Periglacial Preconditioning of Debris Flows in the Southern Alps, New Zealand

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This thesis systematically analyzes environmental conditions in debris flow source areas to assess their significance in debris flow development. Factors like slope gradient and debris availability affect the spatial and temporal distribution of debris flows in high-alpine regions. However, the current understanding of these preconditioning controls is primarily qualitative, limiting their application in debris-flow hazard assessments and climate change impact studies. The research focuses on the influence of frost weathering and permafrost on debris flow occurrences in New Zealand's Southern Alps. It utilizes an extensive debris flow inventory documenting activity over the past 60 years in selected catchments. The study compares debris flow activity with frost-weathering intensity estimates from two models, facilitating a practical comparison of competing frost-weathering hypotheses in the literature. Additionally, it provides new insights into permafrost occurrence through a distributed estimate derived from climatic conditions at active rock glacier sites. This pioneering work offers empirical evidence that frost weathering facilitates debris flow formation and underscores the potential and limitations of regional-scale studies in enhancing our understanding of debris-flow preconditioning factors.