GEOLOGICAL RISKS IN LARGE CITIES: THE LANDSLIDES TRIGGERED IN THE CITY OF ROME (ITALY) BY THE RAINFALL OF 31 JANUARY-2 FEBRUARY 2014

An exceptional rainfall battered the city of Rome ( Italy) from 31 January to 2 February 2014. The event had variable intensity and duration in the different parts of the city. The exceptionality of the event lies in the intensity of rainfall cumulated in 6 hours (return period > 50 years) and in its uneven distribution over the urban area. The event triggered a number of landslides of different type, which caused substantial damage. Researchers from the Centro di Ricerca per i Rischi Geologici (Research Centre on Prediction, Prevention and Control of Geological Risks - CERI) of the University of Rome "Sapienza" carried out field surveys and assessments immediately after the event. The team detected and inventoried 68 landslides, mostly occurring in the sandy and sandy-silty deposits of the Monte Mario, Ponte Galeria and Valle Giulia Formations. The complete inventory of the landslides is accessible via WebGIS on CERI's website http://www.ceri.uniroma1.it/cn/landslidesroma.jsp. The spatial distribution of the landslides evidences that 69% occurred in clastic deposits of sedimentary origin and only 6% in volcanic deposits. This finding disagrees with more general statistical data, based on the inventory of Rome's historical landslides, indicating that almost 41% of slope instabilities occur in volcanic deposits and almost 12% in sedimentary ones. In the data reported here, this apparent contradiction is justified by the fact that most the rainfall under review was concentrated in the north-western portion of Rome's urban area, whose hills accommodate outcrops of dominantly sedimentary deposits from Plio-Pleistocene marine and continental cycles.