For decades, spelunkers have flocked to the flooded caverns of the Czech Republic’s Hranice Abyss, which stretches farther below ground than any other freshwater cave system. Now, a scientific campaign to the cave has revealed it is 1 kilometer deep, more than twice as deep as previously thought. The researchers also say the abyss formed as groundwater seeped down from the surface, not as water percolated up, as previously believed—a finding that could call into question the origin of other deep caves.
Now, scientists have revealed a clearer picture using a combination of geophysical techniques.
Klanica and his colleagues also found evidence of an ancient groundwater drainage system in the limestone, suggesting a new, aboveground origin for the abyss-
The resulting picture revealed a system of deep, trenchlike caverns—some filled with sediment—that had been carved from the limestone, Surprisingly, these sediment-covered trenches extend to about 1 kilometer below the surface—far deeper than previous estimates, the team reported this month in the Journal of Geophysical Research: Earth Surface.