The dynamics of a tectonically-controlled active silicic intrusion at Cordón Caulle volcano (Southern Andes) imaged by InSAR: building to the next eruption?

Abstract:

Cordón Caulle (Southern Andes, 72.15ºW, 40.52ºS) is a large fissural volcano located within a NW-SE elongated and ~30 km long chain that includes Cordillera Nevada caldera and Puyehue stratovolcano. Cordon Caulle has erupted a continuous suite from basalts to rhyolites since the Middle Pleistocene, including rhyolitic magma of the same composition in its past three historical eruptions in 1921, 1960 and 2011. There was significant ground deformation observed before and during the 2011-2012 eruption (VEI 4), and the inverted source depths responsible for the ground deformation are in agreement with petrological results that suggests shallow magma storage. Here we use new RADARSAT-2 and COSMO-SkyMed InSAR time series between March 2012 and June 2015, as well as UAVSAR interferograms between March 2013 and April 2014 to document post-eruptive uplift of more than 0.85 m, with uplift rates of ~0.45 m/yr during March – December 2012, one of the largest worldwide for silicic systems with geodetic instrumentation, and ~19 cm/yr between May 2013 and June 2015. The ongoing uplift has not been related to abnormal seismicity above background. The signal is located between the Cordón Caulle fissures and elongated across the strike of the volcanic chain. Inversion for pressurized sources and a tensile dislocation shows that the ground uplift is most likely produced by a subhorizontal sill ~6 km beneath the surface. The source location and geometry are different than those that produced the co-eruptive deflation signal between June 2011 and March 2012, and a subsidence event between February 1993 and February 1999, but as the source depths are similar, we interpret that the ongoing uplift is produced by the same plumbing system that has been active during the historical eruptions. The fact that the uplift signal is elongated across the volcanic chain, suggests that the active intrusion is tectonically controlled, as has been proposed for the long-term evolution of this volcanic chain.