Rockfall/Rockslide Hazard Analysis in Tuffaceous Coastal Cliffs: the Case of Miseno Cliff, Phlegraean Fields, Italy

Along the coastal stretch of the Phlegraean Fields, an active volcanic district near Naples (Italy), significant erosion processes affect a large part of the coastal cliffs, being the latter mainly composed of fractured volcanic tuff and pyroclastic deposits. Assessing processes related to cliff instability, factors contributing to cliff failures, and evaluation of retreat rates, is essential for effective coastal hazard assessment and management. In view of this, this research aims to identify the main predisposing factor to rockfall/rockslide phenomena in tuffaceous coastal cliffs in this coastal area assessing any relationships between meteorological factors (rain, temperature, wind, etc.), weathering, and structural and geomechanical characteristics of rocks. This was made by using, as an example, the large landslide that affected the Capo Miseno cliff on March 25, 2015, when approximately 87.000 m3 of material detached from the slope, reshaping the morphology of the coastline. In order to determine the triggering factors of this landslide, a database of meteorological measurement time series taken over ∼ 2 years (January 2013–March 2015) was used coupled with a geomechanical survey carried out on the contiguous cliff known as 'Spiaggetta Verde' in 2014, which shares broad characteristics with the considered cliff. This survey shows the presence of several sets of long and deep discontinuities identifying rockfall and rockslide as potential landslide kinematics. In addition, the meteorological analysis demonstrated that several diurnal and seasonal cycles of heating and cooling may lead to deformation and crack opening and propagation. Both increasing temperature and temperature fluctuations may enhance fracturing. However, the predisposing factors identified by the field analyses are not sufficient to make hazard assessments if sea condition factors are not considered in detail. The analysis of the relationships between structural characteristics and meteo-marine forcing factors may be very useful in the perspective of hazard assessment being this study site located in a densely urbanized area.