Pluri-decadal to annual storm-induced geomorphic processes on the Valahnúkur coastal boulder ridge, SW Iceland

• Main Authors: Stéphan, Pierre, Didier, David, Autret, Ronan, Etienne, Samuel, Fichaut, Bernard, Suanez, Serge
• Other Authors: Littoral, Environnement, Télédétection, Géomatique (LETG - Brest), Littoral, Environnement, Télédétection, Géomatique UMR 6554 (LETG), Université de Caen Normandie (UNICAEN), Normandie Université (NU)-Normandie Université (NU)-Université d'Angers (UA)-École Pratique des Hautes Études (EPHE), Université Paris Sciences et Lettres (PSL)-Université Paris Sciences et Lettres (PSL)-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 (IGARUN), Université de Nantes (UN)-Université de Nantes (UN)-Université de Caen Normandie (UNICAEN), Université de Nantes (UN)-Université de Nantes (UN), Université du Québec à Rimouski (UQAR), Service Hydrographique et Océanographique de la Marine (SHOM), Ministère de la défense (1936-.), 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), INQUA, ANR-17-EURE-0015,ISBlue,Interdisciplinary Graduate School for the Blue planet(2017)
• Format: Conference Object
• Language: English
• Published: HAL CCSD 2019
• Subjects: storm; Iceland; boulder; coastal barrier; overwash; [SDE]Environmental Sciences; [SDE.MCG]Environmental Sciences/Global Changes; Reykjanes; Swash
• Online Access: https://hal.science/hal-04670838

International audience While recent studies highlighted the great mobility of boulder beaches related to the impact of storm waves, numerous researches are still needed to better understand the morphodynamic of coastal boulder accumulations and to better interpret fossil boulders deposits. This paper provides original data about storm-induced geomorphic processes and their impact on the Valahnúkur boulder ridge (figure 1). The study site is located west of the Reykjanes Peninsula, in the south-west of Iceland.Firstly, the historical evolution of the boulder ridge was reconstructed from a set of aerial photographs between 1978 and 2010. Photographs were geometrically corrected and georeferenced according to the standard procedure to quantified the shoreline changes. Secondly, four kite and drone surveys were realized yearly between May 2015 and May 2018. The Digital Elevation Models (DEMs) produced using Structure-from-Motion photogrammetry were compared to deduce the morphological changes. Four orthophotographs were analyzed to quantified the movement of boulders. Hydrodynamic conditions were reconstructed using wave buoy and tide gauge measurements. Storminess was first assessed using a POT method. The extreme morphogenetic events were recognized using the 98th percentile of the significant wave height. The storm duration was estimated using the 75th percentile to define the start-time and the end-time of storm events. Wave runup were calibrated from the analysis of a wave/swash motion data set acquired by video monitoring.The historical analysis of shoreline change shows a significant landward retreat of the ridge during the last 40 years. The Highest rates of retreat are recorded in the northern part of the barrier where a large washover fan was formed during the 1990s and reactivated in the 2000s. This suggests a set of overwash events and the episodic flooding of the boulder ridge, probably during major storm events. The southern part of the barrier also shows high migration rates suggesting sediment ...