Experts Seek Clues to How Long Eruption Will Go On

[Guest guest]

Experts Seek Clues to How Long Eruption Will Go On

By HENRY FOUNTAIN and ELISABETH ROSENTHAL

The volcanic eruption that has disrupted air travel in Europe for two days shows

no signs of abating, an Icelandic geophysicist said Friday.

" It is quite variable, it goes up and down a bit, " Pall Einarsson of the

Institute of Earth Sciences at the University of Iceland, said in a telephone

interview. " But on the whole the vigor of the eruption seems very little

changed. "

As the volcano, near Iceland's south-central coast, spewed more ash into the

atmosphere on Friday, the big question for scientists was how long the eruption

might continue, particularly at its current strength. The answer will go a long

way toward determining any lasting impact on air travel, climate and health. But

Dr. Einarsson and others said that, for now, the question was unanswerable.

" There is really no way to know that, " Dr. Einarsson said. " We have quite good

measurements to know what's going on. We can see where the stresses are changing

due to earthquakes and so on. But how it will develop is a very difficult thing

to say. "

Jennie Gilbert, a professor at the University of Lancaster in England who has

studied Icelandic volcanoes, said: " I don't think there's any general feeling

for how this volcano will operate. My best guess is that it will be explosive

for a few days and then might continue at a reduced level. "

Iceland, which is situated along the mid-Atlantic ridge, where the spreading of

two tectonic plates allows molten rock, or magma, to rise, has many volcanoes,

and their eruptions often follow a pattern, Dr. Einarsson said.

" Usually they are most vigorous in the beginning, " he said. " But this volcano is

very different from that. " Both the current eruption, which began on Wednesday,

and an earlier one on the volcano's flank that began March 20, started very

quietly, he said.

Dr. Einarsson said researchers were monitoring the volcano for indications that

the eruption was continuing or starting to taper off. Tremors, for example, are

a sign that hot magma is still coming up through the volcano, cracking the

ground as it moves. Slight deformations in the volcano's surface, as measured by

Global Positioning System devices, suggest that gases are continuing to build up

below as they bubble out of the magma, causing the surface to bulge.

One complicating factor is that the eruption is occurring under an ice sheet,

the Eyjafjallajokull glacier. Melting of the underside of the ice has caused

flooding, forcing evacuations and destroying bridges and roads.

But of more concern for the rest of Europe is how the meltwater might be

affecting the volcano and the ash it is generating.

" Certainly the fact that the eruption is going on underneath the ice sheet is

likely to have an effect on the explosivity of the volcano, " said Colin

Macpherson, a professor in the department of earth science at Durham University

in England.

He likened the situation to putting a hot pan under the kitchen faucet — as the

hot magma hits the cold water it rapidly creates steam. If the steam is

contained by rock, the pressure can build up and a localized explosion can

occur.

Dr. Gilbert said the presence of water can also affect the characteristics of

the sand-like ash that is produced. As the molten rock hits the cold water it is

rapidly quenched, fusing into a glassy material. Then when the pressure builds

up and the volcano explodes, this material breaks up into very fine particles.

" It's like this sort of shattering effect, " she said.

In Britain, the Department of Health's Health Protection Agency warned that some

low level of these particles might settle to ground level, particularly in

Northern Scotland — although they might well not be visible to the naked eye.

As a precaution, the agency on Friday advised people — particularly those with

respiratory conditions like asthma and emphysema — to have medicines on hand and

to limit outdoor activities if they noted signs that particles were present.

They might include a dusty haze or a smell of rotten eggs as well as symptoms

like irritated eyes, runny nose or dry cough.

" Mainly this concerns people with lung conditions who can find the dust

difficult to deal with, " said Dr. , an agency spokesperson. " Any

volcanic rock tends to be sharp particles, so they can trigger asthmatic

reactions. " The ash also contains chemicals that can irritate airways, like

sulfur dioxide, he said.

But, he added, there was so far no evidence of increased emergency room visits,

and the agency was not worried about any long-term health problems from exposure

to the ash. " What we're talking about are early acute effects, " he said,

" nothing long term. "

http://www.nytimes.com/2010/04/17/science/17plume.html