Hellenic Arc The mostly inactive east-west volcanic chain on the Hellenic Plate which is associated with the subduction of the African Plate. Santorini is located in the middle of the arcThe islands were shaped by volcanic activity First activity is estimated at 650000 years ago. -- submarine eruptions and regional uplifting of the southern part of Santorini has under gone a new cycle as of 2011 IN THE PHOTOView of the caldera of Santorini [AE SEEN FROM AKROTIRI]-which was created by a pyroclastic explotion with expanding gases that have awesome features like heavier-than-air emulsions that they are fiercely hot; contain toxic gases; and move at phenomenal; hurricane-force speeds; often over 100 km / hour. They are the most deadly of all volcanic phenomena.