If this was the eruption of a supervolcano on an island I would guess that island no longer exists but was blown into the atmosphere and caused the global cooling.
Or possibly an underwater volcano no one knows about..................
https://www.activenorcal.com/giant-underwater-volcano-discovered-off-the-northern-california-coast/
Or possibly an underwater volcano no one knows about..................
https://freerepublic.com/focus/f-chat/4142850/posts