by ian mckenzie » Aug 2, 2011 6:57 pm
There are lots of water-filled caves beneath active rivers. But there are a surprising number of air-filled caves beneath rivers too. I can think of one we did on the Nomash River on Vancouver Island; the entrance was right beside the river, and it dropped down then crossed beneath the river - in fact took a very small bit of water off the river and passed it thru the cave, a stream beneath the river. We explored it, but quickly, because even a half-inch rise in surface river levels would have sumped the cave beneath completely.
Creekside Pot entrance to Glory 'ole, also in on Vancouver Island, is located immdiately adjacent to a creek and would take a lot of that creek when it rose.
Doolin Cave System in Ireland runs beneath an active stream, and some water leaks into the cave from above. Some day the entire creek will punch into the cave, I guess.
Caledonia Cave in the Caribou Mountains of BC has a stream running overtop, which hooks back and then runs into the entrance. We diverted the thing away from the entrance to facilitate exploration, but it still runs on the surface overtop the cave.
I guess in a sense all caves are located beneath temporary surface waters, whenever it rains up top.