Washington, Oct 7 : Satellite monitoring of the central Andes situated between Peru and Chile has helped an international team of geologists detect a long wavelength signal over the area’s topography.

The area bears 50 active or potentially active volcanoes, spread along a 1500 km-long arc. These volcanic structures mostly rise to between 4000 and 7000 m, are very remote with abrupt slopes, and are often cloaked in snow, making field study extremely difficult.

Now, a team of IRD researchers working in partnership with the University of Chile (Santiago) and the Observatoire de Physique du Globe of Clermont-Ferrand, have focused special attention on the Lastarria-Cordon del Azufre volcanic complex.

With a surface area of 1600 sq. km, it is situated in the central Andes Cordillera at the border between Argentina and Chile near Antofagasta.

The scientists said studies conducted in this region between 1992 and 2000 by a North American team showed that the deformations corresponded to crustal inflation affecting the whole Lastarria-Cordon del Azufre complex.

According to the scientists, though the volcano is not considered active, as the last eruption dates back 9000 years, such inflation could express an underlying activity related to the dynamics of a functioning magma chamber.

Radar interferometry by the European Space Agency’s Envisat between March 2003 and June 2005, also recorded a time-series of eight images of the Lastarria-Cordon del Azufre volcanic complex.

The IRD team used special software to process the images and obtain 28 interferograms.

The data set led to measurement of inflation of about a centimetre affecting the crust over the whole of the area studied.

The scientists said, as in the North American study, they found a long wavelength regional-scale signal covering a surface area of about 45 km long by 35 km wide corresponding to the entire volcanic complex.

A short wavelength signal not previously identified was also revealed, but unlike the first, it was located at the smaller scale of the Lastarria volcano only, they said.

They said the source of the short wavelength signal, located at about 1000 m beneath the summit of the Lastarria volcano, was more uncertain.

Indications, nevertheless, suggested a link with the circulation of hydrothermal fluids, they added. (ANI)