The New Bull Rock (Nová Býčí skála) Cave and the Old Gallery (Stará štola) – an insight into an active fault

Vojtěch A. Gregor, Sborník Muzea Blansko 2012, p. 12-29.

In February 2013 Muzeum Blansko (the Museum of Blansko, City of Blansko, Czech Republic) published its yearly volume of studies and articles in both natural and social sciences – Memoir 2012. The memoirs are called the Sborník Muzea Blansko, SMB.

It used to be policy of the SMB to include a foreign language summary to major studies and articles, preferably in German. That policy has been recently abandoned. As a result, summaries of the following studies were not printed. Instead, they are presented below.

Summary

The Bull Rock (Býčí skála) Cave in the Josefov-Křtiny Valley of the Moravian Karst represents an underground streambed of the Jedovnice Creek and, for a part, also a paleo-resurgence cave of the stream. At high floods the paleo-resurgence part – the main passage of the Old Bull Rock Cave – becomes a flood streambed and the cave entrance(s) an active karst spring. The cave consists of several units named, from the entrance to the terminal Srbský (Serbian) siphon, Stará Býčí skála (Old Bull Rock Cave), Nová Býčí skála (New Bull Rock Cave), Prolomená skála (Broken-in Rock Cave) and Proplavaná skála (Swum-through Rock Cave). The present-day length of the complex, including the Barová jeskyně (Bar Cave), amounts to some 15 km.

Systematic speleological exploration of the Bull Rock Cave began in 1902. It was carried out by members of the Verein der deutschen Touristen in Brünn, Gruppe für Höhlenforschung (VdT-GfH, a German caving group in Brno, under the leadership of Günther Nouackh). In 1912, the cavers focused their attention on the key problem – the terminal point of the cave at the time, the Šenkův (Schenk's, Schenk) siphon. In 1920 their effort was crowned with a success – the overcoming of the siphon and the discovery of the New Bull Rock Cave with the underground Jedovnice Creek. This included diving (G. Nouackh), water pumping and, finally, drilling and blasting of submerged parts of the siphon roof (ceiling). Since 1947, namely from 1973 to 1985, Czech cavers gradually discovered the underground stream of the Jedovnice Creek between the New Bull Rock Cave and the Rudické propadání. They also have discovered the underground course of the creek between the Bull Rock Cave, the Bar (Barová) Cave and the springs in Josefov.

The New Bull Rock Cave, namely the Vysoký dóm (High Dome), Odporný komín (Loathsome Chimney), Stará štola (Old Gallery) and the newly discovered room, HMŠ (Head of a Dead Snail), provide a detailed insight into the interior of a prominent fault – so called JV zlom (SE fault). The fault is a deep-seated feature. It extends from the Precambrian crystalline basement (the Young Cadomian Brno Igneous Massif) through the entire Phanerozoic sedimentary sequence (Devonian basal clastics and carbonates, Mesozoic and Tertiary mantle deposits) to the surface of the Rudice Plateau. In the cave, it contains up to 3 m thick fill of zonal calcite and calcite breccia. The history of episodic movements along the fault goes from the Variscan (Hercynian) orogeny through the Saxon tectogenesis (the origin of the Blansko Graben) to the present. Recent movements are indicated by young breakdown – angular limestone and calcite blocks – in the HMŠ.

The fault and with it associated (sub)parallel fractures control approximately 100 m long stretch of the New Bull Rock Cave to the height of up to 70 m. Several chimneys are located along the fault, most of them with an active dropfall of meteoric water. The aggressiveness of the water accounts for rich, well pronounced corrosion forms. The Mesozoic (Lower and Upper Cretaceous) and Cenozoic (Paleogene) mantle sediments, including chert detritus (from Jurassic limestone) and Pleistocene loess (loess loam), sink and/or are washed down along the fault and through the chimneys. The fault also appears to control, at least to some extent, the course of upper cave levels – i.e., the course of the paleoflow of the Jedovnice Creek.

The New Bull Rock Cave could represent an interesting field trip stop for national and international speleological and geological meetings and congresses.