Ariadne Cave System

The Ariadne cave system is Hungary's third longest and fourth largest cave by vertical extent. It is one of Hungary's specially protected caves. It is the longest and largest cave by vertical extent in the Pilis Mountains.

Description

In the Pilis Mountains within the Danube–Ipoly National Park, on Pilis Mountain, in the outskirts of Pilisszentlélek, near Klastrompuszta, the 9 entrances are located in the Csévi ridges. Among its entrances, the most well‑known and spectacular are the Leány Cave entrance and the Legény Cave entrance, which are also served by a tourist path.

The Ariadne cave system was created by the gradual connection of the eight caves of the Csévi ridges: the Leány Cave, the Legény Cave, the Ariadne Cave, the Rejtekút Cave, the Vacska Cave, the Indikációs Cave, the Gyökeres Cave and the Kőoszlopos Cave. The specially protected cave is 19 300 m long, has a vertical extent of 206 m, a depth of 139 m and a height of 67 m. It is accessible with the approval of the Danube–Ipoly National Park Directorate. The Ariadne Karst and Cave Research Association studies it.

Formation

Most of the passages originated as thermal karst, formed by the action of infiltrating karst water through underwater dissolution and mixing corrosion, when this part of Pilis Mountain had not yet risen out of its surroundings. Later, as the mountain uplifted, the karst water level sank deeper, causing the existing cave passages to become gradually dry, while newer passages formed at greater depths. Thus, moving downward one encounters increasingly younger cave sections, and the character of the passages changes accordingly. The youngest passages, presumed to be at the current karst water level, have not yet been reached. In the dried‑out, inactive passages, water‑draining activity may have occurred during certain geological periods, resulting in the infiltration of loess or sandy‑limestone mud in many places from the surface. Significant amounts of speleothems have formed in most passages, sometimes completely blocking connections. Traces of glacial freeze‑thaw from the Ice Age are also observable, though not to the extent seen in the higher‑located Ajándék Cave.

Scientific investigations

Among the Csévi-szirtek caves, the connection was demonstrated with a new method, air‑pressure tracing investigation. In this framework, an inert, harmless tracer gas was released in summer into the Ajándék Cave, the highest opening of the presumed system, and samples were taken from the airflow exiting the other, lower‑lying entrance. The gas was indeed detected, first in the Indikációs Cave, then in the Leány Cave.

The discovery of new cave sections was targeted by geo‑electrical measurements, resistance measurements, carried out with the cooperation of the ELTE Department of Geophysics and Geomega Ltd., under the leadership of Gergely Surányi. As a result of the precise resistance measurements, a specific‑resistance map of the cross‑section beneath the measuring line was produced, from which a straightforward inference can be drawn about the location of air‑filled passages, since the resistance of air is infinite and that of the rock is some finite value. With the measurements, significant‑size, previously unknown passages were identified at two locations, although their exploration and the practical verification of the measurements have not yet been accomplished. A promising result is that the measurements above already known cave passages precisely located those passages.

Research history

The 1998 report of the Ariadne Karst and Cave Research Association mentions that in 1998 the association could not discover a new passage in the Leány–Legény cave system, but a 600 m portion of the cave was mapped, and the entrances of the caves located on the lower level of the Csévi-szirtek were also measured. In 1998 the association devoted little time to exploratory work in the cave system. The modest work resulted in the discovery of about 20 m of passage in the interior zone of the cave. Because the spatial labyrinth network of the cave is very complex, the greatest emphasis was placed on mapping. The Leány–Legény cave system’s Leány Cave section was surveyed, and two points in the Legény Cave part were already measured across. The survey revealed that some passages had been underestimated in size. Based on this, the system’s length is at least 2500 m, its highest point relative to the entrance is at 34 m, and its depth is 55–60 m. Accordingly, the vertical extent of the cave exceeds 90 m, and with the possible discovery of upper‑level passages it could exceed 100 m.

It seems increasingly likely that the system known on the Csévi ridges could once have formed a connected passage network, which fragmented before the Pleistocene. The passages were formed in the phreatic zone, the ceiling level of the large cave zone can be about 450–470 m. Considering that the polje known on the north side of the Csévi ridges indicates a spreading fault, which the Leány Cave passages approach, it no longer seems utopian that Hungary's deepest cave system is located here (it only needs to be uncovered).

In 1998 Richárd Kovács edited the longitudinal cross‑section map of the Leány–Legény cave system. From 14 May 1998, according to the Ministry of Environment and Regional Development decree 13/1998. (V. 6.) KTM, the Leány‑Legény cave system located in the Pilis Mountains, within the jurisdiction of the Danube‑Ipoly National Park Directorate, may be visited with the directorate's permission. The 2000 Karst Development report mentions that at the 470 m a.s.l. level (Legény‑Leány cave), where there is a vertical shaft in the cave, a former water level can be identified in the same way as in the Ajándék cave. The study includes a figure showing the geographic locations of several caves and freshwater limestone occurrences in the Pilis Mountains. The figure shows how large the vertical extent of the Legény‑Leány cave (named Legény‑Leány on the drawing) is and at what a.s.l. height it is situated.