Rock from upper bits of tundra: igneous lava terrain (4)

I believe the answer is:

tilt

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'rock from upper' is the definition.
'tilt' can be an answer for 'rock' (synonyms). I'm not certain of the 'from upper' bit.

'bits of tundra igneous lava terrain' is the wordplay.
'bits of' says to take the initial letters.
The first letters of 'tundra igneous lava terrain' is 'TILT'.

Can you help me to learn more?

(Other definitions for tilt that I've seen before include "Inclination, joust" , "Stab" , "Lean, slope" , "Lean to one side" , "Incline, slant" .)

I've seen this clue in The Guardian.

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