Dike emplacement at Bardarbunga, Iceland, induces unusual stress changes, caldera deformation, and earthquakes

Abstract

A 45-km-long regional dike was emplaced over a period of 2 weeks in August 2014 at the boundary between the East and North Volcanic Zones in Iceland. This is the first regional dike emplacement in Iceland monitored with modern geophysical networks, the importance of which relates to regional dikes feeding most of the large fissure (e.g., Eldgja 934 and Laki 1783) and lava shield (e.g. early Holocene Skjaldbreidur and Trölladyngja) eruptions. During this time, the dike generated some 17,000 earthquakes, more than produced in Iceland as a whole over a normal year. The dike initiated close to the Bardarbunga Volcano but gradually extended to the northeast until it crossed the boundary between the East Volcanic Zone (EVZ) and the North Volcanic Zone (NVZ). We infer that the strike of the dike changes abruptly at a point, from about N45°E (coinciding with the trend of the EVZ) to N15°E (coinciding with the trend of the NVZ). This change in strike occurs at latitude 64.7°, exactly the same latitude at which about 10 Ma dikes in East Iceland change strike in a similar way. This suggests that the change in the regional stress field from the southern to the northern part of Iceland has been maintained at this latitude for 10 million years. Analytical and numerical models indicate that the dikeinduced stress field results in stress concentration around faults and particularly shallow magma chambers and calderas in its vicinity, such as Tungnafellsjökull, Kverkfjöll, and Askja. In particular, the dike has induced high compressive, shear, and tensile stresses at the location of the Bardarbunga shallow chamber and (caldera) ring-fault where numerous earthquakes occurred during the dike emplacement, many of which have exceeded M5 (the largest M5.7). The first segment of the dike induced high tensile stresses in the nearby part of the Bardarbunga magma chamber/ring-fault resulting in radially outward injection of a dike from the chamber at a high angle to the strike of the regional dike. The location of maximum stress at Bardarbunga fluctuates along the chamber/ ring-fault boundary in harmony with dike size and/or pressure changes and encourages ring-dike formation and associated magma flow within the chamber. Caldera collapse and/or eruption in some of these volcanoes is possible, most likely in Bardarbunga, but depends largely on the future development of the regional dike.

Melt inclusion constraints on petrogenesis of the 2014–2015 Holuhraun eruption, Iceland

“…Magma withdrawal from a shallow magma chamber may also result in caldera subsidence at the volcanic edifice (e.g., Stix and Kobayashi 2008, and references therein). Alternatively, fissure eruptions along rift zones may be driven by pressurization of lower crustal magma reservoirs and the injection of subvertical dykes towards the surface, with associated movement on caldera ring faults resulting from the concentration of dyke-induced stress fields around pre-existing faults and/or shallow magma chambers (e.g., Gudmundsson 1995;Gudmundsson et al 2014). These models have been discussed extensively with respect to volcano-tectonic episodes for volcanic edifices including Kilauea, Hawaii (Ryan 1988;Baker and Amelung 2012); the Afar region of Ethiopia (Wright et al 2006;Jeir et al 2009;Ebinger et al 2010); and mid-ocean ridge segments (e.g., Fialko and Rubin 1998;Dziak et al 1995;Escartín et al 2014).…”

Lateral Magma Flow in Mafic Sill‐complexes

“…Indirect analytical approaches commonly involve: (1) the examination of ground deformation patterns (e.g., using InSAR, interferometric synthetic aperture radar) inferred to relate to the emplacement of magma (e.g., Pedersen, 2004;Wright et al, 2006;Pagli et al, 2012;Sparks et al, 2012); (2) scrutiny of petrological and geochemical data to assess magma contamination, residence times, crystallization histories, and melt source conditions (Cashman and Sparks, 2013, and references therein); and/or (3) mapping the location and crude geometry of crystallized intrusions or present-day zones of melt using geophysical techniques such as potential field, magnetotellurics, and seismicity (e.g., Cornwell et al, 2006;Whaler and Hautot, 2006;Desissa et al, 2013). For example, the application and synthesis of these techniques in the East African Rift system and Iceland have greatly improved our understanding of magma-tectonic interactions and allowed processes controlling continental break-up, such as dike intrusion, to be analyzed in real time (e.g., Ebinger et al, 2010;Gudmundsson et al, 2014;Sigmundsson et al, 2015). It is, however, important to consider that these data poorly constrain intrusion geometries and are commonly interpreted within the classical framework of igneous geology; i.e., magma migration within the Earth's crust is generally facilitated by the vertical intrusion of dikes, extending from a deep magma reservoir or melt source to overlying shallow-level intrusions and volcanoes ( Fig.…”

Volcano Statistics Casebook: Tentative evidence from two real-time analyses for an Earth tide influence on volcano-seismic events

“…This concept has been adopted to explain geophysical observations (e.g., Peltier et al, 2008;Kusumoto & Gudmundsson, 2009) and as a basis for analogue models (Acocella et al, 2000;Holohan et al, 2011), and latterly has been invoked to explain ice surface subsidence at Bárðarbunga in 2014 − 2015 (Sigmundsson et al, 2015). A variant hypothesis, pertinent to the Bárðarbunga case, is that lavas in large fissure eruptions can be fed by regional-scale vertical channelling dikes, injecting magma into shallow sills from much deeper reservoirs (Gudmundsson et al, 2014). Browning & Gudmundsson (2015) adopted this argument in their modelling of the Bárðarbunga episode, suggesting that the ring-fault subsidence in the caldera was triggered by modest upward doming of the volcanic system due to magma injection and pressurization.…”