Lateglacial to Early Holocene glacier fluctuations in the northern Valaisian Alps

Abstract The northern Valaisian Alps represents a glacially overprinted landscape, characterized by abundant glacial deposits and landforms. Well-preserved moraine systems, commonly found in the region, were deposited by glacier fluctuations after the Last Glacial Maximum (LGM). In this study, we focus on the glacial evolution of the tributary valleys of Belalp and Luesgenalp, west of the Great Aletsch glacier, during the Lateglacial and Early Holocene. To reconstruct the glacier advances, a combination of geomorphological mapping, surface exposure dating with cosmogenic 10 Be, and glacier reconstruction were used. Our results indicate that glacier fluctuations occurred at 12.0 ± 0.9 ka in the Belalp valley and 12.0 ± 1.0 ka in the Luesgenalp valley during the Younger Dryas cold phase. Based on the glacier reconstruction, an equilibrium line altitude (ELA) of 2700 m asl was estimated for the maximal extent of these paleoglaciers. ELA depressions of 330 m to 430 m relative to the Little Ice Age for the Unnerbaech paleoglacier in the Belalp valley and 400 m for the Hostock paleoglacier in the Luesgenalp valley were calculated, corresponding to annual temperature decreases of 2.1 to 2.8 °C and 2.6 °C, respectively. The precipitation pattern shows no significant change in the amount of precipitation between YD and today. Our findings are consistent with the YD paleoglaciers documented throughout the Alps and provide insights into the climate dynamics during the Egesen stadial in the Alps. Additionally, our findings contribute to the broader understanding of glacial responses to climatic fluctuations.