The island of Santorini is one of the most visited Greek islands in the Aegean Sea. It is also an island that is sitting on a volcano that hasn’t erupted in over 3,600 years. But, in the last year, scientists have noticed increased sub-surface activity that could be pointing to one in the future. The question everyone is asking is, if this is possible, how soon might it happen? Scientists at the University of Bristol have been studying the clues. The chamber of molten rock beneath Santorini’s volcano expanded 10-20 million cubic meters — up to 15 times the size of London’s Olympic Stadium — between January 2011 and April 2012, according to a new survey carried out by an international team led by Oxford University and including a scientist from the University of Bristol. The research is reported in this week’s Nature Geoscience. The growth of this ‘balloon’ of magma has seen the surface of the island rise 8-14 centimeters during this period, the researchers found. The results come from an expedition, funded by the UK’s Natural Environment Research Council, which used satellite radar images and Global Positioning System receivers (GPS) that can detect movements of the Earth’s surface of just a few millimeters. The findings are helping scientists to understand more about the inner workings of the volcano, which had its last major explosive eruption 3,600 years ago, burying the islands of Santorini under meters of pumice. However, it still does not provide an answer to the biggest question of all: ‘When will the volcano next erupt?’ In January 2011, a series of small earthquakes began beneath the islands of Santorini. Most were so small they could only be detected with sensitive seismometers but it was the first sign of activity beneath the volcano to be detected for 25 years. Following the earthquakes Michelle Parks, an Oxford University DPhil student, spotted signs of movement of the Earth’s surface on Santorini in satellite radar images. Oxford University undergraduate students then helped researchers complete a new survey of the island.