Could someone please clarify somethting about the following sentence, taken out of a work by Roald Dahl?
über die ein gewaltiger Wasserfall herabdonnerte, in gischtsprühende und wild wirbelnde Strudel hinein
Why does 'wild' not agree with Strudel? (It has no ending.) Is it because it is used as an adverb and not an adjective?