An overview of glacier lakes in the Western Italian Alps from 1927 to 2014 based on multiple data sources (historical maps, orthophotos and reports of the glaciological surveys)

Since the end of the Little Ice Age (LIA, ca. 1850 AD) a general and progressive retreat of glaciers started in the European Alps, causing important environmental changes in this high mountain region. The appearance of glacier lakes is one of the most evident environmental effects in the Alps as well as in newly deglaciated areas worldwide. In order to understand conditions of formation and reconstruct evolutionary stages of glacier lakes, it is important to collect and analyse a diversity of data from different time periods. Through the analysis of historical topographic maps and digital orthophotos, we identified and digitalized in a GIS environment glacier lakes (and related features) of the Western Italian Alps (Piemonte and Aosta Valley regions) within the LIA maximum extent boundaries. We produced six glacier lake inventories related to six different time steps: 1930s, 1970s, 1980s, 1990s, 2006-07 and 2012. We provided a general overview of the main morphometric, geomorphologic and geographic features of lakes of each time step and preliminary considerations on changes in the number of lakes within the considered time period. The most detailed analysis has been performed over the 2006-07 time step: 214 detected lakes, covering a total area of about 146 (±1) · 104 m2, ¾ of the lakes measuring less than 6000 m2 as individual area and a half of the total number less than 2000 m2. The mean elevation of lakes was 2776 m a.s.l., 72% being located between 2600 and 3000 m. In general, lakes are localized mainly in the Graian Alps (Rutor-Lechaud, Gran Sassiere-Tsanteleina and Gran Paradiso chains) and in the Pennine Alps (Monte Rosa Group). Moreover, in a dedicated database, we collected information (descriptions, photos, maps) about glacier lakes from the reports of the annual glaciological surveys published by the Italian Glaciological Committee (CGI) since 1928. Finally, we reported two cases of glacier lakes at the Tzére Glacier (Monte Rosa Group, Pennine Alps) and at the Ban Glacier (Monte Leone-Blinnenhorn Chain, Lepontine Alps), in order to demonstrate the importance of integrating data from a diversity of sources (historical maps, orthophotos and reports of the glaciological surveys) for better detailed reconstructions of the condition of formation, evolutionary stages and process dynamics of the lake. Results of the present research can contribute to reconstruct and to interpret the spatiotemporal evolution of the phenomenon and to improve the knowledge about the interactions between glacier and related glacier lakes.