Krakatoa

Sometime prior to his third incarnation, the Doctor witnessed the eruption; during this event, he also hears Primords for the first time ("Inferno"). That same day, a sketch of the Ninth Doctor washes up on a beach on Sumatra - implying, perhaps, that the Ninth Doctor also witnessed the eruption. It eventually finds its way into Clive Finch's collection of artifacts related to the Doctor ("Rose"). The Tenth Doctor and Rose visited Indonesia, encountered the alien Chalderans, and escaped in the TARDIS just as the volcano erupted (Doctor Who Adventures comic strip: "Under the Volcano").