late quaternary hydrological dynamics in the middle kalahari forcing and feedbacks the kalahari region has become a major source of quaternary palaeoenvironmental data derived primarily from the analysis of geomorphological proxies of environmental change one suite of data from palaeolacustrine landforms has recently provided a new record of major hydrological changes in the last 150 ka burrough s l thomas d s g bailey r m 2009 mega lake in the kalahari a late pleistocene record of the palaeolake makgadikgadi system quaternary science reviews in press here we present an improved analysis of the drivers and feedbacks of lake level change utilising information from three main sources data from the lake system itself from analyses of other late quaternary records within the region and from climate modelling simulations using the hadley centre coupled climate model hadcm3 suggest that once triggered the lake body was large enough to potentially affect both local and regional climates surface waters and their interactions with the climate are therefore an important component of environmental dynamics during the late quaternary through its capacity to couple middle kalahari environments to distant forcing mechanisms and to itself force environmental change we demonstrate that the existence or absence of megalake makgadikgadi adds a new level of complexity to the interpretations of environmental proxy records in southern africa s summer rainfall zone

slope development reconstruction at two sites in the bohemian forest mountains although the bohemian forest is generally considered to be geomorphologically a rather stable region there are localities which bear proof of a surprisingly high intensity of recent and even present day processes a multidisciplinary methodology based on the analysis of slope systems was used for researching the present and past dynamics of two hillslopes using the results of direct dilatometric monitoring the slow creep of rock blocks reached a maximum of 1 mm year 1 gps field mapping sedimentology geodetic measurements and dem analyses several common rules have been observed for the behaviour of two model localities and a likely polycyclic development established with recurrence of mass wasting cycles related to material supply thresholds radiometric dating of debris flow activity showed that the cycles span approximately 4000 years in this area of rather stable bedrock conditions at least two factors that decrease slope stability need to act together to activate slope processes i e a favourable structural predisposition dip of major joint or bedding planes and an increase in relief through either glaciation or river incision copyright 2010 john wiley sons ltd

do swarms of migrating barchan dunes record paleoenvironmental changes a case study spanning the middle to late holocene in the pampa de jaguay southern peru swarms of barchan dunes are common in arid environments unlike immobile or slowly moving dunes whose stratigraphy can be used to reconstruct paleoenvironmental changes the high migration rate of barchans seems to prohibit their use as geoarchives in this paper a possible use of barchan swarms for paleoenvironmental reconstructions is presented the approach is based on dune migration in a case study based on 500 dunes in the pampa de jaguay aeolian transport corridor in coastal southern peru middle to late holocene changes in the supply of aeolian material are inferred from calculating the time of dune initiation at the coastline limitations posed by the assumptions underlying this approach are discussed

elliptical inhomogeneities in groundwater flow an analytical description abstract in order to be able to decide whether and how heterogeneities should be taken into account for modelling a groundwater flow problem the magnitude of those disturbances must be estimated therefore in this paper we solve the problem of a uniform flow in a homogeneous medium with an elliptical shaped inhomogeneity with a different value for the permeability and positioned under an arbitrary angle with respect to the undisturbed flow we calculate the ratio of the flow rate through this body with respect to the undisturbed case besides its use in solving groundwater flow problems this formula may be helpful for problems relevant to field reconnaisance

interpreting geoproxies of late quaternary climate change in african drylands implications for understanding environmental change and early human behaviour abstract climate and environmental change in the late quaternary are widely regarded as key drivers of early human development and dispersal in africa robust records of change are required to assess the nature of potential impacts today s late quaternary palaeoenvironmental palaeoclimate reconstructions from the interior southern african basin kalahari are more spatially detailed have a stronger chronometric underpinning and span a longer time range than those of 10 20 years ago but are no less controversial reconstructions for the last 150 ka are usually interpreted in terms of changes in hydrological balance from conditions more humid or more arid than today and expressed in climatological terms as the changing latitudinal interplay between monsoon easterlies and tropical and mid latitude westerlies with more data than ever before why then is the record not yet delivering a more coherent picture of regional climate change this paper deliberately addresses current challenges and controversies including issues often ignored or neglected with the view that it is essential to do so if more robust interpretations of the past are to be generated in the future sources of palaeo data from the interior are predominantly geoproxies reconstructions not based on highly resolved organic or isotope records but on interpretation of spatially extensive geomorphological proxies of past environments despite being increasingly datable using osl their inclusion in syntheses has proved complex not least when interpretations appear to conflict with records from other sources consequently they are sometimes removed from regional syntheses of climate change these omissions are often replaced by spatially exaggerated interpretations of higher quality local records allowing more spatially coherent timeslice interpretations to be presented yet this is counter intuitive to the spatial complexity of conditions present in the palaeoenvironmental proxies or in climatic and environmental systems today in addition the quest to link regional records to master records from ice and ocean cores can force interpretation within a temporal scale that may be inappropriate for their analysis underplaying the reality of complexity within the environmental system there are not necessarily good or bad records of terrestrial palaeoenvironments in interior southern africa rather there are records that contain different suites of information about past land surface hydrological and climate conditions preserved at temporal scales which can sometimes be incomparable consideration of these factors may resolve apparent conflicts between datasets resulting in a better understanding of past environmental dynamics and revealing the nature of environmental variability which may be a key facet to which human development has responded

process of slip surface development and formation of slip surface clay in landslides in tertiary volcanic rocks japan abstract once landslide movement has been initiated the sliding mass tends to move toward a more stable position however landslides that have occurred in some tertiary volcanic rocks in japan show recurrent movement a possible reason for this behavior is that the mineral composition and properties of slip surface materials results in better lubrication along the slip surface as movement continues in order to determine the causes five landslides in japanese tertiary volcanics with different movement histories were studied based on geological investigation the results presented in this paper were obtained by studying the development process and formation of slip surfaces and clays in landslides in these volcanics for rocks of similar types and mineralogies the clay content of slip surface materials can be directly related to the displacement and history of slide movement this study indicates that the type of slip surface ranges from 1 striation type showing only striations on bedrock without clay to 2 brecciated type clayey breccia 3 mylonite type clay with breccia and to 4 clay type clay without breccia if the slip surface occurs in tuff or tuffaceous materials and is subjected to increasing slide movement the smectite content in the slip surface clay increases while the silicate mineral content decreases furthermore the smectite content is observed to increase within the same landslide from the head to the toe portion of the landslide direction of groundwater flow the groundwater along the slip surface above the impervious zone contains an increased concentration of ca ions as the concentration of hco3 ions exceeds 40 mg l an environment is created that promotes the formation of smectite this process indicates that there is an active ion exchange within the groundwater near the slip surface that forms smectite thus the formation of smectite in the slip surface requires the presence of tuff and a sufficient concentration of hco3 ions in the groundwater the study results presented here indicate that frictional resistance decreases as clay content increases the reason for repeated movement of japanese landslides in tertiary tuffs or tuffaceous rocks at or in the immediate vicinity of the slip surface is attributed to 1 an increase in clay materials along the slip surface as the slide movement is repeated and 2 the presence of groundwater that promotes the formation of smectite as is commonly known smectite is one of the clay minerals that has lowest frictional resistance

a method for building 3d models of barchan dunes abstract the distributions of barchan dunes are usually represented by digital terrain models dtms overlaid with digital orthophoto maps given that most regions with barchan dues have low relief a 3d map obtained from a dtm may ineffectively show the stereoscopic shape of each dune the method of building 3d models of barchan dunes using existing modeling software seldom considers the geographical environment as a result barchan dune models are often inconsistent with actual dtms and incompletely express the morphological characteristics of dunes manual construction of barchan dune models is also costly and time consuming considering these problems the morphological characteristics of barchan dunes and the mathematical relationships between the morphological parameters of the dunes such as length height and width are analyzed in this study the methods of extracting the morphological feature points of barchan dunes calculating their morphological parameters and building dune outlines and skeleton lines based on the medial axes are also presented the dune outlines skeleton lines and part of the medial axes of dunes are used to construct a constrained triangulated irregular network c and arcengine are employed to build 3d models of barchan dunes automatically experimental results of a study conducted in tengger desert show that the method can be used to approximate the morphological characteristics of barchan dunes and is less time consuming than manual methods

reconstructing palaeoenvironments on desert margins new perspectives from eurasian loess and australian dry lake shorelines abstract desert margins preserve evidence of more extensive arid conditions in the past and represent global hot spots with respect to climate change the balance of scientific evidence now suggests that dryland landscape reactivation did not correspond simply to ice age aridity peaks as previously assumed this paper provides a new perspective on and more nuanced understanding of desert marginal landscapes as palaeoenvironmental archives the two case studies represent ends of a sediment availability spectrum both environments experience substantial spatial and temporal variability in deposition with implications for reconstructing past environments at individual sites recently generated chronostratigraphic data from the dry subhumid dobrogea loess romania are synthesised to provide quantitative insights into the spatial and temporal organisation of loess plateaux loess accumulation peaks during the lgm and mis4 but not at all sites accumulation rates vary substantially between sites comparison of geographical context yields no clear driving mechanism for this variability secondly two transverse lunette dunes in semi arid willandra lakes australia yield comparable chronostratigraphies and distribution of stratigraphic units a first attempt is made to identify changes in wind regime through time on the australian desert margins and suggests that high latitude climate forcing may have acted upon semi arid australia over millennial scales the novel perspectives generated from the new datasets provide unprecedented insights into past climate circulation and land surface processes along desert margins these new perspectives coupled with the new geochronological and quantitative palaeoclimate proxy tools now available represent the next frontier for palaeoenvironmental research on desert margins

sedimentological and geochemical evidence for palaeo environmental change in the makgadikgadi subbasin in relation to the moz rift depression botswana abstract this work considers new evidence for palaeo environmental change taking place during the pleistocene in northern botswana duricrusted strandlines along the northeastern margin of sua pan provide palaeo environmental data pertaining to the makgadikgadi subbasin msb with inferences regarding the larger makgadikgadi okavango zambezi moz rift depression field xrd and geochemical data show that msb strandlines comprise calcretes lu1 type mgo rich calcretes with silica lu2 type sil calcrete lu3 type and silcrete lu4 type early freshwater episodes appear to have been followed by calcrete dominated drying phases interspersed with repeated silcretisation calcretisation through pan littoral sediments may have been both biogenically and environmentally induced calcite precipitation was in part controlled by the mg ca ratio of pore water in the pan littoral zone suggesting closed basin type evaporative conditions which were followed by a major desiccation interval phases of silcrete precipitation appear to be related to periods when the geochemistry of the lake littoral more closely resembled present day na co 3 so 4 cl type brines silica saturated acidic moderately saline groundwater preceded si precipitation which took place as the ph reduced si mobilisation occurred inter alia as a result of quartz grain dissolution enhanced by diatoms bacteria and algal growth in the moist pan littoral sio 2 rich pore waters migrated through cracked and desiccated calcrete into areas of lower salinity and lower ph resulting in preferential calcite removal and silcrete precipitation approximate tl dates imply that exposed littoral sand underwent calcretisation during the drying phases of extensive palaeo lakes which occurred prior to 110 ka 80 90 ka and 41 43 ka these wet periods compare fairly well with vostok core chronologies for southern africa

multiphase quaternary highstands at lake ngami kalahari northern botswana large lake basins now almost entirely devoid of water in the kalahari s semi arid environment can be clearly identified from landsat imagery of northern botswana these basins are delineated by a series of beach ridges marking the former shorelines of an inundated area that at its largest extent encompassed 60 000 km 2 in the last 30 yr over 150 radiocarbon ages have been produced from three component basins that make up the palaeo makgadikgadi system consisting of the ngami mababe and makgadikgadi basins thepaucityofwellpreservedorganicmaterialintheregionhasledtothese 14 cagesbeingderivedfrominorganiccarbonates whose open system behaviour and polygenetic origin frequently result in unreliable dates from uncertain contexts and then only within the temporal limits of the radiocarbon method the application of optically stimulated luminescence osl dating to beach ridge sediments from lake ngami shaw p a bateman m d thomas d s g davies f 2003 holocene fluctuations of lake ngami middle kalahari chronology and responses to climatic change quaternary international 111 1 23 35 improved chronological resolution but was limited by the use of hand dug pits the new application of osl to samples derived from deep coringofbeachridgeshasallowedaccesstoamuchlonger threedimensional geomorphicrecordthanpreviouslyavailable seventyfour ages new osl ages from shorelines are presented allowing for the first time the opportunity to unravel the complex history of lake stages in the ngami basin multiple lake highstands are identified in the period 0 3 ka to 140 ka with several causes of these events includingtropicalandlocalclimatesandupstream channelavulsion identified tounravelthefullpaleaoclimatic significance of these events it will be necessary to identify the timing of high stands in the other terminal basins within the okavango system 2007 elsevier b v all rights reserved

barchan shaped ripple marks in a wave flume barchans isolated crescent shaped bedforms are believed to be formed under almost unidirectional wind or water ows and limited sand supply the formation of barchan morphologies under the action of purely oscillatory wave motion has not yet been fully investigated the present study attempted to form barchan topography in a wave ume and to compare this with barchans in the eld barchan morphologies of ripple size called the barchan ripples were generated from a at bed by the action of waves the horn width the distance between horn tips of the barchan ripples increased linearly with an increase in the total length the overall length projected on the centre line of the barchan with a coef cient common to barchan dunes in deserts the ratio of horn length to horn width of the barchan ripples was smaller than that of barchan dunes but similar to that of subaqueous barchans in the eld the longer the wave period was the larger the ratio of the body length to horn width became most subaqueous barchans formed under waves in the laboratory and unidirectional ows in the eld had blunter horns than subaerial barchans the shape of the barchan ripples changed with wave period the outer rim became rounder with increasing wave period the relationship between the base area and the height of barchan morphologies seems to be linear with a constant coef cient for the scale from ripples to dunes the barchan ripples showed a linear relationship between the height and the horn width similar to that for barchan dunes the migration speed of the barchan ripples was proportional to the cube of the ow velocity and was inversely proportional to height the same relation with a different value of the coef cient was obtained for barchan dunes copyright 2004 john wiley sons ltd

landscape sensitivity and ecological change in western zambia the long term perspective from dambo cut and fill sediments a series of small shallow seasonally or interannually waterlogged depressions dambos in the upper zambezi valley in western zambia hold shallow peat deposits and are bounded on their western margin by sandy lunette dunes using luminescence dating of sands fossil pollen analyses and the macrocharcoal record from cored peat the long term stability of these landforms and the vegetation they now support is investigated at a site east of the upper zambezi although the upper lunette dune sediments accumulated between 14 2 and 6 1 ka the onset of peat accumulation and preservation within the dambo did not occur until 2800 cal a bp suggesting that only from this point onwards were conditions stable and wet enough year round to allow the formation and preservation of peat during this time results from this study indicate that the long term behaviour of the dambo conforms to a cut and fill dynamic where under more arid conditions the dambo becomes a dry pan providing a sediment source for the adjacent lunette dune in contrast during wetter times when the dambo holds surface water year round it becomes an organic rich sediment repository preserving a fossil pollen record of long term vegetation change

the morphology of barchan shaped sand banks from western torres strait northern australia abstract large barchan shaped sand deposits have been observed in the north west of torres strait these deposits share characteristics of both subaerial barchan dunes and subaqueous sand banks a study of satellite imagery indicate that the deposits migrate in the direction indicated by their horns 10 15 m west per year and that sediment is shed from their horns features that are characteristic of barchan dunes however the orientations of sand dunes superimposed upon the sand banks indicate the presence of mutually evasive channels and circulation of sediment around the sand bank a characteristic of subaqueous sand banks the presence of mutually evasive channels is the criteria used to categorise the deposits as sand banks barchan forms are known to exist in regions with limited sediment supply and unidirectional current or wind regimes in the torres strait both these criteria are met previous work has demonstrated the presence of a net westward current through the torres strait that is driven by the southeast trade winds the relatively high displacement of the wind driven currents during the trade wind season relative to the monsoon appears to provide the necessary unidirectional regime to form barchans the low and typically eastwards displacement of the residual monsoon season current appears to have a negligible affect on the barchan form while seasonal wind driven currents appear to maintain the barchan shape of the sand banks tidal currents actively maintain mutually evasive channels observed by variations in dune orientation on the sand banks a sediment starved environment combined with bedload transport attributed to both wind driven and tidal currents is concluded to create a unique hydrodynamic environment where sand banks can attain a barchan form

barchan ripples under unidirectional water flows in the laboratory formation and planar morphology the purpose of the present study is to investigate the formation and planar shape of barchan ripples generated by laboratory unidirectional water currents and to compare the morphology with that of barchans formed by laboratory waves and flows in natural environments a thin veneer of sand as a sediment source was placed initially at the upstream part of a recirculating flume and the change in bed configurations by the flow was recorded by a video camera two types of formative process were observed one was that barchan ripples grew from barchanoid bedforms and the other was that they developed from a small aggregate of sand particles the barchan ripples in the present test had the same characteristics in the height width relation and in the migration speed as previously reported from the desert environment and wave flume studies an examination of the planar shape of the barchans led to the result that the barchan ripples had larger values of body length width compared with those of barchans formed by water waves in the laboratory and by airflow in natural deserts the horn length width of the barchan ripples was smaller than that of barchan dunes in deserts but larger than that of barchans in oscillatory laboratory flows copyright 2005 john wiley sons ltd

electrical imaging of sliding geometry and fluids associated with a deep seated landslide la clapiere france this paper deals with the applicability of electrical resistivity tomography ert for the recognition of large landslide structures at depths which have never previously been imaged accurately one of the most studied and instrumented deep landslides in europe is taken as an example the la clapiere landslide the first stage of the study consisted of an accurate geological mapping taking into account a morphological analysis of gravitational deformations this allowed a very fine definition of the landslide structure that could be compared with three provided ert profiles performed within the landslide body very good correlations were obtained for the determination of sub horizontal structures and associated fluid circulations it confirmed the position of the sliding surface that reached a maximum depth of 100 m forward computing was however necessary to determine the influence and then the presence of vertical discontinuities it supports the use of ert as an efficient tool for large scale landslide imaging such as deep seated landslides copyright 2010 john wiley sons ltd

mega lake in the kalahari a late pleistocene record of the palaeolake makgadikgadi system abstract a distinct series of beach ridges marking the former shorelines of large inter connected lacustrine basins in the kalahari can be clearly identified from landsat imagery and shuttle radar topography mission srtm data these basins which form the terminal sump of the okavango system in northern botswana are now almost completely dry during the quaternary they were intermittently occupied by large stable lake bodies and are thought to have periodically filled to a point of coalescence inundating an area that at its largest extent encompassed 66 000 km 2 poor chronological control has previously limited the utility of this important palaeo archive as part of a region wide lake palaeo shoreline research programme a systematic optically stimulated luminescence osl dating programme has utilised a lightweight hydraulic auger to take samples at depth from relict shoreline features twenty drill sites have generated 140 samples for dating establishing a firm chronology for multiple lake full phases in all three component basins ngami mababe and makgadikgadi of this mega lake this paper presents the final set of ages in the programme derived from four cores from the western and north eastern shorelines of makgadikgadi and uses these ages to establish a chronology of mega lake high stands during the last 300 ka providing a rare directly dated long terrestrial record of positive hydrological excursions within the southern hemisphere

complex holocene lunette dune development south africa implications for paleoclimate and models of pan development in arid regions closed depressions pan or playa basins are very common landscape features in arid or formerly arid regions many have associated downwind dune assemblages lunettes that have been explained in terms of deflation of sediments from the basin these widespread features have also been used as proxies of late quaternary rainfall and atmospheric circulation change we use a detailed program of optically stimulated luminescence dating at witpan south africa to show that lunette construction may be rapid and spatially complex this study presents 33 ages from 9 sample sites on the dune that show how accumulation of the present dune largely occurred over the past 2 k y but with marked sectoral variability in accumulation rates and timing variability is attributed largely to local sediment supply factors geochemical analysis shows that primary deflation from the pan has not contributed significantly to the construction of much of the current lunette most sand is derived from recycling of older lunette sediments preserved today at only a few locations and from neighboring linear dunes these findings if representative of lunettes in other localities have marked implications for the types of paleoclimatic information that these features may yield

morphology and composition of submarine barchan dunes on the scotian shelf canadian atlantic margin abstract submarine barchan dunes have been mapped on browns bank scotian shelf using multibeam sonar bathymetry and backscatter strength the morphology of subaerial barchans has been studied for almost a century but the advent of multibeam sonar technology now enables a quantitative investigation of their submarine counterparts the browns bank submarine barchans occur at a depth of 60 70 m and are crescentic in planform reaching almost 700 m in horn width and 5 m in height the barchans are convex to the se with steep lee faces to the nw indicating a dominant nw flowing current the barchans overlie a widespread gravel lag covered elsewhere with little or no sand obstacle marks emanate from the lee faces of the barchans and represent a lack of sand deposition and exposure of gravel lag on the sea floor the browns bank submarine barchan sediment texture is gravelly sand or sandy gravel and is primarily composed of subrounded to well rounded quartz grains the allometric relationship between submarine barchan slip face height and distance between horns is markedly different from that of subaerial barchans for the same dune height barchan horn width is about ten times greater in the marine environment the superimposition of megaripples on the stoss slopes of the submarine barchans suggests that the barchans are active and therefore represent an engineering risk to sea floor infrastructure current observations and models indicate that seasonal mean current strength is less than the critical velocity required for barchan migration however the barchans may be active under higher velocity storm induced currents repetitive multibeam sonar mapping is required to detect if barchan migration is occurring over longer time scales

the use of surface monitoring data for the interpretation of landslide movement patterns the tessina landslide is a large seasonally active slope failure located on the southern slopes of mt teverone in the alpago valley of ne italy consisting of a complex system that has developed in tertiary flysch deposits the landslide which first became active in 1960 threatens two villages and is hence subject to detailed monitoring with high quality data being collected using piezometers inclinometers extensometers and through the use of a highly innovative automated electronic distance measurement edm system which surveys the location of a large number of reflector targets once every 6 h these systems form the basis of a warning system that protects the villages but they also provide a very valuable insight into the patterns of movement of the landslide in this paper analysis is presented of the movement of the landslide concentrating on the edm dataset which provides a remarkable record of surface displacement patterns it is proposed that four distinct movement patterns can be established which correspond closely to independently defined morphological assessments of the landslide complex any given block of material transitions through the four phases of movement as it progresses down the landslide with the style of movement being controlled primarily by the groundwater conditions the analysis is augmented with modelling of the landslide undertaken using the itasca flac code the modelling suggests that different landslide patterns are observed for different parts of the landslide primarily as a result of variations in the groundwater conditions the model suggests that when a movement event occurs displacements occur initially at the toe of the landslide then retrogress upslope

recharge to the inter dune lakes and holocene climatic changes in the badain jaran desert western china we present new estimates on evaporation and groundwater recharge in the badain jaran desert western inner mongolia of northwestern china based on a modified penman equation suitable for lakes in china geochemical data and water balance calculations suggest that local rainfall makes a significant contribution to groundwater recharge and that past lake level variations in this desert environment should reflect palaeoclimatic changes the chronology of lake level change established by radiocarbon and u series disequilibrium dating methods indicates high lake levels and a wetter climate beginning at ca 10 ka and lasting until the late mid holocene in the badain jaran desert the greatest extension of lakes in the inter dune depressions indicates that the water availability was greatest during the mid holocene relicts of neolithic tools and pottery of qijia culture 2400 1900 bc suggest relatively intensive human activity in the badain jaran desert during the early and middle holocene supporting our interpretation of a less harsh environment wetter climates during the holocene were likely triggered by an intensified east asian summer monsoon associated with strong insolation

monitoring the process of ground failure in repeated landslides and associated stability assessments abstract field monitoring of two repeated landslide areas namely the sodechi and the yonaihata landslide areas on the island of honshu japan has revealed that the spread of ground failure occurred as in normal landslide even though these landslide events were repeated slides in clayey material a rapid increase in surface displacement the beginning of third stage creep occurred simultaneously with an increase in strain in the ground the cause of local failure along the sliding surface resulting in large continuous landslide movements thus an entire slope began to collapse when the full length of the failure surface became connected ring shear tests of landslide clay were conducted to determine three kinds of shear strength parameters 1 fully softened strength parameter parameter for peak strength of remolded clay 2 specimen separated strength parameter ss newly proposed in this study and 3 residual strength parameter r stability analysis revealed that ss was the most appropriate shear strength parameter to express slope stability in the ground failure transmission stage thus this result provides a first step in applying the mechanism of ground failure transmission to the problem of slope stability by defining the specimen separated strength parameter ss

late quaternary lake level fluctuations in the mababe depression middle kalahari palaeolakes and the role of zambezi inflows abstract a systematic drilling and optical dating programme on middle kalahari beach ridge relict shoreline sediments has enabled the identification of multiple episodes of lake high stands of an extensive palaeolake system at the terminus of the okavango delta northern botswana this paper presents 23 ages from the mababe depression and establishes four shoreline construction phases in the late quaternary coeval with other sub basin lake high stands lake ngami these synchronous lake phases result from a coalescence of the sub basins into a unified palaeolake lake thamalakane covering an area of 32 000 km2 six additional ages are also presented from the chobe enclave to the north of the basin where shoreline ridges were emplaced at the same time as lake thamalakane phases this suggests that increased flow in the chobe and zambezi system significantly contributed to the middle kalahari lake phases in both the post glacial and holocene periods the integration of these new data and their compatibility with other regional and tropical palaeo archives is discussed in the light of understanding quaternary climate drivers within the kalahari

vegetation induced subsurface precipitation of carbonate as an aggradational process in the permanent swamps of the okavango delta fan botswana abstract islands constitute an important geomorphological component of the permanent swamps of the okavango alluvial fan studies of the topography soil chemistry groundwater chemistry and vegetation cover across several islands indicate that many islands form as a result of the subsurface precipitation of calcite and probably amorphous silica which produces vertical expansion creating topographic relief the main agent responsible for this precipitation is transpiration especially by large deep rooted trees which increases the salinity of the groundwater leading to saturation in calcite and silica the process ultimately leads to the development of highly saline groundwater and results in marked zonation of vegetation across the islands numerical modelling of the process suggests that salinization of the groundwater beneath an island takes between 100 and 200 yr high calcite contents in island soils appear to be the product of several cycles of salinization which are interspersed with periods of swamp abandonment during which the more soluble alkali salts are leached from the islands island formation represents an important process in the overall aggradation of the alluvial fan

migration of contaminants in groundwater at a landfill a case study 4 a natural gradient dispersion test abstract a natural gradient tracer test using a chloride solution with an initial injection volume of 0 7 m 3 was performed in the sandy aquifer at the borden site the solution was injected into five well points set 1 m below the water table in an uncontaminated zone situated above the contaminant plume at a location 450 m downflow from the landfill under conditions of natural groundwater flow the tracer slug was monitored for a period of 4 months by withdrawing small volume samples from points in a three dimensional array of bundle type multilevel samplers measurements of hydraulic head were obtained from a network of miniature piezometers soon after injection the tracer slug gradually split into two halves one half moving horizontally at an average velocity of 2 9 10 6 ms 1 and the other horizontally at 8 2 10 7 ms 1 although the split has been attributed to local lateral heterogeneity the nature of the heterogeneity and its influence on the hydraulic head distribution were not clearly distinguishable in the field data obtained before during or after the test the chloride patterns for each of the two halves of the tracer slug evolved into gaussian forms although the patterns demonstrated some irregularity at early time the relatively smooth gaussian forms were unexpected because the aquifer has numerous small scale heterogeneities observed in vertical cores obtained from the tracer zone and because the glaciofluvial origin of the aquifer suggests that heterogeneities are not laterally continuous simulated chloride distributions from a three dimensional analytical solution to the advection dispersion equation were fitted to the field data to obtain best fit estimates of the values of longitudinal transverse horizontal and transverse vertical dispersivity at various travel distances for each of the two halves of the tracer zone this is the first known field test that has permitted the estimation of three principal dispersion coefficients in layered media the longitudinal dispersivity was found to increase from 0 01 m at a distance of 0 75 m from the source to 0 08 m at 11 0 m the transverse horizontal dispersivity increased also to a value of 0 03 m at 11 0 m transverse vertical dispersion was very weak and was accounted for by molecular diffusion the relative lack of vertical dispersion is consistent with the shape of the plume of leachate contamination from the landfill it was concluded that the observed increase in dispersivity along the path of migration is likely caused by heterogeneities information on the dispersion controlling heterogeneities is not yet available as practical field methodologies for their identification and description have not yet been developed until such information is incorporated into mass transport models a realistic solution of the dispersion problem in heterogeneous media will remain elusive

pan floor barchan mounds ntwetwe pan makgadikgadi botswana their origin and palaeoclimatic implications abstract the variety of forms assumed to be dunes and palaeolakes of northern botswana have long been perceived as geoproxies for the elucidation of quaternary palaeoclimates mounds on the floor of ntwetwe pan have been regarded as modified barchans pertaining to a time in the past when conditions were drier than at present the morphology hydrogeology and biology of these placed in the wider context of the palaeolacustrine hinterland indicate that they are not dunes but subaqueous features spring mounds the morphology is inconsistent with barchans conspicuous features are the elevated eyes within the enclosing arms of the crescentic forms that occur furthest from the pan edge seepages discharge from their flanks commonly about 7 m higher than the dry saline pan floor on the top of forms nearer the pan margins permanent pools of potable water occur similarly elevated above the floor hydraulic pressure to sustain the upward discharge of groundwater is provided by the excellent recharge through silicate karst depressions in the hinterland particularly those of the 936 m palaeolake floor groundwater discharge still operating today was formerly much stronger and associated with lacustrine conditions a chronological framework is provided by archaeological remains on the palaeolake floors of the hinterland these indicate that the oldest palaeolake floor pertaining to the quaternary is the 920 m level periods of spring mound formation are associated with both this and the 912 m palaeolake the implications for future luminescence dating targeting palaeoenvironmental reconstruction are discussed in the light of this new model of mound formation

the ion chemistry of lakes and late holocene desiccation in the badain jaran desert inner mongolia china abstract in the markedly arid badain jaran desert one of the least studied areas in the world over a hundred permanent lakes exist among the dunes the geochemistry of water samples from nine lakes and from the groundwater in the desert and on its periphery was investigated ion chemistry of the water from these desert lakes changes considerably on a regional scale we argue that there is a positive correlation between the ages of these lakes and their totally dissolved solids tds varying between 1 2 and 398 2 g l tritium analysis of groundwater in wells gives an age generally older than four decades and younger than 100 years the lacustrine deposits freshwater fauna and shorelines indicate the existence of large water bodies with low salinities in the inter dune hollows of this desert during the early and middle holocene the precipitation in this desert during the early and middle holocene was estimated to be ca 200 mm year on average at least twice as high as at present on the basis of paleoecology tl and radiocarbon ages it was concluded that the huge enrichment of ions in the lakes and decrease of water availability originated from climatic desiccation during the last 4000 years the paleoclimate of the badain jaran desert reported here was remarkably consistent with the late quaternary climatic histories of the regions to the immediate north west east and south of the study area

spatial variability and hydrologic evolution of australian lake basins analogue for pleistocene hydrologic change and evaporite formation abstract processes evident in basins across hydrologic gradients from humid to arid regions today provide analogues for systems that may have operated in some individual basins during periods of past hydrologic change thus lakes in humid regions today with low salinity sedimentary facies and with morphology controlled largely by wave action may closely resemble past lacustral pluvial phases experienced in zones which today are relatively arid and saline conversely playas controlled today by groundwater and in some cases subject to defletion may resemble those arid and dune building stages experienced by basins in sub humid regions today as they underwent glacial age desiccation in any such sequence of spatial or temporal gradients from humid to more arid conditions the frequency of basin filling and drying modulates the rate of evaporitive loss of interstitial waters from the exposed basin surface this in turn controls the salinity evolution of the interstitial and local groundwaters the notion of closed systems for terminal lakes while satisfactory for analysis of surface water budgets is quite inapplicable to the evolution of brines where surfacewater groundwater exchange during the high salinity drying stages becomes a controlling factor affecting all salt budgets in these systems evaporites may only be preserved when the sub surface waters have evolved to salinites near saturation for the salts concerned if sub surface waters are frequently diluted by surfacewater groundwater exchange evaporites will not be preserved in the record even though the surface system appears hydrologically closed the process of interstitial water evolution which controls efflorescence deflation and salt weathering exerts a dominating influence on basin geomorphic expression as well as on hydrochemical fractionation

effectiveness of natural zeroing of the thermoluminescence in sediments the last exposure to sunlight of detrital feldspars and quartz grains in quaternary sediments can be dated directly by thermoluminescence tl methods but the effectiveness of zeroing of the light sensitive tl signal by daylight varies widely depending upon details of the sedimentation processes to document this variability and to help develop objective criteria useful for future sample selection and laboratory procedures i have collected and analyzed several eolian fluvial marine deltaic and lacustrine samples from less than 100 year old deposits as well as suspensions from sediment plumes also underwater spectral irradiance was measured during recovery of suspensions tl properties of polyrnineralic feldspar dominated 2 4 m and 4 11 m size fractions were measured in the laboratory unexpectedly some light sensitive tl was found to remain in all samples however the light sensitive tl was more effectively zeroed in some samples a proximal loess a sandy braided channel deposit tidal flat and upper delta front muds and thin clayey lacustrine laminae than in others a silty braided channel deposit submarine fan muds and silt bearing lacustrine laminae for the first group the minimum relict paleodose obtained with the partial bleach technique is about 0 4 0 3 gy corresponding to a relict tl age estimate of about 200 years for these sediments thus similar sediments excluding fluvial deposits as young as about 2 ka can be accurately and routinely dated without significant correction for a zero point error if one uses the partial bleach technique coupled with integrated optical bleaching energy fluences of less than 1 j cm 2 and wavelengths only above about 550 nm also some simple optical bleaching tests are reported that have a potential use in sample selection and in provenance studies of some surficial detrital sediments finally a simple mathematical model is presented that helps account for the gross features of the observed bleaching response curves

late quaternary paleoenvironments in the southwestern kalahari abstract landforms of the southwestern kalahari in southern africa include linear dune systems pans and associated lunette dunes and the valleys of ephemeral rivers present day climates in the region are transitional from arid to semi arid making the area sensitive to climatic change the linear dunes are part of an extensive system of fixed dunes developed in the surface kalahari sands the dunes were in existence prior to 32 000 yr b p but have been reactivated on a number of occasions since then in conditions of increased wind velocities more nw winds and reduced rainfall especially in northern and eastern parts of the region periods of dune activity probably occurred at 19 000 17 000 10 000 6000 and 4000 3000 yr b p the development of pans in the region has been strongly influenced by changes in groundwater conditions deflation from pans and formation of lunettes occurred in periods when groundwater levels were higher and fluctuated seasonally more than they do today such periods probably occurred 25 000 20 000 yr b p around 10 000 yr b p and just prior to 1000 yr b p still higher groundwater discharges promoted by increased regional rainfall resulted in the formation of spring tufas and seasonal or permanent lakes in the pans which were also fed by surface runoff during the intervals between 33 000 28 000 23 000 21 000 17 000 15 000 and 12 000 11 000 yr b p the headwaters of the major ephemeral streams lie outside the region but within the same climatic zone increased flow in the molopo river occurred prior to 19 000 and between 15 000 and 13 000 yr b p

the shape of the barchan dunes of southern morocco we present detailed shape measurements of several barchan dunes in southern morocco near la youne using these data we disprove the concept of shape invariance of barchan dunes of different sizes nevertheless some parts of the barchan dune scale and we try to distinguish these from non scaling ones furthermore we point out the importance of the exact position of the brink for the overall dune shape finally we propose a simple model for dune shape using our data to determine the model parameters despite its simplicity this model is able to explain the difference between barchans where the crest and the brink coincide and those where they are separated typical side slopes can be obtained and the basic properties of the evolution of a barchan dune can be described

from landform to process morphology and formation of lake bed barchan dunes makgadikgadi botswana abstract a suite of crescentic landforms is visible from remotely sensed imagery within the ntwetwe panpan in the makgadikgadi basin botswana we investigate the most distinct of these landforms using morphometric measurements sedimentary data and optically stimulated luminescence osl signal analysis comparative analysis with previously published barchan morphological data sets suggest the ntwetwe features fall within the spectrum of morphometric parameters found in a range of barchan dunefields from around the world there is currently insufficient comparative morphometric data from sub aqueous dunefields to be able to distinguish the particular formative environment of the dune osl signal analyses however support the hypothesis of grove 1969 grove a t 1969 landforms and climatic change in the kalahari and ngamiland geographical journal 135 191 212 that the last deposition of the sediments within the ntwetwe forms was most likely aeolian in origin luminescence signal analysis is employed to investigate potential transport and bleaching environments of the sediments forming the features but results in this case do not shed further light on the formative conditions of these enigmatic landforms

bedform transport rates for the lowermost mississippi river 1 new methods of data collection and processing are developed to provide quantitative reach scale measurements of bedform transport mass within the tidally influenced mississippi river a multibeam swath profiler was used to collect daily bathymetry over a range of water discharges and bed elevation changes induced by dune migration are measured these values are coupled with bulk physical properties of the bed sediment to constrain mass flux and annual bedform transport is estimated at 2 2 x 10 6 metric tons mt the total annual sand flux from the mississippi river calculated by combining measured bedform transport rates and suspended sediment flux is estimated to be 20 x 10 6 mt survey data also provide information about the spatial distribution of dunes across the channel bottom straight reach segments are commonly mantled by dunes for the entire cross section while bends are typically areas of focused scour devoid of bedforms presumably any sediments associated with migrating dunes are propelled into suspension within bends before redepositing in the subsequent straight reach movement via suspension is therefore an important component for the downriver transport of bed materials in the lower mississippi river

duricrust development and valley evolution process landform links in the kalahari duricrusts are an important landscape component of the kalahari region of central southern africa their exposures within the dry valleys mekgacha of the kalahari provide some of the most widespread surface outcrops of the terrestrial jurassic to holocene kalahari group sediments exposures have been extensively used in the construction of lithostrati graphic sequences on the assumption that valley systems have incised their courses through a pre existing duricrust sequence recent work however has identified the role of groundwater erosion processes in valley development which may have influenced duricrust formation studies of duricrusts from boreholes drilled within two mekgacha show that duricrust type is intrinsically related to the presence of a valley analyses of calcretes and silcretes in a series of profiles and thin sections from the letlhakeng area of botswana also indicate extensive alteration and diagenesis in association with former higher water tables sedimentary sequences within duricrust host materials can be identified but there is no evidence for correlation of duricrust cements between exposures profile studies from the auob valley in namibia however suggest that this valley has incised through a sequence of duricrusts caution is advised in future attempts to correlate duricrust types on the basis of valley exposures with the recommendation that where such exposures are used in a lithostratigraphic context only duricrust host material characteristics and not cementing materials should be considered

relative and absolute dating of land surfaces abstract the dating of land surfaces has long posed problems for geomorphologists relative methods stratigraphic geomorphic topographic are sound and convincing exhumed forms may complicate identification and relationships for both epigene and etch forms have been buried and exhumed but in tectonically undisturbed areas the higher surfaces are older than those preserved at lower levels also surfaces have an age range the relationship of surfaces with volcanic deposits old shorelines and genetically related sedimentary sequences provides sound ages and correlation with dated duricrusts and faults is also useful there are no temporal limits to relative dating for the methods are equally applicable to the dating say of proterozoic surfaces as of those of pleistocene age the disadvantage of such methods is that the necessary evidence is frequently either not preserved or not exposed the so called absolute physical numerical methods and especially those based on exposure age dating with in situ cosmogenic radionuclides are appealing because they produce direct numerical ages and appear to be widely applicable but there are severe temporal limitations and sampling problems complicate and may invalidate interpretation absolute age determinations must be consistent with the stratigraphic and geomorphologic settings the best results are obtained when physicists and earth scientists pool their knowledge and experience a background in local and regional geology is especially important

mechanism of reactivated badu landslide in the badu mountain area southwest china this paper presented the reactivated mechanism of badu landslide according to site investigations monitoring finite element and limit equilibrium analyses finite element analysis incorporating a stability analysis with the finite element stress based method revealed a large railway cut triggered a localized slide in the upper part of badu landslide rather than a global failure and piles in three rows were effective in stabilizing the reactivated zone monitoring results and the limit equilibrium analysis showed that the landslide underwent multi instabilities rather than a global failure due to a rise in groundwater table in rainy season the mechanism of reactivated badu landslide was finally proposed i e grading creeping sliding mechanism which helped designers to propose the most suitable mitigation measures to stabilize the landslide

luminescence based dune chronologies in southern africa analysis and interpretation of dune database records across the subcontinent abstract over 600 luminescence ages have to date been published from southern africa s continental dunefields and isolated dunes providing a rich record of aeolian system dynamics during the late quaternary the majority of records come from sites within the five linear dune dominated dunefields of the kalahari with lesser representation of other major dune areas including the namib and west coast dunefields and of other dune types including lunettes and transverse forms dune database records are analysed not only in terms of the evidence they provide for late quaternary environmental changes over the last 190 ka the purpose for which most ages have been produced but in terms of the analytical techniques used data quality and data presentation as these all impact on how dune luminescence ages have been or should be interpreted as a tool for palaeoenvironmental and dune development studies it is concluded that even despite the number of dated dune records from southern africa there is a marked spatial unevenness within and between dunefields in the data available for assessing dune depositional ages and conditions however this is not a situation that can simply be improved upon by adding more and more ages to the full set of records it is both necessary to appreciate the spatial differences in dune sensitivities to activation and relationships to potential changes in hydrological and other activity controls and to establish better tools and approaches for analysing a rich but presently environmentally ambiguous record of dune accumulation

aeolian processes and sand encroachment problems in kuwait abstract the surface of kuwait is carved in a calcretized clastic sequence of miocene pleistocene age mostly covered by a thin blanket of recent aeolian deposits fast rate of development and increase of human activities contributed to denudation of the vegetative cover and exposure of dry loose sediments to wind action at present kuwait is intensively subjected to aeolian actions manifested by frequent occurrences of sand and dust storms this dictated the need for regional understanding of the magnitude of the aeolian processes their behavior with man made establishments and their long and short term impacts a comparison between the nature and distribution of recent surface sediments in kuwait in 1979 and 1990 shows significant changes that reflect the work of aeolian processes during this period the direct impact of the enhancement of aeolian action is represented by the increase in the rate of sediment transport transportation of fine grained particles in suspension frequently occurs during dust storms usually initiated in southern iraq the particles migrate over kuwait as thick dust clouds and finally settle in the northern part of the arabian gulf bedload transport of sand or saltation frequently occurs during summer whenever wind speed reaches 5 4 m s the average annual sand drift rate in kuwait is about 20 m 3 m width 1 yr 1 the majority of the drift occurring during the period may august to the southeast bedform transport or sand dune movement is also recognized in kuwait sand dunes mostly occur as small barchans of about 3 m height the measured rate of movement of these barchans varies with height a barchan of average height usually moves about 20 m in nine monthes january august the remarkable high rate of sand transport and the increase in development activities in the desert areas are responsible for the enhancement of the sand encroachment problems in kuwait almost all installations roads and farms are significantly affected by the accumulation of considerable amounts of aeolian sand these problems have pronounced adverse environmental and economic impacts

origin of a complex and spatially diverse dune field pattern algodones southeastern california the algodones dune field of southeastern california shows a complex and spatially diverse dune field pattern that is superimposed upon a series of topographic lineations analysis of dune field pattern parameters dune crest length crest orientation dune spacing and defect density derived from aerial images indicates that the dune field pattern represents two constructional generations prominent compound crescentic dunes formed during the first constructional generation a younger generation consists of a variety of simple crescentic dunes linear dunes and zibars statistical differences in the pattern parameters between the dune groups within the second generation are resolved through consideration of the boundary conditions under which the dune pattern evolved and provide explanations for 1 diversity of dune types 2 range in implied constructional times 3 range in crest orientations and 4 the anomalous nature of the population of linear dunes the boundary conditions that have modified pattern development include orographic effects grain size vegetation areal extent and antecedent conditions topographic lineations in the algodones range from the western ramp which defines the field margin to subtle features masked by the pattern of dunes imaging of the western ramp using ground penetrating radar shows high angle cross strata migrating perpendicular to the lineation trend the most plausible hypothesis for the origin of the lineations is as dune ridges sequentially shed from adjacent lake cahuilla which is the source of algodones sands the overall geomorphic complexity of the algodones originates from the emplacement of the dune ridges during stages of lake cahuilla the two generations of dune field construction and the controls exerted by boundary conditions

holocene fluctuations of lake ngami middle kalahari chronology and responses to climatic change abstract lake ngami a 3000 km 2 basin at the distal end of the okavango delta botswana has a complex suite of shorelines ranging from the lake sump at 919 m asl up to 945 m asl linked to topographic thresholds and inflows current and fossil in the okavango system the lake has been ephemeral throughout the 20th century and completely dry since 1982 yet held a substantial body of water up to a level of 930 m asl when visited by european travellers in the mid nineteenth century the historical decline in the lake has been well documented and used as evidence for regional desiccation but the holocene record based on archaeological studies and radiocarbon dating of inorganic carbonates is more speculative a study of a 30 km 2 diatomite at the eastern end of the basin indicates that a substantial freshwater lake at a level of at least 932 m asl was present throughout the holocene linked to a now abandoned inflow of the kunyere river a programme of 18 luminescence age determinations of the peripheral dautsa and magotlwanen shoreline sequences suggests that they are old features that have been constructed on a lacustrine substrate dating back to 90 100 ka or earlier and have been modified by holocene fluctuations in lake level and subsequent aeolian reworking the water level peaked at 936 m asl between 4 and 3 ka returned to 934 m at 2 8 2 ka ponding water into the phatane gap and fell rapidly thereafter to 932 m and thence to historical levels the 936 m level can be correlated with increased throughflow in the okavango delta hence increased rainfall in the catchment the subsequent decline can be attributed to episodic closure and rerouting of okavango distributaries in particular the thaoghe perhaps aided by anthropogenic activities as such the desiccation of the lake is not indicative of regional climatic change

luminescence dating applications in geomorphological research abstract chronological control remains critical to the interpretation of environmental change and to establishing long term rates of geomorphological processes radiocarbon dating will continue to be the central technique for age assessment of carbon bearing sediments deposited in the last ca 40 ka but alternative absolute dating strategies are required for older or non carbon bearing sediments they include uranium series dating of precipitated sediments k ar and ar ar dating of primary volcanic materials and cosmogenic isotopic dating of surface exposure ages an additional family of methods collectively termed luminescence techniques is increasingly providing a basis for the age assessment of detrital sedimentary deposits these methods directly date the deposition of detrital mineral grains typically quartz and feldspar and have been demonstrated to provide accurate deposition chronologies for up to 800 ka although 150 ka is more typical in the past decade a subset of luminescence techniques which employ optical sample stimulation methods called optical dating has made it possible to date samples from a much wider range of depositional systems given that the methods directly date sedimentation they allow direct assessment of depositional dynamism in numerous terrestrial and subaqueous including marine sedimentary systems and have demonstrated particular potential in the elucidation of chronologies from aeolian dune and loess fluvial colluvial coastal and volcaniclastic environments this paper provides a summary of the principles of the luminescence especially optical dating methods and shows how recent developments specifically single aliquot dating procedures have dramatically enhanced the scope and potential of the method the luminescence techniques are increasingly being incorporated into a wide range of geomorphological studies which seek to establish the nature of landscape changes over the past interglacial glacial cycle and beyond

deflation in the dustiest place on earth the bodele depression chad the bodele depression in chad is the largest single source of dust on earth because of a combination of strong near surface winds and a large reservoir of readily eroded and easily entrained low density sediment during the holocene and late pleistocene the bodele depression was host to a great lake palaeolake megachad that is now completely desiccated leaving the lake bed sediments exposed to deflation deflation in the bodele depression is revealed in erosional remnants of lake bed deposits exposed as yardangs on the lake floor erosional remnants indicate that locally up to 4 m of sediment has been removed by deflation optically stimulated luminescence dating shows that this occurred in less than 2400 years giving a rate of deflation of at least 1 6 mm yr 1 a range of other geomorphological features indicate that in some areas rates of deflation may be greater than or equal to 10 mm yr 1 deflation appears to be greatest in an arc around the northeastern margins of the lake basin where the diatomite deposits have been removed and revealed an underlying network of distributary channels preserved as gravel capped ridges the ridges which are part of an inverted topography are interpreted as deltaic distributary channels from an inland delta similar to the okavango delta examples of barchan dunes exist that were flooded by the palaeolake and which have now been exhumed from beneath layers of diatomite the distribution of extensive deflation around the northeasterly upwind end of the bodele depression probably results from a combination of large wind velocities an upwind source of abrasive sand and thinner diatomite deposits around the lake margin satellite image analysis shows that outcropping diatomite covers 24 049 km2 of the bodele depression furthermore the area from which diatomite has been removed by deflation is around 14 000 km2 combining this information with the ages and rates of deflation mentioned above indicates that some 61 000 km3 of diatomite has been eroded from the bodele depression during the past 1000 years

global positioning systems and digital photogrammetry for the monitoring of mass movements application to the ca di malta landslide northern apennines italy abstract a combination of digital photogrammetry and global positioning systems gps surveying has been used to measure landslide surface displacements and to estimate the volume involved in the movement ninety eight percent of landslides mapped as active in the emilia romagna region of northern italy are reactivations of dormant mass movements the ca di malta landslide south of bologna was chosen to test this integrated system a 0 5 m cellsize digital elevation model dem with vertical accuracy of 0 1 m was generated using digital photogrammetric techniques we have used a combination of digital photogrammetry and three gps techniques to monitor landslide movement rapid static surveying in which the survey observations are made for a period of minutes yielded sub centimetre positions for several marked points distributed on a longitudinal axis along the landslide kinematic surveying in which the observations are carried out continuously in this case by a walking person provided models of the surface 1 1 m grid by measuring the position of irregularly distributed points continuous observations over 7 months were made between two gps receivers one positioned within the moving landslide body and the other at a fixed location outside the landslide an automatic procedure was developed to download process and compute relative movement at constant time intervals the accuracy achieved with the gps measurements ranges between several millimetres to a few centimetres for static and kinematic observations respectively this integrated survey technique is a cost effective method that could be applied to other structural and morphological settings the real time monitoring could be coupled with a warning system for landslide hazard management and the repeated kinematic gps surveys derive precise dems of a landslide providing information on geometry volumes and evolution of the phenomenon

fossil spring deposits in the southern great basin and their implications for changes in water table levels near yucca mountain nevada during quaternary time fossil spring deposits are common in the southern great basin and their distribution provides important constraints on the hydrologic response of the regional water table to climate change this information is crucial because the proposed high level nuclear waste repository at yucca mountain will be located 200 400 m above the modern water table water tables will rise in response to a future return to glacial climates but the magnitude of the change and the consequences for radionuclide travel times and overall repository integrity are key uncertainties increased recharge during past pluvial periods in the spring mountains and sheep range caused water tables to rise and ground water to discharge over broad expanses of the las vegas valley system and in nearby pahrump sandy and coyote springs valleys in contrast other valleys in the region contain only small areas of pleistocene discharge resulting from local damming of ground water by faults that cut valley alluvium in these instances which include the valley wells area and piute and northern coyote springs valleys smaller ranges such as the clark and new york mountains supplied the moisture the change in water table levels since the last full glacial period varies between and within valleys from as little as 10 m in several areas to 95 m in the coyote springs valley at yucca mountain the water table has probably changed by 115 m in response to climate change the spring deposits and the mollusk faunas found with them often misinterpreted as lacustrine in origin share many essential features with active spring systems in northeast nevada deposits associated with discharge mainly consist of pale brown silt and sand that is entrapped by dense stands of phreatophytes covering valley bottoms when water tables are high pale green mud containing a mix of aquatic semiaquatic and moist terrestrial mollusks accumulates in wet meadows and marshes associated directly with spring discharge the record in subbasins of the las vegas valley system is dominated by late wisconsin age sediments although pond sediments and alluvium belonging to at least one older pre wisconsin pluvial period are also locally exposed deposits from two even earlier episodes of spring discharge both of which also occurred during rancholabrean time 10 to 450 ka are exposed in the pahrump chicago piute and coyote springs valleys and in the valley wells the records from the pahrump and coyote springs valleys are especially well exposed and likely extend back to at least early pleistocene time

paleolandscape and paleoenvironmental interpretation of spring deposited sediments in dakhleh oasis western desert of egypt abstract iron rich sediments in dakhleh oasis western desert of egypt have been recognized as spring mounds and as archaeological sites where paleolithic materials have been recovered detailed sedimentologic investigation and mapping of these features reveal that spring mound sediments were deposited in a shallow vegetated wetland formed by the discharge of iron rich nubian aquifer waters along the southern margin of the oasis controlled largely by localized faulting and the variable paleotopography of the basin floor the spring sediments represent peri lacustrine or lake independent features and can be differentiated from fully lacustrine deposits on the basis of their sedimentary characteristics as well as the presence of goethite and jarosite in a region where authigenic deposition during pleistocene pluvial activity principally resulted in tufas and lacustrine marls spring mound formation incorporated sediment through the ponding of surface water aeolian entrapment by local vegetation and the formation of iron precipitates in a low energy oxidative and acidic environment that was not dependent upon surface water inputs into the dakhleh basin the potentially interpluvial nature of this water resource makes it an important sedimentary archive for archaeological investigations in the basin the dakhleh spring mounds record a unique groundwater controlled paleoenvironment providing the first evidence of a bog iron in egypt and one of the few occurrences of iron rich wetland remnants in the modern sahara

width height and slope relationships and aerodynamic maintenance of barchans the allometric relationship between the height of barchan dunes and horn to horn widths is re examined the addition of new data from barchans in the namib desert and elsewhere confirms the relationship that the height of a barchan is approximately one tenth of the width of the dune height and width of the dune are closely linked to the three dimensional morphology of the dune in particular the relatively constant mean angles of around 11 at which the side slopes of the dune are maintained we suggest that the 3 d barchan form is directly controlled by aerodynamic processes constant feedback between three dimensional stoss face windward shape of the dune slipface height and horn to horn width and shear stress produces an equilibrium dune form

measurement of landslide displacements using a wire extensometer a continuous recording of landslide displacements is often required in order to better understand the complex relationship between the triggering factors and the dynamics of the movement in this paper we discuss the performance of the borehole wire extensometer and the interpretation of its results the analysis for the case of a translational slide shows that the displacements measured with the wire extensometer are systematically smaller than the movements observed at the ground surface a relationship between the wire readings and the horizontal component of the landslide movement has been established by means of three equations representing different stages of the wire displacement within the borehole the applicability of these equations and the interpretation of the wire extensometer readings have been successfully checked at two landslide sites vallcebre in the eastern pyrenees and alvera in the dolomites

landslides in sado island of japan part i case studies monitoring techniques and environmental considerations abstract a sufficient knowledge on the kinematics and development of landslides helps to adopt proper measures that can be used to protect slopes and the environment in general this can be achieved by adequate monitoring programs this paper presents the findings of intensive monitoring activities carried out on shiidomari and katanoo landslides found in sado island of japan more than one year of observation of the two landslides allowed defining some peculiar futures of their kinematics and style of development the problem of slope instability in the two areas is generally accredited to various factors but both landslides were triggered by heavy rainfalls and snowmelt because of the outline of the area and the presence of relict topographic features the shiidomari landslide is considered to be a large scale reactivation of old slope failures the katanoo landslide is however a first time case geophysical investigations and drilling activities in shiidomari indicated the presence of two slip planes the deepest 80 100 m of these is controlled by existing lineaments monitoring data suggests that the body of the landslide has subsided as much as 1 16 m just below the main scarp but a centimeter in the central region the toe sector also experienced a significant amount of subsidence but this was counter balanced by an uplift on the opposite side of the landslide hence the landslide seems not any more active along the deepest slip surface although it may extend upward and define a series of shallow shear planes around the crown in the case of katanoo the landform characteristics differential weathering the road cut and groundwater fluctuations appeared to contribute much to determine the exact location of the landslide extensional cracks that preceded the landslide can be related to heavy rainfalls and the cold and warm cycles thereafter subsurface investigations and monitoring works indicated that the landslide has two slide blocks with different slip planes during the observation period the upper part of the landslide responded more effectively to rainfall and snowmelt than the middle and lower sections the corresponding movements however appeared to settle about three months after failure there were also little strain transmissions in boreholes and no significant change in the characteristics of the landslide the kinematics of deformation of many of the slopes in sado island resembles that of shiidomari landslide but mass movements along highways and mountain roads are usually similar to katanoo landslides of the type like shiidomari may not show sudden and drastic failures but are usually long lasting and can reactivate repeatedly along new shallow shear planes monitoring works and long term supervisions in these types of landslides are useful to identify impending failures and take the right measures before they brought about large scale destruction to the environment

extraterrestrial dunes an introduction to the special issue on planetary dune systems abstract aeolian dune fields have been described on earth mars venus and titan the plethora of data returned from recent planetary missions has enabled a new era in planetary geomorphic studies much of our understanding of planetary dune systems comes from the application of earth analogs wind tunnel experiments and modeling studies despite the range of atmospheric pressures composition and gravity many of the dune forms on extraterrestrial surfaces are similar to those on earth although some have notable differences in bedform scale and composition as an introduction to the special issue on planetary dune systems this paper summarizes the current state of knowledge of planetary dune studies and highlights outstanding questions that require further investigation

landslide monitoring by using ground based sar interferometry an example of application to the tessina landslide in italy abstract an innovative technique based on radar interferometry and implemented using ground based instrumentation has been applied for monitoring the tessina landslide italy belluno the technique has allowed us to derive multitemporal surface deformation maps of the entire depletion zone of the landslide with a high spatial resolution and accuracy the portable device used in this application is known as linear sar lisa and it is able to provide measurements at 17 ghz with a synthetic aperture of up to 2 8 m the results have been validated by comparing the recorded pixel displacements with independent measurements carried out by a motorized theodolite and electronic distance meter edm on two benchmarks

deformation of stream surfaces in steady axisymmetric flow stream surfaces are used to examine the arrangement of neighboring streamlines in steady divergence free axisymmetric flow expressions are obtained that relate the angle of intersection between stream surfaces with general orientations to the stokes stream function and to the specific discharge vector these expressions are used to quantify deformation to the geometry of streamlines and stream surfaces occurring in axisymmetric flow the stokes stream function is presented for an isolated inhomogeneity in hydraulic conductivity with spheroidal geometry it is shown that axisymmetric flow generated by inhomogeneity rearranges the relative position of a streamline with respect to neighboring streamlines only locally in contrast a persistent rearrangement in the orientation and spacing of neighboring streamlines is observed between large distances upgradient and downgradient from groundwater withdrawal this characterizes all possible rearrangement of neighboring streamlines in axisymmetric flow withdrawal or production is required for a persistent rearrangement to occur

eolian dunes computer simulations and attractor interpretation a simple computer simulation algorithm for the transport of sand by wind produces forms resembling barchan crescentic ridge linear and star natural dune classes sand is moved as slabs composed of many grains that are picked up at random transported in a specified direction and deposited 1 with a probability that depends on the local presence or absence of sand or 2 in shadow zones in the lee of dunes the simulated dune fields are interpreted as complex systems with sand dune classes being dynamical attractors of these systems the evolution of dunes once formed becomes decoupled from the details of eolian sand transport

degradation of linear dunes in northwest ngamiland botswana and the implications for luminescence dating of periods of aridity the long morphodynamic history of the linear dune system of northwest ngamiland comprises both construction and degradation processes here we describe features resulting from the latter crest lowering during wet periods is associated with lateral transfer of sand into the straats weathering and leaching have mobilised iron to the base of the dune profiles and have corroded the quartz grains satellite image interpretation indicates that dune sand has been diluted by bioturbation which transferred damaran saprolite from below the dunes to the surface flooding and waterlogging have modified and in places completely destroyed the original crisply linear morphology small linear collapse features across the linear dunes are associated with open fractures or faults where water infiltration is facilitated the implications for luminescence dating of dune sands to identify periods of aridity are discussed the dunes cannot simply be regarded as providing a stacked record of such periods they are very old and much of the record is missing as a result of crest lowering the chronostratigraphy includes degradational components which must be distinguished from those of construction bioturbation cannot be disregarded as a complication which overprints the luminescence signals

using global positioning system techniques in landslide monitoring the precise determination of point coordinates with conventional global positioning system gps techniques often required observation times of one to several hours in the last few years new gps methods have been developed among them the fast static and real time kinematic with higher productivity and good theoretical precision the main objective of this paper is to ascertain the performance of these methods in landslide monitoring practice we present first of all the basic principles of the gps the equipment and working procedures we discuss afterwards the applicability of the gps to the monitoring of landslide surface displacements compared with the classical surveying methods the gps allows a larger coverage and productivity with similar accuracy furthermore it can work in all kinds of weather conditions and a direct line of sight between stations is not required finally we present an example of the performance of the gps equipment in the landslide of vallcebre eastern pyrenees spain this landslide has been periodically monitored since 1987 with terrestrial photogrammetry and geodetic measurements theodolite electronic distance metres edm the movement extends over an area of 0 8 km2 and has experienced displacements as large as 1 6 m during the period 1996 1997 14 campaigns over a period of 26 months using both static and kinematic gps methods have been carried out the gps measurements have been compared with the results obtained with the edm inclinometers and wire extensometers and checked against fixed stable points the precision achieved with the gps measurements is 12 to 16 mm in the horizontal plane and 18 to 24 mm in elevation 2000 elsevier science b v all rights reserved

seasonal movement of the slumgullion landslide determined from global positioning system surveys and field instrumentation july 1998 march 2002 abstract measurements of landslide movement made by global positioning system surveys and extensometers over a 3 5 year period show that the slumgullion landslide in the san juan mountains of southwest colorado moved throughout the monitoring period but that daily velocities varied on a seasonal basis landslide velocities peaked in the early spring and summer in response to snowmelt and summer thunderstorms respectively velocities were slowest in mid winter when air and soil temperatures were coldest and precipitation was generally low and or in the form of snow with a low water content we hypothesize that the seasonal variability in velocities is due to ground water levels and corresponding pore pressures that decrease when surface water is unavailable or cannot infiltrate frozen landslide material and increase when surface water from melting snow or rainfall infiltrates unfrozen landslide material we also suggest that patches of bouldery debris and fractures created by continuous movement of the landslide are conduits through which surface water can infiltrate regardless of the frozen or unfrozen state of the landslide matrix material therefore the availability of surface water is more important than landslide temperature in controlling the rate of landslide movement this hypothesis is supported by field instrumentation data that show 1 landslide velocities coinciding with precipitation amounts regardless of the depth of freezing of landslide material 2 spring and annual landslide velocities that were greatest when the depth of freezing was also the greatest and 3 a rapid several weeks or less velocity and pore pressure response to rainfall the persistent but seasonally variable movement of the landslide fits the bathtub model for landslide movement described by baum and reid baum r l reid m e 2000 ground water isolation by low permeability clays in landslide shear zones in bromhead e n dixon n ibsen m l eds landslides in research theory and practice proc 8th int symp on landslides cardiff wales vol 1 139 144 in their model the landslide is isolated both mechanically and hydrologically from adjacent materials by low permeability clays these clays cause the landslide to retain water our data support this model by suggesting that pore pressures at the basal landslide surface are always adequate to maintain landslide movement and that any infiltration of water at the surface of the landslide is adequate to rapidly increase landslide velocity