rock weathering rates as functions of time the scarcity of documented numerical relations between rock weathering and time has led to a common assumption that rates of weathering are linear this assumption has been strengthened by studies that have calculated long term average rates however little theoretical or empirical evidence exists to support linear rates for most chemical weathering processes with the exception of congruent dissolution processes the few previous studies of rock weathering rates that contain quantitative documentation of the relation between chemical weathering and time suggest that the rates of most weathering processes decrease with time recent studies of weathering rinds on basaltic and andesitic stones in glacial deposits in the western united states also clearly demonstrate that rock weathering processes slow with time some weathering processes appear to conform to exponential functions of time such as the square root time function for hydration of volcanic glass which conforms to the theoretical predictions of diffusion kinetics however weathering of mineralogically heterogeneous rocks involves complex physical and chemical processes that generally can be expressed only empirically commonly by way of logarithmic time functions incongruent dissolution and other weathering processes produce residues which are commonly used as measures of weathering these residues appear to slow movement of water to unaltered material and impede chemical transport away from it if weathering residues impede weathering processes then rates of weathering and rates of residue production are inversely proportional to some function of the residue thickness this results in simple mathematical analogs for weathering that imply nonlinear time functions the rate of weathering becomes constant only when an equilibrium thickness of the residue is reached because weathering residues are relatively stable chemically and because physical removal of residues below the ground surface is slight many weathering features require considerable time to reach constant rates of change for weathering rinds on volcanic stones in the western united states this time is at least 0 5 my

relative age dating of transported regolith and application to study of landform evolution in the appalachians abstract surficial deposits in the appalachians generally are thin discontinuous and difficult to date in the absence of numerical dates particularly for older deposits relative age indices based on degree of weathering and soil development have been used to distinguish and correlate deposits of different ages a favorite locale of relative age studies has been stream terraces where chronosequences have been developed to shed light on the relationship between time and weathering soil development the lack of applicable numerical dating techniques has led some researchers to establish relative chronosequences in which height of stream or fan terraces above modern river level arl serves as a proxy for time approximate incision rates can then be used to estimate numerical ages of the deposits relative age correlations between the weathering indices on the terraces and comparable indices on dated deposits on the coastal plain and in nearby glaciated regions suggest that ages so estimated are the right order of magnitude relative age indices show correlations with height arl that are as high as those with time perhaps because more data sets are available for relative chronosequences than for true chronosequences analogous relative age sequences can be established for alluvial fans and even for hillslope colluvium many weathering indices have been employed but weathering rind thickness on mafic to intermediate clasts has proved to be a particularly consistent and useful parameter in addition to showing how weathering and soil development progress over time relative age dating has shed light on the manner in which landforms evolve along some rivers for example the areal extent of old highly weathered alluvium far exceeds that of younger alluvium suggesting that formerly floodplains and low terraces were much more extensive than at present in addition the manner in which weathering indices on some river terrace sequences vary with height arl suggests that incision rate has changed through time relative age mapping of alluvial fans produces a map pattern of older and younger fan surfaces that allows the sequence of fan development to be inferred in one case suggesting a scenario different from those previously described for fans mapping also shows that the relative abundance of young intermediate and old fan surfaces varies greatly from one area to another several studies have demonstrated clustering of relative age values into a small number of groups suggesting temporal grouping and thus episodic deposition on fans regression of weathering rind thickness against height above modern drainageways of remnant fan surfaces in two areas suggests that fans are being incised more rapidly in one area than in another relative age of hillslope colluvium also aids geomorphic interpretation young brown colluvium is much more common than old red colluvium near the glacier border where red colluvium rarely occurs at the surface but typically is covered by brown colluvium probably mobilized during the late pleistocene distant from the ice margin however red colluvium is extensively exposed on interfluves relatively stable hillslopes can also be distinguished from active ones in this manner for example colluvium on hillslope noses is somewhat more weathered than that on hollow floors and sideslopes

weathering rinds and the evolution of piedmont slopes in the southern blue ridge mountains the piedmont slopes on the west side of rich and snake mountains in the blue ridge province are composed of dozens of fans and fan remnants of various ages the fans consist of a few meters of flood and debris flow deposits overlying saprolite and deeply weathered bedrock the deposits are rich in amphibolite clasts the weathering rinds of which allowed fan surfaces to be classified into six relative age categories on the basis of rind thickness the presence of reversed remanent magnetism in one old fan deposit indicates an age of at least 780 ka however the magnetization appears to reside in secondary hematite produced by weathering rather than in original magnetite grains so that a minimum age on the order of 1 ma is more likely transverse profiles surveyed across 15 fans and fan remnants show that old surfaces may attain heights as great as 30 m above younger surfaces but that a better index of age is the convexity of the profile young surfaces show only slight transverse convexities but old su

relative age relationships of debris flow deposits in the southern blue ridge north carolina abstract periods of increased landscape instability in the southern blue ridge were assessed with relative ages of three sequences of debris flow deposits the sequences consist of a series of lobate deposits that are expressed as step like landforms on the floors of host valleys data were collected at three sites from soil pits on the toe and apex of debris flow deposits relative ages were obtained by qualitatively and statistically examining data on clast weathering soil color clay content and iron species consistent results among the indicators of relative age demonstrate that they have utility in warm to temperate humid environments at each site the topographically highest debris flow deposits are slightly older than those at lower elevations one deposit at each of the three sites has a relative age that is very similar to that of one deposit at the other sites this similarity in age indicates that an external factor such as extreme precipitation accounts for the formation of debris flows at approximately the same time in the geological past one of the sites however also has deposits that are clearly younger than the deposits at the other sites which indicates that intrinsic factors also affect the formation of debris flows in the region

stream capture and the geomorphic evolution of the linville gorge in the southern appalachians usa abstract the linville river in the blue ridge of north carolina flows across the blue ridge escarpment and through linville gorge a unique topographic feature within the southern appalachians the upper portion of the drainage effectively shifts the eastern continental divide away from the escarpment crest this shift is similar to other locations along the escarpment where streams flowing towards the piedmont have captured drainage area from low relief streams that drain towards the west here we examine the upper linville river for evidence of drainage captures that would have shifted drainage area away from the toe river and into the linville river we used lidar data to reconstruct stream profiles for possible drainage pathways and examined cobble deposits near the headwaters of the north toe river within those deposits on the west side of the linville river we found quartzite cobbles that must have been sourced from bedrock exposed only on the east side of the modern linville river this indicates that portions of the linville valley above linville falls historically drained to the west into the north toe river headward erosion above linville falls resulted in downcutting and multiple stream captures these captures more than tripled the drainage area of the linville river which would have significantly increased discharge downstream this increase in discharge likely drove the geomorphic evolution of the modern linville gorge including resultant downcutting and associated hillslope processes and helps to explain the prominence of linville gorge

comparative geomorphic analysis of surficial deposits at three central appalachian watersheds implications for controls on sediment transport efficiency abstract factors that control the routing and storage of sediments in the appalachian region are poorly understood this study involves a comparative geomorphic analysis of three watersheds underlain by sandstones and shales of the acadian clastic wedge these areas include the fernow experimental forest tucker county west virginia the north fork basin pocahontas county west virginia and the little river basin augusta county virginia gis based analyses of surficial map units allow first order approximation of sediment storage volumes in valley bottoms estimates of volumes are examined in tandem with morphometric analyses and the distribution of bedrock channels to make inferences regarding controls on sediment transport efficiency in the central appalachians the fernow and north fork areas are characterized by v shaped valleys with mixed reaches of alluvial bedrock channels distributed throughout the drainage network in contrast the little river valley is notably wider and gravelly alluvial fill is abundant comparator watershed parameters for the fernow north fork and little river areas include respectively 1 basin area 15 2 km 2 49 3 km 2 41 5 km 2 2 basin relief 0 586 km 0 533 km 0 828 km 3 drainage density 4 2 km 1 3 3 km 1 4 7 km 1 4 ruggedness 2 5 1 7 3 9 5 shreve magnitude 139 287 380 6 total valley bottom area km 2 0 76 km 2 1 86 km 2 3 09 km 2 7 average hillslope gradients 17 2 18 4 22 1 8 total debris fan surface area 0 113 km 2 0 165 km 2 0 486 km 2 and 9 debris fan frequency 2 0 km 2 1 0 km 2 2 8 km 2 the storage volumes in valley bottoms were estimated using map polygon areas and surface heights above channel grade the little river contains significantly higher sediment volumes in floodplain terrace and fan storage compartments total volumes of the valley bottoms are approximately twice that of the fernow and north fork areas combined unit storage volumes for the fernow north fork and little river are 5 2 10 4 m 3 km 2 5 5 10 4 m 3 km 2 and 1 6 10 5 m 3 km 2 respectively a conceptual model postulates that valley width morphometry and style of delivery from hillslopes are the primary factors controlling the efficiency of sediment transport steep debris flow prone hillslopes at the little river deliver high volumes of gravelly sediment at magnitudes greater than transport capacity of the channel patterns of stream power are complex as low order tributaries are under capacity and high order tributaries over capacity with respect to sediment load aggraded alluvial fill insulates valley floor bedrock from vertical erosion and valley widening dominates expansion of the valley width creates a positive response via increased storage capacity and lower unit stream power conversely the fernow and north fork are characterized by diffusive mass movement on hillslopes with incremental bedload transport to higher order tributaries rates of hillslope delivery are balanced by the rate of channel export mixed alluvial bedrock reaches provide the optimal channel configuration for active incision of the valley floor low expansion of valley width promotes high unit stream power and processes of vertical erosion the model implies that the fernow and north fork have been more effective at sediment transport during the late quaternary given similar climatic and tectonic settings variation in bedrock lithofacies is likely the primary factor modulating the efficiency of sediment transport

holocene erosion sedimentation and stratigraphy at raven fork southern blue ridge mountains usa holocene colluvial and alluvial stratigraphy and a radiocarbon chronology are presented for the valley of the lower three kilometers of raven fork a mountain stream draining 194 km 2 of high relief 1 3 km terrain of the southern blue ridge mountains in western north carolina usa which is in a region that lacks good chronological data lower hillslopes alluvial colluvial fans alluvial bottomlands first terrace and floodplain and the modern stream channel are landforms described with respect to soils stratigraphy and sedimentary structures standard methods for subsurface investigations core holes excavation units exposures are used in conjunction with extensive archeological excavations and cultural chronologies radiocarbon ages from each landform are used to calculate long term average rates of sedimentation results indicate that the first half of the holocene experienced somewhat more rapid rates of hillslope sedimentation 0 3 to 1 1 mm yr than the last half of the holocene 0 1 0 2 mm yr on footslopes toeslopes and alluvial colluvial fans prior to historic time we suggest that these subtle differences in the rates of sedimentation were driven by changes in global paleoclimate that favored a high frequency of heavy rainfall including tropical storms and or severe thunderstorms and more and possibly larger floods during the first half of the holocene prehistoric rates of vertical accretion on the first terrace t1 ranged from 0 1 to 0 8 mm yr between about 10 000 and 3000 calendar years ago and incision below t1 formed the late holocene floodplain beginning at about 6000 years ago we suggest that this incision is linked to a reduction in the supply of sediment and a reduction in the magnitude of floods historical rates of sedimentation on all parts of the depositional landscape 2 0 2 7 mm yr on hillslopes and fans and 5 8 6 5 mm yr on floodplains were about an order of magnitude greater than prehistoric rates we attribute these rates to human impacts such as timber harvest and land clearing which caused accelerated erosion we attribute the abundance of fine grained sediment in streams of the southern blue ridge province which is atypical in many mountain streams around the world to the regionally widespread mantle of saprolite as a source of sediment to the fluvial system holocene sedimentation on all depositional landforms in the valley led to sedimentary burial of archeological materials which highlights the need to consider site burial on lower hillslopes and terraces for evaluation of the cultural resources in the southern blue ridge mountains these findings show that the entrenched condition of the raven fork channel was inherited from the middle holocene and can be considered a natural state for this mountain stream casting doubt on the negative connotation that is often assigned to entrenched channels

soil development in till of various ages in northeastern pennsylvania abstract eleven well drained soils formed in till parent materials of varying ages in northeastern pennsylvania were studied to determine changes in the soils with time four profiles three lackawanna and one bath were formed in woodfordian till 15 000 yr b p and two leck kill were formed in altonian till 28 000 75 000 yr b p in these soils the extractable iron oxide extractable aluminum oxide and kaolinite contents increase with age as do the total clay and fine total clay ratio with increasing age the maximum accumulation of these constituents is found deeper in the profile the extractable silicon oxide distribution is constant with depth but it decreases in overall amount with time gibbsite is found only in small amounts in the a horizon of altonian soils but occurs throughout the profile of pre wisconsinan soils although only in small amounts in general differences were found in these soils which separated them into three groups representing varying degrees of soil development a regression equation was derived to predict the age of soils formed from the altonian till based on a clay accumulation index value for soils of known woodfordian and holocene ages the equation log y 1 80 0 992 log x best fit the data with an r 2 value of 0 913 using this equation a mean age of 41 000 yr was calculated for the altonian soils this date was used to derive a second equation to predict ages for pre wisconsinan soils the equation with the highest r 2 value 0 934 was log y 1 81 0 998 log x dates for soils developed in the white deer till and the laurelton till of the pre wisconsinan stage were calculated to be 86 000 and 91 000 yr b p respectively these dates fall within ages estimated for the sangamon interglaciation and thus would appear to be too young for pre sangamonian materials the probable reason for the too young age is that the c horizon material of the pre wisconsinan soils was weathered and did not provide an accurate estimate of clay accumulation for the prediction equation

a ring shear device for the study of till deformation tests on tills with contrasting clay contents abstract deformation of subglacial sediment may have had a profound influence on the geomorphic effects and dynamics of pleistocene ice sheets but data that bear on the rheology of such sediment are few and contradictory a means of studying systematically the mechanical properties of glacial tills is provided by a ring shear device that shears a large annular specimen to high strains at variable rates special features of the device allow continuous observation of the distribution of shear strain measurement of local stresses normal to the direction of shear and isolation of wall effects thus far a linear viscous putty and two tills with different clay contents 4 and 32 by weight have been tested the experiments with till indicate as expected that the presence of dispersed clay minerals reduces markedly both the residual strength and hydraulic diffusivity of till clay also reduces spatial variations in normal stress associated with grain bridges the walls bounding the specimen support only 9 17 of the total resistance to shearing strain was localized in both tills but not in the linear viscous putty strain localization in the tills indicates that their theology departs significantly from linear and bingham viscous models

chronosequence development and soil variability from a variety of sub alpine post glacial landforms and deposits in the southeastern san juan mountains of colorado abstract surficial processes acting on post glacial alpine and sub alpine landscapes vary at small temporal and spatial scales and are thus often difficult to conceptualize in the context of large scale landscape evolution models soils developing in this setting can thus provide valuable information about landform genesis sedimentology and age relatively few post glacial chronosequences have been examined in these settings however particularly for the variety of landforms and parent materials that exist within alpine and sub alpine environments here we examine a chronosequence of relatively young post glacial landforms with varying parent materials and climate histories we dug and described 39 soil pits in the upper conejos river valley of colorado on a variety of deposits and landforms including alluvial fans terraces colluvium glacial till and terminal moraines and compared soil properties with radiocarbon ages from the area our results suggest that some typical chronosequence soil properties e g ph structure color do not correlate with time over short time scales however extractable iron ratios feo fed show a relatively strong correlation with age across late pleistocene and holocene time scales and maximum profile clay content shows a weak but statistically significant relationship with age both of these trends are stronger when examined across a single parent material differences in initial parent material texture and dust inputs seem to be the most significant complicating factors over post glacial time scales soil property development through time is most inconsistent in cumulic alluvial fan soils this observation may indicate that alluvial fans are more responsive to sub basin scale processes as opposed to fluvial terraces that are more likely respond to processes active across the entire basin these differences would explain why stratigraphically similar alluvial fans are mantled by soils with varying development nonetheless horizonation clay content and extractable iron ratios provide a useful tool for correlating young deposits assigning ages and interpreting the geomorphic history of complex post glacial environments

intermittency of illuviation in dystrochrepts and hapludults from the piedmont and blue ridge provinces of north carolina abstract dystrochrepts and hapludults formed from mica gneiss and schist in the piedmont and blue ridge provinces of north carolina have a range of illuvation cutan orientation patterns that is related to various indicators of soil development clay content solum thickness and degree of primary mineral alteration the relationship of cutan orientation patterns to soil development in these soils suggests that clay illuviation is largely intermittent in occurrence lessivage occurs in typic dystrochrepts the soils showing the least morphological development but because of the thinness and coarse texture of the sola the major areas of accumulation may occur beneath the cambic horizons in vertical cracks in the structurally rigid isovolumetrically weathered saprolite the source of clay is relatively easily weathered plagioclase few illuviation cutans are present in argillic horizons of fine loamy hapludults evidence of illuvial clay is lacking because biotite is being altered to sand and silt sized pseudomorphs of kaolinite with little production of clay sized particles once the biotite is entirely kaolinized comminution of the sand and silt sized kaolinite grains supplies clay for clayey argillic horizons to evolve soils at this stage of development have abundant illuviation cutans with strong continuous orientation after the silt and sand sized kaolinite has been comminuted the only primary minerals remaining in any abundance to produce clay sized particles are relatively resistant muscovite and microcline iron continues to concentrate as the clayey hapludults develop masking the anisotropy of the illuviation cutans the increasing lack of distinctness of cutans and their apparent low degree of orientation with increasing degree of soil development indicate that illuviation has largely ceased in the most developed clayey hapludults and the illuvial features are for the most part relict features of an earlier period of clay production

instruments and methods direct measurement of sliding at the glacier bed sliding at the base of trapridge glacier yukon territory canada was measured using a drag spool we describe this simple and inexpensive instrument as well as its installation and operation from 1990 to 1992 seven sites were instrumented with drag spools at six of the sites basal sliding during the period of observation accounted for 50 70 of the total flow observed at the glacier surface the contribution from ice creep is known to be small so most of the remaining surface motion must be attributed to subglacial sediment deformation for the seventh site the observed sliding rate was 90 of the total flow an indication that the sliding contribution varies spatially across the bed diurnal variations in the response of one of our instruments appear to be correlated to subglacial water pressure fluctuations and are interpreted in terms of changes in sliding velocity rather than the opening and closing of basal cavities

techniques for measuring rock weathering application to a dated fan segment sequence in southern tunisia there are a number of techniques for estimating the amount of weathering a clast has undergone these usually have the objective of establishing an ordinal chronology of geomorphological surfaces or investigation of site specific conditions affecting weathering rates three such techniques are applied to a dated sequence of alluvial fan segments in southern tunisia two of these techniques depend on measuring surface roughness the micro roughness meter and a displacement approach and one uses the structural weakening of the rock fabric schmidt hammer the micro roughness meter enables calculation of standard deviation of surface height variation root mean square roughness and surface autocorrelation function of these techniques schmidt hammer rebound values standard deviation root mean square roughness and the displacement technique show systematic changes on the three fan segments which are statistically significant at the 0 05 level however the amount of variance in all datasets is very large indicating the need for caution in application of these techniques for relative dating 1998 john wiley sons ltd

weathering and soil development on fan surfaces as a function of height above modern drainageways roan mountain north carolina abstract a relative age chronosequence has been established for fan surfaces on the west and south piedmont slopes of roan mountain north carolina based on measurements of weathering and soil development indices at 20 sites in addition to standard soil properties measurements were made of amphibolite clast weathering rind thickness maximum surface boulder size and mean size and sorting of a 10 kg whole sediment sample from the c horizon soils lacking bt horizons occur only at high altitudes at or near the heads of young fans excepting these locations the youngest fan surfaces have soils with bt horizons generally less than 60 cm thick hues of 10 7 5yr maximum clay contents less than 35 percent rind thicknesses less than 1 2 mm and maximum boulder diameters of 1 2 m soils of the oldest fan surfaces have bt horizons 75 200 cm thick hues of 5 2 5yr rind thicknesses of 6 14 mm maximum clay contents of 40 60 percent and maximum boulder diameters less than 0 75 m although the youngest fan surfaces are close to the level of modern drainageways the oldest stand as much as 20 m above these drainageways and are obviously relict features an index of fan height above modern drainageways was devised that combines height above lateral drainageways with height above the main stream of the valley into which the fan debouches many weathering and soil development properties correlate significantly with this height index including weathering rind thickness r 0 86 munsell hue 0 65 maximum percent clay 0 59 graphic mean phi units of whole sediment particle size analysis 0 54 maximum boulder diameter 0 52 maximum percent free iron in b horizon 0 50 and thickness of bt horizon 0 49 a soil weathering soil development index using these parameters shows a 0 82 correlation coefficient with the height index a cluster analysis shows that the 20 sites can be placed into three distinct groups suggesting that the formation of fan surfaces may be episodic on long time scales a comparison of the fan map with a county soils map shows that the oldest fan surface is fairly consistently mapped as dillsboro series but that the younger fan surfaces show no consistent relationship to soils mapping

boulder streams debris fans and pleistocene climate change in the blue ridge mountains of central virginia the west slope of the blue ridge mountains in central virginia is a polygenetic landscape containing interglacial and periglacial features this paper proposes a general model relating the distribution and origin of hillslope and toeslope quaternary landforms to climatically influenced geomorphic processes two generations of interglacial debris fans in the study area differ in their degree of soil development and clast weathering boulder streams which clog debris flow chutes for the upper debris fans are interpreted as solifluction features formed during successive periglacial episodes growth of the boulder streams and associated talus slopes can influence the magnitude and frequency of debris flows and fan formation during interglacials

magnetostratigraphy of sediments in mammoth cave kentucky clastic sediment deposits found within the caves of mammoth cave national park have yielded a magnetostratigraphic pattern of magnetic polarity reversals which indicates that they were deposited over a range of at least 1 million and most likely 2 million years

multivariate correlation analysis of seismic piezocone penetration scptu parameters and design properties of jiangsu quaternary cohesive soils abstract a recent trend of geotechnical correlation analysis is to construct a multivariate distribution model to describe the multiple dependency characteristics of different soil parameters in this study the feasibility of this multivariate method to model the multivariate dependency of seven soil parameters including the undrained shear strength ratio overconsolidation ratio sensitivity normalized cone tip resistance normalized sleeve frictional resistance pore pressure parameter and normalized shear wave velocity is studied a database containing 372 sets of observations of these seven parameters is collected from 25 sites in the jiangsu province china two data transformations including the johnson system of distribution and box cox method were used in the construction of the multivariate model for the jiangsu cohesive soils the correlations derived from these two local models were compared with the compiled jiangsu database data points at other testing sites in china and database and correlations published in the literature for validation it was shown that the local models developed in this study were capable of the multivariate dependency of the soil parameters for the jiangsu cohesive soils whereas the global model developed in the literature tends to overestimate the uncertainties associated with the design parameters for the jiangsu soils a potential explanation is that the soil parameters in a local region were less variable with stronger correlations than those over the global sites due to the site specific effect however caution shall be taken if the local models for the jiangsu soils are used at other sites besides the johnson system of distribution is superior to the box cox transformation in the construction of the multivariate distribution model in the sense that the former is more effective to achieve the standard normal distribution especially for the soil parameters with a bounded distribution

quaternary deposits and landscape evolution of the central blue ridge of virginia abstract a catastrophic storm that struck the central virginia blue ridge mountains in june 1995 delivered over 775 mm 30 5 in of rain in 16 h the deluge triggered more than 1000 slope failures and stream channels and debris fans were deeply incised exposing the stratigraphy of earlier mass movement and fluvial deposits the synthesis of data obtained from detailed pollen studies and 39 radiometrically dated surficial deposits in the rapidan basin gives new insights into quaternary climatic change and landscape evolution of the central blue ridge mountains the oldest depositional landforms in the study area are fluvial terraces their deposits have weathering characteristics similar to both early pleistocene and late tertiary terrace surfaces located near the fall zone of virginia terraces of similar ages are also present in nearby basins and suggest regional incision of streams in the area since early pleistocene late tertiary time the oldest debris flow deposits in the study area are much older than wisconsinan glaciation as indicated by 2 5yr colors thick argillic horizons and fully disintegrated granitic cobbles radiocarbon dating indicates that debris flow activity since 25 000 ybp has recurred on average at least every 2500 years the presence of stratified slope deposits emplaced from 27 410 through 15 800 ybp indicates hillslope stripping and reduced vegetation cover on upland slopes during the wisconsinan glacial maximum regolith generated from mechanical weathering during the pleistocene collected in low order stream channels and was episodically delivered to the valley floor by debris flows debris fans prograded onto flood plains during the late pleistocene but have been incised by holocene stream entrenchment the fan incision allows holocene debris flows to largely bypass many of the higher elevation debris fan surfaces and deposit onto the topographically lower surfaces these episodic high magnitude storm events are responsible for transporting approximately half of the sediment from high gradient low order drainage basins to debris fans and flood plains

geomorphological controls on soil fertility of semi arid alluvial fans a case study of the joghatay mountains northeast iran abstract alluvial fans are ideal locations to examine the effect of geomorphic processes and landforms on the soil characteristics the rate of soil development and fertility differs between active surfaces exposed to aggradation and old or relict surfaces subject to degradation the aim of this research is to evaluate the effect of landforms and processes on soil fertility based on the studies on three alluvial fans of different ages relict old and young a total of 36 soil samples were collected from these three alluvial fan surfaces the samples were gathered from different locations of fans apex and toe and landforms gully beds interfluves swales and bars and for each sample nine variables including soil texture acidity ph electrical conductivity ec total neutralizing value tnv available phosphorus ap available potassium ak total nitrogen tn total organic carbon toc and hydraulic conductivity k were measured the results show that the values of tnv ap ak tn and toc increase as clay increases in the relict and old fans the values of tnv toc tn ap ak clay and silt are higher in the interfluves than in the gully beds also in the relict and old fans the rates of clay silt toc tn and ap are higher in the apexes than in the toes in the young fan the values of most variables are higher in the toe compared to the apex the wide and relatively flat interfluves of the apex of old and relict fans have soils that are more fertile compared to the extensively entrenched surfaces of relict and old fan toes with relatively steep sloped interfluves the less fertile soils in the apex of young fan can be attributed to its coarse textured soils and also to repeated flooding and depositional processes overall this study reveals that geomorphological landforms and processes such as aggradation and degradation play an important role in the spatial variation of soil fertility