bluuebunny/crossref_metadata_2025_split huggingface dataset:
Continental rifting and drainage reversal: The clarence river of Eastern Australia
Authors: Haworth R. J. , Ollier C. D. 
Published: February 2007

AbstractThe Clarence River on Australia's east coast has an anomalous drainage pattern. Its right‐bank tributaries are markedly barbed, suggesting reversal, whereas Tertiary volcanism has disrupted its left‐bank drainage. The southeast‐flowing Clarence is closely aligned with the northwest‐flowing Condamine River just across the Continental Divide. The Condamine‐Clarence alignment is continued by a large southern tributary, the Orara River, which flows northwest, away from the sea, to meet the southeast‐flowing Clarence. A broad river with a quite different character flows east from near the Orara‐Clarence junction to the sea. This is essentially an overflow channel.This series of aligned streams, the Condamine‐Clarence‐Orara, represents the remains of an earlier northwest‐flowing stream that extended the full length of the Clarence‐Moreton Basin, an eastern extension of the Great Artesian Basin. During the Jurassic, the Clarence‐Moreton Basin was filled with sediments from the surrounding highlands, including those to the east of the present coastline. Continental rifting from Late Cretaceous times onwards led to the opening of the Tasman Sea, causing the reversal and beheading of the original northwest‐flowing streams and the formation of the Great Escarpment.The evolution of the Clarence River does not fit into most conventional geomorphic paradigms such as cycles, climatic geomorphology or steady‐state landforms. It is the result of a succession of unique events on a very long timescale, and as such is a classic example of evolutionary geomorphology.
Virtual rate and mean distance of travel of individual clasts in gravel‐bed channels
Authors: Hassan Marwan A. , Church Michael , Ashworth Philip J. 
Published: February 2007

AbstractTravel distances in gravel‐bed rivers of tagged particles of various sizes are related to excess stream power estimated for peak discharge. Mean distance of movement, irrespective of grain size, is weakly correlated with stream power, especially near the threshold of movement. There may be several reasons for the weak correlation, including variable effects of bed structure, varying magnitudes of sediment mobilizing events and sampling problems. Grain size itself is of marginal significance. The virtual rate of travel calculated using total time for which the flow is larger than that needed to initiate clast movement also bears a weak relation to the excess stream power over the period. Better results are obtained by relating the virtual rate of travel to the first peak of the flow event only. This implies that the initial seeding of the tagged particles dominates the observations. Nonetheless, an underlying general relation is indicated by the data, which are derived from a wide range of flow regime types.
Delivery of upper‐basin sediment to the lower neuse river, North Carolina, U.S.A.
Authors: Phillips Jonathan D. 
Published: February 2007

AbstractExtensive storage of upper‐basin Piedmont sediment and apparent low sediment supply to streams in lower‐basin Coastal Plain areas generates questions as to the source of alluvium in lower reaches of rivers of the U.S. Atlantic drainage. This was investigated on the Neuse River, North Carolina, using a mineralogical indicator of sediment source areas. The utility of mica flakes for discriminating between Piedmont and non‐Piedmont sources of sediment in the lower Coastal Plain reaches of the Neuse was established on the basis of an examination of the U.S. National Soils Database and of 26 soil surveys of the North Carolina Coastal Plain. From the Neuse River estuary to 48 km upstream there are no mica flakes in floodplain soils or in river bank and channel shelf sediments. Mica flakes become more common upstream. This suggests that a very small proportion of the sediment eroded in the Piedmont portion of the watershed is delivered to the river mouth. The small amounts which presumably do reach the lower Coastal Plain are so diluted by Coastal Plain‐derived alluvium that no Piedmont origin can be discerned. This demonstrates a dominantly Coastal Plain source and underscores the importance of storage and discontinuous transport in fluvial sediment systems. More importantly, results suggest that upper‐ and lower‐basin sediment dynamics are not only non‐linearly related, but may be virtually decoupled.
Lateral migration, thermoluminescence chronology and colour variation of longitudinal dunes near Birdsville in the Simpson Desert, central Australia
Authors: Nanson G. C. , Chen X. Y. , Price D. M. 
Published: February 2007

AbstractThe longitudinal dunes of the Simpson Desert, in the vicinity of Birdsville, have been reworked largely during the Holocene from dunes deposited up to 80000 years ago or earlier. The widespread asymmetry of these roughly northward‐trending dunes, with steeper eastern faces and more gentle western faces, supports wind‐rose data showing sand‐transporting winds from the southwest obliquely intersecting the dunes. While this suggests a change in the wind pattern since the dune field was oriented, it does not indicate that the dunes are necessarily shifting leeward (eastward) as a consequence. It is hypothesized that the direction of migration is controlled by the extent to which the dunes are vegetated. Relatively well‐vegetated dunes can accrete sand on their gentle stoss slopes and erode on their lee slopes causing them to shift westward and hence obliquely into the wind, a condition that probably prevails in wetter regions and during episodes of relatively humid climate. In contrast, in very dry areas or during arid phases, sand can move unimpeded up a sparsely vegetated stoss face and over the crest to form an avalanche or slip face on the lee side, thereby causing the dunes to shift eastward. Despite evidence that longitudinal dune crests can shift laterally to some extent, the dunes in the western part of the Simpson Desert have not migrated, either westward or eastward, more than 100m or so from their Pleistocene cores. Aeolian transport and partial or complete removal of iron cutans from around quartz grains results in dunes of widely varying colour yet of similar age.
Mega‐scale glacial lineations and cross‐cutting ice‐flow landforms
Authors: Clark Chris D. 
Published: February 2007

AbstractLandsat images reveal a previously unsuspected large‐scale pattern of streamlining within drift that is assumed to reflect former phases of ice flow. Such a glacial grain can be regarded as a landform assemblage comprised of a number of components. Drumlins and megaflutes form part of the pattern, but in addition there are two previously undocumented ice‐moulded landform elements: streamlined lineations of much greater proportions, referred to as mega‐scale glacial lineations, and a distinctive cross‐cutting topology within the grain.The ice‐moulded landform assemblage is described and illustrated with reference to examples from Canada. Possible modes of genesis of such landforms are discussed and their glaciological implications outlined. The discovery of this pattern indicates the pervasive nature of subglacial deformation of sediment, and demands a radical re‐interpretation of ice sheet dynamics.
Bagnold's kink: A physical feature of a wind velocity profile modified by blown sand?
Authors: McEwan I. K. 
Published: February 2007

AbstractBagnold (1941) made detailed measurements of the wind profile modified by blown sand. He noted that each velocity profile appeared to be kinked and suggested that the position of the kink corresponded to the height at which an average or a characteristic trajectory extracted the bulk of its momentum from the wind. However, Anderson and Haff (1988) have shown that in aeolian sand transport the grain cloud is made up from a distribution of trajectory paths and that it was an over‐simplification to attempt to describe the complex behaviour of the grain cloud in terms of a single representative trajectory. These recent developments leave the nature and even the existence of the kink observed by Bagnold (1941) open to question.This paper shows that a kink is indeed a physical feature of the modified wind velocity profile and that it is caused, as Bagnold (1941) suggested, by a maximum, occurring at some height above the surface, in the momentum extracted by the grains from the wind. Further comments are made on both the form of the modified wind velocity profile and the fluid shear stress profile in the grain layer. In particular these comments, based upon a theoretical analysis, suggest an experimental means to measure the mean surface fluid shear stress and to gain, from accurately measured wind profiles, a greater insight into the grain cloud which caused the modification.
Rapid uplift, stepped marine terraces and raised shorelines on the Calabrian coast of Messina Strait, Italy
Authors: Dumas B. , Gueremy P. , Lhenaff R. , Raffy J. 
Published: February 2007

AbstractA series of 26 Quaternary shorelines, stepped between present sea level and 556 m, are studied. They are part of the flight of marine terraces of the Aspromonte region. The shorelines were determined using three geomorphological models: wave‐cut platforms and gravel‐built terraces associated with their sea‐cliff foot, and observations of lateral changes between marine terraces and fluvial terraces. The elevation of the sea‐cliff foot is either measured directly, by exposure in cross‐section, or by estimation from geomorphological patterns. With caution, we connect the different landmarks of the shorelines which are discontinuous because of destruction between interfluves or because they are overlain by torrential deposits.The results of mapping show that there are few differential movements from one transect to another and mean uplift rate is 98 cm ka−1. This rate is calculated on the basis of a correlation of the area studied with the Ravagnese Tyrrhenian site, 125 m high, whose date is isotopic substage 5e. Middle and Late Quaternary tectonic activity leads to faulting, slight folding and warping but some scarps associated with faults are actually ancient sea cliffs.
Morphology and causes of recent peat slides on Skerry Hill, Co. Antrim, Northern Ireland
Authors: Wilson Peter , Hegarty Carol 
Published: February 2007

AbstractTwo shallow translational slides occurred in blanket peat on Skerry Hill, Co. Antrim, in November 1991 at sites adjacent to slides activated c. 25 years ago. Heavy rainfall, degraded drainage ditches and slope morphology are considered to have been important factors contributing to peat instability. The failure planes are located close to the peat base, at the boundary between less compact fibrous peat above and more compact humified peat below. The preservation of large blocks and rafts of intact peat and the limited amount of liquefied peat in the debris tongues is thought to reflect the degree of peat humification. There is also some evidence to suggest that the peat was probably undersaturated at the time of failure and this may have assisted preservation of intact peat blocks. Tension cracks, resulting from either short‐term desiccation or long‐term slow mass movement, are thought to have facilitated the rapid transfer of heavy rain to the subsurface peat, causing high pore‐water pressures and lubrication of the failure planes. Vegetation recolonization will probably follow a pattern similar to that observed on the adjacent earlier slides.
A process‐based classification system for headwater streams
Authors: Whiting Peter J. , Bradley Jeffrey B. 
Published: February 2007

AbstractIn this paper we develop a classification system for small headwater streams predicated upon an understanding of the dominant physical processes acting in the channel and its basin, and the conditions under which these processes operate. The variables used to build the classification are hillslope gradient, valley width as compared to channel width, channel gradient, channel depth and sediment size. Using physical laws and morphologic relationships, we recognize domains in which various processes dominate. Channels within the same process domain can be expected to behave in a similar manner in transporting sediment and water and responding to and recovering from basin disturbance, therefore we use the domains to recognize distinct channel types. This classification system provides the foundation for building an approach for identifying basins and streams that are comparably sensitive to landuse.
Anastomosis and the continuum of channel pattern
Authors: David Knighton A. , Nanson Gerald C. 
Published: February 2007

AbstractAnastomosing rivers are characterized by multiple channels separated by islands excised from the floodplain. Their status relative to the continuum concept of channel pattern is assessed with channel pattern defined in terms of three variables—flow strength, bank erodibility and relative sediment supply. Using an ordinal scaling (L(ow)–M(oderate)–H(igh)), the traditional forms of straight, meandering and braided have respective representations of (L,L,L), (M,L/M,L/M) and (H,H,M/H) in terms of those variables. The anastomosing pattern is on average represented by (L,L,M/H) but not so definitively as other forms. Specification of the third element (sediment supply) is particularly hampered by the paucity of data but aggradation, a characteristic of many anastomosing rivers, can be thought of as symptomatic of a moderately high rate of supply relative to the ability for onward transport. A sufficiently high rate of supply to a channel with low flow strength and resistant banks would induce shoaling and/or lateral constriction that locally forces flow out of the main channel and ultimately leads to the cutting of anabranches. A flow regime characterized by concentrated floods of relatively large magnitude is also regarded as highly conducive to the formation of new channels where low bank erodibility constrains channel capacity. Anastomosis may in certain cases represent a transitional form of channel pattern but there is no denying the longevity of some anastomosing systems.
Two types of longitudinal dune fields and possible mechanisms for their development
Authors: Tseo George 
Published: February 2007

AbstractLongitudinal dune fields characterized by nearly uniform interdune spacing are distinguished from longitudinal dune fields characterized by fairly variable interdune spacing and high frequencies of dune coalescence. The empirical and theoretical evidence indicating that the former may be due to helical air currents aligned with the dunes is reviewed. Hypotheses arguing that the latter may arise indirectly from horizontal pressure gradients or bidirectional wind regimes are discussed. Evenly spaced linear sand banks aligned with tidal currents may be shown mathematically to result from energy optimalization within two‐dimensional, sand‐transporting flow regimes, and a similar simple or non‐rotational flow model is considered for the problem of desert longitudinal dunes. An initial complex or rotational flow analysis is undertaken to discern the likely significance of roll vortices in desert sediment transport. An ‘evolutionary timescale’ is estimated for the formation of desert longitudinal dune fields. A simple analysis is performed for the effect of regional sand mass change on longitudinal dune field ordering. Recommendations are made for future empirical and theoretical research.
Derivation of vegetative variables from a landsat tm image for modelling soil erosion
Authors: De Jong Steven M. 
Published: February 2007

AbstractA study was carried out to assess the potential use of satellite thematic mapper (TM) images to produce maps of vegetation‐related variables for erosion modelling. In a Mediterranean study area in southern France the (semi‐)natural vegetation was described at 33 field plots using four quantitative methods: the Fosberg structural classification system, the cover and management factor of the Universal Soil Loss Equation, the leaf area index and the total percentage cover. After radiometric correction of the image, the spectral TM bands were processed following three different methods. Each method aimed at combining the data of the six spectral TM bands into a single band in such a way that the resulting image displayed optimal information on green vegetation cover. The algorithms used comprise the normalized difference vegetation index, the conventional ‘tasselled cap’ transformation and a locally tuned tasselled cap transformation. Only slight differences were found between the different methods to calculate spectral vegetation indices for this particular case. Furthermore, the correlations between the field variables and image‐derived spectral indices are generally small. The largest correlations were found for the normalized vegetation index and the leaf area index (r + 0·71) and for the normalized vegetation index and Fosberg's structural vegetation classes (r + 0·76). However, Fosberg's method results in very general classes, which are of little use for soil erosion models. Furthermore, the spectral indices appeared to be sensitive for the vitality of the vegetation. Consequently, an area covered by a sensed, senescent vegetation will not yield a large value for the spectral index, but its soil is protected against splash erosion. This might lead to a misinterpretation of the soil protective cover when satellite images are used. A final conclusion is that a balance has to be found between the more accurate, but time‐consuming field surveys to gather information on erosion‐controlling factors and a certain loss of accuracy associated with the use of quick and easy remote sensing methods.
Simulation of flow over pool‐riffle topography: A consideration of the velocity reversal hypothesis
Authors: Carling P. A. , Wood N. 
Published: February 2007

AbstractComputer flow simulations using the HEC‐2 step‐backwater routine are used to demonstrate the effect of systematically varying river channel width, riffle spacing and channel roughness on the shear velocity, section‐mean velocity and energy slope in fixed‐bed pool‐riffle sequences.Initial scaling is obtained by utilizing published information on hydraulic parameters within reaches of the River Severn. Subsequently this restriction is relaxed and the effect of varying parameter combinations within realistic limits is explored. The purpose of this exercise is to isolate those scenarios which may preclude or promote the occurrence of a competence ‘reversal’, such that pools scour at high flow whilst deposition occurs on riffles.It is concluded that rivers in which pools are hydraulically rougher than riffles are likely to demonstrate a competence reversal. For prescribed conditions, the critical discharge at which a reversal occurs is a negative function of riffle spacing and riffle width relative to pool width. Downstream variation in hydraulic roughness also has implications for the phase relationship of shear velocity maxima and minima in relation to the extremes in pool‐riffle topography.
Tafoni on coastal slopes, South Devon, U.K.
Authors: Mottershead Derek N. , Pye Kenneth 
Published: February 2007

AbstractCavernous weathering (tafoni development) occurs on coastal slopes in greenschist bedrock at elevations up to 40 m above sea level. The freshly weathered surfaces of the cavern interiors are irregular in morphology, discordant to major rock structure, formed by substantially weakened rock and associated with granular weathering debris. The weathering debris contains soluble elements in proportions similar to those present in seawater, and the penetration of elements associated with sea salts into the weathering surface to estimated depths of at least 0·1–0·2 m is indicated by the presence of chlorine. Scanning electron microscopy and microprobe analyses suggest that rock breakdown occurs principally through limited chemical weathering at grain boundaries. The mechanism for the emplacement of marine salts within sheltered rock surfaces in the tafoni is postulated to be a combination of dry deposition under turbulent atmospheric conditions and wetting by coastal fog.
On the accuracy of heighting from aerial photographs and maps: Implications to process modellers
Authors: Fryer J. G. , Chandler J. H. , Cooper M. A. R. 
Published: February 2007

AbstractA concern to all scientists engaged in modelling landform must be the accuracy with which heights can be obtained from aerial photographs and their derivatives, conventional topographic maps. Morphological information is of importance for terrain description and analysis and increasingly as a critical boundary condition for models of geomorphological processes. This paper offers some cautionary advice in the use of aerial photographs and maps to provide morphological information.Current mapping specifications are reviewed and the prospects for improved accuracy in heighting, given new equipment such as cameras equipped with forward motion compensation, are analysed in the light of recent published material. An analysis is presented of the manner in which random errors in photogrammetric observations can be propagated through a block of aerial photographs. A further analysis is made with the addition of a small systematic error of a type and magnitude occasionally encountered in practice. These analyses show that the use of published map data (digital or not) for producing landform models should be made only after careful assessment of the accuracy of those data and that some of the claims currently being made for height accuracy obtained with new photogrammetric equipment are valid only in special cases.
Subsurface hydrology of layered colluvium mantles in unchannelled valleys—south‐Eastern Brazil
Authors: Fernandes Nelson F. , Coelho Netto Ana L. , Lacerda Willy A. 
Published: February 2007

AbstractThe effects of subsurface hydrology on the evolution of erosive processes inside layered colluvium mantles in unchannelled valleys are investigated. Tensiometer nests are installed in different morphological conditions with their specific depths controlled by the subsurface structure of the colluvium mantle. Daily readings (during one year) and physical and mechanical analyses of the different colluvium layers are carried out.In spite of a highly discontinuous subsurface structure, present topography is the major factor controlling subsurface flow in this landscape. Paleotopographic features, usually resulting from the lateral mobilization of the previous topographic hollow axis, can locally control the preferential expansion of the saturated zone towards areas other than the present hollow axis. During rainy periods, pressure head at the base of the hollow axis increases towards a maximum value which is not increased by subsequent precipitation inputs. New water input is dissipated by direct precipitation onto the saturated zone and exfiltration by seepage at the gully head walls, precluding the development of the excess pore pressures required to trigger failure by landsliding.