Glacier thinning, recession and advance, and the associated evolution of a glacial lake between 1966 and 2021 at Austerdalsbreen, western Norway

The Jostedalsbreen is the largest ice cap in Norway and mainland Europe. Rapid retreat of many of its outlet glaciers since the 2000s has led to the formation of several glacial lakes. Processes causing the formation and expansion of glacial lakes and their interaction with a glacier and terminal moraine have not been widely addressed yet. In this study, we investigate the degradation of the front of the southeast-facing outlet glacier Austerdalsbreen. Based on a variety of remotely sensed data (UAV-based and airborne orthophotos and DEMs, satellite images), we analyze the coincident glacial and proglacial changes of Austerdalsbreen and quantify the evolution of this transition zone during the last decades. In particular, we focus on the short-term evolution of the glacial lake since 2010, we examine the context of a glacier advance in the 1990s, and we report long-term changes by utilizing 1960s imagery. We discuss the evolution and conditions of Austerdalsbreen compared to other outlet glaciers of Jostedalsbreen. Overall, the glacier terminus has experienced a recession in the last decades. The 1990s terminus advance was more restricted than at other nearby outlet glaciers due to glacier surface debris cover, which is a critical factor for the glacier and lake evolution. However, in the most recent period, since 2012, a distinct expansion of a glacial lake is quantifiable. Since the rates of glacier surface lowering also considerably increased since approximately 2017 and the glacier retreated since the beginning of the 2000s with a clear maximum length decrease in 2015, we interpret the recently formed glacial lake as a contributory factor of glacial changes.