How long does it take for a cave to form?
Anything from a few minutes (if a cave is an opening under a rock over hang that is undercut by a stream and suddenly becomes a cave when a slab of rock falls off) to a few months to a hundred or thousand years. A highly abrasive water stream in a soft material environment can make a cave very quickly – take a look at some of the water cut pathways in Mount St. Helens surrounding area and caves in glaciers when melt water with sediment finds a path. The empty cave can form in soft gypsum in a few years, harder limestone may take decades or longer.
