Bajnai Öreg Hole

The Bajnai Öreg Hole is a cave located in the Danube–Ipoly National Park, in the Gerecse Mountains. It is among the caves in Hungary that are specially protected. Archaeological finds have been recovered from it. Deneves also occur in its passages.

Description

It is situated in the outskirts of Bajna, about 1.3 km west of the centre of the settlement. The cave is on the lower part of the steep western side of Őr Hill, at about 220 m above sea level, under a sandstone outcrop; its entrance is 16.5 m wide, but this is divided into two parts by a few large stone blocks. The eastern opening (accessible by a footpath) is 3.5 m wide and 2.1 m high, the western opening is 5 m wide and 1.5 m high. The cave can be reached via the tourist trail marked with a green triangle that starts from Epöl, leading to a cave 70.5 m long, with a vertical extent of 14.1 m, a height of 2.5 m, a depth of 11.6 m and a horizontal extent of 36 m.

The Antechamber in the cave is 18 m long. Ten metres from the entrance it narrows to 8 m, then widens again towards the east, in the direction of the side passage, up to 12 m. At the western end (at the beginning of the inner section of the Main Passage) it is still 7 m wide. Its ceiling is formed by the lower face of a bedding plane that dips 10–12° towards the northeast, therefore its height, ranging from 1.2 to 2 m, is affected by the unevenness of the floor fill. (From this fill, as a result of excavations and investigations carried out here in the 20th century, a rich paleontological and archaeological material has come to light.) This flat ceiling is broken in one place, in the middle of this passage section, by a small dome‑shaped protrusion 0.8 × 2.5 m in size with a 4 m high, bulbous little vault opening. The inner part of the Main Passage is a 17 m long, 3–8 m wide, 1.5–2 m high spacious corridor that slopes gently inward following the rock descent.

In its middle part there is a 5 m high spacious, dome-shaped vault, to which a narrow, further extending up to 2 m long spherical chain is attached. At the entrance of the 26 m long Side Passage, branching from the inner third of the Front Hall towards the north‑east, there is a room 2.5 m wide and only 0.8 m high, but which widens to 7 m at the domed chamber. From the ceiling of this room a spacious dome-shaped vault similar to that of the Main Passage rises up to 4 m high. The interior of the Side Passage consists of a narrow, very steep wormhole and a small pit, whose dead‑end, narrowing to an impassable crack, lies 11.6 m deeper than the level of the cave entrance.

The upper Triassic massive-bedded Dachstein limestone fault zones oriented NW–NE and EN–E–S were the framework for the development of the void system. Based on its speleothems and passage morphology it is a remnant of a thermal karstic spring cave. The cave’s speleothems are very varied. The slab surface forming the ceiling of the Front Hall is almost smooth, marked only by slight irregularities and corrosion cracks. The side walls here are angular and jagged, suggesting freeze‑thaw rock‑splintering processes, but farther from the entrance and on larger surfaces the traces of domes are also clearly visible. The domes of the Main and Side Passages, as well as their terminal sections, are characterized by forms created by the merging of dome chambers and dome vaults. On the ceilings (especially on the dome of the Side Passage) the rock surface is heavily segmented and very broken, divided by deep valleys and grooves along the rock’s microtectonic structures. These small voids and the cracks in the ceiling of the Front Hall are the favourite winter shelters of cold‑tolerant bat species.

In a cave, mineral deposition is observed only in small spots. The barite that was once described on the rock surface here no longer occurs, only appearing in the debris. The side wall of the dome‑shaped chamber of the Side Passage is composed of large‑crystal calcite that can be classified as an early‑stage karst cavity fill, and its ceiling reveals limonitic deposits. On the walls of the terminal small shaft, tiny spots of minute quartz are visible. The cave fill consists of stone‑debris humus and stone‑debris, rock‑powdered clayey loam. The proportion of stone debris is very high in the Main Passage and lower in the inner part of the Side Passage. Relatively poor fauna. In the sections near the entrance, the walls are covered with algal‑mossy coating in large patches. Throughout the entire extent of the cave, there are butterflies, mosquitoes and spiders.

Because of its nature, external weather effects are very pronounced in the cave (especially in winter). It often happens that in the Antechamber, on colder days, the temperature is around -10 °C. The Gerecse Cave Research and Nature Conservation Association carried out bat observations in the Bajnai Öreg Hole, during which the group members identified the presence of 10 bat species: little horseshoe bat, greater horseshoe bat, water bat, long-eared bat, common bat, common pipistrelle, grey long-eared bat, brown long-eared bat, western pipistrelle and barbastelle. Based on the observation data and the occasionally found fresh droppings, it can be considered in the local context a small‑to‑medium‑sized, species‑rich permanent winter bat roost with a small number of species and individuals as an occasional spring and autumn roost, and at the same time a small‑sized, species‑rich breeding site. During the hibernation period, the occurrence of the cold‑tolerant common pipistrelle and western pipistrelle is typical. The open, easily accessible cave can be visited without permission and without basic caving equipment.

In 1986 the cave was first called Bajnai Öreg Hole in the literature. The cave appears in the literature under the names bajnai Öregkő-cave (Kordos 1984), Bajnai Öreg Hole (Vigh 1937), bajnai Öreg-hole (Kordos 1984), Bajnai öreghole (Kadić 1919), Bajnai-Öreg-hole (Bertalan, Schőnviszky 1976), Bajnai Őrkő-cave (Székely 1994), bajnai Őrkő-cave (Bertalan 1976), Bajnai Őrkő-cave (Holényi 1959), Epöli Öreg-hole (Kordos 1984), Kőpest (Dénes 1977), Öregkő Cave (Dénes 1977), Öreglik cave (Jaskó 1957), Öreg-hole (Kordos 1978), Öreghole (Kadić 1919), Öreghole cave (Almády 1988), Őrhegyi-cave (Bertalan 1976), Őrhegyi cave (Kadić 1952) and Őrkő-cave (Jakucs, Kessler 1962).