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Influence of Runout Path Material on Rock and Debris Avalanche Mobility: Field Evidence and Analogue Modelling

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Influence of Runout Path Material on Rock and Debris Avalanche Mobility: Field Evidence and Analogue Modelling Influence of runout path material on rock and debris avalanche mobility: field evidence and analogue modelling. A thesis submitted in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Geological Sciences / Hazard and Disaster Management Anja Dufresne University of Canterbury New Zealand 2009 ii Another day in the office: sunrise at Hari Hari field station, West Coast, New Zealand. iii iv Acknowledgements First and foremost, for much good advice and encouragement, I would like to thank my supervisor Tim Davies; who, with great faith and quiet ambition, succeeded in pulling me over to the landslide side of the force. Thank you to my co-supervisor Jim Cole, who kept the professor and me in check and this project on time. Muchas gracias to Sergio Salinas and Claus Siebe from the Universidad Autónoma Nacional de México, who have endured and encouraged my work at the Jocotitlán debris avalanche just outside Mexico City. I owe my deepest gratitude to Sergio for his unsurpassed patience, field guidance and help, and for procuring coffee in a coffee-less town. For a review of structural geology field work methods and data interpretation I would like to thank Jarg Pettinga. I am grateful to colleagues around the world who have offered their knowledge and ideas in discussions over glasses of red wine and by electronic thought exchange: Mauri McSaveney, Ken Hewitt, Oliver Korup, Ben van Wyk de Vries, Ben Bernard, Tom Shea, and Jóhann Helgason. Danke auch an Björn Gojdka für seine Einsichten. Thank you to the incredible technical team: Rob Spiers (who is bursting with creative ideas that inspire by their ingenious simplicity), Vanessa Tappenden, Cathy Higgins, and Jennifer Jackson. My thanks go to Lis Bowman for trusting me with the engineering department’s high-speed digital video camera. The French Connection: Guillaume Chevalier, merci beaucoup pour les moments fantastiques dans les avalanches de roches et pour la compagnie incomparable. Thank you for help in the field to: Anke Zernack, Jon Proctor, Elke Hanenkamp, and Lucille Tatard; for field site access: Nelson Cook and Steve Staples; and for turning the West Coast inside out: un-equalled-in-enthusiasm digger driver Spike Jones. v I would like to extend my gratitude to Lee Siebert at the Washington Smithsonian Institute for supporting a daunting task, and to all the people he persuaded to get involved in the database project: Steve Sparks, Ben Bernard, Jorge Clavero, Shinji Takarada, Sasha Belousov, Marina Belousova, and, by proxy, Natalie Ortiz. Further afield, I would like to express my humble respect and deepest gratitude to everybody at my nightly sanctuary: the New Zealand Wing Chun / Doce Pares school under otherwordly guidance of Sifu Leigh Jenkins and Sihing Hugh Puttock. Thank you for your dedication in this timeless art. I have learnt incomparable lessons of endurance, letting-go, focus, inner courage, trust, humility, and forces far beyond my perceived physical and mental limits. This project was funded by a three-year New Zealand International Doctoral Research Scholarship, and field work was supported by the University of Canterbury, Department of Geological Sciences Mason Trust. vi Abstract Rock and debris avalanches result from sudden rock slope failure; they occur in a variety of materials and landscapes, and often have a catastrophic and lasting impact on the society, infrastructure, and landscape of the area. In order to fully understand these events, the factors leading to failure and those influencing the course of the event must be investigated. In recent years, increased attention has been given to numerous aspects of rock/debris avalanche emplacement: among these is the influence of runout path material on the behaviour of snow and ice avalanches, pyroclastic currents, debris flows, volcanic debris avalanches and non-volcanic rock avalanches. The fact that substrates are involved in rock avalanche emplacement has been known since Buss and Heim remarked on it in 1881, but few detailed studies on the effects of this involvement on avalanche emplacement exist. One popular hypothesis which has emerged is that the long runout of large rock avalanches can be explained by the basal friction reduction due to overrunning or failure of saturated substrate material. However, the present study shows that this is not the case. From analysis of nearly 400 rock and debris avalanche deposit descriptions it is evident that: (1) avalanches inevitably interact with their runout path material; (2) all large (> 106 m3) rock and debris avalanche events have runout distances that exceed simple frictional model predictions regardless of type or degree of substrate interaction; (3) substrates only add complexities to the ‘long-runout’ avalanche events similar to topographic interference. The complexities resulting from substrate interaction include, for example, characteristic deposit surface features such as longitudinal ridges and flowbands, compressional faults and raised margins from rapid deceleration behind e.g. bulldozed substrates; shearing in a basal mixed zone and consequent changes in basal avalanche mechanical properties; volcanic edifice failure on weak underlying sediments with a change in volcano shape; transformation into more mobile debris flows through the entrainment of large quantities of water or water-bearing materials; and many others. vii viii Table of Contents Acknowledgements ........................................................................................................... v Abstract ............................................................................................................................ vii Table of contents .............................................................................................................. xi List of Figures .................................................................................................................. xii List of Tables ................................................................................................................... xv Introduction ....................................................................................................................... 1 Chapter 1: Avalanche-Substrate Interactions ............................................................. 13 1.1. Problem statement .......................................................................................... 15 1.2. Theoretical considerations ............................................................................. 16 1.3. Substrate erosion and entrainment ................................................................. 26 1.4. Substrate deformation .................................................................................... 41 Chapter 2: Longitudinal Ridges in Mass Movement Deposits ................................... 65 Abstract ................................................................................................................. 67 2.1. Introduction .................................................................................................... 68 2.2. Longitudinal ridges and flowbands: definitions ............................................ 69 2.3. Granular flows – basics and models .............................................................. 71 2.4. Data collection ............................................................................................... 74 2.5. Case studies .................................................................................................... 74 2.6. Other surface morphologies ........................................................................... 81 2.7. Discussion ...................................................................................................... 82 2.7. Conclusions .................................................................................................... 89 Chapter 3: The Round Top Rock Avalanche ............................................................... 91 Abstract ................................................................................................................. 93 3.1. Introduction .................................................................................................... 94 3.2. Study site ........................................................................................................ 95 ix 3.3. Internal avalanche structure ........................................................................... 99 3.4. Deposit morphology..................................................................................... 100 3.5. Substrate types and substrate-avalanche interaction features ...................... 102 3.6. Basal avalanche contact and internal avalanche structures .......................... 105 3.7. Modelling avalanche-substrate interactions ................................................. 107 3.8. Summary and discussion.............................................................................. 110 3.9. Conclusions .................................................................................................. 117 3.10. Online supplementary material .................................................................. 119 Chapter 4 : The Jocotitlán Volcanic Debris Avalanche ............................................. 121 Abstract ............................................................................................................... 123 4.1. Introduction .................................................................................................
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