TRACKING GLACIAL RETREAT IN THE PERUVIAN ANDES: GEOLOGIC MAPPING IN THE CORDILLERA BLANCA DOCUMENTS NEWLY EXPOSED SOURCES OF WATER CONTAMINATION

The Cordillera Blanca in north central Peru, contains the largest collection of tropical glaciers in the world, the highest elevations in the northern Andes Mountains of South America, and provides a natural laboratory to assess the impact of climate change on high alpine ecosystems. The low latitude of the Cordillera Blanca means that the glaciers are vulnerable to the overall warming trend over the past few decades and the region has experienced rapid deglaciation as a result. The extreme topography of the Andes Mountains also generates a rain shadow making the western, much more populated portion of Peru, a desert. Therefore, glacial runoff and snowmelt from the mountains are the primary source of freshwater for the western portion of Peru during the dry season, so water quality and quantity coming out of the mountainous region of central Peru is crucial both locally and nationally. As the glaciers recede in the Cordillera Blanca, a zone of heavily mineralized rock is being exposed. This rock contains pyrite and other sulfide minerals, which when exposed to atmospheric oxygen cause water contamination. The most recent 1:100,000 scale geologic maps of the Cordillera Blanca were published in the mid-1990s, and used base maps from the late 1960s, meaning large areas of the newly exposed, sulfide-bearing units are not mapped on them, causing mismatches between the location of expected and actual water contamination in streams draining the range. Over the past four years groups of students and faculty from multiple institutions have worked to map drainages within the Cordillera Blanca to identify the extent of the mineralized zone and assess the control of bedrock geochemistry on water chemistry. This mapping has allowed us to predict where water contamination may get worse as the glaciers continue to recede.