The Palau Islands are located in the North Pacific Ocean, where old coral reefs rose above the sea.

Which is the adverb clause?

http://www.chompchomp.com/terms/adverbclause.htm

Let me know what you think.

The Palau Islands are located in the North Pacific Ocean, where old coral reefs rose above the sea.

Which is the adverb clause?

nmk,

The adverb clause in the given sentence is "where old coral reefs rose above the sea."