The image to the right, captured by NASA’s Terra satellite at midday on September 13, shows a dense plume of that dust blowing over a sparsely populated agricultural area to the east of Katla and Eyjafjallajökul volcanoes.
But the previous two days saw the dust streaming westward in a thinner layer that shrouded greater Reykjavik, the most populated area of the island nation.
Health officials said the ash produced air pollution levels in the capital that well exceeded the accepted save limits.
The source of the ash was the Grímsvötn volcano, which erupted earlier this year.
While there is no evidence nearby Katla is about the erupt, Icelandic seismologists say it has produced an unusual spike in harmonic tremors during the first two weeks of September.
Scores of earthquakes were also reported on the Reykjanes Ridge, south of the capital.
Image: NASA MODIS Rapid Response System