A VULCANOLOGIST today reassured people in the UK that the ash did not pose a health risk.

But Dr Dougal Jerram, of Durham University's Department of Earth Sciences, said a massive Icelandic eruption in the 18th Century had resulted in thousands of deaths.

He said: "Ash can cause serious health problems but the high altitude of the current plume above the UK means that it is air traffic and not humans on the ground that will suffer.

"Volcanic ash is made up of tiny particles that are created when bubbles break due to gasses in a volcanic eruption.

"Eruptions which are charged with gas start to froth and expand as they reach the surface which results in explosive eruptions and this fine ash being sent up into the atmosphere.

"When the ash is ejected high enough into the atmosphere, it can reach the higher altitude winds and be dispersed around the globe from Iceland to Europe.

"These high winds are exactly where airplanes cruise and that is why they are not allowed to fly.’’ He added: "One of the most influential ever eruptions was the 1783-1784 event at Laki in Iceland when an estimated 120 million tons of sulphur dioxide were emitted, approximately equivalent to three times the total annual European industrial output in 2006.

"This outpouring of sulphur dioxide during unusual weather conditions caused a thick haze to spread across Western Europe, resulting in many thousands of deaths throughout 1783 and the winter of 1784.’’