bluuebunny/crossref_metadata_2025_split huggingface dataset:
Relative instability of colluvium‐filled bedrock depressions
Authors: Crozier Michael J. , Vaughan Elizabeth E. , Tippett J. Mark 
Published: February 2007

AbstractRegolith landslides commonly occur in colluvium‐filled bedrock depressions rather than on ridges, spurs, or sites with planar bedrock surfaces. Drained direct shear tests of colluvium from bedrock depressions in Wellington, New Zealand, indicate the presence of cohesion in all samples, suggesting that thickness of accumulated deposits may become a limiting factor for stability. Critical depths for a range of slope angles were calculated (assuming conditions of infinite limiting equilibrium) and compared to the depth/angle relationships for depression and interdepression regolith occurring in the field. The results indicate that, under saturated conditions, interdepression regolith is not thick enough to permit the development of landslides. Colluvium‐filled bedrock depressions, on the other hand, generally exceed critical depth and must be considered susceptible to landsliding in the absence of any significant root cohesion.The age of deposits and the abundance of unfailed colluvium‐filled bedrock depressions suggest that they have been inactive for most of post glacial time. Stability analysis, verified by observing the occurrence of landslides, indicates that recent instability has been brought about by deforestation.
The development of armour in the Tambo River, Victoria, Australia
Authors: Dunkerley D. L. 
Published: February 2007

AbstractPresent understanding of armour formation and the dynamics of grain entrainment and movement, especially in natural environments with coarse and poorly‐sorted bed material, is still incomplete. There are many details which require further field observation for clarification and hypothesis testing, including aspects of grain interaction during bedload transport. Evidence from the Tambo River suggests that there may be mechanisms of armour development which have significance in certain field situations but which have been relatively neglected in the literature. The particular mechanism envisaged for the Tambo River involves the accumulation on the bed surface of large clasts which had been moving as an overpassing traction carpet. These clasts are not genetically related to the underlying subarmour sediments, but nonetheless act as an armour which protects them from scour, and which hence affects grain mobility and bedload transport rates.
Reconnaissance studies of the tufa deposits of the Napier Range, N.W. Australia
Authors: Viles H. A. , Goudie A. S. 
Published: February 2007

AbstractTufas are widespread in the Napier Range of north Western Australia, an area of tropical seasonal climate and savanna vegetation. The major tufa deposits have been mapped and the different forms described. These include drapes on cliffs, cones at cave entrances or the mouths of ephemeral streams, rimstone pools, and tufa dams. There are at least two generations of tufa cone, with the older being heavily calcreted and eroded. Simple geochemical and petrographical data allow comparison between the different types of deposit here and with deposits from other parts of the world. Thin section observations and scanning electron microscopy enable an initial assessment of the role of organic processes in tufa formation. Obvious organic remains are sparse, although many of the active tufas are composed of filamentous microsparite fabrics, suggesting that algae have influenced the geometry of the deposits. However, the identification of various endolithic algae indicates that they may also be actively involved in the degradation of the deposits.
Use of the schmidt test hammer to detect enhanced boulder weathering under late‐lying snowpatches
Authors: Ballantyne Colin K. , Black Nicola M. , Finlay Donna P. 
Published: February 2007

AbstractBallantyne et al. (1989) presented data that show a significant reduction in Schmidt hammer rebound values for boulders buried by late‐lying snow. McCarroll (1990) questions these findings on the grounds of sampling design, methodology and unexpectedly rapid weathering of boulders at one recently‐deglaciated site. However, analysis of the data using the procedure recommended by McCarroll yields identical results, and his methodological objections appear groundless. The absence of evidence for reduction of rebound values at snowpatch sites investigated by McCarroll may reflect lack of meltwater runoff beneath snowbeds in permafrost areas. The implied rapidity of weathering on recently‐deglaciated ground requires further investigation.
Seasonal changes in iron transport and nature of dissolved organic matter in a humic river in northern Finland
Authors: Heikkinen Kaisa 
Published: February 2007

AbstractChanges in the concentration of iron and dissolved organic matter (DOM), and in the colour and fluorescence properties in the River Kiiminkijoki were investigated as functions of the seasonal flow regime over a two‐year period. The iron concentration in filtrates and the ratio of Fe to DOC in the river increased under low flow conditions and decreased during the flood periods. The colour of the dissolved organic matter increased with increasing iron content, the effect being more pronounced during the warm period of the year than in winter. The ratio of fluorescence to DOC increased during the warm period of the year but not in winter, and decreased rapidly with discharge at the beginning of the flood period in autumn. The results give indications of the origin, formation, nature, and fate of the DOM in the river water. Temperature‐dependent microbiological processes in the formation and sedimentation of iron‐organic colloids seem to be important. Estimates are given for the amounts and transport rates of iron discharged into the Gulf of Bothnia by the river.
Rates of tafoni weathering on uplifted shore platforms in Nojima‐Zaki, Boso Peninsula, Japan
Authors: Matsukura Yukinori , Matsuoka Norikazu 
Published: February 2007

AbstractMany tafoni occur on the faces of marine cliffs on three uplifted shore platforms with different altitudes and with known ages of emergence. The mean value of the ten largest depths of tafoni, D (cm), was obtained and the period of their formation, t (years), was estimated. The relationship between the two variables was found to be D = 20·3 × (1−e−0.005t).
Measurement and calibration of weathering using the schmidt hammer, on wave washed moraines on the upper norrland coast, Sweden
Authors: Sjöberg R. , Broadbent N. 
Published: February 2007

AbstractThe Schmidt hammer has for some years been used to measure the hardness of different rock surfaces and to date relatively boulders in moraine deposits. In this paper applications on isostatically raised boulder‐beaches and rocky shores are described. The research area is the northern Swedish Bothnian coast where present isostatic uplift is between 0.8‐1.0 cm year−1. Elevations above sea‐level can be converted to a timescale. Rebound values (R) of the Schmidt hammer are correlated with the altitude and the degree of rock weathering can be estimated for each site.Eight sites with boulder‐beaches and nine sites with rocky shores have been analysed. For boulder‐beaches correlation‐coefficients of 0.82‐0.97 for weathering values (R) and the elevations above sea‐level were obtained. For the rocky shores these values were calculated to 0.75‐0.97.This method has applications in both geomorphology and archaeology. For example, a deep layer of weathered dolerite in the Nordingrå region, which previously has been regarded as a post‐Weichselian formation, can be shown to be of pre‐Weichselian origin. Several archaeological applications are also mentioned in the paper.
Size characteristics of sediment in interrill overland flow on a semiarid hillslope, Southern Arizona
Authors: Parsons Anthony J. , Abrahams Athol D. , Luk Shiu‐Hung 
Published: February 2007

AbstractThis study examines the size characteristics of sediment removed from a semiarid hillslope by interrill overland flow. Rainfall simulation experiments were conducted on a runoff plot 18 m wide and 35 m long established on a piedmont hillslope in southern Arizona. The top of the plot coincided with the hillslope divide, and its outlet was located within a shallow rill. Samples of runoff were obtained from two cross‐sections located in the interrill portion of the plot upslope of the rill and from a calibrated flume through which was directed interrill overland flow reaching the bottom of the plot. Analyses of sediment contained in these samples showed that sediment in interrill flow is finer than the matrix soil. The fineness of the interrill sediment compared to the matrix soil appears to be due to the inability of interrill overland flow to transport the coarser fraction of the sediment supplied to it by raindrop detachment. This finding implies that the rate of soil erosion in interrill areas is not. as is commonly supposed, limited by the rate at which raindrops can detach sediment but by the rate at which they detach sediment of a size that the overland flow is competent to transport. The relative fineness of sediment eroded from this hillslope is consistent with other evidence for the recent evolution of shrub‐covered hillslopes in southern Arizona.
The application of cellular automata to the erosion of landforms
Authors: Smith Roger 
Published: February 2007

AbstractTwo approaches to modelling surface erosion are described which can be used to explain the development of geomorphological features. The first approach uses non‐linear wave theory and shows how surface gradient discontinuities can arise as the erosion of an initially smooth surface proceeds. For isotropic erosion, surface shapes may be predicted by a simple application of the Huyghens wavefront construction and Snell's law at media boundaries. A second approach uses a computational cellular method. The general shapes predicted by the computer simulations are shown to agree with those determined from the wave approach. The application of the cellular method to problems of geomorphological interest are discussed.
The schmidt hammer, weathering and rock surface roughness
Authors: McCarroll Danny 
Published: February 2007

AbstractMeasures of the differential relief of adjacent feldspar and pyroxene grains provide the first clear negative correlation of Schmidt hammer rebound (R‐) values and degree of weathering. However, weathering and roughness are intimately related, so the latter cannot be seen simply as a source of error limiting the utility of the Schmidt hammer. Only where surfaces had similar textures prior to weathering can R‐values be compared directly. Even where surface texture is well controlled, differences in R‐values should be viewed critically rather than assigned indiscriminately to differences in degree of weathering.
Aeolian dust transport and deposition over crete and adjacent parts of the mediterranean sea
Authors: Pye K. 
Published: February 2007

AbstractMonitoring of dust deposition at several stations on Crete over a three year period has shown that the present‐day depositional flux is of the order of 10‐100 gm−2 yr−1. Most of the dust deposition takes place during a few annual dust [events] which typically last for 1‐3 days. Dust haze episodes are usually associated with southerly or southwesterly winds which transport fine sediment from North Africa. Dust is raised by a wide variety of meteorological conditions which generate strong near‐surface winds in the source areas, but major long‐range transport events are often associated with cold fronts linked to the passage of deep mid‐latitude depressions during winter and spring. Dust haze frequency and deposition rates are highest in western Crete and decrease towards the east, suggesting that transport from Tunisia and neighbouring parts of North Africa is particularly important. The measured rate of dust deposition is well below the minimum level required for loess formation. Deposits which have previously been identified as loess are shown to be uncemented marine marls of Tertiary age. Laboratory analysis of red soils, surface sediments, and bedrock samples has confirmed that many of the soils contain an important aeolian dust component, but it is concluded that a more important source of soil parent material is provided by weathering of local rocks. Many of the soils contain significant amounts of quartz sand which cannot have been transported across the sea from North Africa. Reworking of weathered material and deposited dust is extensive, and is accomplished by both aeolian and fluvial processes. Tectonically‐controlled depressions in the mountains and parts of the coastal lowlands have acted as long‐term sinks in which a thickness of several metres of sediment and soil has accumulated during the Quaternary.
The influence of microform bed roughness elements on flow and sediment transport in gravel bed rivers: Comment on a paper by marwan A. Hassan and ian reid
Authors: Clifford Nicholas J. , Richards Keith S. , Robert Andre 
Published: February 2007

AbstractData from Turkey Brook are used to demonstrate that the interaction between gravel bedforms, flow resistance and bedload transport is a dynamic one, both between and within hydrographs. and that creation of a significant component of form drag through construction of microforms (pebble clusters) may precede the eventual break‐up of the bed in a transport event. This process of drag augmentation', which can be seen as a feedback mechanism delaying transport and can be likened to dilation of a soil tested in a direct shear apparatus, itself appears to be dependent on the characteristics of turbulence, and therefore involves feedback at a finer resolution than envisaged by Hassan and Reid (1990).
Segmentation of alluvial fans in death valley, california: New insights from surface exposure dating and laboratory modelling
Authors: Leb. Hooke Roger , Dorn Ronald I. 
Published: February 2007

AbstractLaboratory experiments, recent paleoenvironmental analyses of rock varnish, and surface exposure dating of geomorphic units have led to new insights into the process of entrenchment and segmentation of alluvial fans, and into the history of Quaternary sedimentation in Death Valley. Entrenchment begins at the fanhead. As the trench deepens, its down‐slope end migrates down‐fan, taking several tens of thousands of years to reach lower parts of the fan. Laboratory experiments suggest, however, that a new segment begins to grow at the toe long before the trench reaches this part of the fan. Furthermore, the initial slope of the segment is not the equilibrium slope. Field evidence supports this model. The tectonic tilting that caused entrenchment and segmentation in Death Valley may have been triggered by loading of the valley with water.Sedimentation on the salt pan in southern Death Valley is not, at present, in equilibrium with that on the fans. Rather, it seems to be adjusting to an increase in the amount of fine material reaching the playa, due in part to breaching of the outlet of Lake Tecopa somewhat after 600 ka BP, and in part to subsidence of different parts of the valley at different rates. Failure to recognize this disequilibrium resulted in errors in earlier estimates of the age of the segmentation events.
Modelling floodplain flows using a two‐dimensional finite element model
Authors: Bates Paul D. , Anderson Malcolm G. , Baird Laura , Walling Des E. , Simm David 
Published: February 2007

AbstractA prototype two‐dimensional finite element flow model for depth‐averaged free surface flows was developed for floodplain environments. Limited refinement of the model's physical representation was undertaken and the enhanced scheme applied to an 11 km river channel/floodplain reach in the U.K. Preliminary model results indicate that this modelling approach can be used to identify dynamic variations in the flow field parameters over length scales of the order of 10‐100 m. Potentially, such data have the ability to permit detailed analysis of short‐term floodplain sedimentary dynamics.
Distribution and formation of rock varnish in southern Tunisia
Authors: Drake N. A. , Heydeman M. T. , White K. H. 
Published: February 2007

AbstractField observations, chemical analysis, electron and light microscopy and radiolabelling experiments provide information on the characteristics, formation and distribution of Fe and Mn rock varnishes in southern Tunisia. Unstable rocks are not surface‐coated, but when broken they commonly reveal internal microbial solution fronts. Stable rocks are coated in Fe, and more rarely Mn, rock varnishes. Radiolabelling indicates the presence of many respiring microbes on both Fe and Mn varnishes. Microscopy shows fungi and bacteria, both on the Fe varnishes and within the rock. Only rare, microcolonial fungi occur on Mn varnishes, suggesting that the microbes are within or beneath the varnish. The abundance of microorganisms supports a biogenic origin for rock varnishes. Different microbial communities appear to be involved in Fe and Mn varnish formation. Microbes appear to live beneath the surface of unstable rocks but coat stable rocks which cannot be penetrated, apparently to avoid u.v. light and desiccation. This explains the concentration of elements that form u.v. opaque minerals and clays. The origin of these elements is external to the substrate. These results suggest that rock varnish dating and paleoenvironmental techniques can be applied in southern Tunisia.
Numerical simulation of vertical marsh growth and adjustment to accelerated sea‐level rise, North Norfolk, U.K.
Authors: French Jonathan R. 
Published: February 2007

AbstractIn parts of North America and Europe, present and future sedimentary deficits translate into major areal losses of coastal salt marsh. Physically based simulations of medium‐ to long‐term adjustment to accelerated sea‐level rise are few, partly due to the difficulty in extrapolating imperfectly understood sedimentation parameters. This paper outlines the implementation and application of a simple one‐dimensional mass balance model designed to simulate the vertical adjustment of predominantly minerogenic marsh surfaces to various combinations of sediment supply, tidal levels and regional subsidence. Two aspects of marsh growth are examined, with reference to sites on the macro‐tidal north Norfolk coast, U.K.: (i) historical marsh growth under a scenario of effective (long‐term) eustatic stability but slow regional subsidence; and (ii) marsh response to various non‐linear eustatic rise scenarios for the next century. In contrast to more organogenic North American marshes, sedimentation rates in Norfolk are strongly time‐dependent. Where the overall sediment budget is so closely linked to marsh age and relative elevation, some form of numerical simulation offers a preferred means of predicting the impact of accelerated sea‐level rise. Simulations performed here show that only the most dramatic eustatic scenarios result in ecological ‘drowning’ and reversion to tidal flat within the conventional 2100 prediction interval. Currently favoured scenarios give rise to accretionary deficits which are clearly sustainable in the short‐term, albeit at the expense of increased inundation frequency and consequent changes in the distribution of marsh flora and fauna.
Interactions between perched and saprolite aquifers on a small, salt‐affected and deeply weathered hillslope
Authors: George Richard J. , Conacher Arthur J. 
Published: February 2007

AbstractA small hillslope was chosen to investigate the role of throughflow as a mechanism responsible for the movement of soil water and solutes towards a saline seep and as a source of recharge to a permanent, regional aquifer at depth. The hydraulic properties, chemical characteristics and physical responses of both systems were studied on a deeply weathered, salt‐affected hillslope. Additional data were also obtained from other sites in south‐western Australia.Regional groundwater flow occurred in a variably textured, deeply weathered material in which the hydraulic conductivity varied from < 0·001 to 0·14m day−1. Perched groundwater flow (throughflow) occurred in the higher permeability (˜ 1·5 m day−1), near‐surface soil materials. Throughflow occurred throughout winter, contributing approximately 530 m3 of fresh (˜ 160 mg l−1 Cl) water to a saline seep. By contrast, the deep aquifer discharged approximately 1100 m3 of waters with salt concentrations of 2000–6000 mg l−1 Cl. Recharge and discharge rates to and from the deep aquifer, were estimated to be of the order of 5–20 mm a−1 and 50–300 mm a−1 respectively.Saturated conditions existed throughout winter within the seep and the immediately adjacent non‐saline area, with up to 60 per cent of the hillslope soils becoming saturated after major rainfall events ( > 20 mm day−1). In the mid‐slopes, in particular along a central depression, saturation of the shallow soils caused macropore channel recharge to take place through the clay‐textured subsoils. Water‐level responses suggest that approximately 25–30 per cent of annual recharge occurred from one storm studied in September 1984. Recharge through macropore channels is a significant mechanism in the concave slope areas on the hillslope. Throughflow was found to be a major source of water, but not salt, contributing to the saline seep. In general, the contribution of throughflow was found to decrease further inland at other sites studied. However, at inland sites where perennial, perched aquifers have developed in deep sands, saline areas have been caused by throughflow and not by deep aquifer discharge.
Reply. Denudational isostatic rebound of intraplate highlands: The Lachlan river valley, Australia
Authors: Bishop Paul , Brown Roderick 
Published: February 2007

AbstractTwo main points are raised in replying to Fabel et al. (1993) in their discussion of the paper by Bishop and Brown (1992). It is argued that local variations in denudation are insufficient to invalidate the key conclusions, especially as the amount of sediment deposited in the Murray Basin is a key (and known) measure of the amount of denudation. The total evidence for rebound is now known to be regional in extent, supporting the relevance of a regional isostatic model. We note that isostatic rebound need not to be continuous, so that evidence of episodic rebound does not conflict with it, and that a lack of isostatic rebound would require a strongly opposing active tectonic regime. That is, a key general conclusion is that denudational rebound should always be assessed as an explanation for uplift before active tectonism is invoked.