Debris-flow release processes investigated through the analysis of multi-temporal LiDAR datasets in north-western Iceland

• Published in: Earth Surface Processes and Landforms
• Main Authors: Morino, Costanza, Conway, Susan, Balme, Matthew, Hillier, John, Jordan, Colm, Sæmundsson, Þorsteinn, Argles, Tom
• Other Authors: School of Environment, Earth and Ecosystem Sciences Milton Keynes, Faculty of Science, Technology, Engineering and Mathematics Milton Keynes, The Open University Milton Keynes (OU)-The Open University Milton Keynes (OU), Laboratoire de Planétologie et Géodynamique UMR 6112 (LPG), Université d'Angers (UA)-Université de Nantes - UFR des Sciences et des Techniques (UN UFR ST), Université de Nantes (UN)-Université de Nantes (UN)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), School of Physical Sciences Milton Keynes, Department of Geography Loughborough, Loughborough University, British Geological Survey Keyworth, British Geological Survey (BGS), University of Iceland Reykjavik
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2019
• Subjects: multi-temporal analysis; NW Iceland; debris flow; LiDAR; release styles; [SDU.STU.GM]Sciences of the Universe [physics]/Earth Sciences/Geomorphology; Ísafjörður; Iceland
• Online Access: https://hal.science/hal-02268377; https://hal.science/hal-02268377/document; https://hal.science/hal-02268377/file/HAL_Morino_etal_ESPL_2019.pdf; https://doi.org/10.1002/esp.4488

International audience Debris flows are fast-moving gravity flows of poorly sorted rock and soil, mixed and saturated with water. Debris-flow initiation has been studied using empirical and experimental modelling, but the geomorphic changes, indicative of different triggering processes, are difficult to constrain with field observations only. We identify signatures to distinguish two different debris-flow release styles by integrating high-resolution multi-temporal remote sensing datasets and morphometric analysis. We analyse debris flows sourced above the town of Ísafjörður (Iceland). Two debris-flow triggering processes were previously hypothesised for this site: (i) slope failure, characterised by landslides evolving into debris flows; and (ii) the fire-hose effect, in which debris accumulated in pre-existing, steep-sided bedrock passages is transported by a surge of water. It is unknown which process dominates and determines the local risk. To investigate this question, we compare airborne LiDAR elevation models and aerial photographs collected in 2007 with similar data from 2013. We find that two new debris-flow tracks were created by slope failures. These are characterised by steep sliding surfaces and lateral leveed channels. Slope failure also occurred in two large, recently active tracks, creating the preparatory conditions for the fire-hose effect to mobilise existing debris. These tracks show alternating zones of fill and scour along their length, and debris stored below the source-area at rest angles >35°. Our approach allows us to identify and quantify the morphological changes produced by slope failure release process, which generated the preparatory conditions for the fire-hose effect. As debris flows are rarely observed in action and morphological changes induced by them are difficult to detect and monitor, the same approach could be applied to other landscapes to understand debris-flow initiation in the absence of other monitoring information, and can improve the identification of zones at ...