World's deepest underwater cave found in Czech Republic - Hranická propast / Hranice abbys - Hranice (Central Moravia) - News Article Locations on Waymarking.com

The article in Guardian (September 30, 2016) informed readers about reaching the greatest known depth of the underwater cave in Hranická propast (Hranice abbys) in Hranice karst in the Czech Republic. The Hranice Abyssis a karst sinkhole located near the town of Hranice in Prerov County. The greatest confirmed depth (as of 27 September 2016) is 473 m (404 m under the water level), which makes it the deepest known underwater cave in the world.

With a total measured depth of 473.5 m, Hranická propast is the deepest abyss in the Czechia and, thanks to a record water depth of 404 m, it is also the deepest flooded abyss in the world. However, its bottom is still not reached. It is located in the Hurka u Hranic National Nature Reserve in the Olomouc Region. Walking access to the Hranická abyss is possible from the Teplice nad Becvou railway station along a nature trail or from the camping site in Hranice along the red tourist sign. The new viewing platform allows a wonderful view of the mouth of the abyss 104 m long, 34 m wide and 69.5 m deep. The apparent bottom of the mouth is formed by a green lake, but the abyss continues much deeper through giant flooded spaces.

People knew the Hranice abyss in ancient times. It appears in folk tales, which attributed its origin to supernatural forces. The first written mention of the Abyss is from 1580 by Tomas Jordan of Klauznburg. Jan Amos Komenský (Comenius) recorded it cartographically on the Map of Moravia so it is the first karst phenomenon drawn on the map in our country. The original drawing of Comenius' map has not been preserved, the work is known from the oldest printed version from 1627.

The Hranická abyss is located in the Hranice karst (Hranický kras), which is located on both banks of the river Becva between the towns of Hranice, Teplice nad Becvou and Cernotín. This small karst area with an area of about 5.5 × 4 km consists of several islands of Devonian limestone protruding from the younger rocks. The Hranice abyss lies on the right bank of the Becva. Directly opposite it, on the left bank of the river, is the largest known cave system in Hranice karst - the Zbrašov Aragonite Caves, which are open to the public.

The Brašov Aragonite Caves and the Hranice abyss were formed by a hydrothermal karst process. This is an atypical way of karstification, in which the spaces are created from the bottom up. The karst factor is not water, but a lukewarm mineral water heavily gassed with carbon dioxide. This aggressive acid emerging from the deep cracks dissolved the limestone massif from below. In the case of the Hranice abyss, it etched the cavity in the limestone so much that the thin ceiling collapsed and the cavity opened to the surface.

The described origin is also the reason for the extreme depth of the Abyss. The Abyss is filled with mineral water containing carbon dioxide, which carries with it trace concentrations of helium. It has been proven that helium comes from depths of about 40 km, i.e. from the Earth's upper mantle. Older theories related the depth of the Abyss only to the thickness of the local limestones. However, the new interpretation shows that thermal fluids permeate unknown rocks below the limestone formation, at the junctions of ancient continents (so-called lithospheric plates) deep in the geological past. The final depth of the Abyss can thus reach difficult values imaginable today, for example in the order of kilometers and their tens. Its measurement (if at all possible) is a matter of the very distant future...

Several hundred meters of abyss' depths are flooded by warm carbonated mineral water, only at the surface a thin layer of surface water is maintained. Below the surface of the mineral water, the same decorations are created as we can admire in the Zbrašov Caves, especially the unique raft stalagmites. Some types of decoration, such as the so-called "soplíky (snots)", are completely specific and their research is being intensively worked on.

Source: excerpted and translated from Wikipedia and Hranická propast portal.