Learn Icelandic: Sterkur straumur kemur einhvaðan að ofan. - A strong current comes from somewhere above.

Einhvaðan specifically means "from somewhere", indicating motion away from an unknown origin. Because the verb koma (to come) involves movement from a source, you must use a directional adverb. Einhvers staðar means "somewhere" in a stationary sense, which would not make sense here.

Since að usually means "to" or "towards", why does að ofan mean "from above"?

This is a classic trap for English speakers! In Icelandic, spatial adverbs ending in -an (like ofan, neðan, innan) already contain the meaning "from [direction]". The preposition að is idiomatically paired with them to describe the surface or direction something originates from. Think of að ofan as a fixed phrase meaning "from above".

If the current was flowing to an unknown place, how would the adverb change?

You would swap out the "motion from" adverb for a "motion towards" adverb. Einhvaðan (from somewhere) would become eitthvert (to somewhere), which is the other focus of this lesson. For example, if it flows "to somewhere up above", you might say Straumurinn fer eitthvert upp.

Could I just write einhvaðan ofan without the að?