One can initially walk steadily over a lot of compacted snow (3,3)
I believe the answer is:
ice cap
'a lot of compacted snow' is the definition.
(ice caps are made of ice and snow)
'one can initially walk steadily over' is the wordplay.
'one' becomes 'i' (Roman numeral).
'initially' indicates taking the first letters.
'walk steadily' becomes 'pace' (to pace is to walk steadily).
'over' is a reversal indicator.
The initial letter of 'can' is 'c'.
'pace' back-to-front is 'ecap'.
'i'+'c'+'ecap'='ICE-CAP'
(Other definitions for ice cap that I've seen before include "Permanent covering of frozen water" , "one providing cover for Pole" , "Cold mass permanently covering the polar regions or mountain peaks" , "Polar feature" , "Permanently frozen mountain-top mass" .)