Combustible heap seen over the mountains (8)
I believe the answer is:
pyrenees
'mountains' is the definition.
(I've seen this before)
'combustible heap seen over' is the wordplay.
'combustible heap' becomes 'pyre' (I've seen this before).
'over' says the letters should be written in reverse.
'seen' in reverse letter order is 'nees'.
'pyre'+'nees'='PYRENEES'
'the' acts as a link.
(Other definitions for pyrenees that I've seen before include "European mountains" , "Mountain range between France and Spain" , "Andorra in these mountains" , "Mountain range in southwest Europe" , "Mountain chain between France and Spain" .)