roll down vs avalanche

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

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

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

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

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

roll down (verb)	avalanche (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