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Caldera collapse associated with rapid deglaciation at Villarrica (Rukapillán) volcano from revised chronostratigraphy

Pablo Moreno-Yaeger1 , Brad S. Singer1, Brian R. Jicha1, Mark D. Kurz2, Marissa M. Tremblay3, Benjamin R. Edwards4, Franco Vera5, Ivo Fustos-Toribio6, and Felipe Flores5

  • Affiliations: 1Department of Geoscience, University of Wisconsin-Madison, Madison, WI, 53706, USA; 2Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA; 3Department of Earth, Atmospheric and Planetary Sciences, Purdue University, IN 47907, USA; 4Department of Geoscience, Dickinson College, Carlisle, Pennsylvania 170313, USA; 5Unidad de Geología y Peligros de Sistemas Volcánicos, Red de Vigilancia Volcánica, Servicio Nacional de Geología y Minería, SERNAGEOMIN, Santiago, Chile; 6Department of Civil Engineering, University of La Frontera, Temuco, Chile

  • Presentation type: Talk

  • Presentation time: Monday 09:45 - 10:00, Room R280

  • Programme No: 1.2.6

  • Theme 1 > Session 2

Abstract

We explore relationships between ice loading and changes in magma composition and eruptive rates at Villarrica (Rukapillán) and elsewhere along the Andean Southern Volcanic Zone. At Mocho-Choshuenco volcano, mafic eruptions before and during the Last Glacial Maximum (LGM, 35 to 18 ka) were followed by silicic eruptions, including caldera-forming rhyolites at 13.5 and 11.5 ka. In contrast, Rukapillán has erupted basaltic andesite during its 180 kyr history, including the 10 km3 Licán Ignimbrite at 16.8 ka, for which the associated caldera has remained obscure. The magma reservoir beneath Rukapillán has responded differently during and after rapid deglaciation than the silicic reservoir beneath Mocho-Choshuenco. To examine the role of ice loading 35-18 ka and rapid unloading 18-16 ka, we have determined eruptive ages using 40Ar/39Ar, 3He, and 14C methods. During the LGM, basaltic lavas displaying ice-contact textures at 1000-1600 masl yield 40Ar/39Ar dates of 21-23 ka. The rim of a 4.2 km caldera preserves truncated lavas 40Ar/39Ar dated at 18-16 ka. Thus, ice during the LGM was >1.5 thick, and immediately after its retreat, caldera collapse was coeval with the eruption of the Licán ignimbrite. We hypothesize that glaciation increased lithostatic stress and that the rapid decrease in stress during ice retreat enhanced volatile exsolution, pressurized the magma reservoir, and subsequently produced an explosive eruption. The rapid response of Villarrica to ice unloading may reflect the low viscosity of basaltic andesitic magma that permits rapid volatile exsolution and bubble ascent in contrast with rhyolitic magmas erupted 3-5 kyr following deglaciation at Mocho-Choshuenco.