Satellite Monitoring of the 2011 Puyehue Eruption:From SAR to Optical Sensors
Bignami, Christian1; Corradini, Stefano1; Merucci, Luca1; Piedra, Juan2; De Michele, Marcello3; Racouls, Daniel3; Stramondo, Salvatore1
1Istituto Nazionale di Geofisica e Vulcanologia, ITALY; 2Gulich Institute, ARGENTINA; 3Bureau de Recherches Géologiques et Minières, FRANCE

Chile has more than 2000 volcanoes, 500 of them considered geologically active with 60 historical eruptive records in the last 450 years. Chile has currently twelve active volcanoes with low eruptive activity (Lascar, San Pedro-San Plablo, Headed Grande-Cerro Azul-Quizapu, Planchon Peteroa Antuco Calbuco, Chaitén, Hudson, Villarrica, Lonquimay-Tolhuaca Choshuenco Mocho, Osorno) and two with middle eruptive activity (Puyehue-Cordon Caulle, Llaima). Among these volcanoes, we focus our work on the complex Puyehue - Cordon Caulle. Such complex is located in the province of Ranco, Region of Los Rios, and it consists of volcanic centers aligned northeast-southwest direction, and covers an area of 40 km2. In the northeast corner of the complex, we find the volcano Cordillera Nevada, in the central section is the Caulle - a fissure system that has delivered large volumes of lava - and in the extreme south is the Puyehue stratovolcano. Like most of stratovolcanoes on the Southern Volcanic Zone of the Andes, Puyehue and Cordón Caulle are located along the intersection of a traverse fault with the larger north-south Liquiñe-Ofqui Fault.
On June 2011, Puyehue volcano began erupting. On 4 June, seismicity increased to an average of 230 earthquakes per hour, at depths of 1-4 km. About 12 events were magnitudes greater than 4, and 50 events were magnitudes greater than 3. The Alert Level was raised to 5. Explosion from Cordón Caulle produced a 5-km-wide ash-and-gas plume that rose to an altitude of 12.2 km. During 4-5 June an ash fall of several centimeters thick was reported in surrounding areas. On 7-8 July explosions were recorded and ash plum was present, reaching 2-3 Km altitude. The eruption continued on the next months. Currently, the seismicity recorded at the volcano continues decreasing trend, remaining at a low level of activity and energy compared to previous months. However, it still remains the possibility of minor explosive events generated. The current study reports the observation and analysis based satellite remote sensing application. In particular we exploited SAR interferometric technique (InSAR) to detect and to measure terrain movements. A series of SAR images acquired by ENVISAT platform, between May and December 2011 (about one image per month) have been processed to infer the displacement occurred during the eruption. Soon after the eruption beginning we found a maximum deflation of about 65 cm, clearly localized at the north-west area with respect the Puyheue caldera. The deformation decreased in the following months, reaching -20 cm on December. In addition, optical images captured by the MODIS sensor have been used to extract ash and gas emissions. The information gathered by both type of sensors allowed to highlight the relationship between surface deformation and the amount of ash and gases emitted by the volcano.