New research shows world’s deepest cave in Moravia is even deeper

Hranice Abyss, photo: Radek Klanica

A team of geologists from the Czech Academy of Sciences say their research shows that the world’s deepest cave – Hranice Abyss in Moravia – is twice as deep as previously measured. One of the team’s geologists, Radek Klanica, spoke to Radio Prague International. I began by asking him about the significance of their research. 

“I think it was quite important to extend the study and try to find out how deep this cave really is, because during the last attempt the remotely operated vehicle stopped at the depth of 400 meters and no one really knew how deep the cave is.”

I understand we still do not definitively know how deep the cave really is. How deep do we think that it is now?

ARESII equipment for electrical resistivity tomography, photo: Radek Klanica

“We tried a study using the geophysical method. By which we can measure different physical fields on the earth’s surface and since these physical fields reflect the distribution of rocks we are able to describe the sub-service.

“We did some quite substantial research. When we combine these results with the geological development of the area, we are able to reveal a new interpretation of the Hrancie Abyss origin and our results suggest that the abyss is 1km deep.”

And that is the final length, or could it be even deeper?

“Well, we think that this is the final depth, but of course the abyss has to be connected to deeper parts of the Earth’s crust, especially the mantel, because the water in the abyss is averaged by carbon dioxide and other elements which geochemical analysis suggests are coming from this depth.

“Our results suggest that the abyss is 1km deep.”

“However, these elements are probably just rising along some faults or small cracks, so we think that the abyss depth of 1km is final.”

Is there a reason why the deepest cave lies in the Czech Republic geologically?

Hranice Abyss, photo: Radek Klanica

Well, the Hranice Abyss is located along the large geological contact between the Bohemian Massive and the Carpathian Mountains, so there can be really large and deep faults in this area.

“However, it is probably just a coincidence that it originated here in this Karst area.”

I understand it formed around 20 million years ago or when exactly?

“The most prevalent idea is related to hydrothermal processes.

“People for a long time thought that the abyss originated from below upward when the ground water gradually dissolved the upper rock thanks to these acidic elements of deeper origin.

Gravity meter for measuring of gravitional acceleration, photo: Radek Klanica

“However, we came up with another explanation which relates its origin to the presence of canyons around 20 million years ago.

“We basically think that the waters which ran on the surface at the time did not run on the edges of the canyon, but that the water found its way into a sub-surface near the canyon and carved its way into the limestone sequences all the way to the bottom of the canyon.”

The cave is also specific because it is not filled with rainwater, but rather with much older water that is bubbling from below. What type of water is this exactly and where did it come from?

“It is mineral water enriched by a lot of specific elements.

“When we try to determine the age of groundwater we analyse especially the presence of chlorofluorocarbons and tritium, which contaminated waters around the earth from around 1950.

“We came up with a new explanation which relates [the cave’s] origin to the presence of canyons around 20 million years ago.”

“The analysis shows that these are virtually not present in this water, so it must be older.”

Polish explorer Kryzstof Starnawski has been exploring the cave for several years now and told National Geographic last year that there is nothing typical about this cave and that new discoveries are made with every dive. What other great questions are there still surrounding the cave?

“Certainly the depth itself.

“We do have some suggestions from our methods, but we cannot be certain that it really is 1km deep.

“I hope that in the future there will be some further dive or some remotely operated vehicle that can reach the bottom of the abyss in order to prove or disprove our theory.”