provenance of quartz in sedimentary mantles and laterites overlying bedrock in west africa evidence from oxygen isotopes abstract silty to sandy mantle and laterite sediments overlying bedrock in west africa cameroon to mali were studied to establish their origin oxygen isotope values of fine quartz 1 to 10 m in diameter separated from the samples have a relatively narrow range 15 to 17 vs smow and are indistinguishable from quartz separated from two harmattan wind dust samples collected in nigeria 15 4 however the oxygen isotope values are distinctly different from those of quartz in samples of basement precambrian granites 10 5 to 12 8 gneiss 13 3 o and a cretaceous shale 23 2 from the same area the 18 o values of quartz from the studied soils and sediments systematically decrease with increasing particle size small oxygen isotopic variations were observed for quartz up to 105 m in size whereas greater stable isotope variations are present in quartz fractions larger than 105 m oxygen isotope and particle size frequency evidence indicate that the fine sand silt size quartz fraction 105 m had a local origin we conclude that the eolian fine quartz was transported by the harmattan winds which blow from the chad basin to the atlantic ocean

a phase resolving cross shore sediment transport model for beach profile evolution abstract a phase resolving wave transformation module is combined with an intra wave sediment transport module to calculate the on offshore sediment transport rates the wave module is based on the boussinesq equations extended into the surf zone the vertical variation of the mean undertow and the intra wave sediment concentrations are calculated the net sediment transport rates are calculated and the equation for conservation of sediment is solved to predict the beach profile evolution the results of the present paper showed that the undertow contribution to the sediment transport rates is not dominating in all parts of the surf zone even for eroding beaches suggesting that other contributions should not be neglected the present model also showed that for the same offshore wave energy the time series of the oscillatory motion is important and that the effect of wave groups cannot be disregarded

deposition of harmattan dust and its influence on base saturation of soils in northern ghana ferruginous soils formed from volta shale deposits in northern ghana are highly weathered have high iron and aluminium oxide contents and a mineralogy dominated by quartz and low activity clays with low effective cec despite their advanced weathering state base saturation values of top soils are generally above 80 and deficiencies of basic cations are uncommon we postulated that the annual deposition of dust from the sahara carried by the harmattan weather system may be responsible for the high base saturation therefore we collected dust material for two entire dry seasons at nyankpala surrounded by highly weathered volta shale deposits and during several events of harmattan and local dust storms at bolgatanga surrounded by a variety of parent materials long distance harmattan dust had a clearly finer particle size distribution than dust collected during local storms but angularity and evidence of weathering on dust particles did not distinguish dust from different sources in bolgatanga soils contained unweathered minerals derived from local parent materials and both local storm and harmattan dust contained large amounts of bases significant amounts of micas and feldspars and k contents up to 3 in the dust collected at nyankpala showed harmattan dust to be the source of k and other bases found on volta shale soils short distance dust in nyankpala was mostly quartz and vegetation ashes dust deposition during one harmattan season at nyankpala amounted to about 15 g m 2 and carried a total of 140 400 300 and 60 mg m 2 of mg ca k and na respectively these amounts could account for the high base saturation of the low cec in volta shale soils

desert loess versus glacial loess quartz silt formation source areas and sediment pathways in the formation of loess deposits abstract pathways are presented which show the proposed sequence of events involved in the formation of loess deposits both hypothetical deposits and those of central china hungary nigeria and tunisia these pathways illustrate the potential role of and inter relationships between a variety of silt generating mechanisms in the formation of loess using these pathways the existence of desert loess is discussed and it is concluded that this depends on how the terms glacial loess and desert loess are applied if desert loess is taken either to signify nonglacial mechanisms of silt production or to characterise the environment from which aeolian entrainment took place then desert loess is a very real and widely distributed deposit however if the term glacial loess is used to refer to the global climatic regime under which the loess deposit has formed rather than the geomorphic mechanisms responsible for silt generation then desert loess would not be an appropriate term for the classification of loess deposits it is suggested that classifying loess deposits with reference to the global climatic regime under which they accumulated would facilitate a greater understanding of the role of environmental conditions at all stages in the formation of loess deposits

sources of non glacial loess size quartz silt and the origins of desert loess abstract descriptions of peridesertic loess deposits and possible non glacial origins for silt size quartz are reviewed including direct release from weathered bedrock results from salt and frost weathering experiments are presented and methods by which sufficient energy can be imparted to sand size grains to release silt size fragments are identified these fragments may then be entrained by aeolian or fluvial action results from fluvial comminution experiments indicate that high energy mixed sediment fluvial systems may be very effective in generating quartz silt purely aeolian attrition is also seen as a major source of silt size and finer material results from aeolian abrasion experiments performed using crushed quartz sand are complemented by trials using sands from deeply weathered granite and pannonian sands from hungary field and laboratory observations are therefore seen to argue for the existence of deposits that can be classified as desert loess

simultaneous seismic and magnetic measurements in the low noise underground laboratory lsbb of rustrel france during the 2001 january 26 indian earthquake since the decommission of the underground launching control room of the ground based component of the french nuclear missile system the whole installation has been turned into a cross disciplinary underground laboratory the lsbb is a unique low noise underground laboratory because of its initial military conception and its location in the regional park of luberon far from large cities industry and heavy traffic the deepest point is 500 m below the surface at this depth a huge and non conventional shielded cylindrical capsule is installed with no metal 1268 m 3 in volume with a residual electromagnetic noise lower than 2 ft hz 1 2 above 10 hz as a result fluctuations of the earth s magnetic field under 10 hz can be recorded at a very low noise level with a low t c squid 3 d magnetometer taking advantage of the main gallery topology a broad band underground seismic array has been deployed since 2001 an analysis of data recorded simultaneously by the seismic underground array and by the magnetometer sensors during the indian earthquake of 2001 january 26 is presented evidence of a magnetic field perturbation induced by the seismic waves at teleseismic distance 6250 km is supported by a polarization analysis of seismic and magnetic signals spectral analysis shows specific frequency bands of perturbation related to physical processes such as ground water flow acceleration within the mountain structure

a one dimensional model for undertow and longshore current on a barred beach a one dimensional model was developed for undertow and longshore current the model predicts time and depth averaged undertow and longshore current velocities with longshore uniformity in depth waves and current it was calibrated with field data obtained over longshore bars at hazaki oceanographical research station hors verification with the other field measurements and large scale experiments showed that the present model predicted well the undertow velocities over the longshore bars while a previous model calibrated with small scale experiment data underestimated the velocities the verification also showed that although the cross shore distributions of the longshore current velocity over the longshore bars predicted with the previous model had peak velocities seaward of the bar crests the distributions predicted with the present model had peaks shoreward of the crests and fitted those measured in the field

pedo sedimentary constituents as paleoenvironmental proxies in the sudano sahelian belt during the late quaternary southwestern chad basin abstract climate and environmental changes since the last glacial maximum in the tropical zone of west africa are usually inferred from marine and continental records in this study the potential of carbonate pedo sedimentary geosystems i e vertisol relics to record paleoenvironmental changes in the southwestern part of chad basin are investigated a multi dating approach was applied on different pedogenic organo mineral constituents optically stimulated luminescence osl dating was performed on the soil k rich feldspars and was combined with radiocarbon dating on both the inorganic 14cinorg and organic carbon 14corg soil fractions three main pedo sedimentary processes were assessed over the last 20 ka bp 1 the soil parent material deposition from 18 ka to 12 ka bp osl 2 the soil organic matter integration from 11 cal ka to 8 cal ka bp 14corg and 3 the pedogenic carbonate nodule precipitation from 7 cal ka to 5 cal ka bp 14cinorg these processes correlate well with the chad basin stratigraphy and west african records and are shown to be related to significant changes in the soil water balance responding to the evolution of continental hydrology during the late quaternary the last phase affecting the vertisol relics is the increase of erosion which is hypothesized to be due to a decrease of the vegetation cover triggered by i the onset of drier conditions possibly strengthened by ii anthropogenic pressure archaeological data from far north cameroon and northern nigeria as well as sedimentation times in lake tilla northeastern nigeria were used to test these relationships the increase of erosion is suggested to possibly occur between c 3 cal ka and 1 cal ka bp finally satellite images revealed similar geosystems all along the sudano sahelian belt and initial 14cinorg ages of the samples collected in four sites gave similar ages to those reported in this study consequently the carbonate pedo sedimentary geosystems are valuable continental paleoenvironmental archives and soil water balance proxies of the semiarid tropics of west africa

medium term 2dh coastal area modelling the state of the art in depth averaged mathematical modelling of 3 d coastal morphology is described for the medium term morphodynamic model type in which constituent models of waves currents and sediment transport based on first physical principles are linked together to describe the time evolution of the bed topography various aspects of the combined system of equations are discussed such as its mathematical character its inherent stability and its equilibrium state the results of an intercomparison of different models are shown for two test cases and the potentials and limitations of the model concept are discussed

simulation of coastal profile development using a boussinesq wave model a phase resolving wave transformation module is combined with an intra wave sediment transport module to calculate the on offshore sediment transport rates the wave module is based on the boussinesq equations extended into the surf zone the vertical variation of the instantaneous currents and concentrations are calculated the net sediment transport rates are calculated and the equation for conservation of sediment is solved to predict the beach profile evolution the results ofthe present paper showed that the undertow contribution to the sediment transport rates dominated only at local areas even for eroding beaches suggesting that other contributions should not be neglected

glacial and interglacial wind regimes over the eastern subtropical atlantic and north west africa analysis of aeolo marine dust deposits in the subtropical eastern atlantic enables the strength of the major wind patterns during the late quaternary to be evaluated and gives an insight into the climate of north africa

potassium release on drying of soil samples from a variety of weathering regimes and c clay mineralogy in china abstract thirty two soil samples from china were analyzed for exchangeable k before and after drying most soil samples were higher in exchangeable k after air drying and ovendrying 60 c than when wet soil clay minerals especially clay size mica affected k released in air dry and oven dry samples according to composition of clay minerals of air dried samples five classes were recognized soil samples with high mica and montmorillonite have the highest exchangeable k samples that contained higher kaolinite than mica had lower exchangeable k samples with higher kaolinite than quartz and mica had still lower exchangeable k samples of sandy soils contained very low exchangeable k when quartz was the main mineral the samples that had kaolinite and gibbsite as the main clay minerals had very low exchangeable k the degree of weathering weathering mean bore an inverse relationship to the amount of k released on drying in air or at 60 c udults and udalfs red earths of southeastern china because of their high k release on being dried are inferred to have received fine mica from the western desert dust rainout reported to liu et al 1981

dust clouds rain types and climatic variations in tropical north africa abstract dust and processes of raindrop formation in the clouds play a very important role in the climatic evolution of tropical north africa sedimentologic stratigraphic pedologic geomorphologic and palynologic data converge to show that a major environmental change occurred in tropical africa about 7000 yr b p in the sudanian and sudano guinean zones wet tropical zone from 15 000 to 7000 yr b p rivers deposited mostly clay while from 7000 to 4000 yr b p they deposited mostly sand during the first period pedogenesis was vertisolic montmorillonite dominant associated with pollen belonging mostly to vegetation typical of hydromorphic soils while during the second period pedogenesis was of ferruginous type kaolinite dominant with pollen belonging mostly to vegetation typical of well drained soils the great change near 7000 yr b p is linked chiefly to a major hydrological change that appears related to a change in the size of raindrops from fine rains associated with considerable atmospheric dust raindrop diameter essentially less than 2 mm to the second period associated with thunderstorm rains raindrop diameter mostly greater than 2 mm the size of raindrops is related particularly to cloud thickness and dust concentration in the troposphere thunderstorm activity is influenced also by fluctuations of the atmospheric electricity modulated by the sun

the role of aeolian dust in ecosystems abstract the recent upsurge in research attention to aeolian dust has shown that dust transport systems operate on very large spatial and temporal scales and involve much larger quantities of sediment than was previously realized an inevitable consequence of this is that researchers from a range of neighbouring disciplines including ecology are beginning to realize that this new knowledge has important implications for their study areas in the present paper we examine the ecological implications real and potential of this expanding knowledge of dust transport systems with a particular emphasis upon the australian dust transport system we track these ecological effects from source to sink at source wind erosion soil vegetation relationships are often dominated by temporal changes in rainfall nine years of measurements in the channel country of the lake eyre basin australia show that vegetation and soils in dune fields can recover from drought whereas on inter fluve grasslands uni directional and negative successional vegetation changes can result from wind erosion during drought on floodplains both wind erosion and vegetation responses are complicated by flood frequency up to 1999 flooding of saline claypans did not increase vegetation but did increase wind erosion through the supply of alluvial fines however after three floods within as many months vegetation became established and wind erosion rates were dramatically reduced wind erosion research attention is now gradually turning from the physical to the organic content of eroded dusts in australia organic matter content can reach 65 by mass but this cannot be explained by removal of soil organic matter alone biological soil crusts not only stabilize soils against wind erosion but contribute to some of the organic dusts the role of dust as a vector for pathogens is an area which deserves greater research attention in the future downwind from source we show that dust contributions to soils are more widespread and more variable in time and space than earlier work on dust derived loess soils has suggested recent studies also show positive dust impacts upon nutrient budgets within distant forest ecosystems and significant contributions to river nutrient loads especially in the arid sectors of internally draining river basins the number of studies of dust impacts upon marine ecosystems is increasing dramatically studies of dust within antarctic ice cores combined with dust modelling provide compelling evidence that increased soluble iron rich dust inputs to the southern ocean have stimulated phytoplankton populations modern process studies are however yet to clearly demonstrate these relationships finally we examine the potential for major dust impacts upon global climates using its positive and negative effects upon solar radiation and precipitation as examples of the complexity and importance of this new research area

variable hfsrnd radiogenic isotopic compositions in a saharan dust storm over the atlantic implications for dust flux to oceans ice sheets and the terrestrial biosphere isotopic characterization of aerosol mineral particles atmospheric dust of varying sizes is essential in classifying source areas and for determining the source of dust deposited over oceans and icesheets however the effect of atmospheric transport on radiogenic isotopic compositions is not well constrained making provenance interpretation difficult in order to investigate the isotopic variability of 176hf 177hf 87sr 86sr and 143nd 144nd we analyzed eight airborne dust samples in two size fractions collected along a cross atlantic transect through a dust storm originating in the sahara in late 2002 past measurements of 176hf 177hf 87sr 86sr and 143nd 144nd of dust have focused primarily on coarse sized particles 30 m whereas far field deposition is primarily finer particles 2 m strontium or neodymium isotopic sorting based on distance is not evident in our dataset however the combined isotopic ratios of the dust collected suggest a saharan origin hafnium isotopic compositions show an east to west trend towards more radiogenic compositions across the atlantic suggesting grain and mineral sorting during dust transport along the 4000 km transect transport models with variable dust particle diameter and wind speed demonstrate the preferential depletion of the high density mineral zircon during transport of dust from the source area the transport model combined with a simple two component mixing model show that the hf isotopic composition changes can be explained by the loss of the mineral zircon during transport modeling of this zircon effect with distance from the dust source in the hf isotopic composition of marine terrestrial and glacial dust deposits may reveal additional information concerning dust transport and sources in the geologic past

characteristics and constituent composition of harmattan dust falling in northern nigeria abstract during the 1984 1985 harmattan season dustfall was collected at six locations in the zaria kano area of northern nigeria from the beginning of november 1984 to late march 1985 the average dustfall at six locations was 580 kg ha the total dustfall during that season may have been of the order of 700 1000 kg ha clay less than 2 m constituted 25 and silt 2 50 m 57 of the dust the rest was very fine sand the dust had higher ph and cation exchange capacity and contained more extractable phosphorus organic matter and exchangeable ca mg k and na but had less extractable a1 and exchangeable acidity than the samples from eight soil profiles with which it was compared the dust also had a higher content of 2 1 layer silicate clay minerals and lower amounts of 1 1 layer silicate clay minerals and fe oxyhydroxides than the soil samples this difference in chemical and physical properties and in constituent composition of the harmattan dust may be expected to have an impact on the characteristics and development of the soils upon which it is falling

dust transport and the question of desert loess formation although contemporary dust storms are frequent in arid and semi arid areas desert loess deposits are poorly developed much of the world s loess occurs in mid latitude areas which experienced glaciation during the pleistocene ocean core evidence indicates that dust transport from sub tropical deserts increased during cold stages of the pleistocene but loess formed only on certain desert margins for reasons which have not been fully explained this paper re examines the mechanisms of dust transport and deposition and the circumstances leading to the accumulation of thick loess typical loess is composed mainly of medium silt grains which are transported in short term suspension a few metres above the ground significant thicknesses of loess form only when dust is trapped within a limited area often relatively close to the source dust particles finer than 20 m are transported mainly in long term suspension over a greater height range and may be widely dispersed the availability of silt and the frequency magnitude and direction of dust transporting winds are important factors governing the potential for loess formation but the existence of a suitable dust trap is particularly important traps may be formed by topographic obstacles areas of moist ground or vegetated surfaces vegetation adjacent to glacial outwash plains and braided meltwater streams trapped dust in mid latitudes during the pleistocene dust blown during glacial periods from certain deserts notably in sinai soviet central asia and china accumulated as loess in neighbouring semi arid regions on the margins of other deserts loess formation was inhibited partly by the absence of vegetation traps during most of the holocene net dust deposition rates in all desert marginal areas have been too low for significant loess accumulation this is mainly due to a reduction in silt availability and a tendency towards landscape stability reported dust storm frequencies during the past 50 years over estimate the longer term holocene dust flux due to the effects of human activities much modern dust owes its origin to erosion of cultivated soils in semi arid areas and is finer than typical loess

particle size fractionation of eolian sand along the sinai negev erg of egypt and israel eolian sand fractions along the west east transport system of the northern sinai peninsula northwestern negev erg of egypt and israel were analyzed in this study with regard to source dune geomorphology eolian transport and paleoclimate the studied erg is composed of active linear seif dunes in northern sinai western part and stabilized vegetated linear dunes in the nw negev dune field eastern part linear seif dunes differ from vegetated linear dunes in their vegetation cover linearity internal structure and dynamics sand samples were analyzed for sand grain morphology and particle size distribution although both dune types are continuous landforms with similar orientations and sand grain roundness values the linear dunes of sinai are coarser grained than the negev vegetated linear dunes the vegetated linear dunes have a variable but higher proportion of very fine sand 50 125 m content and a varying but lower sand fining ratio defined as the ratio of fine sand percentage to very fine sand percentage from these observations we infer that fractionation of sand occurred along the studied eolian transport path during periods of enhanced windiness very fine sands are suggested to have been transported by saltation and low suspension from source deposits and sand sheets we suggest that a significant proportion of the very fine sand fraction of nile delta sands has been transported downwind through northern sinai during the late pleistocene especially when linear dunes reached the nw negev due to last glacial period windiness and probably larger sediment supply generally decreasing wind velocities and increasing precipitation along the west east dune transport path enhanced vegetative cover in the northern negev and enabled deposition of the very fine sand component within the dunes and probably further downwind our results suggest that particle size distribution can elucidate much about erg history over time scales of a glacial interglacial cycle especially in cases where the sand provenance is of a single dominant source

quaternary soils and dust deposition in southern nevada and california eoliandustconstitutesmuchofthepedogenic material in late pleistocene and holocene soils of many arid regions of the world comparisonofthecompositionsand influx rates of modern dust with the eolian component of dated soils at 24 sites in southern nevada and california yields informationon 1 thecompositionandinflux rate of dust in late pleistocene and holocene soils 2 paleoclimate and its effects on the genesis of aridic soils especially with regard to dustfall events 3 the timing and relative contribution of dust from playa sources versus alluvial sources and 4 the effects of accumulation of dust in soil horizons the 2mmfractionsofaandbhorizons of soils formed on gravelly alluvial fan deposits in the study area are similar to moderndustingrainsize contentofcaco3and salt majoroxides andclaymineralogy thus they are interpreted to consist largely of dust the major oxide compositions of the shallow soil horizons are nearly identical to that of the modern dust but the compositions of progressively deeper horizons approachthatoftheparentmaterial theclay mineralogyofmoderndustatagivensiteis similar to that of the av horizons of nearby holocene soils but is commonly different from the mineralogies of deeper soil horizonsandoftheavhorizonsofnearbypleistocenesoils theseresultsareinterpretedto indicate that dust both accumulates and is transformed in av horizons with time changes in soil accumulation rates provide insights into the interplay of paleoclimate dustsupply andsoil formingprocesses modern dust deposition rates are more than large enough to account for middle and late holocene soil accumulation rates at nearly all sites however the early holocene soil accumulation rates in areas near late pleistocene pluvial lakes are much higher than modern rates and clearly indicate a dust deflation and deposition event that caused rapid formation offine grained shallow soil horizons on uppermost pleistocene and lower holocene deposits we interpret late pleistocene soil accumulation rates to indicate that dust deposition rates were low during this period but that increased effective moisture during the late wisconsinan favored translocation of clay andcaco3fromnearthesurfacetodeeper inthesoilprofile pre latepleistocenerates are very low in most areas mainly due to a pedogenic threshold that was crossed when accumulations of silt clay and caco3 began to inhibit the downward transport of eolian material but in part due to erosion

precursory effects in the subionospheric vlf signals for the kobe earthquake abstract the subionospheric vlf omega signal transmitted from tsushima japan geographic coordinates 34 37 n 129 27 e was continuously received at inubo 35 42 n 140 52 e this data was analyzed during an 8 month period centered on the great hyogo ken nambu kobe earthquake m g 7 2 on 17 january 1995 the epicenter located inside of fresnel zone of the vlf path to clarify the possible effect we developed the special tt terminator time method of data processing which was useful for our short vlf path distance 1000 km we discovered a statistically significant change of tt characteristics which began a few days before the main shock and probably continued a few weeks after it as a transient oscillation with period 10 days by simple modelling it was shown that tt changes could be caused by the decrease of the vlf reflection height by 2 km the possible underlying mechanisms of the effect are not defined however an increase of the regular electric field due to radon exhalation before the earthquake or an intensification of planetary waves by seismically influenced atmospheric turbulence might be considered

holocene landscape evolution of the manga grasslands ne nigeria evidence from palaeolimnology and dune chronology this paper presents a synthesis of results from investigations into palaeolimnology and dune chronology in the manga grasslands and adjacent areas of ne nigeria in order to reconstruct the evolution of this semi arid landscape since the late glacial a marked wet phase gave way to a fall in lake levels during the late glacial dune emplacement was active at this time to the south of the manga grasslands but seems to have been absent from the grasslands themselves wet conditions prevailed during much of the early to mid holocene accompanied by periods of significant barchanoid dune reactivation a marked deterioration in climate and vegetation commenced around 4 1 ka bp leading to the formation of the present day semi arid landscape the data suggest that there have been major changes in humidity in this part of subsaharan west africa during the late glacial to holocene and that the relationship between changes in precipitation and aeolian activity is complex

a morphology model for an eroding beach backed by a seawall abstract a morphology model for the prediction of beach erosion in the vicinity of a seawall has been developed the effect of wave reflection off a continuous seawall was included in the different components of the model the morphology model was verified against wave flume and wave basin physical model tests and predicted the beach evolution well for the cases simulated a sensitivity analysis of the numerical model was also performed the numerical results showed that the reflected wave had a small effect on the beach profile evolution and only reduced the volume of erosion close to the seawall slightly the morphology model also showed that for the cases tested the volume of erosion for beaches backed by a seawall was nearly the same as that for a beach without a seawall

interactions between fluvial and eolian geomorphic systems and processes examples from the sahara and australia abstract the remains of once integrated drainage systems are still discernible in many of the hot deserts of the world some of these date back to the mesozoic as in arid western australia where they now form chains of salt lakes others were active in miocene times such as the sahabi rivers that once flowed from chad to the mediterranean a few remained active during quaternary interglacials as in the sahara all contributed sediments that were reworked by wind during drier phases to form desert dunes the desert dunes of australia and of the 9500 km long chain of deserts extending from the sahara through arabia to the thar desert of india originated from sediments eroded from the uplands and deposited in closed interior basins formed during the course of late mesozoic and cenozoic faulting rifting and epeirogenic movements it was the unconsolidated neogene sediments laid down in large subsiding sedimentary basins such as the kufra sirte basin in libya and the chad basin which provided the source material for the late pliocene and quaternary desert dunes of the sahara one effect of the progressive build up of high latitude ice sheets during the neogene was to steepen the temperature and pressure gradients between the equator and the poles resulting in increased trade wind velocities stronger winds were better able to mobilize the alluvial sands of the increasingly dry sahara and adjacent deserts and to fashion them into desert dunes a more subtle form of interaction between eolian and fluvial processes concerns the interplay between desert dust loess accumulation on hill slopes in arid regions and the onset of fine grained valley fill accumulation by sluggish low energy streams in mountain valleys some of these late pleistocene wetlands served as refuge areas for plants reptiles and invertebrates at a time when the surrounding desert plains were very cold and dry as in the flinders ranges of south australia in the arid flinders ranges such valley fills were built up between 35 kyr and 15 kyr ago after which the return of the summer monsoon led to stream channel incision and the formation of a network of gullies often erroneously attributed to human activities understanding the causes of such accelerated erosion can prevent unnecessary and expensive attempts at restoration since the latter are based on the incorrect assumption that overgrazing and present day land use are responsible

on the formation of desert loess sequences of quartz rich coarse 20 63 m silt occur in many low and midlatitude unglaciated arid and semiarid areas and have been termed desert loess the processes by which these deposits are generated have been debated for decades all hypotheses to explain their origin seek to provide mechanisms for the generation of silt sized material without glacial grinding which is the main process involved in the production of coarse silt at high latitudes possible mechanisms for the formation of coarse silt in arid regions include derivation from preexisting siltstones mechanical weathering of silicate rocks and abrasion of sand grains in active dune environments during intense transport events examination of the characteristics of desert loess and field and laboratory experiments to assess the role of dune areas as a source of coarse silt by abrasion and or resuspension of residual fines suggests that many loess sequences are dominated by locally derived coarse silt improvements in the characterization of desert loess particle size mineralogy and geochemistry are needed however to identify sources and sinks of coarse silt especially when combined with climatic back trajectory analysis properly scaled experiments and modeling of particle collisions will also help to better quantify the effectiveness of abrasion in the generation of coarse silt in support of field observations

the nature origin and accumulation of loess abstract loess can be defined simply as a terrestrial clastic sediment composed predominantly of silt size particles which is formed essentially by the accumulation of wind blown dust there are three fundamental requirements for its formation 1 a sustained source of dust 2 adequate wind energy to transport the dust and 3 a suitable accumulation site most loess has been modified to some degree by local reworking bioturbation and syn depositional weathering but a process of loessification is not necessary for a dust deposit to qualify as loess the terms primary loess and secondary loess have previously been used to described wind deposited loess and redeposited loess respectively but it is more accurate to describe material reworked and redeposited by non aeolian processes as loess derived colluvium or loess derived alluvium during the quaternary loess formed in three main situations 1 mid continental shield areas beyond the limits of ice sheets periglacial loess 2 on the margins of high mountain ranges perimontane loess and 3 on the semi arid margins of some lowland deserts peridesert loess peridesert loess is relatively poorly developed partly due to the limited efficiency of silt generating mechanisms in low land deserts compared with glaciation but also important is the tendency in arid areas for dust to be dispersed over a wide area and to be rapidly reworked after deposition particularly in areas which experience frequent climatic changes the remarkably thick loess of china and central asia results from an unusual combination of conditions which has persisted for much of the last 2 3 million years namely rapid uplift of the tibetan plateau and surrounding mountain ranges high rates of sediment production and supply to adjacent basins a strong northwesterly and westerly wind regime and the existence of effective dust traps downwind of the source regions

can mima like mounds be vertisol relics far north region of cameroon chad basin abstract non anthropogenic earth mounds defined as mima like mounds in this study have recently been observed in non carbonate watersheds along the sudano sahelian belt in the chad basin in the diamare piedmont northern cameroon they are particularly well developed within stream networks in less eroded areas they occur as whaleback flattened morphologies or even as buried features all these shapes are composed of clay rich sediment associated with high proportions of secondary carbonate nodules and fe mn micro nodules their soil structure is prismatic to massive and vertical cracks are observed locally grain size distributions emphasize the clay rich nature of the sediment with average clay contents of 32 12 8 n 186 which is significantly higher than the clay content in the adjacent sediments in the landscape mean 10 4 n 21 moreover high proportions of smectite characterize the soil with average contents of 34 7 n 25 at the micro scale the groundmass has a cross striated b fabric with embedded smooth subangular quartz and feldspar grains of the silt size fraction all the characteristics point to altered vertic properties in the clay rich sediment composing the mima like mounds mima like mounds are thus interpreted as degraded vertisols compared to present day vertisols occurring in the piedmont mima like mounds are located upstream it is thus proposed that the vertisol areas were more extensive during a former and wetter period than the present day subsequent changing climatic conditions increased erosion revealing the gilgai micro relief by preferential erosion in micro lows rather than in micro highs mima like mounds of the chad basin might thus result from pedogenesis combined with later erosion these local processes can be inherited from regional climatic variations during the late pleistocene holocene and likely be related to the african humid period

holocene changes in tropical wind intensity and rainfall evidence from southeast ghana abstract remnants of a fixed aeolian dune ridge occur along the southeast coast of ghana just behind the present shoreline aeolian sands also cover extensive areas of the accra plains no dunes are present here the sands mainly occurring as sheets which blanket an early holocene landscape the sediments are of mid holocene age and were deposited during the interval 4500 b p 3800 yr b p when the southwesterly winds were stronger than they are at present and much of tropical africa seems to have been subject to marked aridity the onset of drier windier conditions around 4500 yr b p brought to an end the more equable climates than had characterized much of west africa during the earlier holocene aridity intensified winds and desert expansion between 4500 and 3800 yr b p parallel environmental conditions in tropical continental areas at the height of the late pleistocene glaciation

study of seismic influence on the ionosphere by super long wave probing of the earth ionosphere waveguide abstract investigation of the earth ionosphere waveguide by super long waves has been suggested for study of ionospheric sources related to seismic activity the omega system of phase radionavigation is used as the transmitting apparatus daily phase and amplitude variations have been analysed along seismo active profiles deviations of daily phase and amplitude variations were detected before a number of earthquakes

observations of the 5 day wave in the mesosphere and lower thermosphere the 5 day planetary wave has been detected in the winds measured by the high resolution doppler imager hrdi on the upper atmosphere research satellite uars in the mesosphere and lower thermosphere 50 110 kin the appearances of the 5 day wave are transient with a lifetime of 10 20 days in the two year data set the structures of selected 5 day wave events are in generally good agreement with the 1 1 rossby normal mode for both zonal and meridional components a climatology of the 5 day wave is presented for an altitude of 95 km and latitudes mainly between 40os and 40on

evidence for an aeolian origin of the holocene lateritic surface cover of gabon central africa abstract field granulometric and geochemical data are reported for a set of twenty one samples collected at six sites spread over gabon in the extensive lateritic clayey to sandy layer cover horizon which constitutes the upper part of the profiles of surficial formations granulometric analyses show that this material of homogeneous aspect is a mixture of two fractions a clay fraction and a medium to coarse grained sandy fraction relative proportions of these two constituents show strong variations from one site to another but are almost constant from the bottom to the top of a given profile the coarse grained fraction includes lithic elements of local provenance irrespective of their underlying basement the samples display many common geochemical features including a lack of ca na and mg their major element compositions may be accounted by the combination of a discrete number of mineralogical phases namely quartz kaolinite gibbsite fe oxides hydroxides and subordinate k minerals micas the normative contents of aluminous and ferrous phases regularly increase with the weight percent of clays conversely the quartz regularly decreases this inverse relationship is consistent with mixing between an al and fe bearing clay fraction and a coarse grained fraction dominated by quartz correlations between most immobile trace elements and the weight percent of clays indicate a control of those elements by al and fe bearing phases the main exception is for zr and hf as those elements are probably associated with zircons in the coarse fraction because of the control of the trace element distribution by secondary phases the geochemical signatures of all samples are clearly distinct from those of the upper continental crust and any basement rocks thus the trace element characteristics of the cover horizon carry no sign of any source material being the sole consequence of mineralogical sorting prior to deposit from field granulometric and geochemical data an aeolian origin appears as the most probable for the cover horizon geochronological constraints including archaeological data and 14 c dating indicate that this aeolian event took place during the holocene and probably occurred in less than 3000 y additional works will be necessary to assess the global context which made possible this very fast and extended event over large areas of central africa

quaternary aeolian dust processes and sediments in the australian region abstract aeolian dust processes have played an important role in the evolution of the australian landscape yet little is known of the processes and their sediments two major dust transport pathways are described based upon paleo dune patterns and present day dust storms and related processes these dust pathways have been fed by alluvium deposited in internally draining river basins during the period leading up to and including the late pleistocene aridity rates of dust entrainment transport and deposition were significantly higher than at present the ocean sediments of the tasman sea the pacific and indian oceans received massive amounts of aeolian sediment dust contributions to some australian soils have also been considerable

gas geochemistry applied to earthquake prediction an overview terrestrial gases in groundwater and soil air have been extensively studied in recent years in seismically active areas especially in ussr china japan and united states in search of premonitory changes that might be useful for earthquake prediction concentrations of radon helium hydrogen mercury carbon dioxide and several other volatiles have been found generally to be anomalously high along active faults suggesting that the faults may be paths of least resistance for the terrestrial gases generated or stored in the earth to escape to the atmosphere temporal gas concentration changes with durations of a few hours to many months have been observed before many large earthquakes at a relatively small number of favorably situated stations at epicentral distances of up to several hundreds of kilometers these sensitive stations are generally located along active faults especially at intersections or bends of faults or some other structurally weak zones possibly because of tectonic strain concentration at such places however gas concentrations especially those measured at or near the ground surface may also be significantly affected by meteorological hydrological and other nontectonic changes in the environment the nontectonically induced variations must be carefully eliminated or recognized in the search of true earthquake related anomalies

a new form of the boussinesq equations with improved linear dispersion characteristics part 2 a slowly varying bathymetry abstract a new form of the boussinesq equations applicable to irregular wave propagation on a slowly varying bathymetry from deep to shallow water is introduced the equations incorporate excellent linear dispersion characteristics and are formulated and solved in two horizontal dimensions in an earlier paper we concentrated on wave propagation and diffraction on a horizontal bottom in deep water in this paper these principles are generalized and the boussinesq equations are extended to include terms proportional to the bottom slope which are essential for the shoaling properties of the equations the paper contains a linear shoaling analysis of the new equations and a verification of the numerical model with respect to shoaling and refraction diffraction in deep and shallow water

active sand seas and the formation of desert loess abstract loess is a widespread eolian deposit dominated by coarse silt and very fine sand quartz grains 20 80 m that serve as an important archive of information on quaternary climate change despite the intensive research during the past century on desert loess formation its origin remains poorly understood and is still a fundamental problem in sedimentology the ongoing debate is focused on the first stage of loess formation the production of coarse silt quartz grains although laboratory experiments indicate the potential of dunes with their abundant quartz sand grains as a primary source for generating coarse silt grains this concept has been generally rejected because field based evidence of abrasion from sand grains eolian abrasion is scarce here we have adopted a global view of the sand sea loess association and examine in detail several well known late pleistocene loess regions in different subtropical deserts africa the middle east and arabia this analysis demonstrates that all these loess regions are located downwind of adjacent sand seas together with evidence of mineralogical similarity between the loess and the sand dunes and the contemporaneous deposition of the loess and movement of the dunes these observations suggest that sand seas are an important source for desert loess because there is only limited silt storage in sand dunes we postulate that the silt grains comprising most of the loess are not reworked from the dunes but are generated probably through active eolian abrasion of the sand grains under past climates characterized by intensified winds as a result the role of sand dunes and eolian abrasion in the formation of desert loess may be more important than previously thought

the nature and origin of the aeolian mantles of central northern nigeria abstract evidence is presented here to show that the upland soils of central northern nigeria are formed in aeolian mantles deposited by two aeolian processes aeolian suspension or dust deposition and aeolian saltation or dune sand deposition the soils to the south and west of kano are largely the product of harmattan dust deposition whereas the northern soils appear to originate from dune sand migration from the quaternary dune fields to the east of the study area the spatial pattern of particle size populations or quanta and quartz grain roundness characteristics within the mantles and dune sands indicates that considerable mixing of dune sands and dust has occurred in the formation of these mantles

influence of the inter tropical discontinuity on harmattan dust deposition in ghana the harmattan is a dry dust laden continental wind and in the boreal winter harmattan dust plumes affects many west african countries including ghana when the harmattan is strongest the southern part of ghana is affected by the inter tropical discontinuity itd in this study we investigate if the itd functions as a barrier preventing long transported harmattan dust to settle south of and below it this is done by analyzing a harmattan dust outbreak mapped using earth observation eo data from the spinning enhanced visible and infrared imager seviri onboard the meteosat second generation msg platform coupled with data from west african aeronet stations and comparing these observations with wind data from noaa s air resources laboratory arl program and the mineral suite of samples from seasonal dust deposits in north and south ghana in northern ghana traces of minerals indicate a weak influence of particles from an arid environment which is found consistent with the mapped dust plumes and ne wind directions in southern ghana the mineral composition show no sediments of an arid origin the mapped dust plumes is less intense and the surface wind directions and wind mass trajectories are more varying with lower wind speeds based on the results of this study it is concluded that dust deposited or measured near ground in the harmattan period under the itd and south of it does not contain material from the chad basin due to the local winds conditions less

sr nd isotopic characteristics of the northeast sandy land china and their implications for tracing sources of regional dust abstract the sr nd isotopic study of the northeast sandy land nesl china is of great significance for a thorough understanding of the dust system in this area the 162 bulk

a boussinesq model for waves breaking in shallow water abstract a simple description of wave breaking in shallow water is incorporated in the boussinesq equations by using the concept of surface rollers the roller is considered as a volume of water being carried by the wave with the wave celerity the effect of the roller is included in the vertical distribution of the horizontal velocity which leads to an additional convective momentum term the breaking criterion is related to the local slope of water surface and the thickness of the roller is determined from simple geometrical considerations although the model is simple it is capable of representing a variety of processes such as the initiation and cessation of wave breaking the evolution of wave profiles before during and after wave breaking the initial conversion of potential energy into forward momentum flux and the associated horizontal shift between the break point and the point where the setup in mean water level is initiated results are presented for regular and irregular wave trains and comparison with measurements shows good agreement

data analysis of bed concentration of suspended sediment an empirical relation for the bed concentration of suspended sediment cb defined at a few grain diameters above the bed is developed its derivation is based on the experimental data sets of guy et al in 1966 the values of the near bed concentration were obtained by first isolating the suspended load transport from the observed rates of total load transport by use of a bed load formula the suspended load was then equated to einstein s formulation which allowed the determination of cb the influence of large concentrations of suspended sediment and of the reference level for cb on the calculated values of bed concentration has been analyzed the proposed relation compares satisfactorily to values of near bed concentration obtained from independent data sets the procedure used to derive cb provides a simple method for the calculation of the total transport rate of noncohesive sediment