Simon Hinchliffe Phd Thesis
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THE STRUCTURE AND EVOLUTION OF RELICT TALUS ACCUMULATIONS IN THE SCOTTISH HIGHLANDS Simon Hinchliffe A Thesis Submitted for the Degree of PhD at the University of St Andrews 1998 Full metadata for this item is available in St Andrews Research Repository at: http://research-repository.st-andrews.ac.uk/ Please use this identifier to cite or link to this item: http://hdl.handle.net/10023/15206 This item is protected by original copyright THE STRUCTURE AND EVOLUTION OF RELICT TALUS ACCUMULATIONS IN THE SCOTTISH HIGHLANDS by Simon Hinchliffe, B.A. Hons. (Dunelm) Thesis presented for the Degree of Philosophae Doctor University of St Andrews February, 1998 ProQuest Number: 10170800 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. uest. ProQuest 10170800 Published by ProQuest LLC(2017). Copyright of the Dissertation is held by the Author. All rights reserved. This work is protected against unauthorized copying under Title 17, United States Code Microform Edition © ProQuest LLC. ProQuest LLC. 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106- 1346 I ...................... .................................. hereby certify that this thesis has been composed by myself, that it is a record of my own work, and that it has not been accepted in partial or complete fulfilment of any other degree or personal qualification. Signed: Date: I was admitted to the Faculty of Science of the University of St. Andrews under Ordinance General No. 12 on 1st October 1994 and as a candidate for the degree of Ph.D. in October 1995. Signed: Date: I hereby certify that the candidate has fulfilled the conditions of the Resolution and Regulations appropriate to the Degree of Ph.D. zi) Signature of Supervisors: .................... .... r........................................................... 6 Date: 11 A. Unrestricted In submitting this thesis to the University of St. Andrews I understand that I am giving permission for it to be made available for public use in accordance with the regulations of the University Library for the time being in force, subject to any copyright vested in the work not being affected thereby. I also understand that the title and abstract will be published, and that a copy of the work may be made and supplied to any bona fide library or research worker. Ill For Dad iv Abstract The aim of this thesis is to establish the evolutionary history of relict talus accumulations in the Scottish Highlands through study of their distribution, morphology, structure and sedimentology, and through dating and pollen analysis of buried soil horizons. Analyses of talus morphology demonstrates that though the investigated slopes comprise a basal concavity and upper straight slope, features hitherto interpreted as characteristic of unmodified rockfall accumulations, there is considerable variability in upper slope gradient. Surface relief indicates widespread reworking by slope failure, gullying and debris flows. Sections through gully-side exposures exhibit up to 3.5 m of stacked debris flow deposits, wash layers and buried soils overlying rockfall deposits, indicating a complex history of sediment reworking. Sedimentological analyses indicate that 27-30% of the talus sediments at one site (Trottemish) comprise fine (< 2 mm) particles representing granular weathering of the rockwall and syndepositional accumulation of both fine and coarse debris. The volume of talus on Trottemish implies an average rockwall retreat rate of c. 0.3 mm yr1 since deglaciation, of which 0.08-0.09 mm yr1 reflects granular weathering rather than rockfall. Failure and reworking of talus is inferred to reflect reduced infiltration rates (and high porewater pressures during rainstorms) caused by progressive accumulation of fines. Radiocarbon dating of buried soils indicates that reworking commenced prior to c. 6 cal ka BP, and has been intermittently active during the Holocene. Pollen analyses and charcoal concentration counts provide no evidence for accelerated reworking as a result of anthropogenic interference with vegetation cover, but the timing of reworking events provides support for enhanced activity associated with climatic deterioration after c. 2.7-2.3 cal ka BP. The characteristics of the investigated slopes show that models that treat talus as a free- draining accumulation of rockfall debris have limited applicability, and an alternative model that incorporates progressive reworking by other processes is proposed. Acknowledgements Financial support for this project was provided primarily by a Natural Environment Research Council (NERC) studentship (GT4/94/412/G). The cost of radiocarbon determinations was also covered by NERC and carried out at the NERC Radiocarbon Laboratory, East Kilbride, and at the University of Arizona NSF-AMS dating facility. The research was undertaken whilst at the School of Geography and Geosciences, University of St Andrews, under the supervision of Professor Colin Ballantyne and Professor Graeme Whittington. I am deeply indebted to both Colin and Graeme for their assistance and encouragement throughout the course of my doctoral research, and in particular, for helpful critiques of earlier drafts of this work. Sincere thanks go to Colin Ballantyne, Graeme Whittington, Richard Savage, Stuart Nicholson, Kevin Shepherd, Helen Taylor, Mike 'why-ay-funky- Si' Burn, Sophia Colley, Alex Kirk, Pippa Fyfe, Ian Blyth, Alastair Curry, Vivienne Curry and Jonathan Hinchliffe for assistance in the field (and for the occasional beer afterwards). I am also grateful to John Mackenzie and family for providing a warm and friendly welcome to Skye. Several people have provided technical assistance during the course of the research. Many thanks go to Lois Wood for help with pollen preparations and identification, Richard Batchelor for computing support, Graeme Sandeman for cartographic advice, Jim Allan for assistance with photographs, Dr. John Walden for help with mineral magnetic studies, and Colin Cameron and Dr. Jack Jarvis for instruction on the use of laboratory and field equipment. I am also grateful to Alastair Curry and Dr. Hamish Ross for comments on earlier drafts of this work, and for helpful and stimulating discussions. vi I would also like to thank my friends and fellow postgraduates, in particular, Alastair, Ian, Juliet, Karen, Lisa, Lucio, Pascal, Stuart, the 'Kinnesburn top-floor club' (Dan, Hanne, Mike and Ole), and all at 5 Albany Place, for their friendship and humour, and for providing numerous welcome distractions over the past 3 years. Finally, special thanks go to my family (Mum, Jonathan, Georgina, Ann, David and Gran) for their constant encouragement, and for helping to keep my work in perspective. Vll Table of contents Page no.: Chapter 1 Introduction 1.1 Aims and definitions............................................................................ 1 1.2 Field sites.............................................................................................. 2 1.3 Structure of the thesis.......................................................................... 3 Chapter 2 Talus slopes 2.1 Introduction.......................................................................................... 6 2.2 Unmodified rockfall talus slopes........... ............................................. 6 2.3 Rockfall processes............................................................................. 9 2.4 Models of talus development.............................................................. 10 2.4.1 The angle of repose model 2.4.2 The discrete particle rockfall model 2.4.3 The two facet model 2.4.4 Summary 2.5 Modified talus slopes......................................................................... 21 2.5.1 Talus shift 2.5.2 Translational sliding 2.5.3 Debris flows 2.5.4 Debris flow initiation 2.5.5 Debris flow motion 2.5.6 Debris flow morphology 2.5.7 Debris flow deposits 2.5.8 Gullying 2.5.9 Snow avalanches 2.5.10 Avalanche modified talus 2.5.11 Avalanche sediments 2.5.12 Slushflows 2.5.13 Creep 2.6 Unmodified talus slopes in Britain................................................... 40 2.6.1 Talus form 2.6.2 Talus age 2.7 Modified talus slopes in Britain......................................................... 45 2.7.1 Sliding failure 2.7.2 Debris flows 2.7.3 Debris flow morphology 2.7.4 Debris flow deposits Vlll 2.7.5 Debris flow chronology 2.7.6 Avalanche modified talus 2.7.7 Creep 2.8 Summary.............................................................................................. 55 2.9 Research questions.............................................................................. 56 Chapter 3 The field sites 3.1 Introduction.......................................................................................... 57 3.2 Trottemish............................................................................................ 57 3.2.1 Geology 3.2.2 Glacial history 3.2.3 Periglaciation 3.2.4 Rock slope failures 3.2.5 Vegetational history 3.3 NW Scotland: Quinag, Stac Pollaidh and Baosbheinn.............................................. 71 3.3.1 Geology 3.3.2 Glacial history 3.3.3 Periglaciation 3.3.4 Vegetational history 3.4 Glen Feshie........................................................................................... 81 3.4.1 Glacial