characterization of the mechanisms underlying loess collapsibility for land creation project in shaanxi province china a study from a micro perspective abstract using the major land creation project to bulldoze mountains to build cities implemented in the city of yan an as an example the collapse potential microscopic observations quantitative analyses and qualitative characterization of the microstructures of loess sampled from yan an were investigated to probe the fundamental mechanisms of loess collapsibility at the micro scale the results show that loess in yan an exhibits a severe degree of collapse potential as indicated by its maximum collapse index of 8 10 at a vertical stress value of 600 kpa from a compositional and microstructural perspective a large proportion of loosely arranged skeletal particles are widely separated by variants of clay fabric forming a metastable structure with a high pore area ratio of 32 67 and demonstrating an unstable contact between particles in natural loess these intrinsic microstructural features with a high degree of collapse potential act synergistically to augment collapse when loess is saturated under a certain load the initially high stiffness provided by the delicate clay fabric can be destroyed by its softening dispersion or disruption unsupported skeletal particles are then rearranged significantly into a more stable structure at the same time pores larger than 60 m create favorable spatial conditions for wetting deformation thereby spurring an abrupt reduction in pore size and area particles reorganize into a closely packed structure more interlocking pores of

magnetostratigraphical dating of loess deposits in china the age of chinese loess deposits has long been disputed biostratigraphical and earlier magnetostratigraphical investigations placed the entire loess formation within the pleistocene the new palaeomagnetic measurements reported here on a bore hole section near lochuan shaanxi province suggest a clearly defined magnetic polarity zonation which extends below the olduvai subchron a late pliocene age of 2 4 myr is assigned to the oldest loess sediments measured the intensity variations of natural remanent magnetization nrm and low field magnetic susceptibility are indicative of climatic changes during loess deposition

wetting induced collapse behavior associated with infiltration a case study abstract limited information is available in the literature for interpreting the influence of water infiltration process that contributes to in situ collapse in loess deposits for this reason the focus of the present investigation has been directed to studying the collapse deformation with respect to time in heifangtai china where significant wetting induced collapse deformation is widespread due to multiple years of irrigation activities a method that is based on easy to obtain parameters from constant water content oedometer tests and the wetting soil water characteristic curve is used for predicting the long term wetting induced collapse deformation the proposed method is validated using a field infiltration test the wetting induced collapse behavior in heifangtai is interpreted using the proposed method results of the study suggest that there is a significant difference in total subsidence between the irrigation and non irrigation areas the collapse in the irrigation area occurs during the period when the wetting front advances and the groundwater table gwt forms and rises until the formation of a new hydraulic equilibrium state which is significantly different from its initial condition however the collapse in the non irrigation area is mainly related to the gwt variation the difference in the total subsidence between the irrigation and non irrigation areas is predominantly associated with the propagation of the wetting front the proposed method is simple and can be extended in practical applications for reliably estimating the in situ collapse deformation associated with the water infiltration process

insolation values for the climate of the last 10 million years new values for the astronomical parameters of the earth s orbit and rotation eccentricity obliquity and precession are proposed for paleoclimatic research related to the late miocene the pliocene and the quaternary they have been obtained from a numerical solution of the lagrangian system of the planetary point masses and from an analytical solution of the poisson equations of the earth moon system the analytical expansion allows the direct determination of the main frequencies with their phase and amplitude numerical and analytical comparisons with the former astronomical solution ber78 are performed so that the accuracy and the interval of time over which the new solution is valid can be estimated the corresponding insolation values have also been computed this analysis leads to the conclusion that the new values are expected to be reliable over the last 5 ma in the time domain and at least over the last 10 ma in the frequency domain

microstructural constraints on geotechnical properties of malan loess a case study from zhaojiaan landslide in shaanxi province china abstract the microstructure of malan loess a late pleistocene loess deposit in china dominates its macroscopic geotechnical properties when subject to inundating or humidifying conditions the distinct metastable structure of the malan loess is sensitive to collapse thus its geotechnical properties undergo change the results of triaxial and uni axial compression tests under the humidifying conditions on undisturbed loess samples demonstrate that its geotechnical properties of the top loess were dominated by metastable structure while the basal loess were more influenced by inter particles cementation bond based on analyses from scanning electron microscopy images change of the loess pore structure can be primarily attributed to the ratio of metastable pores 5 m accordingly an end member model is proposed to illustrate how varying in the size and distributions of very large pores 200 m large pores 50 200 m medium pores 5 50 m and small pores

sinkholes in italy first results on the inventory and analysis the italian geological survey apat carried out field surveys and analysis of collapse phenomena sinkholes in italy the main goal of the project is to collect geological geomorphological geochemical and hydrogeological data about the sinkhole prone areas in italy in order to develop a spatial database of the characteristics of each phenomenon the preliminary results of this study provide information on the distribution geological setting and monitoring and remediation actions associated with these natural collapses in italy many italian regions are affected by these natural disasters some of them are caused by karst collapses or anthropic activity however some occur in areas characterized by buried carbonate bedrock up to 190 m as well as by peculiar geological structural and geochemical scenarios in these areas it is not reasonable to ascribe the formation mechanism to karst activity instead these types of cavities quickly develop in terrains with a variable granulometry often in connection with upwelling fluids in this work some natural specific cases have been studied in order to define the relationships between the geology regional tectonic elements mineral spring waters and strong gas vents and the genesis of the sinkholes a first attempt of sinkhole classification is also presented

the influence of loess cave development upon landslides and geomorphologic evolution a case study from the northwest loess plateau china abstract loess caves landslides collapses bank erosion and soil erosion which are independently and interactively shaping the modern loess landscape are widely distributed across the chinese loess plateau the study area is located in a small watershed in huining county gansu province which is one of the areas with the strongest development of loess caves across the loess plateau this area is an ideal site for studying geological hazards and geomorphic evolution on the loess plateau seventeen landslides and 176 loess caves with a density of 887 units km2 were investigated with a uav unmanned aerial vehicle and mapped by gis geographic information system using high resolution uav images and topographic data we carried out an interpretation of loess caves bank erosion and landslides studied the spatial distribution and developmental patterns of loess caves landform morphology and the relationship between loess caves and landslides based on gis spatial analysis mathematical statistics and field surveys and analyzed the influence of loess microtopography on slope landforms finally six typical evolutionary models of soil erosion loess cave development landslide occurrence barrier dam formation are preliminarily proposed the primary slope stage early cave stage accelerated cave stage cave connecting stage landslide creeping stage and landslide dam forming stage this study is a useful exploration and an attempt to reveal the influence of loess cave development on slope stability and disaster chain effects

late glacial climatic changes in eastern france lake lautrey from pollen lake levels and chironomids high temporal resolution analyses of pollen chironomid and lake level records from lake lautrey provide multi proxy quantitative estimates of climatic change during the late glacial period in eastern france past temperature and moisture parameters were estimated using modern analogues and plant functional types transfer function methods for three pollen records obtained from different localities within the paleolake basin the comparison of these methods shows that they provide generally similar climate signals with the exception of the bolling comparison of pollen and chironomid based temperature of the warmest month reconstructions generally agree except during the bolling major abrupt changes associated with the oldest dryas bolling allerod younger dryas and the younger dryas preboreal transitions were quantified as well as other minor fluctuations related to the cold events e g preboreal oscillation the temperature of the warmest month increased by not vert similar5 c at the start of bolling and by 1 5 3 c at the onset of the holocene while it fell by ca 3 to 4 c at the beginning of younger dryas the comparative analysis of the results based on the three lautrey cores have highlighted significant differences in the climate reconstructions related to the location of each core underlining the caution that is needed when studying single cores not taken from deepest part of lake basins

effects of soil structure on soil behaviour illustrated with loess glacially loaded clay and simulated flaser bedding examples soil structure is considered to be a systematic homogeneously repetitive heterogeneity of properties and conditions of soil for upscaling and homogenisation of properties and conditions it is necessary to understand the ways in which soil structures occur and to obtain understanding of the ways in which it influences soil behaviour using three case studies different aspects of the effects of soil structure in soil mechanics are discussed the very loose grain scale packing of loess deposits held together by weak structural bonds between particles results in dramatic propagating failure when the strength of the bonds is exceeded by deformations as illustrated in the first case nonhorizontal stresses induced in the subsurface below moving continental ice sheets result in rotated stress fields within the affected soil the rotated stress field is stored in the structure of the soil as is shown in the second case and influences present day properties and behaviour of these clays it is shown in the third case that there is a large difference in the behaviour of clayey sand depending on whether the clay occurs in the form of the common clay flasers or whether the clay is homogeneously dispersed in the sand the deformation and stress propagation in the case of sand with clay flasers results in local failures and shear planes due to the large contrast in the properties of the materials making up the sedimentary structure the result is that many of the properties of sand with flasers are rather more like the clay of the flasers than the sand incorporation in the engineering practice of effects of common types of soil structure is made possible with the widespread availability of techniques such as numerical modelling these techniques enable the development of appropriate tools for practical application

geological hazards in loess terrain with particular reference to the loess regions of china abstract the considerable morphodynamic energy provided by the continuing tectonic evolution of asia is expressed in high erosional potentials and very high rates of sediment production that make this continent unequalled as a terrestrial source of primary silt many of these environments are hazardous threatening human occupation health and livelihood especially in regions of dense population such as the loess lands of north china dry loess can sustain nearly vertical slopes being perennially under saturated however when locally saturated it disaggregates instantaneously such hydrocompaction is a key process in many slope failures made worse by an underlying mountainous terrain of low porosity rocks gully erosion of loess may yield very high sediment concentrations 60 by weight characteristic vertical jointing in loess influences the hydrology enlarged joints develop into natural sub surface piping systems which on collapse produce a loess karst terrain collapsible loess up to 20 m thick is common on the western loess plateau foundation collapse and cracked walls are common many rapid events following periods of unusually heavy monsoonal rain slope failure is a major engineering problem in thick loess terrain flow slide and spread types being common the results are often devastating in both urban and rural areas an associated hazard is the damming of streams by landslides the human population increases the landslide risk in china notably through imprudent land use practices including careless water management a number of environmentally related endemic diseases arise from the geochemistry of loess and its groundwaters including fluorosis cretinism kaschin beck disease keshan disease and goitre the chinese desert margins also have a major atmospheric dust problem the effect of such dust upon human health in these extensive regions including many large cities has yet to be evaluated but pneumoconiosis is thought to affect several million people in north and west china

present day temperatures in northern scandinavia during the last glaciation scandinavia is generally considered to have been covered extensively with ice throughout marine isotope stages mis 4 2 between 75 and 10 ka here we present evidence for ice free warm conditions in the central area of the scandinavian glaciations during mis 3 our multiproxy data obtained from a lacustrine sequence in northern fin land reveal not only significant response in the northeastern sector of the scandinavian ice sheet to warming during the early part of mis 3 but also indicate rapid climate warming to present day temperatures in this ice free period new climate model simulations for interstadial conditions in mis 3 confirm the high mean july temperatures northeast of the scandinavian ice sheet in response to the high insolation values and the presence of the ice sheet during mis 3

the loess of north central china geotechnical properties and their relation to slope stability abstract loess is an aeolian deposit consisting of predominantly silt sized quartz particles and containing variable amounts of clay sized minerals loess is generally classified as a water softening material because upon wetting the loess fabric rapidly weakens or collapses the strain hardening of malan loess and the brittle failure of lishi and wucheng loess are in strong contrast to the failure behaviour of these loess deposits in a remoulded state from tests carried out on samples with varying moisture contents using a modified bromhead ring shear apparatus it was found that the effective apparent cohesion gradually increases and the effective internal friction angle decreases with an increase in moisture content when the moisture content reaches a material specific threshold the effective cohesion decreases rapidly and the effective internal friction angle stabilises at a residual value the frequent failure of loess slopes in the western part of the chinese loess plateau is closely related to progressive weathering along zones in these slopes which causes a dramatic decrease in strength from the peak strength condition progressive weathering is common in the loess slopes in the western part of the chinese loess plateau during the process shear strength reduction along potential slip surfaces may be achieved by leaching of readily soluble salts destruction of cementation bonds and redistribution of particles localized collapse of the loess fabric causes internal deformation and consequently peak strength conditions are concentrated on a progressively smaller area of the failure plane therefore the mode of failure of loess slopes is generally determined by brittle failure of the undisturbed and unweathered central parts of the slopes it is important that both the weathered and unweathered strength of the loessmaterials in this area be established in order to analyze the stability of existing loessslopes many of which are steepand lie directly above domestic and industrial urban areas

geological and geotechnical characteristics of some loess and loessic soils from china and britain a comparison abstract derbyshire e and mellors t w 1988 geological and geotechnical characteristics of some loess and loessic soils from china and britain a comparison eng geol 25 135 175 loess and loessic deposits cover some 630 000 km 2 of the surface of mainland china the loess plateau of shanxi shaanxi gansu and ningxia being the type region of this formation loess thickness generally exceeds 100 m over large areas of the loess plateau the maximum recorded thickness being 335 m in eastern gansu province near the city of lanzhou in britain loess and loessic deposits form part of a group of materials collectively known as brickearth they occur predominantly as sporadic accumulations in the southeast of england and rarely attain a thickness of more than four metres despite their geographical separation the deposits from china and britain have a remarkable similarity in some of their physical and geotechnical characteristics samples from both locations have been examined and tested in the laboratory and the results are presented the scope of the testing programme involved mineralogical analyses soil microfabric studies using a scanning electron microscope index testing including plasticity grading and density measurements and the investigation of the compressibility characteristics of the soils with particular reference to their susceptibility to collapse a soil structure model based on scanning electron microscope studies is presented and discussed in relation to the perceived mode of formation of the soils and their postdepositional history

hydroconsolidation and subsidence of loess studies from china russia north america and europe abstract various approaches to the widespread problem of the hydroconsolidation and subsidence of loess have been suggested these include considerations of rheology thermodynamics phase movements particle packing interparticle bonding pore structure and distribution catastrophe theory topology and simple structural frameworks chinese north american and most european investigators tend to concentrate on mechanisms of loess collapse the russian literature however retains an extra dimension two approaches the syngenetic and the epigenetic approach to the formation of subsiding loess have been defined in the literature most investigators follow a syngenetic approach which appears to be a consequence of the aeolian idea of loess deposition some russian writers in contrast promote an epigenetic approach in which collapsibility can develop in an originally noncollapsible material which can then suffer from hydroconsolidation and subsidence the basis of the phenomenon is a change in the packing structure of the major loess particles and this can be modelled using simple monte carlo methods to develop appropriate structures this paper aims to review the work done on this important subject serious investigation of hydroconsolidation and subsidence of loess began in the early nineteen forties fifty years ago and this has been reported in a piecemeal manner a detailed critical review of this diverse work is now overdue and this is presented herein in the light of recent work in the united kingdom an attempt is made to describe the process in a phenomenological and a structural sense inherent in this the role of n ya denisov as subsidence pioneer is considered

engineering properties of loess in algeria loess in north africa has been investigated using samples from algeria the specific gravity atterberg limits grain size distribution and dry density were determined the hydro collapsibility properties due to wetting under different stress levels were measured in single oedometer tests the results of this investigation indicate that the properties of algerian loess are similar to those of loess from many parts of the world such as iowa and libya they can be classified as silty loess

failure mechanisms in loess and the effects of moisture content changes on remoulded strength abstract investigations into the failure mechanisms of loess slopes in the loess region of north central china have shown that a majority of mass movements are associated with shallow slab slides predominantly moving under tension the effects of soil moisture content are of paramount importance when dry vertical slopes in loess may exceed 15 m in height but under conditions close to saturation the structural strength of loess rapidly decreases causing failure of the slopes mass failure of loess occurs as collapse due to hydroconsolidation and disintegration of the loess fabric as a result of liquefaction or fluidization and can be associated with progressive failure processes local destruction of the openwork fabric of the loess can lead to small plastic movements within the loess deposits this is as close as loess can come to creep

sinkhole monitoring and early warning an experimental and successful gb insar application abstract sinkholes represent a natural risk that may hit catastrophically without clearly detectible precursors however they are often overlooked by people and administrators therefore sinkhole monitoring and associated early warnings constitute important research topics but currently only a few papers about sinkhole prediction can be found in this paper an experience of sinkhole monitoring and early warning with gb insar is described the latter is a highly precise instrument that is able to produce displacement maps with metric spatial resolution the described activities were carried out on elba island central italy where karstified limestone set off the occurrence of nine sinkholes since 2008 all within less than 3000 m2 causing major damage to an important road and many indirect losses in 1 year of monitoring two deforming areas were detected and the point where a sinkhole was about to propagate to the street level was predicted thus permitting the preventive closure of the road the deformation area was larger than the hole generated by the sinkhole thus showing a subsidence that continued for a prolonged time even after the cavity was filled up the occurrence of a 1 5 m wide sinkhole undetected by the gb insar also showed the lower detection limit of the instrument

loess and palaeoenvironment some results of a european joint programme of research in 1985 a programme of research on the sedimentology and diagenesis of the loess and loessic silts of western europe was initiated jointly by laboratories in leicester meudon caen milan cardiff and southampton involving a limited amount of comparative work on the loess from types sites in the loess plateau of central china preliminary results include the following 1 experimental procedures in particle size analysis clay sample preparation and microscopy have been standardised in all cooperating groups distinctive fabrics indicative of depositional mechanisms have been recognised 2 comparison of aeolian colluvial and alluvial silt by laser scanning and bulk magnetic susceptibility anisotropy methods appears to differentiate aeolian silt from loessic silts re deposited by slope processes and flowing water 3 the variability in the anisotropy of the limon a doublet facies has been assessed by image analysis of scanning electron microscopy sem and optical microscopy strong anisotropy has also been measured in thin section imagery of loess from normandy and poland as the product of freezing and thawing this is confirmed by scanning electron microscopy and by experimental freezing of some silts 4 the clay fabric and mineralogy in western european loess differ from those in chinese loess especially in the case of semi arid deposits 5 distribution of caco3 using thin sections and sem analysis has been determined for loess from normandy and the rh ne valley in france and for some chinese loess at saint vallier zones of caco3 concentration occur masking much of the original loess sedimentary skeleton which is a locally reworked loessic silt with some laminations despite considerable scatter the palaeomagnetic results indicate a reversed polarity throughout placing the whole saint vallier sequence in the matuyama chron these preliminary results suggest the existence of two different palaeoenvironments one typified by central china with arid glacials and humid interglacials and the other represented by western europe with generally high humidities there was stronger weathering and soil development and fewer freezing effects on the lossic succession in northern italy than in western littoral europe

late weichselian valdaian and holocene vegetation and environmental history of the northern timan ridge european arctic russia abstract lake and peat deposits from the timan ridge arctic russia were pollen analysed reconstructing the vegetation history and paleoenvironment since the last glacial maximum lgm 20 18 000 years ago the sites studied are located inside the margins of a large paleolake of about 20 km 2 by us named lake timan this lake developed in the late weichselian more than 30 000 years after the deglaciation of this region and was formed due to increased precipitation and warmer summers that accelerated the melting of stagnant ice within its catchment the lake was drained during the early holocene when the outlet rivers eroded the spillways a new generation of much smaller lakes formed during the holocene when the last remnants of buried glacier ice melted away causing the exposed floor of lake timan to subside since deglaciation the following regional vegetation development has been recorded 1 during the initial stage of lake timan the dominant vegetation was discontinuous steppe tundra with patches of snow bed vegetation 2 a dwarf shrub tundra established during the late weichselian interstadial allerod probably reflecting warmer and moister conditions 3 the younger dryas cooling is recognised by a reversal to steppe tundra and snowbeds on unstable mineral soils and higher palynological richness 4 soon after the transition into the holocene a birch forest established on the timan ridge 5 a cooling starting around 8200 cal years bp initiated the deforestation of the exposed hills in the most protected sites birch trees persisted until later than 4000 years ago reflecting a gradual development into the present treeless dwarf shrub tundra

influence of structure on shear characteristics of the unsaturated loess in lanzhou china abstract loess is typically a kind of soil with metastable structure which makes loess sensitive to collapse and sliding upon wetting such structure has thus profound influence on loess s mechanical behavior however there have been arguments about how the metastable structure influences on loess s mechanical behavior and what the mechanism behind is in this study the influence of structure on shear characteristics of the unsaturated loess in lanzhou city of china was investigated with comparison of variation of shear strength and its parameters between six pairs of the undisturbed and remolded samples it is found that the peak shear strength and strength parameters of the loess significantly reduced once its structure was destroyed while shear behavior of the loess showed little change strength parameter c was much more sensitive to structure of the loess than shear strength reduction of the loess due to change of structure should be largely attributed to breaking up of cementation bonds between particles evidenced by the difference in pore size distribution and microstructure of soil fabrics between the undisturbed and remolded samples the bonds provided by clays and carbonates contributed the most to structure of the loess with minor by soluble salts while matric suction played little role in structure of the loess

loess geohazards research in china advances and challenges for mega engineering projects 2019 loess is a meta stable cemented assemblage of mainly silt and clay sized particles of low plasticity when dry it behaves like a brittle material but when wetted up the fabric rapidly collapses unique geomorphological features include extensive surface erosion soil piping loess karst catastrophic landslides and widespread collapse hydro consolidation the chinese loess plateau is a more or less continuous drape of thick loess covering some 440 000 km2 it is one of china s regions that is most prone to geohazards this paper reviews advances in the research related to loess geohazards drawing particular attention to the need to apply research findings to recent very large mega construction projects in loess terrain such as the mountain excavation and city construction in yan an levelling 78 km2 for urban expansion the lanzhou new district creating 246 km2 of new level ground for construction and large engineered interventions in the landscape for gully control and land reclamation such as those in shaanxi and gansu generating agricultural land covering an area of some 8000 km2 these projects are in response to increasing pressures to facilitate expansion of urban centres their interconnecting infrastructures and their agricultural support systems it is argued that where proper application of scientific knowledge for engineering control e g densification drainage of these new landscapes is absent these projects could generate a substantial and costly geohazard legacy for future generations

magnetism of chinese loess deposits summary the age of chinese loess deposits has long been disputed biostratigraphical and earlier magnetostratigraphical investigations placed the entire loess formation within the pleistocene and ascertained a maximum loess age of about 1 2 myr a new collection of nearly 500 samples from a natural outcrop and a borehole section near lochuan lat 35 8 n long 109 2 e shaanxi province has been dated by magnetic stratigraphy thermal cleaning of the natural remanent magnetization nrm removes a strong secondary component of viscous origin along the present geomagnetic field which resides largely in magnetite the characteristic nrm component is due to haematite which is thought to be of chemical origin rhythmical intensity variations of nrm and initial susceptibility depend on the loess lithology and may reflect climatic changes during loess deposition the palaeomagnetic results are consistent between the two sections and yield a clearly defined magnetic polarity zonation the brunhes matuyama boundary and the jaramillo subchron have been positively identified in both outcrops at exactly the same stratigraphic level the olduvai subchron has been found in the borehole section which records the entire loess sequence most probably the formation of chinese loess began shortly after the matuyama gauss polarity transition therefore a late pliocene age of about 2 4 myr is assigned to the oldest loess sediments measured

new osl dating of uk loess indications of two phases of late glacial dust accretion in se england and climate implications windblown dust deposits or loess locally known in the uk as brickearth blanket many parts of southern england outside the limits of the british and irish ice sheet the best studied loess exposures occur in kent southeast england where the deposits are believed to be late glacial in age new sedimentological evidence is presented for phases of accretion with two distinct units a calcareous brickearth exhibiting periglacial cryoturbation and a non calcareous massive brickearth optically stimulated luminescence osl dating has been applied to chemically isolated modal quartz silts to derive a chronology for sediment accretion and to better understand the palaeoclimatic significance of these deposits

size distribution of loess slides in relation to local slope height within different slope morphologies abstract loess slides are widespread and dangerous gravity induced surface processes on the loess plateau of north central china the local slope height and slope morphology have been considered as important conditioning factors for landslide susceptibility mapping however the quantitative relationship between landslide size and local slope height within different slope morphologies is not very clear in this study an inventory of 155 loess slides was developed based on detailed field investigation and remote sensing image interpretation statistical analysis and gis were applied to find the quantitative relationships between the size of these loess slides and local slope height in different types of slope morphologies the analysis shows that the relationship between the loess slides volume and area exhibits a similar trend within different types of slope morphologies in addition the analysis demonstrated that loess slides are more frequent on local slope height from 40 to 100 m stepped slopes with higher pore water pressure are prone to sliding and approximate 34 19 of total loess slides occur in these stepped slopes moreover the analysis shows that the mean loess slide area and volume rapidly increase with increasing local slope height furthermore the result underlines the fact that both the local slope height and the slope morphology are two fundamental factors that control the occurrence as well as size distribution of loess slides the loess slide size remarkably increases with increasing local slope height within every type of slope morphologies these findings indicate that local slope height can limit the loess slide size and their spatial extent moreover we quantified the correlation between the loess slide size and local slope height using power law form and the scaling exponents of the correlations are different within different slope morphologies

rapid oceanic and atmospheric changes during the younger dryas cold period the younger dryas event which began approximately 12 900 years ago was a period of rapid cooling in the northern hemisphere driven by large scale reorganizations of patterns of atmospheric and oceanic circulation 1 3 environmental changes during this period have been documented by both proxy based reconstructions 3 and model simulations 4 but there is currently no consensus on the exact mechanisms of onset stabilization or termination of the younger dryas 5 8 here we present high resolution records from two sediment cores obtained from lake krakenes in western norway and the nordic seas multiple proxies from lake krakenes are indicative of rapid alternations between glacial growth and melting during the later younger dryas meanwhile reconstructed sea surface temperature and salinity from the nordic seas show an alternation between sea ice cover and the influx of warm salty north atlantic waters we suggest that the influx of warm water enabled the westerly wind systems to drift northward closer to their present day positions the winds thus brought relatively warm maritime air to northern europe resulting in rising temperatures and the melting of glaciers subsequent input of this fresh meltwater into the ocean spurred the formation of sea ice which forced the westerly winds back to the south cooling northern europe we conclude that rapid alternations between these two states immediately preceded the termination of the younger dryas and the permanent transition to an interglacial state the impact of freshwater pulses released from northern hemisphere ice sheets on the north atlantic meridional overturning circulation has been suggested as a likely mechanism for the younger dryas cooling 7 11 in addition a responsive sea ice cover has been proposed as a mechanism that could rapidly alter the heat exchange between the ocean and atmosphere during the last glacial period 12 13 the roles of the ocean and the atmosphere in triggering the climate shifts around the younger dryas are much discussed 9 these hypotheses are difficult to resolve partly because the temporal resolution of most palaeoclimate archives is too coarse to enable the anatomy of the younger dryas stadial to be adequately described 14 to address these questions we here present a lake sediment record at sub annual resolution together with new data on the sea surface conditions of the norwegian atlantic current nwac throughouttheyoungerdryasstadial fig 1

changes in tensile strength and microstructure of loess due to vibration abstract loess soils typically have an open and metastable structure humidification and vibration can modify their microstructure and thus influence their mechanical behavior in the present study to investigate the influence of train vibration on the tensile strength behavior of loess the tensile tests were performed on loess specimens that had been vibrated at a low amplitude for a long period using a modified horizontal extensograph in addition the microstructures of vibrated and non vibrated loess specimens before and after the tensile tests were characterized changes in the loess microstructure due to vibration and that in the tensile test were analyzed the results show that the relationship between uniaxial tensile strength and water content in soil specimen could be represented using a power function the axial displacement at failure varies at the same manner as tensile strength with respect to water content in comparison to intact loess occurrence of less clay bridges and clay buttresses between aggregates or coarse particles is identified in the disturbed specimens while aggregates are seen to be a very little more loose in vibrated specimens after the tensile tests than that before the tensile tests this indicates that vibration reduces the tension resistance and ductility of loess soil structure which could be attributed to loss of bonding strength as a result of breakage of clay cementations and disintegration of aggregates in the tensile test the soil structure goes through two distinct phases of change i e stretching phase and cracking phase in the stretching phase the tensile deformations take place throughout the specimen without altering the contacts between soil particles significantly in the cracking phase weak cementations fail to resist tensile deformation and suffer from breakage once a through crack is developed the specimen breaks in two leading to a catastrophic drop of tensile stress

geotechnical thresholds in the lanzhou loess of china abstract failure of cementation bonds leading to soil structure collapse and slope failure is a major problem encountered in loess slopes in the lanzhou region of china typical physical properties low plasticity indices short range bonds decrease in shear strength upon saturation show little variation throughout the loess strata however important variations in the modes of failure and collapse potential exist which are related to varying thresholds of cementation bond failure and packing transformations when geotechnical thresholds are exceeded metastable loess can rapidly transform from an open to close particle packing a phenomenon enhanced by leaching processes and degradation of cementation bonds geotechnical parameters from laboratory and in situ tests provide an insight into the variation of cementation bond condition which in turn provides enhanced understanding of processes underlying slope instability development and the triggering of catastrophic mass movements in loess

agricultural land degradation by piping erosion in chaco plain northwestern argentina abstract soil piping has been pointed out as an important water erosion agent in a wide range of climatic regions it is responsible for high soil losses in loess derived soils the goal of this study is to evaluate the factors that are acting in the generation of piping processes and explain the mechanism of pipe collapse initiation the study was carried out in loess derived soils located in a rural area of the chaco plain between tucuman and santiago del estero provinces in northwestern argentina pipe collapse types were described and soil loss estimation was performed factors influencing the process were studied under six different categories i e physico chemical and soil mechanical soil mineralogical microstructural biological and land use properties in the study area pipes took place in agricultural fields principally in pastures with slope gradients between 1 and 3 soil pipe collapse occurred in the area as a consequence of sudden wetting of the collapsible soils during summer storms pipe collapse forms vertical pipes or macropores that provide pathways for runoff directly into the soil pipe network in addition tension cracks adjacent to pipe collapses can provide pathways for preferential flow from the surface to the soil pipe network with successive water infiltration the size of the pipes tends to increase and evolves to advanced stages of the process by internal erosion and eventually more pipe collapse blind gully formation is the final step of the piping process after the pipes roof collapse

evidence for stratosphere sudden warming ionosphere coupling due to vertically propagating tides 1 observations of the global positioning system gps total electron content tec are used to study the coupling between the 2009 sudden stratospheric warming ssw and ionospheric perturbations the observations reveal both migrating and nonmigrating perturbations to the semidiurnal tide in the equatorial ionization anomaly crest region that are associated with changes in electric fields induced by the tidal dynamo in particular a significant enhancement is observed in the nonmigrating semidiurnal westward propagating tide with zonal wavenumber 1 sw1 in gps tec during the ssw the sw1 perturbations in the low latitude ionosphere are found to oscillate with a similar period as planetary wave 1 activity in the northern hemisphere stratosphere this connection is attributed to the nonlinear interaction between tides and planetary waves and strongly supports the theory that planetary wave tide interaction is the primary mechanism coupling ssws to ionospheric variability enhancements are also observed in the nonmigrating semidiurnal tide with zonal wavenumber 0 s0 during this time period and may be related to the nonlinear interaction between the migrating semidiurnal tide and planetary wave 2 the connection between planetary wave 2 and s0 is however less clear which may be attributed to differences in the zonal mean zonal winds in the mesosphere and lower thermosphere during the times of peak planetary wave 1 and planetary wave 2 activity we conclude that the changing zonal winds during ssws play an important role in the coupling between ionospheric variability and the forcing from planetary waves of lower atmospheric origin during ssws

neogene clay and its relation to landslides in the southwestern loess plateau china loess occurs widely in northwestern china covering neogene clay and other sedimentary units that overlie the bedrock the neogene clays of the baoji region of shaanxi province north china including the eolian hipparion and paleo sanmen lake fluvial deposits are typical clays of the southern chinese loess plateau these clays are also sensitive key strata controlling the development of large scale landslides along the slope of the loess tableland surrounding the guanzhong basin to investigate the neogene clay types and landslides in the region soil samples were tested and the macro and micro structures of the clay strata were analyzed comprehensive analysis methods including the pipette method and fine x ray diffraction were applied to quantitatively analyze the sample composition and determine the clay mineral types the neogene clays are mainly composed of illite and montmorillonite mixed layer minerals on the williams discrimination diagram of swelling potential both types of clay are medium to strongly expansive soil two case studies illustrate that rainfall reduces the shear strength of the neogene clay and raises the groundwater level rainfall has gradually destroyed the structure of the neogene clay transforming it to sliding belt soil the sliding belt lies mainly within the neogene clay layers significantly affecting the occurrence and characteristics of landslides in baoji the rise in groundwater level and weakening of the shear strength of the neogene clay are important factors in the occurrence of landslides the long term strength is a key factor affecting the development of loess landslides along the loess tableland in baoji

analysis of retrogressive loess flowslides in heifangtai china abstract the heifangtai terrace is located in the arid loess area in northwestern china where a large number of landslides was induced by agricultural irrigation on the terrace resulted in slope retreat at the terrace edge at an estimated rate of 0 024 km 2 yr 1 on the basis of field investigation and monitoring remote sensing and aerial images and laboratory tests we analyzed the characteristics of slope retreat and the failure mechanism of the loess flowslides the retreat of slope is caused by the retrogressive behavior of the loess flowslide of which new failure develops at the backwall of the preceding one the groundwater level variation governs the failure process and mechanism of the flowslides the observed loess flowslides were accompanied by rapid slope deformation high velocity and long runout distance exhibiting liquefaction and fluidization during the movement in the event of a loess flowslide a small scale drained slope failure produces a concave recession first intensifies localized groundwater flow on the slope surface while the flow is being impeded by the deposit which produces an undrained condition with increasing localized pore water pressure and in turn facilitates the subsequent flowslide results of the isotropically consolidated undrained triaxial tests icu and constant shear stress drained triaxial tests csd revealed the strain softening behavior in the saturated reconstituted loess and they showed that the excess pore water pressure is associated with a small axial displacement and possibly facilitated by some alternations in the loess structure at the micro scale

eemian and early weichselian temperature and precipitation variability in northern germany abstract dramatic changes in european vegetation occurred during the transition from the eemian interglacial to weichselian glacial climates correlative with major changes in global ice core and marine records quantitative knowledge of climate change is important for understanding of the climate system and for climate modelling for which reconstructions of this transitional period are of special interest however it has been difficult to quantify the climatic changes involved in the eemian to early weichselian transition from terrestrial archives due to the lack of modern vegetation analogues to circumvent this problem we applied a suitable multivariate probabilistic approach to pollen and plant macrofossil assemblages to reconstruct temperature and precipitation for this transition in central europe our reconstructions span the interval from the beginning of the eemian marine isotope stage mis 5e to the odderade interstadial mis 5a they indicate a relatively stable eemian with increasing precipitation reducing the continentality of the climate with time during the transition from the eemian to the herning stadial mean july and january temperatures decreased by 4 c and by as much as 20 c respectively temperatures remained high enough to support forests during the stadials and we infer that the reconstructed decrease of precipitation below 500 mm per year caused the extirpation of forests during these periods thus we conclude that precipitation although difficult to reconstruct is of vital importance for explaining vegetation change during the eemian and eemian early weichselian transition

loess rock sediment or soil what is missing for its definition abstract loess is commonly defined as an accumulation of windblown silt however the complex mechanisms that are responsible for most of the structural characteristics of loess require a more precise explanation the common definition of loess ignores a set of processes that start during and after the subaerial deposition of silt the term loessification has been used by a number of authors to refer to the quasi pedogenic quasi diagenetic processes that result in the typical aggregation of loess however these mechanisms are rarely described in detail depending on the researcher s background loess is classified as sediment soil or rock this review gives an overview on loess definitions through time and evaluates the main concepts related to loess formation several gaps of knowledge are identified that require a number of specific studies related to different aspects of loess formation in various environments we propose to 1 differentiate primary loessification which initializes the formation of loess structure from secondary loessification which takes place subsequently and 2 define loess like sediments as deposits that experienced loessification but were not transported aeolian mainly aeolian processes and loessification are of equal importance to define loess

physical and mechanical properties of loess discharged from the yellow river into the bohai sea china abstract chinese loess is unique in having great scientific value whilst also playing an important role in societal development large volumes of loess are continually carried by the yellow river from the chinese loess plateau to the bohai sea northeast china forming the yellow river delta the physical and mechanical properties of this loess vary during transportation and these characteristics have been investigated in detail using several samples of estuarine loess collected from tidal flats with different depositional ages the wet densities natural moisture contents specific gravities atterberg limits grain size distributions microstructures and mineral compositions of these samples have been determined our results show that the estuarine loess is classified as silty loess and that its specific gravity plasticity and grain size characteristics were very similar to land derived loess its unit weight and water content increasd during discharge into the sea and its plastic index decreased the estuarine loess also had fewer large pores that were more closely connected than those in land loess as a result of these changes in index properties and pore water chemistry estuarine loess is less susceptible to liquefaction than land derived loess in addition these physical and mechanical properties show strong correlations to the long term depositional history of the delta with older deposits typically having a lower dry density and higher void ratio than younger deposits the results of this study have implications for hazard mitigation and improving our understanding of the mechanisms responsible for loess related geological disasters

development and evolution of loess vertical joints on the chinese loess plateau at different spatiotemporal scales abstract the vertical joints of aeolian loess are ubiquitous on the chinese loess plateau clp the distribution variability of which mainly depends on the differences in structural characteristics of loess water drivers e g rainfall or irrigation loess strata e g sedimentary depth and microtopography this study conducted extensive field investigation and experiments to enhance the understanding of morphologies cross scale transformation mechanism and structural bases of loess vertical joints lvjs moreover the development and evolution processes of lvjs were refined by considering loess sedimentary dynamics results show that 1 lvjs are the product of diagenesis in loess strata during loess historical sedimentary process 2 the pore concentration zones and vertical tubular channels in loess are the structural bases of forming original vertical joints ovjs at the micro mesoscale which is supported by the results from the three dimensional computing tomography ct scanning and scanning electron microscopy sem tests and 3 the morphologies of lvjs vary with the microtopography at different spatiotemporal scales and is characterized by the cross scale transformation mechanism i e that they could transform up i e an expansion behavior or down i e a degradation behavior at the micro meso and sub macro scales under the influences of dry wet cycles loess pile thickening and exogenic forces besides we also propose the development and evolution mechanism of ovjs in loess from the viewpoint of unsaturated loess which would help understand the loess anisotropic genesis structural evolution preferential flow and the occurrence of geohazards such as landslides and soil erosion

thermoluminescence dating of late devensian loesses in southern england scattered across southern england are many isolated deposits of loess like material1 a few such as that at pegwell bay in kent are highly calcareous and unweathered but most have been reworked by fluvial or colluvial processes there is good stratigraphical evidence for a few pre devensian loesses also in kent but dating of more recent loess has so far been based on indirect evidence much work has been done on the pegwell bay loess as it is the most extensive truly aeolian loessic deposit in britain kerney2 compared the late devensian deposits in the isle of thanet and at pegwell bay with similar deposits in holland and belgium where radiocarbon dates have been obtained for interstadial deposits correlation of the east kent deposits with these in northern europe indicates that the loesses in kent were formed between 30 000 and 14 000 yr ago i report here dates for six of the more recent deposits in southern britain from the scilly isles to kent the dates have been obtained on the loess itself using a recently developed thermoluminescence tl dating technique3 4 and confirm the ages as being late devensian

quantitative interpretation of fossil pollen spectra dissimilarity coefficients and the method of modern analogs abstract dissimilarity coefficients measure the difference between multivariate samples and provide a quantitative aid to the identification of modern analogs for fossil pollen samples how eight coefficients responded to differences among modern pollen samples from eastern north america was tested these coefficients represent three different classes 1 unweighted coefficients that are most strongly influenced by large valued pollen types 2 equal weight coefficients that weight all pollen types equally but can be too sensitive to variations among rare types and 3 signal0to noise coefficients that are intermediate in their weighting of pollen types the studies with modern pollen allowed definition of critical values for each coefficient which when not exceeded indicate that two pollen samples originate from the same vegetation region dissimilarity coefficients were used to compare modern and fossil pollen samples and modern samples so similar to fossil samples were found that most of three late quaternary pollen diagrams could be reconstructed by substituting modern samples for fossil samples when the coefficients indicated that the fossil spectra had no modern analogs then the reconstructed diagrams did not match all aspects of the originals no modern analogs existed for samples from before 9300 yr b p at kirchner marsh minnesota and from before 11 000 yr b p at wintergreen lake michigan but modern analogs existed for almost all holocene samples from these two sites and brandreth bog new york

pollen based palaeoclimate reconstructions over long glacial interglacial timescales methodological tests based on the holocene and mis 5d c deposits at sokli northern finland palaeoclimatic reconstructions over long glacial interglacial timescales present major methodological challenges as calibration methods based on modern climate and vegetation patterns may yield biased reconstructions from non analogue palaeoclimates such as severely continental glacial periods in this work we present pollen based summer temperature reconstructions based on holocene and early weichselian marine isotope stages mis 5d c deposits at sokli northern finland we attempt to improve the robustness of reconstructions of continental palaeoclimates by using two calibration sets with one located in the region surrounding the fossil site and another in a more continental region in northwestern russia we assess the reliability of the reconstructions by estimating the compositional fit between fossil and calibration samples and by comparison with independent plant macrofossil based reconstructions we find the fossil samples to fit the extra regional high continentality calibration set better during the early holocene and mis 5d c especially in mis 5d c however even the high continentality calibration set fits the fossil samples poorly compared to the fit achieved in the mid and late holocene thus our results highlight the problem of finding applicable calibration data for pre holocene periods we finally discuss the relative strengths and vulnerabilities of different calibration methods in reconstruction of non analogue palaeoclimates copyright 2013 john wiley sons ltd

prediction of the wetting induced collapse behaviour using the soil water characteristic curve abstract collapsible soils go through three distinct phases in response to matric suction decrease during wetting pre collapse phase collapse phase and post collapse phase it is reasonable and conservative to consider a strain path that includes a pre collapse phase in which constant volume is maintained and a collapse phase that extends to the final matric suction to be experienced by collapsible soils during wetting upon this assumption a method is proposed for predicting the collapse behaviour due to wetting to use the proposed method two parameters critical suction and collapse rate are required the former is the suction value below which significant collapse deformations take place in response to matric suction decease and the later is the rate at which void ratio reduces with matric suction in the collapse phase the value of critical suction can be estimated from the water entry value taking account of both the microstructure characteristics and collapse mechanism of fine grained collapsible soils the wetting soil water characteristic curve thus can be used as a tool five sets of data of wetting tests on both compacted and natural collapsible soils reported in the literature were used to validate the proposed method the critical suction values were estimated from the water entry value with parameter a that is suggested to vary between 0 10 and 0 25 for compacted soils and to be lower for natural collapsible soils the results of a field permeation test in collapsible loess soils were also used to validate the proposed method the relatively good agreement between the measured and estimated collapse deformations suggests that the proposed method can provide reasonable prediction of the collapse behaviour due to wetting

loessic silt deposits in the western himalayas their sedimentology genesis and age abstract loess is abundant in the foreland basins of the himalayas however it is poorly developed within the intermontane basins of the western himalayas and karaloram selected sections were studied from the swat himalaya and the karakoram mountains fieldwork and sedimentological analysis including grain size mineralogy and microfabric showed that the loessic sediments have been reworked and some have undergone weak pedogeneses these silts are not true loess rather a loessic colluvium thermoluminescence tl dates from the loessic sediments in sections from the swat valley provided younger ages than earlier workers had suggested this is consistent with reworking of the loess in these areas it is concluded that care must be taken when using loessic silts for tl in similar mountainous terranes

influence of topography and volume on mobility of loess slides within different slip surfaces mobility of loess slides has been evaluated using an empirical approach based on a detailed field investigation and remote sensing image interpretation for all the loess slides the affected area increases with increasing loess slides volume from the statistical analysis it is seen that the travel distance has an increasing trend while the coefficient of friction has a decreasing trend with the increase in landslide volume landslide volume determine its travel distance and coefficient of friction that can be shown with a regression equation having simple power law form which indicates that the mobility of loess slides increases with increasing volumes by analogy the greater the energy of the sliding loess mass the stronger is the mobility of loess slide a plot of the travel distance of loess slide versus fall height shows a significant positive power law correlation indicating the increase in mobility of loess slide with fall height the negative power law correlation observed between the travel distance and slope inclination implies that the mobility decreases with the increase of slope inclination three datasets of loess slides characterized by different slip surfaces were distinguished the red clay contact landslides have the strong mobility than landslides in loess and bedrock contact

the distribution and geotechnical properties of loess soils lateritic soils and clayey soils in china in china various soils covering vast regions occur loess soils of the yellow river in northern china lateritic soils in southern china and clayey soils in central china the special geotechnical properties of these soils are briefly described the relationship of their material components and microstructural features with their geotechnical properties is studied it is shown that the special geotechnical properties of these soils depend mainly on their material component and microstructural features the distribution of these soils is studied in relation to geographical environment and climatic conditions it is suggested that the formation of the geotechnical properties of these soils have undergone three different development stages

a review of the geotechnical characteristics of loess and loess derived soils from canterbury south island new zealand abstract loess and loess derived soils cover much of canterbury from the foothills of the southern alps to the pacific coast these deposits are of variable thickness from a few metres up to 40 m at the base of slopes on banks peninsula in many areas the primary air fall loess has been reworked by slope processes to form a loess colluvium although primarily silty these soils contain up to 45 clay giving rise to low plasticity clay behaviour these deposits are relatively dense with dry densities of 1 6 t m3 and 1 8 t m3 hence they do not display collapse behaviour common to other loess deposits around the world loess and loess derived soils across canterbury have high dry strength but weaken rapidly with small increases in moisture content in the wetter parts of the region on banks peninsula in particular periodic wetting leads to a variety of slope failures related to internal erosion tunnel gullying and rapid loss of shear strength debris flows soil slides and rotational failure elsewhere in the drier parts of south canterbury loess deposits commonly form vertical exposures and evidence of slope instability is comparatively rare the current understanding of the geotechnical characteristics of these deposits is based on a limited number of studies with restricted geographic extent thus a full understanding of regional and stratigraphic variability is yet to be established macroscale heterogeneities including fissuring development of fragipan cemented horizons and stratification indicates that as well as the general behaviour presented in this paper there may also be significant local variation in addition the effects of soil microstructure including bonding and particle shape and orientation on overall soil behaviour are recognised but have yet to be investigated in detail

variations in loess and palaeosol properties as indicators of palaeoclimatic gradients across the loess plateau of north china abstract new data are presented on micromorphology magnetic susceptibility and particle size characteristics of three soil sediment units at four locations along a wnw ese transect across the loess plateau of north china differences and spatial trends are used to assess the sensitivity of such data as proxies of regional palaeoclimatic gradients the steepest climatic gradient suggested by the magnetic susceptibility for the s1 palaeosol is at the eastern humid end of the traverse micromorphology and particle size analysis show that the loess units in the east are richer in clay than the best developed palaeosols in the semi arid west and that particle size in the west appears to provide a more sensitive record of climatically driven changes than magnetic susceptibility the use of surface and near surface soils as a datum for inferring palaeoprecipitation values is reviewed in the light of recent evidence of substantial degradation of such soils micromorphological and particle size analysis of closely spaced samples from loess palaeosol sequences is a sensitive addition to magnetic susceptibility stratigraphy and correlation

analysis of factors influencing tunnel deformation in loess deposits by data mining a deformation prediction model abstract due to the special properties of loess the deformation of tunnels constructed in loess is generally large and easily induced to control deformation during construction the degree of influence of multiple factors on tunnel deformation is analyzed by data mining and a deformation prediction model is established based on tunnels along the menghua railway of china both objective environment and manual operation are considered the surrounding rock level groundwater condition burial depth excavation method and support close time are selected as the main factors influencing tunnel deformation the influence degree of each factor is calculated through mining statistical data collected from the project finally using influencing factors as evaluation indices a rough set extension model for predicting loess tunnel deformation is established and tested results obtained via the prediction model are in good agreement with field observations the study quantifies the influence degree of each selected factor on deformation of the loess tunnel which in turn can help in deformation control efforts moreover the rough set extension model realizes a multi criteria prediction of the loess tunnel s deformation and provides a practical guide for construction of similar projects

pollen inferred palaeoclimate reconstruction in the alps during the lateglacial and the early holocene how to estimate the effect of elevation and local parameters the modern analogue technique mat was applied to six pollen sequences from the belledonne massif northwestern french alps to estimate the effect of altitude and local parameters on pollen based climate reconstruction during the lateglacial and the early holocene the six sites le vivier 345 m a s l les etelles 700 m a s l la coche 980 m a s l montendry 1330 m a s l le grand leyat 1660 m a s l la gouille 1800 m a s l are located in different vegetation belts mixed deciduous woods conifer woods alpine pastures with maple the main vegetation changes in the past are recorded at each site the evolution of four climate parameters coldest month temperature warmest month temperature mean annual temperature annual precipitation was quantitatively inferred from pollen data using mat the curves obtained were compared to the les etelles site which was the least affected by non local pollen transport the results show consistent trends for the climate parameters reconstructed at the different sites however the reconstruction does not indicate a decrease in temperature values related to the increasing elevation difficulties in reconstructing the altitudinal variations of climate parameters from pollen data during the periods studied are discussed and perspectives for improvement are considered copyright 2009 john wiley sons ltd