World’s deepest freshwater cave in Moravia deeper than previously thought

The Hranice Abyss

The world’s deepest freshwater cave, the Hranice Abyss in Moravia, is even deeper than previously thought. A team of researchers have recently carried out a new survey of the deep limestone cave, using a special underwater robot, reaching a depth of 450 meters. The previous record, measured in 2016, was 404 meters. However, experts say they are still far from reaching the bottom of the pit.

Photo: ČSS ZO 7-02 Hranický kras

To measure the depth of the Hranice Abyss, speleologists used a special, remotely operated underwater robot, dubbed the Death Star, equipped with six cameras and sonar beams. The robot was attached to ropes and was gradually submerged into the deep, limestone cave, flooded with cold and muddy water.

It stopped at a depth of 450 meters, which is the maximum it can reach due its technical limitations, but it still hasn’t hit the bottom of the abyss.

Geologist Michal Geršl says that the ultimate depth could be as much as several kilometres:

Photo: Barbora Sonnková,  Czech Radio

“The gases that come out of the water consist mainly of carbon dioxide, but there is also a tiny amount of helium. It comes from the upper part of the Earth’s mantle, which is around 40 kilometres deep.

“This means that there must be some pathways, which are narrower and narrower and which are obviously not accessible to us, that run in depths that we cannot even imagine.”

In addition to pushing the boundary of the world record, experts have also obtained valuable data about the shape of the flooded part of the abyss. During the dive, the robot took pictures of the rugged karst terrain to create a detailed 3D map.

Michal Guba is the chairman of the speleological society in the Hranice karst:

Photo: Lenka Kratochvílová,  Czech Radio

“It is actually a map at a depth of 200 to 430 meters. Until now, we didn’t even have a sketch of this area. Unfortunately, greater depths are no longer accessible to divers, so only a robot can move around there. Now we have got that mapped out, which is great.”

Mr Guba says the research of the Hranice Abyss is set to continue in the future, as soon as they obtain better technical equipment that will allow them to descend even deeper.

“We have agreed with a Hungarian company with whom we are conducting the survey that they will purchase a new piece of sonar equipment within a year that will have the ability to reach at least 1,500 metres, so we could go as deep as that, if the abyss lets us.”

The Hranice Abyss | Photo: Jana Zemková,  Czech Radio

The Hranice Abyss has held the world record since September 2016, when a team of speleologists, led by the legendary Polish diver Krzysztof Starnawski, submerged into the deep limestone cave. At the time, the robot reached a depth of 404 metres, which was as deep as its rope would allow it to go.

Authors: Ruth Fraňková , Lenka Kratochvílová
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