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

Abstract

The contribution of paraglacial rock-slope failure (RSF) to the excavation of cirques in glacial landscapes is explored in the Tindastoll 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.