STALACTITE, STALAGMITE AND MINERAL FILLINGS

Geyser stalagmites are a phenomenon of the Zbrašov caves that is unique in the world. They have a characteristic conical shape and are up to several centimetres high. There is a hole in the top of the stalagmite and from the longitudinal cross-section it is apparent that the stalagmites “grew” in layers. Their central input channel cannot be proved with certainty, but their porous structure is quite distinct. There are two theories of their origin and growth. One of the theories supposes that they were formed by crystallization of calcium carbonate in places where mineral water sprung to the caves from the depths. The second one inclines towards the opinion that the stalagmites are so-called raft cones which developed on the bottom of cave lakes as accumulations of thin sinter crusts. They were primarily formed by evaporation of water on the lake surface (they were floating – therefore “rafts”). Then they were successively broken by dripping water and finally sank to the lake bottom. Their conical piles on lake bottoms were then strengthened by subsequent recrystallization. Raft stalagmites were already described in the caves around the world and the mentioned theory was applied to the Hranice Karst only when loose formations of similar shapes were discovered by divers in the depths of the Hranice Abyss.

Up to several decimetres thick coatings of the walls and ceilings together with round shapes of “doughnuts” are formed predominantly by calcite with admixture of iron oxides. These hydrothermal sinters were formed on the walls under the surface of underground lakes of mineral water. According to their laminated structure and distinct colours they are also called “the Hranice onyx”.