bluuebunny/crossref_metadata_2025 huggingface dataset:
Creep processes in landslides
Authors: Van Asch Th. W. J.
Published: February 2007

Displacement of landslide blocks after initial slope failure can be very slow. In most cases movement of the blocks is attributed to sliding along a well‐defined slip surface. It is discussed here whether, in addition to these so‐called plastic movements, (continuous) creep processes are involved in the slow displacement. The study was carried out in the downstream part of the Bonne valley in the French Alps, where landslide complexes have developed in varved clay material. Displacements of landslide blocks were measured during a period of three years. Inclinometer measurements in flexible tubes showed that a creep zone developed above the slip surface in a zone about 1 m thick. These field observations on creep processes were supported by soil mechanical analysis. Threshold values for creep found in the laboratory nearly coincide with threshold values calculated from a field creep model developed by Ter‐Stepanian. During the measuring period ±15 per cent of the displacement of the blocks possibly occurred via continuous creep.
Digging by badgers and rabbits on some wooded slopes in Belgium
Authors: Voslamber Berend , Veen Arthur W. L.
Published: February 2007

Eight forest areas, totalling 128.7 hectares, located near the northern border area of the Belgian Ardennes, have been surveyed for soil material brought to the surface by burrowing animals. It appeared that at least 7003.6 kg/ha were present, brought up by badgers and rabbits. The amount turned out to vary a factor 103 between the eight regions. During the half year survey period badgers added some 570 kg to their mounds. On this basis the rate of mass transport effected directly by badgers may be estimated at an insignificant 0.02 gcm−1 y−1. Also, production of available sediment by these animals is relatively unimportant in this temperate humid forest environment.
Carbon dioxide in cave atmospheres. New results in belgium and comparison with some other countries
Authors: Ek Camille , Gewelt Michel
Published: February 2007

More than 600 measurements of the carbon dioxide content of cave air in Belgium lead up to the conclusion that the main factors of its distribution are: (1) a flow originating from the biomass and diffusing in the soil and the voids of bedrock; (2) a trend, discernible in very still air only, to go down by density; (3) in some caves, draughts caused, for instance, by a swift underground stream.

Results in Belgium are compared with published and unpublished data from other countries, showing that CO2 is often less abundant in cold climate caves and in caves of semi‐arid regions (influence of the biomass).

Special attention is paid to human contamination during analyses: the influence of people passing through the cave nearby the operator, but also the influence of the operator himself are discussed, and the use of special precautions (including a CO2‐absorbing mask) in defined critical situations is stressed.
Lichenometric dating of debris‐flow deposits on alpine colluvial fans in Southwest Norway
Authors: Innes John L.
Published: February 2007

Lichenometry provides a suitable means of dating recent debris‐flow activity on alpine colluvial fans. Existing growth curves can be used, provided that anomalous thalli are excluded and allowances are made for differences in the growth rates of Rhizocarpon alpieola and Rhizocarpon section Rhizocarpon thalli. The distribution of flow deposits through time is non‐random and two periods of increased activity (1670‐1720 AD and 1790‐1860 AD) can be identified. There is no evidence for a large increase in debris‐flow activity in the late 19th century, as has been found in Scotland. This can be attributed to the absence of detrimental landuse practices in the Norwegian study areas.
Estimation of the mean velocity of particulate flows by counting
Authors: Culling W. E. H.
Published: February 2007

Using Smoluchowski's theory of the probability after‐effect it is possible to estimate the mean speed or velocity of a particulate flow by counting the number of particles present in a selected region at a sequence of equal time intervals. Apart from a knowledge of the dimensions of the region the only conditions are that the process is, in a wide sense, stationary and that the speeds of individual particles are independent. Subsequent refinements and extensions to the theory by Furth, Ruben, Rothschild and Lindley are incorporated to provide a method of velocity estimation of wide application in geomorphology. Finally, a numerical example on pedestrian speeds is assessed against an independent estimate.
Petrological influence on differential weathering and inselberg development in the Kora area of central Kenya
Authors: Pye K. , Goudie A. S. , Watson A.
Published: February 2007

In the Kora area of central Kenya domed inselbergs are well developed on outcrops of granitoid migmatite, while positive relief features are rare on the surrounding gneiss. Block‐strewn, vegetated hills occur on restricted areas of granoblastite, gabbro, and metagabbro. Schmidt Hammer measurements have shown that the apparent differences in resistance to weathering and erosion are not due to variations in rock hardness, since all the rock types have similar ‘R’ values. The results of geochemical analyses have shown that the migmatites are significantly more potassic than the surrounding gneiss. Samples of migmatite from the inselbergs were also found to be slightly richer in potassium than migmatite samples from the inter‐inselberg areas. The variations in potassium content probably reflect differences in protolith composition, chemical fractionation during partial melting, and the effects of metasomatism. These findings support earlier suggestions that, other things being equal, potassium‐rich granitoid rocks weather more slowly than less potassic rocks.
Tunnel formation processes in the Riverina area of N.S.W., Australia
Authors: Crouch R. J. , McGarity J. W. , Storrier R. R.
Published: February 2007

Soil and site characteristics associated with tunnel erosion are diverse. This contributes to difficulties in identifying areas of potential tunnelling and the reclamation of land affected by this form of water erosion. Soil, site, and tunnel characteristics at three locations having different morphological expressions of this erosion form were examined to determine which features were important in tunnel development in the Riverina Area of N.S.W., Australia.

Soil dispersion was a dominant process at each site and is related to high levels of exchangeable sodium. Field and laboratory studies demonstrated the importance of dispersion and its effect on water movement, particle transport, and subsequent tunnel initiation.

Tunnel initiation mechanisms differed between the sites but could be identified by morphological examination of the tunnels. Potential tunnel eroding sites are characterized by a dispersible layer, a gradient for water flow, and soil characteristics that promote water Sow in defined paths. Appropriate control techniques need to be formulated for each differing form of tunnel erosion.
Geomorphological evolution of a Lowland valley system during the Weichselian
Authors: Van Huissteden J. , Van Der Valk L. , Vandenberghe J.
Published: February 2007

Weichselian geomorphological and fluvial evolution has been recorded in the valley fill of the Reusel, a small tributary of the lower Maas river. It has been studied by means of borehole sections. A first deep incision into the substratum occurred during the Early Weichselian‐Lower Pleniglacial. This was followed by aggradation, at first by a braided river, at a later date by a meandering river, dating respectively from the Lower and Middle Pleniglacial. The Upper Pleniglacial aggradation again points to a braided river system. The end of the Pleniglacial is characterized by aeolian infilling of the valley and decreasing carrying capacity of the river.
A comparison of element outputs in solution, suspended sediments and bedload for a small upland catchment
Authors: Reynolds B.
Published: February 2007

The individual outputs of several elements in solution, suspended solids and bedload were estimated for a stream draining a small upland catchment in mid‐Wales. The data indicate the overall importance of transport in solution, although the solid phase can make a significant contribution to the export of potassium, iron and silicon from the site.
Laboratory simulation of ‘the wick effect’ in salt weathering of rock
Authors: Goudie A. S.
Published: February 2007

‘The wick effect’ is the upward migration of saline solutions into rocks and their subsequent crystallization. Lower Carboniferous sandstone blocks of rectangular shape have been subjected to this process in the laboratory using a range of salt types, a range of salt concentrations, and various mixtures of salts. Some treatments produced severe disintegration, notably sodium carbonate and a mixture of sodium carbonate with magnesium sulphate, whereas other salts (including sodium chloride and gypsum) were much less effective. The debris produced by this experimental salt weathering included appreciable quantities of silt‐sized material, which were analysed with a laser granulometer. Such material could provide a source for desert loess.
A morphodynamic model for beach gradients
Authors: Hardisty J.
Published: February 2007

This paper outlines a general framework for analysis of the problem of beach gradients which divides the system into: (1) the independent controls, (2) the hydrodynamics, (3) the sediment dynamics, and (4) the morphodynamics. A model is derived from the combination of these stages which shows close agreement with field data for wave steepnesses of less than about 0.06, but predicts lower beach gradients than arc observed for steeper waves. The use of ‘analytical feedback’ in the present model rather than the ‘iterative feedback’ which is used in computer simulations demonstrates that differential sediment transport may be responsible for stabilizing the beach gradient.
Erosional and chemical denudation rates in the Southwestern Idaho batholith
Authors: Clayton James L , Megahan Walter F
Published: February 2007

Annual erosional denudation (ED) and chemical denudation (CD) rates are determined on four forested watersheds located in the Idaho batholith, Idaho, U.S.A. Bedrock in the study area is a coarse‐grained quartz monzonite. Annual sediment yields are computed from sediment collected in settling ponds at the watershed mouths and corrected for trapping efficiency. Solution loads for denudation components (Na, K, Ca, Mg, SiO2, A12O3 and FeO) are computed using equations relating concentration to flow and by integration of mean daily flow values. Eleven years of water chemistry data and 19 to 23 years of sediment yield data are used in the denudation estimates. Strong relationships exist between CD, ED and annual water yield, so probability distributions of annual water yield are used in Monte Carlo simulations to establish frequency distributions of annual CD and ED rates.

Mean annual total denudation for the four watersheds (CD + ED) equals 235 kg ha −1 yr−1 or 8‐9 Bubnoffs. The 11 ‐year mean ED rates exceed CD rates for three of the four watersheds, although it is more probable in any given year that CD will exceed ED for three of the watersheds. ED is temporally more variable than CD for all watersheds. Simulations of denudation over 1000‐year periods indicate that the frequency of occurrence of ED is skewed toward higher denudation values, and the modal ED rate is substantially lower than the mean value. CD rates are less skewed, with mean and mode in the same class. Ninety‐seven per cent of CD is composed of Na, Ca and SiO2 fluxes. Episodic high ED rates are related to high peak flows from snowmelt runoff associated with winters of large snow accumulation. Perturbations such as fire or road construction would be expected to accelerate ED more than CD.
Depositional process and alluvial fan‐drainage basin morphometric relationships near banff, Alberta, Canada
Authors: Kostaschuk R. A. , Macdonald G. M. , Putnam P. E.
Published: February 2007

Two distinct types of alluvial fans occur in the Bow River Valley, Alberta, Canada: fluvially dominated and debris flow dominated. Large, gently sloping fans dominated by fluvial processes are associated with large and less rugged drainage basins, and small rugged basins have produced small, steep fans dominated by debris flow processes. Quantitative analysis demonstrates that strong fan‐basin morphometric relationships occur despite a short fan history.

Statistical analysis of fan area‐basin area relationships indicate that debris flow fan areas do not increase in size as quickly as contributing basins. The relationship of fluvial fan area to basin area is not statistically significant. However, this relationship is probably affected by fan erosion. Examination of fan slope to basin ruggedness relationships indicates that fan slope increases more rapidly than basin ruggedness for both fan types. This is likely related to non‐linear discharge and sediment size effects on fluvial fans, and reworking of larger fan surfaces by fluvial processes on debris flow fans.
Estimating wind transport of sand on vegetated surfaces
Authors: Wasson R. J. , Nanninga P. M.
Published: February 2007

Vegetation significantly reduces the transport of sand by wind. We report a generalization of Bagnold's transport equation by finding empirical mathematical expressions to describe the relationships between projected vegetation cover, wind speed outside the area of vegetation, and transport rates. Examples of the use of the equations are given, illustrating the effect of vegetation cover on sand transport, dune encroachment and soil nutrient loss during individual wind storms and over periods of many years.
Field measurement of the velocity of overland flow using dye tracing
Authors: Abrahams Athol D. , Parsons Anthony J. , Luk Shiu‐Hung
Published: February 2007

A new method of computing the mean velocity of overland flow using dye tracing is proposed in which a specified cross‐section is divided into zones of relatively uniform flow characteristics, termed partial sections. The mean surface velocity for each partial section is determined by timing the passage of injected dye, and this figure is multiplied by 0.67, 0.70, or 0.80, depending on whether the flow is laminar, transitional, or turbulent, to give mean velocity. The mean velocity for the entire cross‐section is calculated by multiplying the mean velocity of each partial section by its cross‐sectional area, summing the products for all the partial sections, and dividing by the total area of the cross‐section. A field test shows that mean velocity derived in this manner differs from mean velocity derived by the discharge method (i.e. by dividing discharge measured volumetrically by cross‐sectional area) by an average of only 7.07 per cent. Thus the partial‐section technique appears to provide a reliable method of estimating mean velocity of overland flow.
The characteristics and significance of some lateglacial protalus ramparts in upland Britain
Authors: Ballantyne Colin K. , Kirkbride Martin P.
Published: February 2007

Arcuate and linear protalus ramparts of inferred Loch Lomond Stadial age are widespread in upland Britain outside the limits of contemporaneous glaciers. Survey and analysis of the morphology of nine ramparts suggests that these may have formed at the foot of slowly thickening snowbeds, with rockfall debris accumulating against their distal slopes, and that snowbed melting at the end of the stadial was uninterrupted by prolonged periods of stability or renewed growth. Rampart sediments consist of poorly‐sorted assemblages of clasts with a variable infill of fines. Clast size and shape are strongly influenced by lithology, but rampart clasts are characteristically more angular and ‘slabbier’ than those of similar lithology in ice‐marginal moraines. Ramparts may also be distinguished from moraines by their location, morphology, lack of a true matrix of fines and absence of erratics, and from talus‐foot rock glaciers in terms of their width and the absence of flow structures. The mapped distribution of rampart altitudes across the Scottish Highlands displays a marked regional trend, with the lowest features in the west and south and highest in the Cairngorms. This pattern mirrors that of reconstructed firn line altitudes of Loch Lomond Stadial glaciers, and is inferred to reflect a pronounced eastwards and northwards decline in snowfall during the stadial.
The hurst effect and its implications for extrapolating process rates
Authors: Kirkby M. J.
Published: February 2007

In long‐term records of climatic or hydrological events, persistent periods of high and low values are measured by the ‘rescaled range’, which is defined for a sequence of n consecutive values. As n increases the rescaled range for historic sequences increases as nH for 0·5 < H < = 1. This is the Hurst effect. Sequences of independent random events give H = 0·5, while sequences in which the values are successive positions of a random walk (i.e. the sum of independent events) give H = 1. Intermediate values of H may be obtained from fractal sequences, from sequences with a steadily changing mean, or through a storage model. In all but the fractal case H exceeds 0·5 for a time related to the duration of the changing mean or the response time of the store.

An exponential storage model has been explored in some detail. Storage models have the advantage of offering a plausible physical mechanism for persistence. Analysis of simulated sequences shows that the Hurst effect is evident for about 30 x the response time of the store, so that relatively modest store sizes are enough to explain observed Hurst effects over available periods of record. Comparison with empirical values shows that high H values seem to be associated with large physical stores.

Whether the Hurst effect is due to storage effects or climatic or other change imposed from outside, the effect on longterm process rates is strong. Short‐term measurements of process rates show compressed variances and simple extrapolation is likely to produce large errors. If it is assumed that long‐term rates are strongly influenced by climatic variables, then measurements may be used to obtain parameters of a climatic model for differences in process rates. Errors in extrapolation will be least where the model has a sound physical basis.

A first implication for magnitude and frequency distributions is that the sequence of events may be as important as their distribution over time in determining process impact. A second conclusion is that the geomorphic history of an area is inevitably dominated by a sequence of larger and larger events receding into the past, and that the Hurst exponent over geologic time‐spans measures the extent of that domination.
On the frequency distribution of land slope
Authors: P. O'Neill Michael , Mark David M.
Published: February 2007

Slope frequency distributions are computed from Digital Elevation Models (DEMs) of 18 areas from five different geographic and physiographic regions. Over 160,000 slope estimates are used in the definition of the slope frequency distribution for each area. Analysis of several transformations of the slope data indicates that no single transformation is capable of normalizing all slope distributions. This is, in part, due to the arbitrary placement of the boundaries of the map sheets used in the data collection. The square root of sine, however, provides better results than sine, log‐tangent, or several other transformations. The degree of (positive) skewness of gradients in degrees correlates with the proportion of slopes below 2° or 5° (rs = + 0·93), as does the kurtosis (rs = + 0·91).
An upland soil erosion model derived from the basic principles
Authors: Sharma K. D. , Correia J. F.
Published: February 2007

Starting from the basic erosion principles, an upland soil erosion model to predict soil loss by overland flow from individual storms on forested hillslopes can be derived in the form

where Qs is total soil loss for a storm event, n is roughness coefficient, x is down slope distance, Kf is soil erodibility factor, S is slope, α is slope exponent and Q is runoff. Values of n and α are to be determined for different environments and are 0·58 and 2·1 for a mixed pine forest ecosystem. A significant correlation (r = 0·933, n = 96) fits between the observed and predicted values using this expression, and the model fitting is good.
Copper dispersion in ephemeral stream sediments
Authors: Andrew Marcus W.
Published: February 2007

Sediment transport related parameters in ephemeral streams may be used to model and delineate: (1) average dispersion patterns of copper‐laden sediments; (2) differences in dispersion of copper in bedload and suspended sediments; and (3) variability in the copper‐sediment dispersion patterns. A model that effectively describes dispersion of copper in ephemeral stream sediments in a simple mixing model:

where Cr is the resultant concentration beneath the confluence of the main channel with a tributary, Ct is the concentration of metal in sediments of the tributary, Cm is the metal concentration in main channel sediments, and Xm and Xt are the basin areas or sediment yields of the main channel and tributary channel at their confluence. Variability in metal concentrations about values predicted by this model may be due to the different responses of bedload and suspended load to changes in stream hydraulics, the dynamics of bedload transport, the spatial and temporal variability rainfall within the drainage basin, and chemical mobility of the copper.
210pb as a chronometer and tracer, Burrinjuck Reservoir, Australia
Authors: Wasson R. J. , Clark R. L. , Nanninga P. M. , Waters J.
Published: February 2007

Cores taken at Burrinjuck Reservoir in southeastern New South Wales have been dated using the first appearance of 137Cs, charcoal/bushfire correlations, and annual grass pollen peaks. None of the main 210Pb dating models reproduced the ‘known’ chronology. Correlation analysis shows no significant relationship between original 210Pb (unsupp.) concentration and grain‐size, sedimentation rate or loss on ignition. Differences in sediment source may explain the variations in 210Pb. A simple provenance model has been used to interpret the ratio of original 210Pb (unsupp.)/226Ra as a tracer of topsoils and subsoils. High ratios in the reservoir sediments probably indicate eroded topsoils and low ratios eroded subsoils.
Debris flow during intense rainfall in Snowdonia, North Wales: A preliminary survey
Authors: Addison Kenneth
Published: February 2007

Intense rainfall after the abnormally dry and warm summer of 1983 triggered debris flows in mountainous terrain in North Wales. This preliminary investigation concentrates on a flow which blocked the A5, requiring £56,000 of remedial work. An estimated 118·4 mm of rain fell over steep, rocky catchments in 5 hrs (peak intensity 39·9 mm hr−1) and water emerging from a rock chute mobilized colluvium on lower slopes, in which pore water pressure was probably already rising fast and bulk properties and other geotechnical conditions, including low shearing resistance, were favourable. Debris flowed in a narrow concave track 585 m long, x slope 27·8°, descending 282 m. The scoured channel, levées and debris lobes typical of documented flows elsewhere suggest that flow was rapid, turbulent, and pulsing.
Identification of strength equilibrium rock slopes: Further statistical considerations
Authors: Abrahams A. D. , Parsons A. J.
Published: February 2007

Strength equilibrium slopes are rock slopes whose gradient θ and rock mass strength (RMS) are in adjustment. The identification of such slopes depends on the accurate specification of the strength equilibrium envelope. Previous attempts to delimit the envelope are reviewed and modifications are proposed that permit its more rigorous statistical definition. Because θ can be measured much more reliably than RMS, the structural relation between these variables is estimated by regressing RMS on θ, and the strength equilibrium envelope is defined by the 95 per cent confidence limits. The analysis is performed on a data set of 268 rock slopes, representing all the data on RMS and θ hitherto employed in published studies of strength equilibrium slopes.
Sediment yield in the upper Krishna Basin, Maharashtra, India
Authors: Gole S. P. , McManus J.
Published: February 2007

A 235.5 km2 headwater catchment of the Krishna River in the Deccan plateau lavas is dry for eight months of the year but receives intense monsoonal rains during four months. High initial suspended sediment concentrations fall as rapid vegetation growth provides increasing protection. During a six‐year period annual suspended sediment yields from the deeply weathered kaolinitic soils ranged between 36.9 and 275.3 t km−2 in dry and wet years respectively.
Changes in channel size at river confluences with coarse bed material
Authors: Roy Andre G. , Roy René
Published: February 2007

A 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

On 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

On 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

The 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

The 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

Laboratory 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

Two 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

Combination 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

An 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

Radiocarbon 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

Rock 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

Increasing 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

Size 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

Remeasurements 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

The 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

Appropriate 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

Discharge 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

Analysis 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

A 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

Clast 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.