Ash and weather patterns a volatile mix

ANALYSIS: The weather and the amount of ash ejected determine whether airspace gets affected

ICELAND’S VOLCANOES are ideal for producing massive plumes of airborne ash. They also erupt often enough to cause repeated difficulties for Europe’s airlines, but there are no indications of a pattern to their activity.

Iceland’s largest volcano, Grímsvötn, has caused significant disruption to air travel since it erupted last Saturday. Good news may be on the way, however, because activity at the volcano yesterday fell significantly, according to scientists there.

The flight disruption triggered by Grímsvötn and last year’s eruption of Eyjafjallajökull show how vulnerable air services are when a slumbering volcano awakes.

Yet the travel chaos caused does not all come down to the volcano. Weather conditions play their part – either pushing the ash north to disperse harmlessly over the Arctic, or blowing it down over European airspace.

Both this year and last the weather was against us, but it does not indicate ash incidents are going to become more common, explains Met Éireann climatologist Séamus Walsh. “It is just an unhappy series of events,” he says.

“Generally speaking, those winds follow a pattern from west to east, but last year we had a lot of winds from the north.”

Unfortunately both this year and last an Icelandic volcano started to erupt, and did just what those structures do best – blast huge amounts of ash and steam into the air. “I think it is just a timing issue – chance,” says Walsh.

If the weather is a chance event, so too are volcanic eruptions, explains Pétur Matthiasson of the Icelandic Civil Protection Agency, which responds to these events.

“Grímsvötn is Iceland’s most active volcano,” he says. But its eruptions are intermittent. The last was in 2004, and there were others in 1998 and 1996. “They are usually small, but this is a larger one than before.”

The volcano awoke on May 21st, and Icelandic geologists were taken aback by the scale of the event. Grímsvötn blasted ash and steam almost 20km into the upper atmosphere, and blew out more ash in its first 24 hours than Eyjafjallajökull did over the whole period of its eruption in 2010.

Grímsvötn released 20,000 tonnes of ash a second when the eruption started last Saturday, and has probably ejected half a cubic kilometre of material so far, says Matthiasson.

Since then it has calmed down considerably, he added. Ash output yesterday afternoon was down to one or two thousand tonnes a second, and the plume was reaching no higher than 3km to 5km.

It seems a remarkable chance there have been two years in a row where volcanic ash has caused flight disruption, particularly because the phenomenon seemed to be unknown in Europe before then.

“It depends on how much ash is ejected, and so many other variables,” says Walsh.

It is wrong to believe, as some doubters do, that the ash poses no hazard, however. In 1982, all four engines of a British Airways 747 were knocked out during a flight over the Pacific after it encountered ash from Indonesia’s Galunggung volcano. And in 1989 a KLM 747 had the same problem after flying through ash from Alaska’s Redoubt volcano.

In both cases the pilots managed to get the engines to restart, and no injuries were caused. All the engines had to be replaced, however, and it cost millions of euro to get the aircraft back into the air.

There is no way of knowing how long Grímsvötn will continue blowing its top, although the fact that it was much quieter yesterday is a good sign, says Matthiasson.

“The expectation is that it will not step up [its activity],” he says. “It could happen, but this would be unusual.”

Why this is happening is no secret. Iceland sits on a split in the Earth’s surface, the mid-Atlantic ridge, as Matthiasson points out. It is moving apart at one to two centimetres a year, opening a split that allows lava to move upwards through volcanoes.

Ash production is almost certain with any Icelandic eruption because of the local conditions, says Prof John Gamble, professor of geology at University College Cork. He studies active volcanoes with funding from Science Foundation Ireland.

Ash explosions occur when the hot lava or magma comes in contact with water. Many Icelandic volcanoes are covered by glacial ice that melts when magma emerges, Prof Gamble explains.

Grímsvötn is blanketed by Europe’s largest glacier, Vatnajökull, but it also has a “caldera” – a huge lake that fills the top of the volcano.

Grímsvötn blew when magma hit this water, he says. “The effect is extremely explosive. The magma basically explodes when it hits the cold water.”

The water flashes to steam and blows a hole in the ice, racing upwards and carrying tonnes of pulverised magma ash with it for kilometres into the atmosphere.

The resultant grit contains glass, and it is this element finding its way into aircraft engines that causes major damage.