ANALYSIS OF SEDIMENT AND ASH FROM LAGO PALLARCOCHA, NEVADO COROPUNA, PERU

Lago Pallarcocha (15.57° S/72.72° W; 4,740 m a.s.l.) is a small (15 ha) alpine lake located on the western flank of the Nevado Coropuna volcanic complex in southern Peru. The lake is at least ~ 20 m deep and has a surface conductivity of 34.8 μS. In June 2015 we collected two gravity cores, 21.5 cm and 26.5 cm in length, from the lake; each was sampled at 0.5 cm intervals in the field and selected intervals are being processed to identify diatom communities and to measure grain-size, both of which will be used as paleoclimate proxies for documentation of local climate conditions. Both cores have distinct light grey horizons between 5.5 cm – 6.5 cm and 3.0 cm – 6.0 cm respectively, which are tentatively interpreted as water deposited, air-fall ash. The ash is suspected to be from the February 19^th to March 6^th 1600 eruption of Volcan Huaynaputina, which is located 230 km to the southeast in Peru. This eruption is the largest known explosive eruption in the Andean region during the Common Era. The Plinian style eruption had an estimated Volcanic Explosivity Index of 6 and deposited ash over approximately 300,000 km² in Peru, Bolivia, and Chile (de Silva and Zielinski, 1998). Preliminary SEM/EDS analysis of the ash interval identified minerals consistent with intermediate composition ash (Na-plagioclase) as well as possible glass shards. Assuming that our preliminary identification of the ash source is correct, the implied rates of sedimentation are very low (0.13 mm per yr and 0.075 mm per yr), at least for the upper section of the cores. Ongoing work will focus on using the cores to investigate recent changes to the area’s local climate in order to inform regionally vulnerable populations that are highly susceptible to fluctuation in water resources from the mass ice loss of Nevado Coropuna. Analysis of sediment cores from this unique location (i.e. remote area, proximity to ice cap) will help inform the limited number of climate records in this region.