A paraglacial rock-slope failure origin for cirques: a case study from Northern Iceland

• Published in: Géomorphologie : relief, processus, environnement
• Main Authors: Coquin, Julien, Mercier, Denis, Bourgeois, Olivier, Decaulne, Armelle
• Format: Article in Journal/Newspaper
• Language: English
• Published: Groupe français de géomorphologie 2019
• Subjects: rock slope failure; gravitational spreading; deglaciation; erosion rates; glacial cirques; rupture de versants rocheux; étalement gravitaire; taux d’érosion; cirques glaciaires; geo; archeo; Tindastóll; Iceland
• Online Access: http://journals.openedition.org/geomorphologie/13057

The contribution of paraglacial rock-slope failure (RSF) to the excavation of cirques in glacial landscapes is explored in the Tindastóll Mountain, Skagi peninsula, northern Iceland. We analyze 8 cirques that developed during the Quaternary and 13 paraglacial RSF cavities that developed during the Holocene in this paleo-plateau. From a reconstruction of the pre-Quaternary surface of the plateau, we calculate the excavated volumes of the cirques and RSF cavities and quantify the contribution of Holocene RSF to cirque growth. By extrapolating this contribution to the whole Quaternary, we find that paraglacial RSF is a first-order contributor to the development of cirques. This contribution is twofold: first, paraglacial RSF creates cavities along valley slopes, in which cirque glaciers can develop during subsequent glaciations; second, paraglacial RSF along pre-existing cirque walls promotes cirque widening and deepening. Our results also reveal that Quaternary glacial/paraglacial erosion rates range from 0.02 to 0.17 mm yr‑¹ in the studied cirques. We infer that glaciers are (i) efficient preparatory factors for the destabilization of slopes by paraglacial RSF, (ii) efficient conveyors to evacuate deposits produced by paraglacial RSF in cirques, but (iii) not necessarily predominant agents in the excavation of cirque bedrocks. La contribution des mouvements de masse rocheuse paraglaciaires au creusement de cirques dans des paysages glaciaires est explorée dans la montagne de Tindastóll, dans la péninsule de Skagi, dans le nord de l'Islande. Nous analysons 8 cirques qui se sont développés pendant le Pléistocène et 13 cavités de mouvements de masse rocheuse paraglaciaires qui se sont développées pendant l'Holocène dans ce paléo-plateau. À partir d'une reconstruction de la surface pré-quaternaire du plateau, nous calculons les volumes excavés des cirques et des cavités des mouvements de masse rocheuse et quantifions leur contribution au cours de l'Holocène à l’élargissement du cirque. En extrapolant cette ...