sedimentology of quaternary perched springline and paludal tufas criteria for recognition with examples from guadalajara province spain outcrop scale geometries and bed relationships of ambient temperature freshwater carbonates are poorly understood because many described tufas have been dismantled by erosion and present only part of a particular depositional model at the field scale four end member models encompass the tufa continuum 1 perched springline 2 paludal 3 fluvial and 4 lacustrine tufas individual bed types can occur with variable dominance within several of these models but one or more beds are characteristically dominant only within a single tufa model so it can be differentiated from relatively isolated outcrop fragments two models perched springline tufas and paludal tufas are known in outline only in the literature despite being present within the quaternary deposits of most karstic regions perched springline tufas generally form lobate fan shaped mound morphologies on hillslopes and develop from single or multiple spring resurgences mature deposits show a subhorizontal top and a steep face on the downflow side the steep outer zones of tufa mounds may be developed into cascades with moss curtains or can be dominated by shallow rimstone pools according to face angle tufa deposits lying downslope of the mounds are usually detrital in nature especially if some dismantling of the mound has occurred the relatively thin subhorizontal lobe top deposits commonly contain organic rich deposits paludal tufas develop predominantly in waterlogged valley bottom situations where line sourced waters emerge from valley side and bottom aquifers lime mud precipitation predominates in these sites mud is deposited as subhorizontal laminites that thin towards the valley axis and downstream of resurgences tufa spring mounds may form where lesser volumes of water are involved individual tussocks phytoherm cushions of grasses and rushes are the most diagnostic feature of the model but sapropels and peats may be intercalated diagenesis in both models is rapid lithification of individual beds is virtually instantaneous and always occurs before the decay of the associated living vegetation the resulting highly porous and permeable fabrics remain fresh in holocene tufas but aggrading neomorphism and partial spar infill of vegetation moulds is common in older deposits dissolution in many perched springline tufas is small scale many large cavities are primary but with later coatings of speleothems early removal of organics from paludal tufas is responsible for autobrecciation and differential compaction

periglacial geomorphology and landscape evolution of the tempe terra region mars a systematic survey was undertaken and an investigation carried out into the geomorphological characteristics of lobate debris aprons in the tempe terra region of mars based on the most recent high resolution sub 15 m per pixel imagery and on new topography data this study endeavoured to raise and discuss questions regarding their formation emplacement and modification deformation sequence as well as the role of a mantling deposit found at mid latitude locations on mars furthermore a model for the formation of debris aprons in the tempe terra mareotis fossae settings is proposed image survey in combination with basic morphometric observations within a geomorphological context provided additional insights into the source emplacement and modification of hillslope debris material our results imply that lobate debris aprons are not mainly relicts of remnant degradation but are substantially composed of mantling material probably deposited episodically in the course of planetary obliquity changes and over a long timespan as derived erosion rates suggest crater size frequency statistics and the derivation of absolute ages show ages of sub recent modification and document earlier resurfacing events

hydrogen index and carbon isotopes of lacustrine organic matter as lake level indicators abstract optical and geochemical techniques were applied to organic matter of late quaternary sediments from lakes victoria and rukwa east africa variations in total organic carbon toc and hydrogen content expressed as hydrogen index hi can be related to known changes in lake level and used to identify periods of very low water or subaerial exposure in basinal sequences toc and hi both decline as an exposure surface is approached mainly due to the selective removal of unstable components by bacterial respiration and inorganic oxidation inert organic material of very low hi is typically concentrated at the overlying transgression surface the carbon isotopic composition of the particulate organic matter tends to be less negative in sediments associated with exposure surfaces although weathering may be partially responsible isotopic variations are mainly due to changes in the relative importance of material from plants using c4 photosynthesis such as grasses and sedges growing around the shore and on the exposed lake muds and of material from planktonic algae and terrestrial c3 plants

subsurface settlement profiles above tunnels in clays designers assessing the possible effect of tunnelling on structures relatively close to the tunnel crown need to know how subsurface settlement profiles develop and how these relate to surface settlement profiles the effect on piled foundations or existing tunnels depends on the width of the subsurface settlement profile and on the magnitude of the settlement this note uses available field measurements and centrifuge model test data to determine how the widths of the settlement profiles and the magnitudes of settlement vary with depth above tunnels constructed in clays the results reveal a fairly consistent pattern of behaviour the width of the subsurface settlement troughs at depth is significantly greater than would be predicted by assuming a constant trough width parameter k of 0 5 smaller more realistic subsurface settlements and strains will be predicted if account is taken of the proportionally wider trough widths at depth

modeling the tor dotted crests bedrock edges and parabolic profiles of high alpine surfaces of the wind river range wyoming abstract broad low curvature surfaces common to many alpine landscapes and particularly well expressed in the laramide ranges of the western usa appear to be roughly in steady state with respect to the current surface processes uniform thin order 1 m regolith covers the crystalline bedrock with the exception of occasional tors at ridgecrests the surfaces are commonly edged by bedrock lips at the tops of cliffs that bound the intervening glacial troughs regolith production is low order 10 m year on bare bedrock and reaches a maximum under tens of centimeters of regolith all of these characteristics may be accounted for with a numerical model that is faithful to the periglacial surface processes presently operating on these surfaces hillslope transport is modeled assuming the dominant process is frost creep transport efficiency depends linearly upon local slope and appropriately vanishes in the absence of regolith frost frequency scales the rate of motion while the ratio of frost penetration depth to regolith thickness dictates the degree to which the process is curtailed by available regolith initial conditions include initial mean slope and bedrock roughness and a uniform regolith cover boundary conditions are imposed by dictating that the edges of the calculation space be lowered at a rate appropriate for glacial incision broad convex surfaces emerge over time scales of order 1 million years all surfaces rapidly decouple from the bounding glacial troughs as the high negative curvature at the edges disallows accumulation of regolith these bedrock edges lower at a few microns per year while the troughs lower at many times this rate as the bedrock edges therefore serve as the effective boundary condition for the remaining surface the surfaces operate independently of both lowering and widening of the glacial troughs for a reasonable set of transport and weathering rates the final steady state landscape is sensitive to the initial condition in particular the steeper the initial landscape the more likely tors are to develop as the high curvature disallows accumulation of regolith these tors in turn limit the lowering rate of the crest and the landscape retains significant local relief low relief initial conditions more likely lead to parabolic surfaces that lack tors that tors are more likely on the crests reflects the high initial curvature at the crest tors on the side slopes are eliminated the present high surfaces in the laramide ranges of the western usa imply operation of periglacial surface processes over millions of years the occasional tors imply a steeper rather than flatter initial landscape the strong decoupling of surfaces from glacial troughs justifies their use as local geomorphic markers that allow calculation of relief production since glacial incision was initiated on the other hand their present low curvature does not require a landscape history in which these surfaces were once joined as an initially widespread erosion surface

recurrent spring fed rivers in a middle to late pleistocene semi arid grassland implications for environments of early humans in the lake victoria basin kenya the effect of changing palaeoclimate and palaeoenvironment on human evolution during the pleistocene is debated but hampered by few east african records directly associated with archaeological sites prior to the last glacial maximum middle to late pleistocene deposits on the shoreline of eastern lake victoria preserve abundant vertebrate fossils and middle stone age arte facts associated with riverine tufas at the base of the deposits which are ideal for palaeoenvironmental reconstructions new data from tufas identified on rusinga island and on the mainland near karungu kenya are provided from outcrop thin sections mineralogical stable isotopic and u series dating analyses tufa is identified in four sites nyamita 94 0 3 3 and 111 4 4 2 ka kisaaka aringo 455 45 ka and obware the age ranges of these tufa deposits demonstrate that spring fed rivers were a recurrent variably preserved feature on the pleistocene landscape for ca 360 kyr poor sorting of clastic facies from all sites indicates flashy ephemeral discharge but these facies are commonly associated with barrage tufas paludal environments with 13c values of ca 10 indicative of c3 plants and fossil hippopotamus all of which indicate a perennial water source other tufa deposits from nyamita obware and aringo have a mixed c3 c4 signature consistent with a semi arid c4 grassland surrounding these spring fed rivers the 18o values of tufa from nyamita are on average ca 1 more negative than calcite precipitated from modern rainfall in the region suggesting greater contribution of depleted monsoonal input similar to the last glacial maximum microdebitage and surface collected artefacts indicate that early modern humans were utilizing these spring fed rivers the presence of spring fed rivers would have afforded animals a reliable water source sustaining a diverse plant and animal community in an otherwise arid environment

two dimensional nonlinear diffusive numerical simulation of geomorphic modifications to cinder cones the temporal evolution of simple landforms such as cinder cones by nonlinear diffusive processes is studied through the use of a new 2d numerical model using well established and accurate numerical mathematics and high resolution digital elevation models dems extending 1d profile nonlinear diffusion analyses used in cinder cone hillslope and fault scarp evolution studies we have implemented a 2d numerical model with a spatially and temporally varying sediment transport rate coefficient scaled nonlinearly by the ratio of local slope to critical slope the high accuracy and efficient numerical implementation are documented in the paper and the matlab toolkit developed is used to solve for the developmentof an initial 2d cone form first we examine the nonlinear transport rule and suggest a refinement that accounts explicitly for flux at threshold slopes we find that the maximum diffusion necessarily introduced in the numerical model to avoid infinite rates at the critical slope controls the final morphology especially approaching steady state secondly solving the landscape evolution problem in 2d enables a natural accounting for sediment flux convergence or divergence in the profile thirdly the boundary behavior of a given landscape element controls much of what happens in that domain and so we allow for arbitrary flux magnitude or elevation boundary conditions fourthly landscapes are heterogeneous in their surface cover and so we allow for spatially and temporally varying transport rate k and we permit an arbitrary vertical displacement field within the model domain to test the new formulation for the nonlinear term the effect of variable diffusivity k and the numerical schemes implemented we apply the model to cinder cones built on the flanks of mount etna in 2001 and 2002 2003 we explore the effects of dem resolution with data from the 2001 cone and the utility of spatially variable diffusivity to explain the variation in erosion measured by differencing repeat light detection and ranging lidar surveys gathered in 2004 and 2007 over the 2002 2003 cone complex copyright 2013 john wiley sons ltd

analytical approach for estimating ground deformation profile induced by normal faulting in undrained clay although theoretical models have been developed to predict the location of the failure surface in soil induced by bedrock faulting no analytical tool is available to estimate subsurface ground deformation in this paper a newly developed semi empirical approach is introduced and developed for calculating surface and subsurface deformations induced by normal faulting in undrained clay based on observations from centrifuge model tests the ground deformation mechanisms are identified by three regions namely a stationary zone a shearing zone and a rigid body zone by using an error function to represent vertical displacement continuously the ground deformation profile can be described quantitatively it is revealed that the ground deformation profile depends on vertical displacement of the bedrock hanging wall soil thickness dip angle of the bedrock fault plane and a shape parameter that is a function of the undrained shear modulus normalized by the undrained shear strength validation and consist

paleoenvironmental change in the late middle pleistocene holocene kibish formation southern ethiopia evidence from ungulate isotopic ecology abstract east africa has produced the earliest record of homo sapiens 200 ka and a punctuated record of middle stone age and later stone age behaviors we lack however a detailed late quaternary paleoenvironmental record for the region particularly during humid periods without a regional record hypotheses about the evolution and ecology of early homo sapiens in east africa remain vague and untestable the kibish formation of southern ethiopia presents a long albeit punctuated record of late middle pleistocene to holocene faunal change in east africa which was deposited during humid periods here we present oxygen and carbon stable isotope data of the kibish ungulates and test whether there are environmental changes within the kibish formation significant differences in 18o enamel isotopes are consistent with more humid conditions during the holocene age member iv 13 4 ka than either pleistocene age member i 196 ka or member iii 104 ka mesowear data document a shift toward more attritional wear among grazers in member iv and are correlated with more depleted 18o enamel values suggesting that the wear pattern shift is linked to the onset of more humid conditions during the holocene 13c enamel values show subtle variations through time but do not suggest any major changes in diets we propose that the paleoenvironmental differences evident in member iv based on 18o enamel values mesowear and bovid abundances may be explained by cooler and wetter conditions at the beginning of the holocene in the lower omo valley the evidence suggesting that the holocene humid phase is more pronounced than earlier humid phases may explain why arid adapted grassland ungulates became extinct in east africa by the pleistocene holocene transition but persisted through previous humid phases of the late quaternary

viking landing sites remote sensing observations and physical properties of martian surface materials abstract important problems that confront future scientific exploration of mars include the physical properties of martian surface materials and the geologic processes that formed the materials the design of landing spacecraft roving vehicles and sampling devices and the selection of landing sites vehicle traverses and sample sites will be in part guided by the physical properties of the materials four materials occur in the sample fields of the viking landers 1 drift 2 crusty to cloddy 3 blocky and 4 rock the first three are soillike drift materials is weak loose and porous we estimate that it has a dielectric constant near 2 4 and a thermal inertia near 1 10 3 to 3 10 3 cal cm 2 sec 1 2 k 1 because of its low bulk density fine grain size and small cohesion crusty to cloddy material is expected to have a dielectric constant near 2 8 and a thermal inertia near 4 10 3 to 7 10 3 because of its moderate bulk density and cementation of grains blocky material should have a dielectric constant near 3 3 and a thermal inertia near 7 10 3 to 9 10 3 because of its moderate bulk density and cementation common basaltic rocks have dielectric constans near 8 and thermal inertias near 30 10 3 to 60 10 3 comparisons of estimated dielectric constants and thermal inertias of the materials at the landing sites with those obtained remotely by earth based radars and viking orbiter thermal sensors suggest that the materials at the landing sites are good analogs for materials elsewhere on mars correlation of remotely estimated dielectric constant and thermal inertias indicates two modal values for paired values of dielectric constants and thermal inertias near a 2 and 2 10 3 and b 3 and 6 10 3 respectively these two modes are comparable to the dielectric constants and thermal inertias for drift and crusty to cloddy material respectively dielectric constants and thermal inertias for blocky material are larger but conistent with values in the northern plains our interprertations are compatible with an aeolian origin for drift and similar materials elsewhere on mars the postulate that moderate dielectric constants and thermal inertias larger than 3 or 4 10 3 are produced by cementation of soillike materials is partly consistent with the data the average dielectric constant and thermal inertia and their correlation with one another suggest that most of the surface of mars should present few difficulties to future surface exploration but some surfaces may present difficulties for spacecraft that are not suitably designed

recent glaciation at high elevations on arsia mons mars implications for the formation and evolution of large tropical mountain glaciers 1 the 166 000 km2 fan shaped deposit at arsia mons contains three characteristic facies ridged knobby and smooth which are interpreted as the depositional remains of a cold based glacier that was present on the west northwestern flanks in the late amazonian period of mars history here we consider several high elevation graben on the western flank of arsia mons that are interpreted as the source regions for late stage cold based glaciers that overflowed graben walls advanced tens to hundreds of kilometers downslope experienced subsequent retreat and left distinctive depositional features similar to those associated with cold based glaciers in the dry valleys of antarctica these new observations provide additional support for a cold based glacial interpretation of the tharsis montes fan shaped deposits morphological evidence suggests that the largest of these graben was the primary source region for the most proximal smooth facies lobes at arsia mons and map plane ice sheet reconstructions are consistent with these observations this relationship has significant implications for the relative ages of the individual facies within the fan shaped deposit including the possibility that the smooth facies represents several distinct phases of glaciation the high relief and large elevation differences between the upslope and downslope walls of these graben appear to be critical factors for ice accumulation and the generation collection of rockfall within glacial accumulation zones we suggest that rockfall was the dominant process responsible for debris cover formation on the glaciers sourced within these graben and consider the implications for the entire arsia fan shaped deposit new crater count data suggest that the fill material in the large arsia graben formed within the past 100 myr model age of 65 ma taken together these new observations provide additional evidence for several periods of late amazonian climate change on mars within the past few 100 myr resulting in episodes of tropical mountain glaciation finally mola topography reveals that several lobate features interpreted as remnant debris covered ice from the most recent phase of glaciation are presently hundreds of meters thick suggesting the possibility of long term near surface water ice survival in the equatorial regions of mars

distal tephras of the eastern lake victoria basin equatorial east africa correlations chronology and a context for early modern humans abstract the tephrostratigraphic framework for pliocene and early pleistocene paleoanthropological sites in east africa has been well established through nearly 50 years of research but a similarly comprehensive framework is lacking for the middle and particularly the late pleistocene we provide the first detailed regional record of late pleistocene tephra deposits associated with artifacts or fossils from the lake victoria basin of western kenya correlations of late pleistocene distal tephra deposits from the wasiriya beds on rusinga island the waware beds on mfangano island and deposits near karungu mainland kenya are based on field stratigraphy coupled with 916 electron microprobe analyses of eleven major and minor element oxides from 50 samples at least eight distinct distal tephra deposits are distinguished four of which are found at multiple localities spanning 60 km over an approximately north to south transect new optically stimulated luminescence dates help to constrain the late pleistocene depositional ages of these deposits our correlation and characterization of volcaniclastic deposits expand and refine the current stratigraphy of the eastern lake victoria basin this provides the basis for relating fossil and artifact bearing sediments and a framework for ongoing geological archaeological and paleontological studies of late pleistocene east africa a crucial time period for human evolution and dispersal within and out of africa

sites on the landscape paleoenvironmental context of late pleistocene archaeological sites from the lake victoria basin equatorial east africa open air archaeological sites record only a small fraction of the behavioral traces of mobile forager populations whereas caves and rockshelters were often occupied at least in part for protection from the elements the reasons why human foragers occupied other places on the landscape however briefly are varied and not always readily recoverable we develop a framework for interpreting human use of the landscape and modeling occupation of open air sites using the archaeological and paleoenvironmental record of middle stone age msa sites from rusinga and mfangano islands located near the eastern margin of lake victoria paleoenvironmental reconstructions using fossil faunas suggest an arid grassland setting unlike the present paleoecological modeling of the habitats of extant and extinct bovids combined with gis based reconstructions of lake level change indicate that human occupation of these sites coincided with substantial declines in the level of lake victoria during this time both rusinga and mfangano would have been connected to the mainland and represented local topographic highs within an extensive grassland geological ecological and ethnobotanical observations suggest that these topographic high points would likely have been important sources of stone raw material fresh water and a variety of plant resources for food fuel and other purposes in contrast the grassy lowland plains were probably exploited primarily as a source of large game which included numerous species of large gregarious grazers several of which may have followed now extinct migration routes

ground response to multiple parallel microtunneling operations in cemented silty clay and sand abstractthis paper presents a case history of the successful application of observational method to instruction microtunneling with successive pipe jacking the microtunneling project is the construction of four parallel pipes under guan river in jiangsu china four parallel tunnels with external diameter of 4 160 mm and horizontally spaced at 4 8 m apart were jacked over 450 m in cemented silty clay and sand by two slurry balance microtunnel boring machines mtbm at a depth of 4 6 m under the river bed since the overburden soil is very thin proper control of tunneling operations was of utmost importance for maintaining the stability of the river bed in order to optimize the operation parameters prior to construction under the river bed a field trial was conducted which included measurement of ground surface settlement subsurface settlement and lateral displacement of the subsurface soils as well as excess pore water pressure and earth pressure the relationship between ground response and const

testing the water hypothesis quantitative morphological analysis of terrestrial and martian mid latitude gullies abstract although martian gullies resemble terrestrial counterparts two conflicting hypotheses exist for their formation still invoke fluvial processes on the one hand or lubricated co 2 flows on the other in this work we compared the quantitative morphology of terrestrial gullies known to have formed by liquid water and mid latitude martian gullies in the martian southern hemisphere we also compared these results with measurements of martian dry ravines adjacent to the gullies our results show a similarity between martian and terrestrial gully formation supporting the hypothesis that liquid water was involved in their erosion our results show dry ravines differ morphologically from gullies further suggesting fluidised flows as a likely origin of the latter variations in the relationships across various terrestrial and martian gullies indicate the significance of local environmental and geological conditions our work supports the idea that martian gullies may not have been formed by just one single process but may have evolved through a more complex interaction of processes and environment

size variation in tachyoryctes splendens east african mole rat and its implications for late quaternary temperature change in equatorial east africa abstract this study develops a new proxy for quaternary temperature change in tropical africa through analysis of size variation in east african mole rat tachyoryctes splendens in modern mole rats mandibular alveolar length is unrelated to annual precipitation precipitation seasonality temperature seasonality or primary productivity however it is inversely correlated with mean annual temperature in agreement with bergmann s rule this relationship is observed at temperatures below 17 3 c but not at higher temperatures we apply these observations to late quaternary mole rats from wakondo 100 ka and kisaaka 50 ka in the lake victoria region and enkapune ya muto eym 7 2 3 2 ka in kenya s central rift the lake victoria mole rats are larger than expected for populations from warm climates typical of the area today implying cooler temperatures in the past the magnitude of temperature decline needed to drive the size shift is substantial 4 6 c similar in magnitude to the degree of change between the last glacial maximum and holocene but is consistent with regional temperature records and with scenarios linking equatorial african temperature to northern hemisphere summer insolation size changes through time at eym indicate that rising temperatures during the middle holocene accompanied and potentially contributed to a decline in lake naivasha and expansion of grassland vegetation

maps of subsurface hydrogen from the high energy neutron detector mars odyssey after 55 days of mapping by the high energy neutron detector onboard mars odyssey we found deficits of high energy neutrons in the southern highlands and northern lowlands of mars these deficits indicate that hydrogen is concentrated in the subsurface modeling suggests that water ice rich layers that are tens of centimeters in thickness provide one possible fit to the data

greenfield tunnelling in sands the effects of soil density and relative depth tunnel construction is vital for the development of urban infrastructure systems throughout the world an understanding of tunnelling induced displacements is needed to evaluate the impact of tunnel construction on existing structures recent research has provided insight into the complex mechanisms that control tunnelling induced ground movements in sands however the combined influence of relative tunnel depth and soil density has not been described this paper presents data from a series of 15 plane strain centrifuge tests in dry sand the cover to diameter ratio c d of the tunnels ranges between 1 3 and 6 3 thereby including relatively shallow and deep tunnels the sand relative density varies between 30 and 90 corresponding to loose and dense soils the effects of c d soil density and volume loss on vertical and horizontal soil movements shear strains and ground reaction curves are discussed analysis of surface and subsurface settlement trough characteristics shows that the mechanisms are non linear and the effects of soil relative density and volume loss on deformation patterns are highly dependent on c d the role of soil arching in the definition of the displacement mechanisms and a discussion of the implications of the results to the assessment of damage to existing structures are also provided

abrupt onset and termination of the african humid period rapid climate responses to gradual insolation forcing a detailed ca 100 yr resolution and well dated 18 ams 14 c dates to 23 cal ka bp record of latest pleistocene holocene variations in terrigenous eolian sediment deposition at odp site 658c off cap blanc mauritania documents very abrupt large scale changes in subtropical north african climate the terrigenous record exhibits a well defined period of low influx between 14 8 and 5 5 cal ka bp associated with the african humid period when the sahara was nearly completely vegetated and supported numerous perennial lakes an arid interval corresponding to the younger dryas chronozone punctuates this humid period the african humid period has been attributed to a strengthening of the african monsoon due to gradual orbital increases in summer season insolation however the onset and termination of this humid period were very abrupt occurring within decades to centuries both transitions occurred when summer season insolation crossed a nearly identical threshold value which was 4 2 greater than present these abrupt climate responses to gradual insolation forcing require strongly non linear feedback processes and current coupled climate model studies invoke vegetation and ocean temperature feedbacks as candidate mechanisms for the non linear climate sensitivity the african monsoon climate system is thus a low latitude corollary to the bi stable behavior of high latitude deep ocean thermohaline circulation which is similarly capable of rapid and large amplitude climate transitions

modification of impact craters in the northern plains of mars implications for amazonian climate history we measured the depth wall steepness and ejecta roughness and surveyed the wall and floor morphology of all craters 10 25 km in diameter within the typical vastitas borealis formation in the northern lowlands of mars north of 52 n two of the 130 craters have unusually rough ejecta they are deep have steep walls and are apparently the youngest in the population icy mantles filling the local subkilometer scale topographic lows is the main contribution to ejecta smoothing which occurs at a time scale on the order of tens of myr wall degradation and crater shallowing generally occur at longer time scales comparable to the duration of the amazonian period many craters are shallow due to filling of the crater with specific ice rich material of uncertain origin we use our collected data to infer the nature of the past climate back through the amazonian a period prior to 10 20 myr ago when orbital parameter solutions are chaotic and one must rely on geological data to infer climate conditions we conclude that moderately high obliquity and wide obliquity variations were probable during the last 40 160 myr we tentatively conclude that high obliquity peaks 40 45 may have occurred episodically through the last 210 430 myr a sharp step in the frequency distribution of wall steepness at 20 may indicate a geologically long period prior to that time where obliquity never exceeded 40 45

observations of the north polar region of mars from the mars orbiter laser altimeter elevations from the mars orbiter laser altimeter mola have been used to construct a precise topographic map of the martian north polar region the northern ice cap has a maximum elevation of 3 kilometers above its surroundings but lies within a 5 kilometer deep hemispheric depression that is contiguous with the area into which most outflow channels emptied polar cap topography displays evidence of modification by ablation flow and wind and is consistent with a primarily h2o composition correlation of topography with images suggests that the cap was more spatially extensive in the past the cap volume of 1 2 3 10 6 to 1 7 3 10 6 cubic kilometers is about half that of the greenland ice cap clouds observed over the polar cap are likely composed of co 2 that condensed out of the atmosphere during northern hemisphere winter many clouds exhibit dynamical structure likely caused by the interaction of propagating wave fronts with surface topography

quantification of soil production and downslope creep rates from cosmogenic 10be accumulations on a hillslope profile average soil transport rates over a period of 3500 yr on a convex soil mantled hillslope have been quantified using a mass balance model that incorporates the soil concentration of the cosmogenic isotope 10 be the 10 be model results support the assumption used in most geomorphic models that the soil creep rate is proportional to surface gradient the predicted diffusion coefficient is 360 55 cm 3 yr 1 cm 1 contour length and the average rate of soil production is 0 026 0 007 cm yr within the uncertainty of this technique the data do not reject g k gilbert9s hypothesis that some hillslopes may exist in a condition of dynamic equilibrium with a uniform soil production rate however the model does not require an assumption of dynamic equilibrium and may be an approach that uniquely allows the quantification of a local soil production rate law

investigating gully flow emplacement mechanisms using apex slopes abstract the origin of the martian gullies has been much debated since their discovery by the mars orbiter camera moc malin m c edgett k s 2000 science 288 2330 2335 several previous studies have looked at slope gradients in and around gullies but none have used digital elevation models dems from the high resolution imaging science experiment hirise mcewen a s and 14 colleagues 2007 j geophys res 112 e05 e0505s02 which has a pixel scale down to 25 cm pixel we use five 1 m post hirise dems to measure gully apex slopes the local channel gradient at the upslope extent of the gully debris apron which marks a shift from erosion to deposition the apex slope provides information about whether a flow was likely a typical dry granular flow begins depositing on slopes 21 or fluidized by some extra mechanism depositing on shallower slopes we find that 72 of the 75 gully fans studied were likely emplaced by fluidized flows relatively old gullies appear more likely to have hosted fluidized flows than relatively fresh gullies this suggests a time and location dependent fluidizing agent possibly liquid water produced in a different climate as previously proposed our results do not provide evidence for water rich flows in gullies today

tunneling beneath driven or jacked end bearing piles in sand this paper presents centrifuge model test data that relate to the problem of tunneling beneath driven or jacked end bearing piles in sand the centrifuge model consisted of a tunnel and two piles and allowed for the acquisition of sub surface digital images throughout the tests soil and pile displacements were measured using particle image velocimetry and close range photogrammetry techniques the piles were jacked into the ground in flight prior to tunnel volume loss to ob tain ground stress profiles representative of conditions around driven or jacked piles patterns of displacements and calcu lated soil strains are presented to illustrate mechanisms of displacement and soil behavior the measured soil and pile displacements are compared against greenfield test measurements the results indicate that driving the piles significantly al ters greenfield conditions and that greenfield displacements should not be used as an input for analytical tunnel soil pile in teraction analyses for driven or jacked piles large pile displacements were observed to occur suddenly in the tests illustrating the brittle nature of the soil in the areas affected by pile installation a relationship between relative pile tunnel location and the volume loss at which large pile displacements occurred is presented which provides useful guidance to tun nel design engineers resume cet article presente des donnees d essais en centrifuge modelisant le creusage de tunnels sous des pieux a pointe portante fonces ou a verin dans du sable le modele de centrifuge consiste en un tunnel et deux pieux et permet l acquisi tion d images digitales sous la surface pendant toute la duree des essais les deplacements du sol et des pieux ont ete mesu res a l aide des techniques d images velocimetriques des particules et de photogrammetrie rapprochee les pieux ont ete installes avec un verin dans le sol en vol avant la perte de volume du tunnel afin d obtenir les profils de contrainte du sol re presentatifs des conditions autour des pieux fonces ou a verin les patrons des deplacements et les deformations du sol cal culees sont presentees afin d illustrer les mecanismes de deplacement et le comportement du sol les deplacements mesures du sol et du pieu sont compares a des mesures sur un sol naturel vierge les resultats indiquent que le foncage des pieux al tere significativement les conditions naturelles du sol et que les deplacements du sol naturel ne devraient pas etre utilises comme donnees de base pour les analyses analytiques des interactions tunnel sol pieu pour des pieux fonces ou a verin on a observe que des grands deplacements des pieux se produisent de facon soudaine durant les essais ce qui illustre la nature fragile du sol dans les zones affectees par l installation des pieux une relation entre l emplacement relatif pieu tunnel et la perte de volume a laquelle les grands deplacements des pieux se sont produits est presentee et ainsi offre des informations utiles pour les ingenieurs qui concoivent des tunnels mots cles tunnel pieu sable centrifuge mecanisme de deplacement deformation traduit par la redaction

north south asymmetry in martian crater slopes 1 the presence of an extensive ice rich layer in the near subsurface of the martian regolith could result in viscous creep responsible for softening of craters at middle and high latitudes the temperature of ground ice will vary spatially within a crater owing to the effect of slope on the effective angle of insolation the temperature at a particular latitude will also vary temporally owing to changes in mars obliquity results from numerical simulations of viscous creep indicate that these temperature variations cause the pole facing slopes of craters to be systematically steeper than those of equator facing slopes crater slopes should be most asymmetric between 25 and 40 latitude depending on the thickness of the creeping layer this slope asymmetry predicted from theoretical simulations of regolith creep is not well developed in observed martian crater topography mars orbiter laser altimeter mola topography of craters 16 to 40 km in diameter was analyzed for north south slope asymmetry within seven latitude regions ranging from 60 s to 60 n on the basis of the lack of any systematic slope asymmetry observed in the craters we can place a conservative upper limit of 150 m on the thickness of the ice rich creeping layer assuming a volumetric dust content of 70 and an exponentially decreasing regolith porosity with depth if the creeping layer contains relatively clean ice then the thickness of ice rich material is limited to 100 m or less the observations also suggest that the thickness of this creeping layer is reduced by 30 toward the equator these results imply a global ice rich regolith water volume of 107 km3 comparable to that proposed for a modest sized northern plains ocean

analysis of ground surface settlement induced by a large epb shield tunnelling a case study in beijing china large size shield tunnels have been constructed with the increasing demands because it offers cost efficiency in urban areas one major problem created by shield tunnelling is that ground settlement occurs which is crucial to existing structures a detailed case study of surface settlement induced by the operation of a large diameter earth pressure balance epb shield tunnel in beijing was presented this study provides important new insights into the values of settlement trough parameters of empirical methods the narrower transverse settlement trough was observed in large size tunnels the development of longitudinal settlement can be divided into four stages and methods were further proposed to assess the associated four components of volume loss results demonstrate that the proposed methods can efficiently predict the volume loss and the associated ground settlement within a reasonable accuracy by comparing with the collected field observations in addition a bandwidth of achievable surface settlement for future large epb shield tunnels is suggested via performing analysis on real settlements

predicting 2d ground movements around tunnels in undrained clay a new analytical method is introduced for calculating displacements due to tunnelling this is conceived within the framework of the bound theorems of plasticity but allowing for soil strain hardening the ground displacements due to tunnelling are idealised by a simple displacement mechanism of distributed shearing in the plane of the tunnel cross section the tunnel support pressure corresponding to a certain volume loss is calculated from energy balances of the work dissipated in distributed shear the potential energy loss of soil flowing into the tunnel and the work done by this soil against the tunnel support pressure the calculations are carried out in steps of small volume loss accompanying small reduction in support pressure after each of which the tunnel geometry is updated in this way each reduced tunnel support pressure is related to a complete ground displacement field a simplified closed form solution is also provided for the prediction of maximum surface ground settlement for the par

surface runoff features on mars testing the carbon dioxide formation hypothesis 1 fresh gully like features on mars strongly suggest that fluid flowed on the surface in the recent past here we consider the possibility that co2 vapor supported flows formed the gullies we find that neither condensed co2 nor co2 clathrate hydrate are likely to accumulate in significant quantities in the martian crust in addition if condensed co2 were present under lithostatic pressures exposure to the atmosphere would produce features analogous to terrestrial pyroclastic flows not surface runoff finally the source volume of co2 required to support a flow excludes clustered or episodic gully formation therefore we conclude that co2 cannot have formed the gullies in light of these results liquid water flow remains the preferred formation mechanism for the recent surface runoff features

cosmic ray produced 10be and 26al in antarctic rocks exposure and erosion history we have measured cosmic ray produced t1 2 1 5 million years 10be and t1 2 0 705 million years 26al in purified quartz fractions of selected rock samples from antarctic mountains from these data we calculate 1 mean erosion rates for the limiting case of steady state surface exposure to cosmic rays and 2 minimum exposure ages for the limiting case of no erosion calculated mean erosion rates are very low on the order of a few times 10 5 cm yr we believe the sampling to be sufficient to generalize this result to exposed bedrock in antarctica in favorable cases it is possible to distinguish between the limiting cases steady state erosion seems a better description in such cases most samples including some taken a few meters above the present ice level seem to have been exposed for millions of years without major episodes of burial or abrasion by ice

heinrich events massive late pleistocene detritus layers of the north atlantic and their global climate imprint 1 millennial climate oscillations of the glacial interval are interrupted by extreme events the so called heinrich events of the north atlantic their near global footprint is a testament to coherent interactions among earth s atmosphere oceans and cryosphere on millennial timescales heinrich detritus appears to have been derived from the region around hudson strait it was deposited over approximately 500 250 years several mechanisms have been proposed for the origin of the layers binge purge cycle of the laurentide ice sheet jokulhlaup activity from a hudson bay lake and an ice shelf buildup collapse fed by hudson strait to determine the origin of the heinrich events i recommend 1 further studies of the timing and duration of the events 2 further sedimentology study near the hudson strait and 3 greater spatial and temporal resolution studies of the layers as well as their precursory intervals studies of previous glacial intervals may also provide important constraints

surface characteristics and degradational history of debris aprons in the tempe terra mareotis fossae region of mars abstract we have documented the surface characteristics and degradational history of a population of 65 lobate debris aprons in the tempe terra mareotis fossae region of mars these aprons were compared to other martian debris aprons to evaluate similarities and differences among different populations which can provide insight into the dominant controls on apron development tempe mareotis debris aprons found at the bases of isolated or clustered massifs escarpments and crater interior walls were studied using viking orbiter mars global surveyor and mars odyssey datasets in a gis database six textures related to degradation of apron surfaces are identified in moc images and they are divided into two groups an upper surface group and a lower surface group degradation occurs within an inferred smooth upper surface mantle of ice and debris producing a sequence of pitted ridge and valley and knobby textures of the upper surface group where upper surface materials have been removed smooth and ridged textures of the lower surface group are exposed degradation to various depths may expose lower surface materials which may consist of the main apron mass remnants of mantling deposits or both a combination of geologic processes may have caused the degradation including ice sublimation ice melt and eolian activity apron surfaces have lower maximum thermal inertias and mean surface temperatures than adjacent plains surfaces which may be explained by the trapping of unconsolidated materials in low lying pits and valleys formed by surface degradation or from the disruption of crusts on degraded portions of apron surfaces one feature observed only on tempe mareotis debris aprons are broad ridges which mimic the shape of massif bases for tens of kilometers we propose these to be constructional features that could have formed during cycles of increased debris production apron morphometric parameters including area volume slope thickness relief and h l were compiled and the results show that tempe mareotis aprons have average surface areas volumes and frontal thicknesses that are 2 3 times smaller than eastern hellas aprons within the tempe mareotis population escarpment related aprons are larger than massif related aprons suggesting that aprons with larger source areas have potentially greater volatile accumulation translating into longer apron travel distances and lower h l values

the role of arcuate ridges and gullies in the degradation of craters in the newton basin region of mars abstract a survey of craters in the vicinity of newton basin using high resolution images from mars global surveyor and mars odyssey was conducted to find and analyze examples of gullies and arcuate ridges and assess their implications for impact crater degradation processes in the phaethontis quadrangle mc 24 we identified 225 craters that contain these features of these 188 had gullies on some portion of their walls 118 had arcuate ridges at the bases of the crater walls and 104 contained both features typically on the same crater wall a major result is that the pole facing or equator facing orientation of these features is latitude dependent at latitudes 44 s equator facing orientations for both ridges and gullies are prevalent but at latitudes

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

a distinct class of avalanche scars on mars we report observations of a set of surface features on mars that form a distinct class of avalanche scars these features have a horizontal scale of hundreds of meters but a depth scale of meters distinguishes them from the shallower features known as slope streaks the meters thick avalanche scars have escaped previous attention because of weak contrast between the interiors of the scarred regions and their surroundings often the most visible feature is a shadow cast by the trough wall a band 1 3 pixels wide in mars orbiter camera narrow angle images indicating maximum depths of 4 10 m we investigate the morphology of more than 500 such features slopes upon which the avalanches occur average about 27 impact craters are seen at the heads of some avalanche scars this subset exhibits statistically wider opening angles the scars span an estimated several ma in age those found so far occurred mainly in the olympus mons lower aureole we compare shapes of slope streaks to shapes of meters thick avalanches and the results support the notion that the two classes are distinct the newly discovered avalanches resemble some terrestrial flows of loose dry material such as dry snow and glass beads on the basis of these analogs we suggest a physical model

classification and environmental models of cool freshwater tufas abstract tufa deposits are common in the quaternary record facies developments are dependent upon localised carbonate precipitation generally these take the form of phytoherm build ups together with associated detrital deposits derived from disagragation of the former phytoherm cements differ from speleothems and floe calcite accumulations in being biologically mediated or modified this paper recognises the following five types perched spring line cascade fluviatile paludal and lacustrine facies each type is composed of distinctive constructional and detrital sediment associations these unique sediment combinations are the product of an interplay between angle of slope water discharge rate standing water bodies phytal and microbial colonization and ambient temperature the proposed models will be of value in the interpretation of ancient and partially exposed tufas

the indication of martian gully formation processes by slope area analysis the formation process of recent gullies on mars is currently under debate this study aims to discriminate between the proposed formation processes pure water flow debris flow and dry mass wasting through the application of geomorphological indices commonly used in terrestrial geomorphology high resolution digital elevation models dems of earth and mars were used to evaluate the drainage characteristics of small slope sections data from earth were used to validate the hillslope debris flow and alluvial process domains previously found for large fluvial catchments on earth and these domains were applied to gullied and ungullied slopes on mars in accordance with other studies our results indicate that debris flow is one of the main processes forming the martian gullies that were being examined the source of the water is predominantly distributed surface melting not an underground aquifer evidence is also presented indicating that other processes may have shaped martian crater slopes such as ice assisted creep and solifluction in agreement with the proposed recent martian glacial and periglacial climate our results suggest that within impact craters different processes are acting on differently oriented slopes but further work is needed to investigate the potential link between these observations and changes in martian climate

modelisation numerique des mouvements de terrain meuble induits par un tunnelier the construction of shallow tunnels causes movements that can affect existing structures inducing unacceptable disorders these disorders can not only result from settlements but also from horizontal displacements in the case of tunneling with pressurized face shield boring machines ground movements are found to be the result of complex interactions between soil construction stages and shield drive parameters in this context the direct prediction of final ground movements by empirical or analytical and numerical approaches has proven to be insufficient it is therefore necessary to develop and to validate more accurate simulation tools to allow assessment of the magnitude and distribution of soil movements in relation to construction stages by experimental results of two sections of the lyons d line subway extension 1993 1995 the authors examine various numerical procedures in this paper a two dimensional procedure taking into consideration various stages of construction is proposed the

analysis of tunneling induced ground movements using transparent soil models ground movements induced by shallow tunnels affect the safety of nearby underground and aboveground structures therefore the reliable prediction of these movements is important a transparent soil model is used to investigate not only the surface settlement profile induced by shield tunneling but also the distribution of soil deformation within the soil mass near the tunnel the observed surface settlements are consistent with the normal probability curve commonly used for predicting settlement with only the inflection points or trough width parameters somewhat different the measured data are consistent with field measurements in that the trough width parameter is independent of the volume loss and linearly proportional to the tunnel depth an analysis of the displacement field inside the transparent soil models indicates that the subsurface settlement trough at different depths can be approximated by a normal probability curve and the horizontal displacement can be expressed by the trough width parameter and the volume loss at the point at which maximum horizontal displacement occurs at the point of inflection additionally the measurements indicate that subsurface ground movements can be in excess of the observed surface settlement which can adversely affect underground utilities

late pleistocene desiccation of lake victoria and rapid evolution of cichlid fishes lake victoria is the largest lake in africa and harbors more than 300 endemic species of haplochromine cichlid fish seismic reflection profiles and piston cores show that the lake not only was at a low stand but dried up completely during the late pleistocene before 12 400 carbon 14 years before the present these results imply that the rate of speciation of cichlid fish in this tropical lake has been extremely rapid

phytoliths as paleoenvironmental indicators west side middle awash valley ethiopia phytolith assemblage analysis offers the potential to refine our knowledge of paleoecosystems where grasses and sedges predominate in this work holocene and pleistocene sediments from an arid tropical region in ethiopia have been analyzed for their phytolith content presented as detailed counts and diagrams according to the twiss classification the aim is to test the usefulness of phytolith assemblages to indicate paleoenvironments at middle awash where fossil pollen grains are poorly preserved in sediments that yielded abundant archaeological remains the vegetation in the middle awash subdesertic valley is currently a shrub steppe dominated by c4 grasses adapted to arid conditions with a narrow riparian forest limited to the awash river our results show that modern surface samples holocene and pleistocene sediments contain well preserved and different phytolith assemblages and therefore that no translocation processes from modern soil to geological strata seem to occur fossil records and modern assemblages are interpreted using phytolith ratios to estimate the density of the tree cover the aridity and the proportion of c3 versus c4 grasses as applied to phytolith assemblages from north america and west africa the phytolith assemblages from modern soil samples correctly reflect the proportion of trees and shrubs versus grasses different in the riparian vegetation and the shrub steppe modern phytolith assemblages appear to be a mixed signature of local and regional vegetation phytolith analysis of the holocene sample suggests a grassland where the grass community is constituted by the chloridoideae subfamily adapted to warm and dry conditions and where c3 pooideae cover the highlands phytolith analysis of the pleistocene sample evidences grassland formation with scattered woody elements where c4 panicoideae grasses adapted to warm and humid conditions dominate the grass cover however these conclusions need to be confirmed by more complete study on phytolith assemblages from modern vegetation from ethiopia

geomorphic evidence for the distribution of ground ice on mars high resolution viking orbiter images show evidence for quasi viscous relaxation of topography the relaxation is believed to be due to creep deformation of ice in near surface materials the global distribution of the inferred ground ice shows a pronounced latitudinal dependence the equatorial regions of mars appear to be ice poor while the heavily cratered terrain poleward of 30 latitude appears to be ice rich the style of creep poleward of 30 varies with latitude possibly due to variations in ice rheology with temperature the distribution suggests that ice at low latitudes which is not in equilibrium with the present atmosphere has been lost via sublimation and diffusion through the regolith thereby causing a net poleward transport of ice over martian history

a high resolution 11 400 yr diatom record from lake victoria east africa abstract fine interval 30 45 yr sampling of a core from lake victoria s damba channel shows that numerous abrupt changes in the lake s diatom assemblages have occurred in response to climatic fluctuations over the past 11 400 14 c yr four distinct climatic phases bounded by sudden transitions are inferred 1 variably dry 11 400 10 000 yr b p 2 humid 10 000 7200 yr b p 3 more seasonal 7200 2200 yr b p and 4 more arid 2200 0 yr b p with a dry little ice age event 600 200 yr b p the diatom inferred paleoclimatic history for northern lake victoria closely resembles that inferred from a well dated pollen record from pilkington bay spectral analysis of the diatom record reveals strong periodicities including globally distributed 2360 2550 1400 1030 1130 and 500 cal yr cycles repeated rapid shifts between aulacoseira and nitzschia dominated diatom assemblages suggest that post 1960 changes in the lake s phytoplankton communities have had earlier climate driven analogs

cooling cycles heinrich event 1 and the desiccation of lake victoria abstract east africa s enormous lake victoria dried out at the close of the last glacial but the precise timing and origin of that drying event have not been clarified largely because of uncertainty regarding core stratigraphy and ancient carbon effects on 14 c dates from the lake new dates and re examination of evidence from widely distributed cores shows that desiccation occurred some time between 15 900 and 14 200 calendar years bp and perhaps also ca 18 17 kyr bp these lake level minima were briefer than has been previously suggested and were synchronous with pronounced global climate disruptions including north atlantic ice rafting heinrich event 1 less severe declines occurred during the older and younger dryas intervals dansgaard oeschger type cooling cycles registered in the gisp2 ice core record tracked major lake level regressions in east africa and weakenings of afro asian monsoons during the late quaternary possibly linking the desiccation of lake victoria to century scale reductions in solar radiation output

reconstruction of a semi arid late pleistocene paleocatena from the lake victoria region kenya abstract the effect of changing environment on the evolution of homo sapiens is heavily debated but few data are available from equatorial africa prior to the last glacial maximum the karungu deposits on the northeast coast of lake victoria are ideal for paleoenvironmental reconstructions and are best studied at the kisaaka site near karunga in kenya 94 to 33 ka where paleosols fluvial deposits tufa and volcaniclastic deposits tuffs are exposed over a 2 km transect three well exposed and laterally continuous paleosols with intercalated tuffs allow for reconstruction of a succession of paleocatenas the oldest paleosol is a smectitic paleo vertisol with saline and sodic properties higher in the section the paleosols are tuffaceous paleo inceptisols with alfisol like soil characteristics illuviated clay mean annual precipitation map proxies indicate little change through time with an average of 764 108 mm yr 1 for vertisols calmag and 813 182 to 963 182 mm yr 1 for all paleosols cia k field observations and map proxies suggest that karungu was significantly drier than today consistent with the associated faunal assemblage and likely resulted in a significantly smaller lake victoria during the late pleistocene rainfall reduction and associated grassland expansion may have facilitated human and faunal dispersals across equatorial east africa

interpretation of free field ground movements caused by mechanized tunnel construction abstractthis paper summarizes greenfield ground movements caused by the construction of twin 7 1 m diameter tunnels for london s crossrail project using earth pressure balance epb tunnel boring machines tbm the data include surface deformations from a series of transects in hyde park together with subsurface data from one well instrumented test section although far field ground movements can be well fitted using established empirical methods or simplified analytical solutions elastic half space nonlinear inelastic soil behavior is expected to affect measurements close to the tunnel this paper considers the effects of constitutive behavior on the observed ground movements simple mohr coulomb m c and more complex mit s1 soil models are calibrated using results of high quality laboratory element tests on intact london clay the models are then used in two dimensional 2d numerical simulations in order to optimize three independent cavity deformation parameters that control the spatial dist

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

landscape evolution in martian mid latitude regions insights from analogous periglacial landforms in svalbard periglacial landforms on spitsbergen svalbard norway are morphologically similar to landforms on mars that are probably related to the past and or present existence of ice at or near the surface many of these landforms such as gullies debris flow fans polygonal terrain fractured mounds and rock glacier like features are observed in close spatial proximity in mid latitude craters on mars on svalbard analogous landforms occur in strikingly similar proximity which makes them useful study cases to infer the spatial and chronological evolution of martian coldclimate surface processes the analysis of the morphological inventory of analogous landforms on svalbard and mars allows the processes operating on mars to be constrained different qualitative scenarios of landscape evolution on mars help to better understand the action of periglacial processes on mars in the recent past

momentum transfer and friction in the debris of rock avalanches when a mass of loose dry purely frictional material slides down an incline after release at a given velocity the runout the distance the centre of gravity of the displaced mass moves from its initial position depends on momentum transfer within the mass this can be estimated from the profile of the debris accumulation which also allows more accurate calculation of apparent angles of sliding friction in rockfall avalanches the apparent extreme mobility of the elm and frank slides typical rockfall avalanches is explained by momentum transfer in a loose dry purely frictional material with an angle of friction of 30 key words mass wasting momentum transfer landslide accumulation rock avalanche runout distance

the search for a topographic signature of life landscapes are shaped by the uplift deformation and breakdown of bedrock and the erosion transport and deposition of sediment life is important in all of these processes over short timescales the impact of life is quite apparent rock weathering soil formation and erosion slope stability and river dynamics are directly influenced by biotic processes that mediate chemical reactions dilate soil disrupt the ground surface and add strength with a weave of roots over geologic time biotic effects are less obvious but equally important biota affect climate and climatic conditions dictate the mechanisms and rates of erosion that control topographic evolution apart from the obvious influence of humans does the resulting landscape bear an unmistakable stamp of life the influence of life on topography is a topic that has remained largely unexplored erosion laws that explicitly include biotic effects are needed to explore how intrinsically small scale biotic processes can influence the form of entire landscapes and to determine whether these processes create a distinctive topography

tectonic consequences of martian dichotomy modification by lower crustal flow and erosion the martian hemispheric dichotomy shows compressional features a few hundred kilometers south of the dichotomy boundary and contemporaneous extensional features along the boundary two processes that may have contributed to the observed deformation are lateral lower crustal flow and erosion crustal flow causes a decrease in crustal thickness in the south and an increase in the north the result is compressional surface stresses in the highlands and extensional stresses around the dichotomy boundary the magnitude location and timing of the predicted stresses are consistent with the observed tectonic features and strongly suggest that moderate lateral flow occurred for the nominal heat flux and rheology sufficient lateral flow is generated for a mean crustal thickness of 70 km erosion generates extension in the south and compression in the north opposite to what is observed either erosion only resulted in local as opposed to regional distribution of highland material or the rigidity of the lithosphere was sufficiently high at the time of erosion that significant stresses did not develop

controls on the spacing of first order valleys 1 many landscapes are composed of ridges and valleys that are uniformly spaced even where valley locations are not controlled by bedrock structure models of long term landscape evolution have reproduced this phenomenon yet the process by which uniformly spaced valleys develop is not well understood and there is no quantitative framework for predicting valley spacing here we use a numerical landscape evolution model to investigate the development of uniform valley spacing we find that evenly spaced valleys arise from a competition between adjacent drainage basins for drainage area a proxy for water flux and that the spacing becomes more uniform as the landscape approaches a topographic equilibrium valley spacing is most sensitive to the relative rates of advective erosion processes such as stream incision and diffusion like mass transport such as soil creep and less sensitive to the magnitude of a threshold that limits the spatial extent of stream incision analysis of a large number of numerical solutions reveals that valley spacing scales with a ratio of characteristic diffusion and advection timescales that is analogous to a peclet number we use this result to derive expressions for equilibrium valley spacing and drainage basin relief as a function of the rates of advective and diffusive processes and the spatial extent of the landscape the observed scaling relationships also provide insight into the cause of transitions from rill like drainage networks to branching networks the spatial scale of first order drainage basins the contributing area at which hillslopes transition into valleys and the narrow range of width to length ratios of first order basins

ice driven creep on martian debris slopes 1 accumulations of rocky debris at the base of bedrock escarpments on mars have mean inclinations of 20 well below the angle of repose 35 these inclinations decrease with increasing latitude suggesting a climatic influence we present evidence that these low inclinations are the result of gravitational creep driven by repeated deposition and sublimation of ground ice we estimate the rates of bedrock erosion and ice driven creep on mars and use a simple model to show that the probable time scale for debris slope development is between 20 myr and 2 gyr our results suggest that water ice has shaped martian landscapes throughout the late amazonian period

liquid co2 breakout and the formation of recent small gullies on mars we show that the action of a co2 suspended flow could have produced the recent small gullies on mars and hence that liquid water is not required the model involves the build up of a liquid co2 aquifer behind and below a dry ice barrier dam cap rock in the pore spaces a few meters into the rock from the cliff face and on order of a hundred meters below the top of the cliff brink surface seasonal or obliquity cycle seasonal heating causes pinching out of the dry ice barrier and rapid release of the liquid co2 erosion of the gullies occurs as the rapid vaporization of the liquid co2 with entrainment of rock and clathrate hydrate ice produces a density flow analogous to a terrestrial nue ardente

new chronology for the early miocene mammalian faunas of kisingiri western kenya new total fusion k ar ages indicate that all of the fossiliferous formations that make up the lower part of the early miocene kisingiri sequence in western kenya at rusinga island mfwangano island and karungu were deposited during an interval of less than 0 5 million years at c 17 8 ma ago this contrasts markedly with k ar ages previously published from these detrital tuffaceous formations which suggested that they were deposited over an interval of as much as 7 million years between 23 and 16 ma overlapping the age ranges of all other east african early miocene sites including koru songhor napak bukwa loperot muruarot and buluk in addition the analytical problems revealed by the new kisingiri results cast doubt on biotite ages which provide dating for the most important sites thus the strong differences between the kisingiri fauna and those of koru sonhor and napak long held to be due to ecology because of the apparent overlap in ages may actually be due to a difference in time if this view of the geochronology is correct it may now be possible to identify adaptive trends and evolutionary succession in the east african early miocene faunas

investigating ground movements caused by the construction of multiple tunnels in soft ground using laboratory model tests the prediction of the ground movements above single tunnels in soft ground is well established and can be estimated using semi empirical methods based on the gaussian curve however the prediction

on the kinematics of 2d tunnel collapse in undrained clay a kinematic plastic solution has been developed for ground movements around a shallow unlined tunnel embedded within an undrained clay layer in this solution the pattern of deformation around the tunnel is idealised by a simple plastic deformation mechanism within the boundaries of the deformation mechanism the soil is required to shear compatibly and continuously with no relative sliding at the boundaries the soil is regarded here as a rigid plastic tresca material the plausibility of the proposed mechanism is demonstrated by comparison with limit analysis calculations and centrifuge test results

large scale geomechanical model testing of an underground cavern group in a true three dimensional 3 d stress state the stability of a large cavern group at great depth is discussed on the basis of large scale three dimensional 3 d geomechanical model tests and numerical simulations the model tests are described in detail improvements in the tests were made in terms of experimental techniques and advanced measurement methods the model tests utilized active loading on six sides of a rock mass in a true 3 d stress state during the model construction precast blocks were fabri cated and monitoring holes were defined prior to test initiation newly developed combination ball sliding walls were in stalled on each of the major loading surfaces to reduce the friction induced by model deformation a unique grouting and installation technique employing prestressed cables was adopted in the tests a digital photogrammetric technique dis placement sensing bars using fiber bragg grating fbg technology and mini multipoint extensometers were developed for measuring deformation overloading tests were then conducted for different overburden depths and 3 d numerical analyses were performed to simulate the testing procedures conclusions regarding the stability of the cavern group were developed based on a comparison between the experimental and numerical results resume la stabilited un groupe de grandes cavernes profondes est discutee en utilisant des essais en modele geomeca nique 3 d agrande echelle et des simulations numeriques les essais sont decrits en details dans l article des ameliora tions ont eteapportees aux essais par rapport aux techniques experimentales et aux methodes de mesures les essais comportent des chargements actifs sur 6 faces d une masse de roche de facon a representer un etat des contraintes en 3 d durant la construction du modele des blocs pre moules ont etefabriques et des ports de suivi ont etedefinis avant le de but des essais sur chacune des surfaces majeures de chargement des murs en combinaison bille glissement recemment de veloppes ont eteinstalles afin de reduire la friction induite par les deformations du modele une technique de scellement et d installation unique utilisant des cables precontraints a eteutilisee durant les essais une technique photogrammetrique digitale des sondes de deplacements munies de la technologie d un reseau de fibre bragg et de minis extensiometres multi points ont etedeveloppes afin de mesurer les deformations des essais en surcharge ont eteeffectues pour des pro fondeurs de mort terrain differentes ensuite des analyses numeriques en 3 d ont eteeffectuees dans le but de simuler les procedures de l essai des conclusions en lien avec la stabilitedu groupe de cavernes ont etedeveloppees selon des com paraisons entre les resultats experimentaux et numeriques mots cles essai en modele geomecanique simulation numerique groupe de grandes cavernes souterraines etat des contraintes 3 d reel analyse de stabilite traduit par la redaction

three dimensional nonlinear analyses of a metro tunnel in sao paulo porous clay brazil tropical residual clays with a highly porous structure react to the stress changes induced by tunneling in such a way that surface settlements can be larger than crown level settlements along a tunnel axis this behavior which is not readily simulated by most numerical analyses was also observed in the paraiso tunnel built for the sao paulo metro brazil this is a shallow tunnel driven through porous clayey soils by the sequential method detailed results of field monitoring are presented and discussed 3d finite element analyses that allowed a detailed simulation of the construction sequence have been carried out considering two distinct constitutive models for the soil a simple elastic perfectly plastic mohr coulomb model and the elastoplastic model developed by lade the results of these analyses are compared with the observed behavior as well as with the results from a plane strain finite element analysis it is shown that only the 3d finite element analysis coupled with the more sophisticated soil constitutive model provides a full reproduction of field performance with particular relevance for the deformations in the soil mass over the tunnel

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

antiphasing between rainfall in africa s rift valley and north america s great basin the beginning of the bolling allerod warm period was marked in greenland ice by an abrupt rise in 18o an abrupt drop in dust rain and an abrupt increase in atmospheric methane content the surface waters in the norwegian sea underwent a simultaneous abrupt warming at about this time a major change in the pattern of global rainfall occurred lake victoria latitude 0 which prior to this time was dry was rejuvenated the red sea which prior to this time was hypersaline freshened lake lahontan which prior to this time had achieved its largest size desiccated whereas the chronologic support for the abruptness of the hydrologic changes is firm only for the red sea in keeping with evidence obtained well away from the northern atlantic in the santa barbara basin and the cariaco trench the onset and end of the millennial duration climate events were globally abrupt if so the proposed linkage between the size of african closed basin lakes and insolation cycles must be reexamined

tunnels in sands the effect of size depth and volume loss on greenfield displacements this paper examines the effect that tunnel size depth and volume loss have on greenfield soil displacements above tunnels in sandy ground the results of a series of plane strain centrifuge tests

implications of late quaternary mammalian fauna from lukenya hill south central kenya for paleoenvironmental change and faunal extinctions abstract late quaternary paleoenvironmental data for east africa are derived primarily from montane sources and thus we know little about the changing composition of east african savannas four archaeological sites at lukenya hill in the savanna of the athi kapiti plains of kenya that date to the last 40 000 yr preserve a large mammalian fauna the prehistoric hunters concentrated on migratory ungulates and virtually ignored the resident inselberg ungulates throughout the occupation faunas of the last glacial maximum are dominated by an extinct small alcelaphine antelope arid adapted ungulates are present that are regionally absent historically and pelorovis is present as well the small alcelaphine and arid adapted ungulates are absent in the holocene deposits this suggests that there was an expansion of dry savannas during the last glacial maximum the last glacial maximum aridity combined with a lack of pastoral set fires would have resulted in a vegetative mosaic distinct from the present dry woody growth and dry and or tall grass all of which are poor forage for ungulates would have been common where seasonally moist short grasslands are presently extant these conditions favored the large bodied highly hypsodont species in africa that became extinct with the onset of wet conditions during the early holocene

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

the pleistocene prehistory of the lake victoria basin abstract late pleistocene sedimentary biogeochemical and fossil data from the lake victoria basin the largest lake in africa suggest that its reduction or desiccation during periods of increased aridity repeatedly facilitated the dispersal of c 4 grassland ecosystems across the basin archaeological evidence from middle stone age and later stone age sites suggest that human groups diffused into the basin during intervals of declining lake levels likely tracking the movement of the dense and predictable resources of shoreline environments as well as the dense but less predictable c 4 grass grazing herbivores repeated cycles of lake expansion and contraction provide a push pull mechanism for the isolation and combination of populations in equatorial africa that may contribute to the late pleistocene human biological variability suggested by the fossil and genetic records latitudinal differences in the timing of environmental change between the lake victoria basin and surrounding regions may have promoted movements across within and possibly out of africa

evaluating closely spaced twin tunnelling induced shear stiffness change by subsurface settlement in clayey ground cases of closely spaced twin tunnels demonstrate that ground settlement above the 2nd tunnel referred to as t2 constructed after the first tunnel t1 exhibits pronounced differences from that above t1 the differences can be attributed to the disturbance induced by t1 construction based upon closed form plasticity solutions for an unloading cylindrical cavity this study employs subsurface settlement troughs to determine the shear modulus change during twin tunnelling observations of 1 g model tests for twin tunnelling in overconsolidated kaolin clay are interpreted from literature after t1 construction for positions with different radial distances but a constant angle with respect to the vertical line above the tunnel center the graph of radial displacement tunnel radius versus tunnel radius radial distance exhibits good linearity further analyses demonstrate that the shear stiffness decreases as the angle increases in comparison during t2 construction the shear modulus of soils close to t1 degrades while the other side increases in light of the observations of combined axial torsional tests the tendency of shear modulus change can be attributed to the rotation of principal stress axes the findings can explain the differential settlements over closely spaced twin tunnels in clayey ground

distributions of ground movements parallel to deep excavations in clay an empirical procedure for fitting a complementary error function erfc to settlement and lateral ground movement data in a direction parallel to an excavation support wall is proposed based on extensive optical survey data obtained around a 12 8 m deep excavation in chicago the maximum ground movement and the height and length of an excavation wall define the erfc fitting function the erfc fit is shown to apply to three other excavation projects where substantial ground movement data were reported key words excavations clays ground movements performance data

middle stone age archaeology at olduvai gorge tanzania abstract this paper describes the motivation procedures and results of archaeological and geological field survey of the ndutu unit olduvai gorge conducted in june and july of 2013 survey focused upon the area of olduvai gorge between the second fault and the obalbal depression although selective survey occurred in other areas in and around the gorge over 72 archaeological find spots were recorded and hundreds of middle stone age msa artifacts were recovered as was a small sample of fauna geological observations provisionally suggest that the ndutu was formed in part from a series of pyroclastic density flow and ash fallout events from neighbouring volcanoes this contrasts slightly with previous interpretations of the deposits in that at least some of the beds are thought to be in primary stratigraphic context our initial field findings are conducive to discussions of a number of issues directly relevant to the msa in east africa and overall we conclude that there is strong potential for olduvai s ndutu unit to shed light on the behavior adaptations and evolution of homo sapiens prior to during and just after its physical emergence