Expert: No health threat from Icelandic ash
Updated on 15 April 2010
As the volcanic ash cloud from Iceland forces closure of UK airspace, experts say its high altitude means it is unlikely to prove a health threat.
The ash plume from the Eyjafjallajokull volcano in Iceland has caused severe disruption for British airlines and passengers, grounding planes at airports across the country.
But one expert believes it is too high in the sky to cause health problems for the population.
Durham University volcanologist Dr Dougal Jerram said: "Ash can cause serous 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.
"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 aeroplanes cruise and that is why they are not allowed to fly."
Dr Jerram added that previous eruptions on Iceland had proved to be more harmful.
He said: "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."
There is only a risk to people with breathing issues on the ground if the dust starts to fall to earth. But it is slight.
The Met Office's Volcanic Ash Advisory Centre reported that the Icelandic ash plume was swirling southwards above the UK at a height of between six and eleven kilometres.
That means it is between 20 and 36 thousand feet; exactly the height that planes in UK Airspace operate in, sparking the closure of UK airspace.
The fear is not the cloud, which is nigh on invisible close up to the naked eye, but the particle size of the fine dust within it. There is a lot of dust entering the atmosphere at any given time.
In Africa for example, every year up to 1,500 million metric tons of dust from the soil alone is carried upward by winds. There are also billions upon billions of dust particles from farming, air pollution and smoke.
In normal conditions, of course, all clouds carry minute dust particles. That is what water droplets attach themselves too and build upon to become rain.
In this case though, the ash particles are a different prospect altogether. They are what is known as small tephra. This is actual bits of glass, rock, clay and sand that have been steamed, pulverized and steamed again in the volcanic eruptions.
The miniature particles, less than 2 millimetres in diameter, are thrown up, hot, into the atmosphere in their billions and swirl and spread around. Rising as air currents move them until temperatures cool and they fall back to earth.
The risk to aircraft flying into the ash cloud comes, say scientists at St Andrews University, because their engines suck in air at high speed and compress it along with the dust particles and blast them out again at even higher speeds.
Air with volcanic tephra within it can simply wreck the turbine blades in the engines, causing catastrophic failure.
At this stage no-one is predicting where and how the ash cloud will dissipate.
It could move and thin out over Europe; it could move eastward to Scandinavia; it could, depending on the climatic conditions simply hover over the UK for a while.
In the past very fine ash particles have remained high in the atmosphere for years, circling the globe spread around the world by high-altitude winds.
