fluid infiltration and transport of major minor and trace elements during regional metamorphism of carbonate rocks wepawaug schist connecticut usa geochemical alteration of metacarbonate layers due to fluid infiltration during greenschist and amphibolite facies metamorphism was investigated based on 149 whole rock analyses of the wepawaug schist usa ankerite albite ank ab rare ankerite oligoclase ank ol biotite bt amphibole amp and diopside di index mineral zones developed during progressive metamorphism acadian orogeny and devolatilization co2 h2o s loss ank ab ank ol and bt zone rocks were altered along some lithologic contacts and in reaction selvages around veins mass changes included gains of na y and in many cases p and fe k rb and ba were typically lost and sr was lost except where calcite precipitated in and around calcite bearing veins na gain and k loss reflect muscovite destruction and albite growth in response to infiltration of fluids from surrounding metapelitic and metapsammitic metaclastic rocks at higher metamorphic grades k rb and ba were lost when biotite broke down to form amphibole or diopside these elements were transported out of metacarbonate layers down chemical potential gradients at lithologic contacts and in selvages na was lost as plagioclase reacted to form clinozoisite zoisite czo zo calc silicates cm to dm scale thickness rich in amphibole and czo zo amp zones or diopside and zo di zones formed at layer margins and in selvages via extreme metasomatism including major 1 addition of al si and in many rocks fe 2 destruction of calcite and 3 loss of ca and volatiles volatile losses near 90 percent relative to low grade precursors demonstrate that calc silicate formation resulting from al si metasomatism is an important source of co2 to be considered when assessing regional devolatilization al mass gains for calc silicates indicate that large quartz veins and some lithologic contacts were loci for massive time integrated fluid fluxes of 105 m3 m 2 heavy rare earth elements hree were gained in the ank ab through the amp zones and a di zone example gained light and mid ree including sm and nd the ree gains coincide with gains of y and in most cases p suggesting that p and y complexes transport ree volume was lost progressively from the unveined interiors of metacarbonate beds attaining 20 to 30 percent loss in the di ii zone mass addition due to veining reduced volume losses and in some cases produced volume gains reaction transport modeling indicates that fluid flow was mostly layer parallel was focused along lithologic contacts fractures and permeable horizons and was accompanied by diffusion and or mechanical dispersion at high angles to the flow directions the metasomatic fluids infiltrated from surrounding metaclastic and or syn metamorphic igneous rocks thus interaction of fluids derived from different rock types must be considered when assessing mass transfer in lithologically diverse mountain belts

frost and soils implications for paleosols paleoclimates and stratigraphy abstract frost is a pedogenetic agent this paper describes the use of frost features in soil for paleoclimatic and stratigraphic interpretation it is possible to differentiate periods of frost activity from those of temperate pedogenesis by macroscopic and microscopic criteria and to distinguish between soils with pre syn and epigenetic frost effects an experimental approach is necessary to determine initial frost effects because they are usually difficult to observe at natural active sites work with ecologists also clarifies the evolution of frost affected soils under climatic and vegetational constraints vegetation has important effects on the thermal and hydraulic regimes of soils and on erosion susceptibility the recognition of fossil cryosoils often allows the reconstruction of sequences of paleoclimatic events in periods or environments with little or no micropaleontological evidence the interrelations between frost and other pedogenetic processes allow a better understanding of climatic evolution and deterioration throughout the neogene and especially during the quaternary and the holocene most of the inherited frost features in european soils are younger than 480 ka bp the differentiation between frost and tectonic perturbations is very important for calculation of soil erosional budgets

effects of dispersed particulates on the rheology of water ice at planetary conditions we have investigated the effects of initial grain size and hard particulate impurities on the transient and steady state flow of water ice i at laboratory conditions selected to provide more quantitative constraints on the thermomechanical evolution of the giant icy moons of the outer solar system our samples were molded with particulate volume fractions of 0 001 to 0 56 and particle sizes of 1 to 150 m deformation experiments were conducted at constant shortening rates of 4 4 10 7 to 4 9 10 4 s 1 at pressures of 50 and 100 mpa and temperatures 77 to 223 k for the pure ice samples initial grain sizes were 0 2 0 6 mm 0 75 1 75 mm and 1 25 2 5 mm stress strain curves of pure ice i under these conditions display a strength maximum u at plastic strains e 0 01 after initial yield followed by strain softening and achievement of steady state levels of stress ss at e 0 1 to 0 2 finer starting grain size in pure ice generally raises the level of u petrography indicates that the initial transient flow behavior is associated with the nucleation and growth of recrystallized ice grains and the approach to ss evidently corresponds to the development of a steady state grain texture effects of particulate concentrations 0 1 are slight at these concentrations a small but significant reduction in u with respect to that for pure water ice occurs mixed phase ice with 0 1 is significantly stronger than pure ice the strength of samples with 0 56 approaches that of dry confined sand the magnitude of the strengthening effect is far greater than expected from homogeneous strain rate enhancement in the ice fraction or from pinning of dislocations orowan hardening this result suggests viscous drag occurs in the ice as it flows around the hard particulates mixed phase ice is also tougher than pure ice extending the range of bulk plastic deformation versus faulting to lower temperatures and higher strain rates the high pressure phase ice ii formed in 0 56 mixed phase ice during deformation at high stresses bulk planetary compositions of ice rock 0 4 0 5 are roughly 2 orders of magnitude more viscous than pure ice promoting the likelihood of thermal instability inside giant icy moons and possibly explaining the retention of crater topography on icy planetary surfaces

martian seasonal co2 ice in polygonal troughs in southern polar region role of the distribution of subsurface h2o ice the mars orbiter camera onboard the mars global surveyor has obtained several images of polygonal features in the southern polar region in images taken during the end of the southern spring when the surrounding surface is free of the seasonal frost co2 ice still appears to be present within the polygonal troughs in earth s polar regions polygons such as these are indicative of water ice in the ground below we analyzed the seasonal evolution of the thermal state and the co2 content of these features our 2 d model includes condensation and sublimation of the co2 ice a self consistent treatment of the variations of the thermal properties of the regolith and the seasonal variations of the local atmospheric pressure which we take from the results of a general circulation model we find that the residence time of seasonal co2 ice in troughs depends not only on atmospheric opacity and albedo of the co2 ice but also and most significantly on the distribution of water ice in the regolith optical properties of the atmosphere and surface co2 ice can be independently obtained from observations to date this is not true about the distribution of water ice below the surface our analysis quantifies the dependence of the seasonal cycle of the co2 ice within the troughs on the assumed distribution of the water ice below the surface we show that presence of water ice in the ground at a depth smaller than the depth of the troughs reduces winter condensation rate of co2 ice this is due to higher heat flux conducted from the water ice rich regolith toward the facets of the troughs

fracture networks in frozen ground fractures in frozen ground self organize into networks through interactions between sequentially emplaced fractures tensile stress and the developing fracture pattern from this viewpoint we model the development of networks on a lattice representing the ground surface on which fractures initiate propagate and arrest under a combination of uniform thermally induced tensile stress stress reduction near existing fractures and stochastic parameterization of heterogeneity in frozen ground and in insulating snow tensile stress from cooling tensile strength propagation threshold fracture depth and elastic properties are chosen to approximate properties of frozen ground using these parameters model networks assemble with properties similar to natural ice wedge networks including 1 individual fracture paths have lengths ranging from tens to hundreds of meters 2 fractures intersect to enclose regions with characteristic spacing between fractures of approximately 22 m 3 intersections between fractures are predominantly orthogonal with less common three way approximately equiangular intersections joint distributions of relative orientation and spacing between fractures from modeled networks and ice wedge networks at espenberg alaska are comparable at the level of variability in natural examples this similarity is consistent with the hypotheses that networks self organize by stress interactions between sequentially placed fractures in frozen ground and that networks are insensitive to the many details of fracture dynamics omitted from the model spacing between fractures in modeled networks is influenced by sub optimal placement of fractures during network development and increases nonlinearly with the length scale of stress reduction around a fracture three way approximately equiangular intersections form where modeled fractures arrest on the outside of bends in earlier fractures

geometrical aspects of sorted patterned ground in recurrently frozen soil a model for sorted patterned ground shows that some types arise from density driven rayleigh free convection that occurs during thawing of water saturated recurrently frozen soils the regularly spaced convection cells result in an uneven melting of the underlying ice front frost action causes stones to be upthrusted and to form in a pattern on the ground surface that mirrors the corrugation in the underlying ice front the implications of the water circulation direction in the cells on the sorting process are considered

fluid flow mineral reactions and metasomatism a general model that relates fluid flow along a temperature gradient to chemical reaction in rocks can be used to quantitatively interpret petrologic and geochemical data on metasomatism from ancient flow systems in terms of flow direction and time integrated fluid flux the model is applied to regional metamorphism quartz veins and a metasomatized ductile fault zone

sand veins and wedges in cold aeolian environments sedimentary structures formed by the progressive primary infilling of thermal contraction cracks with sand are termed primary sand veins and sand wedges in addition to simple vein or wedge shapes irregularities can be caused by sand veins branching from their sides and toes primary sand wedges form widely in sandy polar deserts locally in sandy areas of tundra and probably in seasonally frozen ground there are no unique criteria for distinguishing primary sand veins and wedges from sand veins and wedges of other origins identification of the former depends on the occurrence of distinctive features not always present and on evaluation of their lithofacies and palaeoenvironmental contexts care and caution are advocated in the use of ancient relict primary sand veins and wedges as quantitative palaeoenvironmental indicators because modern active wedge distribution is poorly known and hence inferred thermal climatic threshold values are questionable it is suggested that ancient relict primary sand wedges exceeding 2 m in depth and with well developed vertical lamination probably indicate the former occurrence of continuous permafrost whereas sand veins and narrow sand wedges frost cracks are potentially ambiguous as they may form not only in the active layer above and within continuous permafrost but also in seasonally frozen ground in non permafrost areas

permeability generation and resetting of tracers during metamorphic fluid flow implications for advection dispersion models advection dispersion fluid flow models implicitly assume that the infiltrating fluid flows through an already fluid saturated medium however whether rocks contain a fluid depends on their reaction history and whether any initial fluid escapes the behaviour of different rocks may be illustrated using hypothetical marble compositions marbles with diverse chemistries e g calcite dolomite quartz are relatively reactive and will generally produce a fluid during heating by contrast marbles with more restricted chemistries e g calcite quartz or calcite only may not if the rock is not fluid bearing when fluid infiltration commences mineralogical reactions may produce a reaction enhanced permeability in calcite dolomite quartz or calcite quartz but not in calcite only marbles the permeability production controls the pattern of mineralogical isotopic and geochemical resetting during fluid flow tracers retarded behind the mineralogical fronts will probably be reset as predicted by the advection dispersion models however tracers that are expected to be reset ahead of the mineralogical fronts cannot progress beyond the permeability generating reaction in the case of very unreactive lithologies e g pure calcite marbles cherts and quartzites the first reaction to affect the rocks may be a metasomatic one ahead of which there is little pervasive resetting of any tracer centimetre scale layering may lead to the formation of self perpetuating fluid channels in rocks that are not fluid saturated due to the juxtaposition of reactants such layered rocks may show patterns of mineralogical resetting that are not predicted by advection dispersion models patterns of mineralogical and isotopic resetting in marbles from a number of terrains for example chillagoe marulan south reynolds range australia adirondack mountains old woman mountains notch peak usa and stephen cross quarry canada vary as predicted by these models

formation of recent martian gullies through melting of extensive water rich snow deposits the observation of gullies on mars indicates the presence of liquid water near the surface in recent times1 2 which is difficult to reconcile with the current cold climate gullies have been proposed to form through surface runoff from subsurface aquifers1 3 or through melting of near surface ice under warmer conditions4 but these gullies are observed to occur preferentially in cold mid latitudes2 where the presence of liquid water is less likely and on isolated surfaces where groundwater seepage would not be expected making both potential explanations unsatisfactory here i show that gullies can form by the melting of water rich snow that has been transported from the poles to mid latitudes during periods of high obliquity within the past 105 to 106 years refs 5 6 melting within this snow7 can generate sufficient water to erode gullies in about 5 000 years my proposed model for gully formation is consistent with the age and location of the gullies and it explains the occurrence of liquid water in the cold mid latitudes as well as on isolated surfaces remnants of the snowpacks are still present on mid latitude pole facing slopes and the recent or current occurrence of liquid water within them provides a potential abode for life

mass movement slope streaks imaged by the mars orbiter camera narrow fan shaped dark streaks on steep martian slopes were originally observed in viking orbiter images but a definitive explanation was not possible because of resolution limitations pictures acquired by the mars orbiter camera moc aboard the mars global surveyor mgs spacecraft show innumerable examples of dark slope streaks distributed widely but not uniformly across the brighter equatorial regions as well as individual details of these features that were not visible in viking orbiter data dark slope streaks as well as much rarer bright slope streaks represent one of the most widespread and easily recognized styles of mass movement currently affecting the martian surface new dark streaks have formed since viking and even during the mgs mission confirming earlier suppositions that higher contrast dark streaks are younger and fade brighten with time the darkest slope streaks represent 10 contrast with surrounding slope materials no small outcrops supplying dark material or bright material for bright streaks have been found at streak apexes digitate downslope ends indicate slope streak formation involves a ground hugging flow subject to deflection by minor topographic obstacles the model we favor explains most dark slope streaks as scars from dust avalanches following oversteepening of air fall deposits this process is analogous to terrestrial avalanches of oversteepened dry loose snow which produce shallow avalanche scars with similar morphologies low angles of internal friction typically 10 30i for terrestrial loess and clay materials suggest that mass movement of low cohesion martian dusty air fall is possible on a wide range of gradients martian gravity presumed low density of the air fall deposits and thin unresolved by moc failed layer depths imply extremely low cohesive strength at time of failure consistent with expectations for an air fall deposit of dust particles as speed increases during a dust avalanche a growing fraction of the avalanching dust particles acquires sufficient kinetic energy to be lost to the atmosphere in suspension limiting the momentum of the descending avalanche front the equilibrium speed where rate of mass lost to the atmosphere is balanced by mass continually entrained as the avalanche front descends decreases with decreasing gradient this mechanism explains observations from moc images indicating slope streaks formed with little reserve kinetic energy for run outs on to valley floors and explains why large distal deposits of displaced material are not found at downslope streak ends the mass movement process of dark and bright slope streak formation through dust avalanches involves renewable sources of dust only leaving underlying slope materials unaffected areas where dark and bright slope streaks currently form and fade in cycles are closely correlated with low thermal inertia and probably represent regions where dust currently is accumulating not just residing

petrography of locally produced pottery from the dutch colonial cape of good hope south africa abstract thin section petrographic analysis of 17th and 18th century coarse earthenware excavated from dutch colonial sites at the cape of good hope south africa distinguishes locally produced and imported wares results of the identification and textural analysis of mineral inclusions in the ceramic fabrics of suspected local products and suspected and known imported vessels were compared with the known geologic raw material sources of the european rhine meuse river system and local weathered cape granite enabling a characterization of the local products the angular poorly sorted and rounded inclusions combined with the retention of easily decomposed minerals and polycrystalline quartz in suspected local samples mirror the mineralogy of the cape granite historically documented as a clay raw material source at the dutch settlement this profile contrasting significantly from that of the fluvial european source strongly supports the inference of local provenance for the suspected local vessels

geomorphic analysis of lobate debris aprons on mars at mars orbiter camera scale evidence for ice sublimation initiated by fractures 1 lobate debris aprons known to be geomorphic landform indicators of the presence of ground ice are of special interest for future missions devoted to the research of water on mars lobate debris aprons in fretted terrains of deuteronilus and protonilus mensae 35 50 n show typical convex shapes interpreted to be the result of viscous deformation at the scale of mars orbiter camera moc high resolution images the surface of these debris aprons shows complex patterns with small pits and buttes these patterns can be explained by the mantling of dust the accumulation of interstitial ice and the subsequent removal of ice by sublimation the sublimation of the ground ice is especially initiated and accelerated by subsurface heterogeneities like fractures theoretical quantification of sublimation rates therefore minimizes sublimation which is not a homogeneous process at least over the landforms studied crater counts show that the sublimation occurred in the last tens of millions of years up to the recent past in the point of view of future searching of subsurface ice only surface layers are submitted to sublimation favoring the conservation of ground ice in deeper layers since the formation of the landform the geophysical survey of lobate debris aprons would give interesting insights into the subsurface distribution of ice and its seasonal variations especially in order to measure current sublimation of ground ice

field measurement of high temperature bulk reaction rates i theory and technique knowledge of metamorphic reaction rates is crucial to accurately interpret rock and mineral chemistry the local equilibrium assumption used in geochronology geothermobarometry and material flux estimates requires that local reaction rates among system phases are fast relative to local rates of p t x change natural metamorphic reaction rates are essentially unknown and difficulties and disagreements exist regarding extrapolations of existing laboratory data to natural conditions growing recognition of natural effects that could be attributed to slower reaction rates justifies the need for a field based quantification of reaction rates to assess the accuracy of lab based predictions we describe in detail the theory and methodology of a technique for extracting bulk reaction rates directly from isotopic data derived from natural samples baxter and depaolo 2000 reaction rates measured using this technique may be judiciously applied to isotopic exchange or net reaction kinetics in other natural systems the technique requires collection of whole rock and garnet 87sr 86sr data along a sampling traverse normal to a lithologic contact where there was prior to metamorphism a sharp isotopic discontinuity garnet data provide information on syn metamorphic conditions and the time interval for the exchange process forward modeling of the reactive transport process using numerical methods and the equations for diffusive reactive transport allow determination of the reaction rate and bulk sr diffusivity that provides the best fit to the data measurement of reaction rates is best constrained if an isotopic step is preserved at the contact the size of which is directly proportional to the bulk reaction rate this contribution is intended to serve as a template for future use and development of this technique to acquire natural reaction rate data from metamorphic systems

improved general circulation models of the martian atmosphere from the surface to above 80 km we describe a set of two new generation general circulation models of the martian atmosphere derived from the models we originally developed in the early 1990s the two new models share the same physical parameterizations but use two complementary numerical methods to solve the atmospheric dynamic equations the vertical resolution near the surface has been refined and the vertical domain has been extended to above 80 km these changes are accompanied by the inclusion of state of the art parameterizations to better simulate the dynamical and physical processes near the surface boundary layer scheme subgrid scale topography parameterization etc and at high altitude gravity wave drag in addition radiative transfer calculations and the representation of polar processes have been significantly improved we present some examples of zonal mean fields from simulations using the model at several seasons one relatively novel aspect previously introduced by wilson 1997 is that around northern winter solstice the strong pole to pole diabatic forcing creates a quasi global angular momentum conserving hadley cell which has no terrestrial equivalent within such a cell the coriolis forces accelerate the winter meridional flow toward the pole and induce a strong warming of the middle polar atmosphere down to 25 km this winter polar warming had been observed but not properly modeled until recently in fact thermal inversions are generally predicted above one and often both poles around 60 70 km however the mars middle atmosphere above 40 km is found to be very model sensitive and thus difficult to simulate accurately in the absence of observations

nonlinear dynamics of ice wedge networks and resulting sensitivity to severe cooling events patterns of subsurface wedges of ice that form along cooling induced tension fractures expressed at the ground surface by ridges or troughs spaced 10 30 m apart are ubiquitous in polar lowlands1 fossilized ice wedges which are widespread at lower latitudes have been used to infer the duration2 3 4 and mean temperature5 6 of cold periods within proterozoic2 and quaternary climates3 4 5 6 7 8 9 10 11 12 13 and recent climate trends have been inferred from fracture frequency in active ice wedges14 here we present simulations from a numerical model for the evolution of ice wedge networks over a range of climate scenarios based on the interactions between thermal tensile stress fracture and ice wedges we find that short lived periods of severe cooling permanently alter the spacing between ice wedges as well as their fracture frequency this affects the rate at which the widths of ice wedges increase as well as the network s response to subsequent climate change we conclude that wedge spacing and width in ice wedge networks mainly reflect infrequent episodes of rapidly falling ground temperatures rather than mean conditions

a model for water transport and ice lensing in freezing soils a one dimensional model for water transport and ice lensing in incompressible saturated and solute free soil specimens is proposed for the simulation of small scale frost heave tests in the laboratory the model considers 1 open system freezing in which the variables t and pw are independent 2 an ice lens that continues to grow as long as enough energy is available in the frozen fringe to produce the work required for mass transfer to the ice lens and 3 a new ice lens that forms when the vertical strain in the frozen soil reaches the instantaneous tensile failure strain the proposed frost heave model is amenable to computer simulation procedures which provide predictions of rate of frost heave and rate of pore freezing front penetration as functions of applied load thermal and water flow regimes and soil properties position time of initiation and ultimate thickness of individual ice lenses emerge also as a part of the solution a quantitative comparison of observed and simulated responses for various boundary conditions is shown for a reference soil known as devon silt the model was found to exhibit many of the characteristics observed in frost heave tests on devon silt and predicted the effects of overburden pressure on frost heave rate

inter ethnic social interactions in 16th century la florida sourcing pottery using siliceous microfossils abstract a case study is presented to test the notion that minority pottery types from 16th century contexts at the fountain of youth foy site in st augustine reflect population movements from the north that preceded major political reorganizations in the region petrographic methods are employed to trace the manufacturing origins of early historic period aboriginal pottery in northeast florida fragments of siliceous microfossils including sponge spicules opal phytoliths and most notably diatoms were identified in the matrix of some early historic period aboriginal pottery from foy as well as in some clay samples from the coastal region of northeast florida and southeast georgia diatom taxa are identified and their spatial distribution is assessed the distribution of microfossils supports the nonlocal manufacturing origins of some samples from st augustine and conform to expectations about the historic movement of certain aboriginal groups to the settlement

perennial water ice identified in the south polar cap of mars the inventory of water and carbon dioxide reservoirs on mars are important clues for understanding the geological climatic and potentially exobiological evolution of the planet1 from the early mapping observation of the permanent ice caps on the martian poles2 3 the northern cap was believed to be mainly composed of water ice whereas the southern cap was thought to be constituted of carbon dioxide ice however recent missions nasa missions mars global surveyor and odyssey have revealed surface structures4 altimetry profiles5 underlying buried hydrogen6 and temperatures of the south polar regions that are thermodynamically consistent with a mixture of surface water ice and carbon dioxide7 here we present the first direct identification and mapping of both carbon dioxide and water ice in the martian high southern latitudes at a resolution of 2 km during the local summer when the extent of the polar ice is at its minimum we observe that this south polar cap contains perennial water ice in extended areas as a small admixture to carbon dioxide in the bright regions associated with dust without carbon dioxide at the edges of this bright cap and unexpectedly in large areas tens of kilometres away from the bright cap

geographic variations in the thermal and diffusive stability of ground ice on mars to investigate the stability of ground ice within the top several meters of the martian regolith time dependent models of the thermal and diffusive behavior of the regolith have been developed the geographic distribution of thermal inertia and albedo as well as the latitudinal variation in insolation have been included in calculations of surface and subsurface temperatures between 60 latitude ground ice was found to be stable where the annual mean surface and subsurface temperatures were below the atmospheric frost point this generally occurs poleward of the mid latitudes the latitude poleward of which ground ice is stable varies by about 20 to 30 from one longitude to another geographic variations in thermal inertia and albedo are the primary factors controlling regional variations in ice stability calculations of temperatures at high and low obliquity suggest that ground ice would be stable globally at high obliquity and would not be stable between 60 latitude at low obliquity thermally driven diffusion of atmospheric water vapor within the regolith was modeled accounting for both ordinary molecular and knudsen transport and equilibrium between ice vapor and adsorbed phases atmospheric water vapor was found to be able to supply the top few meters of the regolith with ice in regions where the annual mean surface temperature was below the atmospheric frost point ice was found to begin condensing in as short as 1000 martian years rapid accumulation of ice in the pore space of the upper layers of the regolith acted to choke transport to lower layers and slow the diffusion process even so after 105 martian years in some cases as much as 30 to 40 of the available pore space accumulated ice the total amount of subsurface ice ranged from a few to more than 25 g cm2 within the top few meters in regions of stability ground ice was found to form below a depth where the annual average vapor pressure over ice was equal to the annual average atmospheric vapor pressure near the surface atmospheric vapor was not found to accumulate as ice below a depth where the seasonal temperature oscillations gave way to the geothermal gradient the time scales for condensation of ground ice were found to be comparable to that of orbital oscillations suggesting that the present geographic distribution of ground ice may depend on the orbital history of mars

small scale polygonal features on mars seasonal thermal contraction cracks in permafrost a time dependent viscoelastic model of thermal stress in martian ice rich permafrost is developed to test the hypothesis that small scale polygonal features observed from orbit and by the viking lander 2 are the result of thermal contraction cracking as commonly occurs in terrestrial permafrost results indicate that significant tensile stress occurs in martian ice rich permafrost as a result of seasonal cycles in the ground temperature using conservative rheological parameters appropriate for ice at low temperatures tensile stresses poleward of about 20 to 30 latitude easily exceed the tensile strength assumed to be 2 to 3 mpa and fractures should readily form in the equatorial regions special conditions may allow tensile stresses to approach the tensile strength these results support a thermal contraction origin of observed small scale polygonal features and emphasize the utility of these features as valuable morphological indicators of ground ice

characteristics and origin of polygonal terrain in southern utopia planitia mars results from mars orbiter laser altimeter and mars orbiter camera data giant polygons on mars with several kilometers in diameter were first observed in mariner 9 and viking orbiter images and their origin formation and evolution have remained enigmatic since that time new data obtained by the mars orbiter laser altimeter mola and the mars orbiter camera moc on board the mars global surveyor spacecraft now permit analysis of topography and morphology of the polygonal terrain in unprecedented detail mola data show that 1 giant polygonal terrain in utopia is located at the lower slopes of a basin structure that is the utopia basin 2 the onset of polygonal terrain in utopia is close to the same elevation in several profiles and lies at about the same elevation as a terrace which was interpreted as a shore line of an ancient body of standing water within the utopia basin proper 3 polygonal terrain occurs over a wide range of elevations on regional slopes of 0 1 4 the depths of the troughs range from 5 m to 115 m averaging about 30 m and tend to be greater toward the center of the utopia basin 5 the mean width of polygonal troughs is of the order of 2 km ranging from 0 5 to 7 5 km data from the mars orbiter camera moc indicate that 1 the troughs are generally broad graben like features with varying morphologies i e terraces and lobateness and dimensions widths and depths 2 trough morphology has been modified by aeolian processes 3 polygonal troughs are weakly interconnected at moc resolutions and there are no smaller polygons observed within the giant polygons 4 circular depressions which are probably related to subsurface collapse sometimes occur at the bottoms of polygonal troughs 5 small scale polygonal terrain on the ejecta blankets of young craters with fluidized ejecta in the investigated area exhibits different characteristics i e smaller size presence of rims greater degree of interconnections than giant polygons in the viking images we see that 1 old impact craters are increasingly buried with younger materials toward the basin center and that 2 a large number of superposed impact craters on polygonal terrain exhibit distinctive ejecta morphologies such as rampart ejecta blankets and single and double lobate ejecta blankets mola and moc observations are consistent with the formation of polygonal terrain in the area of a former standing body of water but polygon size seems too large to be readily accounted for by desiccation or freezing processes alone on the basis of the observed characteristics we propose that the giant polygons are primarily of tectonic origin being caused by uplift of the floor of the utopia basin there are several candidates for the cause of uplift 1 the removal of the load representing former standing bodies of water water thickness estimated for the utopia basin is about 1 km in this scenario removal of this load comparable to loads placed on terrestrial continental lithosphere by the laurentide and scandinavian ice sheets by loss of the water or ice could cause uplift of the floor and polygon formation 2 the freezing and expansion of residual water buried by sediments or in the near subsurface or 3 a combination of these from the discussion of alternative models in the light of the mola and moc data we conclude that formation of giant polygons by tectonic uplift of the basin floor is most likely and deserves further investigation

high latitude patterned grounds on mars classification distribution and climatic control patterned grounds such as polygonal features and slope stripes are the signature of the presence of ground ice and of temperature variations in cold regions on earth identifying similar features on mars is important to understand its past climate as well as the ground ice distribution in this study young patterned grounds are classed and mapped from the systematical analysis of mars observer camera high resolution images these features are located poleward of 55 latitude which fits the distribution of ground ice found by the neutron spectrometer onboard mars odyssey thermal contraction due to seasonal temperature variations is the predominant process of formation of polygons formed by cracks which sizes vary from 15 to 300 m the small 40 m widespread polygons are very recent and degraded by the desiccation of ground ice from the cracks which enhances the effect of ice sublimation the large polygons 50 to 300 m located only around the south co2 polar cap indicate the presence of ground ice and thus outline the limit of the co2 ice cap they could be due to the blanketing of water ice deposits by the advances and retreats of the residual co2 ice cap during the last thousand years large 50 250 m and homogeneous polygons similar to ice wedge polygons hillslope stripes and solifluction lobes may indicate that specific environments such as crater floors and hillslopes could have been submitted to freeze thaw cycles possibly related to higher summer temperatures in periods of obliquity higher than 35 these interpretations must be strengthened by higher resolution images such as those of the hirise mission of the mars reconnaissance orbiter because locations with past seasonal thaw could be of major interest as potential landing sites for the phoenix mission

fluid production and isograd reactions at contacts of carbonate rich and carbonate poor layers during progressive metamorphism with increasing temperature during prograde metamorphism reactions will occur first at the lithological contacts of mixed pelite and calcsilicate terranes at these interfaces a fluid of lower chemical potential of h2o and co2 than that required to produce a fluid in either layer can be produced whether reaction is caused by fluid infiltration or is initially fluid absent if the interface region does not allow fluid transport then as temperature increases a fluid pressure greater than lithostatic can develop at some degree of over pressure relative to rock pressure the fluid hydraulically fractures the rock and a gradient in fluid composition away from the contact can be produced these phenomena occur at the compositional interfaces whenever univariant reactions in the differing layers cross on a temperature vs mole fraction of co2 diagram with slopes of opposite sign the first occurrence of these reaction products at lithological contacts delineates an isograd that defines temperature as well as the mole fraction of co2 at constant pressure in systems open to fluid transport these isograds can be contrasted with fluid producing isograds in closed systems as an illustration of possible effects the reactions quartz clinozoisite muscovite anorthite k feldspar h2o and phlogopite quartz calcite tremolite k feldspar h2o co2 at 4 kbar are analysed and equations for fluid production and transport are developed

dynamics of periglacial sorted circles in western spitsbergen a working hypothesis for the development and maintenance of sorted circles which are finegrained soil domains delineated by borders of coarser material involves clast motion relative to soil and intermittent circulatory motion of soil in the active layer the hypothesis is compatible with the observed size regularity sorting microtopography surface soil motion vegetation cover and subsurface organic carbon content of soil patterns studied in spitsbergen theoretical considerations of buoyancy driven convection suggest that intermittent convection of thawed soils is plausible and that the requisite bulk density decrease with depth arises naturally from moisture gradients that develop during the thaw consolidation of ice rich soils these considerations also help in understanding the dependence of sorted circles on soil characteristics and on moisture moreover they point to the possible use of sorted patterns as paleoclimatic indicators based on the expected relation between pattern size and active layer depth

spatial relationships between patterned ground and ground ice detected by the neutron spectrometer on mars 1 patterned grounds like polygonal features are the signature of climatic effects in periglacial regions on earth identifying similar features on mars is important for an understanding of the past martian climate in this study we mapped fresh patterned landforms from the systematic analysis of mars orbiter camera high resolution images we show that most of them are distributed at latitudes poleward of 55 making a climatic control likely this distribution correlates to the distribution of ground ice detected by the neutron spectrometer aboard mars odyssey this correlation is likely the consequence of the neutron spectrometer detecting ice no deeper than about 1 m patterned ground formation requires ice in this range of depth because these features are triggered by the propagation of a thermal wave that is driven by seasonal or diurnal changes in insolation which affect the temperature in the uppermost ground layers sublimation seems to play a role in the shaping of many of the small patterns observed at latitudes between 55 and 70 no widespread polygonal features are correlated to the equatorial regions where hydrogen is detected by the neutron spectrometer

numerical simulation of selforganized stone stripes geometrically regular stripes of stones are found on many unvegetated alpine and polar hillslopes known as sorted stripes because of the characteristic textural sorting between surface stones and fine grained soil they contrast markedly with the lack of order typical of natural landscapes the spacing of the stripes can range from centimetres to metres about 10 20 times the average stone diameter1 2 with individual stripes extending down slope for many tens of metres fig 1 a variety of formative mechanisms have been proposed3 but it is still unclear how such orderly stripes can arise spontaneously and what dictates the spacing here we present two dimensional computer simulations in which the displacement of surface stones is governed by the preferential growth of needle ice in stone free regions of soil during each freezing cycle regular patterns of stones and soil that closely resemble natural stripes are found to emerge spontaneously from the model as a result of identifiable feedbacks between soil texture ice growth and local slope

delineation of isograds in siliceous dolomitic marbles along the sharbot lake frontenac terrane boundary of the grenville province southeastern ontario this study presents details of the mineralogy and petrology of siliceous dolomitic marbles of the sharbot lake domain along the frontenac terrane boundary in the grenville province of southeastern ontario the location of four mineral isograds in the marble and the related univariant reactions were identified in the almonte carleton place area delineation of the isograds is based on detailed mapping petrographic analysis of coexisting mineral assemblages and a polybaric t xco2 diagram calculated using thermobarometric data from associated gneissic rocks where t is temperature and x is fluid composition the t x section is based on a field gradient of 32 c km the isograds correspond to the first appearance of tremolite 5 dolomite 8 quartz h2o tremolite 3 calcite 7 co2 diopside tremolite 3 calcite 2 quartz 5 diopside 3 co2 h2o diopside dolomite tremolite 3 calcite dolomite 4 diopside h2o co2 and forsterite diopside 3 dolomite 2 forsterite 4 calcite

ice wedges on hillslopes and landform evolution in the late quaternary western arctic coast canada in rolling to hilly areas of the western arctic coast of canada anti syngenetic wedges which by definition are those that grow on denudational slopes are the most abundant type of ice wedge through prolonged slope denudation hilltop epigenetic wedges can evolve into hillslope anti syngenetic wedges and some bottom slope anti syngenetic wedges by means of deposition from upslope can evolve into bottom slope syngenetic wedges the axis of a hillslope wedge is oriented perpendicular to the slope so the wedge foliation varies according to the trend of the wedge with respect to the slope because the tops of hillslope wedges are truncated by slope recession the mean chronological age of anti syngenetic wedge ice decreases with time so the growth record for an old wedge is incomplete summer and winter measurements show that a thermally induced net movement of the active layer of hillslope polygons tends to transport material from their centres towards their troughs independent of the trends of the t

evidence for major mass transfer and volume strain during regional metamorphism of pelites systematic examination of published sedimentary and metamorphosed pelite analyses has revealed evidence of significant mass transfer and volume strain during regional metamorphism statistical analysis of the data shows that barrovian zone metamorphism of pelitic schist generally causes increases in the whole rock concentrations of the low solubility elements ti and all the observed increases in ti and al contents as functions of metamorphic grade are almost certainly due to residual enrichment caused by the removal of other more soluble species application of mass balance principles to the petite compositional trends indicates that the average pelite may lose as much as 30 of its mass and volume during progressive metamorphism from subgreenschist to amphibolite facies conditions the bulk of the lost mass is silica not volatiles in addition other elements particularly ca na and k appear to be highly mobile in deep crustal metamorphism contrary to conventional interpretations it is concluded that the regional metamorphism of pelites is not an isochemical process

observational evidence for an active surface reservoir of solid carbon dioxide on mars high resolution images of the south polar residual cap of mars acquired in 1999 and 2001 show changes in the configuration of pits intervening ridges and isolated mounds escarpments have retreated 1 to 3 meters in 1 martian year changes that are an order of magnitude larger than can be explained by the sublimation of water ice but close to what is expected for sublimation of carbon dioxide ice these observations support a 35 year old conjecture that mars has a large surface reservoir of solid carbon dioxide the erosion implies that this reservoir is not in equilibrium with the present environment and that global climate change is occurring on mars

migration of reaction and isotopic fronts in infiltration zones assessments of fluid flux in metamorphic terrains abstract criteria are presented for recognising fluid infiltration driven reactions in metamorphic rocks and quantifying the associated fractionations of oxygen and carbon isotopic compositions in medium or high grade metamorphic rocks with local equilibrium between fluid and solid phases reactions or isotopic changes driven by infiltrating fluid are expected to migrate as relatively sharp fronts with limited diffusive broadening fluid leaving such reaction fronts is compositionally buffered by the reacting phases in suitably reactive rocks a series of reaction fronts will develop each driven by infiltration of fluid buffered by the upstream reaction knowledge of the spatial arrangement of such fronts allows calculation of the time integrated fluid fluxes total fluid volume per unit area distinctive stable isotope fractionations are predicted adjacent to infiltration driven reactions with the distribution and magnitude of the fractionation effects dependent upon the relative velocities of the reaction and isotopic fronts the various possibilities are illustrated by reference to a hypothetical infiltration driven decarbonation reaction the calculated isotopic fractionations do not in general resemble those predicted by the open or closed system water rock ratio calculations

global distribution and migration of subsurface ice on mars a thermal diffusive model of h2o kinetics and equilibrium was developed to investigate the long term evolution and depth distribution of subsurface ice on mars the model quantitatively takes into account 1 obliquity variations 2 eccentricity variations 3 long term changes in the solar luminosity 4 variations in the argument of subsolar meridian in planetocentric equatorial coordinates 5 albedo changes at higher latitudes due to seasonal phase changes of co2 and the varying extent of co2 ice cover 6 planetary internal heat flow 7 temperature variations in the regolith as a function of depth time and latitude due to the above factors 8 atmospheric pressure variations over a 104 year time scale 9 the effects of factors 1 through 5 on seasonal polar cap temperatures and 10 knudsen and molecular diffusion of h2o through the regolith the migration of h2o into or out of the regolith is determined by two boundary conditions the h2o vapor pressure at the subsurface ice boundary and the annual average h2o concentration at the base of the atmosphere these are controlled respectively by the annual average regolith temperature at the given depth and seasonal temperatures at the polar cap starting from an arbitrary initial uniform depth distribution of subsurface ice h2o fluxes into or out of the regolith are calculated for 100 selected obliquity cycles each representing a different epoch in mars history the h2o fluxes are translated into ice thicknesses and extrapolated over time to give the subsurface ice depth as a function of latitude and time the results show that obliquity variations influence annual average regolith temperatures in varying degrees depending on latitude with the greatest effect at the poles and almost no effect at 40 lat insolation changes at the pole due to obliquity argument of subsolar meridian and eccentricity variations can produce enormous atmospheric h2o concentration variations of 6 orders of magnitude over an obliquity cycle superimposed on these cyclic variations is a slow monotonic change due to the increasing solar luminosity albedo changes at the polar cap due to seasonal phase changes of co2 and the varying thickness of the co2 ice cover are critically important in determining annual average atmospheric h2o concentrations despite the strongly oscillating character of the boundary conditions only small amounts of h2o are exchanged between the regolith and the atmosphere per obliquity cycle 10 g cm2 the net result of h2o migration is that the regolith below 30 40 lat is depleted of subsurface ice while the regolith above 30 40 lat contains permanent ice due to the depth of penetration of the annual thermal wave this result is supported by recent morphological studies the rate of migration of h2o is strongly dependent on average pore capillary radius for which we have assumed values of 1 and 10 m we estimate that the h2o ice removed from the regolith would produce a permanent ice cap with a volume between 2 106 and 6 106 km3 this generally agrees with estimates deduced from deflationary features at lower latitudes depositional features at higher latitudes and the mass of the polar caps

simple models of co2 release from metacarbonates with implications for interpretation of directions and magnitudes of fluid flow in the deep crust simple one dimensional models of coupled advection hydrodynamic surroundings can account for basic t fluid composition reaction dispersion reaction are used to investigate processes of co2 release progress relationships observed in much of the acadian orogen of from metacarbonate beds during deep crustal 8 kbar acadian new england the results provide an alternative to up t flow prograde metamorphism in new england usa two broad models scenarios that account for these relationships by large pervasive in which reaction progress is controlled by gradients in h2o co2 horizontal fluid fluxes up regional t gradients fluid composition between diverent rock types are presented in the first divusional exchange of volatiles across lithologic contacts is significant co2 generated during prograde temperature t rise is transported away from metacarbonate layers to surrounding 1 metapelitic layers which generate h2o by dehydration and or 2 key words metamorphism fluid flow flow direction carbon dioxide

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

exposed water ice discovered near the south pole of mars the mars odyssey thermal emission imaging system themis has discovered water ice exposed near the edge of mars southern perennial polar cap the surface h2o ice was first observed by themis as a region that was cooler than expected for dry soil at that latitude during the summer season diurnal and seasonal temperature trends derived from mars global surveyor thermal emission spectrometer observations indicate that there is h2o ice at the surface viking observations and the few other relevant themis observations indicate that surface h2o ice may be widespread around and under the perennial co2 cap

a model for sorted patterned ground regularity sorted patterned ground refers to polygons nets or stripes defined by rocky borders which are the result of sorting in soil subjected to frost action this paper presents a model in which convection cells driven by unstable density stratification in the aqueous phase result in uneven melting of the underlying ice front during thawing the resulting undulatory ice front with regularly spaced peaks and troughs provides the pattern which results in the regularity observed for certain types of patterned ground in addition the model predicts the width to depth of sorting ratio for both polygons and stripes and explains the characteristic hexagonal shape of sorted polygons the transition from sorted polygons to sorted stripes on sloped terrain and the formation of sorted polygons under water the predicted ratio of width to depth of sorting of 3 81 for sorted polygons is compared with the ratio of width to depth of sorting of 3 57 found from a linear regression analysis of 18 field study data

diatoms as indicators of provenance in finnish sub neolithic pottery abstract the clays of finland originated from glacial deposits formed during the deglaciation of the weichselian ice sheet and during the different stages of the baltic sea the analysis of the fossil diatom flora is of central importance in the study of its developmental history the diatoms in the clay indicate its sedimentary environment which can be linked to the stages of the baltic sea the siliceous valves of diatoms tolerate heating up to 1400 c and can consequently be identified in ceramics fired at lower temperatures several diatom analyses have been made in finnish sub neolithic comb ware pottery in order to determinate the origin of their clay materials according to the results of these studies prehistoric potteries used clays deposited during the yoldia and the ancylus stages the criteria used in selecting raw materials were identical to those of modern ceramic industries further details as to provenance of clay materials have been illustrated in connection with research on pottery from the aland islands in the example from kymi south eastern finland changes in the composition of the diatom flora have been found to correlate with changes in pottery decoration styles

pathological martian craters evidence for a transient obliteration event we have detected three unusual low relief circular features 1 2 to 2 1 km in diameter in the northwest noachis highlands which may be craters that have undergone isostatic deformation they may shed light on the existence nature and timing of suspected widespread martian erosion obliteration events and offer clues to a type of martian terrain softening in the surrounding area we find an anomalous deficiency of craters in the 3 11 km diameter range and evidence that larger older craters have undergone relief softening and infill we discuss three different hypotheses to explain these features two of which involve martian ice this region may have undergone a transient event in which a near surface permafrost layer several hundred meters deep underwent partial melting or softening this would allow relaxation of kilometer scale craters and softening of larger craters crater data presented here suggest that this event happened some time in mid martian history whether the event was regional or related to global scale events is uncertain though it may represent a class of events that also happened in other martian areas

south polar layered deposits of mars the cratering record data from the mars orbiter laser altimeter mola and mars orbiter camera moc instruments aboard the mars global surveyor mgs were used in a detailed search of a selected part of the south polar layered deposits spld for impact craters impact craters with diameters from 0 8 to 5 km were identified from a mola derived shaded relief map and were primarily validated using individual mola tracks and in select cases moc narrow angle images the resultant crater population determined in this study is at least four times the density of the crater population previously recognized from these new statistics we estimate the mean apparent surface age of the spld to be 30 100 ma depending on the established production model isochrons used all of these craters are considerably shallower than other martian craters in the same diameter range we attribute this shallowness to be the cause of the lower detection rates of previous studies there is a correlation between crater depth and rim height which suggests that both erosion and infilling have affected the crater forms a similar study of the north polar layered deposits uncovered no craters in this diameter range a limited population of craters smaller than 800 m was uncovered in higher resolution moc narrow angle images these do not appear to have been degraded to the same degree this separate population implies a surface exposure age of only 100 000 years and perhaps indicates an event that erased all small craters and degraded and infilled the larger ones

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

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

north south geological differences between the residual polar caps on mars polar processes can be sensitive indicators of global climate and the geological features associated with polar ice caps can therefore indicate evolution of climate with time the polar regions on mars have distinctive morphologic and climatologic features thick layered deposits seasonal co 2 frost caps extending to mid latitudes and near polar residual frost deposits that survive the summer the relationship of the seasonal and residual frost caps to the layered deposits has been poorly constrained mainly by the limited spatial resolution of the available data in particular it has not been known if the residual caps represent simple thin frost cover or substantial geologic features here we show that the residual cap on the south pole is a distinct geologic unit with striking collapse and erosional topography this is very different from the residual cap on the north pole which grades into the underlying layered materials these findings indicate that the differences between the caps are substantial rather than reflecting short lived differences in frost cover and so support the idea of long term asymmetry in the polar climates of mars

metastability of liquid water on mars abstract a simple model of local heat transport on mars demonstrates that transient melting of ice may occur in depressions and gullies nearly anywhere on the planet where thin ice is illuminated by normal incidence insolation an experiment has been performed to confirm the model of evaporation rate at low pressure reduction of radiative cooling due to gully geometry is shown to be important since appropriate meteorological topographic and optical conditions may occur on slopes nearly anywhere on the planet hydrological features such as gullies would likely form only where such ice might accumulate notably in sheltered locations at high latitudes it is suggested that cold trapping of winter condensation could concentrate a sufficient amount of ice to allow seasonal melting in gullies

physical modelling of gelifluction and frost creep some results of a large scale laboratory experiment an experimental slope was constructed in a 5 m 5 m square refrigerated tank the slope was formed of four sections each consisting of regolith soil collected from a distinct bedrock lithology the four lithologies utilized were granite limestone mudstone and slate the slope was subjected to freezing and thawing from the surface downwards water was supplied at the base of the soil during freezing frost heaving and surface downslope soil movement were determined after each of 15 freezing cycles and the profiles of soil movement with depth for each soil type were measured at the end of the 15th cycle the experimental soils were non cohesive those derived from granite and limestone were respectively sandy and gravelly in texture while those derived from mudstone and slate were silt rich mass movement in the granite and limestone soils was due mainly to frost creep and was associated with the growth of needle ice in the mudstone and slate soils gelifluction was dominant as a result of high moisture contents caused by the melting of segregation ice mean per cycle rates of downslope soil transport for the granite limestone mudstone and slate soils were 5 8 cm3 cm 1 6 9 cm3 cm 1 21 2 cm3 cm 1 and 31 2 cm3 cm 1 respectively units referring to the volume of soil passing a unit width of slope per cycle mass movement rates were shown to be strongly related to the silt content of the soils