Jama na Dubasnici

Survey of Jama na Dubasnici (gif, 12 k)

DEPTH:                 276 m
LENGTH:                -
LOCATION:              Dubasnicka povrs

The cave is located in the central part of a heavily karstified area of Dubasnicka povrs, covered with dolines and dense forest. The entrance to the cave lies at 840 m a.s.l. The cave is known to local foresters by the name "Gaura Frndjefund", which on local Vlaski language means "bottomless pit".

The first explorations were held by DI "V.M.Manda" at the beginning of the eighties, without reaching the bottom of the pit. The complete exploration was done by the joint group made by ASAK and SOB from Belgrade, and SD "Platak" from Rijeka. Due to an inaccurate survey (the first results showed the depth of -320 m), in 1982. and 1983. new explorations were held, but without success, due to huge ice deposits at the entrance. In 1984 the cave was completely surveyed and explored, by the joint group of ASAK, SOB and DI "V.M.Manda".

When explored for the first time, Jama u Dubasnici was the first known cave in Serbia with the depth exceeding 200 m. From 1980 till September 2000, it was the deepest cave explored in Serbia.

The cave entrance is located in a doline which is 15 m deep and 40 m in diameter. The entrance part consists of three separate pits which join at the depth of 80 m. In its first 40 meters, the cross-section of the pit remains a simple 4 x 10 m elliptical shape. Later on, the cross-section becomes more complex, guided mainly by the orientation of initial fissures. The shaft breaks at 120 m, where a deposit of wood and a boulder choke are encountered. Further on, down to150 m, the dimensions of the pit are rising to 12 x 7 m, while the walls are eroded by water in greater extent. The next terrace is encountered at the depth of 175 m. It is formed of meter-scale boulders covered with rock debris. Below the terrace, the final 53 m deep pit leads to the ending chamber. In its eastern part, at the bottom of the pit, a 10 m high boulder pile is encountered. The ending chamber has an elongated shape, 81 m long and 45 m wide, with the height of 15 m. Its floor is completely covered with clay.

The cave is formed in Upper-Jurassic limestone, with calcite incrustrations and layers of sandy limestones. In its surface parts, the rock is heavily tectonized, and the fissures are filled with calcite filling. At greater depths, the number of fissures is decreasing, only the initial fissures, which led to the forming of the cave, being left visible.

The travertine coating in the northern and southern part of the ending chamber indicate the presence of water circulating from those directions, while generations of calcite deposits on the walls and the floor indicate the significant hydrological activity of the cave. Characteristics of the deposits in the ending chamber, and the water-level traces on the walls, indicate that in certain periods, a slowly dripping water accumulation appears in the ending chamber.

text by Mihajlo Mandic

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