About 20 km south of Chyl Ustun, in the Tuy-Moyun mountains, lies the deepest cave in Kyrgyzstan. It is named after Fersman and has a depth of 240 meters. Other well-known caves are also located here: Surprise (450 meters long) and Victory (1200 meters long). Their underground halls and passages are adorned with crystalline formations of various colors.
Fersman (4580/-219 m). It is located approximately 2 km west of the Dangi gorge. The Aravan River cuts a deep canyon through the Tuy-Muyun mountain, on the left bank of which is the deepest cave - the Fersman Abyss, with a depth of 240 m.
The worked-out radium mine, colloquially known as Fersman Cave, is a grim, smoky underground realm, with a network of tunnels, drifts, and natural cavities. Continuous spans reach up to 200 meters. The cave was exploited as a radium deposit, and later for uranium since the early 20th century. By the end of the 1950s, it was completely exhausted and closed (the entrances were sealed or blown up).
The total length of ancient karst cavities and artificial workings in the Fersman system is 4130 m.
The entrance hole, measuring 0.5-1 m, is oriented to the northwest.
The cave, a horizontally inclined karst cavity, is embedded in Paleozoic limestones of the Upper Devonian - Lower Carboniferous. It is named in honor of Academician A. E. Fersman.
The cave is located in a karst hollow on the right bank of the Terpeli stream, 6 km northeast of the village of Tochilny. The entrance to the cave opens at the bottom of a large elliptical-shaped karst sinkhole (5x13 m), oriented with its long axis from southeast to northwest.
The entrance hole, measuring 0.5-1 m, is oriented to the northwest. Following it is a vertical shaft 3.5 m deep. From the bottom of the shaft, an inclined corridor 3 m long leads into a vast grotto measuring 6x14 m, oriented from east to west. From it, three dead-end passages lead upward to the north, each 5-7 m long. Their floors are covered with a layer of karst clay, and stalactites grow on the ceiling of one of them. They are also present on the ceiling of the grotto. Here, in the vault of the grotto, two organ pipes rise up to 5-6 m. In the far part of the grotto, there is a limestone pillar-ostanets 1 m high, supporting the vault. 4 m from it, in the southern wall of the grotto, speleologists uncovered a passage in the debris - the beginning of a system of meandering passages with a total length of 37 m. They extend along tectonic fractures stretching from northwest to southeast (a section of a major tectonic fault - the Ashinsky fault). Immediately behind the entrance on the right is a low passage 10 m long; its ceiling in the far part is dotted with conical stalactites.
The main passage of the system stretches first to the southeast (12 m), then turns at a right angle to the northeast (8 m) and again to the southeast (7 m). The meander ends with 3 passages ranging from 2 to 7 m long, narrowing to impassable cracks. In the northwest wall of the passage, an impassable hole was discovered, behind which a fairly large cavity is visible - possibly a continuation of the cave.
The floor of the main passage of the system has a slight slope to the southeast. Along its entire length, a canyon-like channel of an underground stream, 0.2-0.3 m wide and up to 1-1.5 m deep, is traced in the monolithic limestone rock. It is filled with water, and the bottom is covered with coarse gravel. The cave features dripstone calcite formations (stalactites, stalagmites, small stalagnates-columns, ridges, flag-like drips of white color, and rare eccentric stalactites-helictites).
The total length of the cave passages is 107.6 m, with a depth of 14.3 m; the average width of the passages is 1.6 m; the average height is 1.9 m; the floor area is 82 m²; the volume of the cavity is 90 m³.
The cave was discovered and explored in August 1994 by young speleologists from the Chelyabinsk club "Omega" (led by P. N. Sivinsky) and the Miass club "Agat" (A. P. Kozlov).
