Reconstruction of spatial and temporal variability of debris flow in northern Apennines (Italy): Case study of the Alpe di Succiso area

Debris flows are within the most common and extensive natural hazards in mountain areas, where they may impact humans and their assets. On the surroundings of Alpe di Succiso (2000 m a.s.l., Reggio Emilia Province, Italy) multiple debris flows can be found but there is no information about the spatial and temporal variability. To fill the gap, various methods such as geomorphological mapping, geo-mechanical classification of source areas, grain size analysis, dendro-geomorphic method and climate data have been used to assess the spatial extent and the past occurrence of debris-flow events. Here the preliminary results of the analysis performed in the Fossa Lattara Site, NW of Alpe di Succiso, are shown.

The landforms and deposits present in the surroundings of Alpe di Succiso are the product of different morphogenesis (glacial, gravitational, and torrential) which revealed the evolution of the morpho-climatic conditions that have affected the study area over time. Field work has been carried out to identify the morphological features of debris flows revealing distinctive features such as detachment scarps, debris flow cones, lobes, levees, and channels.

To understand the slope stability mechanism of the source area, a discontinuous survey was conducted and it is found that wedge failure is common. Additionally, in both source and depositional areas, grain size analysis was performed by using various methods: direct field measurement was used for particles greater than 16 mm, a sieve analysis covered the range from 2 to 16 mm, and the laser granulometer technique was applied to particles smaller than 2 mm. Notably, the coarser particles were abundant in depositional area than source area.

On forested areas, dendro-geomorphic analysis contributes to detection of trends of debris flow. Dendro-geomorphic technique is based on the identification of growth anomalies recorded by the annual rings of trees disturbed by debris flows. For debris flow dating, identification of reaction wood, abrupt growth changes and eccentric growth are essential.  Trees samples from debris flow area and reference sites (undisturbed areas) have been collected on site to cross date climate influences and debris flow events. According to the dendro-chronological preliminary results, the debris flow was identified in 1989, 2013 and 2017. Further, debris flow events are linked with precipitation events of the study area.

Moreover, daily rainfall depths in the period 1961-2022 have been collected from ARPAE Emilia Romagna database to understand the impact of climate change on debris flow and it is observed that daily precipitation intensity (dpi) has increased from 1961 to 2022. Seasonal variations are also observed. Noticeably, in the months of December, January, and February the sum of dpi has increased by 162 to 220 mm. Future studies will be performed to analyze the effects of climate change on debris flow.