The last volcano eruption near Santorini & Therasia island complex was in 1950, in the Central caldera, forming the landscape of of Old & New Kammeni, more or less as we know it today. The other force that effects the landscape of Santorini is mass tourism and infrastructure explosion coming with it, which is hard to neglect, yet it is still possible. Large parts of the island complex keep quiet, waiting for the next volcanic eruption in the area. Most probably it will come from the Southeast and the Kolumbo crater, an active underwater volcano ~8km away from Santorini, which last erupted in 1650.

Reference: Waiting for Cousteau – Jean Michel Jarre, 1950