Brad S. Singer¹*, Nathan L. Andersen¹, Hélène Le Mével¹, Kurt L. Feigl¹, Charles DeMets¹, Basil Tikoff¹, Clifford H. Thurber¹, Brian R. Jicha¹, Carlos Cardona², Loreto Córdova³, Fernando Gil³, Martyn J. Unsworth⁴, Glyn Williams-Jones⁵, Craig Miller⁵, Judy Fierstein⁶, Wes Hildreth⁶, Jorge Vazquez⁶

1 University of Wisconsin–Madison, Dept. of Geoscience, Madison, Wisconsin 53706, USA
2 Observatorio Volcanológico de los Andes del Sur (OVDAS) and SERNAGEOMIN, Chile, and Universidad de Concepción, Chile
3 Observatorio Volcanológico de los Andes del Sur (OVDAS) and SERNAGEOMIN, Chile
4 University of Alberta, Dept. of Physics, 116 Street and 85 Ave., Edmonton, Alberta T6G 2R3, Canada
5 Dept. of Earth Sciences, Simon Fraser University, 8888 University Drive, Burnaby, British Columbia V5A 1S6, Canada
6 U.S. Geological Survey, 345 Middlefield Road, MS 977, Menlo Park, California 94025, USA

ABSTRACT

Explosive eruptions of large-volume rhyolitic magma systems are common in the geologic record and pose a major potential threat to society. Unlike other natural hazards, such as earthquakes and tsunamis, a large rhyolitic volcano may provide warning signs long before a caldera-forming eruption occurs. Yet, these signs—and what they imply about magma-crust dynamics—are not well known. This is because we have learned how these systems form, grow, and erupt mainly from the study of ash flow tuffs deposited tens to hundreds of thousands of years ago or more, or from the geophysical imaging of the unerupted portions of the reservoirs beneath the associated calderas. The Laguna del Maule Volcanic Field, Chile, includes an unusually large and recent concentration of silicic eruptions. Since 2007, the crust there has been inflating at an astonishing rate of at least 25 cm/yr. This unique opportunity to investigate the dynamics of a large rhyolitic system while magma migration, reservoir growth, and crustal deformation are actively under way is stimulating a new international collaboration. Findings thus far lead to the hypothesis that the silicic vents have tapped an extensive layer of crystal-poor, rhyolitic melt that began to form atop a magmatic mush zone that was established by ca. 20 ka with a renewed phase of rhyolite eruptions during the Holocene. Modeling of surface deformation, magnetotelluric data, and gravity changes suggest that magma is currently intruding at a depth of ~5 km. The next phase of this investigation seeks to enlarge the sets of geophysical and geochemical data and to use these observations in numerical models of system dynamics.

DOI: 10.1130/GSATG216A.1

Manuscript received 12 Mar. 2014; accepted 5 June 2014.