ALBERT

Description: Gradual inflation of magma chambers often precedes eruptions at highly active volcanoes. During such eruptions, rapid deflation occurs as magma flows out and pressure is reduced. Less is known about the deformation style at moderately active volcanoes, such as Eyjafjallajokull, Iceland, where an explosive summit eruption of trachyandesite beginning on 14 April 2010 caused exceptional disruption to air traffic, closing airspace over much of Europe for days. This eruption was preceded by an effusive flank eruption of basalt from 20 March to 12 April 2010. The 2010 eruptions are the culmination of 18 years of intermittent volcanic unrest. Here we show that deformation associated with the eruptions was unusual because it did not relate to pressure changes within a single magma chamber. Deformation was rapid before the first eruption (〉5 mm per day after 4 March), but negligible during it. Lack of distinct co-eruptive deflation indicates that the net volume of magma drained from shallow depth during this eruption was small; rather, magma flowed from considerable depth. Before the eruption, a approximately 0.05 km(3) magmatic intrusion grew over a period of three months, in a temporally and spatially complex manner, as revealed by GPS (Global Positioning System) geodetic measurements and interferometric analysis of satellite radar images. The second eruption occurred within the ice-capped caldera of the volcano, with explosivity amplified by magma-ice interaction. Gradual contraction of a source, distinct from the pre-eruptive inflation sources, is evident from geodetic data. Eyjafjallajokull's behaviour can be attributed to its off-rift setting with a 'cold' subsurface structure and limited magma at shallow depth, as may be typical for moderately active volcanoes. Clear signs of volcanic unrest signals over years to weeks may indicate reawakening of such volcanoes, whereas immediate short-term eruption precursors may be subtle and difficult to detect.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Sigmundsson, Freysteinn -- Hreinsdottir, Sigrun -- Hooper, Andrew -- Arnadottir, Thora -- Pedersen, Rikke -- Roberts, Matthew J -- Oskarsson, Niels -- Auriac, Amandine -- Decriem, Judicael -- Einarsson, Pall -- Geirsson, Halldor -- Hensch, Martin -- Ofeigsson, Benedikt G -- Sturkell, Erik -- Sveinbjornsson, Hjorleifur -- Feigl, Kurt L -- England -- Nature. 2010 Nov 18;468(7322):426-30. doi: 10.1038/nature09558.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Nordic Volcanological Center, Institute of Earth Sciences, University of Iceland, Askja, Sturlugata 7, Reykjavik IS-101, Iceland. fs@hi.is〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/21085177" target="_blank"〉PubMed〈/a〉

Description: Crust at many divergent plate boundaries forms primarily by the injection of vertical sheet-like dykes, some tens of kilometres long. Previous models of rifting events indicate either lateral dyke growth away from a feeding source, with propagation rates decreasing as the dyke lengthens, or magma flowing vertically into dykes from an underlying source, with the role of topography on the evolution of lateral dykes not clear. Here we show how a recent segmented dyke intrusion in the Baretharbunga volcanic system grew laterally for more than 45 kilometres at a variable rate, with topography influencing the direction of propagation. Barriers at the ends of each segment were overcome by the build-up of pressure in the dyke end; then a new segment formed and dyke lengthening temporarily peaked. The dyke evolution, which occurred primarily over 14 days, was revealed by propagating seismicity, ground deformation mapped by Global Positioning System (GPS), interferometric analysis of satellite radar images (InSAR), and graben formation. The strike of the dyke segments varies from an initially radial direction away from the Baretharbunga caldera, towards alignment with that expected from regional stress at the distal end. A model minimizing the combined strain and gravitational potential energy explains the propagation path. Dyke opening and seismicity focused at the most distal segment at any given time, and were simultaneous with magma source deflation and slow collapse at the Baretharbunga caldera, accompanied by a series of magnitude M 〉 5 earthquakes. Dyke growth was slowed down by an effusive fissure eruption near the end of the dyke. Lateral dyke growth with segment barrier breaking by pressure build-up in the dyke distal end explains how focused upwelling of magma under central volcanoes is effectively redistributed over long distances to create new upper crust at divergent plate boundaries.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Sigmundsson, Freysteinn -- Hooper, Andrew -- Hreinsdottir, Sigrun -- Vogfjord, Kristin S -- Ofeigsson, Benedikt G -- Heimisson, Elias Rafn -- Dumont, Stephanie -- Parks, Michelle -- Spaans, Karsten -- Gudmundsson, Gunnar B -- Drouin, Vincent -- Arnadottir, Thora -- Jonsdottir, Kristin -- Gudmundsson, Magnus T -- Hognadottir, Thordis -- Fridriksdottir, Hildur Maria -- Hensch, Martin -- Einarsson, Pall -- Magnusson, Eyjolfur -- Samsonov, Sergey -- Brandsdottir, Bryndis -- White, Robert S -- Agustsdottir, Thorbjorg -- Greenfield, Tim -- Green, Robert G -- Hjartardottir, Asta Rut -- Pedersen, Rikke -- Bennett, Richard A -- Geirsson, Halldor -- La Femina, Peter C -- Bjornsson, Helgi -- Palsson, Finnur -- Sturkell, Erik -- Bean, Christopher J -- Mollhoff, Martin -- Braiden, Aoife K -- Eibl, Eva P S -- England -- Nature. 2015 Jan 8;517(7533):191-5. doi: 10.1038/nature14111. Epub 2014 Dec 15.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Nordic Volcanological Center, Institute of Earth Sciences, University of Iceland, IS-101 Reykjavik, Iceland. ; Centre for the Observation and Modelling of Earthquakes and Tectonics (COMET), School of Earth and Environment, University of Leeds, Leeds LS2 9JT, UK. ; GNS Science, PO Box 30368, Lower Hutt 5040, New Zealand. ; Icelandic Meteorological Office, IS-150 Reykjavik, Iceland. ; 1] Nordic Volcanological Center, Institute of Earth Sciences, University of Iceland, IS-101 Reykjavik, Iceland [2] Icelandic Meteorological Office, IS-150 Reykjavik, Iceland. ; Canada Centre for Mapping and Earth Observation, Natural Resources Canada, 560 Rochester Street, Ottawa, Ontario K1A 0E4, Canada. ; Department of Earth Sciences, University of Cambridge, Madingley Road, Cambridge CB3 0EZ, UK. ; Department of Geosciences, University of Arizona, Tucson, Arizona 85721, USA. ; Department of Geosciences, The Pennsylvania State University, University Park, Pennsylvania 16802, USA. ; Department of Earth Sciences, University of Gothenburg, SE-405 30 Gothenburg, Sweden. ; Seismology Laboratory, School of Geological Sciences, University College Dublin, Belfield, Dublin 4, Ireland.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/25517098" target="_blank"〉PubMed〈/a〉

Description: A hallmark of schizophrenia pathophysiology is the dysfunction of cortical inhibitory GABA neurons expressing parvalbumin, which are essential for coordinating neuronal synchrony during various sensory and cognitive tasks. The high metabolic requirements of these fast-spiking cells may render them susceptible to redox dysregulation and oxidative stress. Using mice carrying a...

Description: On 2008 May 29, two magnitude M W ~ 6 earthquakes occurred on two adjacent N-S faults in the western South Iceland Seismic Zone. The first main shock was followed approximately 3 s later by the rupture on a parallel fault, about 5 km to the west. An intense aftershock sequence was mostly confined to the western fault and an E-W aligned zone, extending west of the main shock region into the Reykjanes oblique rift. In this study, a total of 325 well-constrained focal mechanisms were obtained using data from the permanent Icelandic SIL seismic network and a temporary network promptly installed in the source region following the main shocks, which allowed a high-resolution stress inversion in short time intervals during the aftershock period. More than 800 additional focal mechanisms for the time period 2001–2009, obtained from the permanent SIL network, were analysed to study stress changes associated with the main shocks. Results reveal a coseismic counter-clockwise rotation of the maximum horizontal stress of 11 ± 10° (95 per cent confidence level) in the main rupture region. From previous fault models obtained by inversion of geodetic data, we estimate a stress drop of about half of the background shear stress on the western fault. With a stress drop of 8–10 MPa, the pre-event shear stress is estimated to 16–20 MPa. The apparent weakness of the western fault may be caused by fault properties, pore fluid pressure and the vicinity of the fault to the western rift zone, but may also be due to the dynamic stress increase on the western fault by the rupture on the eastern fault. Further, a coseismic change of the stress regime—from normal faulting to strike-slip faulting—was observed at the northern end of the western fault. This change could be caused by stress heterogeneities, but may also be due to a southward shift in the location of the aftershocks as compared to prior events.

Description: 〈span〉〈div〉SUMMARY〈/div〉The occurrence of deep low-frequency (DLF) microearthquakes beneath volcanoes is commonly attributed to mass transport in the volcanic plumbing system and used to infer feeding channels from and into magma reservoirs. The key question is how magmas migrate from depth to the shallow crust and whether magma reservoirs are currently being recharged. For the first time since the improvement of the local seismic networks in the East Eifel region (Rhineland-Palatinate, Germany), we detect and locate recurrent DLF earthquakes in the lower crust and upper mantle beneath the Laacher See Volcano (LSV), using a joint data set of permanent sensors and a temporary deployment. So far, eight DLF earthquake sequences were observed in four distinct clusters between 10 km and 40 km depth. These clusters of weak events (〈span〉ML〈/span〉〈 2) align along an approximately 80° south-east dipping line south of the LSV. Moment tensor solutions of these events have large shear components, and the irregular dispersion and long coda of body waves indicate interaction processes between shear cracks and fluids. We find a rotation of P-axes orientation for shallow tectonic earthquakes compared to DLF events, indicating that the stress field in the depth interval of DLF events might favor a vertical migration of magma or magmatic fluids. The caldera of LSV was formed by the last major eruption of the East Eifel Volcanic Field only 12.9 kyr ago, fed by a shallow magma chamber at 5-8 km depth and erupting a total magma volume of 6.7 km〈sup〉3〈/sup〉. The observed DLF earthquake activity and continuous volcanic gas emissions around the LSV indicate an active magmatic system, possibly connected with an upper mantle melt zone.〈/span〉

Description: The Kolumbo submarine volcano in the southern Aegean (Greece) is associated with repeated seismic unrest since at least two decades and the causes of this unrest are poorly understood. We present a ten-month long microseismicity data set for the period 2006–2007. The majority of earthquakes cluster in a cone-shaped portion of the crust below Kolumbo. The tip of this cone coincides with a low Vp-anomaly at 2–4 km depth, which is interpreted as a crustal melt reservoir. Our data set includes several earthquake swarms, of which we analyze the four with the highest events numbers in detail. Together the swarms form a zone of fracturing elongated in the SW-NE direction, parallel to major regional faults. All four swarms show a general upward migration of hypocenters and the cracking front propagates unusually fast, compared to swarms in other volcanic areas. We conclude that the swarm seismicity is most likely triggered by a combination of pore-pressure perturbations and the re-distribution of elastic stresses. Fluid pressure perturbations are induced likely by obstructions in the melt conduits in a rheologically strong layer between 6 and 9 km depth. We conclude that the zone of fractures below Kolumbo is exploited by melts ascending from the mantle and filling the crustal melt reservoir. Together with the recurring seismic unrest, our study suggests that a future eruption is probable and monitoring of the Kolumbo volcanic system is highly advisable. Key Points Seismicity is clustered in a cone-shaped volume beneath Kolumbo; the cone's tip coincides with a melt reservoir at 2–4 km depth Seismicity swarms occupy nearby, yet different portions of the crust, ruling out an origin on a single fault Swarms were likely triggered by a combination of fluid pressure perturbations and redistribution of elastic stresses