bluuebunny/crossref_metadata_2025_split huggingface dataset:
Erosion of the eastern United States observed with 10Be
Authors: Brown Louis , Pavich Milan J. , Hickman R. E. , Klein Jeffrey , Middleton Roy 
Published: February 2007

AbstractThe problem of identifying areas of accelerated erosion in a dynamic landscape is complicated. The limited history of sediment yield measurements makes this task difficult even if geomorphic evidence is available. Beryllium‐10, a cosmogenic isotope produced by cosmic rays interacting with the earth's atmosphere and surface, has chemical and physical properties that make it useful as a tracer for erosion and sediment transport processes. The rarity of the stable isotope, 9Be, allows 10Be to be detected with accelerator mass spectrometry in natural materials at extremely low levels. Backgrounds for rocks and sediments below 105 atom per g are now attainable, a value to be compared with an average deposition rate of 1.3 × 106 atom cm−2 yr−1. The affinity of Be for the components of soil and sediment is sufficiently high that it is effectively immobilized on contact, thereby allowing 10Be to function as a tracer of sediment transport. To a good approximation all the 10Be transport out of a drainage basin is on the sediment leaving it. The number of 10Be atoms passing the gauging station can be determined by measuring the concentration of the isotope in the sediment, if the annual sediment load is known. The ratio of the 10Be carried from the basin by the sediment to that incident upon it, called the erosion index, has been determined for 48 drainage basins within the same physiographic province, which allows them to be reasonably compared, all of which have sediment yield data. Basins located in the Atlantic coastal plain have an average index of 0.3 with the maximum observed being 0.9. Basins located between the fall line and the mountains, a region called the Piedmont, have an average value of 2.2 with individual values ranging from 0.6 to 6.7; this marked difference is thought to result from two centuries of farming on land of moderate gradient. Basins in the highland regions reflect local conditions with low indices for those in grass and timber and high indices associated with destructive land use. The data allow an estimate of the erosion index for the pre‐colonial Piedmont, which then allows the pre‐colonial sediment yield to be calculated. A number of basins have also been examined world wide with similar conclusions derived. An important deviation from the rule is noted for rivers that erode large regions of loess, such as the Mississippi, Hwang Ho, and Yangtze. Large aeolian deposits were laid down during the ice age in these basins, deposits that brought inherited 10Be with them and that are easily eroded.
Holocene debris cone evolution in Glen Etive, Western Grampian Highlands, Scotland
Authors: Brazier Vanessa , Whittington Graeme , Ballantyne Colin K. 
Published: February 2007

AbstractStratigraphic investigations, radiocarbon dating of buried soils and pollen analyses were employed to reconstruct the history of development of a fluvially‐reworked debris cone in Glen Etive. Paraglacial aggradation of debris flow deposits resulted in cone formation between c. 10000 yr B.P. and c. 4000 yr B.P. until supplies of sediment from upslope were effectively exhausted and debris flow activity ceased. There ensued a prolonged period of stability and soil development on the cone surface. This ended sometime after c. 550 yr B.P. when human interference (including burning) resulted in destruction of the natural vegetation cover and triggered fluvial incision and the development of an alluvial fan of reworked sediment that buried the lower part of the debris cone. The wider implications of these findings are discussed.
Hydraulic geometry and changes in flow velocity at a river confluence with coarse bed material
Authors: Roy André G. , Roy René , Bergeron Normand 
Published: February 2007

AbstractA survey of flows was conducted at a river confluence with coarse bed material. Bridges were installed on both tributaries, at the confluence and farther downstream on the receiving stream. At these stations, flow velocities were measured over a dense grid for seven conditions ranging from very low flows to the bankfull stage. Hydraulic geometry relationships established at all four stations revealed that flow is accelerated through the confluence as stage rises. At bankfull discharge, average velocity is 1.6 times higher at the confluence than on either tributary. Flow acceleration occurs at and above intermediate flow stages and is concentrated at the centre of a linear pool located at the confluence. The development of a zone of high shear stress is also associated with the cell of high flow velocity. Flow acceleration is dissipated at the exit of the pool where water surges over boulder ribs. The acceleration is not related to the development of flow separation zones as observed by Best and Reid (1984) for wide junction angles, nor is it explained by the reduction of the friction exerted by the banks. Acceleration is associated with the plan geometry of the confluence, with the lateral slopes which permit water to converge, and with a reduction in grain roughness at the confluence. Owing to the curvature of the tributary and to the acute angle of entry, relative power losses through the confluence decrease with increasing stages.
Bed load transport in braided gravel‐bed stream models
Authors: Ashmore Peter E. 
Published: February 2007

AbstractBed load transport rate was measured in ten self‐formed small‐scale gravel braided streams developed in a laboratory flume at several different values of steady discharge and flume gradient. The streams are approximate Froude models of typical prototype braided streams but of no particular river. Slight viscous effects may be present in the models because particle Reynolds numbers are close to 70. Total bed load discharge was measured every fifteen minutes throughout each 60 hour run. In addition, 80 channel cross‐sections were measured in each run to establish the average channel geometry.Total bed load transport rate correlates well with total discharge and total stream power, although at a given stream power bed load discharge is greater when braiding is less intense and the width/depth ratio is lower. Analysis using unit stream power and cross‐section average bed shear stress reveals that the laboratory data conform to existing empirical bed load transport relationships. However, comparison with field data from gravel‐bed rivers shows discrepancies that may be due to differences in bed material size gradation and bed sediment structure.At constant discharge, wide fluctuations in bed load discharge occur with some regularity. Periods range from 2 to 10 hours in the models, which is equivalent to several tens of hours in a prototype. The presence of these long‐period fluctuations compounds the problems of field measurement of bed load in braided streams.
A rational explanation of cross‐profile morphology for glacial valleys and of glacial valley development
Authors: Hirano Masasgige , Aniya Masamu 
Published: February 2007

AbstractThe fact that the cross‐profile of the glacial valley could be well approximated by parabolas (Y = aXb, b = 2.0) is explained by the variation principle, assuming that the glacier erosion works towards minimizing thefriction between ice and bedrock. The variation principle proves that the ideal or fully‐developed morphology of the glacial valley should be a catenary, the curve which a chain hanging from two fixed points forms. Maclaurin's series expansion of the catenary equation shows that a parabola is a very good approximation of the catenary; hence, the good approximation of the cross‐profile by parabolas.Different catenaries are generated by changing the form ratio (depth/rim width) and are then approximated by Y = aXb by the method of last‐squares. The b values obtained become only fractionally larger than 2.0 with invreasing form ratios of up to 1.0, indicating that b values would range, in practice, between 1.0 and about 2.0 Two types of trend in the relationship between b values and the form ratio were obtained from several glaciers. For one type the b value becomes larger with increasing form ratios, and for the other the opposite. The first type is called the Rocky Mountain model after its source of data and represents overdeepening of the glacial valley development. The second type is caalled the Patagonia‐Antarctica model, representing a widening, instead of a deepening, process of development. These differences are attributed to the nature of the glaciers which produced these valleys, i.e. alpine glaciers and continental ice sheets.
Particle dislodgement from a flat sand bed by wind
Authors: Willetts Brian B. , Rice And M. Ann 
Published: February 2007

AbstractThe rate, with respect to area and time, at which grains are dislodged from a sand bed for given wind conditions is an important factor in determining the grain transport rate and the intensity of grain activity in each of the transport modes. The literature of the subject contains little direct information about particle dislodgement.The paper describes a series of experiments in which dyed sand grains, spread on the surface of quartz dune sand in a wind‐tunnel, were photographed at five second intervals while the sand was exposed to wind. The data on rate of loss of coloured grains was used, for two of three chosen size fractions, to deduce the dislodgement rate for each size fraction. The variation of this dislodgement rate with shear velocity is shown graphically for values of u* between 24 cm s−1 and 50 cm s−1. Because of the artificial method of distribution of the coloured sand grains, the results should be applied with caution to natural conditions.The interpretation of the observations of dyed grain loss involved the numerical simulation of the process which comprises removal of coloured grains, slightly offset by replenishment as upwind coloured grains settle briefly in the observed zone. An estimation of grain excursion length has to be incorporated in the simulation. This estimation was made by trial, but general corroboration was found from earlier work.Comparisons are made between dislodgement rates obtained thus and rates estimated by Anderson (1986) and by Jensen and Sorensen (1986). Reasonable agreement with the latter is found in the u* range 30 cm s−1.
River adjustment to changes in sediment load: The effects of tin mining on the Ringarooma River, Tasmania, 1875–1984
Authors: Knighton A. D. 
Published: February 2007

AbstractThe mining of alluvial tin in the Ringarooma basin began in 1875, reached a peak in 1900–20, and had virtually ceased by 1982. During that time 40 million m3 of mining waste were supplied to the main river, quickly replacing the natural bed material and requiring major adjustments to the channel.Based on estimates of sediment supply from more than 50 widely scattered mines and the frequency of flows capable of transporting the introduced load, the river's transport history is reconstructed using a mass‐conservation model. Because of the lengthy time period (110 years) and river distance (75 km) involved, the model cannot predict detailed change but it does reproduce the main pattern of sediment movement in which successive phases of aggradation and degradation progress downstream. Peak storage is predicted in that part of the river where braiding and anastomosis are best developed.Aggradation was most rapid in the upper reaches close to major supply points, becoming slower and later with distance downstream. Channel width increased by up to 300 per cent where the valley floor was broad and braiding became relatively common. Bridges had frequently to be replaced. While bed levels were still rising in lower reaches, degradation began in upper ones, notably after 1950, and by 1984 had progressed downriver over 30 km. Rates of incision reached 0·5 m yr−1, especially in the early 1970s when record high flows occurred. As a result of degradation the bed material became gravelly through either reexposure of the original bed or lag concentration of coarser fractions. Also a narrower unbraided channel has developed. The river is beginning to heal itself and upper reaches now have reasonably stable beds but at least another 50 years will be required for the river to cleanse its channel of mining debris.
The effects of fire on the surface properties and seed germination in two shallow monoliths from a rangeland soil subjected to simulated raindrop impact and water erosion
Authors: Chartres C. J. , Mücher H. J. 
Published: February 2007

AbstractThis paper describes the methods used and some preliminary results of simulated erosion studies on soils with cryptogamic crusts from a semiarid rangeland environment. Two 0·3 m2 shallow monoliths were collected from the upper 20 cm of a Typic Haplargid from the semiarid Australian rangelands and subjected to a range of rainfall intensities and durations representing potentially erosive summer and winter rainfall events. One of the monoliths was cleared of vegetation by a simulated low intensity bushfire. Macro‐ and micromorphological properties of the surface, as well as runoff and erosion losses, were measured during the experiment. Runoff and erosion losses were, as expected, greater for all conditions on the burned than on the unburned monolith. Intensive rainfall damaged the cryptogamic crust unprotected by vegetation by widening and deepening desiccation cracks around the cryptogams, and breaking away and dispersing larger soil fragments from the crack margins. The burned and eroded surfaces provided a much poorer environment for seed entrapment, germination, and growth than did the unburned surface.
Physical and chemical characteristics of a metal‐contaminated overbank deposit, west‐central South Dakota, U.S.A.
Authors: Marron Donna C. 
Published: February 2007

AbstractA metal‐contaminated overbank deposit in west‐central South Dakota resulted from the discharge of a large volume of mine tailings into a river system between the late 1800s and 1977. The deposit along the Belle Fourche River is typically up to 2 m thick and extends about 90 m away from the channel along the insides of meander bends. The sediments contain above‐background levels of copper, iron, manganese, zinc, and particularly arsenic, which is commonly two orders of magnitude above background level in the contaminated sediments. Carbonate minerals in the deposit limit the desorption of arsenic by preventing acid formation. Arsenic concentrations provide a measure of the dilution of mine tailings by uncontaminated sediment.The arsenic appears to have been transported and deposited as arsenopyrite, but is now at least partially associated with iron oxides and hydroxides. Within individual samples, arsenic concentration has an inverse relation with grain size that results from the more efficient accumulation of arsenic on the greater surface area of the smaller particles. Arsenic concentration is inversely related to the sample weight percent finer than 16 μm, however, as a consequence of the dilution of the contaminated sediments by uncontaminated sediment with a finer grain‐size distribution. Dilution by uncontaminated sediment from tributaries cause arsenic concentrations to decrease by a factor of 3 along 100 km of floodplain. An influx at high streamflow of uncontaminated sediment from terraces and the premining floodplain as well as from tributaries causes arsenic concentrations in parts of the contaminated deposit that are farthest away from the channel to be two to three times less than arsenic concentrations in overbank sediment that is immediately adjacent to the channel.
Superwaves and superfloods: The bombardment hypothesis and geomorphology
Authors: Huggett R. J. 
Published: February 2007

AbstractThe bombardment of the oceans by asteroids and comets leads to the propagation of very large waves—superwaves. On approaching continental margins, superwaves may grow to heights large enough to spill on to the land, flooding extensive areas of continental lowland. The waters from these superfloods, in running back to the sea, would be capable of carrying out enormous amounts of work, possibly diverting rivers, cutting gorges, forming valley meanders, and leading to the widespread aggradation of coarse deposits produced by incoming superwaves stripping the soil and regolith cover and denuding weathered bedrock. Calculations of the magnitude and frequency of superfloods, based on current asteroidal impact rates, indicate that the superflooding of continental margins, including the British Isles, could have occurred several times since the start of the Pliocene. Thus, there seems to be a case for reviving some of the views of the old diluvialists, and exploring the worth of neodiluvialism as a system of Earth surface history.
Collisions of quartz grains with a sand bed: The influence of incident angle
Authors: Willetts B. B. , Rice M. A. 
Published: February 2007

AbstractThe velocities with which grains were observed to emerge from a sand bed after an intersaltation collision at u* = 40 cm s−1 are reported for four bed attitudes, from horizontal bed to adverse bed slope 15°. The principal effect of bed angle is to alter the magnitude and direction of the ricochet velocity. However, emergent velocities of dislodged grains are consistent with reptation path lengths comparable to the length of the upwind face of ripples in the corresponding wind.Calculations of the loss of forward momentum at collision, using the data for the range of bed attitudes studied suggest that creep is most vigorous on the sloping upwind face of the ripple and diminishes at the crest. As a result, the crest would be expected to accumulate the coarse material which moves predominantly by creep.The saltations originating in ricochet from the sloping back of the ripple are more vigorous and more concentrated in plan than are those originating at the crest. However, the saltation path length is at least an order of magnitude greater than the ripple wavelength and the probability distribution of path lengths is quite dispersed. Consequently it is very unlikely that these spatial patterns of ricochet are preserved sufficiently distinctly in the saltation cloud and subsequent collision distribution to be the agent of ripple development.This study therefore supports a view of moving grain interaction with the bed in which saltation provides the power to mobilize grains but ripple growth is associated with reptation and particularly with a pattern of impact which develops with the bed relief. Creep is more active on upwind facing slopes than at the crest, which therefore is a zone of net creep grain deposition.
Lateral migration of linear dunes in the Strzelecki desert, Australia
Authors: Rubin David M. 
Published: February 2007

AbstractLinear dunes in the Strzelecki Desert trend roughly south‐north. Sand transport, which is toward the NNE, has caused the dunes to migrate eastward while they extend or migrate northward. Eastward lateral migration is evidenced by: (1) asymmetrical shape of the dunes; east‐facing slopes are several times as steep as west‐facing slopes; (2) asymmetrical accumulation of loose recently transported sand (relatively abundant on east‐facing slopes); (3) asymmetrical outcropping of older semiconsolidated aeolian sand on the dune surface (more abundant on west‐facing slopes); and (4) east‐dipping foreset beds that underly the west‐facing flanks of some dunes. Dunes in the Strzelecki Desert are still active in the sense that sand is transported along and across many dune crests. However, the dunes are composed primarily of Pleistocene strata, indicating that the trend of the dunes was established before the Holocene.The obliquity of the dunes to the transport direction is not merely an aberration of the wind regime of the last few decades. Preferential accumulation of sand on east‐facing flanks indicates that the dunes migrated eastward several metres during the Holocene. Moreover, the west‐facing flanks of some dunes have experienced a minimum of tens of metres of erosion. This asymmetric erosion and deposition were caused by dune obliquity and lateral migration that may have begun as early as the Pleistocene.Dunes in the Strzelecki Desert and in the adjacent Simpson Desert display a variety of grossly different internal structures. Computer graphics experiments demonstrate that many of these differences in structure can be explained by different angles of climb of the dunes.
An experimental study of complex response in river channel adjustment downstream from a reservoir
Authors: Jiongxin Xu 
Published: February 2007

AbstractAn experimental study is described which attempts to reveal the complex response process of river channel adjustment downstream from a reservoir. A descriptive model has been established which identifies three adjustment stages. In stage I following the change of water and sediment input, the width‐depth ratio of river channel (w/d) and the river channel gradient (s) both decrease, but the river channel sinuosity (r) increases. In stage II, because of feedback from the changing boundary conditions, w/d starts to increase, r decreases, and the rate of gradient decrease becomes very slow. In stage III, equilibrium is reestablished, w/d, r, and s tend to constant values, and the system recovers its stable state.
Autogenic and allogenic denudation in carbonate karst by the multiple basin method: An example from Svartisen, North Norway
Authors: Lauritzen Stein‐Erik 
Published: February 2007

AbstractIn carbonate karst basins, adequate denudation rates are difficult to estimate when there are allogenic inputs. It is shown that the common practice of correcting for allogenic input by Corbel's modified formula leads to erroneous results unless the karst ratio is very high. When choosing small basins that are subsets of each other, assumptions of hydrologic and lithologic uniformity may be satisfied. Then the autogenic and allogenic components of the denudation may be calculated by a linear model of uniform mixing. The model was tested in a subarctic stripe karst in North Norway, yielding an autogenic denudation rate of 32.5 ± 10.2 mm ka−1. The mean annual runoff is 2600 mm. The result is supported by independent denudation rates from comparable areas, micro‐erosion meter data as well as the total post‐glacial corrosion deduced from pedestal and vein heights.