The magma chamber under volcano Hekla is now almost full, according to Páll Einarsson, professor in geophysics at University of Iceland.
Hekla, which is the most active volcano in Iceland, could erupt with very short notice, Páll told Morgunblaðið, adding that people should not climb the mountain.
During the last eruption, in 2000, it took just 79 minutes from the first quake until eruption, and Páll says that was longer than in previous eruptions.
Hekla has erupted more than 20 times in the last 1,000 years. The last big eruption in Hekla was in 1947.
A webcam of Hekla can be viewed here.