New eruptions in Iceland's Bardarbunga volcano system prompted authorities to raise the warning level for the risk of ash to aviation to the highest level of red.
The area has been hit by thousands of earthquakes over the last two weeks and scientists have been on high alert.
In 2010, an ash cloud from the Eyjafjallajokull volcano, in a different region of Iceland, closed much of Europe's air space for six days.
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It will be increasingly humid and thundery with highs of 30C or more today.
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Drink lots of water, stay out of the sun during the middle of the day, and take particular care of vulnerable people.