structural characterization of natural loess and remolded loess under triaxial tests this paper characterizes the microstructural evolution of saturated natural loess from a site in jingyang china during triaxial test along two stress paths for comparison the same soil in remolded state is also characterized mercury intrusion porosimetry mip scanning electron microscopy sem and environmental scanning electron microscopy esem were used for the microstructure investigation results show that the microstructure of natural loess is similar to that of remolded loess before the consolidated undrained cu triaxial tests including conventional triaxial compression ctc test and reduced triaxial compression rtc test on the contrary their microstructures are different after the tests deeper examination shows that loading led to a significant change of inter aggregate pores without modifying the intra aggregate pores in addition the volume of inter aggregate pores after the rtc test is greater than that after the ctc test under the same consolidation stress the microstructure features of natural and remolded loess after the tests are further used to analyze the macro mechanical behavior for better understanding the relationship between them the results show that it is the cementation bonds of which breakage is influenced by stress path and confining pressure that play important roles in the strength and deformation behavior

a new method for evaluating loess collapsibility and its application abstract collapsibility affects loess engineering stability currently there are two methods used to determine the collapsibility of loess the traditional indoor collapsibility test indoor test method and the field immersion test field test method however for the same loess site the collapse values under overburden pressure obtained by the two methods are quite different for sites that cannot be tested in situ it is easy to misjudge the collapsibility of the loess foundation when depending only on indoor test results to improve the accuracy of the indoor collapsibility determination the characteristics of the compression curves obtained from confined compression tests at six different loess sites are analyzed in this paper the compression curves of loess under different states are normalized and described by the composite power exponential model the collapsibility of loess is closely related to its structure a new method for analyzing and evaluating the collapsibility of loess is proposed the method combines the relationship between the compression characteristics and initial structural properties of loess and the relationship between the initial structural properties and physical comprehensive indexes to verify the applicability and accuracy of the new method the collapse values under overburden pressure of two test sites along the xi an metro line 5 were calculated using the physical indexes of loess at different depths and compared with the values calculated from the indoor test and field measured values the results show that the calculated value of the new method is closer to the measured value of the field test than is the calculated value of the indoor test and the new method can correctly determine the collapsibility type and grade of the site the new method provides a simple and feasible means by which to correctly and quickly evaluate site collapsibility in loess engineering which is beneficial for conducting loess site collapsibility evaluations under full operation to develop and implement the measures of foundation treatment in loess areas the method can be used as a reference at loess sites where field tests cannot be performed

particle packing from an earth science viewpoint abstract particle packings are relevant to many aspects of the earth sciences and there is a long history of the study of packings from an earth science viewpoint packings have also been studied in connection with other subjects and disciplines allen 1982 produced a major review which provides a solid base for earth science related studies this review complements allen s work and in particular focuses on advances in the study of random packings over the last ten years transitions from packing to packing may be as important as the packings themselves and possibly easier to model this paper places emphasis on certain neglected works in particular morrow and graves 1969 and the packing transition envelope kahn 1956 and the measurement of packing parameters griffiths 1962 on packings in one dimension and getis and boots 1978 on packings in two dimensions certain packing problems are relevant to current areas of study including structure collapse in loess hydroconsolidation flowslides in very sensitive soils wind erosion jewel quality in opals and the structure and functions of sand dunes the region where interparticle forces become active particles

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

three dimensional geological structures and sliding factors and modes of loess landslides loess environments such as the chinese loess plateau are geologically fragile because of their great thickness loose structure crisscrossing ravines and gullies broken terrain dry climate severe erosion and unevenly distributed rainfall as a consequence loess areas are highly prone to environmental problems and geological hazards the geological structure of the loess is one of the main factors that controls occurrence of these geohazards this study investigated the mechanism of loess landslides and their sliding control mode from the perspective of their geological structure using this mechanism a three dimensional geological model of loess landslides was established the study shows that the structural planes in loess divide a complete slope into separate blocks which enables the fast and deep infiltration of surface water via seepage channels and reduces the shear strength of the soil mass inducing landslides the development and formation of loess landslides are primarily controlled by structural planes and influenced by infiltrated water softening the structural plains various types of structural planes may combine and form structural bodies of different types and scales which control the type depth and scale of loess landslides

a deep convective chimney in the winter greenland sea 1 during two cruises to the greenland sea in winter 2001 a narrow convective chimney extending from the surface to a depth exceeding 2400 meters was discovered and mapped in detail the feature was observed to be stable over a period of a month and its centre moved only 700 m in that time its diameter was only 10 km at a time when deep convection is thought to have ceased in the greenland sea the existence of this feature is a challenge to our understanding of the causes and impacts of open ocean winter convection

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

preface to the special issue on loess engineering properties and loess geohazards this paper was published in the journal engineering geology and the definitive published version is available at https doi org 10 1016 j enggeo 2017 11 017

factors controlling sediment yield from small intensively cultivated catchments in a temperate humid climate abstract data on sediment yield from 26 small cultivated catchments 10 10 000 ha in central belgium were collected based on sedimentation rates in small flood retention ponds area specific sediment yield varies from 0 4 to 20 6 t ha 1 year 1 for catchments ranging from 7 to 4873 ha various catchment properties were analysed in order to understand this large variation in sediment yield catchment area alone explains 64 of the observed variance in area specific sediment yield although no other parameter could explain more it is concluded that catchment area is not a valid parameter to link with sediment yield overall catchment geomorphology e g presented by the hypsometric integral is much more important in controlling sediment yield the lack of data however made this not very clear a multiple regression model including three morphological catchment properties is a valuable tool to predict total sediment yield t year 1 from catchments in central belgium this model has an efficiency of 0 81 furthermore it was concluded that the within catchment spatial distribution of parameters for instance slope steepness is very important but difficult to obtain one single representative value the use of spatially distributed erosion and sediment delivery models is therefore necessary accurate sediment yield data like the one presented in this study however are needed to validate these models

mantle dynamics uplift of the tibetan plateau and the indian monsoon convective removal of lower lithosphere beneath the tibetan plateau can account for a rapid increase in the mean elevation of the tibetan plateau of 1000 m or more in a few million years such uplift seems to be required by abrupt tectonic and environmental changes in asia and the indian ocean in late cenozoic time the composition of basaltic volcanism in northern tibet which apparently began at about 13 ma implies melting of lithosphere not asthenosphere the most plausible mechanism for rapid heat transfer to the midlithosphere is by convective removal of deeper lithosphere and its replacement by hotter asthenosphere the initiation of normal faulting in tibet at about 8 3 ma suggests that the plateau underwent an appreciable increase in elevation at that time an increase due solely to the isostatic response to crustal thickening caused by india s penetration into eurasia should have been slow and could not have triggered normal faulting another process such as removal of relatively cold dense lower lithosphere must have caused a supplemental uplift of the surface folding and faulting of the indo australian plate south of india the most prominent oceanic intraplate deformation on earth began between about 7 5 and 8 ma and indicates an increased north south compressional stress within the indo australian plate a tibetan uplift of only 1000 m if the result of removal of lower lithosphere should have increased the compressional stress that the plateau applies to india and that resists india s northward movement from an amount too small to fold oceanic lithosphere to one sufficient to do so the climate of the equatorial indian ocean and southern asia changed at about 6 9 ma monsoonal winds apparently strengthened northern pakistan became more arid but weathering of rock in the eastern himalaya apparently increased because of its high altitude and lateral extent the tibetan plateau provides a heat source at midlatitudes that should oppose classical symmetric hadley circulation between the equator and temperate latitudes and that should help to drive an essentially opposite circulation characteristic of summer monsoons for the simple case of axisymmetric heating no dependence on longitude of an atmosphere without dissipation theoretical analyses by hou lindzen and plumb show that an axisymmetric heat source displaced from the equator can drive a much stronger meridianal monsoonlike circulation than such a source centered on the equator but only if heating exceeds a threshold whose level increases with the latitude of the heat source because heating of the atmosphere over tibet should increase monotonically with elevation of the plateau a modest uplift 1000 2500 m of tibet already of substantial extent and height might have been sufficient to exceed a threshold necessary for a strong monsoon the virtual simultaneity of these phenomena suggests that uplift was rapid approximately 1000 m to 2500 m in a few million years moreover nearly simultaneously with the late miocene strengthening of the monsoon the calcite compensation depth in the oceans dropped plants using the relatively efficient c4 pathway for photosynthesis evolved rapidly and atmospheric co2 seems to have decreased suggesting causal relationships and positive feedbacks among these phenomena both a supplemental uplift of the himalaya the southern edge of tibet and a strengthened monsoon may have accelerated erosion and weathering of silicate rock in the himalaya that in turn enhanced extraction of co2 from the atmosphere thus these correlations offer some support for links between plateau uplift a downdrawing of co2 from the atmosphere and global climate change as proposed by raymo ruddiman and froehlich mantle dynamics beneath mountain belts not only may profoundly affect tectonic processes near and far from the belts but might also play an important role in altering regional and global climates

numerical study on signatures of atmospheric convective cells in radar images of the ocean current and wind variations at the ocean surface can give rise to a modulation of the sea surface roughness and thus become visible in radar images the discrimination between radar signatures of oceanic and atmospheric phenomena can be quite difficult since signatures of different origin can have very similar shapes and magnitudes and are often superimposed upon each other in this work we employ a numerical radar imaging model for an investigation of typical properties of radar signatures of atmospheric convective cells and of theoretical differences between such atmospherically induced radar signatures and those of oceanic phenomena we show that main characteristics of observed multifrequency multipolarization radar signatures of atmospheric convective cells over the gulf stream are reproduced quite well by the proposed model this encourages us to vary wind and radar parameters systematically in order to get a general overview of the dependency of atmospherically induced radar signatures on these parameters finally we compare typical characteristics of radar signatures of atmospheric and oceanic phenomena and we present simulated radar images of a scenario of superimposed atmospheric convective cells and oceanic internal waves we show that the proposed model supports the experimental finding that radar signatures of oceanic phenomena are stronger at horizontal hh than at vertical vv polarization while atmospherically induced radar signatures are better visible at vv polarization

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

intrinsic dynamics and long term evolution of a convectively generated oceanic vortex in the greenland sea 1 nonstationary dynamics realistic long term evolution and influence on local convection characterizing an oceanic vortex similar to those observed in the central greenland sea were investigated using in situ data a hierarchy of numerical models and an analytical theory a non hydrostatic model for the simulation of convective plumes was nested into a regional ocean ice model forced and initialized by a global atmosphere ocean ice model in the central greenland sea water masses similar to those observed in a convectively generated vortex and a corresponding numerically reconstructed 3d velocity were imposed in the non hydrostatic model under atmospheric oceanic realistic conditions and forcing the simulated vortex evolved as an almost circular nonstationary long lived predominantly anticyclonically rotating feature as time elapsed it detached from the sea surface and became an intermediate vortex which influenced the local convective preconditioning its inertial pulsations shape and velocity structure closely resemble corresponding characteristics of recently discovered theoretic nonstationary anticyclones

identification of spatio seasonal hydrogeochemical characteristics of the unconfined groundwater in the red river delta vietnam abstract groundwater has been the primary source of daily water supplies for people living in the red river delta the second largest delta in vietnam for this reason identification of hydrogeochemical properties of the groundwater is indispensable for sustainable utilization of groundwater sources in this study the spatio seasonal hydrogeochemical characteristics of groundwater in the unconfined aquifer of the red river delta have been investigated by systematically applying self organizing maps som and gibbs diagrams the groundwater chemistry dataset used in the analysis is composed of eight major dissolved ions i e ca2 mg2 na k hco 3 cl so 4 2 and co 3 2 and total dissolved solids that are collected from 47 groundwater monitoring wells within the study area during the dry and rainy seasons the som application classified the hydrogeochemical data into five clusters which revealed three basic representative water types high salinity one cluster low salinity two clusters and freshwater two clusters the spatial distribution of clusters and water types were identified in particular the low salinity type was found not only in the downstream area but also in the northeastern parts of the upstream and middle stream areas where the groundwater was mainly classified into one specific cluster in which agricultural activities were considered to influence groundwater chemistry cluster changes from the dry to rainy seasons were detected in approximately one fifth of the observations wells dilution by surface water may significantly affect the chemical characteristics of the unconfined aquifer during the rainy season based on gibbs diagrams rock weathering was found to be the main process in the evolution of chemical composition of freshwater type whereas the chemical structure of the low and high salinity types was primarily controlled by saltwater intrusion or anthropogenic activities

centrifuge model testing of a loess landslide induced by rising groundwater in northwest china abstract considerable artificial irrigation in the heifangtai area has caused the continued rise of groundwater levels which has resulted in several large scale landslides in the loess platform area considering the no 13 landslide of jiaojia in the heifangtai area as a geological archetype a series of centrifuge tests was conducted to study the deformation and failure characteristics of the slope due to the continuous rise in the groundwater level meanwhile the pore water pressure earth pressure deformation and evolution characteristics of the slope were monitored and recorded in real time furthermore isotropically consolidated undrained triaxial testing icu was conducted to investigate the static liquefaction of loess specimens which was related to the slope instability the centrifuge test results showed that a series of parallel and steep tension cracks at the top of the slope were present before the landslide which was caused by the rising groundwater the icu experimental results showed that as the pore water pressure increased strong strain softening and static liquefaction of saturated loess soils were found which was related to the sudden destruction of the slope

on the remote sensing of oceanic and atmospheric convection in the greenland sea by synthetic aperture radar 1 in this paper we discuss characteristic properties of radar signatures of oceanic and atmospheric convection features in the greenland sea if the water surface is clean no surface films or ice coverage oceanic and atmospheric features can become visible in radar images via a modulation of the surface roughness and their radar signatures can be very similar for an unambiguous interpretation and for the retrieval of quantitative information on current and wind variations from radar imagery with such signatures theoretical models of current and wind phenomena and their radar imaging mechanisms must be utilized we demonstrate this approach with the analysis of some synthetic aperture radar sar images acquired by the satellites ers 2 and radarsat 1 in one case an ers 2 sar image and a radarsat 1 scansar image exhibit pronounced cell like signatures with length scales on the order of 10 20 km and modulation depths of about 5 6 db and 9 10 db respectively simulations with a numerical sar imaging model and various input current and wind fields reveal that the signatures in both images can be explained consistently by wind variations on the order of 2 5 m s but not by surface current variations on realistic orders of magnitude accordingly the observed features must be atmospheric convection cells this is confirmed by visible typical cloud patterns in a noaa avhrr image of the test scenario in another case the presence of an oceanic convective chimney is obvious from in situ data but no signatures of it are visible in an ers 2 sar image we show by numerical simulations with an oceanic convection model and our sar imaging model that this is consistent with theoretical predictions since the current gradients associated with the observed chimney are not sufficiently strong to give rise to significant signatures in an ers 2 sar image under the given conditions further model results indicate that it should be generally difficult to observe oceanic convection features in the greenland sea with ers 2 or radarsat 1 sar since their signatures resulting from pure wave current interaction will be too weak to become visible in the noisy sar images in most cases this situation will improve with the availability of future high resolution sars such as radarsat 2 sar in fine resolution mode 2004 and terrasar x 2005 which will offer significantly reduced speckle noise fluctuations at comparable spatial resolutions and thus a much better visibility of small image intensity variations on spatial scales on the order of a few hundred meters index terms 3314 meteorology and atmospheric dynamics convective processes 4275 oceanography general remote sensing and electromagnetic processes 0689 4279 oceanography general upwelling and convergences 4255 oceanography general numerical modeling

hillslope chemical weathering across parana brazil a data mining gis hybrid approach article i nfo self organizing map som and geographic information system gis models were used to investigate the nonlinear relationships associated with geochemical weathering processes at local 100 km 2 and regional 50 000 km 2 scales the data set consisted of 1 22 b horizon soil variables p c ph al total acidity ca mg k total cation exchange capacity sum of exchangeable bases base saturation cu zn fe b s mn gammaspectrometry total count potassium thorium and uranium and magnetic susceptibility measures and 2 six topographic variables elevation slope aspect hydrological accumulated flux horizontal curvature and vertical curvature it is characterized at 304 locations from a quasi regular grid spaced about 24 km across the state of parana this data base was split into two subsets one for analysis and modeling 274 samples and the other for validation 30 samples purposes the self organizing map and clustering methods were used to identify and classify the relations among solid phase chemical element concentrations and gis derived topographic models the correlation between elevation and k means clusters related the relative position inside hydrologic macro basins which was interpreted as an expression of the weathering process reaching a steady state condition at the regional scale locally the chemical element concentrations were related to the vertical curvature representing concave convex hillslope features where concave hillslopes with convergent flux tends to be a reducing environment and convex hillslopes with divergent flux oxidizing environments stochastic cross validation demonstrated that the som produced unbiased classifications and quantified the relative amount of uncertainty in predictions this work strengthens the hypothesis that at b horizon steady state conditions the terrain morphometry were linked with the soil geochemical weathering in a two way dependent process the topographic relief was a factor on environmental geochemistry while chemical weathering was for terrain feature delineation

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

provenance of loess material and formation of loess deposits on the chinese loess plateau abstract results of a multiple isotopic chemical and mineralogical analysis of loess from the three northwestern inland basins the junggar basin the tarim basin and the qaidam basin and the loess plateau region of china are summarized they suggest a qualification of the conventional views that the three northwestern basins were the important source areas of the loess plateau and that the sand deserts were the primary single source of the chinese loess it is argued that the gobi stony desert in southern mongolia and the adjoining gobi and sand deserts the badain jaran desert tengger desert ulan buh desert hobq desert and mu us desert in china rather than the three inland basins are the dominant source areas of the loess plateau however although these gobi and sand deserts are regarded as the main source regions they serve as dust and silt holding areas rather than dominant producers the mountain processes including glacial grinding frost weathering salt weathering tectonic processes and some fluvial comminution in the gobi altay mts hangayn mts and the qilian mts have played an important role in producing the vast amounts of loess sized material for forming the loess plateau

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

coexistence of atmospheric gravity waves and boundary layer rolls observed by sar abstractboth atmospheric gravity waves agw and marine atmospheric boundary layer mabl rolls are simultaneously observed on an environmental satellite envisat advanced synthetic aperture radar asar image acquired along the china coast on 22 may 2005 the synthetic aperture radar sar image covers about 400 km 400 km of a coastal area of the yellow sea the sea surface imprints of agw show the patterns of both a transverse wave along the coastal plain and a diverging wave in the lee of mount laoshan 1133 m peak which indicate that terrain forcing affects the formation of agw the agw have a wavelength of 8 10 km and extend about 100 km offshore model simulation shows that these waves have an amplitude over 3 km finer scale 2 km brushlike roughness features perpendicular to the coast are also observed and they are interpreted as mabl rolls the fft analysis shows that the roll wavelengths vary spatially the two way interactive triply nested grid 9 3 1 km weather research and forecasti

wind blown origin of the pliocene red clay formation in the central loess plateau china abstract in order to determine the depositional processes of the pliocene red clay formation deposited directly beneath the plio pleistocene loess in the chinese loess plateau four red clay sections spanning over 400 km are studied grain size analysis of closely spaced samples in the sections shows that the particles of the red clay are very fine with the sand fraction 63 m being negligible and that all the curves indicating changes in different grain size parameters have a similar pattern the grain size records in the upper part of the four sections are almost identical with the median grain size centered at 4 8 m the ree patterns of 28 samples from the jiaxian red clay section are all characterized by lree enrichments relatively flat hree and slight negative eu anomaly being similar to those of eolian loess and the average upper continental crust these lines of evidence point to a wind blown origin of the red clay deposits accumulation of the loess soil sequences in the chinese loess plateau during the past 2 6 ma can be therefore regarded as the continuation of the pliocene atmospheric dust deposition observations of spatial grain size changes in the loess plateau suggest that the eolian red clay might be transported mainly by the westerlies differing significantly from the overlying loess that was transported essentially by the east asia winter monsoonal winds

atmospheric boundary layer rolls observed by the synthetic aperture radar aboard the ers 1 satellite two synthetic aperture radar sar images acquired by the european remote sensing satellite ers 1 over the jade weser estuary in the german bight of the north sea on january 2 and 20 1992 are analyzed the images show sea surface manifestations of atmospheric boundary layer rolls this is inferred from the orientation of the quasi periodic sea surface patterns which are aligned approximately with the wind direction from the ratio of the wavelength of the patterns to the height of the boundary layer and from the conditions encountered in the atmospheric boundary layer as measured quasi simultaneously by radiosondes the atmospheric boundary layer rolls were generated by a dynamic instability on january 2 and by a thermal instability on january 20 for the first time quantitative estimates of variations of the wind velocity at the sea surface associated with the atmospheric rolls are extracted from a spaceborne radar sar image it is shown that wind velocities derived from sar image intensity variations are in agreement with theoretical estimates

magnetostratigraphic record of the late miocene onset of the east asian monsoon and pliocene uplift of northern tibet abstract widespread eolian red clay underlying the plio pleistocene loess palaeosol succession in northern china has been dated magnetostratigraphically back to 8 35 ma indicating that the east asian monsoon started at about the same time as the indian monsoon an initial sedimentation rate of 11 m myr increased gradually to 17 5 m myr by 6 ma and then decreased to 6 m myr between 5 ma and 3 5 ma a marked increase in sedimentation rate and grain size beginning between 3 5 ma and 3 1 ma indicates that the east asian winter monsoon strengthened at this time and intensified further after 2 6 ma the temporal coincidence of the stronger winter monsoon and the pliocene uplift of northwestern tibet just before the onset of the northern hemisphere glaciation indicate that the three events could be causally linked

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

characterizing hydrological processes on loess slopes using electrical resistivity tomography a case study of the heifangtai terrace northwest china abstract from the perspective of engineering geology loess has long been considered as a homogeneous and porous material it is commonly believed that water penetrates loess via pores and in some cases causing mass movements however several researchers have expressed doubts about this mechanism as a cause of slope failures in loess and moreover the actual hydrological processes operating in loess deposits and their effect on slope failures have not been fully investigated here we present the results of an electrical resistivity survey of the heifangtai loess terrace in northwestern china designed to characterize the hydrological processes in loess slopes and their relationship with slope failures the heifangtai loess terrace is located on the fourth terrace of the yellow river and consists of 57 m thickness of aeolian loess 2d and 3d electrical resistivity tomography ert was used to monitor the movement of ground water before and after irrigation and rainfall events and the evolution of a sink hole in the toe of the landslide deposits our main findings are as follows 1 based on the 2d ert results the depth of infiltration into the thick unsaturated loess is not more than 5 m in the profile at the top of the landslide 2 electrical resistivity decreased as a result of water infiltration through sinkholes and this process can increase the soil water content and induce soil liquefaction which can eventually result in land sliding 3 landslide deposits block the groundwater drainage channels through the loess which results in the concentration of water in the toe of the landslide consequently groundwater together with rainfall triggers the failure of sinkholes or cracks which may induce a continuing process of new slope failures at the sites of past landslide

experimental case study of seismically induced loess liquefaction and landslide abstract the 1920 haiyuan ms 8 5 earthquake induced a large number of fluidized loess landslides in china characterized by low slope angles long run out distances and fluidized movement the mechanism of these landslides has aroused considerable interest although additional research is needed to understand more fully the behavior of the loess and the failure mechanism field investigation was conducted on the shibeiyuan landslide and loess samples collected for later laboratory analysis by conventional geotechnical tests triaxial compression tests and ring shear tests the field survey revealed that the shibeiyuan landslide occurred on a concave slope

environmental geology in loess areas of china there are several unfavorable geological hazards in the loess area of china the major purposes of environmental geology studies in this region are to expound the causes of these hazards and to determine treatments geological hazards include endemic diseases depletion of groundwater land subsidence ground fissures soil erosion and collapsibility of loess this article is a summary of studies regarding these hazards keshan disease and kaschin beck disease for example can be prevented and cured by adding selenates to table salt ponds can be constructed on the loess plateau and dikes around farmlands to collect rainfall to recharge groundwater resources excess extraction of groundwater is the major cause of land subsidence ground fissures in xi an are primarily caused by tectonics but over extraction of ground water strengthens its activity observation stations should be established in order to forecast and prevent landslides planting trees in a regional shelterbelt is the primary measure necessary to prevent soil erosion as a result of these geological studies valuable experience in preventing collapse of loess in china has been gained

detecting decadal changes in enso using neural networks the present manuscript analyzes monthly equatorial pacific indices by using a specific neural algorithm the so called self organizing maps soms the main result is a change found in the nature of the transitions between cold to warm and warm to cold extreme events from 1950 to present around the late 1970s som is an unsupervised clustering technique which allows one to reduce high dimensional data space in this case three indices over 636 months in terms of a smaller set of three dimensional reference vectors 100 characterizing pertinent situations these reference vectors which are displayed on a two dimension map are closely related by a topological relationship leading us to discriminate la nina conditions from the opposite el nino conditions in a second step a hierarchical agglomerative clustering hac method is used to further group the reference vectors into a small number of clusters 12 whose spatial and temporal characteristics can be analyzed and interpreted in terms of physical parameters schematically these 12 clusters can be divided into two warm clusters six neutral or transition clusters and four cold clusters in each particular group warm neutral cold the clusters mainly differ from each other by the amplitude of the anomalies their spatial patterns and their temporal variability some clusters are found to be strongly linked to the boreal spring period while others have barely any records during that season other clusters are associated with records mainly observed either prior to or after 1980 this suggests that the method is able to identify changes in the variability of the tropical pacific basin observed on decadal time scales 1976 climate shift in our case each monthly record can be summarized by the cluster to which it belongs the temporal evolution of this value during extreme enso events shows similar patterns persistence in specific clusters and transition between groups of clusters associated with comparable el nino or la nina events the methodology described in the present study som plus hac is suggested to be useful both for seasonal enso predictability and for the detection of decadal changes in enso behavior

sediment yield variability in spain a quantitative and semiqualitative analysis using reservoir sedimentation rates an existing dataset of area specific sediment yield ssy for 60 catchments in spain that was retrieved from sediment deposition rates in reservoirs avendano salas c sanz montero e rayan c gomez montana 1997 sediment yield at spanish reservoirs and its relationship with the drainage basin area in proceedings of the 19th symposium of large dams florence 1997 icold international committee on large dams pp 863 874 reveals that catchment area alone explains only 17 of the variability in ssy in this study an attempt to explain the remaining variability in ssy was made using a quantitative and a semiqualitative approach for 22 catchments during a field survey the 22 selected catchments were characterised by topography vegetation cover lithology shape and the presence of gullies in the broad vicinity of the reservoir this information was used to develop a factorial scoring index model that provides a fairly accurate and reliable prediction of ssy a classical multiple regression model using climatic topographic and land use properties derived from regional datasets could not explain as much variance as the qualitative index model nor did it appear to be as reliable the same conclusion could be drawn when using the corine soil erosion risk map of southern europe the low prediction capability of the multiple regression models and the corine soil erosion risk map could be attributed mainly to the fact that these methods do not incorporate gully erosion and that the land cover data are not a good representation of soil cover both variables have been shown to be of great importance during the field surveys future assessments of ssy could be quickly and efficiently made using the proposed factorial scoring index model in comparison with other models which demand more data the index model offers an alternative prediction tool d 2002 elsevier science b v all rights reserved

moisture content effect on the creep behavior of loess for the catastrophic baqiao landslide abstract understanding the creeping behavior of loess is of great importance as large scale loess landslides are closely related with creep behavior at present it is still challenging to predict and estimate the long term stability of such landslides this is in a large degree due to the poor understanding of moisture control on creep behavior of loess the purpose of this study is to decipher the loess creep behavior under various moisture contents mcs using loess specimens obtained from baqiao landslide xi an of china using multi loading triaxial creep tests under different mcs of 9 12 15 18 and 21 based on the laboratory test results a series of relationships between the creep rate at the steady state creep stage and the initial strain and initial shear modulus are revealed meanwhile a method for obtaining the long term strength of loess specimens namely the steady state creep rate slope method scrsm is proposed scrsm resolves the issue in several conventional methods such as the isochronous stress strain curve method the tangent method of steady creep rate when mcs are of concern such an improvement is primarily due to a better way of finding the inflection point of the steady state rate it is found that scrsm is robust and accurate to determine the long term strength of loess specimens furthermore we propose a modified burgers model with a newly introduced nonlinear parameter n to overcome deficiencies of conventional creep models this modified burgers model is flexible to fit the creep test curves of loess and can describe the curves at the accelerated creep stage more accurately lastly the main factors triggering the baqiao landslide is analyzed considering stratum lithology rainfall and excavation in general this study provides a basis for understanding the evolutional process of loess landslides as well as guidelines for prevention controlling and prediction of loess landslides

analysis of earthquake induced groundwater level change using self organizing maps for a better understanding of possible physical links between geophysical observables and earthquake characteristics it is important to analyze statistical spatiotemporal patterns in nature related to such events for this purpose characteristic changes in groundwater level gwl were observed before and after the 2016 kumamoto earthquake in japan previous research has shown that self organizing maps som can be used to classify complex patterns of gwl change during different parts of the earthquake sequence in this study we used before and after earthquake gwl data as input vectors to som in total 64 observed gwls were classified into 12 different clusters most shallow wells displayed gwl difference that was small during the foreshock first earthquake and large during the main shock second earthquake upstream deep wells showed relatively large difference in water level from 1 to 2 days after the earthquakes the gwl rapidly increased just after the earthquake then tended to gradually decrease from september most of the shallow wells in the unconfined aquifer rapidly recovered to initial gwls within several hours to several days because of hydrostatic pressure however most of the deep wells in the confined aquifer needed longer time to recover in some cases several weeks to several months these findings are important for the physical understanding of earthquake effects on the groundwater environment disaster prevention and possibility for development of earthquake precursors

investigation of multifrequency multipolarization radar signatures of rain cells over the ocean using sir c x sar data radar signatures of rain cells are investigated using multifrequency multipolarization synthetic aperture radar sar images acquired from the space shuttle endeavour during the spaceborne imaging radar c x band sar sir c x sar missions in april and october 1994 in sir c x sar images radar signatures of rain cells over the ocean usually consist of irregularly shaped bright and dark patches that strongly depend on radar frequency and polarization the radar signatures of rain cells observed in sir c x sar imagery of the ocean originate from 1 the scattering and attenuation of the microwaves by raindrops and ice particles in the atmosphere and 2 the modification of the sea surface roughness induced by the impact of raindrops and by wind gusts associated with rain cells raindrops impinging on the sea surface generate ring waves which enhance the sea surface roughness but they also generate turbulence in the upper water layer which reduces the sea surface roughness depending on the radar wavelength ocean areas struck by rain can have higher or lower normalized radar cross section nrcs than the surrounding rain free area in ocean areas where heavy rain is impinging on the sea surface the x and c band nrcs is usually enhanced and the l band nrcs is reduced from the phase difference between the horizontally and vertically copolarized signals estimates of the rain rate are obtained the present analysis shows further that the presently used wind speed retrieval algorithms for the scatterometers aboard the ers and adeos satellites may yield biased wind fields if several rain cells lie within a scatterometer resolution cell

evaluation of sedimentation vulnerability at small hillside reservoirs in the semi arid region of tunisia using the self organizing map small hillside reservoirs are fundamental for the sustainability of the water resources in the semi arid region of tunisia where the government has constructed small dams since 1990 however flash floods and severe erosion are jeopardizing the life of those small hydraulic structures prompting an assessment of the vulnerability of semi arid catchments to erosion in this study we investigated the degree of erosion in 23 catchments by considering six variables related to erosion the specific sediment yield the hypsometric integral the topographic index the rainfall related attribute as well as lithological and vegetation cover more importance was assigned to the hypsometric integral and how it controls erosion vulnerability the self organizing map of kohonen a robust clustering method was implemented to analyze the patterns of the six variables the results revealed four groups of catchments with different vulnerabilities to erosion in addition there is a global trend of increasing erosion risk from the southwest to the northeast of the semi arid region of tunisia

human impact on geomorphic processes and hazards in mountain areas in northern spain abstract the temporal occurrence of slope movements their contribution to relief evolution and human influence on those processes in two study areas of northern spain are presented the work is based on temporal analyses covering 100 ka in one study area and 43 years in the other temporal analysis has been the basis for quantitatively assessing the magnitude of human influence and developing landslide susceptibility and hazard models with known independently tested prediction capability the results obtained in one study area show a relationship between landsliding periods and increasing precipitation during upper pleistocene and holocene significant increases of landslide frequency and mobilisation rate were also found around 5500 and 200 years ago those moments coincide with two periods of intensified human presence and activities neolithic and industrial revolutions the increase observed represents about one order of magnitude from pre neolithic to present a similar increase has been found between 1954 and 1997 in the other study area the latter increase shows no relationship with changes in climate parameters or seismic activity a fairly good correlation has been found between landslide frequency and socioeconomic indicators of human activity sedimentation rates in two neighbouring estuaries were determined and significant increases particularly in the second part of last century were also found evidence obtained suggest that the increases observed in the frequency of slope instability events and therefore hazard denudation and sedimentation rates are due to a greater extent to indirect geomorphologic changes caused by human action rather than climate change detailed analysis of landslide frequency during that 43 year period has also been used to produce and validate landslide susceptibility models and obtain landslide hazard maps with known prediction accuracy validation tests were carried out comparing susceptibility maps based on landslides that have occurred in the past with the ones occurring in several later periods prediction capability of models could thus be determined validation of susceptibility maps using data derived from the temporal analysis of landslides was used to obtain hazard maps expressed as probability of new ruptures in a given time period on the basis of past trends in terrain behaviour possible impacts of a growing influence of human activities on the terrain have been incorporated into the assessment of future hazards by considering different scenarios

near isothermal conditions in the middle and lower crust induced by melt migration simple one dimensional thermal models that include the effects of melt migration have been developed the models show that long lived plutonism results in a quasi steady state geotherm with a rapid temperature increase in the upper crust and nearly isothermal conditions in the middle and lower crust the thermal structure of the crust strongly influences deformation metamorphism and plutonism1 2 3 models for the geothermal gradient in stable crust predict a steady increase of temperature with depth this thermal structure however is incompatible with observations from high temperature metamorphic terranes exhumed in orogens1 4 5 6 global compilations7 of peak conditions in high temperature metamorphic terranes define relatively narrow ranges of peak temperatures over a wide range in pressure for both isothermal decompression and isobaric cooling paths here we develop simple one dimensional thermal models that include the effects of melt migration these models show that long lived plutonism results in a quasi steady state geotherm with a rapid temperature increase in the upper crust and nearly isothermal conditions in the middle and lower crust the models also predict that the upward advection of heat by melt generates granulite facies metamorphism and widespread andalusite sillimanite metamorphism in the upper crust once the quasi steady state thermal profile is reached the middle and lower crust are greatly weakened due to high temperatures and anatectic conditions thus setting the stage for gravitational collapse8 exhumation and isothermal decompression after the onset of plutonism near isothermal conditions in the middle and lower crust result from the thermal buffering effect of dehydration melting reactions that in part control the shape of the geotherm

open ocean convection observations theory and models we review what is known about the convective process in the open ocean in which the properties of large volumes of water are changed by intermittent deep reaching convection triggered by winter storms observational laboratory and modeling studies reveal a fascinating and complex interplay of convective and geostrophic scales the large scale circulation of the ocean and the prevailing meteorology two aspects make ocean convection interesting from a theoretical point of view first the timescales of the convective process in the ocean are sufficiently long that it may be modified by the earth s rotation second the convective process is localized in space so that vertical buoyancy transfer by upright convection can give way to slantwise transfer by baroclinic instability moreover the convective and geostrophic scales are not very disparate from one another detailed observations of the process in the labrador greenland and mediterranean seas are described which were made possible by new observing technology when interpreted in terms of underlying dynamics and theory and the context provided by laboratory and numerical experiments of rotating convection great progress in our description and understanding of the processes at work is being made

clustering spatio seasonal hydrogeochemical data using self organizing maps for groundwater quality assessment in the red river delta vietnam summary the red river delta rrd is the second largest delta in vietnam and its local communities depend on groundwater sources for water supply a clear understanding of the groundwater hydrogeochemical properties particularly their changes from the dry to rainy seasons and spatial characteristics is invaluable and indispensable for the management and protection of this important water resource in this study self organizing maps was systematically applied for the first time to investigate the seasonal and spatial hydrogeochemical characteristics of groundwater in the pleistocene confined aquifer of the rrd the hydrogeochemical characteristics clustered by som were further examined using the gibbs diagrams the groundwater chemistry dataset used in the analysis comprised eight major dissolved ions i e ca 2 mg 2 na k hco 3 cl so 4 2 and co 3 2 and total dissolved solids that were collected from 52 groundwater monitoring wells within the study area during the dry and rainy seasons based on the results the hydrogeochemical groundwater data of the confined aquifer monitoring wells for the delta were classified into 8 clusters which revealed three basic representative water types high salinity 2 clusters low salinity 3 clusters and freshwater 3 clusters the high salinity types were located in the middle stream and coastal areas of the rrd while the low salinity types were observed near the western and northeastern boundaries of the delta cluster changes from the dry to rainy seasons were detected in approximately one third of the observation wells the increase in groundwater recharge during the rainy season is the main reason for these changes based on gibbs diagrams the source of soluble ions in the groundwater of the freshwater types was found to be the weathering of rock forming minerals while evaporation and marine activities leaching from salty paleowater and salt water intrusion were found to be the main factors affecting the chemistry of the groundwater characterized by the low and high salinity types respectively

influence of early diagenesis on geotechnical properties of clay sediments romania black sea abstract the geotechnical properties of clay sediments were investigated using laboratory and in situ measurements as part of the geohazard assessment in the romanian sector of the black sea affected by landslides and seafloor deformation features the sediments were characterized as predominantly high plastic silty clay of high compressibility low undrained shear strength low cohesion and moderate sensitivity a shallow increase in shear strength exceeding the general trend could have been reconciled with evidence for the precipitation of iron sulfides and calcium carbonates related to early diagenetic reactions of sulfate reduction e g cryptic sulfur cycle and anaerobic oxidation of methane comparison of the compression behaviour of natural and reconstituted samples indicated that precipitation of these materials at particle contacts produced cementation the analysis of deeper sediments sharing similar geochemical properties illustrated that the early precipitation of even low quantity of sulfur and carbonate cements allowed clays to develop sufficient strength to preserve an abnormal high water content even under tens of meters burial depth because this cementation process was observed to be associated with an enhanced sensitivity and a strain softening response to undrained shearing it was concluded that such early diagenesis should be considered as a key environmental factor leading to weak layer formation that may influence the susceptibility of seafloor to failure

the mechanics of a saturated silty loess and implications for landslides the results from an intensive experimental investigation on a loess that was retrieved from a typical silty loess zone in the north western chinese loess plateau are presented and interpreted triaxial and oedometer tests were performed on intact and reconstituted samples in a saturated condition the soil behavior was found to be strongly affected by structure the compression paths of the intact samples crossed the intrinsic compression line of the reconstituted soil and reached well defined gross yield points after which the compression paths converged towards the intrinsic compression lines two critical state lines were defined for the intact and reconstituted soils in the volumetric plane as a result of a robust element of natural structure comparisons were made with a structured clayey loess retrieved from the south eastern loess plateau it was found that the effects of structure on the behavior of the two loess soils are similar though they are very different in natural properties this indicates that their natural structures might have experienced similar forming processes perhaps related to their common origin catastrophic flowslides commonly occur in the study area and the patterns of behavior observed in the laboratory tests may create some new insights into mechanisms of landslide initiation and subsequent movement as discussed in the study

a study of a flowslide with significant entrainment in loess areas in china flowslides are a frequent type of natural disaster in loess areas and may result in the significant loss of properties and or casualties the dagou flowslide is a typical event in a loess area and is accompanied by significant sediment entrainment to analyze the mechanisms responsible for flowslides and to obtain the parameters for a runout analysis a field investigation was conducted specimens were sampled on site to carry out laboratory tests including a triaxial test sieve analysis and chemical component analysis the parameters were used in the runout study employing an energy based runout model an analytical entrainment model was adopted to calculate the entrainment after considering physical properties and the mechanism of the entrainment process of the loess finally the entrainment model was incorporated into the runout model to simulate the post failure process of this case energy dissipation due to the deformation of slices was considered as it was thought to be important for a slide with a significant deformation the simulation results were compared with the measurements including runout distance total volume erosion depth deposition height at different sections and velocities at specific locations the results indicate that the energy based runout model together with the entrainment model can capture the kinematic characteristics of the dagou flowslide therefore it is feasible to use this model to predict the runout characteristics of flowslides in similar areas copyright c 2017 john wiley sons ltd

comparison of sar derived wind speed with model predictions and ocean buoy measurements as part of the alaska synthetic aperture radar sar demonstration project in 1999 and 2000 wide swath radarsat sar imagery has been acquired on a regular basis in the gulf of alaska and the bering sea during 1998 and 1999 similar data were acquired off the east coast of the united states as part of the stormwatch project the radar cross section measurements from these images were combined with wind direction estimates from the navy operational global atmospheric prediction system model to produce high resolution maps of the surface wind speed for this study 2862 sar image frames were collected and examined averaged wind estimates from this data base have been systematically compared with corresponding wind speed estimates from buoy measurements and model predictions and very good agreement has been found the standard deviation between the buoy wind speed and the sar estimates is 1 76 m s details of the sar wind extraction procedure are discussed along with implications of the comparisons on the c band polarization ratio

climate change loess and palaeosols proxy measures and resolution in north china the loess plateau of north china is a key region for the study of records of quaternary climatic change various techniques to abstract climatically sensitive data were first applied to the classic loess palaeosol site at luochuan and current views on climatic change in asia have been strongly moulded by results from this central part of the loess plateau data including the magnetic susceptibility granulometry mineralogy geochemistry micromorphology fossil content and inorganic and organic carbon content of asian loess palaeosol series have been used singly and in combination as surrogate measures of palaeoclimates to infer climatic changes with particular reference to changes in the asian monsoon some of this work is reviewed and the status of a number of parameters as climatic proxies is discussed some lithostratigraphic sequences from which proxy measures of climate have been derived are incomplete as shown by erosion surfaces water laminated zones and truncated palaeosol profiles while others provide records of relatively low resolution most descriptions of quaternary climatic changes based on studies of the loess emphasize alternations in the relative dominance of warm and moist v cool dry and dust laden monsoons some recent studies of the much higher resolution loess palaeosol successions on the western margins of the loess plateau have suggested that such changes may sometimes be out of phase with the inference that the current climate model is too simple means of testing this hypothesis are proposed

impact of reservoir impoundment caused groundwater level changes on regional slope stability a case study in the loess plateau of western china due to its impact on regional groundwater levels the impoundment of a reservoir is an important consideration for assessing the stability of surrounding slopes this study presents a method for risk assessment and control of landslides in regions where groundwater levels can be affected by reservoir water levels the method is illustrated with a case study of the hongzhuang reservoir in yanan city northern shaanxi province china a groundwater numerical model was developed using modflow and the groundwater flow fields were calculated for different reservoir water levels safety factors were then obtained and the slope stability was analyzed moreover a probabilistic slope analysis was performed by monte carlo simulation to evaluate the reliability of slope stability and the probability of slope failure finally a reasonable reservoir water level was determined according to the acceptable risk level and a comprehensive risk mitigation method was proposed considering water level control relocation and drainage measures

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

mesoscale shallow convection in the atmosphere this paper is a review of the observational experimental theoretical and numerical studies of mesoscale shallow convection msc in the atmosphere typically msc is 1 to 2 km deep has a horizontal length scale of a few to a few tens of kilometers and takes distinctive planforms linear and hexagonal the former is called a cloud street roll or band while the latter is called mesoscale cellular convection mcc comprising three dimensional cells msc is characterized by its shape horizontal extent convective depth and aspect ratio the latter is the ratio of the horizontal extent to that in the vertical for cells the horizontal extent is their diameter whereas for rolls it is their spacing rolls usually align along or at angles of up to 10 from the mean horizontal wind of the convective layer with lengths from 20 to 200 km widths from 2 to 10 km and convective depths from 2 to 3 km the typical value of aspect ratio ranges from 2 to 20 rolls may occur over both water surface and land surfaces mesoscale convective cells may be divided into two types open and closed open cell circulation has downward motion and clear sky in the cell center surrounded by cloud associated with upward motion closed cells have the opposite circulation both types of cell have diameters ranging from 10 to 40 km and aspect ratios of 5 to 50 and both occur in a convective layer with a depth of about 1 to 3 km both the magnitude and direction of horizontal wind in the convective layer change little with height msc results from a complex and incompletely understood mix of processes these processes are outlined and their interplay is examined through a review of theoretical and laboratory analyses and numerical modeling of msc

magnetostratigraphy and paleoclimatic interpretation of a continuous 7 2 ma late cenozoic eolian sediments from the chinese loess plateau an almost 300m thick eolian sequence of late cenozoic sediments which includes 162 5m of quaternary loess paleosols and 126m of late tertiary eolian red clay from the central part of the chinese loess plateau was investigated to determine the magnetostratigraphy the results show that eolian dust accumulation and by inference the related east asia paleomonsoon had begun by 7 2ma as paleomonsoon are largely controlled by the tibetan plateau this implies that the plateau had reached some critical elevation by 7 2ma the section also documents a rapid increase in eolian dust accumulation in the late cenozoic at 3 2ma that is probably due to the influence of global ice volume on the east asian monsoon

a new interpretation of multifrequency multipolarization radar signatures of the gulf stream front radar signatures which are observed on sir c x sar multifrequency multipolarization synthetic aperture radar images of the gulf stream off the u s east coast are compared with results of simulations with a numerical radar imaging model based on in situ data current and wind variations are included into the model as well as a variation of the thermal stability of the marine atmospheric boundary layer across the gulf stream front according to our model predictions all of these parameter variations can cause radar signatures of similar shape and modulation depth but due to specific dependencies of radar signatures on variations of surface currents and winds we show that it is possible to distinguish between radar signatures of oceanic and atmospheric origin in multifrequency multipolarization images and to estimate the corresponding current and wind variations independently for one set of radar images we derive a most likely scenario of oceanic and atmospheric parameters during the time of the image acquisition for which good overall agreement between observed and simulated radar signatures is obtained at most radar channels

temporal patterns of nonseismically triggered landslides in shaanxi province china abstract examination of the temporal patterns of landslide events provides valuable insights into the baseline information used to determine landslide activity and perform risk assessment in a given area we collected a catalog of historical nonseismically triggered landslides that occurred over 22 years in shaanxi province china we found that the annual number of slides was significantly related to the annual number of falls the average annual numbers of slides and falls were approximately 17 and 10 respectively the active and nonactive periods of landslides alternated within the time series of the annual number of landslides an empirical power law correlation exists between the complementary cumulative frequency and the annual number of landslides the monthly distribution of landslide events is significantly associated with monthly rainfall most landslide events occurred in the rainy season between july and october the average time intervals of falls and slides from july to october were approximately 12 days and 8 days respectively moreover the temporal distribution of landslide events is clustered owing to the impact of nonuniformly distributed rainfall activities most of the landslides concentrated in one or two months of a year furthermore the nonzero values in the landslide time series are nonuniformly spaced the complementary cumulative frequency distribution of the time intervals between landslide events can be adequately fitted by an exponential function based on these equations the temporal probabilities of landslide events can be predicted in addition most of the nonseismically triggered landslides in shaanxi province were triggered by long term antecedent rainfall and high intensity intraday rainfall

three dimensional observations of a deep convective chimney in the greenland sea during winter 1988 89 abstract all available temperature data including moored thermistor hydrographic and tomographic measurements have been combined using least squares inverse methods to study the evolution of the three dimensional temperature field in the greenland sea during winter 1988 89 the data are adequate to resolve features with spatial scales of about 40 km and larger a chimney structure reaching depths in excess of 1000 m is observed to the southwest of the gyre center during march 1989 the chimney has a spatial scale of about 50 km near the limit of the spatial resolution of the data and a timescale of about 10 days the chimney structure breaks up and disappears in only 3 6 days a one dimensional vertical heat balance adequately describes changes in total heat content in the chimney region from autumn 1988 until the time of chimney breakup when horizontal advection becomes important a simple one dimensional mixed layer model is surprisingly successful in reproducing autumn to winter bulk temperatur

modeled radar surface signature of deep ocean convection deep ocean convection the process by which the deep waters of the world s oceans are created and renewed plays a key role in the global thermohaline circulation and hence the world s heat balance the process of deep ocean convection involves a vigorous overturning of the ocean water column down to depths of 2000 3000 m in an area probably not larger than 50 km in diameter this paper details the results of a theoretical study to identify remotely sensible surface signatures for deep ocean convection due to the all weather capability efforts have focused on the microwave part of the spectrum particularly the high resolution imaging capability of synthetic aperture radar sar the goal of this research is to use the sar surface signature or fingerprint to identify and characterize areas of convection in the open ocean this information is then used to improve model parameterizations for deep convection used in general circulation models electromagnetic simulations of remote sensing signatures of deep ocean convection have been performed based on existing hydrodynamic models simulated surface signatures of deep convection are presented for various hydrodynamic and imaging conditions along with a discussion of applicability of these simulations to real sar data key findings are the existence of a definite identifiable radar surface signature in convective regions and a set of conditions under which one would expect to observe these signatures

an improved composite surface model for the radar backscattering cross section of the ocean surface 2 model response to surface roughness variations and the radar imaging of underwater bottom topography in the companion paper we have presented an improved composite surface model for the calculation of normalized radar backscattering cross sections nrcs of the ocean surface the proposed model accounts for the impact of the full two dimensional ocean wave spectrum on the radar backscatter and was shown to reproduce measured absolute nrcs values for a variety of radar configurations and wind speeds satisfactorily after some reasonable tuning of the input ocean wave spectrum this paper focuses on the modulation of the nrcs in the presence of spatially varying surface currents first the sensitivity of the nrcs to intensity variations of different ocean wave spectral components is investigated then the hydrodynamic modulation of the wave spectrum over underwater bottom topography in tidal waters is computed in different ways and the resulting radar signatures are discussed the composite surface model yields comparable radar signatures at high 10 ghz x band and low 1 ghz l band radar frequencies which is in much better agreement with experimental results than the predictions of a first order bragg scattering model on the other hand measured variations of the nrcs at high radar frequencies appear to be still underestimated in some cases which may be due to shortcomings of our description of the wave current interaction by conventional weak hydrodynamic interaction theory possible improvements of the theory are discussed and requirements for future experiments are formulated

a nonhydrostatic mesoscale ocean model part i well posedness and scaling abstract the incompressibility and hydrostatic approximations that are traditionally used in large scale oceanography to make the hydrodynamic equations more amenable to numerical integration result in the primitive equations these are ill posed in domains with open boundaries and hence not well suited to mesoscale or regional modeling instead of using the hydrostatic approximation the authors permit a greater deviation from hydrostatic balance than what exists in the ocean to obtain a system of equations that is well posed with the specification of pointwise boundary conditions at open or solid boundaries these equations formulated with a free surface boundary model the mesoscale flow field accurately in all three dimensions even the vertical it is essential to retain the vertical component of the coriolis acceleration in the model since it is nonhydrostatic

synergistic use of satellite observations and numerical weather model to study atmospheric occluded fronts synthetic aperture radar sar images reveal the surface imprints of atmospheric occluded fronts an occluded front is characterized as a low wind zone located between and within two zones of higher winds blowing in the opposite directions on the left and right sides of the occluded front a group of four sar images reveal that the width of an individual occluded frontal zone and the wind magnitudes outside fronts vary greatly from case to case in this paper we performed a case study to analyze an occluded front observed by an environmental satellite envisat advanced sar and ascat scatterometer along the west coast of canada on november 24 2011 the two way interactive triply nested grid 9 3 1 km weather research and forecasting wrf model was utilized to simulate the evolution of the occluded front the occluded front moved toward the east during a 24 h model simulation and the movement between 18 00 and 21 00 utc matched the occluded front positions derived from the concurrently collected surface weather maps from the national oceanic and atmospheric national weather service archives the wrf simulated low wind zone associated with the occluded front and ocean surface wind speed match well with the sar and scatterometer wind retrievals high wind outside the front zone became weaker during the front evolution whereas the width of the occluded frontal zone was contracted laterally analysis of the wrf model derived potential temperature field suggests that the occlusion process occurred below the 800 mb level the structure of the occluded front studied here not only follows the conventional conceptual model and also supports the findings of a novel wrap up conceptual model for an atmospheric frontal occlusion process

geomorphometric feature analysis using morphometric parameterization and artificial neural networks this paper presents a semi automatic method using an unsupervised neural network to analyze geomorphometric features as landform elements the shuttle radar topography mission srtm provided detai

landslides triggered by excavation in the loess plateau of china a case study of middle pleistocene loess slopes abstract the frequent occurrence of catastrophic landslides caused by excavation in a loess slope is one of the commonly encountered engineering problems in the loess plateau middle pleistocene loess slopes were selected as a case study for current research the distribution of excavation induced loess landslides was studied by field investigation on the basis of centrifuge model tests the deformation features and failure mechanism of a homogeneous loess slope and a double paleosol interlayer loess slope under different excavation slope angles were analyzed and compared it was shown that the response of horizontal earth pressures in the lateral region of the excavation zone has a close relationship with the failure of the slope displacement measurements showed that the deformation stages of loess slopes due to excavation are independent of the paleosol interlayer the excavation slope inclinations and soil properties significantly affected the failure process and division of the slope the characteristics that excavation induced loess landslides always occur in hysteresis and abruptness were interpreted by the analysis of the failure process the influence of blade penetration during the excavation performed was quantitatively estimated finally based on the result of stress path tests an improved unloading constitutive model was proposed to simulate the deformation of soils in the lateral and bottom of the excavation area

collapsibility composition and microfabric of the coastal zone loess around the bohai sea china abstract coastal loess is a special loess deposit that is distributed around the bohai sea the primary objective of this study was to investigate the physical index mineralogical characteristics and collapse potential of coastal loess the secondary objective was to survey the effect of fine silt particles particle size 5 10 m 6 64 7 64 on the collapse process we tested the specific gravity moisture content dry density atterberg limits grain size distribution mineralogy and collapsibility characteristics in a laboratory generated scanning electron microscopy sem images and performed mercury intrusion porosometry mip tests the results of this investigation indicated that coastal loess has a moderately severe collapse potential the collapsibility coefficient decreases with an increase in the initial water content it initially increases and then decreases with an increase in vertical pressure as revealed by the mip test the collapse produces a smaller porosity and the middle pores are primarily responsible for the collapse the relationship of the collapsibility coefficient and particles with a diameter 7 64 have the same tendency in terms of their effect on collapse these results and analyses are important to improve the engineering construction safety in coastal zone loess areas and achieve a better understanding of loess properties compared with loess from a typical loess paleosol section

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

late quaternary landscape evolution in a small catchment on the chinese loess plateau abstract late quaternary landscape evolution was analysed with reference to a small 0 08 km 2 drainage basin system in southeastern gansu province southwestern chinese loess plateau in this region v shaped valleys with broad valley floors are prominent landscape features whose basic shape already existed prior to mis 2 during mis 2 the valley bottoms were infilled with fluvially reworked loess today forming accumulation terraces infrared optically stimulated luminescence irsl dating of these loess like deposits assigned them to the time span ranging from 22 5 to 17 7 ka bp during the late holocene valley fills were partly eroded and the receiving stream channel was deepened by at least 25 m close to the confluence of the study site s channels these alternating erosion and accumulation phases were triggered by climatic factors or human impact in the most recent past the high landscape sensitivity of the chinese loess plateau has led to increasing soil conservation measures that have effectively confined surface erosion however the lack of drainage on the artificial terraces induces piping processes

intelligent estimation of spatially distributed soil physical properties abstract spatial analysis of soil samples is often times not possible when measurements are limited in number or clustered to obviate potential problems we propose a new approach based on the self organizing map som technique this approach exploits underlying nonlinear relation of the steady state geomorphic concave convex nature of hillslopes from hilltop to bottom of the valley to spatially limited soil textural data the topographic features are extracted from shuttle radar topographic mission elevation data whereas soil textural clay silt and sand and hydraulic data were collected in 29 spatially random locations 50 to 75 cm depth in contrast to traditional principal component analysis the som identifies relations among relief features such as slope horizontal curvature and vertical curvature stochastic cross validation indicates that the som is unbiased and provides a way to measure the magnitude of prediction uncertainty for all variables the som cross component plots of the soil texture reveals higher clay proportions at concave areas with convergent hydrological flux and lower proportions for convex areas with divergent flux the sand ratio has an opposite pattern with higher values near the ridge and lower values near the valley silt has a trend similar to sand although less pronounced the relation between soil texture and concave convex hillslope features reveals that subsurface weathering and transport is an important process that changed from loss to gain at the rectilinear hillslope point these results illustrate that the som can be used to capture and predict nonlinear hillslope relations among relief soil texture and hydraulic conductivity data

engineering properties and zoning of loess and loess like soils in china the widely distributed loessic soils of china are described concentrating on the collapsible soils of the upper strata of the loessic series a general trend of gradual steady reduction in the tendency to collapse on wetting is found going in the direction from northwest to southeast cases of damage and flooding tests of pits are cited for illustration results of electron microscope studies of structural features of loess specimens from different locations are compared with the engineering behavior especially the susceptibility to self subsidence and degree of collapsibility in view of this trend and the differences between loessic soils of different regions a preliminary zoning of the loessic soils was made resulting in seven zones as shown on a schematic map

a nonhydrostatic mesoscale ocean model part ii numerical implementation abstract the nonhydrostatic model with a free surface is numerically implemented in boundary fitted curvilinear coordinates to model the mesoscale circulation in an ocean basin with natural topography a semi implicit numerical scheme is used and the directional inhomogeneity in the elliptic equation for pressure is exploited to speed up the computation of its solution while using the multigrid method the model is used to simulate the circulation in the gulf of mexico we observe the formation of the loop current and several eddies the flow is very strongly controlled by the topography and our numerical experiments reveal that in the bottom layers the flow along topographic contours is in the opposite direction of the anticyclonic circulation in the top layers

undrained shear behavior of loess saturated with different concentrations of sodium chloride solution abstract a series of ring shear tests was conducted on saturated loess to investigate the effects of nacl concentration in pore water and desalinization on the shear behavior under undrained conditions the loess samples were taken from the ground surface of a frequently active landslide in china were saturated by de aired distilled water with different concentrations of nacl and then were sheared undrained after that the samples were retrieved remolded re set into the shear box and re saturated by passing through de aired distilled water such that the samples were desalinized and then were sheared undrained again through comparing the undrained shear behavior the effects of nacl in the pore water and desalinization on the undrained shear behavior of loess were examined the results showed that the variation of nacl concentration in pore water can strongly affect the shear behavior of saturated loess both the peak shear strength and steady state strength increased with increase of nacl concentration until a certain value after which they decreased with further increase of nacl concentration meanwhile the peak shear strength and steady state strength of the desalinized samples recovered to those of the original sample hence the effects of salinization are reversible these findings may be of practical importance to better understand the repeated occurrence of some irrigation induced loess landslides in china

influence of environmental factors on the wetting front depth a case study in the loess plateau abstract reliable information on the wetting front depth and variation of water contents within the zone of wetting is required for addressing geotechnical problems in loess deposits such as estimation of the collapse deformation and assessment of the slope stability for this reason a field test was conducted at a site in the loess plateau of china to obtain data on soil water contents and temperatures at different depths for a period of one year the variation of water contents was interpreted from the influence of environmental factors and soil temperature and used to determine the maximum wetting front depth in the loess soils in the study region in addition a commercial software vadose w was used to simulate the flow behaviour in unsaturated loess taking account of the influence of environmental factors a reasonable agreement was found between the results of field investigations and numerical simulations the study results are useful as they provide valuable information about the wetting front depth and water content variation in unsaturated loess in response to environmental factors the field investigations and numerical simulations summarized in this paper can serve as a reference for future studies on other soils

on polarimetric characteristics in sar images of mesoscale cellular convection in the marine atmospheric boundary layer 1 convection is an important phenomenon in the marine atmospheric boundary layer mabl previous spaceborne radar studies of such have been limited to single polarization data and therefore their focus was on the variation in intensity of the radar return which was constrained by the existence of a single polarization image pattern representing different atmospheric and oceanic phenomena in this paper we study the polarimetric characteristics of mesoscale cellular convection mcc in the mabl using high resolution data from fully polarimetric hh vv hv and vh radarsat 2 rs 2 synthetic aperture radar sar images in conjunction with closely collocated mesoscale atmospheric model simulations to identify the mcc signatures to compare the polarimetric characteristics of mcc with those of the ocean surface our analysis also includes 641 open ocean surface quad polarization rs 2 sar images collocated with 52 national data buoy center buoys the open ocean surface sar images exhibit different polarimetric characteristics from those of mcc thus we differentiate mcc from other open ocean phenomena based on identifiable polarimetric sar characteristics