The chamber of molten rock beneath a volcano on a Greek island expanded 300 million-700 million cubic feet in a little more than year, researchers say.
A team led by Oxford University scientists said the growth of the magma lifted the surface of Santorini, in the Aegean Sea, 5.5 inches from January 2011 through April 2012.
In January 2011, a series of small earthquakes began beneath Santorini and adjacent islands, the first sign of activity beneath the volcano to be detected for 25 years, the team said.
The researchers used global positioning systems and radar to map the changes occurring on the islands.
"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," Juliet Biggs of Bristol University said.
Although the amount of molten rock that has arrived beneath Santorini in the past year is the equivalent of about 10-20 years growth of the volcano, this doesn't mean that an eruption is about to happen, the researchers said, and in fact the rate of earthquake activity has dropped off in the past few months.
Santorini had its last major explosive eruption 3,600 years ago, burying it and surrounding island under yards of pumice, researchers said.