unexpectedly vs circumstantially

unexpectedly and circumstantially both are adverbs.

Word	Noun	Adjective	Verb	Adverb
unexpectedly	No	No	No	Yes
circumstantially	No	No	No	Yes

As adverbs, unexpectedly and circumstantially are synonyms defined as:

Other synonyms of unexpectedly include accidentally, by chance.

unexpectedly (adverb)	circumstantially (adverb)
without advance planning	insofar as the circumstances are concerned
in a way that was not expected	without advance planning
	in minute detail
	according to circumstances