Activity in an Icelandic volcano turned less fierce on Tuesday, officials said, producing less force behind eruptions that for five days shut most European airports because of a massive ash cloud.
Late on Tuesday most European airspace had reopened, however strong winds higher up continue to make conditions uncertain, leaving airport authorities across Europe still at the mercy of clouds of ash.
The volcano under the Eyjafjallajokull glacier, about 120km (75 miles) southeast of the capital Reykjavik, has been erupting for almost a week. There are concerns the eruption could set off the neighbouring, larger Katla volcano, but officials said no activity had been detected.
"You have to choose your words very carefully but at least the scientists tell us that the activity is going down. We cannot make the assumption that the worst is over but we hope it is," Rognvaldur Olafsson, the Icelandic department of civil protection's chief inspector told Reuters.
"We have less ash fall, and also there seems to be a little less activity in the crater."
However, the Icelandic Meteorological Office has continued to note strong northwesterly winds at higher levels. "That is why it is difficult to say (about the impact on air traffic)," said Gudrun Nina Peterson of the Icelandic meteorological office.
European airspace was closed because of fears the ash might damage aircraft if they flew through it.
An Icelandic web camera has shown a steady stream of smoke coming from the volcano and rising into the air in huge plumes, although the column was much lower than previous readings of six to 11km (four to seven miles).
Bjorn Oddsson, a geophysicist who flew over the volcano on Tuesday along with other scientists and officials, said the activity in the crater was decreasing and that this could indicate a break in the eruption will follow.
Kristin Vogfjord, a meteorologist, agreed the volcano had become more stable.
"There is a relatively strong, continuous low frequency tremor. It is being felt and observed in the countryside east of the volcano," she said.
The tremors could be caused by lava splatters inside the crater or by shaking inside the vent of the volcano.
"Apparently the lava is not flowing out of the craters, but there is lava in one of the craters," she added.
She said scientists were observing the neighbouring Katla volcano.
The University of Iceland's Institute of Earth Sciences says Katla is one of the most active volcanoes on Iceland. Its last major eruption was in 1918, and it is also covered by a glacier.
"We have no indication there is an eruption because there is no seismicity and the volcano is not expanding," added Vogfjord.
Few Icelanders have been affected by the eruption, with mainly sparsely populated farm lands nearby hit by some flooding and falling ash.
The capital city has suffered no ash fall as yet and a police official said the winds would have to be strong and in the right direction to take ash as far as Reykjavik.
