Segmented lateral dyke growth in a rifting event at Bárðarbunga volcanic system, Iceland

Abstract

On 31 August a new eruption began from the same fissure and is still ongoing at the time of writing. After 4 September the movement associated with the dyke was minor, suggesting an approximate equilibrium between inflow of magma into the dyke and magma flowing out of it feeding the eruption. Minor eruptions may have occurred under Vatnajškull; shallow ice depressions marked by circular crevasses (ice cauldrons) were discovered in the period 27/08-07/09, indicating leakage of magma or magmatic heat to the glacier causing basal melting ( Fig. 1 and 2b). On 5 September, aircraft radar profiling showed that the ice surface in the centre of the B ‡r!arbunga caldera had subsided 16 m relative to the surroundings, resulting in a 0.32±0.08 km 3 subsidence bowl ( can be compared to a 1 day interferogram over the ice surface spanning 27 -28 August (Fig. 1), that has maximum line-of-sight (LOS) increase of 57 cm, indicating 55-70 cm of subsidence, during 24 hours. From 24 August to 6 September 16 M≥5 earthquakes occurred on the caldera boundary.Over 22000 earthquakes were automatically detected 16/08-06/09 2014, 5000 of which have been manually checked. Four thousand of these have been relatively relocated, defining the dyke segments. Ground deformation in areas outside the Vatnajškull ice cap, and on nunataks within the ice cap, is well mapped by a combination of InSAR, continuously recording GPS sites, and campaign GPS measurements. The GPS observations and analysis give the temporal evolution of the three-dimensional displacements used in the modelling (Fig. 1). Interferometric analysis of synthetic aperture radar images from the COSMO-SkyMed, RADARSAT-2 and TerraSAR-X satellites was used to form 11 interferograms showing LOS change spanning different time intervals (Supplementary Fig. 2). The analysis of seismic and geodetic data is described in Methods.Initial modelling of the dyke, with no a priori constraints on position, strike or dip, show the deformation data require the dyke to be approximately vertical and line up with the seismicity (Extended Data item 4). We therefore fixed the dip to be vertical and the lateral position of the dyke to coincide with the earthquake locations.We modelled the dyke as a series of rectangular patches and estimated the opening and slip on each patch ( Fig. 3a; see Supplementary Figures 3-4 for slip and standard deviations of opening). We used a Markov-chain Monte Carlo approach to estimate 7 the multivariate probability distribution for all model parameters (Methods) on each day 16/08-06/09 2014 (Fig. 2d). The results suggest that most of the magma injected into the dyke is shallower than the seismicity, which mostly spans the depth range from 5 to 8 km below sea level (see Fig. 2c and Methods). While magma may extend to depths greater than 9 km near the centre of the ice cap, towards the edge of the ice cap where constraints from InSAR and GPS are much better, significant opening is all shallower than 5 km (Fig. 3a). The total volume intruded into the dyke by 28 August was 0.48-0...

Interaction between Transform Faults and Rift Systems: A Combined Field and Experimental Approach

“…In regard to the influence of igneous intrusions on the formation of the structures in the studied area, we are aware that tension fracture opening can occur along a rift also as a consequence of magmatic pressure (Gudmundsson, 1987a(Gudmundsson, ,b, 1995Opheim and Gudmundsson, 1989;Trippanera et al, 2014Trippanera et al, , 2015Sigmundsson et al, 2015). In fact, it is well-known that, at the tip of an advancing dyke, tensile stresses can increase due to magma injection (Rubin and Pollard, 1988;Rubin, 1992) and exceed the Coulomb failure threshold, triggering earthquakes in the brittle crust (Brandsdóttir and Einarsson, 1979;Einarsson and Brandsdóttir, 1980;Feigl et al, 2000;Cattin et al, 2005).…”

“…As classically accepted, the magmatic pressure from intruding dykes may induce tension fracture opening at depth and at the surface (Gudmundsson, 1987a(Gudmundsson, ,b, 1995Opheim and Gudmundsson, 1989;Sigmundsson et al, 2015). An overpressured dyke exerts tensile stresses along its tip line, which are capable of producing an advancing fracture; once the fracture has formed, the magma intrudes along it and the dyke propagates (review in Tibaldi (2015), and reference therein).…”

Tremor-rich shallow dyke formation followed by silent magma flow at Bárðarbunga in Iceland

“…The horizontal locations are spread in a NNE-SSW direction which is consistent with the elongation of the location error ellipse in that direction (not shown). We determine that the epicentre of the tremor is laterally consistent with the dyke location (as de ned by relatively relocated earthquakes at 5 to 8 km depth 10 ) and cauldron C1 to C3 locations. In this instance the tremor depth is not constrained by array analysis but is determined in the next section with the aid of full waveform numerical simulations (see supplementary gure 2e for a location precision test using a well located earthquake).…”

“…From August 16 th , 2014 a dyke accompanied by 5 to 8 km deep earthquakes formed beneath Bárdarbunga volcano propagating initially in a SE direction. Propagation speeds and directions changed multiple times with an average direction towards the NNE migrating about 48 km in 11 days 10 . On August 29 th , 2014 a 4 hour long subaerial eruption started near the tip of the dyke 5 km north of the glacier rim.…”

Imagining the Unimaginable: Communicating Extreme Volcanic Risk

“…The 2014-15 volcanic eruption in Holuhraun, north of Vatnajökull, in Iceland represents an analogue for such an eruption, albeit at about a tenth of the magnitude scale. Precursory activity to this eruption was roughly two weeks in duration, with evidence for dyke propagation (Sigmundsson et al 2014) from a central volcano, starting on 16 August 2014 and the first subaerial eruption on 29 August. Based on this scenario, there would be roughly two weeks' warning that magma was rising.…”