OVPF reported that a seismic crisis at Piton de la Fournaise began at 1457 on 9 April and was accompanied by rapid deformation beneath the S flank.
Seismicity indicated that a fissure opened at 1900 but could not be visually confirmed due to weather conditions.
The Alert Level was raised to 2-2.
During an overflight at 0840 on 10 April scientists observed a NNW-oriented fissure, 700 m S of Château Fort.
Activity was focused at two vents, each producing lava fountains that were no higher than 30 m tall, though fountains also rose from other parts of the fissure.
Slow-moving ?a?a lava flowed SE and then curved E and advanced 1.6 km to 1,800 elevation.
The N end of the fissure was no longer active.
Two cones had formed over the main vents and were growing larger; by 11 April the more northern vent was the larger of the two.
Fountains rose 30-60 m and the lava flow had advanced to 1,750 m elevation.
By 1900 on 11 April the lava flow was 3.2 km long and had reached 1,690 m elevation.
Lava fountaining continued at the two vents during 12-13 April, rising 20-60 m.
The lava flow continued to advance; by 13 April the flow was about 3.6 km long and had reached 1,500-1,550 m elevation.
Source: Observatoire Volcanologique du Piton de la Fournaise (OVPF)