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

This thesis represents one of the few studies so far that systematically analyses environmental conditions within debris flow source areas to determine their relative importance for debris flow development. Environmental site conditions, such as slope gradient and debris availability, influence the spatial and temporal distribution of debris flows in high-alpine areas. However, current understanding of these preconditioning controls is mostly qualitative and inadequate for debris-flow hazard assessments and climate change impact studies. The author's research investigates the role of frost weathering and permafrost in the occurrence of debris flows in the Southern Alps of New Zealand. Analyses are based on an extensive debris flow inventory, documenting debris flow occurrence and activity over the last 60 years in selected catchments. Debris flow activity is compared to frost-weathering intensity estimates from two models, allowing the practical comparison of two competing frost-weathering hypotheses currently discussed in literature. Information on permafrost occurrence is based on a new distributed permafrost estimate for the Southern Alps, derived from climatic conditions at active rock glacier sites. This pioneering thesis provides empirical evidence that frost weathering promotes debris-flow formation. It further highlights the potential and limitations of regional-scale studies for advancing our understanding of debris-flow preconditioning factors. von Sattler, Katrin