Rockfall of spill and rubble (8)
I believe the answer is:
landslip
'rockfall' is the definition.
(I've seen this before)
'spill and rubble' is the wordplay.
'rubble' indicates anagramming the letters (I've seen this in other clues).
'spill'+'and'='spilland'
'spilland' anagrammed gives 'LANDSLIP'.
'of' is the link.
(Other definitions for landslip that I've seen before include "Avalanche" , "Earth movement" , "Fall of earth, stones, etc down slope" , "Rockfall" .)