outflow cave, effluent cave

outflow cave - a cave from which a stream flows or formerly did so and which cannot be followed upstream to the surface.

Gillieson, 1996

outflow cave : Cave from which stream flows out or formerly did so. Synonym, effluent cave.

Monroe, 1970

FUNCTION	from which stream flows out or formerly did so
RESULT	from which a stream flows or formerly did
ATTRIBUTE	which cannot be followed upstream to the surface