Geomorphic Hazard Analyses in Tectonically-Active Mountains: Application to the Western Southern Alps, New Zealand A thesis submitted in partial fulfilment of the requirements for the Degree of Doctor of Philosophy in Hazard and Disaster Management in the Department of Geological Sciences University of Canterbury by Theodosios Kritikos 2013 Franz Josef Glacier, West Coast, South Island New Zealand “Human society is organized for a stable earth; its whole machinery supposes that, while the other familiar elements of air and water are fluctuating and untrustworthy, the earth affords a foundation which is firm. Now and then this implied compact with nature is broken, and the ground trembles beneath our feet. At such times we feel a painful sense of shipwrecked confidence; we learn how very precious to us was that trust in the earth which we gave without question. If the disturbance be of a momentary an unimportant kind we may soon forget it, as we forget the rush word of a friend; if it be violent, we lose one of the substantial goods of life, our instinctive confidence in the earth beneath our feet” by N. S. Shaler, March 1887 “The Stability of the Earth,” Scribner’s Magazine, Vol.1, No.3, p.259. Abstract On-going population growth and urbanization increasingly force people to occupy environments where natural processes intensely affect the landscape, by way of potentially hazardous natural events. Tectonic plate boundaries, active volcanic regions and rapidly uplifting mountain ranges are prominent examples of geomorphically hazardous areas which today accommodate some of the world’s largest cities. These areas are often affected by more than one hazard such as volcanic eruptions, earthquakes, landslides, tsunamis, floods, storms and wildfires, which frequently interact with each other increasing the total impact on communities. Despite progress in natural hazards research over the last two decades, the increasing losses from natural disasters highlight the limitations of existing methodologies to effectively mitigate the adverse effects of natural hazards. A major limitation is the lack of effective hazard and risk assessments incorporating hazard interactions and cascade effects. Most commonly, the assessment of risks related to different hazards is carried out through independent analyses, adopting different procedures and time-space resolutions. Such approaches make the comparison of risks from different hazard sources extremely difficult, and the implicit assumption of independence of the risk sources leads to neglect of possible interactions among hazard processes. As a result the full hazard potential is likely to be underestimated and lead to inadequate mitigation measures or land-use planning. Therefore there is a pressing need to improve hazard and risk assessments and mitigation strategies especially in highly dynamic environments affected by multiple hazards. A prominent example of such an environment is the western Southern Alps of New Zealand. The region is located along an actively deforming plate boundary and is subject to high rates of uplift, erosion and orographically-enhanced precipitation that drive a range of interrelated geomorphic processes and consequent hazards. Furthermore, the region is an increasingly popular tourist destination with growing visitor numbers and the prospect for future development, significantly increasing societal vulnerability and the likelihood of serious impacts from potential hazards. Therefore the mountainous landscape of the western Southern Alps is an ideal area for studying the interaction between a range of interrelated geomorphic hazards and human activity. In an effort to address these issues this research has developed an approach for the analysis of geomorphic hazards in highly dynamic environments with particular focus on tectonically-active mountains using the western Southern Alps as a study area. The approach aims to provide a framework comprising the stages required to perform multi-hazard and risk analyses and inform land-use planning. i This aim was approached through four main objectives integrating quantitative geomorphology, hazard assessments and GIS. The first objective was to identify the dominant geomorphic processes, their spatial distribution and interrelationships and explore their implications in hazard assessment and modelling. This was achieved through regional geomorphic analysis focusing on catchment morphometry and the structure of the drainage networks. This analysis revealed the strong influence and interactions between frequent landslides / debris-flows, glaciers, orographic precipitation and spatially-variable uplift rates on the landscape evolution of the western Southern Alps, which supports the need for hazard assessment approaches incorporating the interrelationships between different processes and accounting for potential event cascades. The second and third objectives were to assess the regional susceptibility to rainfall-generated shallow landslides and river floods respectively, as these phenomena are most often responsible for extensive damage to property and infrastructure, injury, and loss of lives in mountainous environments. To achieve these objectives a series of GIS-based models was developed, applied and evaluated in the western Southern Alps. Evaluation results based on historical records indicated that the susceptibility assessment of shallow landslides and river floods using the proposed GIS-based models is feasible. The output from the landslide model delineates the regional spatial variation of shallow landslide susceptibility and potential runout zones while the results from the flood modelling illustrate the hydrologic response of major ungauged catchments in the study area and identify flood-prone areas. Both outputs provide critical insights for land-use planning. Finally, a multi-hazard analysis approach was developed by combining the findings from the previous objectives based on the concepts of interaction and emergent properties (cascade effects) inherent in complex systems. The integrated analysis of shallow landslides, river floods and expected ground shaking from a M8 plate-boundary fault (Alpine fault) earthquake revealed the areas with the highest and lowest total susceptibilities. Areas characterized by the highest total susceptibility require to be prioritized in terms of hazard mitigation, and areas with very low total susceptibility may be suitable locations for future development. This doctoral research project contributes to the field of hazard research, and particularly to geomorphic hazard analyses in highly dynamic environments such as tectonically active mountains, aiming to inform land-use planning in the context of sustainable hazard mitigation. ii Acknowledgments This research project has benefited from the help and support of many people. First and foremost I would like to express my deepest appreciation to my senior supervisor Professor Tim Davies for his fantastic support, guidance, encouragement throughout my PhD journey. His open mind and critical thinking were invaluable for developing my research skills. Special thanks to my associate supervisor Dr. Thomas Wilson who offered great advice and support over the duration of the project. His sharp eye for the detail and insightful comments have been instrumental in continuously improving the quality of my research. I would also like to express my gratitude to the University of Canterbury for financial support through the Doctoral Scholarship and Mason Trust. I wish to acknowledge the special contribution of Noah Snyder who provided many useful discussions on geomorphic analysis and I am grateful to have worked with him. Acknowledgement must be extended to Erin Hawke and Rodney Barker from the Department of Conservation who kindly provided useful data and information during the initial stages of my research project. Huge thank you to all the fantastic technical and administrative staff of the Department of Geological Sciences for their support and assistance. To my fellow postgraduate students, the many wonderful friends and my officemates thank you for making me feel at home in a place far, far away...from mine. Finally, I owe my deepest gratitude to my family and my partner. Thank you for believing in me, your never-ending support, patience and understanding throughout the doctorate, and over my university years. I couldn’t have done this without you. iii Table of contents Abstract ................................................................................................................................................ i Acknowledgments .............................................................................................................................. iii Table of contents ............................................................................................................................... iv List of Figures ................................................................................................................................... viii List of Tables .................................................................................................................................... xiii Terminology ...................................................................................................................................... xv 1. Chapter 1: Introduction .............................................................................................. 1 1.1 Tectonically active mountains .....................................................................................................