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Study of the deformation field of two active Mexican stratovolcanoes (Popocatepetl and Colima Volcano) by time series of InSAR data.

Virginie Pinel(1), Andy Hooper(2), Servando De la Cruz-Reyna(3), Gabriel Reyes-Davila(4) and Marie-Pierre Doin(5)

(1) IRD, LGIT-Universite de Savoie-Campus Scientifique, 73376 Le Bourget du Lac Cedex, France
(2) Nordic Volcanological Center, Askja, University of Iceland Sturlugata 7, IS-101 Reykjavik, Iceland
(3) UNAM, Ciudad Universitaria, Del. Coyoacan, Mexico DF CP 04510, Mexico
(4) Universidad de Colima, av. Universidad 333, Colonia Las Viboras, 28040 Colima, Mexico
(5) Ecole Normale Superieure, 24 rue Lhomond, 75231 Paris Cedex 05, France

Abstract

Although SAR interferometry has proven to be a reliable method to measure displacements due to magma movement at depth, andesitic stratovolcanoes remain difficult to survey using this technique. The main causes are their specific geometry (steep topography), which induces strong tropospheric artefacts, and environmental conditions (e.g., possible vegetation, ash and/or snow cover) leading to a loss of coherency. These types of andesitic stratovolcanoes are also among the most hazardous ones, mainly because of the drastic and rapid changes of their level of activity. In this study, we measure ground motions of the two most active Mexican stratovolcanoes: Popocatepetl and Colima Volcano, using InSAR. Popocatepetl (19.023N, 98.622W, summit elevation 5426 m) and Colima Volcano (19.514N, 103.62W, summit elevation 3850 m) have produced Plinian eruptions, pyroclastic flows and large sector collapses in the past. During the last 15 years, their almost continuous activity has been characterized by a succession of eruptive cycles (dome construction followed by dome-destruction explosions and episodes of lava and/or pyroclastic flows). The most recent stage of eruptive activity at Colima began in September 2004 as an episode of extrusion of andesitic lava followed by intermittent explosive activity. To quantify the deformation, we analyse for each volcano, several time series of 30 ENVISAT images acquired from December 2002 to July 2006. Conventional interferometry shows that coherency is restricted to the lava flows of the summit area and the base of the volcano and there is a lack of coherency on the vegetated slope of the volcanoes. Most interferograms also show a strong tropospheric artefact mainly due to the variation of water vapor stratification between satellite passes. We further process the time series using both the Stanford method for persistent scatterers (StaMPS, Hooper et al., 2007) and a derived small baseline approach. Tropospheric delays were estimated for each interferogram using data from a global atmospheric model (NARR). Maximum value is 10 rad/km which corresponds to more than 4 fringes on the slopes of the volcanoes. These delays were validated using the correlation between the wrapped phase and the elevation after having corrected for a ramp effect induced by orbital errors. The tropospheric effect was removed from the wrapped phase in order to improve the unwrapping process and link the signal obtained for the summit area with that available at the base of the volcanoes. On Popocatepetl no significant deformation has been observed except for a small and localised subsidence on the SW flank. Colima summit area exhibits a constant and almost linear subsidence of about 1cm/year centred on the summit but enhanced around the 1998 lava flow. This subsidence is modelled considering both a deflating magma source at depth and the effect of the dome and lava flows load.

Hooper, A., P. Segall and H. Zebker, Persistent Scatterer InSAR for Crustal Deformation Analysis, with application to volcan Alcedo, Galapagos, Journal of Geophysical Research, 112, B07407, doi:10.1029/2006JB004763, 2007

 

Workshop presentation

Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry