GNGTS 2022 - Atti del 40° Convegno Nazionale

406 GNGTS 2022 Sessione 3.2 complex lava tube network promoted lava field lengthening as far as the coastline, destroying villages and partially damaging the western part of Catania (Branca et al. , 2013). The 1669 event was accompanied by an intense seismic swarm. Between 11 and 25 March the lava field covered 72% of the total area, and three branches of the lava field were developed; whereas at the end of March, the central branch reached the old site of Misterbianco. In thosemonths, the ephemeral vents led to the formation of new lava flows that developed in the Misterbianco territory, producing a gradual thickening of the lava field (Branca et al. , 2013). As a result, the thickness of the lava field reaches 21 m in a quarry located about 300 m northeast of the study area (Fig. 2b). Overall, the morphology of the lava field consists of toothpaste lavas, often appearing fractured and tilted with the presence of several ephemeral vents and small tumuli (Fig. 2c). The Chiesa Madre: historical background. The oldest document mentioning the Chiesa Madre dates back to the 14 th century; during time the structure was modified with the addition of new rooms, a central nave, new altars and chapels were added (Garozzo 2017-2018). Today the building is characterised by a Latin cross plan with a nave 26 m long and 9 m wide along which there are eight altars (Fig. 3a). The presbytery has a rectangular-shaped room with a pseudo-apse: it also has an entrance door on the left, which was closed during the eruption with massive stones in order to prevent lava flowing into the church. A smaller door located to the right gives access to the gothic chapel. Along the southern wall of the nave there is the bell tower, which is the only original element standing out from the 1669 lava. Multidisciplinary surveys. A diagnostic multidisciplinary survey was performed in the Mother Church site, including both the inner of the building and the environmental setting on a surface of ca. 10 ha. For this study, we applied the following four different methods: i) aerial photogrammetry by drone to obtain a high-resolution mapping of the studied site within the 1669 lava flow; ii) ground-penetrating radar (GPR) to detect voids below the church floor related to buried structures (i.e. tombs, crypts etc.); iii) terrestrial laser scanner (TLS) to recognize fractures and deformations in structural and architectural elements; iv) infrared thermography (IRT) to identify modifications before the 1669 lava flow not reported in the historical documents. Structure-from-Motion aerial photogrammetry. The aerial photographic survey of the Misterbianco site produced a high-resolution digital surface model (DSM) and an orthophotomosaic by using the Structure-from-Motion technique (SfM). We used a DJI Phantom 4 ProV 2.0 in order to acquire 540 aerial images with a constant flight altitude of about 50 m above ground level. The photogrammetric acquisition was characterized by the following steps: i) identification of key points and image matching followed by scattered point cloud; ii) filtering of the scattered point cloud thus deleting incorrect geometry of those points characterized by significant coupling errors; iii) generation of the dense point cloud; iv) generation of the digital surface model (DSM) and of the orthophotomosaic (Fig. 1e). Terrestrial Laser Scanner. The TLS survey of the Mother church was performed through the integrated use of laser scanning and photogrammetric technologies, in order to acquire geometric and spatial data of the historical heritage. For this purpose, we used a TOPCON GLS- 2000S scanner, featuring a maximum distance of 130 m, with field angles of 360° (horizontal) and 270° (vertical). The survey was performed from outside to inside of the building with 11