A computer enhanced image of the volcano under the Eyjafjallajokull glacier in Iceland taken by the TerraSAR-X satellite on Thursday evening.
Experts Seek Clues to How Long Eruption Will Go On - NYTimes.com
Experts Seek Clues to How Long Eruption Will Go On
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. Michael Clark, 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.”