## 2 Study Area  
The study area, which is the former brown coal mine \"Friendship of Nations--Babina\", is located in western Poland, close to the border with Germany (Figure 1). The mine was in operation from 1921 until 1973. It is a unique post-mining area, as, initially, the brown coal was mined through a system of shallow underground workings that followed the complex geometry of coal deposits, a result of glaciotectonic processes, and were accessed through a system of inclined shafts. The depth of the underground workings reached up to 100 m below the terrain level. Since the 1960s, the deposits were also mined from the surface in several open pits. The overlying waste rocks were deposited in external and internal waste heaps. After the end of mining, due to economic reasons, the area was subjected to reclamation measures aimed at the restoration of vegetation. These activities included, in the first phase, the levelling of steep slopes in the pits and on the heaps. In the second phase, the pits were filled with water and trees were planted in the remaining area. The second stage was never finished. Details of the reclamation activities are described in [50]. Four study fields were established in the scope of the research project within the border of the former mining field, and the presented study concerns geophysical surveys carried out in test field three (Figure 1). This test field was established in the area of underground mining activity. In terms of geology and geomorphology, the study area is located in the south-east part of the glaciotectonic structure called the Muskau (Muzakow) Arch. It is a terminal moraine in the shape of a regular arc, open to the north, with an arm span of about 20 km, length of approximately 40 km, and width of around 5-6 km. The central part the arch is divided by the valley of the Nysa Luzycka river, which is also the border between Poland and Germany. The structure was formed as a result of the load exerted by a moving glacial ice sheet during the Marine Oxygen Isotope Stage (MIS) 12, also known as the Elsterian glaciation [51]. The original moraine, that reflected the shape of an ice lobe, was eroded and modelled during the following MIS 6 (Salle) glaciations. In the effects of glacial erosion processes, the height of the moraine was greatly reduced, and deeper glaciotectonic structures, dating back to the MIS 12 period, were exposed in numerous places. The ablation moraines, often perpendicular to the older glacial structures, are a trace of the glacial accumulation from this period. The Middle and Upper Miocene deposits, deformed during the MIS 12 and MIS 6 glaciations, were tilted and raised from a depth of about 150 m below ground level. The deformation forms of the Paleogene and Neogene deposits are of different sizes, ranging from over a dozen meters to several kilometers. These are mainly continuous compression structures, such as folds and diapirs, as well as discontinuous structures that are dominant in the area, such as overhangs and glaciotectonic scales (Figure 2). These glaciotectonic structures are clearly visible in the present-day relief of the terrain. Distinct geomorphological forms include elongated lowering of the terrain in the zones of disturbed brown coal deposits. Their origin is related to the process of compaction of brown coal caused by weathering. The width of the lowered zones reaches 30 m, with a length of up to 2 km and a depth between 3 and 5 m. They are filled with Holocene alluvial deposits and peats. These subsided forms are divided by deposits of ablation moraines. Together, these represent a stripe-like arrangement of the geological relief and landscape composition [52; 53]. Figure 1: General location of the study area: (**a**) location of the Muskau Arch (**b**) test field three; (**c**) extent of the Muskau Arch. The specific study area is test field three, which is located in a glaciotectonic complex called the Nowe Czaple zone, and is dominated by fold-type structures.