Two years of InSAR monitoring of volcanic activity at Piton de la Fournaise (Réunion Island) using ASAR-ENVISAT data
Pierre Tinard(1) , Jean-Luc Froger(1)
, Pierre Briole(2)
, Thomas Staudacher(3)
, Valérie Cayol(1)
, Yo Fukushima(1)
, and Thierry Souriot(1)
Laboratoire Magmas and Volcans,
5, rue Kessler,
63038 Clermont-Fd Cedex,
(2) Institut de Physique du Globe de Paris, 4, place Jussieu, 75005 Paris, France
(3) Observatoire Volc. du Piton de la Fournaise, 14 RN3, km 27, 97418 La Plaine des Cafres, La Reunion, France
After an unusually long period of 65 months of rest, Piton de la Fournaise volcano (Réunion Island) started erupting on March 1998. This event marks the beginning of a new cycle of activity which still continues today. In the last two years, Piton de la Fournaise had 8 eruptions (April 2003 to May 2005). This period also coincides with the
beginning of systematic data acquisition by the ASAR radar on board of the ENVISAT satellite. With respect to ERS satellites, ENVISAT allows to acquire images in seven different swaths which significantly improves the monitoring capability of InSAR. It increases the revisit time from 35 days to 2.5 days and enhances the data quality for interferometric purpose.
In order to monitor the volcanic activity, we use 105 ASAR images acquired between February 2003 and May 2005. We produce a dataset of more than 390 interferograms which provides a unique record of the ground displacements associated with each individual eruption. The February 2005 eruption gave the opportunity to compute three interferograms just a couple of hour after the satellite passed over the erupting volcano, leading to near real time InSAR monitoring of volcanic activity. Accurate maps of the ground displacements and lava flows were computed and provided to the Volcano Observatory of Piton de la Fournaise in less than a half-day, thanks both to ESA facilities
and to our optimized interferometric processing chain.
For most of the past two years eruptions, the observed ground displacements are compatible with the opening of eastward-dipping dykes in the N10°E and S10°E volcano rift zones. Using a 3D mixed boundary element method for elastic media coupled with a neighbourhood algorithm, we determined the characteristics of the dykes formed. The best-fit models converge towards a set of dyke dipping 45° to 55° eastward whose bottoms lie at around 1 500 m asl (depth 800 – 1 000 m). The repetition of dyke intrusions may have weakened the volcanos flank and then promoted the large displacements of the January 2004 event.