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

4P1_1D-O21

Room B1Date/Time: July 24 16:30-16:45

Deformation of Cordon Caulle Volcano (Chile) measured by InSAR from 2007 to 2011
Jennifer A Jay1 , Matthew E Pritchard1 , Fidel Costa2 , Luis E Lara3
1Cornell University, USA, 2 Earth Observatory of Singapore, Singapore, 3 SERNAGEOMIN, Chile
E-mail: jaj88@cornell.edu

We combine petrological and ground deformation data to constrain the subsurface magmatic and hydrothermal
processes related to the 2011-2012 rhyodacite eruption of Cordon Caulle volcano in southern Chile.

The

geochemical data indicate that the phenocryst-poor rhyodacite erupted in 2011-2012 is very similar to that ofthe 1960 and 1921-1922 eruptions. The calculated pre-eruptive conditions for the 3 erupted magmas are also
indistinguishable: 900 +/- 20 deg C, 4 +/- 0.5 wt percent H2O, and 150 +/- 20 MPa. This implies that either(1) there has been no significant intrusion of magma in about 100 years while still erupting about 2 km3 (DRE)in the 3 eruptive periods, or (2) that all new additions are rhyodacitic melt that are indistinguishable from that inthe shallow reservoir and is probably generated much deeper, in the lower crust. Using InSAR, we have founda complex history of ground deformation preceding the eruption at Cordon Caulle, and the nature of the several
distinct inflation events are informed by this petrological data. This is one of the few large rhyodacite eruptions withdetailed images of ground deformation in the years before the eruption.
InSAR studies show that Cordon Caulle has undergone episodes of deformation since at least 1996 and has varied
between subsidence and uplift in different locations of the volcanic complex. Between 2007 and 2009 we observe
two distinct uplift episodes, both with a maximum uplift signal of 18.5 cm at the center of deformation. We also findan episode of deformation occurring sometime between Feb-Mar 2010 located in the Cordillera Nevada caldera
with 10 cm uplift within the caldera and 10 cm subsidence on the eastern rim of the caldera. This deformation
episode is likely related to the nearby Trahuilco hot springs, which is fed by a shallow steam-heated aquifer and is
the main outflow of the Cordon Caulle geothermal system. We do not observe any deformation from late 2010 toearly 2011, when the ALOS satellite ceased operation. Petrological studies of the clinopyroxene exsolution lamellaein the 2011 eruptive products indicate the existence of a large (10 km3) long-lived (5 ka) shallow magma reservoir.
We hypothesize that the 2007-2009 uplift episodes could have resulted from an injection of magma into the base ofa pre-existing rhyodacite magma reservoir with minimal interaction between the 2 magma sources. Initial modelingof the 2008-2009 deformation pattern using one inflating point source puts the deformation source at about 7 km
depth with a volume change of 0.03 km3. Assuming an appropriate value for magma compressibility, the combinedmodeled reservoir volume change from 2007-2009 could account for the volume of the 2011-2012 DRE erupted
material of 0.8 km3. However, this simple model does not provide an accurate fit to all available ascending anddescending interferograms, suggesting that a more complicated source may be involved, such as a prolate spheroidor faulting.

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