When novarupta in Alaska erupted around 100 years ago it drained a nearby volcano (Katmai or something like that?). They first thought the drained volcano was the one that erupted, but it was another crater around a mile away I think. NPS has a good article on it: https://www.nps.gov/articles/aps-v11-i1-c2.htm

Correction: the erupting crater was 6 miles from Mt. Katmai!

Novarupta was largest of 20th century BTW.