Reconstructing the Holocene evolution of glaciers in the Olivares Basin (33°S), Chile

Andean glaciers are critical water resources, yet their future evolution under climate change remains uncertain. Reconstructing past glacier change is essential for understanding glacial sensitivity to climate, but records of postglacial evolution in the Central Chilean Andes, particularly between 33°S–35°S, remain sparse. This gap is striking given the significant glacier losses already documented in the Maipo River Basin, including rapid recession in the Olivares Basin (33°S), where satellite imagery shows terminus retreat of 0.5–2.5 km since 1973.
To understand recent changes in the context of long-term postglacial change, I present a reconstruction of Holocene glacier evolution in the Olivares Basin. Geomorphological mapping, derived from remote sensing and field surveys, was used to produce a basin-wide inventory of glacial landforms. Within the Salto del Olivares sub-basin, cosmogenic 36Cl whole rock exposure age dating of samples from moraines M2 and M3 yielded a Gaussian weighted mean age of 9.59 ± 2.25 ka (n = 7), constraining the early Holocene glacier extent. These results are then synthesised into a broader reconstruction of postglacial change between the early Holocene and recent decades. This was then used to constrain the results of numerical simulations of glacier evolution, which indicates that early Holocene climatic conditions were between 0.75–1.25°C colder and 40–60% wetter than today. The combined geomorphological, geochronological, and modelling evidence reveals that early Holocene glacier retreat was punctuated by climatically driven readvances, producing several overrun terminal moraines at Salto del Olivares. In contrast, observations since 1955 demonstrate sustained terminus recession, consistent with anthropogenic climate forcing. These results highlight the sensitivity of the Olivares Glaciers to precipitation, a pattern echoed elsewhere in the Andes. These results further indicate that when in equilibrium with climate, these glaciers occupy a broad area of near-zero mass balance, implying their persistence depends on limited but sustained perennial accumulation.