The Hranice Abyss is so deep that it could accommodate the Burj Khalifa, the tallest building in the world.
The Hranice Abyss, known as Hranická propast in Czech, is the deepest known freshwater cave in the world, according to Live Science. Geologists believe it may extend over a kilometer below the Earth’s surface, more than twice the depth of the second-deepest freshwater cave.
The Hranice Abyss is located in eastern Czech Republic. (Photo: Alamy)
The Hranice Abyss challenges long-held scientific beliefs that deep caves form from the bottom up, with warm groundwater rich in acids rising and dissolving the bedrock. A study published in 2020 in the journal Geophysical Research: Earth Surface suggests that this is not how the Hranice Abyss was formed. Instead, evidence indicates that water has eroded the cave from the top down.
Scientists first described the Hranice Abyss in 2016 after conducting multiple dives into the cave. The research team then deployed remotely operated vehicles (ROVs) to explore many corners that divers could not access and measured a maximum depth of 473.5 meters. This makes the Hranice Abyss the deepest freshwater cave in the world, surpassing the Pozzo del Merro, which is 392 meters deep in Italy. However, the recorded depth is limited by the length of the fiber optic cable attached to the ROV.
The 2020 study utilized gravitational and seismic imaging methods to investigate the depth of the Hranice Abyss. The results showed that the cave is more than double the depth previously measured by the ROV, deep enough to accommodate the tallest building in the world, the Burj Khalifa (828 m).
The mouth of the Hranice Abyss is a sloping chamber with a small lake at the bottom, according to the latest research. The underwater portion of the cave is an irregular vertical cylinder with a diameter of 10 to 30 meters. The water temperature inside the cave ranges from 14.5 to 18.8 degrees Celsius, depending on the time of year.
Extensive mapping has also revealed that the bottom of the cave connects to a nearby sinkhole known as the Carpathian Foredeep. The sinkhole is located 1.2 kilometers from the cave entrance, formed 19 million years ago and filled with sediment, meaning it is not visible on the surface today.
The Hranice Abyss formed after the sinkhole, approximately 14 to 16 million years ago, when water began to seep through soluble rocks like limestone. This process gradually created a deep cavity over time, eventually forming a channel for water to flow from the surface down to the bottom of the sinkhole. However, as sediment sealed the mouth of the sinkhole, water began to accumulate within the channel, leading to the creation of the water-filled cave.
