Fall caused by slip at the end of the mountain pass (8)
I believe the answer is:
collapse
'fall' is the definition.
(collapse can mean to fall down)
'slip at the end of the mountain pass' is the wordplay.
'slip' becomes 'lapse' (lapsing is a kind of slipping).
'at the end of' says to put letters next to each other (some letters go at the end of others).
'the mountain pass' becomes 'col' (col is a kind of mountain pass).
'lapse' put after 'col' is 'COLLAPSE'.
'caused by' acts as a link.
(Other definitions for collapse that I've seen before include "Break down - fall" , "Give way, fail suddenly" , "Fall down suddenly like escallop" , "Sudden fall" , "Sudden breakdown" .)