RESEARCH ARTICLE Hypogenic Versus Epigenic Origin of Deep Underwater 10.1029/2020JF005663 Caves Illustrated by the Hranice Abyss (Czech Key Points: — • Hypogenic and epigenic evolution is Republic) The World's Deepest considered for deep underwater caves Freshwater Cave • Geophysical models show geometry Radek Klanica1 , Jaroslav Kadlec1 , Petr Tábořík2,3 , Jan Mrlina1 , Jan Valenta2 , and extent of the Hranice Abyss 1 1 • A new formation model of the Světlana Kováčiková , and Graham J. Hill Hranice Abyss based on epigenic 1 2 formation is presented Institute of Geophysics, Czech Academy of Sciences, Prague, Czech Republic, Faculty of Science, Institute of Hydrogeology, Engineering Geology and Applied Geophysics, Charles University, Prague, Czech Republic, 3Institute of Rock Structure and Mechanics, Czech Academy of Sciences, Prague, Czech Republic Correspondence to: R. Klanica, Abstract Extremely deep freshwater filled cave systems are common in karst systems globally. The
[email protected] origin and evolution of such caves are usually attributed to hypogenic (bottom‐up) processes, in which acidic groundwater dissolves limestone from below. However, these deep cave systems can form by epigenic Citation: (top‐down) processes, with meteoric waters descending from the surface underground. The Hranice Abyss Klanica, R., Kadlec, J., Tábořík, P., Mrlina, J., Valenta, J., & Kováčiková, S., (Czech Republic), with a reached depth of 473.5 m, is the deepest mapped extent of such a system et al. (2020). Hypogenic versus epigenic globally, although its maximum depth is unknown. Multiple geophysical data sets (gravity, electrical origin of deep underwater caves resistivity tomography, audiomagnetotellurics, and seismic refraction and reflection) are used to investigate illustrated by the Hranice Abyss (Czech Republic)—The world's deepest fresh- the extent and formation of the Hranice Abyss.