Deformation derived from GPS geodesy associated with Bárðabunga 2014 rifting event in Iceland
Friday, 18 December 2015
Poster Hall (Moscone South)
On August 16, 2014 an intense seismic swarm started below the eastern part of Bárðarbunga caldera in the north-western corner of Vatnajökull ice-cap, Iceland. This marked the onset of the first rifting event in Iceland since the Krafla fires (1975-1982). The migration of the seismicity was corroborated by ground deformation suggesting lateral injection of magma, from the Bárðarbunga system, into a dyke. The seismicity migrated out of the caldera forming a dyke with roughly three segments, changing direction each time until August 28 when the migration stopped around 10 km south of Askja Volcano, eventually leading to a short lived eruption in Holuhraun north of Dyngjujökull. On the morning of August 31 a fissure eruption started in Holuhraun which lasted for roughly 6 months until February 27. Prior to the onset of the activity on August 16, at least since May 2014, subtle signs of inflation where observed on continuous GPS sites around the volcano indicating a volume increase in the roots of the Bárðarbunga volcanic system. When the activity started on August 16, the deformation pattern indicated a deflation centered within the caldera simultaneously with the lateral growth of the dyke also reflected in the migration of seismicity, along segments of variable strike. A maximum widening of 1.3 m occurred between stations on the opposite site of the dyke spaced 25 km apart. Displacements indicated the fastest rate of widening at any time in the most distal segment of the dyke throughout its evolution. After the dyke stopped propagating, the inflation continued decaying gradually. On September 4, five days into the second fissure eruption, the movements associated with the dyke where no longer detectable. As the fissure eruption continued the slowly decaying contraction was observed around the Bárðarbunga central volcano both in the piston like subsidence of the caldera floor, observed with a GPS instrument located on the ice surface within the caldera, as well as in the region around the caldera outside and within the ice cap, with no detectable deformation associated with the formed dyke or the eruptive fissure. The post eruptive deformation is mostly characterised by complicated pattern of signals most likely related to superposition of post rifting and relaxation of the central volcano.