bluuebunny/crossref_metadata_2025_split huggingface dataset:
A development of the lichenometric method applied to the dating of glacially influenced debris flows in southern chile
Authors: Winchester V. , Harrison S. 
Published: February 2007

AbstractLichenometry is a dating technique that has problems relating to questionable assumptions. The development of a size frequency approach, previously used in attempts to resolve some of the problems, is described and applied to the dating of four debris flows marginal to the San Rafael Glacier in Southern Chile. This study provides examples of the development's application, its problems and directions for further work. The size frequency approach, based on new assumptions, uses parameters derived from population size frequency distributions of the lichen species Placopsis patagonica to provide relative and absolute dating for rock surfaces. Changes in the shapes of distributions suggest the relative age of populations. Absolute dating is based on a curve (spanning a 24 year time period) derived from mean diameter size/age correlations. A stratified random sampling design permits the use of inferential statistics. Standard deviations and confidence intervals show error margins, the degree of relatedness between neighbouring populations, and populations that are anomalous. One‐way analysis of variance is used to indicate where populations may safely be grouped. The size frequency approach appears to be particularly suitable for use on unstable debris flows where secondary movements are common. The approach also demonstrates that lichen growth and colonization are sensitive to aspect differences and other variations in microhabitat.
Fire and ecosystem heterogeneity: A mediterranean case study
Authors: Kutiel Pua 
Published: February 2007

AbstractThe response of a Mediterranean ecosystem to fire is summarized in this paper. The results were obtained over a 3‐year period at sites with a known fire history on Mt Carmel, Israel. The results give some idea of the complexity and variability of the ecosystem response to fire, and about factors that could determine these responses. It also shows how fire increases species and landscape diversity.
Discussion: Bulk sampling of coarse clastic sediments for particle‐size analysis
Authors: Dunkerley D. L. 
Published: February 2007

AbstractGale and Hoare (1992) have provided a figure relating maximum particle diameter in a coarse clastic sediment to the size of sample required to generate a reproducible measure of the particle‐size distribution of that sediment. However, they fail adequately to justify the basis for the criterion of sample adequacy adopted in their proposal. Additionally, there is a range of separate issues neglected by Gale and Hoare (1992) which makes their conclusion inapplicable in many situations. A fundamental issue that they neglect is the purpose lying behind a grain‐size analysis: this issue determines what grain size measures are appropriate, rather than the empirical, seemingly purpose‐independent, approach of Gale and Hoare (1992).
‘real’ geomorphology revisited
Authors: Richards Keith 
Published: February 2007

AbstractSome of the reasons are given for the editorial (Richards, 1990) now discussed by Rhoads (1994) and Bassett (1994). These include the lack of interest generally displayed by geomorphologists in matters of scientific philosophy and method, and the instrumentalist view of research often presented to postgraduate students given present funding imperatives. It is suggested that in a revision of views about the validity of a hypothesis‐testing, critical rationalist methodology might have considerable implications for the practice of environmental sciences, and that accordingly the debate initiated by Rhoads and Bassett is worthy of continuation.
A field test of tubino's (1991) model of alternate bar formation
Authors: Welford Mark R. 
Published: February 2007

AbstractThis study investigates the fluvial dynamics of straight natural stream channels. In particular, this experimental field study quantitatively assesses a physically based non‐linear mathematical theory of alternate bar formation under unsteady natural flow conditions within a straight alluvial stream. The study site is an artificially straightened section of the Embarras River located approximately 16 km south of Champaign, Illinois. Data were collected on channel form, gradient, alternate bar dimensions, bed sediment size and flow stage over a 2 year study period.Both linear and non‐linear steady flow hydrodynamic theories suggest that alternate bars are critical to the process of meander development. But these theories do not predict bar development for unsteady flow conditions, which typically occur in natural alluvial channels. Tubino (1991) suggests that bar evolution for a flood hydrograph can be divided into three parts: (1) a period of limited bar growth during the rising stage of the flood; (2) a stage of modest bar decay near the peak of the flood; and (3) a stage of non‐linear bar growth during the prolonged falling stage of the flood.Bars developed during the falling limb of a hydrograph, and exhibited sequential development rather than the uniform growth along the reach predicted by Tubino's model. As flow stage decreased, short, low, fine‐grained bars were superimposed on long, high and coarser‐grained bars that developed under preceding high flow stages. These results suggest that the process of bar formation in artificially straightened natural streams with heterogeneous bed material may occur under different flow conditions and in a different manner than predicted by theoretical models. Further work should focus on attempting to isolate the physical mechanisms responsible for alternate bar formation in straight natural streams with heterogeneous bed material and flashy hydrologic flow regimes.
Within‐storm variations in runoff and sediment export from a rapidly eroding coal‐refuse deposit
Authors: Smith Laurence C. , Olyphant Greg A. 
Published: February 2007

AbstractMeasurements of rainfall, runoff and sediment export from a barren deposit of coal mine refuse in south‐western Indiana were collected during three storms in the summer and autumn of 1990. Interfluve sheetwash, sediment mass flux, sediment concentration and, to a lesser extent, trunk gully discharge all responded quickly to changes in rainfall intensity. Grain‐size distributions varied considerably during storms, containing exclusively fine‐grained sediment at low sediment discharges but very large quantities of coarse (> 2mm) sediment at peak sediment discharges. Although data from a fairly long, multipulsed storm indicate that sediment production is limited by supply, the imbricated layer of flat chips that exists at the surface of the deposit is apparently mobilized during most high‐intensity pulses of rainfall, thereby producing large volumes of coarse sediment during summer thunderstorms.
Deterministic uncertainty in landscapes
Authors: Phillips Jonathan D. 
Published: February 2007

AbstractDeterministic complexity (chaos) may be common in geomorphic systems, but traditional definitions may have limited practical utility for empirical geomorphology. These definitions are based on sensitivity to initial conditions, which in geomorphology are both unknown and unknowable. Further, chaos analysis depends on distinguishing deterministic complexity from stochastic complexity. This is problematic in geomorphology because some stochastic complexity is virtually always present in addition to any chaos that may be present. While it is important to recognize that some complex, apparently random patterns may derive from inherent non‐linear system dynamics, this is of limited use in explaining process–response relationships or mechanics of landscape evolution. A more general term, which subsumes chaos, is deterministic uncertainty, i.e. uncertainty associated with an identifiable but unknown or uncertain source. An analysis of landscape entropy shows that such underlying constraints produce spatial patterns which are apparently chaotic. For the case of geologic controls, the apparent contribution of deterministic chaos to the landscape entropy is a direct non‐linear function of the extent of geologic constraints. However, the underlying constraints and their contribution to observed spatial patterns can also be interpreted in non‐chaotic terms. Examples are given, involving geologic constraints on stream channel networks and parent material control of surface soil textures. Because both randomness and chaos may be more apparent than real, the concept of deterministic uncertainty is more useful in process geomorphology than that of chaos.
Variability of bedload transport and channel morphology in a braided river hydraulic model
Authors: Warburton Jeff , Davies Tim 
Published: February 2007

AbstractThis paper investigates variability in bedload transport and channel morphology for 11 replicate experimental runs in an approximately 1:50 braided river model. The experiments, each of 90 h duration, were carried out in a 20 × 3m tilting flume. All the experiments started with the same initial conditions. Bedload transport was measured at 5 min intervals in a collection drum at the exit from the flume. The model showed reasonable hydraulic similarity when compared to prototype rivers. Results show that mean bedload transport rates for the 11 runs vary in the range 0·98 to 1·49gs−1 (mean + 1·21, coefficient of variation 11 per cent). Within‐run transport rates commonly vary from close to zero, to two and occasionally three or four times the mean rate. Within the bedload series, several irregular phases of transport intensity can be observed, but time series analysis of the data show little underlying serial structure (an AR(2) autoregressive model is appropriate). Channel patterns are narrow/braided, are established quickly and remain relatively stable throughout the runs, although channel widths increase between 20 and 103 per cent over the 11 runs. Channel behaviour varies from aggradational to transitional between aggradation and degradation. Time‐averaged bedload transport rate is weakly correlated with braiding intensity. In general, these results demonstrate that for a given set of controlling variables, bedload transport and channel morphology can be approximately replicated.
Dynamics of fluvial and slope processes in the changing geomorphic environment of singapore
Authors: Chatterjea Kalyani 
Published: February 2007

AbstractThe nature and rates of fluvial and slope processes change over time and space as urbanized areas replace forested land in Singapore. Storm‐based and time‐based data, from undisturbed rainforests, heavily disturbed construction sites, urban grass‐covered slopes and an experimental plot, are collected to observe the impact of rainwater on the soil moisture conditions, surface microtopography, runoff generation, sediment movement, and ground lowering in the three different categories of land use.The undisturbed forested environment is characterized by high throughfall (58% of total rainfall) and frequent negative soil moisture suctions. The slow and unconcentrated overland flow during heavy storms is restricted by the forest floor microtopography. No rills develop. Ground lowering is recorded as 3·2–3·4 mm a−1. But sediment movement is episodic and suspended sediment concentrations in overland flow are 172–222 mg l−1. During urban construction, gully development is rapid on the bare slopes, runoff generation, voluminous, and sediment‐laden discharges (5200–75498 mg l−1) lead to sediment plumes at channel mouths. Ground lowering rates are measured at 132·4 mm a−1. Once grass‐covered, runoff carries less suspended sediment (800 mg l−1) and ground lowering rates are reduced, but depend on the condition of the cover, ranging from 0·2 to 8·2 mm a−1.As urban development continues, environments are altered both in time as well as spatially.
A one‐person, one‐instrument method for precision barometric altimetry
Authors: Goldrick Geoff 
Published: February 2007

AbstractThis paper describes an adaptation of the ‘leap‐frog’ method of barometric altimetry which enables altimetric surveys to be undertaken by a single operator using a single barometer with no requirement for base stations. The method involves two readings at each station, the first bracketed by readings at the previous station, and the second bracketed by readings at the subsequent station. Linear interpolation is used to estimate what the readings would have been at each station at the time that readings were taken at the adjacent stations. Under suitable meteorological conditions errors are generally less than ±1 m, which is sufficiently accurate for a wide variety of geomorphological applications. The method has significant advantages in terms of cost and/or time over more accurate methods such as electronic distance measurement surveys or survey quality global positioning systems. The paper is accompanied by a Microsoft Excel template spreadsheet, BAROSURV.XLT, which converts temperature and pressure readings to relative elevations, and graphs the results. Notes on the use of BAROSURV.XLT are included in the ASCII text file BAROSURV.NOT.
A digital surface roughness meter
Authors: Brian Whalley W. , Rea Brice R. 
Published: February 2007

AbstractGeomorphological studies often require precise devices to measure surface roughness or variations with high precision and good repeatability. A digital measurement device is described, which provides these features and can be linked to a small, light and portable recorder and processor. Such an arrangement allows rapid, accurate data recording by a single operator and can be used in the laboratory or field. With interchangeable measurement rods the vertical range of the instrument is 150 mm, with an actual measured range of 30 mm per rod. The potential accuracy is 0·001 mm with an operating temperature range of+5 to +40°C. Its light weight, relatively low cost and precision make it a useful measuring device which can be adapted for many tasks simply by modification of the stand.
Sea‐level rise: A review of recent past and near‐future trends
Authors: Gornitz Vivien 
Published: February 2007

AbstractGlobal mean sea level is a potentially sensitive indicator of climate change. Global warming will contribute to worldwide sea‐level rise (SLR) from thermal expansion of ocean water, melting of mountain glaciers and polar ice sheets. A number of studies, mostly using tide‐gauge data from the Permanent Service for Mean Sea Level, Bidston Observatory, England, have obtained rates of global SLR within the last 100 years that range between 0·3 and 3 mm yr−1, with most values concentrated between 1 and 2 mm yr−1. However, the reliability of these results has been questioned because of problems with data quality and physical processes that introduce a high level of spatial and temporal variability. Sources of uncertainty in the sea‐level data include variations in winds, ocean currents, river runoff, vertical earth movements, and geographically uneven distribution of long‐term records. Crustal motions introduce a major source of error. To a large extent, these can be filtered by employing palaeo‐sea‐level proxies, and geophysical modelling to remove glacio‐isostatic changes. Ultimately, satellite geodesy will help resolve the inherent ambiguity between the land and ocean level changes recorded by tide gauges.Future sea level is expected to rise by ∼ 1 m, with a ‘best‐guess’ value of 48 cm by the year 2100. Such rates represent an acceleration of four to seven times over present rates. Local land subsidence could substantially increase the apparent SLR. For example, Louisiana is currently experiencing SLR trends nearly 10 times the global mean rate.These recently reduced SLR estimates are based on climate models that predict a zero to negative contribution to SLR from Antarctica. Most global climate models (GCMs) indicate an ice accumulation over Antarctica, because in a warmer world, precipitation will exceed ablation/snow‐melt. However, the impacts of attritional processes, such as thinning of the ice shelves, have been downplayed according to some experts. Furthermore, not all climate models are in agreement. Opposite conclusions may be drawn from the results of other GCMs. In addition, the West Antarctic Ice Sheet is potentially subject to dynamic and volcanic instabilities that are difficult to predict. Because of the great uncertainty in SLR projections, careful monitoring of future sea‐level trends by upgraded tide‐gauge networks and satellite geodesy will become essential.Finally, because of the high spatial variability in crustal subsidence rates, wave climates and tidal regimes, it will be the set of local conditions (especially the relative sea‐level rise), rather than a single global mean sea‐level trend, that will determine each locality's vulnerability to future SLR.
Dune mobility and vegetation cover in the Southwest Kalahari desert
Authors: Wiggs Giles F. S. , Thomas David S. G. , Bullard Joanna E. , Livingstone Ian 
Published: February 2007

AbstractAs part of a wider project investigating the palaeoenvironmental significance of partially vegetated linear dunes in the southwest Kalahari, data collected in the latter part of 1992 concerning dune movement and vegetation cover suggest that sediment transport is occurring on some dune surfaces, and that the majority of surface activity occurs on the crests and upper slopes of the dunes. The data suggest that the limiting variables on surface sediment movement vary on different parts of a dune. On interdunes and lower dune slopes the primary limiting variable is available wind energy, while on dune crests and upper slopes it is vegetation cover. Ground cover by litter has much greater importance in protecting the surface sediment from erosion than rooted vegetation. From individual data points, no evidence is found to support a threshold vegetation cover below which sediment movement occurs. Rather, a gradient of activity is suggested whereby a reduction in vegetation cover increases the potential for sediment movement and surface change. However, dunes with differing amounts of mean vegetation cover display differing degrees of surface activity, and at this scale, a vegetation cover threshold in the region of 14 per cent may be recognized.
The Spey Bay geomorphological study
Authors: Riddell Keith J. , Fuller Terence W. 
Published: February 2007

AbstractThe Spey Bay coastline and the estuary of the River Spey exhibit a rapidly evolving planform. They provide an opportunity to study geomorphological changes in a coupled coastal/estuarine system which can be measured over hours and days rather than the years and decades associated with more slowly evolving landscape features. Attempting to understand coastal and estuarine geomorphology provides engineers and earth scientists with an exciting intellectual challenge. This is not, however, simply an academic challenge because the successful management of coastal and estuarine environments depends on improving this understanding. The impetus behind our work in this area is the protection of land‐use interests. It is in this context that Babtie Dobbie Limited have been employed in studying the River Spey since 1962. This paper is based on a practical case study performed for coastal and river engineering purposes between 1990 and 1992. The case study was formulated using the results and conclusions of earlier geomorphological studies of the area undertaken over the past 32 years. Knowledge gained from previous studies was crucial in designing the detailed methods and techniques employed in the 1990–1992 geomorphological study. Methods used included historical analyses, photogrammetry, numerical modelling, geographic information systems (GIS) and interpretation of the complex processes which drive landform changes in the estuary and along the adjacent shoreline. The improved understanding of geomorphological processes that has been achieved has enabled engineers to formulate a new management strategy. Central to this strategy are engineering solutions to river and coastal stability and flooding problems which are in sympathy with the environment and which take maximum advantage of our understanding of geomorphological processes.
Turbulent flow structure in a gravel‐bed river: Markov chain analysis of the fluctuating velocity profile
Authors: Kirkbride Alistair D. , Ferguson Rob 
Published: February 2007

AbstractThree electromagnetic current meter probes were deployed in a Canadian gravel‐bed river to obtain simultaneous records at 10 Hz of streamwise (u) and vertical (v) velocity components at three heights above the bed. By looking at the positive and negative signs of the instantaneous fluctuations from the time‐average values of each velocity component at each height, the fluctuating velocity profile of u or v can be treated as a Markov chain with eight states and its statistical properties can be tested against null hypotheses based on the absence of spatial structure. We report results of this novel approach.The most common states of the u profile were those with either higher‐than‐average or lower‐than‐average velocities at all heights; these ‘high speed’ and ‘low speed’ states persisted for up to 3 s. The most common v profiles were all‐upwards or all‐downwards, but these persisted for shorter times than the high speed and low speed u profiles. Analysis of transition probabilities shows statistically significant tendencies for acceleration from the low speed u profile, and change from all‐upwards to all‐downwards v profile, to take place progressively from the uppermost probe downwards, in a sweep‐like way. Deceleration from the high speed to low speed u profile and change from all‐downwards to all‐upwards v profile (burst‐like behaviour) do not show such clear patterns.The results are interpreted in terms of the advection of inverted wedges of relatively high‐momentum fluid, followed by more chaotic structures. A separate set of flow visualization experiments over a mixed gravel bed in a flume supports the presence of advected wedge structures, the decelerating part of the sequence corresponding to irregular ejections of near‐bed fluid.
Textural, geochemical and mineralogical evidence for the origin of peoria loess in Central and Southern Nebraska, USA
Authors: Winspear N. R. , Pye K. 
Published: February 2007

AbstractPossible sources of Peoria loess in central Nebraska have been investigated through the fingerprinting of the textural, geochemical and mineralogical characteristics of the loess and possible source sediments, with statistical comparison of the textural and compositional fingerprints. The results of the investigation contrast with the ‘desert loess’ model proposed by Lugn (1960), and are instead consistent with the derivation of the Peoria loess in Nebraska primarily from fluvio‐glacial outwash sediments carried by the ancestral North and South Platte River systems from the Rocky Mountain Front Ranges during the late Pleistocene.