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Remote sensing for ground deformation analysis during the eruptive event of July 2001 at Mt. Etna

Alessandro Bonforte(1) and Giuseppe Puglisi(1)

(1) Istituto Nazionale di Geofisica e Vulcanologia, Piazza Roma, 2, 95123 Catania, Italy


The July - August 2001 Mt Etna eruption has been studied using the DinSAR technique and monitored through both continuous GPS measurements on a network of permanent and static stations, as well as daily static and kinematic GPS measurements, made by INGV-CT, on geodetic network. This eruption, one of the most important lateral eruptive events in the last 30 years, was characterized by an unusual eruptive style, with lava flow emissions at different altitudes along a complex fracture system. A seismic swarm dated the dyke emplacement on July 12th .

At the beginning of 2001, ERS-2 gyroscopes had serious mechanical problems and they could not be used to get the necessary platform attitude information. As a consequence, the Doppler Centroid of ERS-2 images varied randomly from one observation to the next thus making the generation of SAR interferograms impossible. A back-up attitude control system was activated and tuned by the ESA-ESRIN staff, and in June 2001, the interferometric capability of ERS-2 was partially recovered. In fact, the POLIMI team, in cooperation with T.R.E. (POLIMI commercial spin-off), was able to obtain clear surface deformation maps related to the July 11th and August 15th 2001 passages.

Fortunately, the July 11th passage occurred just before the beginning of the seismic crisis accompanying the dyke intrusion. A preliminary analysis of this interferogram shows an extremely interesting pattern that appears associated to a decimetre ground deformation at the summit area of the volcano and at the Valle del Bove area. The volcano is split into two different areas showing opposite deformation on the two sides of the dyke. In particular, the eastern area located in the Valle del Bove shows a strong subsidence, while the western area shows an opposite behaviour with an evident uplift. The subsequent available images extended our dataset and permitted obtaining several pairs to validate and compare the interferometric data.

In the same period, several GPS surveys were carried out on the eruptive area. This GPS data allowed the near real time monitoring of the eruption and, by accurate post processing and inversions, to obtain an accurate eruptive model. Exploiting the opportunity that GPS and SAR data are available for the same volcanic episode, we validate the model obtained by inverting the GPS data by using the suitable interferograms.

The GPS data and SAR interferograms are in agreement with the deformation pattern expected in such kind of event, where the displacements are caused by magmatic sources and locally modulated by major structural features.


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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