WHAT’S ALL THE FUSS ABOUT
The Hranice Abyss is officially, according to the total measured depth of 473.5 meters, the deepest abyss in Czech Republic. In addition, the flooded section at currently documented depth of 404 meters, makes it the deepest underwater cave in the world. Recent explorations unraveled new frontiers for further exploration as the actual bottom has not been discovered.
The abyss is located in natural reservation of Hurka, in the municipality of the city Hranice in Olomouc County. The site is accessible on foot via educational trek path (marked by red color orientation signs) originating from the train station Teplice nad Becvou, or from the city official car camping spot. Brand new viewing deck allows visitors to experience bird eye view of the dry part ending with a little green pond, the entrance to the flooded part. The conical hole is 104 meters long, 34 meters wide and 69.5 meters deep.
ETYMOLOGY OF THE NAME
The name of this extraordinary natural site “the Abyss” has been firstly mentioned in hand written maps of South Morava by J.A. Komensky in the year of 1627. Later on, just before the Second World War, we can find several newspaper articles comparing “the Abyss” to, not so far away, gorge known as Macocha – where the dry part is much deeper and ends with a dry cave of the same name, renaming “the Abyss” to “the little Abyss”. However, such naming has not been generally accepted and from the 1960s the site retains name “Hranice Abyss” until this very day.
First written reference of the existence of the Hranice Abyss has been noted in the year of 1580 by Tomas Jordan from Klauznburk. Later, as mentioned above, Jan Amos Komensky has noted the site to one of the first maps of Morava, making Hranice Abyss to be the first geological site of such kind to be officially recorded. Unfortunately, the original hand written maps have disappeared in time, and only a printed reproduction from 1627 provides such indication.
The Abyss is located in Hranický Kras, which is situated on both banks of the Bečva River between the towns of Hranice, Teplice nad Bečvou and Černotín. This small karst area of approximately 5.5 x 4 km in size and is formed by several “islands” of Devonian limestone, emerging from the younger rocks. Directly on the left bank of the river, there is the largest known cave system of the Hranický kras - Zbrašovské aragonitové jeskyně, which are open to the public. The Abyss lies on the right bank of the river.
HOW HAS THE ABYSS BEEN CREATED
Zbrasovske Aragonite Caves and Hranice Abyss have been created by the same hydrothermal erosion process. The creation of these caves is unique due to the fact that the vast underground cavities have been created from bottom up, rather than the regular, top bottom process. The water present is acidic saturated with carbon dioxide. Combination of these chemical characteristics with adequate water pressure provides ideal conditions for dissolving the limestone. In fact, thanks to the combination of these factors we are now-a-days able to explore this fantastic underwater cave. Without it, the ceiling of one of the cavities would not collapse, and there would be no entry point to the flooded labyrinth.
WHY IS IT SO DEEP
Few years ago, the general consensus estimated the depth of the Hranicka Abyss equivalent to the thickness of the limestone. However, with new chemical analyses of the water, apart from the above mentioned chemical composition, there are also trace amounts of helium. By several measurements in time, from various depths, we are certain that the helium dissolved in water comes from 40 km below the surface – from the top earth crust. This allows for a new theory, where we can, with high confidence, claim that thermal fluids, before surfacing pass through extremely old layers of earth crust, so called lithospheric plates. In other words, this would make Hranice Abysses depth of unimaginable depths that can range from a single to tens of kilometers. Unfortunately, we have currently no technological capability to prove such theses.
The few hundred meters of depth of the abyss is continuously flooded with warm water rich in carbon dioxide. It is only a tiny layer of surface water that maintains regular fresh water properties. Under this thin fresh water surface, we can find same decoration as we can admire in Zbrašovské jeskyně, especially unique raft stalagmites. Some types of decorations, such as the so-called "volcanoes", are quite specific and we are intensively researching them.
FLORA AND FAUNA
The abyss is also a phenomenon in terms of bats. In the part called the Suchá Rotunda, dry dome of the cave, we have discovered the only one colony of large underground bats in the Czech Republic. Their habitat in the Abyss system is the northernmost occurrence of this species north of the Alps. In addition, the Abyss is provides the right environment for sustaining four critically endangered bat species and other five species included in the NATURA 2000 system. The open part of the Abyss also creates favorable conditions for the growth of critically endangered hart's-tongue fern.
Contributed by: Barbora Šimečková, Milan Geršl, January 30, 2017