avalanche vs roll down

avalanche is a noun but roll down is not a noun.

Word	Noun	Adjective	Verb	Adverb
avalanche	Yes	No	Yes	No
roll down	No	No	Yes	No

As verbs, avalanche and roll down are synonyms defined as:

avalanche and roll down: gather into a huge mass and roll down a mountain, of snow

avalanche (noun)	roll down (noun)
a slide of large masses of snow and ice and mud down a mountain
a sudden appearance of an overwhelming number of things

avalanche (verb)	roll down (verb)
gather into a huge mass and roll down a mountain, of snow	gather into a huge mass and roll down a mountain, of snow