World’s deepest freshwater cave goes down farther than we thought

In the context of the universe, our home planet—Earth—is less than a speck of dust. Less than a grain of sand.

But to us? It is an enormous world, full of hidden mysteries that we still don't know everything about. Tops on the list of 'alien worlds' here on Earth? The deep sea environments found at the bottom of the ocean. And just behind those? Caves.

Both of these places have a lot in common. They're deep, dark, and united by their great unknowableness. The Hranice Abyss in the Czech Republic (for 'Hranice' say pRah-neet-zuh). We do know that this is the deepest freshwater cave in the world. And thanks to a recent study, we now know that it goes deeper than we ever even imagined.

We just don't know exactly how deep that is!

New depths

Originally, the depth of the Hranice Abyss was said to be at least 473 metres (1551 feet). This is almost like burying the CN Tower underground and it already gave the Hranice Abyss the title of deepest freshwater cave on Earth. As the map attached to this tweet shows, this was already very impressive.

Map of the world's deepest underwater cave, the Hranice Abyss. We still don't know how deep it really is... pic.twitter.com/ywbsNd0eAA

— Amazing Maps (@Amazing_Maps) October 6, 2016

But thanks to a study released in August 2020, the cave has been proven to be at least one kilometre deep—that's 1,000 metres or 3,280 feet. You could almost bury two CN Towers, end-to-end, at that depth. Remarkable!

So how deep is it?

This is the big question at Hranice. Researchers have been trying for centuries to figure out its exact depth and even with all of the modern technology at our disposal, the true answer escapes us.

The new number—at least 1 km deep—wasn't found by diving or sending a probe. It was found by using geophysical sensors like a gravimeter to map out what is actually in the rocks below. (You could think of it like using radar through the rocks!) This technique is useful to get an estimation, or a very solid guess. But it can't produce a concrete number.

Will a probe or a human ever make it to the very bottom of the Hranice Abyss? If one does, that will be quite the epic journey!