UAV and geophysical approaches for the study and monitoring of sinkholes in evaporitic and alluvial environments

Alice Busetti¹, Michele Fernetti¹, Davide Martinucci^1,2, Emanuele Forte¹, Luca Zini¹ & Chiara Calligaris^1
1University of Trieste, Department of Mathematics, Informatics and Geosciences, Via Weiss 2, Trieste.
²Esplora SRL.
Corresponding author e-mail: calligar@units.it

In Friuli Venezia Giulia region (NE Italy), sinkhole phenomena associated with evaporitic bedrock are particularly widespread and active, despite the fact that this bedrock is scarcely exposed. In this regard, the most recent event occurred in Esemon di Sopra, in the municipality of Raveo. The sinkhole suddenly opened on April 21st, 2022, on an alluvial terrace alongside the Degano River riverbed. The cylindrical collapse feature, has a diameter of 18 meters and a depth of 15 meters. It developed less than 200 meters from both the main road and the inhabited area of Esemon di Sopra. In the immediate vicinity of the sinkhole, a natural gas pipeline network is also present. The paroxysmal phase developed due to the presence of a void within the loose detrital material, which was partially visible during the first surveys. Given the nature of the material involved, the sub-vertical walls immediately began to evolve with subsequent collapses. In this context, the use of drone-based photogrammetry proved to be of fundamental importance, allowing, in complete safety, a three-dimensional reconstruction of the sinkhole morphology and a detailed analysis of the depositional sequence. Integrated geophysical surveys have been conducted to improve our understanding of the spatial variability of sediments and bedrock. In March 2024, a LiDAR survey was carried out, which highlighted the morphometric changes of the sinkhole’s shape. The Esemon di Sopra event fits within a broader framework of instability affecting the valley areas of the Tagliamento River basin, where, however, no phenomena of such magnitude had been recorded for over eighty years. A similar historical case occurred in the early 1960s, south of the village of Quinis (Municipality of Enemonzo), on the alluvial terrace of the Tagliamento River, where two sinkholes opened with diameters of 45 meters and 15 meters, and a depth of 15 meters. The centre of this hamlet is still affected by subsidence, as evidenced by differential analyses of satellite images (D-INSAR) and geophysical investigations. Furthermore, to monitor ongoing movements, a robotic total station was recently installed as part of the PNRR GeosciencesIR Project.

sinkhole, evaporites, LiDAR, UAV, geophysical surveys.