Kacper Jancewicz

UAV and SfM in Detailed Geomorphological Mapping of Granite Tors: An Example of Starościńskie Skały (Sudetes, SW Poland)

The paper presents an example of using photographs taken by unmanned aerial vehicles (UAV) and processed using the structure from motion (SfM) procedure in a geomorphological study of rock relief. Subject to analysis is a small rock city in the West Sudetes (SW Poland), known as Starościńskie Skały and developed in coarse granite bedrock. The aims of this paper were, first, to compare UAV/SfM-derived data with the cartographical image based on the traditional geomorphological field-mapping methods and the digital elevation model derived from airborne laser scanning (ALS). Second, to test if the proposed combination of UAV and SfM methods may be helpful in recognizing the detailed structure of granite tors. As a result of conducted UAV flights and digital image post-processing in AgiSoft software, it was possible to obtain datasets (dense point cloud, texture model, orthophotomap, bare-ground-type digital terrain model—DTM) which allowed to visualize in detail the surface of the study area. In consequence, it was possible to distinguish even the very small forms of rock surface microrelief: joints, aplite veins, rills and karren, weathering pits, etc., otherwise difficult to map and measure. The study includes also valorization of particular datasets concerning microtopography and allows to discuss indisputable advantages of using the UAV/SfM-based DTM in geomorphic studies of tors and rock cities, even those located within forest as in the presented case study.

Evolution of sandstone mesas – following landform decay until death

Mesas are residual landforms typical for layered rock sequences, formed due to tableland dissection and cliff retreat. Caprock cliffs are characteristic elements of mesa morphology. Mesas have finite lifetimes and over time are reduced in area, transforming into buttes and eventually into irregular arrays of boulders. Thus, they are ‘born’, when separated from a plateau, and ‘die’, when the caprock completely disintegrates. In this paper, sequential development of sandstone-capped mesas is first inferred from theory and then verified on the basis of field observations and landform inventories from a sandstone tableland of the Elbe Sandstone Mountains in the eastern part of Germany. Finally, selected morphometric parameters of mesa morphology, potentially indicative of their evolutionary phases, are computed from a high-resolution digital terrain model. Both field evidence and results of morphometric analysis indicate that mesas evolve along various pathways and, tending towards specific end-members, illustrate the principle of equifinality. Space-for-time substitution, if applied with care, may also be helpful in deciphering the geomorphic history of mesas and tracing their life until disappearance.