Patch of loose rock that aptly rhymes with "debris" (5)
I believe the answer is:
scree
(Other definitions for scree that I've seen before include "Loose debris on a mountain slope" , "Mass of loose rocks at the base of a cliff" , "Small loose stones on a mountainside" , "Loose stones around a mountain" , "Sloping mass of loose rock at the base of a cliff" .)