A glaciological baseline for the upper Olivares basin, Chilean Central Andes

Santiago de Chile, with near 6.7 million of inhabitants, is located at the foot of the Andes, in the Maipo river basin, where there are approximately 424 km2 of ice, being the biggest glaciers, those located at the upper Olivares basin. Very little has been researched in recent years about the ongoing changes taking place in the area or about the glacier meltwater contribution or about the human impact on the glaciers. In order to tackle this deficiency, we began a research program in 2012, aiming to complete a glaciological baseline for this area, including glacier mass, energy and hydrological studies. For this purpose, we have established a detailed monitoring program on two glaciers where we installed 3 automatic weather stations, two arrays of stakes for mass balance studies, two automatic photographic cameras for monitoring albedo changes and two runoff stations, among several other instruments. Also, we have surveyed 5 glaciers with our airborne radar and lidar systems, allowing mapping their surface topographies at different seasons and the bedrocks underneath the ice. Analysis of satellite images shows generalized glacier area shrinkage, with a mean area lost of 25.5% since 1967 (total of 68.6 km2 in 1967 among 6 studied glaciers). The collected radar ice thickness data (maximum ice thickness of 223 m), allowed calculating a total volume of water equivalent of 3 km3 storage in 5 main glaciers of the basin. The GPS surveys of several stakes resulted in surface ice velocities between 1 and 5 m/yr. The mass balance studies showed high summer ablation rates, with an important role of sublimation, expressed as penitentes with heights of up to 1.5 m. Runoff contributed by Olivares Alfa glacier averaged 461 l/s between January and April 2013 with peaks of up to 2000 l/s, confirming the importance of glacier meltwater for the basin during summer months (January-March). The above numbers are some of the results obtained in the area, illustrating the importance of these glaciers and the need for maintaining a monitoring program with further intensive studies.