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Postglacial eruptive history at Laguna del Maule, Chile, used to reconstruct timing of paleolake filling and catastrophic demise

Judy Fierstein

Abstract

Postglacial eruptive history at Laguna del Maule volcanic field (LdM) on the Argentina-Chile border (36° S) was established using tephrostratigraphy and mapping to document >100 eruptive events from vents near the eponymous Laguna during the last 16 kyrs. Largest of these was a 15 ka Plinian eruption of high-silica rhyolite from a now-submerged vent near the center of the present-day lake. Explosive eruption of >35 km3 of pyroclastics deepened the basin below its natural outlet of 2,150 m, resulting in subsequent formation of a basin-bottom lake. A later eruption ~11.2 ka from a vent 5 km away produced a rhyolitic lava flow that dammed the outlet, enabling the lake to fill 200 m higher than its original natural threshold. Silt accumulating in the lake bottom preserved much of the LdM postglacial explosive history as intercalated tephra layers, now exposed at different elevations around the basin. Combined with radiocarbon dating, these tephra-silt sections capture the history of the deepening lake until it reached its highstand at an elevation of 2,350 m. Breaching of the lava dam resulted in a catastrophic flood down the Río Maule, leaving behind a distinct highstand terrace around the basin. Tephrostratigraphy shows the paleo-Laguna del Maule began filling as much as 4,000 years before its outlet was dammed by lava, after which it reached its highstand over a period of ~2 kyrs, drained catastrophically ~9 ka, but remained a lake more than 20 meters higher than the initial blockage for at least another 2 kyrs.