One of Iceland's most feared volcanoes looks ready to erupt, raising fears of a new ash cloud over Europe.
The Hekla volcano is close to the ash-spewing Eyjafjoell, which last year caused the world's biggest airspace shut down since World War II, affecting more than 100,000 flights and eight million passengers.
Experts have said measurements of Hekla - dubbed "Gateway to Hell" by locals - indicate magma movement.
"The movements around Hekla have been unusual in the last two to three days," University of Iceland geophysicist Pall Einarsson said.
While this might not necessarily mean an immediate blast, "the volcano is ready to erupt," he stressed.
"The mountain has been slowly expanding in the last few years because of magma build up," he explained.
Another geophysicist, Ari Trausit Gudmundsson, said measurements around Hekla were very "unusual" and the volcano looked ready to blow.
"Something is going on," he said, stressing though that "if or when the volcano erupts is unclear."
The volcano, is one of Iceland's most active, has erupted some 20 times over the past millennium, most recently on February 26, 2000.
It is so active that scientists estimate about 10 percent of the tephra - the solid matter ejected when a volcano erupts - produced in Iceland over the past millenium, about five cubic kilometres, comes from this one volcano.
News of a possible imminent eruption comes just over a month after the violent eruption at the Grimsvoetn volcano, in the southeast of the country.
That episode subsided after less than a week, but due to more favourable winds for Europe, it caused much less air traffic disruption.
Asked about what kind of disruptions could be expected if Hekla erupts, Mr Gudmundsson said the volcano tends to "produce both ash and lava within the first seconds of an eruption."
Lava eruptions are far less disruptive to air travel, and "if the next eruption is of the same character (as the previous ones) it is unlikely that it will have any effects on flights in Europe," he said.
"But of course this depends on the size of the eruption, which is something that is impossible to predict," he added.
Rongvaldur Olafsson, from the Icelandic Civil Protection Authority, said no immediate safety precautions were being taken but that the mountain was being watched very closely.