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 PHOTO: VIEW OF POMICE FROM THE MINIONIAN EXPOSTION-IN THE BACK CITY PYRGOS