Eyjafjallajokull's most recent previous eruption, from late 1821 to early 1823, also had quite viscous lava.

ECONOMIST: Volcanoes and air travel: Small eruption in Iceland | The

But a combination of circumstances meant that, though comparatively small, Eyjafjallajokull's current eruption punched above its weight in the ash-production league in its early days, emitting much more fine ash than is normal.

ECONOMIST: Volcanoes and air travel: Small eruption in Iceland | The