Dating of a rock avalanche in Skagafjörður,, Northern Iceland: pieces of evidence of a paraglacial origin

• Main Authors: Mercier, Denis, Decaulne, Armelle, Cossart, Etienne, Feuillet, Thierry, Sæmundsson, Þorsteinn, Jónsson, Helgi Páll
• Other Authors: Littoral, Environnement, Télédétection, Géomatique (LETG - Nantes), Institut de Géographie et d'Aménagement Régional de l'Université de Nantes (IGARUN), Université de Nantes (UN)-Université de Nantes (UN)-Université de Rennes 2 (UR2), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Université de Brest (UBO)-Université de Caen Normandie (UNICAEN), Normandie Université (NU)-Normandie Université (NU)-École pratique des hautes études (EPHE), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS), Laboratoire de Géographie Physique et Environnementale (GEOLAB), Université Blaise Pascal - Clermont-Ferrand 2 (UBP)-Université Clermont Auvergne 2017-2020 (UCA 2017-2020 )-Université Clermont Auvergne (UCA)-Institut Sciences de l'Homme et de la Société (IR SHS UNILIM), Université de Limoges (UNILIM)-Université de Limoges (UNILIM)-Centre National de la Recherche Scientifique (CNRS), Pôle de recherche pour l'organisation et la diffusion de l'information géographique (PRODIG), Université Paris 1 Panthéon-Sorbonne (UP1)-Institut de Recherche pour le Développement (IRD)-École pratique des hautes études (EPHE), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Paris-Sorbonne (UP4)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), Náttúrustofa Norðurlands vestra (NNv), Ríkisins, Sveitafélag Skagafjarðar
• Format: Other/Unknown Material
• Language: English
• Published: HAL CCSD 2011
• Subjects: geo; psy; Skagafjörður; Iceland
• Online Access: https://hal.archives-ouvertes.fr/hal-00661174

International audience The Skagafjörður area counts several large slope mass movements especially on the eastern side of the fjord. They are initiated from the top of the rockwall where a more or less developed scars are still observed. A significant number of those landforms have been described by Jónsson (1957), who interpreted those landforms as a result of post-glacial rockwall debuttressing, following the shrinking of the large ice bodies in the early Holocene. However, no attempt of dating has yet been carried out on the debris masses. The aims of this research are to discuss its possible paraglacial origin by combining four dating benchmarks: (i) the dating of a succession of raised beaches on which the rock avalanche material lies. The higher beaches, exceeding 65 m a.s.l., have been dated older than 12000 BP. Beaches between 43 and 50 m a.s.l. have been dated older than 11300 and 9900 BP and beaches at 22-31 m a.s.l. between 9900 and 9600 BP. Regression below the present sea level occurred about 9000 BP (Rundgren et al., 1997). As the rock avalanche deposit does not display visible evidence of being impacted by the glacio-isostatic rebound (no inherited sea cliffs are seen at higher elevation than the actual sea level), we estimate the rock avalanche occurred later than 9000 BP. (ii) the tephrochronological dating from the excavations made in the upper part of the mass, where peat areas developed since the setting of the rock avalanche goes back to 4500 years BP, with the H4 Hekla acid white thick layer found at 140 cm depth. The deposits from Hekla are well known in the area, and the five most common ash layers were discovered in the opened section, providing a significant time marker. (iii) 14C dating of birches (Betula sp.) trunk and branches pieces found 80 cm below the H4 layer. The results are not yet available, but the period around 8000 BP is considered at those latitudes as a warm period, favourable to tree development. (iv) basalt samples were collected on the rock avalanche deposit, at ...