On Mon, 23 Mar 2009 21:42:55 -0700 (PDT), Frogwatch
wrote:

Very true. Natural rockfalls in caves are very rare. Most of the
rocks that could fall already did so long ago. In all my years of
caving, I only saw one rock fall by itself.

Some mountain climbing involves walls, that is more than 60 deg.
Water will seep into cracks in the rock and freeze at night, expanding
the crack. It stays in place for the time being, glued in place by the
ice. Next day, when the climbers are on it, the ice melts, and the
rocks loosened the night before come down in a steady shower.
The Eiger, in the Alps, is notorious in the literature, and a movie,
for deadly falling rock. Caves don't usually have freeze/thaw. And,
while you can get seriously wet in a cave, there is no wind.

Casady