bluuebunny/crossref_metadata_2025_split huggingface dataset:
A quantitative scanning electron microscope study of evidence for lichen weathering of limestone, Mendip Hills, Somerset
Authors: Viles Heather 
Published: February 2007

AbstractMany saxicolous lichens may cause physical and chemical weathering of limestone substrates, but their geomorphological importance has not been fully determined. A simple method of producing quantitative descriptions of lichen material and petrographic evidence of weathering using the SEM has been developed and tested on samples from the Mendip Hills, England. The technique reveals a variable and often sparse distribution of lichen material and associated weathering effects below a thin, clearly defined lichen thallus.
Slope form, erosion, and hydrology in some Belizean Karst depressions
Authors: Day Michael 
Published: February 2007

AbstractDetailed slope surveys were made in seven karst depressions in central Belize. Four major slope types were identified—inclined bedrock slopes, staircases, broken cliffs, and talus slopes. Depression bases are dominated by inclined bedrock and talus slopes, midslopes largely by broken cliffs, and near hill summits by staircases. Erosional weight loss tablets deployed in 1975–1981 and 1980–1985 show significant variations between the different slope types, with a maximum near depression bases. Throughfall measurements in 1980 and 1985 show that midslope and near‐summit sites receive 10–20 per cent less water than do depression bases. Surface runoff, monitored using coloured dyes, is of limited distance and duration but still contributes to surface corrosion and morphology. Vadose seepage, monitored by tracing water from the surface to a small, shallow cave, is rapid, and subsurface corrosion exceeds that at the surface.Overall, near‐surface form and process are consistent with hydrological models of depression development (Williams, 1983, 1985) and surface processes contribute significantly to overall depression form. Moreover, surface activity complements that in the subcutaneous zone by directing recharge into the epikarstic aquifer.
Limited modification of mid‐latitude landscapes by ice sheets: The case of northeast Scotland
Authors: Hall Adrian M. , Sugden David E. 
Published: February 2007

AbstractThe paper uses a case study in Scotland to examine the amount and processes of landscape modification by Quaternary ice sheets. There is an inverse correlation between the distribution of landforms of glacial erosion and pre‐glacial landscape remnants in northeast Scotland. The implication is that in places ice sheets can preserve a pre‐glacial landscape unscathed, while elsewhere they remove the pre‐glacial weathered rock. The location of glacial protection or erosion is strongly influenced by the topography and its influence on former ice sheet flow and basal thermal regime. The classic glacially eroded landscape of areal scouring can be produced by the removal of only 10–50 m of weathered rock. Furthermore rock basins, often regarded as the hallmark of glacial erosion, may be directly inherited from the pre‐glacial pattern of deep weathering.
Limestone landform studies and their curriculum applications
Authors: Paterson Keith 
Published: February 2007

AbstractThis paper reviews the educational merits and application of limestone landform studies in British secondary schools and considers these in the context of recent developments within geomorphology and the geography curriculum. The relevance of both traditional and newer approaches to the field study of karstforms is highlighted together with developments in classroom activities. School‐based work is shown to have benefitted considerably from advances in educational technology.
Dissipative systems: Implications for geomorphology
Authors: Huggett R. J. 
Published: February 2007

AbstractA recent revolution in the study of nonlinear dynamical systems in the physical sciences has shown the worth of regarding systems as dissipative. The nature of dissipative systems in equations, bifurcations, and fluctuations. Some speculations are then made concerning the implications of dissipative system theory for geomorphology. It is suggested that geomorphological systems containing bifurcations will have both deterministic (universal and necessary) and probabilistic (historical happenstance) elements; they will have more than one solution (configuration) and this fact calls into question notions of process domains leading to the development of characteristic forms; they will possess varying degrees of susceptibility to change induced by fluctuations; and they will respond differently to local, regional, and global fluctuations.
Thin surface soil layers attributable to rain‐flow transportation on low‐angle slopes: An example from semi‐arid tropical Queensland, Australia
Authors: Coventry R. J. , Moss A. J. , Verster E. 
Published: February 2007

AbstractParticle‐size analyses have been made on surface soils and a thin, overlying sandy pavement at 16 sites along a gently sloping transect at Torrens Creek in North Queensland. The transect is 1590 m long and has a maximum gradient of 0.018 (less than 1°). The sandy pavement is enriched in coarse components due to the sorting and differential downslope transport of the finer soil fractions. Particle movement is ascribed to the action of raindrops impacting very shallow, flowing water. The process, referred to as ‘rain‐flow transportation’, is active wherever overland flow is too weak to generate rills and channels and occurs in areas of very low slope with permeable surface soils that allow rapid infiltration during storms. Rain‐flow transportation is discussed with particular reference to the development of soil profiles in an old, subdued landscape of semi‐arid tropical Australia.
A unified theory of particulate flows in geomorphic settings
Authors: Culling W. E. H. 
Published: February 2007

AbstractParticle aggregates can be regarded as a fourth state of matter which with differing energy levels can display behaviour associated with the other three. This provides the basis for a unified theory of particulate flow in the land scape, ranging from the solid‐like soil creep, through plastic flows like solifluction to fluidized phenomena exemplified by fluvial sediment flows wherein bed and suspended loads relate to dense and dilute phases of fluidized beds and therefore to liquids and gases respectively.The theory of the liquid state is central to any unified theory and this is presented with the aid of Eyring's rate process theory and Frenkel's theory of holes. Applications to geomorphology are noted, to be given detailed treatment on a subsequent occasion.
Historical development of the saltmarsh at Wells, Maine
Authors: Jacobson Heather A. 
Published: February 2007

AbstractComparisons of maps and aerial photographs dating from the late 1700s to the present document the recent development of an 8 km2 saltmarsh that is situated behind a barrier spit in southern Maine. Tidal channels that were relatively narrow in 1794 became wider by 1872. The reduction of marsh bordering tidal channels is interpreted as evidence that marsh accretion could not keep pace with rising sea‐level. This suggests that the rate of sea‐level rise had increased, although a change in discharge or sediment load caused by extensive settlement and land clearance may also have been involved.Meander patterns of the tidal streams changed considerably throughout the time period covered by the maps, demonstrating that the streams of this marsh are more dynamic than some others that have been widely reported in the literature. These differences in stream dynamics are probably related to the differences in sedimentological structure of the marshes.Between 1872 and 1956 the barrier spit eroded on its inside (shoreward) edge, probably in response to the construction of riprapping and houses along the spit, and the subsequent reduction of overwash and aeolian transport of sediment.Modification of the tidal inlet and adjacent marsh during the 1960s, including jetty construction, dredging, and filling of portions of the marsh surface, affected the marsh only locally. One tidal stream has been migrating rapidly apparently in response to compaction of peat by dredge spoils and consequent local disruption of the marsh hydrology. Except for this migration, erosion of the marsh edge occurred immediately after the inlet modifications; planimetric changes in the marsh and its streams have been minor since then.
Application of a diffusion‐erosion model to alluvial channels which degrade due to base‐level lowering
Authors: Begin Ze'ev B. 
Published: February 2007

AbstractThe applicability of a diffusion‐erosion model that predicts transient longitudinal profiles of degrading alluvial channels has already been demonstrated in laboratory experiments, and is here applied to some field examples. By fitting simulated longitudinal profiles to measured ones for several streams (with discharge 0.04<Q5<680 m3s−1) diffusion‐erosion coefficients, K, were determined which are well correlated to discharge and drainage area.Headward knickpoint migration which results from base‐level lowering was also treated through the diffusion‐erosion model. Theoretically, the distance of a knickpoint from the mouth of a tributary should be proportional to the square root of the time that elapsed since the base‐level was lowered. Field observations are in accordance with these theoretical considerations.Use of the model is discussed for prediction of erosion and for assessment of the age of alluvial fault scarps crossed by streams.
The complex nature of creep movements on steeply sloping ground in Southern Rwanda
Authors: Moeyersons Jan 
Published: February 2007

AbstractLong term soil creep motion is often represented as a type of laminar flow, with velocity vectors parallel to the slope and constant in time. Records on a hillslope in Southern Rwanda reveal that creep movements there compare more with turbulent flow, characterized by a A1 humic horizon superlayer, creeping over a subsoil affected by more irregular creep deformation.
Sediment size variation in a braided reach of the Sunwapta River, Alberta, Canada
Authors: Dawson Martin 
Published: February 2007

AbstractThe downstream diminution in sediment size in a braided reach of the proglacial Sunwapta River, Alberta, Canada, was examined statistically to identify the sources of the observed variation about an expected exponential relationship between clast size and distance. Major deviations from this hypothetical relationship, such as a relative increase in grainsize, may be attributed to the effects of tributary sediment inputs and downstream changes in channel behaviour, whilst local variation is associated with complex patterns of sediment deposition observed at a bar scale. A comparison of diminution coefficients, calculated for separate lithologies and for subreaches along the river, with those obtained from previous studies, is used as an indicator of river behaviour and sediment transport processes. It is shown that rates of diminution vary within the reach in response to differing rates of aggradation and to the backwater effects created by tributary alluvial fans. The relatively high values for the calculated diminution coefficients indicate that processes of differential transport are the main cause of the grain size decrease.
Settling‐velocity distributions and sorting processes on a longitudinal dune: A case study
Authors: Hartmann Daniel , Christiansen Christian 
Published: February 2007

AbstractThe processes acting on a longitudinal dune are inferred from the response in the area size‐sorting characteristics of the sediment of the active layer. The sediment size distributions are determined by settling and are best described by a log‐hyperbolic model which provides the most information on size‐sorting processes. Size‐sorting characteristics are markedly different across the low round‐crested part of the dune from cross‐sections of the high more sharp‐crested part. This results in changes in textural parameters along the lee‐side consistent with changes in the lee‐side separation vortex. This is the first time that the effect of wind speed up on the lee‐side is observed to be reflected in the sediment; it can only be detected with the very sensitive log‐hyperbolic parameters.
Bedload transport in two gravel‐bedded streams
Authors: Carling P. A. 
Published: February 2007

AbstractBedload transport measurements in two upland streams are considered as a function of the excess stream power exerted on the bed by the flow.During low flows when the framework gravels remain undisturbed, fine sediments are winnowed from the bed‐surface layer once a threshold of 3·4 W m−2is exceeded and the transport rate is strongly supply limited. However for stream powers in excess of 15 W m−2framework gravels are mobilized and the efficiency of the transport process approaches a local maximum of about 1 per cent for discharges up to 2/3 of bankfull.An inverse depth dependence in the efficiency of the transport process was noted but although bedload calibre increased as a function of discharge its influence on efficiency could not be demonstrated. However it was suspected that the size‐sorting relationships of the bed‐material in a number of rivers in relation to the transport efficiency might profitably be examined further.
Tree ring information and rainfall characteristic for landslide in the Kobe District, Japan
Authors: Kashiwaya Kenji , And Takashi Okimura , Kawatani Takeshi 
Published: February 2007

AbstractHeavy rainfall on the south side of the Rokko Mountains has often caused severe landslides and debris flows. Analysis of the annual summation of rainfall in excess of 100 mm/day shows that the rainfall in this area has dominant periodicities of about 25–30, 10–13, and 5–7 years. The period of about 25–30 years corresponds to that of occurrence of the natural disasters produced by heavy rainfall; years when the maximum rainfall correspond to years when there have been severe landslides and debris flows in the area. Temporal change in this rainfall may provide a first approximation for erosional force. Analyses of tree ring width from these mountains indicate that the sequences have a dominant periodicity of about 25–30 years. Cross‐spectral analyses for rainfall and ring width in this area show high coherency for the periods of about 25–30 years; evidence that variations in the ring width may be used as proxy data for erosional force.
The effect of forestry drainage operations on upland sediment yields: A study of two peat‐covered catchments
Authors: Francis I. S. , Taylor J. A. 
Published: February 2007

AbstractThe suspended sediment yields of two adjacent, paired, catchments on blanket peat in mid‐Wales were compared before and after preafforestation drainage works. Catchment A was ploughed whilst an adjacent catchment (B) was left unploughed. After eight months Catchment B was also ploughed. The ploughing strategy in both catchments was designed to minimize sediment loss. However, suspended sediment loss increased 2·5 times following ploughing in Catchment A, whilst no such increase occurred at this time in Catchment B. Subsequently, suspended sediment yields in Catchment B increased 4·8 times after it was ploughed. Organic sediment was lost mainly from furrow sides, and erosion pins showed maximum ground recession in summer, due to peat wastage. Summer desiccation prepared sediment for transport, and organic suspended sediment loads were highest in the autumn. Sediment loads were limited by vegetation colonization and some reduction in sediment loss was due to the presence of unploughed strips adjacent to stream courses.
Morphodynamic and experimental assessments of wave theories in intermediate water depths
Authors: Hardisty J. 
Published: February 2007

AbstractAlthough the near‐bed, wave induced currents predicted by the various wave theories are responsible for seabed sediment transport, it is presently unclear which theory should be included in coastal geomorphic models. The theoretical expressions for near‐bed, shorenormal flows are re‐examined and the predictions are tested with morphodynamic and laboratory data. Five wave theories (Airy, Stokes, Cnoidal, Solitary, and Gerstner) are summarized here and arranged to predict the maximum onshore and offshore near‐bed flows and the flow asymmetry as functions of the wave period, the wave height, and the water depth. Morphodynamic argument suggests that only Stokes and Cnoidal wave theories predict the asymmetry required to generate prototype seabed profiles in intermediate water depths. Laboratory measurements of wave induced near‐bed flows are then reported and analysed. The results suggest that Stokes wave theory over‐predicts the observed peak flows. A correction is derived which is shown to be analogous to the pressure attenuation corrections which are routinely applied to wave recording, seabed mounted transducer measurements.
Fractal techniques and the surface roughness of talus slopes
Authors: Andrle Robert , Abrahams Athol D. 
Published: February 2007

AbstractLinear plots of log N against log G, where N is the number of steps of length G to span a transit, are conventionally used as evidence that geomorphic surfaces are self‐similar fractals (i.e. the surfaces have a constant fractal dimension). In this study 42 transits on talus slope surfaces in Niagara and Letchworth Gorges, western New York, are investigated to ascertain whether they are self‐similar. Log N‐log G plots, which r2 values in excess of 0·99 suggest are linear, are found upon more rigorous testing to be curvilinear. It is concluded that the talus slope surfaces are not self‐similar, and that log N‐log G plots are relatively insensitive to departures from self‐similarity.The curvilinearity of the log N‐log G plots is explained with the aid of a randomized square‐wave model of the talus slope surfaces. This model is used to extend the range of measurement beyond that which was possible in the empirical analysis. The negative of the gradient of the log N ‐log G relation at a point is the fractal dimension D. Measurements made upon the randomized square‐wave model indicate that the relation between D and scale of measurement has an asymmetrical wave shape with a peak (i.e. maximum D) where the scale of measurement is equal to the characteristic scale of roughness. In other words the value of D for a surface is not absolute but depends on the scale of measurement relative to the scale of roughness.Linear regression analysis reveals that at the scale of measurement employed in this study, D is positively correlated with particle size. This is because the values of D fall on the right‐hand tail of the wave‐shaped relation between D and scale of measurement. Transects (normal to the direction of slope) are found to have higher values of D than profiles (parallel to the direction of slope), and this is explained in terms of particle orientation, shape, and juxtaposition.Because D varies continuously with scale of measurement, there are considerable difficulties in using it to characterize and compare the surface roughness of talus slopes. Generalizing from talus slopes to other ground surfaces, it is evident that to the extent that any natural ground surface has a characteristic scale of roughness, it will depart from self‐similarity, and D should be used with caution in quantifying the roughness of the surface. Geomorphologists are therefore urged to be more rigorous in their testing of self‐similarity before employing D to characterize surface roughness.
Monitoring surface change on a Namib linear dune
Authors: Livingstone Ian 
Published: February 2007

AbstractIn tackling the apparently intractable problem of linear dune initiation and maintenance there has been a move away from large‐scale deductive models to smaller‐scale field studies of individual dunes. This paper reports a study of surface change on a large, complex linear dune in the Namib Desert, southern Africa.The dune surface responds to a markedly seasonal wind regime. In summer westerly winds erode sand from the west flank of the dune and deposit it on the easterly lee side of the dune crest. In winter this pattern is reversed. Easterly winds erode sand from the east slope and deposit it on the west slope. The crest therefore moves back and forth some 15 m each year returning at the end of a year's cycle to its position at the beginning. The position of the base of the dune appears to remain fixed, even though sand is moving throughout the dune system. The dune does extend northward along some resultant of the westerly and easterly winds.Despite relatively high levels of activity, especially at the dune crest, there is no evidence of the breakdown of the linear dune form. The conclusion must therefore be that linear dunes can be maintained in bimodal wind regimes and are not necessarily related to unidirectional parallel regimes as others have suggested.
Assessment of visual interpretation of thematic mapper (TM) images for land use and cover in Sudan
Authors: Ali Abdalla Elsadig 
Published: February 2007

AbstractThree thematic mapper (TM) images, a band 3 image, a band 4 image and a 432 colour composite image of Khartoum were compared for detection, identification and recognition of land use and cover classes in hydrology in Sudan. Simple visual interpretational techniques were employed for this purpose. The results show that visual interpretation procedures can be very useful for an inventory of hydrologic land use and cover using Landsat TM photographic products. This is an important conclusion for developing countries where digital techniques are very expensive at the present and many developing countries cannot afford to make use of them.
Error in polygon overlay processing of geomorphic data
Authors: Smith James W. F. , Campbell Ian A. 
Published: February 2007

AbstractPredictive models for calculating sediment yield and discharge require accurate areal data. Such models may be unrealistic when using digitized data given the potential error involved in compiling and digitizing thematic polygon maps.The estimation of boundary variability for digitized polygon maps of a 0·34 km2 area of badlands in Dinosaur Provincial Park, Alberta shows the effects of positional errors introduced during mapping and digitizing processes. Polygon overlay of maps of surface features and slopes produced high frequencies of very small polygons and some unlikely combinations of slopes and surface features, and decreased reliability in areal measurements in the composite map. At an epsilon band width of 0·7 m, a reasonable estimate of boundary variability, 31·7 per cent of the resultant overlaid map can be considered unreliable.
A Markov model for beach changes on the holderness coast of England
Authors: Mason Susan J. , Hansom James D. 
Published: February 2007

AbstractMarkov models offer an objective and quantitative method of assessing beach changes. For a stretch of the Holderness coast a beach classification scheme was devised and a probabilistic first order matrix model based on surveyed profile data was produced. This could describe and predict transitions between beach types and between different time periods. Different profile types dominated different coastal locations and seasonal variations were seen. In order to improve the accuracy of prediction throughout the year a second, ‘winter’, model was added to the original ‘summer’ one. Although the models had been prepared independently of wave conditions, a comparison of the wave record and beach transitions revealed that waves under 0·3–0·5 m high produced fairly static beaches; when waves were between 0·5 and 1·0 m the beach was more dynamic and variable, while waves over 1·0 m led to the depletion of the upper beach. This was broadly in accordance with published theory. Markov models have the advantage that they can be adjusted periodically if conditions change, and are thus useful for prediction on coasts for which no wave records exist.