Application of ASAR-ENVISAT Data for Monitoring Andean Volcanic Activity : Results from Lastarria-Azufre Volcanic Complex (Chile-Argentina)

Jean-Luc Froger(1) , Dominique Remy(2) , Sylvain Bonvalot(2) , and Marianela Franco Guerra(3)

(1) IRD LMV UR163 / UMR6524, 5 rue Kessler, 63038 Clermont-Ferrand, France
(2) ─░RD UR154 / UMR5563, Toulouse, 31000 Toulouse, France
(3) Universidad de Chile, Blanco Encalada 2002, Santiago, Chile


KEY WORDS : Radar interferometry, geodetic surveys, ground deformations, Andes, volcanoes

With respect to the previous ERS-1 and ERS-2, the Advanced Synthetic Aperture Radar (ASAR), on board the ENVISAT Satellite (ESA), features extended capabilities that could potentially be relevant for the monitoring of active volcanoes. Here we present the preliminary results of an interferometric study made with ASAR data on a selection of South American volcanoes where deformation signals had been previously evidenced or are expected. An interesting result is the detection of a present-day active ground deformation on the Azufre-Lastarria area (Chile-Argentina) indicating that process, identified during 1998-2000 by Pritchard and Simmons (2004) from ERS data, is still active. The phase signal visible on ASAR interferograms (03/2003-06/2005) is roughly elliptical with a 45 km NNE-SSW major axis. Its amplitude increases as a function of time and is compatible with ground uplift in the line of sight of the satellite. The ASAR time series (up to 840 days, 7 ASAR images) indicates variable deformation rate that might confirm the hypothesis of a non uniform deformation process. We investigated the origin and the significance of the deformation using various source modeling strategies (analytical and numerical). The observed deformation can be explained by the infilling of an elliptical magmatic reservoir lying between 7 and 10 km depth. As the deformation is correlated with a large, although subtle, topographic depression surrounded by a crown of monogenetic centers, it could represent the first stage of a new caldera forming. A short wavelength inflation has also been detected on Lastaria volcano. It could result from the on going infilling of a small subsurface magmatic reservoir, eventually supplied from the deeper one. All these observations point out the need of a closer monitoring of this area in order to assess future volcanic hazard.

ACKNOWLEDGEMENTS ERS/ENVISAT radar data are aquired through ESA research projects ENVISAT-AO #857 (JL. Froger & co-I) and Category 1 #2899 (S. Bonvalot & co-I). This research is supported by IRD (Dept DME, DSF) and UMR5563, UMR6524.



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