Abstract
AbstractRetreating glaciers give way to new landscapes with lakes as an important element. In this study, we combined available data on lake outlines with historical orthoimagery and glacier outlines for six time periods since the end of the Little Ice Age (LIA; ~1850). We generated a glacial lake inventory for modern times (2016) and traced the evolution of glacial lakes that formed in the deglaciated area since the LIA. In this deglaciated area, a total of 1192 lakes formed over the period of almost 170 years, 987 of them still in existence in 2016. Their total water surface in 2016 was 6.22 ± 0.25 km2. The largest lakes are > 0.4 km2 (40 ha) in size, while the majority (> 90%) are smaller than 0.01 km2. Annual increase rates in area and number peaked in 1946–1973, decreased towards the end of the 20th century, and reached a new high in the latest period 2006–2016. For a period of 43 years (1973–2016), we compared modelled overdeepenings from previous studies to actual lake genesis. For a better prioritization of formation probability, we included glacier‐morphological criteria such as glacier width and visible crevassing. About 40% of the modelled overdeepened area actually got covered by lakes. The inclusion of morphological aspects clearly aided in defining a lake formation probability to be linked to each modelled overdeepening. Additional morphological variables, namely dam material and type, surface runoff, and freeboard, were compiled for a subset of larger and ice‐contact lakes in 2016, constituting a basis for future hazard assessment.
Highlights
The current period of atmospheric temperature rise has led to intense glacier retreat in most mountain regions worldwide since the mid-19th century (e.g., Zemp et al, 2015) and the formation of numerousglacial lakes [e.g., Aggarwal et al, 2017; Buckel et al, 2018; Emmer et al, 2016; Federal Office for the Environment (FOEN), 2021]
A growing number of such new glacial lakes formed since the end of the Little Ice Age (LIA) around 1850 as a consequence of climatic change
29 new lakes appeared in that decade, which hosted less than 30% of the total area increase, whereas the majority of the new lake area can be assigned to 61 growing lakes that existed before 1973
Summary
The current period of atmospheric temperature rise has led to intense glacier retreat in most mountain regions worldwide since the mid-19th century (e.g., Zemp et al, 2015) and the formation of numerous (peri-)glacial lakes [e.g., Aggarwal et al, 2017; Buckel et al, 2018; Emmer et al, 2016; Federal Office for the Environment (FOEN), 2021]. The location of possible future glacial lakes can be estimated by (1) calculations of glacier thickness (Farinotti et al, 2017; Linsbauer et al, 2012) or (2) a combination of slope threshold and (visually defined) glacier-morphological criteria (Frey et al, 2010; Magnin et al, 2020). Both methods (thickness method, visual method, summarized below) indicate glacier bed overdeepenings but do not hint at the likelihood of lake formation inside an overdeepening. These categories zero to five can be seen as a representation of lake formation probability (Magnin et al, 2020)
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