Niscemi, that's why the hill is landsliding. Casagli: immediate monitoring with satellites

Niscemi's belvedere no longer exists. The landslide that hit the municipality in the province of Caltanissetta has widened and currently has a face of four and a half kilometres, but subsidence continues. Technicians have stated that the entire hillside is landsliding towards the Gela plain. A landslide that has ancient origins. The town stands, in fact, on an unstable subsoil affected by landslides documented as far back as the 18th century and already reactivated in 1997. This time, on 16 January, the first criticality began in the western part of the town. Then, on 25 January, a second landslide of greater magnitude reactivated an old front near the southern part of the inhabited centre, compromising the stability of numerous buildings in the area, literally causing many houses to crumble, compromising a large part of the local road system and causing the interruption of essential services.

Subsequent checks have shown that the entire ridge on which the town of Niscemi rests is moving, putting the stability of dozens of buildings in the town at risk. "The entire hill is giving way towards the Gela plain," said National Civil Protection chief Fabio Ciciliano, after the first inspection in Niscemi. "The checks," Ciciliano explained, "show that it is not just the visible part that is moving: it is the entire slope that is descending. And he announced that the houses on the ridge of the landslide can no longer be inhabited. The first inspections were carried out together with Professor Nicola Casagli, a scientific member of the department's competence centre, professor of geology at the University of Florence and president of the National Institute of Oceanography and Experimental Geophysics.

'Here in Niscemi,' Professor Nicola Casagli explains to Kaleidoscope, 'there was a large landslide, one of the largest that has occurred in Italy in recent decades. The mechanism is quite well-known, that of a vertical escarpment that then curves. And then there is a slide on a weakly inclined plane, almost immediately at the front, at the contact between a sand bar on which the town is located and a clay substrate, which is where the movement develops'.

For Casagli, 'the country has no problems in the vast majority. There may be problems in the coming days on the edge, where an escarpment has formed. Because this escarpment is formed on sand, we are taught from childhood that we can make sandcastles out of sand in certain situations. But if the sand castle gets too dry or too wet, it then becomes a pile of sand. This will happen at the edge of the escarpment and is already happening with sand cones resulting from the disintegration of the escarpment sand. This means that the first rows of buildings in Niscemi will be affected and will be affected permanently. At the moment, a buffer zone of 150 metres has been established, which is very precautionary and therefore exaggerated compared to the real possibility of the phenomenon evolving. We expect in the next few days, on the basis of monitoring data, to restrict it to a zone of reasonable safety'.

"The monitoring," explains Professor Casagli, "will essentially be done with radar satellites of the European Space Agency, Italy and Argentina, with different characteristics that will allow us to have a complete and total mapping of the centre, of the surroundings of the landslide, in order to predict its evolution. Since it is such a large landslide and without a good frontal viewpoint, we decided to use satellites precisely to have a complete panorama of the landslide and not just punctual and insignificant measurements of the whole".