There was a fresh lava eruption near the Bardarbunga volcano in Iceland yesterday, leading to authorities raising the alert for planes.
Iceland's Met Office said there had been "a very calm lava eruption... hardly seen on seismometers".
Planes were banned from flying within 6,000 ft of the volcano peak until the red alert was lowered to orange.
Iceland's Eyjafjallajokull volcano erupted in 2010, producing ash that disrupted air travel across Europe.
Eruption will cause 'less disruption'
BBC transport correspondent Richard Westcott says that even if a big cloud of volcanic ash were emitted, it would not cause the same level of disruption to flights that brought Europe to a halt four years ago.
He says new equipment that airliners and engine makers have been testing would allow planes to identity and fly around ash clouds.