations surprisingly increased drag due to changes in bed morphology does not appear to be the cause of the slope dependency because both the magnitude and trend of the critical shields stress are similar for flume experiments and natural streams and significant variations in bed morphology in flumes is unlikely instead grain emergence and changes in local flow velocity and turbulent fluctuations seem to be responsible for the slope dependency due to the coincident increase in the ratio of bed roughness scale to flow depth i e relative roughness a model for the local velocity within the grain roughness layer is proposed based on a 1 d eddy viscosity with wake mixing in addition the magnitude of near bed turbulent fluctuations is shown to depend on the depth averaged flow velocity and the relative roughness extension of the model to mixed grain sizes indicates that the coarser fraction becomes increasingly difficult to transport on steeper slopes

identification of mars gully activity types associated with ice composition the detection of geologically recent channels at the end of the 20th century rapidly suggested that liquid water could have been present on mars up to recent times a mechanism involving melting of water ice during ice ages in the last several million years progressively emerged during years following the first observations of these gullies however the recent discovery of current activity within gullies now suggests a paradigm shift where a contemporary co2 ice based and liquid water free mechanism may form all gullies here we perform a survey of near infrared observations and construct time sequences of water and co2 ice formation and sublimation at active gully sites we observe that all major new erosive features such as channel development or lengthening systematically occur where and if applicable when co2 ice is observed or probable co2 ice layers are however estimated to be only 1 mm to 1 cm thick for low latitude sites which may have implication for potential formation mechanisms we also observe that part of current gully activity notably the formation of some new deposits is poorly compatible with the presence of co2 ice in particular all new bright deposits reported in the literature have a low co2 ice probability while water ice should be present at most sites our results confirm that co2 ice is a key factor controlling present day channel development on mars and show that other mechanisms potentially involving sublimation or melting of water ice are also contributing to current gully activity

channel scour and fill by debris flows and bedload transport abstract in steep channels debris flows are known to dramatically increase in volume under the effect of channel erosion however the critical factors controlling channel erosion by debris flows are not well documented by field studies this is particularly true for the effect of slope on the depth at which erodible beds are scoured during debris flows and during bedload transport this topic has been addressed by intensive cross section resurveys 54 cross sections of debris flows n 5 and flow events n 9 that occurred in two torrents of the french prealps the manival and real torrents between 2009 and 2012 this study provided evidence that debris flow scouring increases with slope whereas this is not the case for bedload transport no slope effect detected during floods a functional relationship defined from a piecewise regression model is proposed as an empirical fit for the prediction of channel erosion by debris flows with a critical slope threshold at 0 19 95 confidence interval 0 17 0 21 this slope threshold is interpreted as the transition between the transport limited and supply limited regimes associated with the upstream decreasing erodible bed thickness the erodible bed was also characterized by quantifying erosion deposition and surface roughness with multidate terrestrial laser scans tlss in a short reach of high sensitivity of the manival torrent debris flow erosion occurred preferentially on smooth surfaces corresponding to the unconsolidated gravel deposits from bedload transport a 20 cm resolution roughness profile from an airborne laser scan als and a slope profile of the whole channel were used to detect the unconsolidated sediment deposits that can potentially feed future debris flows

evidence for debris flow gully formation initiated by shallow subsurface water on mars abstract the morphologies of some martian gullies appear similar to terrestrial features associated with debris flow initiation erosion and deposition on earth debris flows are often triggered by shallow subsurface throughflow of liquid water in slope mantling colluvium this flow causes increased levels of pore pressure and thus decreased shear strength which can lead to slide failure of slope materials and subsequent debris flow the threshold for pore pressure induced failure creates a distinct relationship between the contributing area supplying the subsurface flow and the slope gradient to provide initial tests of a similar debris flow initiation hypothesis for martian gullies measurements of the contributing areas and slope gradients were made at the channel heads of martian gullies seen in three hirise stereo pairs these gullies exhibit morphologies suggestive of debris flows such as leveed channels and lobate debris fans and have well defined channel heads and limited evidence for multiple flows our results show an area slope relationship for these martian gullies that is consistent with that observed for terrestrial gullies formed by debris flow supporting the hypothesis that these gullies formed as the result of saturation of near surface regolith by a liquid this model favors a source of liquid that is broadly distributed within the source area and shallow we suggest that such liquid could be generated by melting of broadly distributed icy materials such as snow or permafrost this interpretation is strengthened by observations of polygonal and mantled terrain in the study areas which are both suggestive of near surface ice

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

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

the perfect debris flow aggregated results from 28 large scale experiments 1 aggregation of data collected in 28 controlled experiments reveals reproducible debris flow behavior that provides a clear target for model tests in each experiment 10 m3 of unsorted water saturated sediment composed mostly of sand and gravel discharged from behind a gate descended a steep 95 m flume and formed a deposit on a nearly horizontal runout surface experiment subsets were distinguished by differing basal boundary conditions 1 versus 16 mm roughness heights and sediment mud contents 1 versus 7 percent dry weight sensor measurements of evolving flow thicknesses basal normal stresses and basal pore fluid pressures demonstrate that debris flows in all subsets developed dilated coarse grained high friction snouts followed by bodies of nearly liquefied finer grained debris mud enhanced flow mobility by maintaining high pore pressures in flow bodies and bed roughness reduced flow speeds but not distances of flow runout roughness had these effects because it promoted debris agitation and grain size segregation and thereby aided growth of lateral levees that channelized flow grain size segregation also contributed to development of ubiquitous roll waves which had diverse amplitudes exhibiting fractal number size distributions despite the influence of these waves and other sources of dispersion the aggregated data have well defined patterns that help constrain individual terms in a depth averaged debris flow model the patterns imply that local flow resistance evolved together with global flow dynamics contradicting the hypothesis that any consistent rheology applied we infer that new evolution equations not new rheologies are needed to explain how characteristic debris flow behavior emerges from the interactions of debris constituents

a new approach to estimating hazard posed by debris flows in the westfjords of iceland abstract the aim of this study is to improve the assessment of hazard posed by debris flows to the people and settlements of northwest iceland by studying very recent examples from above the town of isafjor ur and other nearby localities debris flows are a recognised hazard in the region above isafjor ur they occur with particularly high frequency and have appreciable volumes up to 14 000 m 3 we have used airborne laser altimeter lidar and differential global positioning system gps data to produce isopach maps of flows that occurred in 1999 2007 and 2008 our data show that these flows begin depositing at higher slope gradients and are also more mobile than hillslope debris flows reported by other authors above a 19 slope erosion is initiated independent of the distance along the flowpath using the isopach maps and associated field observations we have found a relationship between ground slope and patterns in deposition volume we have used this finding as a basis for an empirical model that enables an estimate of the total travel distance and final thickness of future debris flows to be calculated this has enabled us to identify areas of the town which are at risk some of these are not obvious without this analysis this model is notable for its simplicity which allows future debris flow characteristics to be predicted without the need to determine the precise fluid dynamic parameters of the flow such as viscosity and velocity which are required to implement more complex models

a geomorphic analysis of hale crater mars the effects of impact into ice rich crust abstract hale crater a 125 150 km impact crater located near the intersection of uzboi vallis and the northern rim of argyre basin at 35 7 s 323 6 e is surrounded by channels that radiate from incise and transport material within hale s ejecta the spatial and temporal relationship between the channels and hale s ejecta strongly suggests the impact event created or modified the channels and emplaced fluidized debris flow lobes over an extensive area 200 000 km2 we estimate 1010 m3 of liquid water was required to form some of hale s smaller channels a volume we propose was supplied by subsurface ice melted and mobilized by the hale forming impact if 10 of the subsurface volume was ice based on a conservative porosity estimate for the upper martian crust 1012 m3 of liquid water could have been present in the ejecta we determine a crater retention age of 1 ga inside the primary cavity providing a minimum age for hale and a time at which we propose the subsurface was volatile rich hale crater demonstrates the important role impacts may play in supplying liquid water to the martian surface they are capable of producing fluvially modified terrains that may be analogous to some landforms of noachian mars

insights into rock ice avalanche dynamics by combined analysis of seismic recordings and a numerical avalanche model 1 rock ice avalanches larger than 1 106 m3 are high magnitude low frequency events that may occur in all ice covered high mountain areas around the world and can cause extensive damage if they reach populated regions the temporal and spatial evolution of the seismic signature from two events was analyzed and recordings at selected stations were compared to numerical model results of avalanche propagation the first event is a rock ice avalanche from iliamna volcano in alaska which serves as a natural laboratory with simple geometric conditions the second one originated on aoraki mt cook new zealand southern alps and is characterized by a much more complex topography a dynamic numerical model was used to calculate total avalanche momentum total kinetic energy and total frictional work rate among other parameters these three parameters correlate with characteristics of the seismic signature such as duration and signal envelopes while other parameters such as flow depths flow path and deposition geometry are well in agreement with observations the total frictional work rate shows the best correlation with the absolute seismic amplitude suggesting that it may be used as an independent model evaluation criterion and in certain cases as model calibration parameter the good fit is likely because the total frictional work rate represents the avalanche s energy loss rate part of which is captured by the seismometer deviations between corresponding calculated and measured parameters result from site and path effects which affect the recorded seismic signal or indicate deficiencies of the numerical model the seismic recordings contain additional information about when an avalanche reaches changes in topography along the runout path and enable more accurate velocity calculations the new concept of direct comparison of seismic and avalanche modeling data helps to constrain the numerical model input parameters and to improve the understanding of rock ice avalanche dynamics

a classification of mineral systems overviews of plate tectonic margins and examples of ore deposits associated with convergent margins abstract in this contribution i presents definitions of mineral systems followed by a proposed classification of mineral deposits the concept of mineral systems has been tackled by various authors within the framework of genetic models with the aim of improving the targeting of new deposits in green field areas a mineral system has to be considered taking into account by and large space time patterns or trends of mineralisation at the regional scale their tectonic controls and related metallogenic belts this leads to a suggested classification of mineral systems together with a summary of previous ideas on what is without doubt a kind of mine field because if a classification is based on genetic processes these can be extremely complex due to the fact that ore genesis usually involves a number of interactive processes the classification presented is based on magmatic magmatic hydrothermal sedimentary hydrothermal non magmatic and mechanical residual processes an overview of plate tectonics convergent and divergent margins is discussed next convergent plate margins are characterised by a tectonic plate subducting beneath a lower density plate convergent plate margins have landward of a deep trench a subduction accretion complex a magmatic arc and a foreland thrust belt an important feature is the subduction angle a steep angle of descent is exemplified by the mariana or tonga kermadec subduction systems conducive to porphyry high sulphidation epithermal systems whereas in an intra arc rift systems with spreading centres is conducive to the generation of massive sulphide deposits of kuroko affinity a shallower subduction zone is the domain of large porphyry cu mo and epithermal deposits the implications of this difference in terms of metallogenesis are extremely important continent continent arc continent arc arc amalgamation of drifting microcontinents and oceanic collision events are considered to be a major factor in uplift the inception of fold and thrust belts and high p metamorphism examples are the alpine himalayan orogenic belt formed by the closure of the tethys oceanic basins and the great central asian orogenic belt caob a giant accretionary collage of island arcs and continental fragments the closing of oceanic basins and the accretion of allochthonous terranes result in the emplacement of ophiolites by the obduction process divergent plates include mid ocean ridges passive margins and various forms of continental rifting at mid ocean spreading centres magma chambers are just below the spreading centre once the oceanic crust moves away from the ridge it is either consumed in a subduction zone or it may be accreted to continental margins or island arcs spreading centres also form in back arc marginal basins transform settings include transtensional with a component of tension due to oblique divergence transform or strike slip sensu stricto and transpressive with a component of compression due to oblique convergence strike slip faults that form during extensional processes lead to the formation of pull apart basins mineral systems that form at convergent margins the topic of this special issue are succinctly introduced in table 1 table 2 table 3 table 4 table 5 table 6 table 7 as follows principal geological features of selected mineral systems at convergent plate margins and back arcs table 1 their recognition criteria table 2 principal geological features of selected ore deposits of back arc basins and post subduction rifting table 3 and of subduction related magmatic arcs table 4 their respective recognition criteria table 5 accretionary and collisional tectonics and associated mineral systems table 6 principal geological features and associated mineral systems of transform faults table 7

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

quantitative analysis of debris torrent hazards for design of remedial measures debris torrents which are rapid flows of soil and organic debris down steep mountain channels are a major natural hazard in many parts of british columbia a series of recent occurrences along the

initiation and flow conditions of contemporary flows in martian gullies understanding the initial and flow conditions of contemporary flows in martian gullies generally believed to be triggered and fluidized by co2 sublimation is crucial for deciphering climate conditions needed to trigger and sustain them we employ the ramms rapid mass movement simulation debris flow and avalanche model to back calculate initial and flow conditions of recent flows in three gullies in hale crater we infer minimum release depths of 1 0 1 5 m and initial release volumes of 100 200 m3 entrainment leads to final flow volumes that are 2 5 5 5 times larger than initially released and entrainment is found necessary to match the observed flow deposits simulated mean cross channel flow velocities decrease from 3 4 m s 1 to 1 m s 1 from release area to flow terminus while flow depths generally decrease from 0 5 1 m to 0 1 0 2 m the mean cross channel erosion depth and deposition thicknesses are 0 1 0 3 m back calculated dry coulomb friction ranges from 0 1 to 0 25 and viscous turbulent friction between 100 200 m s 2 which are values similar to those of granular debris flows on earth these results suggest that recent flows in gullies are fluidized to a similar degree as are granular debris flows on earth using a novel model for mass flow fluidization by co2 sublimation we are able to show that under martian atmospheric conditions very small volumetric fractions of co2 of 1 within mass flows may indeed yield sufficiently large gas fluxes to cause fluidization and enhance flow mobility

seasonality of present day martian dune gully activity martian slope gullies are argued to be evidence for recent liquid water flow on the surface of mars to explain the source of water a wide range of environmental conditions and processes has been invoked however a lack of information about the environmental context or timing of gully activity makes it difficult to evaluate the theories here we present new observations of extensive gully modification over the past 6 mars years within dune gullies with slope gully morphology observed activity within 18 gullies in 7 dune fields constrains timing to winter which is consistent with observed slope gully activity these observations show that fluvial processes are unlikely to cause present day martian dune gully activity and imply that co 2 frost accumulation may play the dominant role

ultrahigh resolution topographic mapping of mars with mro hirise stereo images meter scale slopes of candidate phoenix landing sites 1 the objectives of this paper are twofold first to report our estimates of the meter to decameter scale topography and slopes of candidate landing sites for the phoenix mission based on analysis of mars global surveyor mgs mars orbiter camera moc images with a typical pixel scale of 3 m and mars reconnaissance orbiter mro high resolution imaging science experiment hirise images at 0 3 m pixel 1 and second to document in detail the geometric calibration software and procedures on which the photogrammetric analysis of hirise data is based a combination of optical design modeling laboratory observations star images and mars images form the basis for software in the u s geological survey integrated software for imagers and spectrometers isis 3 system that corrects the images for a variety of distortions with single pixel or subpixel accuracy corrected images are analyzed in the commercial photogrammetric software socet set bae systems yielding digital topographic models dtms with a grid spacing of 1 m 3 4 pixels that require minimal interactive editing photoclinometry yields dtms with single pixel grid spacing slopes from moc and hirise are comparable throughout the latitude zone of interest and compare favorably with those where past missions have landed successfully only the mars exploration rover mer b site in meridiani planum is smoother moc results at multiple locations have root mean square rms bidirectional slopes of 0 8 4 5 at baselines of 3 10 m hirise stereopairs one per final candidate site and one in the former site yield 1 8 2 8 slopes at 1 m baseline slopes at 1 m from photoclinometry are also in the range 2 3 after correction for image blur slopes exceeding the 16 phoenix safety limit are extremely rare

matrix granulometry of catastrophic debris flows december 1999 in central coastal venezuela abstract after 2 days of intense precipitation devastating flooding and debris flows affected the central coast of venezuela on december 15 16 1999 these events killed nearly 30 000 people and destroyed or damaged 126 000 homes i visited the disaster area in march 2000 coastal valleys affected by debris flows were extensively covered by an interstitial matrix that included large amounts of often impressive boulders up to 35 40 tons in weight granulometric analyses of four matrix samples from the naiguata valley showed they were all similarly coarse their main constituent was sand and grains data suggest the following events must have taken place in coastal venezuela torrential rains quickly caused flooding along creeks and rivers which must have rapidly attained hyperconcentrated streamflow bulking of stream alluvium in flood surges may also have taken place however the storm triggered widespread landsliding along the steep unstable flanks of the coastal cordillera many slides started in upper basin areas underlain by gneiss bedrock pena de mora such slides released vast amounts of coarse sandy debris which mixed with turbulent floodwaters to produce numerous granular noncohesive debris flows these flows despite their coarse matrix exhibited intense particle collisions and interactions thus were able to effectively mobilize vast masses of large boulders

new and recent gully activity on mars as seen by hirise 1 fresh appearing gully deposits are found at tens of sites in the southern hemisphere of mars these deposits have latitudinal and azimuthal dependences similar to the overall preferences of southern hemisphere gullies suggesting that most gullies can undergo such events definite changes are seen at ten sites including two previously reported these include visible modification of gully channels and aprons those formation intervals constrained to better than one mars year tend to include winter and exclude summer suggesting seasonal activity this seasonal activity is consistent with proposed models for gully formation driven by co2 frost although at least some of the new deposits are probably due to dry granular flow with no volatile involvement as these deposits are capable of effecting distinct topographic changes to gully aprons and channels they represent a significant component of recent gully evolution

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

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