Q&A: How long will Iceland volcano hit Europe flights?

LONDON (Reuters) - The Icelandic volcano currently making northern Europe a no-fly zone could potentially affect international travel for months with the key questions how long the eruption lasts and whether it continues to spew ash.

WHAT IS CAUSING IT?

The eruption under the Eyjafjallajokull glacier -- 10 times more powerful than another nearby at last month -- produced a column of ash and steam that prompted serious flooding, considerable damage and displaced hundreds of people.

That ash cloud then spread south west toward Europe around 18 km above sea level, prompting authorities to ground aircraft across the region to reduce the threat to aviation.

HOW LONG WILL IT LAST?

British air traffic control authorities say UK airspace will be closed until 0600 on Friday at the earliest while meteorological authorities across Europe continue to monitor the cloud.

Predicting the duration of both the eruption and the cloud is difficult. However, a previous eruption lasted more than 12 months. Much also depends on whether it continues to produce ash and whether the wind continues to carry that ash toward Europe.

"I would expect this shutdown to last a couple of days," said Prof Bill McGuire of the Aion Benfield UCL Hazard Research Center. "But if the eruption continues -- and continues to produce ash -- we could see repeated disruption over six months or so."

Most experts say the most likely scenario is for the intensity of the eruption to vary, potentially producing occasional threats to European aviation.

"What has happened overnight is that the volcano has... exploded quite a lot more violently and put ash very high up," said Matthew Watson, lecturer on geophysical natural hazards at Bristol University. "If it does go back to what it's doing before -- and I don't have a crystal ball but I would think that is quite likely -- then essentially what you are doing is waiting for the airspace to clear."

The 1783 eruption of the Icelandic Laki volcano spread a cloud of ash and sulfurous gases across Europe for most of the summer of that year and into 1784, resulting in high summer temperatures and poor air quality that boosted mortality rates in several countries. There is no suggestion at this stage that this eruption will yield a similar sulfurous gas cloud, so the impact should be less.

Much would also depend on whether the current eruption destabilizes and produces an eruption from the nearby Katla volcano. Is that did erupt, the impact would be increased.

WHAT ABOUT THE IMPACT?

Iceland's location means the eruption could prompt wider disruption to international flights, hurting the industry just days after industry body IATA reported airlines were slowly climbing out of recession.

"Iceland sits right on one of the key routes between Europe and the USA and... depending on meteorological conditions it could also affect flights from Europe to Asia so there are two big international flows which could be affected by this," said John Strickland, director of air transport consultancy JLS Consulting.

"Even if the skies over northern Europe look clear you can still get disruptions to other flights or have to take more circuitous routes which adds costs and maybe even requires planes to land because they can't go on the direct route."

Shutdowns of airspace on this level are relatively unprecedented. In the short term, they will result in lost revenue and increase costs for airlines. Quantifying that is harder.

British Airways said seven days of cabin strikes in March -- during which 20 percent of its longhaul and 40 percent of shorthaul flights were canceled, a much lower proportion than that hit by the cloud -- cost it around $10 million a day.

The Association of British Travel Agents estimated the cloud was hitting the travel plans of around 200,000 British people per day.

"It's too early to say how much this will cost the UK travel industry but it doesn't take much of this type of disruption for the cost to run up to several millions of pounds per day, given the need for refunds and related costs," a spokeswoman said.

Sustained shutdowns or a summer of disruption might prompt some business and leisure travelers to make other arrangements or cancel travel. Any alterations to weather could impact crop yields.

A British Ministry of Defense spokesman said flights to Afghanistan had been affected and that returning and medical evacuation flights might be taken to other countries if necessary. Search and rescue helicopters were operating below the level of the cloud, a spokeswoman said.

Some previous volcanic eruptions -- such as Mount Pinatubo in the Philippines in 1991 and Mount Chichon in Mexico in 1982 -- spewed so much debris into the atmosphere they cooled the planet for months. But scientists say this eruption is too small to have any global impact.

"This is not like Pinatubo. So far the scale is not big enough to have a global effect," said Hans Olav Hygen, a climate researcher at the Norwegian Meteorological Institute.

(Editing by Ralph Boulton)

(Additional reporting by Alister Doyle and Rhys Jones)