Szurdok-völgyi No 2 Sinkhole

The Szurdok-völgy 2nd water sinkhole is a water sinkhole cave located in the Szurdok in the Pilis Mountains on the edge of Pilisszentkereszt, within the Danube–Ipoly National Park. It is among the caves specially protected in Hungary.

Description

At the entrance of the cave at the popular hiking site there is a resting place. The closed cave can be visited with the permission of the Danube–Ipoly National Park Directorate and using rope‑technical equipment.

The largest air‑space passage of the spacious, active water sinkhole cave explored to a depth of 80 m is the 18 m large shaft, which has a diameter of 4 m at its bottom. The water flowing in the cave ceases to flow only in extreme drought (for example such a case occurred in the summer of 2012). In the cave, which has truly become a water sinkhole and still functions as a water sinkhole today, there is little stalactite. However, many repaired ancient artifacts can be seen in the upper shaft. Unusual elements such as spherical pebbles, some weighing up to 5 kg, and the most spherical andesite blocks occur in it. This is not the only water sinkhole in the gorge.

In 2012 the cave was named Szurdok-völgy 2nd water sinkhole in the scientific literature for the first time. The cave is also mentioned as Szentkereszti water sinkhole (Kocsis 2014) and Szurdok-völgy No 2 water sinkhole (Kocsis 2014).

Research history

The 1914 Cave Exploration mentions that there are only three water sinkhole caves in the Pilis highlands. In addition to the Macska Cave and the Üröm water sinkhole cave, there is another one along the ridge of Hosszú-hegy near the Macska Cave, in the rocky gorge of the ravine near Pilisszentkereszt. A small stream runs through this ravine, losing part of its water here. Karl Jordan and several companions entered, years ago, the cavity visible at the bottom of the bed after diverting the stream water. However, because the channel was extremely narrow and the stream above them, blocked by a dam, threatened a water breakthrough, they were forced to interrupt their venture soon.

The MKBT Information 2011 November–December issue states that the Anubisz Barlangkutató Group's several years of research work and the extraction of a prominent stone from the point corresponding to the Pilisszentkereszt gorge streambed brought the long‑awaited result: the group entered the only active stream cave in the Pilis Mountains. The cave is estimated to be 130–140 m long and its explored depth about 70–80 m. How much of a stream it is is shown by the fact that the group members could work longer periods underground in neoprene dry‑suits even despite the very dry weather of recent months. The water of the Dera stream emerges in the cave’s chambers and shafts through partially blocked swallow holes opening at the surface of the gorge’s limestone bed.

The cave’s largest shaft is 27 m deep, beginning with a diameter of 3–4 m and widening to 7–8 m at the bottom. In wetter weather one can admire a waterfall of similar height here, descend and climb it when visiting the cave. An intense airflow from below is detectable in the lower passages of the cave. The phenomenon may indicate a large, as yet undiscovered stream branch coming from the Pilis side, or that the Szurdok‑völgy No 2 water intake is connected with those water‑formed, air‑filled cave passages located on the upper part of Hosszú‑hegy. The group sealed the cave because of the many hikers trekking in the gorge. After prior arrangement, the cave can be visited by researchers possessing rope‑technical knowledge.

The 2011 report of the Anubis Cave Exploration Group states that the group on July 15, 2011, during a field walk at the eastern entrance of the Pilisszentkereszt ravine, on the side of the valley floor stream bed next to the rest area, discovered a previously unknown cave. While moving along the stream bank, the group members were surprised to notice that through a clearly discernible opening of 30×30 cm a cold air stream was flowing to the surface. They noted a few stones loosely placed in the entrance constriction of the cave and saw a shaft starting in the stalagmite, 6 m deep and 1×1.5 m in diameter. Upon reaching the floor of the shaft they saw the entrance of several parallel twin shafts branching from the side wall of the passage. Most of these were 10–30 cm in diameter, but the main shaft and another passage were so enlarged that it seemed possible to pass through them, because looking down they saw a small chamber (1.5×2 m) 1.5 m lower.

From the two passages cold air rose very intensely, but the smaller side passages branching from the main passage also exhibited this. While standing at the bottom of the shaft they heard water flowing somewhere below them and the sound of the water echoed back with a tone suggesting sizable passages. They moved aside two or three stones, then descended the one tube-like passage to the small chamber, from which through a window-like opening (50×40 cm) they saw a large twin shaft, oval in cross‑section, 1.5 m wide, 3 m long and 15 m deep. They descended the shaft on a rope to a roughly 2 m wide horizontal stalagmite ledge. At that point it became clear that they had found an active water-bearing cave, the only one of its kind in the Pilis Mountains. Through many small and large ledges, partly blocked at choke points, the water of the surface Dera Creek flowed down with a large water flow.

The walls of the pit showed very clearly the striking forms of cold-water erosion, which were completely different from the usual forms of caves in the Pilis Mountains. Descending 8 m from the stalactite rim, they reached a stable subfloor of 1.5 × 3 m area composed of large stone blocks, through a continuously widening sloping fissure 2.5 m wide and 70 cm high. At this point the fissure opens into a significantly sized pit 4 m wide and 27 m deep, whose lower part has a diameter of 7–8 m. The floor of this pit is a smooth, slightly sloping compact stalactite mirror and completely lacks the fallen stone blocks that have accumulated at the bottom of pits of this size on the talc floor. From one side wall, in several places straightened, a walkable, 15 m long, streamside side branch begins, whose nicely loosened stalactite forms the bed. At the end of the side branch the stream water disappears in an air‑filled sand siphon.