Comparison of the Bardarbunga 2014-2015 rifting event, slow caldera collapse and major effusive eruption with the 1975-1984 Krafla and 2005-2010 Dabbahu, Afar, rifting episodes

Abstract:

Activity in the Bardarbunga volcanic system in Iceland during 2014-2015 includes a major lava eruption (about 1.5 km³) and gradual caldera collapse (about 66 m), connected by a 50 km long dyke that formed mostly over 2-4 weeks after the onset of activity on 16 August 2014. This episode of dyking along the divergent plate boundary in Iceland is one of the best observed rifting events in the world, with seismic and deformation data showing how dyke barriers were overcome by the build-up of pressure at the dyke tip. Observations from these events can be compared to two other instrumentally recorded rifting episodes at two subaerial spreading centers: the 1975-1984 Krafla rifting episode in Iceland and the 2005-2010 Dabbahu (northern Manda Hararo) rifting episode in Afar, Ethiopia. In these cases, it has been inferred that magma is supplied to the crust in an intermittent manner, and stored at multiple positions and depths. During rifting episodes, magma is laterally intruded in dykes within the brittle upper crust releasing accumulated extensional strain. Cumulative extension of the ground at Krafla and Dabbahu averaged about 5 m, over 60-80 km long segments of the fissure swarms involved. Eruptions resulted in relative small volumes, mainly occurring near the end of the rifting episodes. An outstanding feature of the Bardarbunga events is the slow caldera collapse; not observed either at Krafla or Dabbahu. The erupted volume in the Bardarbunga events is also about an order of magnitude larger than the total erupted volume during the Krafla and Dabbahu rifting episodes. The slow caldera collapse at Bardarbunga is inferred to be responsible for the larger erupted volume in the 2014-2015 events compared to the other events; magma was driven out laterally from beneath Bardarbunga by the collapsing overburden above a magma source. Following such an event, the pressure within a magma source may take a long time to reach a sufficient level capable to creating another rifting event, unless magma inflow from depth proceeds at a fast rate.