Before revision: Ruby Falls is an underground waterfall within a cave in Tennessee, USA A subterranean waterfall, tierous waterfall, or underground waterfall is a waterfall located underground, usually in a cave or mine.<ref 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.
After revision: Ruby Falls is a tierous waterfall within a cave in Tennessee, USA A subterranean waterfall, tierous waterfall, or underground waterfall is a waterfall located underground, usually in a cave or mine.<ref 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.