Seismic activity surrounding the Bárðarbunga volcano gradually increased from 2007 to 2014, with a brief pause during the nearby eruption at Grímsvötn in 2011. By the summer of 2014 activity reached a level similar to that just before the Grímsvötn eruption. In May 2014 there was a small earthquake sequence of about 200 events. GPS data recorded a displacement of 14 cm in the region since the beginning of the phase of unrest, compared to a figure of 2 cm over the rest of Iceland. This displacement is attributed to the separation of two continental plates: the Eurasian Plate in the east and the North American Plate in the west. Further earthquake swarms were detected: one at Bárðarbunga caldera, attributed to subsidence due to the magma chamber emptying; and another at the head of a dyke which extends approximately 40 km outwards from the vent, at a depth of 5-8 km below the surface. Evidence of minor sub-glacial eruptions occurred as early as 23 August when tremors were detected, but it was not until 29 August when lava erupted onto the surface at the fissure, forming a crater and substantial lava field to the north of the glacier in Holuhraun.