The Greek island of Santorini is showing increasing signs of volcanic activity, a U.S. researcher says.

Monitoring stations on the island indicate the Santorini caldera is awake again and rapidly deforming, said Georgia Tech researcher Andrew Newman, who has studied Santorini since 2006 after placing more than 20 GPS stations on the popular tourist island.

"After decades of little activity, a series of earthquakes and deformation began within the Santorini caldera in January of 2011," Newman said. "Since then our instruments on the northern part of the island have moved laterally between five and nine centimeters (2 inches to 3-1/2 inches).

"The volcano's magma chamber is filling, and we are keeping a close eye on its activity."

The chamber has expanded by nearly 500 million cubic feet since last January, Newman said.

"That could be dangerous," he said. "If the caldera erupts underwater, it could cause local tsunamis and affect boat traffic, including cruise ships, in the caldera. Earthquakes could damage homes and produce landslides along the cliffs."

Santorini has been relatively calm since its last eruption in 1950, a Georgia Tech release said Tuesday.