Mountain has long and hot history

The last time Mt Eyjafjallajokull erupted, it kept going for more than a year. Then it triggered a more powerful eruption from its neighbouring volcano, Katla.

Volcanologists warn that the Icelandic volcano causing havoc over the skies of Europe has a history of long eruptions. The eruption from 1821 to 1823 was followed by a much bigger eruption of Katla in 1823.

But New Zealand volcanologist Gill Jolly said that disruption to air travel would last only as long as the weather pushed the ash over Europe.

"History does matter ... if a volcano tends to erupt in short sharp bursts that's what it will tend to do in the future but volcanos are also very unpredictable beasts," she said.

A change of wind direction could soon limit the disruption to Iceland and Scandinavia even if the ash kept coming.

"The winds have brought it down over Europe - it is quite an unusual wind direction for there. A couple of good depressions ... .should blow it all away."

Volcanic ash is very abrasive and can cause havoc with aircraft engines and car engine filters.

Dr Jolly, of volcano-watchers GNS Science, said flights were diverted in 2007 after a very small eruption of Mt Ruapehu because it was dark and scientists could not see the size of the ash cloud.

GNS was trying to send scientist Bruce Christenson to study Eyjafjallajokull - but he could not get on his flight to Europe.