Tölcsér Pothole

The Tölcsér-pothole is a cave located in the Budai Mountains within the Danube–Ipoly National Park.

Description

The Tölcsér-pothole is situated in the outskirts of Remeteszőlős, east of the town centre. It is on the Danube side of Remete Hill, in a forest, in a highly protected area, at about 350 m above sea level, in a rock group, and the cave has a 2 × 3 m natural, funnel‑shaped, vertically oriented entrance. The entrance is reachable by an indistinct path. Its location is difficult to find; the guiding points are a garage protruding from the line of the rear fence of the Remeteszőlős gardens, and a mustard‑yellow house, above which, on the north side of a sparse forest section, the cave mouth is located about 60 m from the rear fence of the gardens.

The thoroughly surveyed pothole is 30 m long, 19.9 m vertically extended, 19.9 m deep and 5 m horizontally extended. It formed in Upper Triassic Dachstein limestone along a tectonic fracture, due to decisive dissolution activity and frost‑induced granular disintegration near the entrance. Its tube‑shaped form has a vertical slope and the characteristic cross‑section types are the tube section and the fissure section. The cave is essentially a vertical fissure, segmented by a narrower cross‑section part five metres deep. At several points small spherical caps have formed and near the entrance weakly developed finger‑like formations appear. Its endpoint is its deepest point. Visiting the freely accessible part of the cave requires the use of about 25 metres of rope and rope‑technical equipment.

In 2005 the cave was first called Tölcsér-pothole in the literature.

Research history

In December 1995, during a field exploration, the Anubis Cave Research Group discovered the cave. In rock climbing they found a 0.5–1 metre diameter, water‑filled spherical chamber. They were intrigued that the cavity opening breaking to the surface began its passage with a full cross‑section in stalactite. The researchers deepened the fill that formed the floor of the spherical chamber. The humus layer deposited 30–40 centimetres thick was later replaced by several stone blocks, probably fallen from the main ceiling when the spherical chamber broke to the surface. When the stones were removed, it became visible that the side walls of the cavity lean strongly toward the centre, and therefore they assumed that if the passage continues vertically, its cross‑section would decrease greatly.

At a depth of one meter the spherical niche almost became horizontal, from its stalagmite floor a 70‑centimetre‑diameter passage started, which was filled with larger stone blocks weighing 20–30 kilograms. At 1.5 metres deep, when the last large stone was removed, the terminal passage opened, and a mine shaft of a size walkable by a person became visible. They expected a 15–20 metre deep mine from the falling time of the stones. The first 5–6 metre part of the passage seemed slightly difficult to walk but traversable. They were able to descend to the mine’s constriction with rope safety. But at this point the side walls of the mine below the constriction widened like a bell, and further progress could only be made by using rope‑technical equipment.

They advanced further in the mine and reached, at 17 metres depth, the cave’s debris‑filled floor level. At the terminal section the shaft was chamber‑shaped, wide and 9–10 metres in diameter. On the chamber walls, in some places, beautiful stalactite draperies are visible, but most prominently very dissolved, 20–30 centimetre thick, scalenohedral calcite crystal crust can be observed. In places where the dissolution effect was less pronounced, very striking 2–3 centimetre diameter calcite crystals can be seen and the wall is locally covered with montmilch. The floor’s clay fill contained fox and other small‑mammal bones. Further progress from the deepest chamber is possible only with difficult excavation work.

The group's 1995 report included a description of its exploration and a longitudinal section cave map sketch. In 2005 Zsolt Polacsek surveyed it and, based on the survey, drew a 1:100 scale floor plan cave map. In that year János Magyarósi, Antal Handl and Zsolt Polacsek surveyed it and, based on the survey, drew a 1:100 scale longitudinal section cave map. According to the data of the Danube–Ipoly National Park Directorate, the planned section B of the M0 motorway western sector, between primary road 10 and primary road 1, has its alignment directly touching the cave between the 89th and 90th kilometre sections.