90 Years of Glacial Lake Area Change in the Cordillera Vilcanota of the Peruvian Andes: Applying Historical Oblique Aerial Photography in Environmental Change Studies

Keywords: Andes, environmental change, cryosphere, glacial lakes, alpine environments, Peru
Abstract Type: Paper Abstract

Abstract

The Shippee-Johnson Aerial Expedition of 1931 produced large-format oblique aerial photographs of glaciers and glacial lakes in the Cordillera Vilcanota of the Peruvian Andes, providing an opportunity to assess glacial lake area change during the last 90 years. The Multitemporal glacial lake mapping was conducted using photographs from 1931, Corona satellite imagery from the 1960s, as well as Landsat and Sentinel satellite imagery from the 1970s until 2021. Lake area changes were determined using semi-automated and manual methods in ArcGIS Pro. The number of glacial lakes increased by 175 (+115%) from 152 in 1966 to 327 in 2021, while their total area increased by 14.3 km2 (+155%) from 9.3 km2 in 1966 to 23.7 km2 in 2021. During the same period, only five lakes disappeared, either as a result of a disconnection from the receding glacier, enhanced drainage, or glacial lake outburst floods (GLOFs). To extend the change analysis back to 1931, decades before the satellite era, the Shippee-Johnson photos were paired with 2021 Google Earth images. Lake boundaries in ten of the image pairs were mapped using Photoshop and Google Earth Studio. While the glaciers continuously receded over the last 90 years, the total area of the photographed glacial lakes did not change significantly. Our study shows that the evolution of glacial lakes in mountains under climate change conditions is complex. Furthermore, it documents that historical oblique aerial photographs represent a valuable source in extending glacial change records and other environmental changes in alpine ecosystems in the Peruvian Andes.