“Border Abyss” was twice as deep as it was thought

The Border Abyss in the Czech Republic is the deepest flooded cave in the world. Another expedition to the abyss showed that it is much deeper than previously thought. In 2016, cavers determined that the depth of the cave is 475.5 meters, but new data says that this figure is twice as much.

In 2016, researchers using a remote-controlled underwater vehicle estimated the depth of the abyss at 473.5 meters. However, the fiber-optic communication cable did not allow the device to penetrate deeper, so the true size of the cave remained a mystery.

This time, the expedition managed to learn a little more about the abyss using a combination of geophysical methods. First, the scientists collected data on the array of electrodes on the surface, which showed how easily the limestone conducts electricity. This helped scientists find empty areas in the soil. They then used special sensors to look for deviations in gravitational thrust and recorded reflected seismic waves caused by the explosion of small charges. So scientists were able to make a rough map of what is underground.

The findings revealed a system of deep, trench-like limestone caves. As it turns out, this network of trenches extends about a kilometer below the surface, much deeper than previous estimates.

Scientists say that in addition to the depth of the Border Abyss, specialists will most likely have to reconsider its origin. The abyss is located in a karst, that is, in a place where water very quickly dissolves rocks, forming voids. Most caves form from top to bottom (from the surface) when water from rain or melted snow penetrates the ground, “eating” the rock and creating cracks that expand over time. Deep caverns, however, can also form from the bottom up, when acidic groundwater heated by the earth’s mantle rises upward due to boiling. Previously, researchers believed that the Border Abyss belongs to the second category, because its waters contain isotopes of carbon and helium, which come from the depths of the Earth. However, on a new expedition, researchers found evidence of an ancient drainage system in the limestone, suggesting a surface origin of the abyss.

This study means scientists may have to rethink the origins of other deep caves, supposedly formed from the bottom up.

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