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  • Tolonen, Miika (2023)
    The island of Suur-Pellinki is located near the town of Porvoo in the southern Finland. The bedrock in the area consists of different rock types such as plutonic rocks and rock types that are rare in the southern Finland, for example agglomerate and different kinds of metavolcanites. The bedrock has undergone several tectonic events, of which Svecofennian orogenesis (1.9-1.8 Ga) has been the most notable. The orogenesis caused compression, extension and shearing of the bedrock, and signs of these stresses can be seen as fractures, folds, foliations and faults. The development of unmanned aerial vehicles, such as drones, has been significant in recent years. Thus, usage of them has increased in different fields of science, of which geosciences are not an exception as drones are used in data collecting. In this study, a drone was used to study outcrops of Suur-Pellinki. Four outcrops were photographed by a drone, and photographs were used to build three-dimensional models. The models were built in Pix4D and Metashape software using Structure-from-Motion photogrammetry. In addition, the models were exported to GeoVis3D software, in which orientation of fractures was studied. The aim was to study the bedrock with traditional fieldwork methods and technology that has not been used in the area. It was studied if three dimensional modelling can provide any significant additional benefits over traditional fieldwork methods. Moreover, the aim was to find ways to operate a drone efficiently and build three-dimensional models straightforwardly. The bedrock was found to be undergone extensional and differently oriented compressional events during the orogeny, and the maximum principal stress (σ1) orientations had been firstly NW-SE and later NE-SW. These stress orientations formed the main structures of the bedrock such as fractures, folds, and foliation, which is prevalent in metavolcanites of the area. In addition, some strike-slip faults were seen in the area, which have not been studied significantly in the previous studies. The three-dimensional models turned out to be useful in order to study the bedrock. Critically, building of the models was not fast and straightforward. The final resolution of the models is under three centimetres, which let to study even the smallest structures of the bedrock.