ice mass vs berg

ice mass and berg both are nouns.

Word	Noun	Adjective	Verb	Adverb
ice mass	Yes	No	No	No
berg	Yes	No	No	No

As nouns, berg is a hyponym of ice mass; that is, berg is a word with a more specific, narrower meaning than ice mass:

ice mass: a large mass of ice
berg: a large mass of ice floating at sea; usually broken off of a polar glacier

Other hyponyms of ice mass include glacier, iceberg, ice cap, icecap, ice field, floe, ice floe.

ice mass (noun)	berg (noun)
a large mass of ice	a large mass of ice floating at sea; usually broken off of a polar glacier