Subterranean waterfall
A subterranean waterfall, tierous waterfall, or underground waterfall is a waterfall located underground, usually in a cave or mine. They are a common feature in cave systems where there are vertical or near vertical geological structures for the weathering process to exploit, and sufficient gradient between the sink and the rising. Notable examples include Ruby Falls, 44 metres (144 ft) high, in Chattanooga, Tennessee and Gaping Gill in the Yorkshire Dales, UK with a fall of 98 metres (322 ft). The highest known subterranean waterfall is in Vrtoglavica Cave in Slovenia, and is at least 400 metres (1,300 ft).