Unveiling the evolution of a glacier through geomorphological analysis and surface exposure dating: Nautárdalsjökull (Northern Iceland)

The Nautárdalur valley, located on the Tröllaskagi Peninsula, northern Iceland (65°29′19″ N, 18°22′19″ W), hosts the Nautárdalsjökull– previously classified as a rock glacier – and studied in detail between 1977 and 1994. In this study, we apply combined surface-exposure dating techniques — 36 Cl cosmic-ray exposure (CRE), Schmidt Hammer, and lichenometry—to boulders of a debris mantle covering massive ice, to reconstruct the origin and evolution, and assess the current condition of this formation. Photogrammetry-based boulder tracking from 1994 to 2021 was conducted to assess surface dynamics and check stability of sampled boulders and hence reliability of exposure-age results. Detailed geomorphological mapping was carried out to infer the relative ages of surface deposits and to cross-check dating outcomes. Boulder tracking reveals average surface velocities of 0.20–0.25 m yr -1 and substantial surface lowering in recent decades, associated with the development of collapse features. 36 Cl CRE ages range from 3.6 ka for outermost boulders to 0.6 ka for the innermost ones. The oldest ages fall within the range of Neoglacial advances documented in Tröllaskagi, while younger ages correspond to the Little Ice Age (LIA; 14th to 19th centuries). Lichenometric dates are influenced by snow persistence and avalanche activity, particularly for surfaces older than ∼130 years. Age distribution and geomorphology of the debris cover indicate that the so-called Nautárdalsjökull rock glacier is indeed an ice-cored moraine complex formed during at least three Neoglacial advances, dated to approximately 3.6–2.4 ka, 1.1–0.9 ka and LIA.