Constraints on the timing of debris-covered and rock glaciers: An exploratory case study in the Holar area, northern Iceland

Eighteen samples for Cl-36 Cosmic-Ray Exposure (CRE) dating were taken from glacially polished bedrocks, moraine boulders, fossil/active rock glaciers and debris-covered glaciers in Fremri-Grjakdalur and Holadalur cirques in the Viainesdalur, Hofsdalur and Ha nsdalur valleys, close to Holar village, in the Trollaskagi peninsula, northern Iceland. Boulder sampling was preceded by a study of the boulder stability with the twofold aim of: ensuring that the surfaces to be sampled were stable enough for the reliable application of CRE dating, and to better understand the relation between the glacier dynamics and exposition history. The results show that the glaciers which occupy the valleys in Trollaskagi began their retreat around 16 ka. Later, the glaciers advanced again around 11 ka within the cirques, and small moraines were formed. Thereafter, these small glaciers retreated and evolved into rock glaciers as debris from paraglacial processes accumulated on the glacier surface. The fronts of these rock glaciers stabilized definitively shortly after their formation and became eventually fossil after the melting of their center dot internal ice. New rock glaciers and debris-covered glaciers formed afterwards, which still have internal ice at present, although their current dynamics are mostly related to subsidence. The stabilization of these rock glaciers and debris-covered glaciers is dated to the period between 7 and 3 ka, although they may have been reactivated during cold neoglacial periods. This research demonstrates the potential interest in applying CRE dating methods to debris-covered glaciers and rock glaciers to determine their origin, evolution and phase of cessation of internal movement until they finally lost their internal ice and became fossil. (C) 2020 Elsevier B.V. All rights reserved.