Found mountain hollowed out by a jet of water (8)
I believe the answer is:
fountain
'jet of water' is the definition.
(I've seen this before)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for fountain that I've seen before include "Give out" , "Artificially-produced jet of water" , "Artificial jet of water" , "Ornamental water feature" , "Ornamental water-jet" .)