Inflation-Deflation Signals at Eyjafjallajökull Volcano, Iceland, During a Period of Intermittent Unrest

Abstract:

The ice-capped Eyjafjallajökull volcano, south Iceland, had been dormant for 170 years when it first showed signs of a new unrest period in 1994, the third one known during historical time in Iceland (the past 1100 years). It culminated during a flank and summit eruption in 2010. Previous known eruptions at Eyjafjallajökull volcano occurred in year 500 (pre-settlement), in 1612 and 1821-23.

The resent unrest period was characterized by intermittent swarm activity and crustal uplift. The first seismic swarm was recorded during 1994 and was accompanied by inflation, suggesting a sill intrusion at ~6.5 km depth beneath the south-eastern flank. A similar but longer episode of seismic swarms and crustal uplift took place again in 1999-2000, also modelled as a sill centered at the south-eastern flank. A deeper swarm was recorded in 1996, near the crust mantle boundary (20-24 km depth) indicating injection of magma from the mantle into the crust. In spring 2009, several deep seismic events were detected again, followed by swarm activity during the summer and a small crustal signal indicating inflation at the southern flank. This was followed by a new period of escalating seismicity and inflation, indicating a complicated pattern of intrusion activity from December 2009 until the two eruptions broke out in March and April 2010. Geodetic and seismic data show that the three-week-long basaltic flank eruption was fed by a deep source (20-30 km). The intrusive activity triggered the more silicic and explosive six-week-long summit eruption. Two weeks into the summit eruption a new swarm of deeper earthquakes and inflation was detected, indicating that a new wave of material was being fed into the system from depth. This changed the phase of the eruption, again to an explosive phase and was repeated at least two more times during the next two weeks. The summit eruption ended in late May but since July 2010 GPS measurements indicate inflation of the volcano.

Here, we focus on the 18-year-long period preceding the 2010 events. We have improved the seismic catalog locations by applying a double-difference relocation method and reanalyzed GPS campaign data between 1992 and 2009 which not only show the uplift during the intrusion episodes but also the subsidence following the inflation periods, caused by the cooling and contraction of the new intrusions.