Cordon-Caulle 2011 Eruption Characterized through DInSAR
Euillades, Pablo Andrés1; Velez, Maria Laura2; Grosse, Pablo3; Euillades, Leonardo Daniel1; Caselli, Alberto4
1CONICET & CEDIAC FI UNCuyo, ARGENTINA; 2University of Buenos Aires, ARGENTINA; 3CONICET, ARGENTINA; 4University of Rio Negro, ARGENTINA

The 2011-2012 eruption of the Puyehue-Cordón Caulle volcanic complex has been one of the major eruptions of the past years, with both explosive and effusive activity and a VEI of 3. A first eruptive stage, initiated on June 4, produced an ash and gas plume that rose to about 14 km and lasted 27 hours. A second stage, lasting from mid June 2011 until April 2012, was characterized by lava emission and weaker plumes. Ash fall heavily affected an area of about 70,000 km2 across the Chile-Argentina border.
In this contribution, we analyze surface deformation related to the eruption by using ENVISAT ASAR images. We processed six scenes acquired between February 7, 2011 and July 7, 2011 in mode I6 (40° look angle). The resulting set of interferograms allows us to characterize a pre-eruptive period and an initial co-eruptive period.
Pre-eruptive interferograms appear contaminated by atmospheric fringes, so no clear deformation patterns can be observed. The interferogram between March 9, 2011 and April 8, 2011 shows a clear example of atmospheric stratification, recognizable by the topography-correlated fringes around the Puyehue edifice, the Cordillera Nevada caldera and along the lava flows located southwest of the rift zone. The Pearson correlation coefficient between unwrapped phase and height is 0.81. In an attempt to correct for the topography correlated phase component, we subtracted a ramp computed from the best fit linear trend. The remaining fringes highlight an oval shaped pattern representing line-of-sight (LOS) shortening roughly located near the center of the Cordon-Caulle fissure system. The interferogram between February 7, 2011 and March 9, 2011 shows a similar pattern at the same location but with opposite sign, and the interferogram between February 7, 2011 and April 8, 2011 does not show the pattern at all. This analysis allows attributing the pattern to possible atmospheric turbulence occurring around March 9. Interferograms involving the scene acquired on May 8, 2011 show a different, smaller oval-shaped subsidence pattern, elongated NW-SE and located just east of an inferred magma chamber. The absence of this pattern in the previous interferograms indicates that it is related with phenomena arising between April 8 and May 8, 2011.
The clearest interferogram showing co-eruptive deformation was computed between May 8, 2011 and June 7, 2011, i.e. one month before and three days after the eruption began. It shows a main subsidence pattern with a radius of at least 10 km centered in the Cordon-Caulle fissure system, 12 km NW of the eruption vent. Subsidence magnitude is about 85 cm LOS projected. Other patterns of minor magnitude can be observed to the southwest (shortening) and northeast (shortening) of the eruption vent. Both could be related to magma migration and injection in the eruption conduit. Modeling efforts for interpreting these results in terms of elastic parameters are on-going.