block up vs close off

block up and close off both are verbs.

Word	Noun	Adjective	Verb	Adverb
block up	No	No	Yes	No
close off	No	No	Yes	No

As verbs, close off is a hyponym of block up; that is, close off is a word with a more specific, narrower meaning than block up:

Other hyponyms of block up include block off, shut off, close.

block up (verb)	close off (verb)
render unsuitable for passage	block off the passage through
	isolate or separate
	stem the flow of