Zonal study of supratidal coastal boulder deposits : from Brittany to Iceland

• Main Author: Autret, Ronan
• Other Authors: 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 Bretagne occidentale - Brest, Serge Suanez, Samuel Étienne
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: HAL CCSD 2018
• Subjects: Rocky coasts; Coastal boulder; Cliff-top storm deposits; Storm; Extreme waves; Côtes rocheuses; Blocs littoraux; Blocs cyclopéens; Tempêtes; Vagues extrêmes; [SHS.GEO]Humanities and Social Sciences/Geography; Iceland; North Atlantic; Northeast Atlantic
• Online Access: https://theses.hal.science/tel-01880992; https://theses.hal.science/tel-01880992/document; https://theses.hal.science/tel-01880992/file/These-2018-SML-Geographie-AUTRET_Ronan.pdf

Cliff-top storm deposits (CTSDs) corresponding to boulder accumulations are locally identified along the North–Atlantic coasts (Iceland, Scotland, Ireland, France), where they are defined as one of the most remarkable morphosedimentary storm signature. Their study aims to understand the effects of high energy storm waves on these specific rocky cliffed coasts facing deep–water and exposed to energetic wave–climates. Recent works demonstrated the role of high energy storm waves (instead of tsunami waves) in transporting and supplying in boulders these deposits. In the context of climate change, and the possible intensification and/or increase in frequency of extreme meteo-oceanic events, CTSDs appears as a potential geomorphological indicator for the monitoring of these changes on high-energy rocky coasts. This thesis propose an analysis of their morphosedimentary dynamics based on field observations realized at high (64°N) and medium (48°N) latitude of the Northeast Atlantic basin. In the present work, their morphosedimentary dynamics have been annually surveyed using low altitude aerial photographs. Results shows two different hydrosedimentary circulation patterns of CTSDs. The first one concerns inland boulder transport, corresponding the directions of the incident waves. This pattern confirms the contemporary edification of ridges. The second one concerns longshore or seaward boulder transport, describing a longitudinal drift of this sedimentary material.The processes of quarrying and transport of CTSDs are concomitant and can repeatedly occur during one single event and/or winter, including during regular storms. The retrospective analysis of sea weather forecast favorable to these processes during the last 70 years showed an infraannual frequency with no particular periodicity nor tendency. Les blocs supratidaux de tempête que l’on trouve au sommet des falaises vont à l’encontre du schéma classique qui décrit l’érosion des falaises. Généralement, le recul des escarpements rocheux se fait au rythme des ...