quantification of holocene asian monsoon rainfall from spatially separated cave records abstract a reconstruction of holocene rainfall is presented for southwest china an area prone to drought and flooding due to variability in the east asian monsoon the reconstruction is derived by comparing a new high resolution stalagmite 18 o record with an existing record from the same moisture transport pathway the new record is from heshang cave 30 27 n 110 25 e 294 m and shows no sign of kinetic or evaporative effects so can be reliably interpreted as a record of local rainfall composition and temperature heshang lies 600 km downwind from dongge cave which has a published high resolution 18 o record wang y j cheng h edwards r l he y q kong x g an z s wu j y kelly m j dykoski c a li x d 2005 the holocene asian monsoon links to solar changes and north atlantic climate science 308 854 857 by differencing co eval 18 o values for the two caves secondary controls on 18 o e g moisture source moisture transport non local rainfall temperature are circumvented and the resulting 18 o signal is controlled directly by the amount of rain falling between the two sites this is confirmed by comparison with rainfall data from the instrumental record which also allows a calibration of the 18 o proxy the calibrated 18 o record provides a quantitative history of rainfall in southwest china which demonstrates that rainfall was 8 higher than today during the holocene climatic optimum 6 ka but only 3 higher during the early holocene significant multi centennial variability also occurred with notable dry periods at 8 2 ka 4 8 4 1 ka 3 7 3 1 ka 1 4 1 0 ka and during the little ice age this holocene rainfall record provides a good target with which to test climate models the approach used here of combining stalagmite records from more than one location will also allow quantification of rainfall patterns for past times in other regions

modeling soil seal as a nonuniform layer a quantitative conceptual model of soil sealing is proposed based on the assumption that the compaction of the upper soil layer by raindrops and the washed in material result in a nonuniform change in bulk density which can be approximated by an exponential function the change in density causes in turn variations in soil properties such as porosity water retention and hydraulic conductivity empirical functions are suggested to simulate the pattern by which these properties vary as dependent upon the density change the model was calibrated using data of two experimental studies related to crust properties of three different soils sandy loam loam loess and clay loam the model reproduced quite well the observed features of the experimental sealing characteristics seals developed in two different flow systems subjected to simulated rain were analyzed 1 seal developed under saturated conditions over a shallow soil bed and 2 seal developed under unsaturated flow conditions the proposed model highlights some soil parameters that are quite important and should be observed in soil sealing investigations it also presents a basis for quantitative analysis of the soil sealing phenomenon in terms of measurable physical parameters

a three thousand year record of north atlantic climate annual band counting on three radiometrically dated stalagmites from nw scotland provides a record of growth rate variations for the last 3000 years over the period of instrumental meteorological records we have a good historical calibration with local climate mean annual temperature mean annual precipitation regional climate north atlantic oscillation and sea surface temperature sst strongest at 65 70 n 15 20 w although the correlation with the latter breaks down prior to the instrumental record this suggests that the climatic factors that force nw scottish climate and therefore our stalagmite growth varied through time and include winter nao strength the strength of the thermohaline circulation and possibly solar output spectral analysis was performed on the stalagmite growth rate time series a spectral frequency of 50 70 years is predominant in two stalagmites that were deposited from 1000 to 3000 bp a slightly longer frequency of 72 94 years is dominant from 1000 bp to present these are the same as that observed in ocean gcm output for the north atlantic region ssts our stalagmites provide high resolution precisely dated evidence of a similar periodicity predominating over the last 3000 years in a climate proxy record known to be sensitive to changes in forcing functions relevant to the north atlantic sector

surface crusting in two alluvial soils of northen niger valentin c 1991 surface crusting in two alluvial soils of northen niger geoderma 48 201 222 surface crusting was studied in a sandy soil and a clay loam soil in northern niger in a subdesert to desert environment light microscopy electron microscopy image analysis and soil physics were used to study and explain different crusting processes in experimental plots two 1 m2 plots on each soil were subjected to rainfall simulation in the field under natural and tilled surface conditions this study demonstrates that kinetic energy of rainfall is the major crusting factor for the sandy soil waterlogging and subsequent slaking led to the formation of structural and depositional crusts in the tilled clay loam plot in this case a surface crust can be formed regardless of kinetic energy of the rainfall this was substantiated through double ring infiltrometer measurements in both soils infiltration was severely hindered by crusting the relationships of crusting to water and wind erosion were more ambiguous four types of crusts could be defined from this study in terms of structure genetic processes and properties it could also be demonstrated that crust control practices should take into account the texture of the original soil materials

an annually laminated stalagmite record of the changes in thailand monsoon rainfall over the past 387 years and its relationship to iod and enso abstract northern thailand is the most flood prone region in thailand during the indian ocean dipole iod and el nino southern oscillation enso events an annual growth rate profile covering the period from 1622 to 2008 ad was derived from the laminated stalagmite nj 0901 from this area by comparing stalagmite nj 0901 to a contemporaneous stalagmite from the same cave and correlating the growth rate of nj 0901 with meteorological data from the most recent 100 years the stalagmite record proved to be a paleoclimate proxy of thailand monsoon tm rainfall this is the first annually laminated speleothem record that has been traced back four centuries this record provided a long term perspective and a valuable insight into tm rainfall and allowed us to investigate variations in the monsoon activity that was associated with iod and enso our results indicate that both iod and enso are significant climate modes that impact tm rainfall but the effect of the interaction iod and enso on tm rainfall remains unclear

cyclic rapid warming on centennial scale revealed by a 2650 year stalagmite record of warm season temperature 1 a 2650 year bc665 ad1985 warm season mjja may june july august temperature reconstruction is derived from a correlation between thickness variations in annual layers of a stalagmite from shihua cave beijing china and instrumental meteorological records observations of soil co2 and drip water suggest that the temperature signal is amplified by the soil organism co2 system and recorded by the annual layer series our reconstruction reveals that centennial scale rapid warming occurred repeatedly following multicentenial cooling trends during the last millennia these results correlate with different records from the northern hemisphere indicating that the periodic alternation between cool and warm periods on a sub millennial scale had a sub hemispherical influence

a runoff capability classification system based on surface features criteria in semi arid areas of west africa abstract an analysis of the factors influencing infiltration and runoff was carried out using data obtained under simulated rainfall conditions on 87 plots in arid and semi arid areas of west africa arranged in a hierarchical sequence one of the key factors to emerge from this typological classification is the type of surface crust together with faunal activity vegetation cover and surface roughness this parameter permits the inclusion of a unit surface factor in the classification system each unit surface is characterized in terms of genetic morphological and hydrological properties at a higher level the combination of these unit surfaces allows a soil surface features unit to be defined based on an original mapping method the samples once defined in this system were found to correspond to homogeneous criteria both in terms of evolution dynamics and hydrological behaviour furthermore such cartography could be successfully extrapolated through remote sensing image analysis making possible a classification of the runoff capability of small watersheds based on objective and standardized criteria

clay dispersion an important factor in channel runoff generation in a semi arid loess covered area with very low rain intensities abstract overland flow is usually regarded as an important contributor to storm channel flow this observation is certainly applicable to dryland areas where base flow is often irrelevant particularly in small watersheds this study examines channel runoff generation in the extensive loess covered areas that characterize the mildly arid area of western israel where the average annual rainfall is 280 mm hydrological data point to a peculiar hydrological behavior of the ephemeral streams that experience a high frequency of sporadic channel flow events even in extreme rain events peak discharges are exceptionally low indicative of a limited contributing area hydrographs are characterized by very steep rising and falling limbs usually representative of saturated areas located in the vicinity of the runoff recording station based on this observation we advanced the hypothesis that storm runoff originated in the limited area of the active channel with negligible runoff from the adjoining hillslopes we argue that a quasi permanent surface seal at the top of the alluvial deposit drastically limits the hydraulic conductivity of the alluvial fill allowing runoff generation at very low rain intensities the occurrence of the surface seal is ascribed to the combination of two main factors a high clay content 40 where the dominant clays are smectite and illite characterized by a laminar structure and a high water absorption capacity the swelling of the clay particles considerably reduce the porosity of the alluvial material allowing runoff generation at very low rain intensities while limiting the depth of water penetration in the channel itself data presented fit the concept of partial area contribution identified in humid areas however the application of this concept to dryland areas is based on completely different reasons

late pleistocene palaeoclimatic and palaeoenvironmental reconstruction of the dead sea area israel based on speleothems and cave stromatolites abstract calcite speleothems are a hitherto hardly documented occurrence in the nowadays arid to hyper arid rain shadow dead sea area of eastern israel speleothem ages u th from two caves on the dead sea fault escarpment and two caves from arid rain shadow areas surrounding the dead sea span the last three glacial cycles from ca 354 to 12 ka and suggest episodic moist local palaeoclimate mainly during glacial periods of marine isotopic stages mis 6 and 4 to 2 previously reported u th ages of stromatolites deposited in the late pleistocene lake lisan and preserved in caves of the dead sea fault escarpment suggest that regional relatively moist climate affected the lake catchment area during the late part of relatively warm mis 3 lasting until middle cold mis 2 as well as at the mis 5 to 4 interglacial glacial transition speleothem deposition periods spanning the 38 4 0 5 to 16 4 0 3 ka time interval i e late mis 3 to early mis 2 representing moist periods in the lake area are coeval to regional moist conditions inferred by the stromatolite record a direct connection is thus implied between local and regional climate at the latest pleistocene based on correlation between two independent data sets this connection implies that glacial climate has generally been moister than interglacial climate during the last glacial interglacial cycle at both local and regional scales around the dead sea and its predecessors

cave air and hydrological controls on prior calcite precipitation and stalagmite growth rates implications for palaeoclimate reconstructions using speleothems abstract hourly resolved cave air p co 2 and cave drip water hydrochemical data illustrate that calcite deposition on stalagmites can be modulated by prior calcite precipitation pcp on extremely short timescales a very clear second order covariation between cave air p co 2 and drip water ca 2 concentrations during the winter months demonstrates the effects of degassing induced pcp on drip water chemistry estimating the strength of the cave air p co 2 control on pcp is possible because the pcp signal is so clear at our drip site a one ppm shift in ca 2 concentrations requires a p co 2 shift of between 333 and 667 ppm this value will undoubtedly vary from site to site depending on drip water flow rate residence time drip water cave air p co 2 differential and availability of low p co 2 void spaces in the vadose zone above the cave high resolution cave environmental measurements were used to model calcite deposition on one stalagmite in crag cave sw ireland and modelled growth over the study period 222 m over 171 days is extremely similar to the amount of actual calcite growth 240 m over the same time interval strongly suggesting that equations used to estimate stalagmite growth rates are valid although cave air p co 2 appears to control drip water hydrochemistry in the winter drip water dilution caused by rain events may have played a larger role during the summer as evidenced by a series of sudden drops in ca 2 concentrations dilution followed by much more gradual increases in drip water ca 2 concentrations slow addition of diffuse water this research demonstrates that pcp on stalactites cave ceilings and void spaces within the karst above the cave partially controls drip water chemistry and that thorough characterisation of this process at individual caves is necessary to most accurately interpret climate records from those sites

perturbation electric fields and disturbance currents investigated during the 25 september 1998 great storm this study investigates the ionosphere s response to the 25 september 1998 great storm and utilizes multi instrument observations covering the australian 140 e geographic and indian 75 e longitude sectors results show the domination of eastward westward electrojet at 140 e 75 e its causative net eastward westward perturbation electric e field drove the forward reverse plasma fountain caused the presence absence of the equatorial ionization anomaly eia these strong longitudinal differences were due to a combination of various lt dependent e field driven and competing mechanisms perturbation e fields are identified as prompt penetration e field ppef and disturbance dynamo e field ddef due to the later earlier local time at 140 e 75 e the undershielding ppef was eastward westward directed early in the main phase a series of periodic substorms occurred during the recovery phase the substorm related eastward ppefs became overpowered by westward ddefs over india but remained dominant in the australian sector thus eastward ppefs westward ddefs dominated at 140 e 75 e at 140 e these eastward ppefs exhibited a strong positive correlation with the variations of both the cross polar cap potential drop and the asymmetric ring current significantly increased the net equatorial upward e b drift and thus caused eia development with plasma bubbles scintillating gps signals based on the strong and independent correlation of these asymmetric ring current events with both the eia development and the scintillation activity we propose that the asy h index could provide a natural tool for modeling eia development and scintillation episodes during severe storms characterized by periodic substorm related eastward ppefs

hydropedology of a mildly arid loess covered area southern israel extensive loess covered areas characterize the mildly arid areas of western israel where average annual rainfall is 280 mm hydrological data point to a peculiar hydrological behavior of the ephemeral streams the frequency of sporadic flash floods is very high however even in extreme rain events peak discharges are extremely low hydrographs are usually characterized by very steep rising and falling limbs representative of saturated areas extending over a limited part of the watershed following this observation we advanced the hypothesis that storm channel runoff originated in the channel itself with negligible contribution from the adjoining hillslopes the study was based on two complementary approaches the hydrological approach was based on the detailed analysis of rainfall runoff relationships in a small watershed 11 km2 and on the analysis of the hydrological characteristics of the drainage network the second approach was based on the toposequence concept several boreholes were dug along a hillslope 400 m long chemical data obtained show no significant difference in the downslope direction similar results were also obtained for the particle size distribution and soil moisture content data obtained perfectly fit the concept of partial area contribution as it presents an extreme case of hydrological discontinuity at the hillslope channel interface the lack of pedological trends in the downslope direction is an additional indication of the limited connectivity between the hillslopes and the adjoining channel the limited connectivity is attributed to the prevalence of low rain intensities in the study area the present study is also relevant to our understanding of pedological processes in dry land areas the high frequency of intermittent low intensity rainstorms limits runoff generation and flow distances and casts doubt on the general application of the toposequence approach this article is protected by copyright all rights reserved

very high frequency and seasonal cave atmosphere pco2 variability implications for stalagmite growth and oxygen isotope based paleoclimate records abstract cave air p co 2 at two irish sites varied dramatically on daily to seasonal timescales potentially affecting the timing of calcite deposition and consequently climate proxy records derived from stalagmites collected at the same sites temperature dependent biochemical processes in the soil control co 2 production resulting in high summer p co 2 values and low winter values at both sites large large amplitude high frequency variations superimposed on this seasonal cycle reflect cave air circulation here we model stalagmite growth rates which are controlled partly by co 2 degassing rates from drip water by considering both the seasonal and high frequency cave air p co 2 variations modeled hourly growth rates for stalagmite cc bil from crag cave in sw ireland reach maxima in late december 0 063 m h 1 and minima in late june early july 0 033 m h 1 for well mixed diffuse flow cave drips such as those that feed cc bil high summer cave air p co 2 depresses summer calcite deposition while low winter p co 2 promotes degassing and enhances deposition rates in stalagmites fed by well mixed drips lacking seasonal variations in 18 o integrated annual stalagmite calcite 18 o is unaffected however seasonality in cave air p co 2 may influence non conservative geochemical climate proxies e g 13 c sr ca stalagmites fed by seasonal drips whose hydrochemical properties vary in response to seasonality may have higher growth rates in summer because soil air p co 2 may increase relative to cave air p co 2 due to higher soil temperatures this in turn may bias stalagmite calcite 18 o records towards isotopically heavier summer drip water 18 o values resulting in elevated calcite 18 o values compared to the equilibrium values predicted by calcite water isotope fractionation equations interpretations of stalagmite based paleoclimate proxies should therefore consider the consequences of cave air p co 2 variability and the resulting intra annual variability in calcite deposition rates

dynamic evolution of the unsaturated hydraulic conductivity of a developing crust understanding the evolution of hydraulic parameters during the different stages of crust formation is necessary to predict in ltration in crusted soil however only a few studies have focused on the dynamics of parameters that control in ltration through a developing crust this study reports the results of laboratory experiments carried out with a speci c device the drip in ltrometer which enables a crust to form at the surface and the evolution of the pressure head and the hydraulic conductivity of the soil horizon underneath the crust to be followed simultaneously two soils of different susceptibility to crusting were used in the experiments a silt loam and a silty clay loam of the bassin de paris france the results show matric potential in the unsaturated range developing below the surface from the early stage of crust formation the values of matric potential show an increasing trend from the early stage of crust formation and at the late stage respectively for the silt loam and the silty clay loam soils the hydraulic conductivity of the sub crust shows signi cant changes from the early stage for the silt loam soil but only at the nal stages for the silty clay loam the initial value of the hydraulic conductivity of the sub crust drops by more than 50 per cent for silt loam compared to about 35 per cent for silty clay loam the decrease of hydraulic conductivity beneath the surface crust is related to the changes in the soil matrix induced by the migration of particles detached from aggregate breakdown the different stages of crust formation were characterized by the variation of the unsaturated conductance of the soil crusted layer calculated from the relationship between the ux density through the crust and the sub crust pressure head the results revealed rapid sealing at the surface of the silty loam soil whereas sealing occurs gradually at the surface of the silty clay loam the difference in the susceptibility to crusting and the difference in moisture characteristics between the two soils are probably the causes of the contrast in temporal variation of the sub crust matric potential copyright 2004 john wiley sons ltd

significance of primary hilltop loess in reconstructing dust chronology accretion rates and sources an example from the negev desert israel 1 although high latitude loess sequences have been studied extensively for reconstructing past climates loess in desert margins has been mostly overlooked moreover many low latitude loess studies have focused on secondary reworked sequences for which paleoclimatic inferences are complicated owing to postdepositional processes acting under local control in this respect the spatial distribution of the loess and its different types are crucial in this study we differentiate primary and secondary loess using remote sensing and field criteria we present remote sensing and geographic information system procedures for mapping loess distribution in general and for identifying pristine hilltop loess sequences in particular then we present the mineralogical and textural analyses combined with optically stimulated luminescence ages of one such primary hilltop loess sequence in the negev desert that show that the late pleistocene negev loess started accumulating at 95 ka much earlier than previously proposed 70 ka it was preceded by a previously unknown middle pleistocene period of loess formation at 180 130 ka the ages also suggest that the threshold of dust accretion rate needed for loess formation is 0 02 mm a 1 30 g m 2 a 1 a factor of 2 or more lower than previously thought 0 04 to 1 0 mm a 1 our results also provide insights into causes of late pleistocene loess accretion and its close association with regional dune field activity the methodology for mapping the loess distribution may potentially be generalized to help understanding loess formation in other more remote desert areas

nature formation and effects of soil crusts formed by water drop impact abstract research was conducted to investigate 1 the structure formation and nature of soil crusts which develop as a result of raindrop impact under controlled conditions of simulated rain and 2 the crust effect on infiltration rates scanning electron microscope sem observations performed on sandy sandy loam and clayey soil samples show the crust to be composed of two layers 1 a skin 0 1 mm thick and 2 a layer 2 3 mm thick with a higher bulk density in which aggregates have been destroyed a washing in zone described by earlier investigators could not be detected the soil beneath the crust maintains its original structure and particle orientation the chemical composition of the rain water was found to have a significant but not very large effect on the infiltration rate vs cumulative rain curve of the clayey soil material only final infiltration rate was about 20 lower when distilled water was applied compared to tap water electrical conductivity 0 6 mmho cm 1 an increase of the bulk density from 1 35 1 48 g cm 3 in undisturbed soil to 1 74 1 88 g cm 3 in crusts was found the amount of eroded material increased gradually with increase of runoff and decrease of infiltration at steady state the erosion rates were 0 45 1 25 and 0 76 g m 2 min 1 in the sandy sandy loam and clayey soil specimens respectively percentages of clay and silt in the eroded material were higher than in the bulk samples three stages to describe the changes in nature and effects of crusts during their formation are suggested 1 the rate of infiltration decreases to a point at which runoff beings 2 the initiation of runoff until infiltration and runoff rates become stabilized and 3 infiltration and runoff maintain steady rates

non linearities in drip water hydrology an example from stump cross caverns yorkshire drip rate data have been collected at 15 min intervals at six locations in stump cross caverns n england since 1998 the different drip sites cover a wide range of drip rates from 2 drips s to 2 drips h and in general the variability of drip rate increases with mean drip rate in our continuous data sampling we observe rapid discharge increases which appear to be synchronous between drips sites and which can be explained by flow switching of the water overlying the cave during times of high infiltration rate such as intense rain storms or rapid snowmelt a test for non linearity white test in the drip series provides very strong evidence that many of the drip sequences are non linear we conclude that at our drip sites there is a non linear input weather and non linearities within the karst system leading to non linear dripping which is independent of drip rate our results have implications for stalagmite palaeoclimatology where such widespread non linearities have not been taken account of

clay distribution over the landscape of israel from the hyper arid to the mediterranean climate regimes abstract the current study evaluates clay distribution in modern surface sediments mainly soils to which desert dust is a major contributor the mineralogical composition of the clay fraction of seventy seven samples was analyzed by x ray diffraction twenty nine soil and dust samples were also analyzed for their bulk chemical composition the samples are settled dust soils developed on various sedimentary rocks stream and lake sediments they were collected along a climate gradient from hyper arid to mediterranean regimes in israel the purpose of the study is to decipher the main factors that control variable clay distribution along this gradient including annual precipitation substrate type and topography the common clay composition for most samples of all sources is illite smectite is kaolinite illite trace amounts of chlorite palygorskite goethite and quartz might be present pedogenic processes are recognized even under arid climate where loessial soils display kaolinite depletion and more illitic is phases than dust two main processes shape clay composition under a mediterranean climate regime regardless of the parent material a smectitization process occurs in leached low permeable clayey soils and reaches optimum evolution with 90 smectite or smectitic is this evolutionary trend is also recognized in poorly drained soils of catenary chains that are related to other soil types like terra rossa hamra and pale rendzina kaolinitization and apparently illite pedogenic formation occur in well drained red mediterranean soils of the terra rossa and hamra types to the detriment of smectitic is phases of parent materials in the most evolved terra rossa and hamra soils kaolinite becomes the principal mineral and illite is significantly enriched pedogenic evolution of the clay fraction mineralogical composition affects bulk chemical composition of most soil types clay inheritance from the bedrock is rather limited in leached soils it is widely recognized in pale rendzina soils by the presence of smectite or smectite and palygorskite derived from late cretaceous or eocene chalks respectively streams clay composition like that of dust is fairly uniform as streams average various sources across their drainage basins however composition variations can be attributed to local contribution from certain sources

illite in aridic soils desert dusts and desert loess abstract in some desert loess deposits notably those of central asia illite dominates the clay fraction in others such as in the near east and north africa illite is a minor component the interaction between desert loess deposits and aridic desert soils via desert dusts is used to explain the difference in illite contents vertical profile distribution of illite as well as vertical distributions of soluble and exchangeable potassium are taken to indicate that illite forms pedogenetically in the surface horizon of aridic soils once formed it is stable and accumulates it is postulated that the potassium required for the illitazation process is introduced by aeolian dusts the process is facilitated by wetting and drying cycles dusts originating in deserts where they are presently produced by desert weathering of various rocks are defined as primary or juvenile dusts they have low illite contents such are the dusts that are carried from the eastern sahara and sinai peninsula northeast towards the middle east where they form local loess deposits the central asian dusts on the other hand have been subjected to numerous cycles of deflation and deposition resulting in relatively long residence times in the pedogenic environment of aridic soils this results in the enrichment of these dusts with illite the central asian desert loess deposits that interact with these dusts are consequently enriched with illite similar processes of illite enrichment may have operated in other areas such as australia

morphology genesis and classification of surface crusts in loamy and sandy soils abstract in an attempt to organize the knowledge of soil crusting processes and to group soil crusts on the basis of common morphological features and physical properties we synthesized and reinterpreted information from previous publications as a result we propose a classification system for surface crusts formed by rainfall in loamy and sandy soils although this system does not aim to be comprehensive it was designed from the study of a great number of crust samples collected in the temperate and tropical zones thus corresponding to a wide range of environmental and land use conditions three main classes of crusts structural erosion and depositional were distinguished each with subclasses where possible correspondence has been made with former systems this system helps predict infiltrability in accounting not only for total porosity of surface crusts but also for pore shape and continuity since crust classes are genetically related this classification system also supplies some insight into predicting soil degradation and selecting the most suitable control techniques

rain infiltration into loess soils from different geographic regions abstract loess soils are among the most erodible soils therefore evaluating and enhancing infiltration is paramount in controlling soil loss a laboratory study was conducted to evaluate the relative difference in infiltration among selected loess surface and subsurface soils from belgium canada china and the united states representing the major loess belts of the northern hemisphere soils were subjected to simulated rainstorms of constant intensity i 41 1mm h 1 duration 2 hours and energy rate 27 0 j m 2 per mm of rain infiltration runoff and soil water pressure were continuously monitored infiltration was described by a linear relationship for the pre ponding period and by a power series for the post ponding period differences in infiltration response were attributed to differences in soil properties such as differences in organic matter particle size swelling clay content fe oxyhydroxides and carbonates despite the high organic carbon content and coarser texture of the canadian loess surface soil the presence of highly expansive smectitic clay caused a rapid reduction in infiltration rates indicating the importance of soil mineralogical constituents in surface seal development