A fissure eruption began in Holuhraun, north of Vatnajökull glacier, just after midnight. Lava fountains were visible on a webcam by Míla at two minutes past midnight. White steam can now be seen coming up from the eruption site.
According to Martin Hensch, an earthquake specialist at the Icelandic Met Office, volcanic activity was detected on the office’s meters between 0.20 and 2.00 am, mbl.is reports. RÚV reports that lava has flowed to the southeast from the fissure.
A possible explanation for the white strokes is that the lava, which appears to be rather thin, has come into contact with water close to the fissure.
It's not considered likely that water has come in contact with the magma itself when it comes up, because that would probably result in a more explosive eruption. It's also possible that the lavea comes into contact with underground water close to the surface.
Seismic activity remains constant, also occurring 10-12 km (6-8 miles) south of the fissure, under Dyngjujökull outlet glacier in the northern Vatnajökull.
This is of special interest, because a sub-glacial eruption would take on a different character and might cause much more damage, produce more ash and a possible flood.