Cerro Barrancas: a highly productive and hazardous eruptive center in the Laguna del Maule Volcanic Field, Chile

PATRICIA SRUOGA; MANUELA ELISSONDO; JUDITH FIERSTEIN; NATHAN ANDERSEN; ALEJANDRA ARBOLEYA

Puerto Varas

Congreso; Cities on Volcanoes9; 2016

IAVCEI SERNAGEOMIN

The postglacial record of the Laguna del Maule Volcanic Field (LMVF) (36° 10´S, 70° 30? W) includes rhyolite and rhyodacite lava flows, domes, tephra falls and pyroclastic flows related to 24 vents. Ongoing uplift of >20 cm/year since 2007 makes unraveling its eruptive history imperative in a hazard assessment. The Barrancas center in the southeastern part of LMVF has been an especially productive and long-lived vent complex. Much of its ~5.5 km3 postglacial eruptive volume is preserved in the headwaters of Río Barrancas, Argentina. Detailed mapping, combined with petrographic, grain-size, textural and geochemical analyses, reveal two overlapping edifices, each with multi-stage growth: Edifice 1 began 14.5 ka with an early episode of dome building. A subsequent explosive event and partial dome collapse produced block-rich pyroclastic flows that traveled ~13 km from source, filled the upper Barrancas valley with deposits ~60 m thick and created the plateau called Pampa del Rayo. Edifice 2 was built by sequences of explosive and effusive events, ultimately producing 8 obsidian flows and 3 pumice cones. One of the lava flows has been dated at 5.6 ka. Edifice 2 tephra falls and pyroclastic flows made a quickly thinning pyroclastic wedge on top of the older block-rich deposit from Edifice 1. Fall deposits from other LMVF vents underlie, overlie, and are intercalated within the Edifice 2 pyroclastic sequence. Ongoing tephrochronology studies and Ar/Ar dating will undoubtedly improve our understanding of this volcano which?if it were to erupt again?could have widespread effects in Chile and Argentina, particularly in southern Mendoza and northern Neuquen provinces.