Military camp declared strength, lengthening column (10)

I believe the answer is:

stalagmite

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'lengthening column' is the definition.
Although both the answer and definition are singular nouns, I don't understand how they can define each other.

'military camp declared strength' is the wordplay.
'military camp' becomes 'stalag' (German prison camp in World War 2. I am not sure about the 'military' bit.).
'declared' indicates a 'sounds like' (homophone) clue.
'strength' becomes 'might' (might is a kind of strength).
'might' sounds like 'mite'.
'stalag'+'mite'='STALAGMITE'

Can you help me to learn more?

(Other definitions for stalagmite that I've seen before include "Effect of dripping" , "A mound of calcium carbonate" , "Column made by dripping water" , "One that grows up" , "What may form on cave floor" .)

I've seen this clue in The Independent.

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