irrupt

Irrupt and "erupt" have existed as discrete words since the 1800s. Both are descendants of the Latin verb rumpere, which means "to break," but "irrupt" has affixed to it the prefix ir- (in the sense "into") while "erupt" begins with the prefix e- (meaning "out"). So "to irrupt" was originally to rush in, and "to erupt" was to burst out. But it's sometimes hard to distinguish the precise direction of a violent rush, and "irrupt" came to be used as a synonym of "erupt" in the senses "to become active or violent especially suddenly" and "to break forth," as in our example sentence.