A giant ball of molten rock has expanded under the volcanic Greek island of Santorini - raising the isle and triggering earthquakes in the area, a new study says.
Scientists say the chamber of magma beneath Santorini's volcano increased by up to 20 million cubic metres - 15 times the size of London's Olympic Stadium - between January 2011 and April 2012.
The growth lifted the island by between 8cm and 14cm during the period, according to the survey led by Oxford University.
It triggered a series of small earthquakes near the island, around 120 miles off the Greek mainland - the first seismic activity in the area in 25 years.
But scientists say the movements do not mean an eruption is about to happen, with the rate of earthquakes dropping off in recent months.
Following the earthquakes, Michelle Parks, from Oxford University's Department of Earth Sciences, spotted signs of movement of the Earth's surface on Santorini using satellite radar images and Global Positioning System (GPS) receivers.
She estimated the magma below the popular tourist spot is growing at up to 20 times its normal rate.
"During my field visits to Santorini in 2011, it became apparent that many of the locals were aware of a change in the behaviour of their volcano," she said.
"The tour guides, who visit the volcano several times a day, would update me on changes in the amount of strong smelling gas being released from the summit, or changes in the colour of the water in some of the bays around the islands."
Co-author, Dr Juliet Biggs, from the University of Bristol, said: "People were obviously aware that something was happening to the volcano.
"But it wasn't until we saw the changes in the GPS and the uplift on the radar images that we really knew that molten rock was being injected at such a shallow level beneath the volcano.
"Many volcanologists study the rocks produced by old eruptions to understand what happened in the past, so it's exciting to use cutting-edge satellite technology to link that to what's going on in the volcanic plumbing system right now."
The volcano's last major eruption was 3,600 years ago, when it buried Santorini and nearby islands under metres of pumice.