A comprehensive exposure-age dating approach to interpreting complex glacial and periglacial landscapes: The landform mosaic of Alnesdalen, a Norwegian alpine drainage basin

Our aim was to use two exposure dating techniques in combination to understand the age and development of the full complement of glacial and periglacial landforms in the Alnesdalen drainage basin, southern Norway. This required the development of a comprehensive, landscape-scale approach based on 32 10Be dates from 9 landforms and 121 Schmidt-hammer dates from 106 landforms, which identified a palimpsest landscape consisting of a mosaic of landforms of different ages. The approach enabled a spatial and temporal reconstruction of Late Glacial and Holocene glacial variations, and a deeper understanding of the periglacial, paraglacial, and paraperiglacial response of the landscape to environmental change. Results suggest that the whole of the Alnesdalen drainage basin was ice-covered by the Scandinavian Ice Sheet at the Last Glacial Maximum and that deglaciation of the valley sides and floors occurred during the Bölling-Allerød Interstadial (~14.6–12.9 ka). Dated ice-marginal moraines establish the limits of the Scandinavian Ice Sheet and of local glaciers during the Younger Dryas Stadial (~12.9–11.7 ka). Glacier extent at the maxima of the Early Holocene ‘Erdalen Event’ (~10.2 ka) and the Late-Holocene ‘Little Ice Age’ (~0.3 ka) is clarified. The periglacial response to environmental change was dominated by paraglacial processes. In the Bölling-Allerød Interstadial, large rock-slope failures were activated and talus slopes, pronival ramparts, snow-avalanche fans, large-scale patterned ground, boulder fields and boulder pavements began to form. Permafrost aggradation during the Younger Dryas may have led to the formation of a short-lived rock glacier. Large-scale patterned ground, boulder fields and boulder pavements became inactive in a seasonal-frost climate before the onset of the Early Holocene Thermal Maximum. The wide range of Holocene exposure ages from periglacial landforms with diachronous surfaces, including snow-avalanche fans, talus slopes and pronival ramparts, indicate low-levels of periglacial activity throughout a relatively benign Holocene.