Alastair M.D. Gemmell

Fluctuations in the thermoluminescence signal of suspended sediment in an alpine glacial meltwater stream

Abstract Analysis of the thermoluminescence (TL) signal from suspended sediment samples from the Dora di Ferret river in northern Italy reveals two scenarios for entrainment, transport and bleaching of the TL signal. In clear weather, a simple diurnal fluctuation in luminescence intensity is apparent, but the correlation with sediment concentration in the stream is very low. Storm events in contrast cause large amounts of unbleached sediment to be mobilised and entrained in the flow, producing a significant positive correlation between TL intensity and sediment concentration. Such storm events may be identified by an initial dip in the intensity of the TL signal, believed to be due to zeroed grains on the surface of valley slopes being washed off the slopes, followed by a major rise in signal as erosion starts to incorporate previously unbleached sediment into the flow.

Zeroing of the TL signal in sediment undergoing fluvioglacial transport. An example from Austerdalen, Western Norway

Abstract Study of levels of natural TL in sediment undergoing fluvial transport in Austerdalen, Norway, shows that bleaching does occur, but does not follow a regular pattern. This is attributed to the incorporation of older, unbleached material into the sediment load as a result of riverbank erosion. Levels of residual TL are high enough to raise doubts about the accuracy of fine-grain TL dating of fluvioglacial sediments which have experienced only a short distance of transport.

Thermoluminescence dating of glacially transported sediments: Some considerations

Abstract Theoretical considerations imply that the suitability of glacially-deposited sediments for thermoluminescence (TL) dating will be influenced by transport routes within the ice, and by facies of deposition. Measurments on sediments obtained from the Austerdalsbreen glacier in western Norway indicate that zeroing of sediment does not occur at the base of a valley glacier, but that englacial and supraglacial sediments showed evidence of bleaching but not total zeroing. Analysis of sediments from recent glacial and fluvioglacial landforms showed no evidence that they had been zeroed prior to deposition. Results indicate that the TL-age of glacial landforms will be a function of the derivation and travel paths of the sediments of which it is composed rather than of the form itself. It is concluded that as knowledge of the rates of bleaching associated with various facies of transport and deposition of glacial sediments improves, so the potential of the technique to act as a diagnostic sedimentological tool will increase, even when dating of glacial deposits by TL is impossible.

Environmental controls on the TL age of modern (zero-age) proglacial outwash sediments

Abstract Thermoluminescence (TL) signals from suspended sediment in an Icelandic meltwater stream exhibit small-scale random fluctuations over time, but show sufficient consistency to indicate that larger-scale fluctuations in TL are systematic rather than random. It is concluded that diurnal TL fluctuations are related to changes in sediment source and ambient conditions during transport. The results suggest ‘young’ fluvioglacial sediments may prove difficult to date using standard TL techniques.

Fractal dimensions of diamictic particle-size distributions: Simulations and evaluation

It has been proposed that deformation tills have fractal particle-size distributions, reflecting scale-invariant debris-comminution processes. Numerical simulations, however, show that fractal dimensions (m) typical of deformation tills can be produced by the mixing of Gaussian parent populations, analogous to the mechanical mixing of coarse-, medium- and fine-grained sorted sediments. The simulated distributions have high r2 values (>0.98) and narrow 95% confidence limits, indicating that fractal analysis cannot distinguish diamictons that have been created by shearing from those formed by other mechanisms, such as the mixing of preexisting sediments. The fractal dimensions of diamictons reflect the relative amounts of coarse and fine material in the distribution, but are not uniquely diagnostic of particular genetic processes.

A Pliocene age and origin for the strandflat of the Western Isles of Scotland: a speculative hypothesis

A series of very wide (up to 15 km) raised shore platforms in the Scottish Hebrides are identified and described for the first time and are considered part of a high rock platform shoreline in the western isles of Scotland described by W. B. Wright in his classic Geological Magazine paper a century ago as a ‘preglacial’ feature. Subsequent interpretations suggesting that the platforms were produced during the Pleistocene are rejected here in favour of a speculative hypothesis that the features are part of the well-known strandflat that is extensively developed across large areas of the northern hemisphere. It is argued that the Scottish strandflat developed during the Pliocene and was later subjected to extensive Pleistocene glacial erosion such that only a few areas of platform have survived in the Scottish Inner Hebrides (ice-proximal) while they are well-preserved in the Outer Hebrides (ice-distal). Support for a Pliocene hypothesis is provided by the marine oxygen isotope record for this time interval which points to prolonged periods of relative sea level stability as would be required for the production of such wide features. This hypothesis for the formation of a Scottish strandflat not only provides an elegant explanation for the origin and age of the raised rock platform fragments that occur throughout the western isles of Scotland, but it may also have relevance for other coastal areas of the northern hemisphere (e.g. Norway, Greenland, Alaska) where the strandflat is a well-developed feature.

First Steps towards an Interactive Real-Time Hazard Management Simulation.

This paper reports on the construction and initial testing of a computer-based interactive flood hazard management simulation, designed for undergraduates taking an applied geomorphology course. Details of the authoring interface utilized to create the simulation are presented. Students act as the managers of civil defence utilities in a fictional town, and have to respond to changes in local conditions to prevent a flood disaster. An SMS messaging service presents the managers with real-time situation updates, and enables them to respond immediately. No significant difference is observed between the standard of student performance under these conditions of authentic assessment in the simulation and that attained in the other, more traditional, elements of assessment in the course. Future refinements intended to overcome identified weaknesses in the simulation are outlined.

‘Competitive’ simulation in the teaching of applied geomorphology: an experiment

Abstract The use of a team approach for project work in many areas of geography can be expanded to provide the student with an enhanced range of experience through the introduction of a ‘competitive’ bidding element. This element simulates a commercial environment so that teams of students compete to convince assessors that their proposal should win the ‘contract’ for a postulated commercial enterprise such as a freight terminal or the site for an industrial development. An example, based around the selection of a routeway for a natural gas pipeline, is presented.

Scottish Landform Example 40: The Buchan Gravels Formation: A Remnant Deposit of a Palaeo-landscape

Abstract The Buchan Gravels Formation (BGF) takes the form of a series of gravel deposits of intriguing age and origin in North-East Scotland. The BGF is divided into two geographically-distinct groups, the Windy Hills Gravel Member (WHGM) and the Buchan Ridge Gravel Member (BRGM). The WHGM occurs in central Buchan, and is predominantly composed of quartzite gravels considered to have been deposited by eastwardly-flowing rivers. In contrast the BRGM is found in eastern Buchan, and is composed largely of flint-rich gravels, the precise origins of which are still under debate. Both gravel members are of considerable age, judging by the number of rotted clasts they contain. In addition, both presently occupy high ground, despite seeming to have originated as water-lain deposits. Although of unknown age, the BGF members provide evidence of topographic inversion since their deposition, and quite possibly preglacial age.

Recent publications relating to the geography of Scotland 1992–93

The following list, whilst not exhaustive, is intended to cover the main publications of relevance to the geography of Scotland that appeared in 1995. Some items omitted from previous lists have also been included. Publications of the Scottish Association of Geography Teachers and papers in the Scottish Geographical Magazine are not included: these are, of course standard sources. As before, dissertations, annual reports and local authority planning reports have been excluded.