Landslides in flysch formations in the Northern Apennines, Italy

In the Northern Apennines three main flysch formations are present, covering more than 60% of the entire area: the Monghidoro Formation (Upper Cretaceous), the Macigno Formation (Upper Oligocene-Middle Miocene), and the Marnoso-arenacea Formation (Middle-Upper Miocene). Different types of rock movements occur in the three formations, owing to their different tectonic styles and jointing patterns: mainly rock block slides are observed in the Marnoso-Arenacea Formation; rock slumps are more frequent in the Monghidoro and Macigno Formations. Thirty large landslides, still active or dating from the last 400 years, have been examined from the geomorphic and geotechnical viewpoint: they range from 1 to 3 km in length and from 1 x 10(5) to 1 x 10(7) m(3) in volume. The back-analysis showed that, notwithstanding the high values of peak friction angles (28 - 30 degrees), the slides occurred on slopes from 15 degrees to less than 10 degrees, generally linked to intense rainfall. Some statistical analyses on the main parameters have been performed, aimed at obtaining detailed knowledge of the most common and most unstable formations of the Northern Apennines.