bluuebunny/crossref_metadata_2025_split huggingface dataset:
Changes in channel size at river confluences with coarse bed material
Authors: Roy Andre G. , Roy René 
Published: February 2007

AbstractA field survey of thirty stream junctions from a small watershed, together with data collected by Miller (1958), allowed us to investigate morphometric adjustments occurring at confluences. The model proposed by Roy and Woldenberg (1986) was slightly modified and used as a tool for morphometric analysis. Two parameters are necessary in order to evaluate the rate of change in channel size at a confluence: the area ratio (channel capacity above the confluence: channel capacity below the confluence) and the discharge ratio (discharge of the minor tributary: discharge of the major tributary). Our data show that total channel capacity tends to decline below most confluences. A reduction in cross‐sectional area implies an increase in average flow velocity. This interpretation is consistent with Lyell's observations and with results from recent flume experiments (Best and Reid, 1984).
Salt fretting in the valley cliff of the Asama volcano region, Japan
Authors: Matsukura Y. , Kanai H. 
Published: February 2007

AbstractOn the pumice flow deposits of the Asama volcano, Japan, many salts such as halite (NaCl), gypsum (CaSO4·2H2O), hexahydrite (MgSO4·6H2O) and mirabilite (Na2SO4·10H2O) crystallize at the base of south‐facing valley cliffs. The zone of salt efflorescence and of resulting polygonal rind correspond to the zones of notch formation and high water content. The main conditions for salt crystallization and polygonal rind formation are: (1) the existence of groundwater containing a high concentration of Cl−, SO, Ca2+, Mg2+, and Na+; (2) a valley cliff material with a high capillary action and small tensile strength; and (3) low humidity and a high ground‐surface temperature derived from the direct incidence of sunshine. Given the right conditions, salt weathering can occur not only in the arid regions but also in humid, temperate inland regions.
The upper pleistocene loess of southern Tunisia: A statement
Authors: Coudé‐Gaussen Geneviève , Rognon Pierre 
Published: February 2007

AbstractOn the Matmata Plateau, the sedimentological characteristics of the peri‐desert loess and the interbedded palaeosols (particle‐size distribution; chemical and mineralogical composition of major components; trace elements; clay mineral assemblage; heavy mineral assemblage; SEM‐examined surficial textures of the quartz and palygorskite grains) show notable homogeneity: they also indicate its allochthonous origins (the main sedimentary source being the Great Eastern Erg), its transport as an aeolian suspension sediment prior to deposition, and moderate pedogenesis acting during deposition.The emplacement of the loess was synchronous with a ‘pluvial’ steppe palaeoenvironment moister than at present, as shown by 18O and 13C data. The palaeosols point to a weak pedogenesis and colluvial and alluvial reworking that were contemporary with the aeolian deposition. 14C radiometric dating suggests a main period of pluvial dust‐fall/loess deposition in the Upper Pleistocene (until 10 000 yr BP) and a shorter one in the Middle Holocene.
The application of uranium series disequilibrium concepts to sediment yield determination
Authors: Plater A. J. , Dugdale R. E. , Ivanovich M. 
Published: February 2007

AbstractThe determination of uranium series disequilibria in fluvial environments is proposed as a method of calculating catchment mass balances. The technique is based on two main principles. Firstly, 234U is more mobile than 238U, especially during the early stages of weathering. Secondly, uranium is far more mobile than either thorium or protactinium. Consequently, teaching during weathering results in the loss of the uranium found in the fresh rock, leaving the two immobile daughters behind. The ratio of uranium carried by sediment to that dissolved, US/UW can, therefore, be determined from river water and sediment isotopic activity ratios. Fluxes of uranium can then be calculated from average concentrations in the water and the associated sediment, from which a sediment yield can be inferred.The Witham catchment in Lincolnshire has been used to test the proposed method. A US/UW ratio of between 5 and 7 is determined and a sediment yield of 2.51 ± 2.12 tonnes yr−1 km−2 is proposed. Although some problems concerning environmental chemistry have arisen, the validity of the approach is confirmed by the close correspondence between the results obtained and those inferred by earlier workers using more conventional methods.
Earth pillar formation on the Mountain Pine Ridge, Belize
Authors: Francek Mark 
Published: February 2007

AbstractThe roadcuts of Belize's Mountain Pine Ridge feature numerous coarsely textured earth pillars less than 10 cm in height. Preferential impregnation of iron occurs over a buried pebble resulting in a dripline. The higher concentration of iron along the buried pebble's dripline is later oxidized and exposed to the surface by rainsplash erosion. For slopes greater than five degrees, the intensity of sheetwash erosion is great enough to remove pillars. Earth pillar genesis thus seems a function of laterization, slope angle, and sheetwash intensity.
The declining but non‐rejuvenating base level—The Lisan lake, the Dead Sea area, Israel
Authors: Bowman D. 
Published: February 2007

AbstractLaboratory experiments investigating the effects of a lowering base level do not simulate natural eustatic lowering along concave river profiles. The field data on this issue are also quite limited. In evaluating the control exercised by lowering base level on a drainage network, distinction must be made between its influence and those of other hydromorphological processes operating within the basin. Field data on morphological relations, based on photogrammetric mapping and longitudinal profiling, have been gathered in the Dead Sea area, Israel, where a rapid fall in base level has occurred during the Holocene. The study area is an entrenched fan delta with a sequence of 14 unpaired fan terraces which die out at intersection points within an alluvial fan system.The results suggest that the intersection points did not function as base levels. The receding base level played only a passive role, allowing entrenchment without transmitting a head‐cutting feedback basinwards. The arid environment caused a delay in transmission of information through the system. The results support the model of short, episodic, and discontinuous erosional events, inherent in the evolution of drainage basins. It is suggested that base level effects in temperate and humid regions are not transferrable to arid zones.
A note on the characteristics and possible origins of desert varnishes from southeast Morocco
Authors: Smith B. J. , Whalley W. B. 
Published: February 2007

AbstractTwo substrate‐controlled varnish types were identified from arid southeast Morocco: (1) patchy varnish interspersed with ‘silica glaze’ on silicified limestone and (2) a complete varnish cover on partially‐silicified limestone. Electron probe microanalysis was used in conjunction with scanning electron microscopy to investigate their chemical composition. In both instances, varnishes are predominantly silica and iron‐rich with localized concentrations of manganese. Inorganic fixation of iron and manganese is the preferred explanation, with manganese and iron derived predominantly from external sources—possibly wind‐blown dust. Some iron and silica may also be derived by outward migration from within the substrate, particularly on partially silicified limestone.
A deductive model of karst evolution based on hydrological probability
Authors: Smart C. C. 
Published: February 2007

AbstractCombination of a conduit flow law with the exceedance probability of stream discharge allows the estimation of the exceedance probability of water level in a simple conduit aquifer. The probability of water levels higher than available relief is interpreted as the probability of surface as opposed to underground runoff. Very high probability of surface runoff implies a fluvial environment, whereas very low probabilities define a mature karst or ‘holokarst’, Intermediate probabilities identify ‘fluviokarst’.Overflow probability depends on available relief, mean discharge, and especially conduit radius. Growth rate of the underground conduit depends on saturation deficit which thus controls the rate of evolution of the fluvial landscape, through fluviokarst to holokarst. However, variations of discharge and sedimentation through time can cause dramatic reversion of karst drainage into less mature states. Landscapes experiencing such periodic rejuvenation will have a confused morphology. A functional definition of landscape may be more objective and pertinent than arbitrary interpretation of form.
Acid rain damage to carbonate stone: A quantitative assessment based on the aqueous geochemistry of rainfall runoff from stone
Authors: Reddy Michael M. 
Published: February 2007

AbstractAn onsite experimental procedure was used to identify and quantify acid rain damage to carbonate stone, based on the change in rain runoff chemical composition. Observed changes in runoff from stone are attributed to the interaction of acidic species present in the rain with the stone surface. Onsite data obtained during the summer and fall of 1984 at three locations in the northeastern United States indicate that carbonate stone surface recession is related to acid deposition. Although the study is continuing, current data are not adequate to distinguish differences in the acid‐stone reaction between limestone and marble nor among the three study sites. A single linear relation between carbonate stone surface recession (the dependent variable) and hydrogen ion loading to the stone surface (the independent variable) appears to describe the data set.
A radiocarbon‐dated gelifluction lobe in the Nachvak Fiord area, northern Labrador, Canada
Authors: Evans David J. A. , Rogerson Robert J. 
Published: February 2007

AbstractRadiocarbon dates obtained on organic materials overridden by a gelifluction lobe allow some estimate of past gelifluction rates for a site near sea level in northern Labrador. The calculated mean gelifluction rate for the last 400 years is in the order of 8 mm yr−1, somewhat higher than the average gelifluction rate described from other locations in the Canadian Arctic. The lobe contains two lithostratigraphic units: an inner diamicton, probably representing a buried gelifluction lobe, overlain by a silt/clay unit which may have been emplaced abruptly as a solifluction sheet. Mean creep rates for these units were in the order of 5 mm yr−1 and 15 mm yr−1 respectively. The area is presently subsiding, and transgressive beach material overlies terrestrial organics which are approximately 300 years old.
A non‐destructive method of determining rock strength
Authors: Allison Robert J. 
Published: February 2007

AbstractRock material strength is an important component of many geomorphological studies. Current methods for determining this parameter result in sample destruction, preventing further analysis. A new non‐destructive technique is described for indirectly determining material strength, by measuring Dynamic Young's Modulus. Tests have been conducted on Jurassic Portland Limestone and Upper Cretaceous Chalk to assess the apparatus. Young's Modulus is becoming an increasingly important rock material property.
Sources of suspended and deposited sediment in a broadland river
Authors: Garrad P. N. , Hey R. D. 
Published: February 2007

AbstractIncreasing rates of bank erosion and sediment deposition have been reported from the Norfolk Broads since the early 19th century. The major sources of both suspended and deposited sediment in the rivers and Broads is quantified using sediment mineralogy, identified by X‐ray diffraction. This indicates that higher proportions of bank derived sediment are present in suspension in the waterway during the summer months, due primarily to bank erosion by motor craft. Dated sediment cores show how the sources of inorganic sediment have changed over time. Whilst in the past upland catchment sources dominated, at present material is mainly derived from river bank material.
Using quartz grain size and shape analysis to distinguish between aeolian and fluvial deposits in the Dallol Bosso of Niger (West Africa)
Authors: Bui E. N. , Mazzullo J. M. , Wilding L. P. 
Published: February 2007

AbstractSize and Fourier‐shape characteristics of quartz sand grains were determined by computerized image analysis in order to distinguish between aeolian and fluvial soil parent materials in the Dallol Bosso in Niger. Factor analysis of grain‐size distributions gave four sand end‐members that can be related to fluvial transport dynamics operating when the sediments were initially deposited. The medium to fine (and more angular shaped) sand fractions are being reworked by wind. Aeolian deposits were well sorted whereas fluvial deposits were poorly sorted in both size and shape. Although gross‐shape characteristics (lower harmonics of Fourier series expansion) indicated a common source rock for all sands, the aeolian sands were well rounded whereas the fluvial sands tended to be more angular (upper harmonics of Fourier series).
Remeasurement of weathering rates, St. Paul's Cathedral, London
Authors: Trudgill S. T. , Viles H. A. , Inkpen R. J. , Cooke R. U. 
Published: February 2007

AbstractRemeasurements of weathering rates at six sites on the base of the balustrade of St. Paul's Cathedral gave substantially lower mean results (0.06 mm a−1, 1980–1985) than for earlier results (0.14 mm a−1, 1980–1981). Statistical analysis of the data showed that for five of the sites there were no significant differences between the measurement periods. The only significant spatial difference was for the southwest (exposed) site which was greater than the other sites for 1980–1981, but not at later times. This site also showed the only significant decrease over time. If this site is included in the statistical analysis, the whole set shows a significant decrease over time; omitting this site from the data removes any significant differences over time. The results for this one site for 1980–1981 thus have significant bias on the data body as a whole.Methodological problems, such as rock erosion by the probe and temperature effects, are thought to have minimal effect on the interpretation of the data. Calibrations showed that measurements were accurate to ±0.006 mm and that only results of a change ≥ 0.02 mm were reliably interpretable as different.Remeasurements of the Lead Plug Index (LPI) for the top of the balustrade in 1987 gave a mean rate for 1718–1985 of 0.081 mm a−1. This is not significantly different from the 1718–1980 mean rate of 0.078 mm a−1 but the data are not directly comparable, the 1987 sample being smaller than the 1980 set. For the 1987 data, the only statistically significant differences are for the southeast rate ≧ northeast and for a rise in rate in the northeast quadrant. The LPI data are comparable to most of the 1980–1985 MEM data.The conclusion is that most erosion rates have neither increased nor decreased significantly in the measurement time, except for a significant decrease at one (southwest) site from 1980–1981 to 1981–1982. Such a sustained level of erosion gives cause for concern in the context of stone conservation. Causative factors of air quality are discussed and while SO2 levels have decreased, NO2 and smoke levels show increases. An overall decrease in stone decay in association with the decrease in SO2 levels is thus not in evidence.
Niveo‐aeolian sedimentation of loess and sand: An experimental and micromorphological approach
Authors: Dijkmans J. W. A. , Mücher H. J. 
Published: February 2007

AbstractThe concept of a ‘niveo‐aeolian influence’ on the genesis of northwest European Pleistocene aeolian sand and loess deposits has been advocated in the past both to explain the presence and the absence of lamination. Field experiments were carried out on artificially deposited alternating layers of sand and snow, and of loess and snow, to investigate the role of a niveo‐aeolian mode of deposition on resulting sedimentary structures.Field observations of sand plots revealed minor changes in surface morphology typical of denivation surfaces. The thin sections showed a characteristic porous structure. Deformations of the depositional structure and indications for erosion and redeposition were limited. However, the originally smooth aeolian sedimentary surface of the loess changed considerably. The thin sections showed also a porous, spongy structure. Indications were found for disturbances by frost action, liquefaction during melting of the snow and ice, and redeposition of loess by meltwater.The experimental results strongly suggest that sand and loess deposited as niveo‐aeolian material are characterized both by a porous structure, and that the original sedimentary structure of the sand is not affected by snowmelt, whereas loess becomes non‐laminated. Thus, the intercalation of snow during sedimentation of sand and loess does not in itself induce a laminated structure.
On modelling installation designs for soil water instrumentation, with particular reference to casagrande type piezometer systems
Authors: Kemp M. J. , Nash D. F. T. , Anderson M. G. 
Published: February 2007

AbstractAppropriate installation design of soil water monitoring equipment is necessary to ensure the meaningful interpretation of the resultant data. For example, although piezometers are widely used in monitoring positive pore water pressures, the limits on the shape factor of the system in terms of the ceramic tip and filter design have not been fully studied. The filter design boundary conditions are investigated here using a finite element analysis, in which threshold ceramic tip and filter characteristics (permeability and dimensions) are identified. From the modelling results, it is possible to select the most suitable design installation.
Geologic influences on fluvial hydrology and bedload transport in small mountainous watersheds, Northern New Mexico, U.S.A.
Authors: Kelson Keith I. , Wells Stephen G. 
Published: February 2007

AbstractDischarge characteristics in six adjacent mountainous watersheds in northern New Mexico, U.S.A., vary substantially between basins underlain by different lithologies. Relatively resistant gneisses and granites underlie two basins (drainage areas: 43 and 94 km2) that have high unit discharge (0·010 to 0·14 m3s−1 km−2), high bankfull discharge, and sustained high discharge. Less resistant sandstones and shales underlie four basins (drainage areas: 96 to 215 km2) that have relatively low unit discharge (0·001 to 0·005 m3s−1 km−2), relatively low bankfull discharge, and peak discharges that are not sustained as long as those in the crystalline terrane.Analysis of snowmelt‐runoff water budgets suggests that three factors control hydrologic conditions in the basins. First, area‐elevation distributions appear to control the timing and amounts of water input. These distributions probably reflect the erosional resistance of the different lithologies. Second, lithology appears to control runoff production in areas having minor amounts of storage. Third, glacial deposits in headwater regions control discharge duration and timing via storage and return flow releases. The amount of return flow released by glacial deposits, however, is probably controlled by the permeability of underlying bedrock. Therefore it appears that the duration, timing, and magnitude of discharge events in the study area are controlled both directly and indirectly by lithology.Stream power and shear stress estimates derived from bankfull discharge and bed‐material size data suggest that higher bedload transport rates and larger bedload particle sizes exist in streams draining crystalline rocks than in streams draining sedimentary terrane. It appears that source‐area lithology, by controlling discharge production, also influences stream power, bedload transport capabilities, and therefore total amounts of bedload transport.
Downdrift coarsening of beach foreshore sediments at tidal inlets: An example from the coast of New Jersey
Authors: Nordstrom Karl F. 
Published: February 2007

AbstractAnalysis of grain size statistics of upper foreshore sediments on sand beaches at two tidal inlets in New Jersey, U.S.A. reveals that sediments are coarser at beaches flanking the inlets than updrift, although sediments become finer downdrift at the broad, regional scale. The local reversal of the regional trend in size grading is attributed to: (1) the offshore diversion of the finer sands along the surf zone on the ebb tidal delta, and (2) the removal of the finer sands from the inlet flank beach caused by low wave energy conditions at low stages of the tide and by deflation. Sediments thus become coarser at inlet beaches as a result of alterations in the interaction of waves with the beach and as a result of aeolian processes, not solely as a result of increased tidal current velocities as previously reported. The distance along the New Jersey barrier islands over which inlet processes are likely to affect changes in sediment size updrift averages less than 1100 m, but the impacts of inlets on the sedimentary record can be extended greater distances as a result of inlet migration.
A note on suspension transport in the beach gradient model
Authors: Hardisty J. 
Published: February 2007

AbstractA previous model for nearshore orthogonal gradients (Hardisty, 1986) was based upon a simple bedload function and identified feedback relationships between the equilibrium seabed gradient and wave induced flow asymmetry. That model is developed here with the inclusion of suspended load transport, first order shoaling transformations, second order wave induced flows, and a measure of the sediment grain size. The results are compared with some of the general features of prototype geomorphologies.
Clast size variations on talus: Some observations from northwest Ireland
Authors: Wilson Peter 
Published: February 2007

AbstractClast size variations are reported for a relict talus slope in northwest Ireland. Alternating longitudinal zones of coarse debris below buttresses and less coarse debris below gullies give the talus pronounced lateral variations in clast size that are related to joint spacing variations in the talus source area. Longitudinal variations in clast size are also present. The talus accumulated predominantly by the process of rockfall. Other processes frequently associated with lateral size variations were not significantly effective during talus development. Talus sliding may have modified some patterns of rockfall size grading.
Ferromanganese rock varnish in north Norway: A subglacial origin
Authors: Whalley W. Brian , Gellatly Anne F. , Gordon John E. , Hansom James D. 
Published: February 2007

AbstractA thin, dark brown rock varnish is described from ice‐smoothed bedrock on the forefield of a glacier in North Norway. It occurs only in narrow strips (ca 100 mm or less wide) which run roughly parallel to the ice front and along the top edges of small treads of a series of bedrock steps. The varnish is hard, thin (< 10 μm) and consists of an iron/manganese deposit, greatly enriched in these elements compared with the composition of the underlying gabbroic bedrock. It is suggested that the varnish formation is due to localized changes in Eh/pH conditions in subglacial regelation ice and meltwater at the top of the bedrock steps. These changes may be due to CO2 and/or O2 degassing from water held at higher pressures under the ice than in cavities downstream where the ice is decoupled from the bedrock. Glacier retreat rates indicate that the varnish has remained exposed subaerially at the surface for about twenty years, and its restricted occurrence suggests that it is not of biological origin but rather is essentially authigenic. Possible subglacial origins for associated iron and silica precipitates are also suggested.