Cliff-top boulder morphodynamics on the high–energy volcanic rocky coast of the Reykjanes Peninsula (SW Iceland)

• Published in: Marine Geology
• Main Authors: Autret, Ronan, Didier, David, Suanez, Serge, S., Stéphan, Pierre, Ammann, Jérôme, Baudry, Jérémy, Erlingsson, Björn, Sigurðarson, Sigurður
• Other Authors: Laboratoire de Dynamique et de Gestion Intégrée des Zones Côtières (LDGIZC), Université du Québec à Rimouski (UQAR), Northern and Arctic Coastal Research Lab, Laval University, Department of geography, Center for Northern Studies, Littoral, Environnement, Télédétection, Géomatique (LETG - Brest), Université de Brest (UBO)-Université de Rennes 2 (UR2)-Institut Universitaire Européen de la Mer (IUEM), Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS)-Nantes Université (Nantes Univ)-Littoral, Environnement, Télédétection, Géomatique UMR 6554 (LETG), Université de Brest (UBO)-Université de Rennes 2 (UR2)-Centre National de la Recherche Scientifique (CNRS)-Institut de Géographie et d'Aménagement Régional de l'Université de Nantes (Nantes Univ - IGARUN), Nantes Université - pôle Humanités, Nantes Université (Nantes Univ)-Nantes Université (Nantes Univ)-Nantes Université - pôle Humanités, Nantes Université (Nantes Univ)-Nantes Université (Nantes Univ)-Institut de Géographie et d'Aménagement Régional de l'Université de Nantes (Nantes Univ - IGARUN), Nantes Université (Nantes Univ), Geo-Ocean (GEO-OCEAN), Université de Bretagne Sud (UBS)-Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS), Institut des Sciences de la MER de Rimouski (ISMER), University Centre of the Westfjords, Icelandic Road and Coastal Administration (IRCA), Institut Paul Emile Victor (IPEV - French Polar Institut), ANR-17-EURE-0015,ISBlue,Interdisciplinary Graduate School for the Blue planet(2017), ANR-10-LABX-0019,LabexMER,LabexMER Marine Excellence Research: a changing ocean(2010)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2023
• Subjects: boulder; cliff-top; storm; basaltic coast; survey; Iceland; [SDU.STU.GM]Sciences of the Universe [physics]/Earth Sciences/Geomorphology; [SDE]Environmental Sciences; [SDU.OCEAN]Sciences of the Universe [physics]/Ocean; Atmosphere; Reykjanes
• Online Access: https://cnrs.hal.science/hal-03883167; https://cnrs.hal.science/hal-03883167/document; https://cnrs.hal.science/hal-03883167/file/MARGO-D-22-00270_Autret-et-al.pdf; https://doi.org/10.1016/j.margeo.2022.106984

International audience Cliff-top boulder deposits (CBDs) are morphological indicators of high-energy conditions. Since 2014, a monitoring of CBDs dynamics has been undertaken on the south-western coast of Iceland (Reykjanes Peninsula) to monitor their long-term activation (quarrying, transport and deposition) as a proxy of the inter-annual winter storminess variations and basaltic cliff erosion processes in a context of rocky coast progradation. Annual topomorphological surveys of four study sites were conducted and Structure-from-Motion photogrammetry was performed to quantify CBDs displacements. Hydrodynamic conditions were analyzed based on offshore waves and water level. Results show that CBDs activation occurs every winter, regardless of the variability of hydrodynamic conditions. Depending on the site and the year, more than 2% and 17% of the CBDs accumulated above 8 m to 10 m asl at the top of the cliffs are regularly mobilized. While inland movements represent the main mode of transport of blocks (between 50% to 60%), seaward and longshore movements are also well represented (10% to 20%). Longshore displacement is favored by the wide tabular morpho-structural setting of the wave-scour cliff-top platforms, which is explained by the structure of pāhoehoe lava flows. The activation of CBDs –measured from the volumes of displaced boulders–, shows a good correspondence with the frequency and duration of storms. However, as was the case during the winter of 2018-2019, it was rather the intensity of two highly morphogenic episodes combining storm waves and especially very high spring tide water levels, that generated the largest boulders displacements. Substantial interannual activation of the CBDs confirms that they constitute an important and still understudied proxy of the morphogenic system of high-energy rocky coasts, whose the dynamic in terms of carrying, transport, and deposition, could significantly increase with rising sea level.