It seems likely that the first 50 years of jet travel across the North Atlantic enjoyed, in historical terms, particularly clear skies. - The Economist
SHOOT: Which means we're in for darker skies in the future. Nature Rules.
Iceland is peculiarly volcanic because it is formed by the intersection of a hotspot and a mid-ocean ridge. The hotspot has pushed the spreading ridge up to the surface and supplemented its activities with some extra volcanism on the side. There are 33 large volcanoes on the island, or just offshore, which have erupted since the end of the last ice age, around 12,000 years ago.
The fineness of the ash is, says Thorvaldur Thordarson, an Icelandic volcanologist, unusual.
Studies of ash captured from the air show that for every one of the largest particles (about 300 microns) there are a million or more in the 2 micron range. So though the total volume of the eruption, put at about 0.14 cubic kilometres, is low, the amount of ash capable of travelling long distances is high.