IAVCEI 2013 Scientific Assembly - July 20 - 24, Kagoshima, Japan
Forecasting Volcanic Activity - Reading and translating the messages of nature for society

3P2_1B-O23

Room B1

Date/Time: July 23 18:15-18:30

Accelerating unrest within a large rhyolitic magma system during 2007-2013 at Lagunadel Maule volcanic field, Chile
Helene Le Mevel1 , Kurt Feigl1 , Tabrez Ali1 , M. Loreto Cordova2 , Charles DeMets1 , Bradley S. Singer1
1

Department of Geoscience, University of Wisconsin-Madison, U.S.A., 2 Observatorio Volcanologico delos Andes del Sur (OVDAS), SERNAGEOMIN, Temuco, Chile
E-mail: lemevel@wisc.edu

The Laguna del Maule (LdM) volcanic field is remarkable for its unusual concentration of post-glacial rhyolitic lava
coulées and domes that were erupted between 20 to less than 2 thousand years ago. Covering more than 100
square kilometers, they erupted from 24 vents encircling a ∼20 km diameter lake basin on the range crest of theAndes. This recent concentration of crystal-poor rhyolite is unparalleled both in the Andes and globally. Geodetic
measurements at the LdM volcanic field show rapid uplift since 2007 over a ∼20km diameter area centered on thewestern portion of the young rhyolite domes. By quantifying this active deformation and its evolution with time, weaim to investigate the storage conditions and dynamic processes in the underlying rhyolitic reservoir that drive theongoing inflation. Analyzing interferometric synthetic aperture radar (InSAR) data, we infer the following evolutionof the deformation: the rate of vertical displacement is negligible from 2003 to 2004, and then accelerates from atleast 200 mm/yr in 2007 to more than 300 mm/yr in 2012 (Feigl et al., 2013, in review). The deformation signal
is modeled as inflation of a 7.5 km by 5.5 km sill at a depth of 5 km, assuming a rectangular dislocation in a half
space with uniform elastic properties. The sill’s maximum rate of inflation is 51 ± 8×106 m³/yr in 2012. In total, thevolume increase of the source is about 160 million cubic meters since inflation began, no later than March 2007.
Three continuous GPS stations installed in April 2012 around the lake confirm this extraordinarily high vertical uplift
rate of more than 280 mm/yr and a significant radial expansion. As of January 2013, the rapid deformation persistsin the InSAR and GPS data. During this interval, the rate of deformation at Laguna del Maule is higher than at anyother volcano that is not actively erupting. For example, the remarkable recent inflation episodes at the Yellowstone(Chang et al., 2010) and Santorini calderas (Newman et al., 2012;Parks et al., 2012) exhibit rates two to five times
slower than at LdM. Using the dynamic models, we can calculate changes in the local stress field. In particular,a large increase in stress in the magma chamber roof might lead to initiation and/or reactivation of ring faults. A
finite element model is being developed to describe the configuration of the magmatic system and overpressure
responsible for the observed uplift. Several hypotheses are considered for driving the deformation, including: (1)an intrusion of basalt into the base of a melt-rich layer of rhyolite leading to heating, bubble growth and subsequent
increase pressure in the reservoir, and/or (2) the possibility of inflation of a hydrothermal system above the rhyolite
melt layer.

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