Book review: image analysis, sediments and paleoenvironments

Book review of: Image analysis, sediments and paleoenvironments (Developments in Paleoenvironmental Research, Volume 7). Edited by Pierre Francus, Dortrecht: Springer, 2004, hardback ISBN 1-4020-2061-9

Chesil Beach grain-size report: a technical report on the impact of beach management works and evaluation of the Sedimetrics Digital Gravelometer software

Chesil Beach grain-size report: a technical report on the impact of beach management works and evaluation of the Sedimetrics Digital Gravelometer softwar

Sediments and landforms in an upland glaciated-valley landsystem: upper Ennerdale, English Lake District

The genesis of moraines associated with British glaciers of Younger Dryas age has proved controversial in recent years. A number of alternative hypotheses exist and, whilst it is generally accepted that such features are polygenetic in origin, some workers have argued that not all of the proposed mechanisms are valid. This paper seeks to explore these issues, using a case study from the English Lake District. A landsystems approach is adopted, integrating information at a variety of spatial scales to explain the development of the sediment-landform associations in upper Ennerdale. The evidence suggests that landform development resulted from a combination of icemarginal deposition and englacial thrusting. It is probable that thrusting resulted from flow compression against a reverse bedrock slope, combined with the confluence of ice from two separate source areas. It is argued that, whilst englacial thrust moraines may not be commonly associated with British Younger Dryas glaciers, under certain conditions englacial thrusting is an important process in landform development

A transferable method for the automated grain sizing of river gravels

The spatial and temporal resolution of surface grain-size characterization is constrained by the limitations of traditional measurement techniques. In this paper we present an extremely rapid image-processing-based procedure for the measurement of exposed fluvial gravels and other coarsegrained sediments, defining the steps required to minimize the errors in the derived grain-size distribution. This procedure differs significantly from those used previously. It is based around a robust object-detection algorithm that produces excellent results on images exhibiting a wide range of sedimentary conditions, crucially, without any user intervention or site-specific parameterization. The procedure is tested using a dataset comprising 39 images from three rivers with contrasting grain lithology, shape, roundness and packing configuration and representing a very wide range of textures. It is shown to perform more consistently than the best existing automated method, achieving a precision equivalent to that obtainable by Wolman sampling, but taking between one sixth and one twentieth of the time. The error in area-by-number grain-size distribution percentiles is typically less than 0.05 Ï

Maximising the accuracy of image-based surface sediment sampling techniques

Recent years have seen increased interest in automated methods, utilizing photographs collected with a hand-held digital camera, for determining the grain-size distribution of coarse river sediments. Such methods are as precise as traditional field methods, and have considerable time and cost advantages. Nevertheless, several unresolved issues pertaining to their deployment remain to be addressed. Using datasets collected from seven gravel-bed rivers, this paper examines four key issues: (i) the minimum area required to obtain a representative sample; (ii) the effect of lower-end truncation on grain-size percentiles; (iii) the effect of river-bed structure such as imbrication and hiding; and (iv) the potential benefits of using individual particle measurements rather than the number (or mass) of particles per size class to calculate percentiles. It is demonstrated that sampling areas of between 50 and 200- times that of the largest grain are adequate to achieve percentile errors of <10% (in mm). The appropriateness of lower-end truncation depends on the study aims and sediment properties. It has a limited effect on higher percentiles, except where sand is a major constituent. Understanding the influence of bed structure on image-derived size information is complicated by the absence of error-free benchmarks against which accuracy may be evaluated, but it is likely that other errors are more important. The use of individual particle measurements to calculate percentiles in preference to classified data is shown to have a small, but appreciable, effect on precision. These results will assist practitioners in making appropriate operational decisions to maximize data quality using image-based grain-size data capture

Essential ancillary data requirements for the validation of surrogate measurements of bedload: non-invasive bed material grain size and definitive measurements of bedload flux

Achieving a significant advance in understanding the sedimentary dynamics of rivers, especially those with coarse-grained beds, depends upon the acquisition of data that adequately reflect sediment flux. In a similar vein, the successful development of a functional relation between bedload flux and contemporary hydraulics that is transferable from river to river requires an understanding of relations between the immediate source of bedload – the river bed – and the flow. This would benefit from deployment of a quick but efficient method of assessing the grain-size distribution of river-bed material, since this is one of several determinants of bedload flux and is a property that can be readily established in a previously ungauged channel. This paper reminds hydraulic engineers and geomorphologists of the need to deploy a method of data capture that allows the performance of surrogate measures of bedload to be assessed adequately. In particular, it highlights the performance and short-comings of the Birkbeck Sampler. This is an automatic slot sampler that provides a continuous, direct and sensitive measure of bedload flux that is as definitive as is feasible in the complex confusion of a river in spate. It has been deployed in a wide range of river environments and has proved to be both reliable and durable, having provided bedload records on ephemeral channels for more than a decade in one case. The paper also indicates a need for the use of a method that facilitates rapid and frequent surveys of river-bed materials in order to understand bedload dynamics that are measured by any means, not least those that detect bedload surrogates. The Digital Gravelometer is described, along with its advantages and limitations. Time-savings alone make this a valuable addition to the river scientist’s tool-kit

Internal structure and significance of ice-marginal moraine in the Kebnekaise Mountains, northern Sweden

Despite a long history of glaciological research, the mode of formation and palaeoenvironmental significance of moraine systems in the Kebnekaise Mountains, Sweden has remained uncertain. These landforms offer the potential to elucidate glacier response prior to the period of direct monitoring and provide an insight into the ice-marginal processes operating at polythermal valley glaciers. This study sets out to test existing interpretations of Scandinavian ice-marginal moraines which invoke ice stagnation, pushing, stacking/dumping, and push-deformation as important moraine forming processes. Moraines at Isfallsglaciären were investigated using ground-penetrating radar to document the internal structural characteristics of the landform assemblage. Radar surveys revealed a range of substrate composition and reflectors, indicating a debris-ice interface and bounding surfaces within the moraine. The moraine is demonstrated to contain both ice-rich and debris-rich zones, reflecting a complex depositional history and a polygenetic origin. As a consequence of glacier overriding, the morphology of these landforms provides a misleading indicator of glacial history. Traditional geochronological methods are unlikely to be effective on this type of landform as the fresh surface may post-date the formation of the landform following reoccupation of the moraine rampart by the glacier. This research highlights that the interpretation of geochronological datasets from similar moraine systems should be undertaken with caution

The potential of small unmanned aircraft systems and structure-from-motion for topographic surveys: a test of emerging integrated approaches at Cwm Idwal, North Wales

Novel topographic survey methods that integrate both structure-from-motion (SfM) photogrammetry and small unmanned aircraft systems (sUAS) are a rapidly evolving investigative technique. Due to the diverse range of survey configurations available and the infancy of these new methods, further research is required. Here, the accuracy, precision and potential applications of this approach are investigated. A total of 543 images of the Cwm Idwal moraine–mound complex were captured from a light (b5 kg) semi-autonomous multi-rotor unmanned aircraft system using a consumer-grade 18 MP compact digital camera. The imageswere used to produce a DSM(digital surfacemodel) of themoraines. The DSMis in good agreement with 7761 total station survey points providing a total verticalRMSE value of 0.517mand verticalRMSE values as lowas 0.200mfor less densely vegetated areas of the DSM. High-precision topographic data can be acquired rapidly using this technique with the resulting DSMs and orthorectified aerial imagery at sub-decimetre resolutions. Positional errors on the total station dataset, vegetation and steep terrain are identified as the causes of vertical disagreement. Whilst this aerial survey approach is advocated for use in a range of geomorphological settings, care must be taken to ensure that adequate ground control is applied to give a high degree of accuracy

Origin and significance of dispersed facies basal ice: Svínafellsjökull, Iceland

Dispersed facies basal ice – massive (i.e. structureless) ice with dispersed debris aggregates – is present at the margins of many glaciers and, as a product of internal glacial processes, has the potential to provide important information about the mechanisms of glacier flow and the nature of the subglacial environment. The origin of dispersed facies is poorly understood, with several hypotheses having been advanced for its formation, and there is disagreement as to whether it is largely a sedimentary or a tectonic feature. We test these established hypotheses at the temperate glacier Svínafellsjökull, Iceland, and find that none fully account for dispersed facies characteristics at this location. Instead, dispersed facies physical, sedimentological and stable-isotope (δ18O, δD) characteristics favour a predominantly tectonic origin that we suggest comprises the regelation and strain-induced metamorphism of debris-rich basal ice that has been entrained into an englacial position by tectonic processes operating at the base of an icefall. Further thickening of the resultant dispersed facies may also occur tectonically as a result of ice flow against the reverse bed slope of a terminal overdeepening. Lack of efficient subglacial drainage in the region of the overdeepening may limit basal melting and thus favour basal ice preservation, including the preservation of dispersed facies. Despite the relatively low sediment content of dispersed facies (∼1.6% by volume), its thickness (up to 25 m) and ubiquity at Svínafellsjökull results in a significant contribution to annual sediment discharge (1635–3270 m3 a−1) that is ∼6.5 times that contributed by debris-rich stratified facies basal ice

Origin, evolution and dynamic context of a Neoglacial lateral-frontal moraine at Austre Lovenbreen, Svalbard

Moraines marking the Neoglacial limits in Svalbard are commonly ice cored. Investigating the nature of this relict ice is important because it can aid our understanding of former glacier dynamics. This paper examines the composition of the lateral-frontal moraine associated with the Neoglacial limit at Austre Lovénbreen and assesses the likely geomorphological evolution. The moraine was investigated using ground-penetrating radar (GPR), with context being provided by structural mapping of the glacier based on an oblique aerial image from 1936 and vertical aerial imagery from 2003. Multiple up-glacier dipping reflectors and syncline structures are found in the GPR surveys. The reflectors are most clearly defined in lateral positions, where the moraine is substantially composed of ice. The frontal area of the moraine is dominantly composed of debris. The core of the lateral part of the moraine is likely to consist of stacked sequences of basal ice that have been deformed by strong longitudinal compression. The long term preservation potential of the ice-dominated lateral moraine is negligible, whereas the preservation of the debris-dominated frontal moraine is high. A glacier surface bulge, identified on the 1936 aerial imagery, provides evidence that Austre Lovénbreen has previously displayed surge activity, although it is highly unlikely to do so in the near future in its current state. This research shows the value of relict buried ice that is preserved in landforms to aiding our understanding of former glacier characteristics. © 2013 Elsevier B.V. All rights reserved