bluuebunny/crossref_metadata_2025_split huggingface dataset:
Downslope movement of in situ clasts on forested hillslopes, Virginia
Authors: Mills Hugh H 
Published: February 2007

AbstractDownslope movements of 109 clasts ranging in intermediate diameter from 30 to 870 mm were monitored over a five‐year period on hillslopes in the Valley and Ridge province of southwest Virginia. Gradients ranged from 8° to 42°. Regression on slope tangent, depth of clast base below ground surface, clast size, and clast shape explained 70 per cent of clastmovement variance. A substantial part of the unexplained variance appears due to variation in substrate and slope aspect. Additional measurements made on two steep boulder streams showed extremely low rates.
Slope properties, slope processes and soil erosion risk in the tropical rain forest of Kalimantan Timur (Indonesian Borneo)
Authors: Besler Helga 
Published: February 2007

AbstractThe landforms of the study area at the margin of the Central Kalimantan Mountains are relatively young and covered by undisturbed primary rain forest receiving an annual rainfall of 4147 mm. The most important variables for slope processes and their interrelations were studied by simple means along slope profiles on a representative hill. Weathering and erosion appear to be in a dynamic equilibrium leading to parallel slope retreat. Measurable denudation occurred within a fortnight with rates of 10 to 22 mm, varying with litter cover and slope exposition. As the forest is planned for ‘limited production’, the soil‐erosion risk for changing conditions was estimated using the model by Morgan et al. (1982). Results from field work and from calculations alike show the enormous importance of a protective ground cover.
Dunes of the Gran Desierto Sand‐Sea, Sonora, Mexico
Authors: Lancaster N. , Greeley R. , Christensen P. R. 
Published: February 2007

AbstractThe Gran Desierto Sand‐Sea contains dunes of crescentic and star form in simple, compound, and complex varieties. The dunes have developed in bimodal to complex wind regimes of intermediate energy. Transitions from simple through compound to complex crescentic dunes are associated with regional changes in wind regimes. Growth of large star dunes takes place by merging of smaller crescentic and reversing dunes from southerly directions and reworking of sand by northerly and westerly winds. Although wind regimes appear to be the major control of dune morphology in this sand‐sea, there is a close correlation between the spacing of simple crescentic dunes and the grain size of the coarse 20th percentile.
Plate tectonics, palaeoenvironments and limestone geomorphology in West‐Central Britain
Authors: Douglas Ian 
Published: February 2007

AbstractThe variety of active, exhumed, and buried limestone landforms of northern England, North Wales, and the Isle of Man arises in part from the way in which Dinantian (Lower Carboniferous) sedimentation was affected by a tilt‐block basement structure evolved during the closure of the Iapetus Ocean suture to the north, and partly to subsequent plate tectonic movements associated with the closure of the proto‐Tethys ocean, the opening of the Atlantic Ocean and the Alpine orogeny. Landforms created during the Dinantian now form important exhumed and buried landscape features. The Permian half‐graben structures of the eastern Irish Sea‐Cheshire‐Worcester Basins account for many of the contrasts between the upland karsts of the Pennines and the lowland karsts of coastal areas.
Quantum theory and geography
Authors: Biggs Robin A. 
Published: February 2007

AbstractThe application of Newtonian physics to complex fluvial and atmospheric processes is suggested to be inadequate. In the 1970s a number of exciting cosmological theories were developed which formed the basis for models of the early expansion of the Universe. Since these models derive from Einstein's ten gravitational field equations (rather than Newton's single equation) they possess a deep subtlety and may well be of interest to geographers in the explanation of fundamental patterns.
Medium‐term effects of afforestation on sediment dynamics in a water supply catchment: A mineral magnetic interpretation of reservoir deposits in the macclesfield forest, N.W. England
Authors: Stott A. P. 
Published: February 2007

AbstractShort term increases in stream sediment loads during pre‐afforestation ground preparation have often been followed by a return to low sediment loads. However, in the Macclesfield Forest in the southern Pennines, comparison of the magnetic characteristics of soils and downstream reservoir deposits suggest that significant changes in the processes of soil erosion occur later in the cycle of forest management at the time of canopy closure. A preliminary magnetic mixing model indicates that the proportion of reservoir sediments derived from the subsoil (below 0·3 m depth) has increased from 30 to 70 per cent between 1929 and 1981. Changes in hydraulic stresses subsequent to road construction and forest development, in association with unstable Pleistocene deposits, may provide an explanation for these events.
On the use of resistance envelopes to identify the controls on slope stability in the tropics
Authors: Anderson M. G. , Kemp M. J. , Shen J. M. 
Published: February 2007

AbstractIn tropical and sub‐tropical slopes, soil suction may in certain circumstances play a role in maintaining slope stability. Resistance envelope methods are outlined that provide a means of assessing the threshold soil water conditions for stability. In addition, this technique enables the likely failure depth to be identified. Application to slopes in St. Lucia, West Indies, show the accordance of resistance envelope predictions with stability analysis results. A methodology for the geomorphological investigation of stability processes in tropical slopes is proposed.
Suction‐controlled triaxial testing: Laboratory procedures in relation to resistance envelope methods
Authors: Anderson M. G. , Kemp M. J. 
Published: February 2007

AbstractIn certain tropical slopes it appears possible that soil suction may play a significant role in maintaining stability. This communication outlines a laboratory suction‐controlled triaxial test that can be undertaken to validate the threshold suction predicted by resistance envelope methods. It is shown that for two sites examined in St. Lucia, West Indies, the results from such a test confirm results obtained by use of resistance envelopes.
Effects of forest land management on erosion and revegetation after the eruption of Mount St. Helens
Authors: Collins Brian D. , Dunne Thomas 
Published: February 2007

AbstractThe 1980 eruption of Mount St. Helens covered soils with a tephra blanket and killed the forest tree cover in a 550 km2 area. After the eruption, rates of sheetwash and rill erosion, and plant cover were measured on tephra‐covered hillslopes which had been subject to three land‐management practices: grass seeding; scarification, and salvage logging. On rapidly‐eroding hillslopes subject to grass seeding, limited plant covers were established only after erosion had declined sharply. Logging of trees downed by the eruption and scarification of previously logged surfaces slowed erosion, although the effect was small because erosion rates had already slowed substantially by the time these two practices were implemented. The factors controlling erosion, revegetation, and their relative timing at Mount St. Helens are similar to those following explosive volcanic eruptions elsewhere, suggesting that grass seeding is not likely to be effective at slowing erosion following most tephra eruptions, and that early mechanical disturbance could be an effective erosion‐control measure. The results also indicate that even without deliberate conservation measures, processes which mechanically disturb a surface layer of low hydraulic conductivity (such as frost‐action or trampling) can radically reduce runoff and erosion before revegetation has an important effect.
Threshold relations for the transport of sediment by overland flow on desert hillslopes
Authors: Abrahams Athol D. , Luk Shiu‐Hung , Parsons Anthony J. 
Published: February 2007

AbstractAlthough the Shields relation was developed for rivers, it has been applied to sediment transport by overland flow. According to the Shields relation, where the critical boundary Reynolds number Re*c exceeds 40, the critical Shields number F*c is independent of both Re*c and the ratio of the critical flow depth to particle diameter dc/D. Analyses of data collected from runoff plots in southern Arizona reveal that F*c is positively correlated with both Re*c and dc/D. Thus the Shields relation does not apply to overland flow on debris‐covered desert hillslopes.Multiple regression analysis is employed to develop alternative threshold relations in which critical boundary shear stress τc is related to D and dc/D (R2 = 0.782) and to D and Sc (critical gradient) (R2 = 0.625). The computed R2 values derive in large part from the spurious correlations of dc/D and Sc with τc. Nevertheless, the relations may be utilized to predict τc. In this regard, the latter relation is likely to prove more useful than the former because Sc is generally known, whereas dc is not.An investigation of the functional relation between τc and D reveals that τc varies approximately with D2 for overland flow on the desert hillslopes under study, whereas the Shields relation predicts a linear relation (i.e. a D exponent of 1). This result is consistent with Cheng's data which show that F*c varies with (dc/D)−1 where 0.4 < dc/D < 2 and may be explained in terms of increased energy dissipation both in separation zones downslope of particles and in distortion of the water surface as dc/D decreases. Consequently, larger values of τc, and hence F*c, are required to initiate the transport of particles of a given size D as dc decreases.
Dimension and entropy in the soil‐covered landscape
Authors: Culling W. E. H. 
Published: February 2007

AbstractBoth the Hausdorff dimension and the K‐entropy supply a measure of the irregularity of the landspace surface. The relationship between the two measures is investigated over a variety of terrains in Britain and a method of calculating the entropy is checked against an independent estimate of the dimension with reasonable agreement. The calculation of the K‐entropy requires that the landscape surface be represented by an homogenous ergodic random field. This condition is satisfied by the tendency of soil‐covered terrains to progressively approximate to a form well represented by a Gaussian field.Gaussian random fields can either be very smooth, possessing derivatives of all orders at every point or they are highly irregular and non‐differentiable everywhere. Within the regular conceptualization the Rice‐Kac theory is used to predict the numbers of crossing points and the extent of excursion sets. These predictions are tested against an example terrain from the High Weald of East Sussex with very good agreement, apart from predictions of local maxima. A worked example of the calculation of the K‐entropy is given as an appendix.The potential role of information theory in geomorphology extends beyond the use made of entropy in this investigation. In particular ergodic theory has important practical and theoretical implications.
Failure and flow on a 35° slope: Causes and three‐dimensional observations
Authors: Dowdeswell Julian A. , Lamb Henry F. , Lewin John 
Published: February 2007

AbstractA well‐vegetated 35° slope in upland Wales, U.K., failed during a winter flood event. Failure was linked to high magnitude rainfall and diversion of flowing water onto the slope. Mass movement began with gravitational slumping, which was transformed rapidly into a debris flow. Three‐dimensional characteristics of the active debris flow are reconstructed from mudlines on 58 trees still standing in the flow path. Mudline formation only on the up‐flow side of trees indicates the relatively high viscosity of the debris flow. Mudline height is a function of the maximum thickness and velocity of the flow at any tree.
Mechanisms associated with the erosion of sand dune cliffs, Magilligan, Northern Ireland
Authors: Carter R. W. G. , Stone Gregory W. 
Published: February 2007

AbstractA fifteen year history of coastal dune recession at Magilligan, Northern Ireland has revealed both time and space contrasts in processes and morphology. Since 1968 ‘storm’ frequency has increased, while dune retreat reached a peak (5·4 m) in 1978–1979. Three types of dune eroding events are noted, resulting from particular wave/wind/tide combinations. The spatial variability in dune scarping is associated with vegetation and soil development, and slope failures range from granular avalanches to retrogressive rotational slumps.
A comment on ‘a note on the characteristics and possible origins of desert varnishes from Southeast Morocco’ by Drs. Smith and Whalley
Authors: Dorn Ronald I. 
Published: February 2007

AbstractThis note queries the discussion of the origins of ‘desert varnishes’ (Smith and Whalley, 1988), with particular reference to manganese‐rich conditions. The case for a biotic model of varnish development is proposed and illustrated as opposed to the abiotic model put forward by Smith and Whalley.
A note on the characteristics and possible origins of desert varnishes from Southeast Morocco. A reply to comments by R. I. Dorn
Authors: Smith B. J. , Whalley W. B. 
Published: February 2007

AbstractThis reply to Dorn (1989) argues that a biotic origin is not the only way in which desert varnishes may be formed. It is suggested that a variety of initial conditions may result in similar end products. It is agreed that the dissimilar views of the authors may result from their different philosophies concerning the classification of Mn/Fe varnishes.
Aeolian sand drift from the intertidal zone on a temperate beach: Potential and actual rates
Authors: Sarre Robert D. 
Published: February 2007

AbstractThis paper compares the amount of sand that is potentially moved into a coastal dune system from a beach using estimates based solely on the wind force, with actual measured amounts. The actual sand inputs are determined by measuring sand level changes each month over a period of eighteen months, along a 1760‐m section of foredune on Braunton Burrows, Southwest England. The calculation procedure used to estimate the potential rates of sand drift is based on the capacity of the wind force to transport sand using a published transport equation (White, 1979). The results show that the actual movement rates are markedly smaller than the potential rates for all months except in the summer. Meteorological variables and the watertable level in the adjacent dune system are used in an empirically derived regression equation in an attempt to explain the large discrepancy between the potential and actual movement rates. The resulting corrected potential movement rates are a closer estimate to the actual rates, but there remains much unexplained variance.
Fractal techniques and the surface roughness of talus slopes: Reply
Authors: Andrle Robert , Abrahams Athol D. 
Published: February 2007

AbstractThere is discussion of the role of the self similar fractal model (SSFM) as a dominant paradigm in geomorphology; and how it may be applied appropriately. There is also a difference in the interpretation of curvature in logarithmic plots of step length vs total number of steps. Thirdly there is disagreement about interpreting application of the model to the talus clast transects; and finally on the significance of the dimensions obtained (D < 1·27) along the transects.
Hillslope erosion by rainstorms–a magnitude‐frequency analysis
Authors: De Ploey Jan , Kirkby Michael J. , Ahnert Frank 
Published: February 2007

AbstractDaily rainfall data for four stations in Europe and east Africa are used to obtain, by means of magnitude‐frequency analysis, a measure of the Cumulative Erosion Potential (CEP) that takes into account rainfall characteristics, soil water storage, and granulometric properties of soils. The CEP has the advantage of being calculated from generally available published rainfall data, so that wide regional coverage is possible. Together with additional data on the surface configuration and on seasonal variations of rainfall and plant cover, the CEP can provide a basis for estimating hillslope erosion by overland flow.
Rock resistance to erosion: Some further considerations
Authors: Augustinus Paul C. 
Published: February 2007

AbstractRock resistance to erosion is an often described factor in geomorphic studies, and is generally considered to strongly influence the shape of erosional landforms. However, the property of the rock mass that enables it to resist erosion is rarely considered, and its measurement is rarely justified and assessed adequately. Allison (1988, 1990) examined the intact strength properties of several types of carbonate rocks and considered that dynamic Young's modulus is a good indicator of rock material strength for geomorphic purposes, and cast doubts on the reliability of Schmidt hammer tests for this purpose. Alternative approaches to rock characterization from the view point of evaluating rock intact strength are considered.
Test of Hack's slope to bed material relationship in the Southern Eifel Uplands, Germany
Authors: Schröuder Rolf 
Published: February 2007

AbstractThe local reach gradient of small gravel bed rivers (drainage area 0‐8‐110 km2) in the Eifel, West Germany, is adjusted to transport the river bed sediments. Transport of gravel becomes possible under high flow conditions (Shields entrainment factor ≈‐03).Mean bed material size for riffle sections increases with distance downstream. For small drainage areas channel slope is a negative exponential function of drainage area, while for the larger region the additional influence of bedload size has to be considered.Good agreement with Hack's data (1957) for Virginia and Maryland, U.S.A., is achieved (S = 0.0066 (D50/A)‐ 40., r = 0.67).
The evolution of tidal creek networks, mary river, northern Australia
Authors: Knighton A. David , Woodroffe Colin D. , Mills Kevin 
Published: February 2007

AbstractTidal creek networks have in 50 years extended over 30 km inland across the coastal plains of the Mary River in northern Australia, invading freshwater wetlands and destroying the associated vegetation. The networks have grown at an exponential rate through a combination of main channel extension and tributary development, with concomitant widening of the creeks. A large tidal range, very small elevational differences over the plains, and the availability of preexisting channel lines (notably in the form of palaeochannels) have been major factors contributing to the rapid rate of expansion.Close parallels exist between these networks and terrestrial networks as regards modes of growth and planimetric properties. A channel is initiated when the diffuse flow of a seepage zone becomes concentrated through localized scour. Subsequent development is characterized by the rapid extension of long first‐order channels, with most tributary addition occurring later. Model tests suggest that branching was more likely on exterior links in the early stages but that exterior and interior link branching became more equally likely through time. Although the headward limits of the main creeks seem to have been reached, tributary infilling will continue to progress upstream. Only in the most downstream parts is a stable drainage density being approached.The networks not only satisfy the laws of drainage network composition and the basic postulates of the random model but also depart from topologic randomness in similar ways to terrestrial networks. Both topologic and length properties have changed during evolution but largely at the link rather than network scale. The close correspondence with terrestrial networks may be due to the low relief and the relatively unconstrained nature of growth in which availability of space was the main determining factor.
Burst‐like sediment suspension events in a sand bed river
Authors: Lapointe Michel 
Published: February 2007

AbstractIn a much quoted paper, Jackson (1976) hypothesized that turbulent [bursting] motions such as those documented in laboratory boundary layers play a major role in alluvial sediment suspension. To date, the hypothesis remained largely untested, due to difficulties in monitoring turbulent suspension in rivers. This study provides field data documenting burst‐like turbulent motions over a sandy bed channel and quantifying the role of these motions in sand suspension. The data were collected in a 10 m deep channel of the Fraser River near Mission, British Columbia, Canada. Turbulent fluctuations of both flow components, downstream and normal to the bed, along with the output of an optical suspended sediment sensor, were monitored 1 m above the river bed. Typical flow velocities averaged 0·9 ms−1 at the sensors, where mean suspended sediment concentrations were 500 mgl−1; decimetre height small dunes on the backs of larger, half‐metre amplitude dunes covered the channel bed in the area.Brief but intense, burst‐like [ejection and inrush] events were identified in the flow records, where they are responsible for a high degree of [intermittency] in shear stress over the dunes: 80 per cent of the turbulent momentum exchange across the 1 m level can be ascribed to such brief (3‐8 s duration) events, active under 12 per cent of the time. In addition, the record of fluctuating sediment concentrations reveals these burst‐like motions to be highly effective in vertically mixing suspended sediment and thus, ultimately, in maintaining suspended sediment transport above the dune bed. The bulk (60 and 90 per cent in two deployments) of the vertical sediment mixing was accomplished by intense events active some 10 per cent of the time.No discrete recurrence timescale for these ‘burst‐like’ mixing events is evident, however. Rather, a continuous variation of return periods was observed as a function of the magnitude of vertical mixing event considered. To that extent, conceptual models of sediment transport in terms of burst events with a predictable recurrence such as proposed by Jackson (1976) may be misleading.
Secondary flow in anabranch confluences of a braided, gravel‐bed stream
Authors: Ashmore P. E. , Ferguson R. I. , Prestegaard K. L. , Ashworth P. J. , Paola C. 
Published: February 2007

AbstractMeasurements of the primary and secondary velocity components were máde in two, active, braided river anabranch confluences with a simple Y‐shaped plan form, in the gravelly Sunwapta River (D50 of approximately 30 mm). Flow velocity was measured at regularly‐spaced intervals using a bidirectional electromagnetic current meter and the measured downstream and cross‐stream velocities were converted to primary and secondary velocities to yield the secondary circulation. The primary (downstream) velocity field shows two high velocity streams from the two tributaries which merge (and, in some cases, accelerate) into a single high velocity core over the thalweg. Primary flow velocity declines as the flow expands and diverges at the downstream end of the confluence.The secondary circulation is dominated by two helical cells, back‐to‐back, plunging over the thalweg and diverging at the bed. This is the first confirmation of this flow structure in confluences, based on field measurements. The strength of the secondary cells declines downstream through each confluence, and laterally away from the thalweg area in cross‐section. There is also a tendency for one cell, from the larger of the tributaries, to override the other. The secondary and primary flow structure and strength differs slightly between the two confluences and this is reflected in differences in scour hole form.