Iceland's Eyjafjoell volcano has been stable in recent days, but ash disrupting flights in Europe was likely emitted last week and could continue causing chaos for a while to come, a volcanologist said on Tuesday.
"The problem with the disruption in the flights is that the ash we see (over Europe) is not from today or yesterday. It is much older," said Bjoern Oddsson of the Institute of Earth Sciences at the Iceland University.
"Ash can travel around in the atmosphere due to winds, and we really don't know when it will settle down. So even if the volcano stops, we can look at this problem for a couple of weeks after," he said.
The volcano began erupting on April 14, releasing ash that last month caused the biggest aerial shutdown in Europe since World War II, affecting more than 100,000 flights and eight million passengers over a week.
The ash output reached its second highest point last Thursday, spewing a plume as high as 10,000 metres (32,800 feet) into the air, forcing the cancellation of hundred more flights in Europe.
"On May 5 and 6 we had a pulse where (the ash) increased, and that pulse has fallen down again," Oddsson said, adding that at its height last week, Eyjafjoell was emitting between 300 and 400 tonnes of ash per second.
"Yesterday (Monday), we had a very small pulse between noon and 3:00 pm (1200-1500 GMT), where the ash rose up to 6,000 metres, but in general it is status quo," he said, adding that on average in recent days the volcano had emitted about 50 tonnes of ash per second.
"We base this calculation on the height of the plume and on the colour of the plume ... Today, it is not black, so it is not very dense," he said.
There was no way of knowing when the eruption would end, Oddsson said, adding that "we can continue to see these pulses of higher plumes (but) over a seven day period, (the volcano activity) is more likely to decrease than increase."
"We are more happy than not with what we are seeing today," he said.