fully softened shear strength at low stresses for levee and embankment design abstractshallow slides in levee and other embankment slopes are usually controlled by effective normal stresses less than 12 kpa 250 psf for first time slides in fine grained soils the fully softened shear strength is frequently used to model the strength of embankment soils because it represents the shear strength remaining after the effects of overconsolidation compaction desiccation or other strengthening processes have been removed because of wetting infiltration stress relief swelling and weathering however there is limited fully softened strength data at effective normal stresses less than 50 kpa 1 000 psf so existing correlations in this stress range must be extrapolated this paper presents new fully softened shear strength data at an effective normal stress of 12 kpa 250 psf and recommendations for estimating and modeling the stress dependent fully softened shear strength envelope directly or as a power function in stability analyses

impact crater degradation on venusian plains in venusian plains impact craters without extensive low backscatter ejecta deposits are more likely to have low backscatter floors be embayed by volcanic deposits and exhibit fractures as compared to craters with extensive low backscatter ejecta we interpret these trends as evidence of ongoing degradation of low backscatter ejecta by aeolian activity weathering and volcanism using a crater age sequence based on extent of preservation of low backscatter ejecta together with monte carlo simulations we find that tectonic activity has extended over a longer time period than volcanism

a simplified ice ocean coupled model for the antarctic ice melt season abstract in the antarctic ocean sea ice melts mostly by warming of the ocean mixed layer through heat input mainly solar radiation in open water areas a simplified ice upper ocean coupled model is proposed in which sea ice melts only by the ocean heat supplied from the air the model shows that the relationship between ice concentration i e fraction c and mixed layer temperature t converges asymptotically with time c t relationship which agrees with observed c t plots during summer in the sector 25 45 e this relationship can be used for estimating the bulk heat transfer coefficient between ice and ocean by fitting to observations and a value of 1 2 10 4 m s 1 is obtained the model shows that the ratio of the heat used for melting to the heat input through open water is inclined to be determined as a function of ice concentration for typical conditions in the antarctic ice melt season the ratio ranges mostly between 0 7 and 0 9 when the model is extended to two dimensions in the meri

novae on venus geology classification and evolution 1 novae are radially fractured centers 100 300 km in diameter and 64 have been identified on venus dense radial fracturing and upraised topography are common and massive amounts of volcanism are seen in some novae are interpreted to be the result of updoming and fracturing of the surface due to interaction of mantle diapirs with the lithosphere and radial fracturing caused by dike emplacement we analyzed the topography and character of deformational and morphological structures of all 64 novae leading to a better understanding of their evolution and relation to diapir dynamics and their age we subdivided novae into four topographic classes 1 upraised 2 annular 3 flat and negative and 4 plateau like novae are located mostly in areas of regional rises and rift zones with a small number in the lowlands about one half the novae studied show association with rifts in some of these the rift troughs surround nova rises and form plateau like novae plateau like novae may predate postdate or form simultaneously with rifts our analysis generally confirms and updates previous models of novae evolution with the following geological factors being important 1 depth of the neutral buoyancy level of the rising mantle diapir 2 rheological characteristics of the overlying lithosphere 3 whether or not the visco plastic material above the diapir undergoes spreading and 4 the nature and influence of regional stress and rift structures these combined factors exert control on the direction of nova evolution and appear to determine the primary characteristics of nova such as topography tectonics and volcanism we found clear evidence for 1 the important role of dike swarm emplacement in the formation of radial patterns of novae and 2 the formation of concentric tectonic features during the relaxation stage of novae novae have multiple evolutionary stages and are long lived structures stratigraphic analysis of all 64 local areas showed a similarity in the sequence of regional geologic units we found that 40 3 of the novae population started to form before emplacement of regional plains with wrinkle ridges and that 11 3 completed their activity before this time 88 7 of the population of novae was active after regional plains formation in contrast to novae coronae activity was greatest before formation of regional plains which may be due to thickening of the lithosphere with time detailed structural analysis shows that novae evolution does not always lead to the formation of corona like features

a numerical investigation of the 1997 1998 ronne polynya the summer season of 1997 1998 marked an unprecedented extent of open water in the southern weddell sea not observed since satellite observations began in the early 1970s wind patterns during the summer period tended to be more southerly than in years with typical summer ice coverage leading to the hypothesis that the polynya opened due to ice advection away from the ronne ice shelf and subsequent enhanced melting through the open water albedo feedback mechanism a numerical model is run using a bulk forcing data set from the 1980s for model spin up and the control run initiation of the polynya by the anomalous wind pattern is investigated numerically by substituting winds from the 1997 1998 period for the control winds while a narrow polynya is present in the control run it opens considerably with the 1997 1998 winds to the extent observed in the satellite images if solar radiation flux is not allowed to heat the mixed layer the sea ice in front of the ronne ice shelf shows some opening but the polynya does not form to the extent observed demonstrating the important role played by open water albedo feedback the mixed layer heat budget analysis shows the predominant balance in these three runs was derived from surface forcing and that the upwelling of heat from the deep ocean was not a significant driving force for the 1997 1998 ronne polynya further analysis of the fresh water budget indicates that the mixed layer salinity increased in areas of open water during the 1997 1998 season by as much as 0 5 psu

volcaniclastic debris avalanche on motomachi area of izu oshima japan triggered by severe storm phenomenon and mechanisms abstract heavy rainfall and strong wind associated with typhoon wipha hit izu oshima island japan and triggered catastrophic landslides on the western slope of oshima volcano on 16 october 2013 these landslides were shallow but large in scale and the displaced landslide materials were characterized by rapid and long runout movement a massive landslide resulted in 36 people dead and 3 missing with 46 buildings being completely destroyed in the downstream area of motomachi district to understand the initiation and movement of these shallow landslides we surveyed the landslide area and found that in addition to heavy rainfall strong wind may also have played a key role in increasing the instability of the slopes we took samples from the source areas and examined their static and dynamic shear behaviors under naturally drained or undrained conditions test results showed that high pore water pressure can be built up and maintained within the displaced landslide material and increase landslide mobility even though the thickness of displaced landslide materials is 0 7 1 2 m this may then give a rational explanation on the fluidization process of the displaced landslide materials we also examined the windthrow features of trees subjected to different wind speed through monitoring the ground motion by seismometer and portable anemometer and then performed cyclic shear tests on the materials laying above the sliding surface the test results suggest that the windthrow may have promoted the buildup of excess pore water pressure within the saturated soil layer and thus favoured the occurrence of slope failure therefore it is suggested that in the prediction of shallow landslides on forested slopes subjected to heavy storm both the effects of rainfall and strong wind should be taken into account

sea ice and iceberg dynamic interaction 1 a model of iceberg motion has been implemented in the los alamos sea ice model cice individual bergs are tracked under the influence of winds currents sea surface tilt coriolis and sea ice forcing in turn sea ice is affected by the presence of icebergs primarily as obstacles that cause the sea ice to ridge on the upstream side or create open water on the downstream side of the bergs open water formed near icebergs due to sea ice ridging and blocking of sea ice advection increases level and ridged ice downstream of the bergs through increased frazil ice formation resulting anomalies in sea ice area and thickness compared with a simulation without icebergs are transported with the sea ice flow expanding over time although local changes in the sea ice distribution may be important for smaller scale studies these anomalies are small compared with the total volume of sea ice and their effect on climate scale variables appears to be insignificant

drained residual shear strength at effective normal stresses relevant to soil slope stability analyses abstract an extensive torsional ring shear testing program has been conducted to measure the drained residual shear strength of soils at the wide range of effective normal stress 10 to 700 kpa usually mobilized in reactivated and first time landslides soils mudstones and shales of different plasticity and gradation were tested in the program the effects of the change in nonlinearity of shear strength envelope over the utilized normal stress ranges on slope stability analyses were investigated using this data new empirical residual shear strength correlations were developed as a function of soil index parameters and wide range of effective normal stresses in essence the correlations are presented as revised versions of those previously developed for a limited number of normal stresses utilizing the same soil index parameters comparisons were made with a considerable amount of back calculated shear strength data reported in the literature for reactivated landslides as well as results predicted from existing shear strength correlations to verify the increased suitability of the new correlations for use in slope stability analyses a numerical expression was also introduced to express the residual shear strength correlations for direct incorporation in slope stability software

polynya dynamics a review of observations and modeling 1 polynyas are nonlinear shaped openings within the ice cover ranging in size from 10 to 105 km2 polynyas play an important climatic role first winter polynyas tend to warm the atmosphere thus affecting atmospheric mesoscale motions second ocean surface cooling and brine rejection during sea ice growth in polynyas lead to vertical mixing and convection contributing to the transformation of intermediate and deep waters in the global ocean and the maintenance of the oceanic overturning circulation since 1990 there has been an upsurge in polynya observations and theoretical models for polynya formation and their impact on the biogeochemistry of the polar seas this article reviews polynya research carried out in the last 2 decades focusing on presenting a state of the art picture of the physical interactions between polynyas and the atmosphere sea ice ocean system observational and modeling studies the surface heat budget and water mass transformation within these features are addressed

surface modification of venus as inferred from magellan observations of plains in sedna planitia clear stratigraphic relations can be discerned among volcanic flow units young flows exhibit sar specific cross section values similar to fresh terrestrial basalt flows whereas older flows exhibit backscatter signatures similar to degraded terrestrial basalt flows total degradation of 1 m depth over 0 6 b y is inferred for the sedna area from radar signatures impact crater abundances and ejecta superposition relations with respect to volcanic flow units analyses of parabolic ejecta deposits associated with the crater stuart imply that the material is typically centimeters in thickness a relatively small fraction 10 of venusian impact craters exhibit prominent parabolic ejecta deposits these craters are interpreted to be relatively young and parabolic deposits are interpreted to be dispersed by aeolian activity over at least tens of millions of years the inferred dispersal rate 10 3 m yr is too low to produce the degradation of flows at sedna planitia and it is concluded that the dominant flow modification process is in situ weathering in addition elevation dependent weathering is inferred in western ovda regio where plains above 6054 km radius have enhanced reflection coefficients as compared to adjacent plains at lower elevations the inferred rate of generation of high reflection coefficient materials is no more than 10 2 m yr based on the inability of aeolian activity to cover high reflectivity surfaces with normal reflection coefficient materials and the ubiquitous nature of high reflectivity surfaces at high elevations surface modification rates on venus are orders of magnitude lower than on earth venusian rates are also much lower than the inferred rate of aeolian dispersal of friable materials on mars but are comparable to the estimated rate of weathering and erosion of martian bedrock low surface modification rates imply that it will be possible to determine regional scale age variations on venus based on the degree of preservation of volcanic landforms and microwave signatures

ice ocean processes over the continental shelf of the southern weddell sea antarctica a review 1 interactions between the southern ocean and the weddell sea ice shelves are important both to the antarctic ice sheet and to the production of globally significant water masses here we review the interaction between the filchner ronne ice shelf and the shelf sea in which it floats the continental shelf processes leading to the production of weddell sea deep and bottom waters from the original off shelf source waters are discussed and a new view is offered of the initial production of high salinity shelf water data from ship based measurements at the ice front from glaciological methods and from measurements made within the sub ice shelf cavity itself are used to describe the pattern of flows beneath the ice shelf we also consider the variability observed within the cavity from tidal to interannual time scales and finish with a discussion of future research priorities in the region

wrinkle ridges stress domains and kinematics of venusian plains wrinkle ridges are nearly ubiquitous landforms on the plains of venus by analogy with similar structures on other planets venusian wrinkle ridges are inferred to trend normal to the direction of maximum principal compression in the crust an inference that is verified by geometrical relationships with positive and negative relief features on venus because plains are the dominant terrain on venus wrinkle ridges provide an excellent opportunity to determine the orientations of shallow crustal principal stress trajectories over most of the planet in most places there are two or more sets of wrinkle ridges and commonly one of these persists over a very large area defining a regional stress domain intersection relationships indicate that these domains differ in age

remapping the thickness distribution in sea ice models in sea ice models with multiple thickness categories the ice thickness distribution evolves in time the evolution of the thickness distribution as ice grows and melts is analogous to one dimensional fluid transport and can be treated by similar numerical methods one such method remapping is applied here thickness categories are represented as lagrangian grid cells whose boundaries are projected forward in time the thickness distribution is approximated as a linear or quadratic polynomial in each displaced category and ice area and volume are transferred between categories so as to restore the original boundaries in simple test problems and in a single column model with forcing typical of the central arctic remapping performs significantly better than methods previously used in sea ice models it is less diffusive than a scheme that fixes the ice thickness in each category and behaves better numerically than a scheme that represents the thickness distribution as a set of delta functions also remapping converges faster i e with fewer thickness categories than the alternative schemes with five to seven categories the errors due to finite resolution of the thickness distribution are much smaller than the errors due to other sources linear remapping performs as well as the more complex quadratic version and is recommended for climate modeling its computational cost is minimal compared to other sea ice model components

orogenic tectonism on io 1 we catalog 143 ionian mountains montes and mountain like features mensae tholi plana and small peaks in order to investigate orogenic tectonism on io from this comprehensive list we select 96 mountains for which there are sufficient coverage and resolution to discern spatial relationships with surrounding geologic features three of the 96 mountains are probably volcanoes 92 appear to be tectonic massifs and 1 is ambiguous of the 92 tectonic mountains 38 abut paterae volcanic or volcano tectonic craters with irregular or scalloped margins this juxtaposition is unlikely to be a coincidence as the probability of it occurring by chance is 0 1 we propose instead that orogenic faults may act as conduits for magma ascent thus fueling patera formation near mountains as resurfacing buries a shell of material from io s surface to the base of the lithosphere its effective radius is reduced and it heats up we calculate the lithospheric volume change due to subsidence and thermal expansion as a function of lithospheric thickness conservation of volume dictates that this material must be uplifted at io s surface by estimating the total volume of the mountains we are able to place a lower limit of 12 km on io s lithospheric thickness we hypothesize that in some cases mountain formation may be facilitated by asthenospheric diapirs impinging on the base of the lithosphere the resulting lithospheric swell could focus the compressive stresses that drive orogenic tectonism this model is one of several possible mechanisms for uplifting isolated mountains such as are observed on io

evidence for rapid regional plains emplacement on venus from the population of volcanically embayed impact craters we have reexamined the population of craters on venus believed to be embayed by lava flows and discuss the reliability of criteria for determining the volcanic embayment state of a crater presenting nonvolcanic processes which may produce similar crater morphologies we conclude that 29 craters have been embayed by lava flows from the exterior and an additional 27 craters are ambiguous cases 3 6 of the total crater population all of the embayed craters are embayed by the stratigraphically youngest lava flows except for five to 11 craters embayed by stratigraphically older regional plains deposits which are typically deformed by wrinkle ridges through geologic mapping of an area covering over 8 of the surface we examined the spatial relationships between wrinkle ridged plains and stratigraphically older plains units and estimate that a large portion of the wrinkle ridged plains are thinner than 500 m which is thin enough for the rims of the largest half of preexisting craters to be preserved there are not enough craters embayed by the wrinkle ridged plains to support a model in which the plains were erupted directly onto an ancient surface given the number of large craters embayed by thin deposits of wrinkle ridged plains we develop a simple statistical model to overestimate the number of craters on the preplains surface this model suggests that the average age of the surface beneath the plains plus the average length of time over which the plains were emplaced was of the order of tens of millions of years the short exposure age for the preplains surface indicates that some event or events must have erased the ancient population of craters from the surface before the emplacement of the wrinkle ridged plains

global distribution and characteristics of coronae and related features on venus implications for origin and relation to mantle processes coronae on venus range from 60 to over 2000 km across and are characterized by a complex range of morphologies the annuli around coronae range from about 10 to 150 km across and have tectonic features ranging from extensional to compressional to a combination of both topographically coronae are domes plateaus plateaus with interior lows and rimmed depressions a subset of features classified here as coronae corresponds to depressions and is interpreted to consist of large scale calderas a number of features have been identified with many of the basic characteristics of coronae similar interior deformation associations with volcanism high topography but lacking a distinct tectonic annulus these features tend to be somewhat smaller than coronae and may represent failed coronae or coronae in an early stage of evolution the size distribution of coronae and coronalike features with maximum widths greater than about 250 km is well represented by a power law of the form n d kd where n is the number of coronae with maximum widths greater than d km and 3 05 the spatial distribution of coronae is not random the features are concentrated in a few groups and along several chains coronae are similar in many morphologic characteristics to major volcanic shield structures and volcanic rises such as western eistla regio the largest corona artemis is actually larger than several volcanic rises on venus coronae and volcanic rises appear to be surface manifestations of mantle plumes there is no evidence of any systematic variation in age along chains of coronae as occurs in hotspot chains on earth instead a number of multiple and overlapping coronae may indicate limited movement of the surface above a hotspot or mantle plume the morphology and size distribution of coronae highlands and major shields suggest that mantle upwelling on venus operates either on several spatial scales with coronae representing smaller scale upflows and major volcanic rises representing larger convective upwellings or on several temporal scales with coronae representing shorter duration upflows and major volcanic rises representing long term upwellings

hemispheric sea ice distribution sets the glacial tempo the proxy record of global temperature shows that the dominant periodicity of the glacial cycle shifts from 40 kyr obliquity to 100 kyr eccentricity about a million years ago using climate model simulations here we show that the pace of the glacial cycle depends on the pattern of hemispheric sea ice growth in a cold climate the sea ice grows asymmetrically between two hemispheres under changes to earth s orbital precession because sea ice growth potential outside of the arctic circle is limited this difference in hemispheric sea ice growth leads to an asymmetry in absorbed solar energy for the two hemispheres particularly when eccentricity is high even if the annual average insolation is similar in a warmer climate the hemispheric asymmetry of the sea ice decreases as mean arctic and antarctic sea ice decreases diminishing the precession and eccentricity signals and explaining the dominant obliquity signal 40 kyr before the mid pleistocene transition

spatially distributed three dimensional slope stability modelling in a raster gis abstract we present a grass gis implementation of a three dimensional slope stability model capable of dealing with shallow and deep seated slope failures r rotstab it exploits a modified version of the revised hovland method and evaluates the slope stability over a large number of randomly selected slip surfaces ellipsoidal or truncated in shape for each raster cell in the modelling domain the factor of safety is taken from the most critical slip surface this results in an overview of potentially unstable regions without showing the individual sliding areas furthermore the model produces a susceptibility index for each cell based on the proportion of slip surfaces with a low factor of safety we test the model in the collazzone area umbria central italy where detailed information on shallow and deep seated landslides morphology and lithology is available the rate of true predictions landslide plus non landslide ranges from 54 7 to 81 2 for shallow landslides and from 58 5 to 87 4 for deep seated landslides depending on the adjustment of the uncertain geotechnical parameters in the same order the rate of true landslide predictions decreases from 80 2 to 19 9 shallow and from 64 3 to 3 6 deep seated so that an increase of the true landslide prediction rate can only be achieved at the cost of a significant increase of the false alarm rate the results for shallow landslides are very similar to those yielded with the infinite slope stability model in terms of the minimum factor of safety but differ substantially in terms of the spatial patterns the evaluation of the landslide susceptibility index yields areas under the roc curves of 0 68 0 70 shallow landslides r rotstab 0 61 0 65 shallow landslides infinite slope stability model and 0 59 0 63 deep seated landslides we conclude that the r rotstab model outperforms the infinite slope stability model

assessment of non linear rock strength parameters for the estimation of pipe jacking forces part 1 direct shear testing and backanalysis abstract a method of backanalysis was used for the assessment of pipe jacking forces from three pipe jacking drives in laminated shale and interbedded lithological units of metagraywacke siltstone greywacke and phyllite found in the highly weathered and fractured lithologies of the tuang formation malaysia direct shear tests were conducted on reconstituted tunneling rock spoils sampled from three pipe jacking sites the direct shear test results were initially assessed using the mohr coulomb failure criterion which demonstrated severe shortcomings in capturing the nonlinear shear strength behavior of the reconstituted tunneling rock spoils subsequently a simple power law function was proposed together with the generalized tangential method to obtain useful equivalent tangential cohesion c t p and friction angle t p for the assessment of pipe jacking forces in fractured lithologies the outcomes from this study show that the tangential mohr coulomb strength parameters can be used to backanalyze the frictional coefficient avg and the vertical stress at the tunnel crown ev these backanalyzed values were successfully related back to the measured jacking forces and jacking speeds for pipe jacking drives in various geological conditions and lubrication efforts the use of the backanalyzed parameters c t p t p avg and ev in the assessment of pipe jacking forces from highly weathered rocks comprising of laminated and interbedded lithological units could lead to the prediction of jacking forces using numerical models a companion paper to this study has also been produced to evaluate the reliability and suitability of these backanalyzed parameters for assessing pipe jacking forces using the finite element method

predicting fractures in glacially related fine grained materials and a synthetic soil of bentonite and sand using soil texture abstract scientists and engineers from many disciplines have been studying the formation of fractures in fine grained natural geologic materials and fill naturally occurring fractures in the fine grained materials can create preferential flow paths which can allow water to infiltrate quickly resulting in recharge to underlying aquifers but also allowing contaminants to pass through to aquifers potentially threatening ground water drinking water sources they can also create zones of weakness that allow piping in dams and slip zones in fill materials glacially related fine grained materials are widely distributed across the northern hemisphere including the u s states of minnesota wisconsin michigan iowa illinois indiana and ohio canada and much of northern europe it has been difficult to predict the presence of these fractures the objective of this research was to analyze soil textures of fractured soils and determine boundary conditions for predicting the likelihood of fractures in similar materials graphically representing the predictive model on the usda soil texture ternary diagram an extensive midwestern u s data set 275 data points including ohio iowa michigan and wisconsin soil samples was studied the texture data of those glacially related fine grained materials containing fractures indicate that those with 6 5 clay can be predicted to support fractures an auxiliary experiment using bentonite suggests that this predictive model may be applicable beyond the clay mineralogies common to the u s midwest this is a promising method of predicting which soil textures are most likely to form fractures and can be a useful field tool for engineering geologists soil scientists and other environmental professionals it is immediately applicable to the u s midwestern sites and with additional analyses using other soils could be used more widely across glaciated north america and northern europe

pore structure characteristics of debris flow source material in the wenchuan earthquake area abstract wide grading loose soils wgls are a special slope deposit that often serve as a source for debris flows in the western mountainous area of china previous research indicated that rainfall infiltration induced the migration of fine particles within soil slopes and lead to the initiation of shallow failure and subsequent debris flows clearly soil pore structure exerts a profound influence on seepage during rainfall infiltration which is closely related to soil permeability and corresponding internal erosion the current understanding of the mechanisms of fine particle migration is limited because of the complexity of wgls micropore structure the challenge lies in how to systematically characterize wgls pore structure so that it provides a foundation for future numerical simulations of fine particle migration induced debris flows in this study the characteristics of wgls pore structure were analyzed quantitatively using scanning electron microscopy the results revealed that wgls predominantly contained micropores and mesopores the pore size distribution exhibited a bimodal nature with one peak occurring at a pore diameter of 12 m and another at 72 m the pore complexity of all samples exceeded 0 75 which indicates a low aspect ratio for each pore the average diameter of the fine particles that migrated was then determined with a laboratory seepage test a preliminary jamming probability analysis based on three dimensional micropore reconstruction and average fine particle diameter indicate that jamming is most prevalent along the slope

year round pack ice in the weddell sea antarctica response and sensitivity to atmospheric and oceanic forcing using a dynamic thermodynamic numerical sea ice model external oceanic and atmospheric forcings on sea ice in the weddell sea are examined to identify physical processes associated with the seasonal cycle of pack ice and to identify further the parameters that coupled models need to consider in predicting the response of the pack ice to climate and ocean circulation changes in agreement with earlier studies the primary influence on the winter ice edge maximum extent is air temperature ocean heat flux has more impact on the minimum ice edge extent and in reducing pack ice thickness especially in the eastern weddell sea low relative humidity enhances ice growth in thin ice and open water regions producing a more realistic ice edge along the coastal areas of the western weddell sea where dry continental air has an impact the modeled extent of the weddell summer pack is equally sensitive to ocean heat flux and atmospheric relative humidity variations with the more dynamic responses being from the atmosphere since the atmospheric regime in the eastern weddell is dominated by marine intrusions from lower latitudes with high humidity already it is unlikely that either the moisture trans port could be further raised or that it could be significantly lowered because of its distance from the continent the lower humidity source ocean heat transport variability is shown to lead to overall ice thinning in the model response and is a known feature of the actual system as evidenced by the occurrence of the weddell polynya in the mid 1970s

the ronne polynya of 1997 98 observations of air ice ocean interaction the ronne polynya formed in the weddell sea antarctica during the period november 1997 february 1998 to an extent not seen previously in the 25 years of all weather satellite observations the vessel hms endurance traversed the polynya region and took sea ice physical oceanographic and meteorological measurements during january and early february 1998 these observations together with satellite imagery and weather records were analyzed to determine the causes of the anomalous condition observed and to provide comparisons for numerical modeling experiments the polynya area analyzed from satellite imagery showed a linear nearly constant increase with time from mid november 1997 through february 1998 it had a maximum open water area of 3 105 km2 and extended 500 km north of the ronne ice shelf at 76 s to 70 s the ice and snow structure of floes at the northern edge of the polynya showed the ice there had formed in the previous mid to late winter october 1997 or earlier and had been advected there either from the eastern weddell sea or from the front of the ronne ice shelf analyses of the wind fields showed anomalous spring summer wind fields in the polynya year with a strong southerly to southwesterly component compared to the mean easterly winds typical of summer conditions these southerly wind conditions in both magnitude and direction therefore account for the drift of ice northward the predominant summer easterly winds usually fill the southern weddell sea with ice from the east and the high albedo surfaces reflect the solar radiation preventing warming of the surface ocean waters and consequent sea ice melt instead high incident solar radiation from november 1997 to february 1998 was absorbed by the open water rather than being reflected there by both melting ice and preventing ice formation and thereby sustaining the polynya we conclude that open water albedo feedback is necessary to allow the observed polynya formation since similar drift conditions prevail in winter arising from southerly winds also and usually result in extensive new ice formation in front of the ronne ice shelf the strong southerly winds therefore have quite opposing seasonal effects leading to high ice production in winter as usually found and extensive open water if they occur in spring and summer as seen in this atypical event in 1997 98 in this case the atypical southerly winds may be associated with an el ninno southern oscillation enso induced atmospheric circulation pattern

impact craters on regional plains on venus age relations with wrinkle ridges and implications for the geological evolution of venus 1 a global assessment of impact craters on venus 30 km in diameter shows that 146 craters are completely or partially superposed on the regional plains that dominate the surface and typically are deformed by wrinkle ridges in this study we found that 10 of these craters are deformed by wrinkle ridges pre wr 93 craters are superposed on wrinkle ridges post wr and 43 craters were found to be ambiguous cases we compared our findings with the results of a similar study by mcgill 2004 done for craters of all sizes but for 1 3 of the surface of venus we found that the percentage of pre wr craters found by mcgill 2004 among the unambiguous cases 15 is close to our percentage 10 but we are in disagreement on the classification of a significant number of specific craters and in this analysis we describe the major reason for the disagreements we then summarize published data on the crater densities for different plains on venus we assess monte carlo modeling of volcanic resurfacing which competed with the ongoing formation of impact craters on the basis of these data and analyses we conclude that the mean age of the regional plains is close to the mean global surface age of venus and that the potential time span of regional plains emplacement was relatively short we interpret our results as evidence that wrinkle ridging on venus was a distinct tectonic phase that occurred rather early in post regional plains time probably within the first 10 although the exact duration remains uncertain regional and global stratigraphic relationships strongly support the hypothesis that wrinkle ridging on venus predominantly occurred during a specific phase of history the geologic record of wrinkle ridging and post plains tectonic evolution of volcanic plains on the moon and mars show interesting similarities to those of venus

sea ice and oceanic processes on the ross sea continental shelf we have investigated the spatial and temporal variability of antarctic sea ice concentrations on the ross sea continental shelf in relation to oceanic and atmospheric forcing sea ice data were derived from nimbus 7 scanning multichannel microwave radiometer smmr brightness temperatures from 1979 1986 ice cover over the shelf was persistently lower than above the adjacent deep ocean averaging 86 during winter with little month to month or interannual variability the large spring ross sea polynya on the western shelf results in a longer period of summer insolation greater surface layer heat storage and later ice formation in that region the following autumn newly identified pennell and ross passage polynyas near the continental shelf break appear to be maintained in part by divergence above a submarine bank and by upwelling of warmer water near the slope front warmer subsurface water enters the shelf region year round and will retard ice growth and enhance heat flux to the atmosphere when entrained in the strong winter vertical circulation temperatures at 125 m depth on a mooring near the ross ice shelf during july 1984 averaged 0 15 c above freezing sufficient to support a vertical heat flux above 100 w m2 monthly average subsurface ocean temperatures along the ross ice shelf lag the air temperature cycle and begin to rise several weeks before spring ice breakout the coarse smmr resolution and dynamic ice shelf coastlines can compromise the use of microwave sea ice data near continental boundaries

chronology of the formation process of venusian novae and the associated coronae 1 venusian radial features novae have been interpreted to represent the initial stage of the corona evolution thus they are hypothesized to be older than the corona rim structure however based on recent studies the majority of novae that are located in the inner part of the coronae seem to postdate corona formation the topography as well as the mutual age relationships of coexisting coronae and novae indicates that nova formation may have taken place during different corona evolution phases in this study we present a chronology for nova formation that offers an explanation of both age and location relations of the novae inside the coronae due to the proven age differences between coronae and novae located within them we conceive most of the novae within the corona annulus as representations of reactivation of the corona location we believe that the morphology the topography and the age relations of corona annulus and nova radial features depend on the stage of corona evolution during the reactivation period or event when the nova is formed our model explains the observed regularity between nova location and age relations of the corona nova joint structure better than the assumed movement of the lithosphere or migrating mantle plumes

water mass modification over the continental shelf north of ronne ice shelf antarctica 1 we use new data from the southern weddell sea continental shelf to describe water mass conversion processes in a formation region for cold and dense precursors of antarctic bottom water the cruises took place in early 1995 1998 and 1999 and the time series obtained from moored instruments were up to 30 months in length starting in 1995 we obtained new bathymetric data that greatly improve our definition of the ronne depression which is now shown to be limited to the southwestern continental shelf and so cannot act as a conduit to northward flow from ronne ice front large scale intrusions of modified warm deep water mwdw onto the continental shelf occur along much of the shelf break although there is only one location where the mwdw extends as far south as ronne ice front high salinity shelf water hssw produced during the winter months dominates the continental shelf in the west during summer ice shelf water isw exits the subice cavity on the eastern side of the ronne depression flows northwest along the ice front and reenters the cavity at the ice front s western limit during winter the isw is not observed in the ronne depression north of the ice front the flow of hssw into the subice cavity via the ronne depression is estimated to be 0 9 0 3 sv when combined with inflows along the remainder of ronne ice front reported elsewhere sufficient heat is transported beneath the ice shelf to power an average basal melt rate of 0 34 0 1 m yr 1

deformational models of rifting and folding on venus tectonic features on venus with characteristic widths and or spacings can be used to place quantitative constraints on the structure of the mechanical lithosphere through geophysical modeling we develop theoretical models for both compressional buckling and extensional rifting deformation based on classical elastic plate models with characteristic spacings determined by the flexural parameter modified to account for the effects of a realistic rheology this rheology consists of a relatively weak crust overlying a more creep resistant mantle in both layers the upper portions deform by frictional yielding on preexisting faults with a yield stress that increases linearly with depth and the lower portions deform by non newtonian temperature dependent creep for extensional deformation a graben model is used in which the primary structure of the rift is formed in the strong mantle layer and secondary faulting occurs in the brittle crustal layer the introduction of a weak zone in the lower crust that acts to decouple these two layers allows the formation of rifts with the large widths and depths observed on venus the compressional folding model utilizes an elastic buckling approach in which the non elastic yielding of the upper and lower portions of the layer modifies the elastic folding wave length this approach avoids the unreasonably high stresses that are required for conventional buckling models the two scales of deformation observed in radar images 15 25 km and 100 300 km can be related to the elastic flexural properties of the crust and mantle respectively which are separated by an intermediate weak zone in the lower crust these results imply that for regions in which both scales of deformation are present the crust is 5 15 km thick and the thermal gradient is 10 15 km l in regions such as ishtar terra where only the smaller features are observed the crust may be considerably thicker the apparent structure seen in high resolution images of the beta regio rift with the major faults located at the edges of an extended linear central depression lends support to the assumption of a graben mechanism of rift formation

sea ice melting processes inferred from ice upper ocean relationships in the ross sea antarctica 1 sea ice melting processes are inferred from various summer sea ice and upper ocean data obtained in the ross sea in january 1999 using spatially 30 km averaged continuous data an ice concentration water temperature plot ct plot shows that the temperature at a depth of 7 m increases as ice concentration decreases in the ice interior region the ct plot is explained by a simple ice upper ocean coupled model in which sea ice melting is caused only by heat input through open water the bulk heat transfer coefficient between ice and ocean kb is estimated to be 1 2 10 4 m s 1 these findings are supported by the relationship between ice concentration and heat content in the mixed layer estimated from conductivity temperature depth ctd data salinity at a depth of 7 m salt deficit in the mixed layer associated with sea ice melt estimated from ctd data and their relationships with ice concentration also suggest that melting is mainly caused by atmospheric heat input through open water and that local balance of salinity nearly hold the time evolution of ice concentration calculated from the ice upper ocean coupled model with the estimated kb corresponds with that derived from the special sensor microwave imager ssm i confirming the model s applicability and the value of kb

venus astra novae estimates of the absolute time duration of their activity abstract in order to assess the age relations between astra novae features with extensive radial fracture graben systems and their surroundings and to determine the duration of their activity we undertook a photogeologic analysis of magellan images of 78 astra 49 dark parabola craters and 114 clear halo craters for seven of these 78 astra it was found that the astrum forming faulting started before or close to the time of emplacement of regional plains and extended into the second part of post regional plains time because the mean age of the regional plains is close to the mean surface age of venus which is estimated to be 750 m y this means that the duration of activity of these seven astra was several hundred millions of years this is longer than the duration of activity of ongoing mantle plumes on earth but shorter than the duration of activity of the plume feeding the martian volcano olympus mons the basic morphologic characteristics of these seven astra as well as their age relations with other geologic units are similar to those of the majority of other astra therefore such a long duration could also be typical of some other astra we confirm the two phase pre and post regional plains evolution of astrum forming faulting suggested in previous studies for the first phase we show evidence for purely tectonic faulting caused by the diapiric rise of a mantle plume for the second phase we find evidence supporting the interpretation of other studies that the observed faults resulted from subsurface dike intrusions produced by magmatism associated with the plume we also found that faulting during the second phase was not instantaneous but distributed over a long period of time

rifts and large volcanoes on venus global assessment of their age relations with regional plains we report on the results of synoptic global mapping of rifts and large volcanoes on venus and detailed mapping in six areas illustrating the relationships among these features rifts and large volcanoes were subdivided into old transitional for volcanoes only and young features the geologic event separating old features from young ones is the formation of wrinkle ridges on the regional plains global mapping showed that the postplains rifts dominate in the population of rifts both in terms of number of mapped segments and in area the postplains volcanoes are more abundant in terms of number and area occupied than those that are transitional in age and these in turn dominate over the old ones these data show that in post regional plains time rifting and formation of large volcanoes are significantly more important processes than in the immediately preceding period the time period during which regional plains were emplaced and old and partly transitional large volcanoes formed was much shorter than the postplains time therefore the mean rate of formation of large volcanoes during this first period was significantly higher than in the subsequent time similarly the relatively short time duration of the plains emplacement time indicates that the mean rate of old rifting was higher than in more recent time this study shows prominent changes with time in the absolute rates and roles of rifting and large volcano formation this supports the directional model of the geologic evolution of venus during the last several hundred million years as opposed to the nondirectional model which predicts a more random occurrence of geologic processes throughout history

the morphology and evolution of coronae on venus coronae on venus are large circular to ovoidal surface features that have distinctive tectonic volcanic and topographic expressions they range in diameter from less than 200 km to at least 1000 km new data from the magellan spacecraft have shown coronae to be among the dominant tectonic forms on the planet and have revealed their morphology in unprecedented detail typical coronae are dominated by concentric tectonic features and have a raised rim a central region higher than the surounding plains but in many instances lower than the rim and commonly a peripheral depression or moat some coronae also show significant amounts of radial tectonic structure and in most cases this predates the concentric features in addition there are other features on venus recognized for the first time in magellan data that consist of domical rises with intense radial tectonic patterns and little or no concentric structure all of these features commonly are associated with moderate to large quantities of volcanism in fact some radially fractured domes have undergone so much volcanism that volcanic construction appears to have played a significant role in establishing their topography we explore a model of corona formation that links these forms into a genetic sequence the model begins with the ascent of a mantle diapir upward mantle flow driven by its ascent forces the lithosphere above the diapir upward producing a gentle dome with a radiating pattern of extensional fractures as the diapir impinges on the underside of the lithosphere it flattens and spreads transforming the uplift to a more flat topped shape in this flattened near surface configuration the diapir can cool rapidly with the resultant loss of buoyancy the raised plateau can relax to form a central sag a raised rim and a depressed moat concentric tectonic features develop primarily during the latter stages of corona formation and hence are best preserved on mature coronae volcanism takes place during all phases of the uplift and may diminish as the relaxation occurs our analyses to date suggest that this scenario is broadly consistent with many of the coronae on venus however there is enormous diversity in corona morphology and features are present that require substantial deviations from this simple model in particular some circular depressions appear corona like in synthetic aperature radar images but may in fact be large calderas some of the variations observed in corona morphology may ultimately be interpretable in terms of variations in the behavior of individual diapirs and in the local properties of the venusian lithosphere

the mechanisms behind shallow failures in slopes comprised of landslide deposits in areas hit by the 2008 wenchuan earthquake that occurred in sichuan province china debris flows are often generated from landslide deposits during heavy rainstorms the broadly graded and unconsolidated landslide deposits respond to rainfall in very complex mechanical and hydraulic manners an artificial rainfall test was conducted to simulate the rainfall infiltration and surface runoff processes occurring on the landslide deposit slope at the wenjiagou gully china with heavy rainfall rates 140 mm h incorporated an innovative flume was designed to collect the slope interflow and surface runoff separately sensors to monitor the pore water content pwp and volumetric water content vwc were deployed the results indicated that there were four stages in the hydrological response of landslide deposits during the artificial rain event infiltration a slow increase in interflow surface runoff begins a rapid increase in interflow surface runoff slowly increases and a steady state bed gradient increase will lead to pwp rapidly ascending and regressive failure happening concomitant with the observed increases in pwp and vwc the shear strength of the landslide deposits decreased and led to the occurrence of small scale shallow failures surface runoff interflow and fine particle migration effects are presented to interpret the process of shallow failure and although shallow slope failure is the result of interaction with the above three factors induced by rainfall the key underlying factor is the characteristically loose structure of landslide deposits c 2014 elsevier b v all rights reserved

geophysical models for the formation and evolution of coronae on venus coronae are large circular features on venus characterized by an annulus of concentric tectonic features interior fracturing volcanism and generally upraised topography they are suggested to form over sites of mantle upwelling and modified by subsequent gravitational relaxation we examine this proposition using two geophysical models to determine whether and under what conditions these mechanisms can produce the topography and tectonics exhibited by coronae in the magellan altimetry data and radar images our results show that mantle diapirism can produce the domical topography of novae which may be coronae in the earliest stage of formation the model stresses induced at the surface by a mantle diapir imply the formation of radially oriented extensional fracturing as observed in novae the dimensions of novae indicate that the diapirs responsible for them are smaller than about 100 km in radius and that the elastic lithosphere is less than 32 km thick diapirs that have reached the top of the mantle are expected to spread and flatten producing plateaulike rather than domical topography we model a flattened diapir at the top of the mantle and show that it will result in plateaulike uplift the volume of the flattened model diapir is similar to that of the spherical diapirs derived for novae we model gravitational relaxation of isostatically uncompensated plateaus and show that they relax to the topographic forms associated with coronae and that the model stresses are consistent with the development of the annulus of tectonic features around coronae

evaluation of pipe jacking forces based on direct shear testing of reconstituted tunneling rock spoils abstractthe installation of underground trunk sewer lines in the tuang formation of kuching city malaysia used trenchless technology in the form of the pipe jacking method the evaluation of pipe jacking forces mainly involves empirical models developed for soils with rather limited considerations for drives through weathered rock therefore a novel approach is proposed to evaluate strength parameters by reconstituting and subsequently shearing scalped tunneling rock spoils in the direct shear apparatus the direct shear results are then applied to a well established pipe jacking force model which considers arching theory the outcomes indicate that the backanalyzed frictional coefficients avg are not only reliable but also related to their surrounding geologies because of soil structure interaction this study also highlights the significance of lubrication and effect of rock arching in assessing jacking forces the successful characterization of reconstituted tunneling rock spoils in this paper ha

the mechanics of surficial failure in soil slopes it is not safe to employ the classical infinite slope failure analysis procedure in which the coulomb failure criterion is used because a very large portion of the factor of safety is assigned to the effective cohesion which is not present in the soil part of the problem arises from the normal stresses used in the drained direct shear tests which are high relative to the normal stresses prevailing in surficial failures the real effective strength envelope is curved and it is proposed to model it by a power function whose parameter values may be determined from the usual shear tests performed at the normal stress magnitudes usually employed based on the factor of safety calculations from the curved failure envelope and observations from field rainfall infiltration experiments the mechanics of surficial failure of slopes is explained

interannual variability and ventilation timescales in the ocean cavity beneath filchner ronne ice shelf antarctica 1 multiyear time series of ocean current and temperatures from beneath filchner ronne ice shelf antarctica demonstrate both seasonal and interannual variability the seasonal signal is visible at all measurement sites although it was swamped for a 2 year period 1999 2001 when extraordinarily light sea ice cover in the southern weddell sea during the 1997 1998 austral summer caused an anomalously large pulse of high salinity shelf water to flush beneath the ice shelf the pulse was observed twice at an instrumented site near the berkner island coast once on its way to the filchner depression and once after the signal had propagated around the depression and returned to the site as an anomalously large pulse of ice shelf water the timings of the signal allow an estimate of 24 30 months for the flushing timescales of the sub ice shelf ocean cavity indicating that the cavity is highly responsive to external forcing a timescale for the full ventilation of the cavity of 4 5 years is obtained from the length of time the sub ice shelf conditions take to return to their original state a timescale significantly shorter than previous estimates

post glacial seasonal diatom record of the mertz glacier polynya east antarctica an ultra high resolution post glacial laminated sediment record from mertz ninnis trough east antarctic margin eam has been analysed using sem backscattered electron imagery secondary electron imagery and quantitative diatom abundance laminations are classified using visually dominant diatom species and terrigenous content four biogenic diatom ooze laminae types one diatom bearing terrigenous lamina type and one diatom bearing terrigenous sub lamina type have been identified diatom ooze lamina types comprise near monogeneric hyalochaete chaetoceros spp resting spore laminae laminae characterised by corethron pennatum laminae characterised by rhizosolenia spp and mixed diatom assemblage laminae diatom bearing terrigenous lamina and sub lamina types comprise mixed diatom assemblage terrigenous laminae and sub laminae characterised by porosira glacialis resting spores formation of each of these lamina types is controlled by seasonal changes in nutrients oceanographic regimes and the mertz glacier polynya dynamics

the global resurfacing of venus the impact cratering record on venus is unique among the terrestrial planets fully 84 of the craters are in pristine condition and only 12 are fractured remarkably only 2 5 of the craters and crater related features are embayed by lava although intense volcanism and tectonism have affected the entire planet furthermore the spatial and hypsometric distribution of the craters is consistent with a completely random one including stochastic variations monte carlo simulations of equilibrium resurfacing models result in a minimum of 17 times more embayed craters than observed or unobserved nonrandom crater distributions for resurfacing areas between 0 03 and 100 of the planet s surface these models also are not consistent with the number and nonrandom distribution of volcanoes and the nonrandom distribution of embayed and heavily fractured craters the constraints imposed by the cratering record strongly indicate that venus experienced a global resurfacing event about 300 m y ago followed by a dramatic reduction of volcanism and tectonism this global resurfacing event ended abruptly 10 m y the present crater population has accumulated since then and remains largely intact thermal history models suggest that similar global resurfacing events probably occurred episodically in the past the tesserae statistically have the same average surface age crater retention age as the rest of the planet but they probably represent older rock units deformed by earlier episodes of global resurfacing although they largely survived the latest global resurfacing event their surfaces were severely deformed by it monte carlo simulations indicate that only about 4 6 of the planet has been volcanically resurfaced since the global event and that the lava production rate has been no more than 0 01 0 15 km3 yr during this time this rate is significantly less than the current rate of intraplate volcanism on earth 0 33 0 5 km3 yr most of venus recent volcanism occurs in the beta atla themis region and most of the recent tectonism is associated with the major global scale tectonic disruption zones that lie within and connect the equatorial highlands the approximately 33 of the planet s surface bounded by latitudes 30 n and 30 s longitudes 60 and 300 e contains twice as many heavily fractured craters and 1 4 times more lava embayed craters as the planetary average this region includes most of the major tectonic belts in the equatorial region because the craters are indistinguishable from a statistically random distribution both spatially and hypsometrically this concentration of strongly fractured and embayed craters is considered indicative of a continuing low level of limited extension and volcanic activity in this region over the past 300 m y however these craters are simply fractured and or embayed and very few have been subjected to complete tectonic disruption complete burial and subsequent removal from the surface as was the case during the global resurfacing event we show that neither the present level and style of geologic activity nor anything less than global resurfacing could have produced the observed cratering record the effects of recent geologic activity are much less than those of the earlier global resurfacing event when the record of all the early heavy bombardment and much of the later light bombardment was erased from the surface by massive volcanism and tectonic activity episodic regional resurfacing events that had global effects also occurred on earth e g the mid cretaceous superplume and probably on mars on mars they may have triggered the catastrophic releases of water that formed the outflow channels