The eruption has been spectacular (Image: Dr Matthew Roberts)
A spectacular volcanic eruption under an Iceland glacier has forced airlines to divert flights to avoid flying through gas emissions from the blast.
The volcano first erupted on Monday, sending thick black smoke and ash heading towards continental Europe.
Since then, GrÝmsv÷tn volcano has produced a steady stream of ash and lava, with explosions sending ash up to 12,000m (40,000ft) in the air.
It is thought to have been caused by drainage of a lake under the glacier.
As the lake drained, this pressure was released, allowing magma to rise to the surface. It was like lifting the lid off a pressure cooker
Dr Matthew J Roberts, Icelandic Meteorological Office
Officials say people or homes are not at risk from the eruption of GrÝmsv÷tn, which is in an unpopulated area of the island.
But ash from the eruption under Vatnaj÷kull glacier - Iceland's biggest - has landed in Norway, Sweden and Finland. The eruption was also violent enough to set off earth tremors.
The ashfall in Iceland has caused some problems for wildlife in the area. Farmers have brought their sheep inside to prevent them from grazing on land covered with shards of abrasive "glass-like" material deposited by the eruption.
Oli Thor Arnarsson, of the Icelandic Meteorological Office, said a change in the wind could send the cloud toward central Europe.
"We are speculating that the eruption should be clear tomorrow. But if there are more eruptions, we may have ash over central Europe," he said.
Trans-Atlantic flights had been diverted south of Iceland to avoid the ash cloud, and domestic flights to the northeast of Iceland were cancelled.
Dutch airline KLM said it had cancelled 59 flights, stranding hundreds of passengers at Amsterdam's Schiphol Airport, because of the cloud of ash hanging above Europe.
"Because of company rules we can't fly below it and we can't fly above it," said airport spokesman Frank Houben.
In addition to visibility problems, abrasive particles released into the air by the volcano can get inside aircraft engines.
"It's the equivalent of sandblasting an aircraft engine with grit," Dr Matthew J Roberts of the Icelandic Meteorological Office in Reykjavik, Iceland, told the BBC News website.
"As the aeroplane draws in large quantities of air, suspended particles cause abrasion inside the engine that can result in the aircraft stalling."
This happened once in 1989, when a 747 flew through an ash cloud from an eruption of the Redoubt volcano in Alaska, US. The engines stopped, causing the plane to lose several hundred metres in altitude.
Luckily, the pilots managed to restart the engines after several attempts, averting a catastrophe.
Over the last few weeks, increased seismic activity below the Vatnaj÷kull ice cap warned scientists that an eruption was likely.
At 2010GMT on Monday evening, researchers detected a series of tremors from the GrÝmsv÷tn volcano beneath Vatnaj÷kull, prompting monitors to issue a public warning.
The earthquakes were followed at 2150GMT by a sequence of volcanic tremors that confirmed an eruption was underway. Shortly after, doppler radar detected the first volcanic plume breaking through the ice.
"The volcano was maintained under pressure by the weight of a lake above it. As the lake drained, this pressure was released, allowing magma to rise to the surface," Dr Roberts explained.
Expansion of a lake may have caused the eruption
"It was like lifting the lid off a pressure cooker."
GrÝmsv÷tn last erupted six years ago and before that in 1995 and 1993, causing flooding.
The volcano lies on the Atlantic Rift, the meeting of the Euro and American continental plates.
The three major volcanoes of Iceland - Hekla, Katla and GrÝmsv÷tn - lie on the same plate boundary.
During the late 18th Century, continuous volcanic eruptions in Iceland heavily damaged a quarter of the island nation, and blotted out the sun's light for several years.