Real-time GPS Monitoring of the 2014-2015 Bárðarbunga Rifting Event in Iceland

Abstract:

On August 16, 2014 an intense seismic swarm originated below the eastern part of Bárðarbunga caldera. The seismicity migrated 50 km NNE until August 28 when the migration stopped 10 km south of Askja Volcano. This eventually lead to an eruption in Holuhraun, north of Dyngjujökull, which lasted nearly six months. The migration of seismicity coincided with displacements of continuous GPS (cGPS) stations, suggesting a lateral dyke formation in the Bárðarbunga volcanic system. The volume of the dyke was estimated in near-real time by modeling of geodetic displacements of GPS stations in the vicinity of Bárðarbunga. At the beginning of the swarm, there was only one cGPS station located conveniently enough to observe the dyke propagation. It was therefore evident that more cGPS stations were needed in order to get reliable estimates of the magma volume being intruded into the upper crust. Between August 20th 2014 and July 10th 2015, 14 new cGPS stations were added in the vicinity of Bárðarbunga.

24 hour GPS solutions weren't suitable enough to monitor the rapidly evolving events during the dyke propagation, so 8 hour solutions were implemented, giving deformation estimates three times each day. For a better visualisation of the developing activity, a map on the Icelandic Meteorological Office's website was made public, showing the rapid development of geodetic displacements and seismicity in near-real time. The 8 hour solutions were used to estimate the volume change of the magma source under Bárðarbunga and the dyke.

A few days before the eruption in Holuhraun began on August 31, large earthquakes (>M5.0) started occurring in the caldera of Bárðarbunga and soon after, an ongoing collapse of the caldera was discovered. To monitor this subsidence, which ended up being about 66 meters, a GPS device was placed within the caldera. For the purpose of monitoring significant changes in the rate of caldera subsidence, the volume change of a spherical source beneath the volcano was modeled using far-field GPS stations surrounding the caldera, which correlated very well with the subsidence rate measured by the GPS within the caldera.