Inventory and evolution of glacial lakes in Switzerland since the Little Ice Age

Retreating 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 prioritisation of formation probability, we included glacier-morphological criteria such as glacier width and visible crevassing. About 40% of the modelled overdeepened area actually filled with water. The inclusion of morphological aspects clearly aided in linking a lake formation probability to a modelled overdeepening. Additional morphological variables, namely dam type and material, surface runoff, and freeboard, were compiled for a subset of larger and ice-contact lakes in 2016, constituting a basis for future hazard assessment. All datasets generated in this study are provided. Lake outlines directly taken from Swisstopo (Swisstopo, 2020a) fall under the national copyright and are therefore only presented in point format, whereas lake outlines strongly modified from the original outlines by Swisstopo as well as lake outlines generated in this study are fully provided as polygons. Lake data is provided for each date as well as an overview shapefile including a summary of all lake parameters, and a subsample of the lakes, for which hazard parameters were derived from auxiliary base datasets (digital elevation model, orthoimagery). A list as well as a description of the datasets and the respective parameters is given below.