We contrived with lieutenant to break mother's fall down a mountain? (9)

'fall down a mountain?' is the definition.
I can't judge whether this definition defines the answer.

'we contrived with lieutenant to break mother's' is the wordplay.
'contrived' indicates anagramming the letters.
'with' means one lot of letters goes inside another.
'lieutenant' becomes 'lt' (abbreviation for lieutenant).
'to break' is an insertion indicator (inserted letters break into the word).
'mother' becomes 'mater' (old-fashioned term for mother).
'we' is an anagram of 'ew'.
'ew' placed around 'lt' is 'eltw'.
'eltw' inserted within 'mater' is 'MELTWATER'.

Can you help me to learn more?