bluuebunny/crossref_metadata_2025_split huggingface dataset:
Response of loess materials to simulated translocation by water: Micromorphological observations
Authors: Mücher H. J. , de Ploey J. , Savat J. 
Published: February 2007

AbstractStructural differences between loess material deposits produced by splash, flow without splash and by rainwash (i.e. combined splash and flow) respectively were reported earlier (Mücher and de Ploey (1977)). Deposits from splash alone proved to be non‐layered and had incurred almost no additional particle sorting. Deposits from flow without splash were well layered, while individual laminae displayed excellent sorting. Rainwash produced poorly layered deposits with poorly sorted individual laminae. Only horizontal and subhorizontal bedding, and no cross bedding, were observed. Similar features appeared in samples from naturally layered loess deposits collected from excavations.The present paper focuses on the granulometric character of the artificially created layers. Experiments normally involved the combined use of an erosion and a sedimentation flume. Slope angles of the flumes varied mainly form 0.25 to 4 degrees. Precipitation intensities varied from 7 to 120 mm per hour. Unit discharges ranged from 0.2 to 9.2 cm3/cm,s. Flow was laminar or smooth turbulent, either subcritical or supercritical (Froude numbers between 0.5 and 3.8). Raindrop impact had little influence on the flow velocity and thickness of the surficial water film, but it significantly increased transportation capacity and flow competence (Savat (1976, 1977)).Undisturbed samples were collected during the experiments, and impregnated with unsaturated polyester resin. Thin sections of 20 μm thickness were studied under a polarizing microscope. Comparative observations were made on naturally layered loess materials.During rainwash, clay size particles are removed and exported, whereas laminae with particles from 10 to 50 microns are more frequently produced than those with particles from 10 to 30 microns.Flow without splash produced relatively more laminae with grains smaller than 30 microns diameter.Striking in all samples is the absence of laminae composed of 30–50 μm grains. Aggregates were only deposited by smooth turbulent flow, either disturbed or undisturbed by raindrop impact.In view of the experimental results, the naturally formed loess deposits may be interpreted as follows: the bulk of the loess from the excavation near Tongrinne, Belgium, was reworked under influence of turbulent rainwash. Only one sample contained laminae consisting of clay, particles smaller than 10 μm, and of particles from 10–30 μm respectively, suggesting deposition from flow without splash. This was taken from a gully infilling.A gully fill from the excavation Heverlee near Leuven, Belgium, is characterized by poorly sorted laminae, dominated by the coarser silt fractions. This suggests infilling under influence of turbulent rainwash.
(Re)deposition of loess in southern Limbourg, The Netherlands. 1. Field evidence for conditions of deposition of the lower silt loam complex
Authors: Vreeken W. J. , Mücher H. J. 
Published: February 2007

AbstractThis is the first of five papers on a study clarifying conditions and processes during and between the periods of loess accumulation in the southern Netherlands. The research approach involves studies of the stratigraphic, sedimentological, and paleopedological frameworks, micromorphological and analytical characterization of the deposits, and interpretation of micromorphological data in the light of independent process simulating experiments conducted on comparable test materials.Lower or Middle Pleistocene Maas terrace Sands and Gravels overlie Middle Miocene Sands, and are separated by a stoneline complex, consisting of four components, from various silt loam units, which have been grouped into the Lower, Middle and Upper Silt Loam complexes. There is also one intra‐silt loam stoneline. The stonelines range from pre‐Saalian to early Middle Pleniglacial Weichselian in age and variably represent periods of deflation, hillslope erosion, and channel erosion. The present paper reports the results of a macroscopic field study of the Saalian, Eemian, and Early Weichselian Lower Silt Loam stratigraphical units and provides a brief overview of the remaining units, which will be detailed in a future paper. The lateral variability of the units is drawn to scale in a profile 475 m long.The Lower Silt Loam complex comprises an early Saalian channel deposit and a Saalian eolian unit with penecontemporaneous reworking by sheetflow. It is surmounted by the Eemian Rocourt paleosol. This is followed by a Lower Silt Loam unit consisting of older local silt loam material reworked and redeposited by sheet and shallow channel flow, which is in turn surmounted by a paleosol that may be the Early Weichselian (Warneton) or late Eemian in age. The last and largest Lower Silt Loam unit was deposited from channel, and subsequently sheetflow on a major erosional surface, which bevels all older silt loam units. Above this are calcareous Middle Silt Loams.The geomorphic evolution of a dry valley or del can be traced to an early Saalian channel. But, various paleochannels are no longer evident in the present landscape.
(Re)deposition of loess in southern Limbourg, The Netherlands. 2. Micromorphology of the lower silt loam complex and comparison with deposits produced under laboratory conditions
Authors: Mücher H. J. , Vreeken W. J. 
Published: February 2007

AbstractIn this second of five papers on conditions and processes associated with loess accumulation in the southern Netherlands, micromorphology has been used first to characterize deposits ascribed to eolian, fluvial, overland flow, and masswasting processes, and second to recognize features characteristic of deposits produced by simulated processes using comparable testing materials (Mücher and De Ploey (1977); Mücher et al. (1981)).The present paper deals with two stratigraphic units of the Lower Silt Loam complex in the Nagelbeek excavation. These are the Saalian Lower Silt Loam A (unit IV). which seems to consist of eolian material, reworked by sheetflow and modified by Eemian pedogenesis, and the Early Weichselian Lower Silt Loam C (unit VIb), which probably results from channel flow deposition and local masswasting followed by sheetflow deposition. Microscopically, lamination in unit IV suggests alternating eolian conditions and deposition from laminar to smooth turbulent afterflow or meltwater flow. Then followed a period in which deposits of rainwash with smooth turbulent flow, alternated with very thin deposits from laminar flow without splash. Unmodified eolian deposition, or colluviation from splash alone, becomes more dominant upwards. Sedimentary lamination has been accentuated by pedogenic clay illuviation.Unit VIb starts with reworked pedorelicts from Eemian and Early Weichselian paleosols, deposited from rainwash with smooth turbulent flow. Lamination resulted from smooth turbulent to laminar flow without splash. This is followed by intercalations originating from either eolian deposition or splash deposition, and overland flow deposits with evidence for a finely‐branched system of very small rills. Microscopic examination of lobate portions of mass movement deposits within unit VIb does not confirm this origin because of the scale limitations of thin sections. It merely reveals structures that predate the mass movement.
The development of blowouts in ‘de blink’, a coastal dune area near Noordwijkerhout, The Netherlands
Authors: Jungerius P. D. , Verheggen A. J. T. , Wiggers A. J. 
Published: February 2007

AbstractSurface changes in six blowouts in the coastal dunes near Noordwijkerhout between s‐Gravenhage and Zandvoort were measured weekly over a period of two years at 80 erosion pin sites. Readings were correlated with wind variables derived from nearby Valkenburg airbase for the same weekly periods. The values of the wind variables is determined by the number of hours that specific average wind speeds and directions were recorded.The first part of this paper deals with the process of wind erosion. Special attention is given to the relationship between surface changes and wind speed, wind direction, season and rain. Surface changes are associated with wind speeds as low as 1.25 m/s, but net lowering, i.e. erosion, is best correlated with wind speeds between 8.75 and 10 m/s. At higher wind speed there is a tendency for the blowouts to be filled in. Winds from an easterly direction generally correlate with accumulation, whereas winds from the west correspond with accumulation at low speeds and with erosion at high speeds. Springtime and autumn are the most important seasons for blowout development. The effect of rain seems to be limited: the correlations are not improved by excluding rainy days, perhaps because wet sand will be dried rapidly by strong winds.In the next part of the paper, the response of blowouts to the erosion process is discussed. Wind erosion is dominant at the windward side because contrarily to what is often assumed the erosivity decreases as soon as the air is loaded with sand. As a result, blowouts grow southwestwards against the prevailing wind. Nevertheless, much sand is also shifted by winds from other directions. The forms of the blowouts determine in their turn the efficacy of the wind. The errosivity of the wind is most pronounced in circular blowouts, it decreases as the blowout grows in length.Finally, a model of blowout development is proposed which is controlled by width, depth and length ratios.
Reddening of dune sands—evidence from southeast India
Authors: Gardner Rita A. M. 
Published: February 2007

AbstractThin section, SEM, and TEM analyses have indicated that the red ‘teri’ sands of southeast India have formed from weathering in situ of coastal dune sands. The data does not support a detrital origin for the red sands. C14 dates indicate that dune deposition and weathering, to a maximum depth of 10 m, leading to the formation of a hematite, koalinite and illite rich matrix has taken place rapidly over the past 25,000 years. It is postulated that garnet was a major source of hematite (ferric oxide).
Influence of porefluid salinity on instability of sensitive marine clays: A new approach to an old problem
Authors: Carson M. A. 
Published: February 2007

AbstractThe geographic association between earthflow occurrence, sensitivity of the sediment and salinity of the interstitial fluid has been examined in an area of exposed marine (Champlain Sea) deposits in the Lachute region northwest of Montreal, Quebec. Mapping of earth resistivity, as a means of calculating porefluid salinity, revealed that areas of large earthflows (>20 ha) coincided with sediment of very low porefluid salinity. Earthflow scars were absent from intervening areas of higher salinity (>5 gl−1). Mapping of the thickness of the clay deposit by seismic refraction showed, furthermore, that low porefluid salinity occurred only in areas of relatively thin (<25 m) deposits resting upon more permeable drift or rock. Finally, laboratory tests confirmed that high sensitivity was restricted to areas of low porefluid salinity. The study thus provides a geomorphological verification of the importance of ‘salt depletion’ as a prerequisite for earthflow occurrence, and, by implication, presents mapping of porefluid salinity as a method of delineating zones which should be safe from landslide retrogression in this type of sediment.
Heathland vegetation, soil moisture and dynamic contributing area
Authors: Gurnell Angela M. 
Published: February 2007

AbstractGurnell (1978) demonstrated the potential of the composition of wet heathland vegetation as an indicator of hydrological processes in a small heathland catchment. The present paper investigates this potential and demonstrates that on a hillslope in the study catchment simple prediction equations for pressure head based entirely on position on the slope can be substantially improved by the inclusion of vegetation related variables. It is suggested that in this context the vegetation composition is largely reflecting soil permeability and that the remaining scatter around the prediction equations results from other factors controlling micro‐scale variations in the vegetation pattern.
The influence of organic debris on channel morphology and bedload transport in a New Zealand forest stream
Authors: Mosley M. Paul 
Published: February 2007

AbstractThe behaviour and form of, and bedload sediment transport through, a 3.5 m wide forest stream have been monitored for nearly three years. Bedload transport is highly episodic and spatially variable, and is controlled less by water discharge than by sediment availability. Organic debris in the channel creates temporary base levels and sites at which coarse sediment may remain stored for long periods; collapse or disruption of log and debris jams makes sediment available for transport in only a small proportion of the runoff events that are actually competent to move the material. Even then, sediment travels only a short distance before being redeposited, frequently behind debris accumulations further downstream. Rates of sediment transport during a given runoff event can vary markedly over short distances along the stream, again depending on whether sediment was made available for transport by log jam collapse upstream. Organic debris is therefore a major constraint on the application of physical laws and theories to explaining sediment movement in, and the morphology of, this stream.
Bed‐form‐dependent pulsating flow in medano creek, southern colorado
Authors: Schumm S. A. , Bean D. W. , Harvey M. D. 
Published: February 2007

AbstractSome sand‐bed streams exhibit unsteady supercritical flow in the form of periodic bores that propagate downstream. The bores are formed by unstable antidunes, which store water while growing in amplitude and then release the stored water, when the antidunes wash out to form a plane bed. A cyclic process of antidune growth, oversteepening, antidune breaking, then bed‐form washout produced bores on regular periodic intervals of roughly 15 s in Medano Creek, Great Sand Dunes National Monument, Colorado. This periodic bore‐generating pulsating flow, is bed‐form dependent, and it requires sufficiently high flow velocities and sediment transport rates to form unstable breaking antidunes. The Froude number maximum is 1.8, below that required for slug flow.Pulsating flow has been observed in flumes, arroyos, and rivers, and it may be more common than initially anticipated. Its high erosive capacity can influence both channel morphology and the character of associated sedimentary deposits.
Environment and provenance in the development of recent alluvial deposits in epirus, nw greece
Authors: Macleod D. A. , Vita‐Finzi C. 
Published: February 2007

AbstractThe valleys of Epirus, in NW Greece, are floored by alluvium laid down in historical times. In an attempt to evaluate the relative importance of diagenesis and of parent material in determining its local character, the alluvium was compared with the principal source deposits, namely the red beds of the late Quaternary Kokkinopilos Formation and the brown Mediterranean soils that have developed on flysch outcrops. Rehydration of the haematite pigment after deposition coupled with silt‐clay depletion during redeposition of the red beds is responsible for the drab colour of the valley‐floor deposits in limestone catchments. Where the alluvium was derived from brown soils, little mineralogical change has occurred. Some reduction and mobilization of iron has affected Kokkinopilos beds still in place, possibly during periods of seasonal waterlogging under oak forest, to produce a veining pattern akin to that found in pseudo‐gley soils.
Rapid deglaciation as an initiator of volcanic activity: An hypothesis
Authors: Hall Kevin 
Published: February 2007

AbstractVolcanic activity on sub‐Antarctic Marion Island is found to have occurred only during the interglacials. The present volcano distribution is associated with a radial and peripheral fault system, the location of which appears to be related to the former glacier distribution. An hypothesis is presented suggesting that the faulting is a result of deglaciation and that the specific location of the faults is due to the differential stresses occurring between ice‐covered and ice‐free areas during isostatic uplift. The faulting initiates volcanism due to the location of the island within a volcanic region.
Automatic sampling of stream water during storm events in small remote catchments
Authors: Martin R. P. , White R. E. 
Published: February 2007

AbstractIn order to study the relationship between water composition and stream flow rate, it is desirable to sample at a frequency related to flow rate, especially during storm events. In a rural catchment of 18 ha near Oxford, the rate of rainfall was found to be linearly related to discharge on the rising limb of the stream hydrograph. A sampling system was therefore designed in which electrical pulses from a tipping‐bucket raingauge were used to initiate and control the action of an automatic water sampler. A threshold rainfall intensity is set above which sampling commences. Sampling then continues at regular increments of rainfall until the intensity drops below the threshold, after which sampling occurs at regular intervals during the period that the stream flow reverts to normal.The CMOS electrical circuits which control the sampling also operate a cassette tape recorder which records the time of each tip of the raingauge and operation of the sampler. Since the sytem is designed to impose very little additional load on the battery which powers the water sampler, and can operate unattended for at least a fortnight, it is ideal for use in small, remote catchments. The system has been extended to include measurements of water temperature and could provide other measurements as well.
Erosion of strip‐mine dumps in la salle county, illinois: Preliminary results
Authors: Haigh Martin J. , Wallace William L. 
Published: February 2007

AbstractDirect measurement of slope retreat on three unvegetated slope profiles on unmodified, pre‐1939, strip‐mine dumps revealed average ground losses ranging from 29 to 33 mm/year. Measured ground losses are twice those estimated from the Universal Soil Loss Equation. Slope length seems less significant than frost action in influencing erosion on these slopes.
Flow variability and hillslope hydrology
Authors: Huff D. D. , O'Neill R. V. , Emanuel W. R. , Elwood J. W. , Newbold J. D. 
Published: February 2007

AbstractExamination of spatial variability of streamflow in headwater areas can provide important insight about factors that influence hillslope hydrology. Detailed observations of variations in stream channel input, based on a tracer experiment, indicate that topography alone cannot explain flow variability. However, determination of changes in channel input on a small spatial scale can provide valuable clues to factors, such as structural geology that control subsurface flows.
Equilibrium and time scales in geomorphology: Application to sand‐bed alluvial streams
Authors: Howard Alan D. 
Published: February 2007

AbstractEquilibrium is defined as a single‐valued, temporally invariant functional relationship between the values of an output variable and the values of the input variable(s) in a geomorphic system. Disequilibrium occurs if the output deviates from the functional relationship by more than a consensual degree. Natural geomorphic variables are characterized by a relaxation time. Output variables are insensitive to cyclical inputs with frequencies much greater than the relaxation time, but can respond completely for sufficiently low frequencies. Rapid trends, recent step changes or pulse inputs, and intermediate frequency inputs can cause disequilibrium.The gradient of sand‐bed alluvial channels (the output variable) is determined by sediment and water delivery from slopes (the input variables), and changes in this hydraulic regime require regrading by erosion and deposition. Initial stages of adjustment to changed regime in a long, unbranched channel with sediment and water delivery only at the upstream end propagate downstream, but later stages of adjustment occur simultaneously throughout the reach. In a dendritic channel network the gradient responds rather uniformly throughout the network to changes in regime during all stages of adjustment. The time scale of adjustment to changed regime depends upon the size of the channel network (or stream length), the sediment and water discharges, and to a lesser degree upon the magnitude of the change.Grade as defined by Mackin (1948) is synonymous with equilibrium as used in this paper if ‘a period of years’ is replaced by ‘a time period commensurate with the relaxation time of the gradient’. The use of the term grade is best restricted to a single‐valued relationship between channel gradient and the hydraulic regime.
The permanence of stream networks in britain: Some further comments
Authors: Burt T. P. , Gardiner A. T. 
Published: February 2007

AbstractThe conclusions of Ovenden and Gregory (1980) are reviewed in the context of a stream network on the blanket peat moorland of the Southern Pennines. The very great disparity between the 1:10560 map network and the present channel system suggests that the original survey only included the major tributaries. Map accuracy in areas of peat moorland must therefore be treated with some caution particularly if no air photograph or field checking can be done. Some problems of network definition in the peat moorlands are also briefly discussed.
Reexamination of the rate of desert varnish formation reported south of barstow, California
Authors: Elvidge Christopher D. 
Published: February 2007

AbstractDesert varnish is reported to have formed in 25 years on desert pavement stones in an abandoned road south of Barstow, California. It has been discovered that stones buried close to the surface of the roadbed and adjacent desert pavement bear the same dark desert varnish as the exposed stones at the surface. This and other observations refute the claim of 25 year old varnish.
Pedogenic zones in postglacial sediment of lake manitoba, Canada
Authors: Teller James T. , Last William M. 
Published: February 2007

AbstractThe postglacial sediment record of Lake Manitoba is composed dominantly of silty clay to clayey silt with little variation in most physical, chemical, and mineralogical properties. Distinct in the sedimentary sequence of this large lake, however, are four zones that have a low moisture content, blocky to pelletal structure, and gleyed colour. All of these zones formed during the warmest and driest postglacial period in the region, 9500 to 4500 years ago. Although several possible hypotheses can be formulated regarding the origin of these zones including changes in sedimentation rate, clay mineralogy, lake chemistry, and depth of winter freezing, the most likely explanation is that they represent pedogenic horizons. Formation by pedogenesis during dry or extremely low water conditions is not mutually exclusive of the other hypotheses, and several are favoured by low water conditions.
The role of sidewall processes in gully development; some N.S.W. examples
Authors: Blong R. J. , Graham O. P. , Veness J. A. 
Published: February 2007

AbstractLittle attention has been paid to the role of sidewall processes in gully development. Simple estimates of linear incision/sidewall erosion ratios at two localities in New South Wales, Australia suggest that sidewall erosion is responsible for more than half the gully volume. Studies at three localities where overland flow and throughflow are limited to only one sidewall indicate that these processes are responsible for 10‐30 per cent of gully volume. These observations have important implications for gully management.