Chile volcano Calbuco causes flight problems Published duration 24 April 2015

image copyright AFP/Getty Images image caption The more dense the volcanic ash, the more risk it poses for aircraft passing nearby

International flights are being delayed or cancelled because of concerns over the ash cloud created by the Calbuco volcano in Chile.

The eruption on Thursday created a cloud of ash that went up 20km (12 miles) into the air.

Volcanic ash can be extremely dangerous to aircraft as the fine particles can damage engines.

Many international flights have been affected in the last few hours, with one forced to turn back to Australia.

Qantas flight QF27 was five hours into its journey to Santiago when it had to turn back to Sydney late on Friday.

A Qantas spokeswoman in Sydney said it returned because of concerns over the ash cloud.

Two flights from the United States to Buenos Aires, one with Delta Air Lines and one with American Airlines, had to return to their departure airports.

One Air France flight from Paris to Santiago had to land in Sao Paulo, Brazil, and another destined for Buenos Aires landed in Rio de Janeiro.

All the passengers are likely to have to remain in Brazil until at least Saturday, a spokesman for Air France said.

image copyright Reuters/Nasa image caption This satellite image of the Calbuco volcano, taken on 23 April, shows the spread of the ash cloud

image copyright Reuters image caption Ash has covered vast areas around the Calbuco volcano

image copyright AFP/Getty Images image caption The ash cloud has led to delays or cancellations to flights from Europe, Australia and the United States

The Air France spokesman said: "We don't want to take any risks as safety is our main priority. At this time, we'd advise anyone travelling with us to South America to keep on monitoring the situation. We will decide what happens to any other flights."

Buenos Aires is about 2,000km (1,243 miles) from the volcano, but Air France said their own control centre in Paris had warned of a potential risk to flights in the area.

media caption Having lain dormant for decades, Chile's Calbuco volcano has roared into life sending a huge column of ash several kilometres into the air and forcing the evacuation of more than five thousand people.

A spokesman for Argentina's National Civil Aeronautic Administration said: "They were cancelled as a preventive measure, for fear that after landing they might not be able to take off later.

"We do not discount the possibility that other airlines might take the same decision."

In March, the Villarrica volcano, 200km (125 miles) north of Calbuco, erupted in the early hours of the morning , spewing ash and lava into the sky.

image copyright AFP/Getty Images image caption The Calbuco volcano continued to emit ash on Friday, two days after erupting

While some flights in Chile and Argentina were cancelled after that eruption, there was very little effect on international flights.

Flight cancellations depend on the density of the ash emitted by a volcano.

Dense ash can clog a jet's fuel and cooling system and lead to the failure of an engine.