THESIS: A 3HE-BASED HOLOCENE GLACIAL CHRONOLOGY FROM VILLARRICA VOLCANO, CHILE

Abstract

Understanding past glacier changes is crucial for deciphering climate variations and predicting the cryosphere’s response to future climate shifts. Villarrica volcano is located in the Southern Volcanic Zone (SVZ) and was covered by the Patagonian Ice Sheet (PIS) during the Last Glacial Maximum (LGM) and continues to host glaciers today. Moraines on the flanks of Villarrica demarcate past glacial extents from the latest Pleistocene to the late Holocene, indicating more extensive ice cover than today. However, the post-LGM glacial history on Villarrica and across the SVZ is poorly constrained, limiting our understanding of how glaciers in the Southern Hemisphere behaved during the last deglaciation and Holocene when climate conditions were drastically changing. To constrain the timing of glacial events during the late Holocene, we analyzed olivine- hosted cosmogenic 3He from 25 moraine boulder samples. Our new surface exposure dating chronology reveals several glacial advances occurred during the late Holocene associated with moraine abandonment during the Neoglacial period at 3350 ± 140 a and 1740 ± 225 a, the Little Ice Age (LIA) between 720 ± 340 a and 370 ± 220 a, and modern retreat at 100 ± 50 a. The Neoglacial advances are likely associated with increased Southern Westerly Winds (SWW) and shifts in its position favoring more moisture delivery and glacier growth, while LIA and modern glacial advances are likely due to reduced ablation from decreased temperatures. Our chronology highlights two phases of the latest Holocene glacial retreat in the Southern Hemisphere, which is consistent with both LIA glaciation elsewhere in Patagonia and paleoclimate evidence of delayed industrial-era warming in the Southern Hemisphere beginning around the year 1900.