| 1. |
- Sigmundsson, F., et al.
(författare)
-
Segmented lateral dyke growth in a rifting event at Bardarbunga volcanic system, Iceland
- 2015
-
Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 517:7533
-
Tidskriftsartikel (refereegranskat)abstract
- Crust at many divergent plate boundaries forms primarily by the injection of vertical sheet-like dykes, some tens of kilometres long(1). Previous models of rifting events indicate either lateral dyke growth away from a feeding source, with propagation rates decreasing as the dyke lengthens(2-4), or magma flowing vertically into dykes from an underlying source(5,6), with the role of topography on the evolution of lateral dykes not clear. Here we show how a recent segmented dyke intrusion in the Bardarbunga 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 Bardarbunga 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 Bardarbunga 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.
|
|
| 2. |
- Geirsson, H., et al.
(författare)
-
Overview of results from continuous GPS observations in Iceland from 1995 to 2010
- 2010
-
Ingår i: Jökull. - 0449-0576. ; 60:1, s. 1-21
-
Tidskriftsartikel (refereegranskat)abstract
- Iceland is a natural laboratory for a variety of processes associated with crustal deformation, such as earthquakes, magmatic events, tectonic plate motions, and glacial load changes. Continuous GPS (CGPS) measurements started in Iceland in 1995, and since then data from the network have helped to shed light on many different active deformation processes. The number of CGPS sites in Iceland tripled during 2006–2008, as a result of an international collaborative effort coordinated by Icelandic scientists. By early 2010 the number of CGPS stations in Iceland had reached 64, located primarily around and within the North- American–Eurasian plate boundary zone. Since its initiation, the CGPS network has played an important role in monitoring volcanoes and seismogenic areas, most notably during the 2009–2010 Eyjafjallajökull volcano unrest. Plate spreading of up to 2 cm per year usually dominates the horizontal motion observed at the CGPS sites, while uplift is observed at many of the stations due to recent retreat of the Icelandic ice caps. Co-seismic and post-seismic deformation of the largest earthquakes in 2000 and 2008 in the South Iceland Seismic Zone were captured by the network, and high-rate (1 Hz) CGPS observations helped to identify two magnitude 6 mainshocks in 2008 that were separated in time by only 2–3 seconds. The CGPS network has thus enabled us to monitor deformation occurring over days to months caused by migration of magma or fluids, post-seismic transients, rapid deformation caused by earthquakes and eruptions, as well as the long term plate spreading signal.
|
|
| 3. |
|
|
| 4. |
- Drouin, V., et al.
(författare)
-
Deformation in the Northern Volcanic Zone of Iceland 2008-2014: An interplay of tectonic, magmatic, and glacial isostatic deformation
- 2017
-
Ingår i: Journal of Geophysical Research-Solid Earth. - : American Geophysical Union (AGU). - 2169-9313 .- 2169-9356. ; 122:4, s. 3158-3178
-
Tidskriftsartikel (refereegranskat)abstract
- GPS measurements spanning 2008 to 2014 are used to derive the surface velocity field across the Northern Volcanic Zone (NVZ) of Iceland, a subaerial part of the divergent boundary between the North American and Eurasian plates. No volcanic activity nor magmatic intrusions were detected in the zone during this time period. We infer an extensional rate of 17.4(-0.3)(+0.2) mm/yr in direction 292.0(-0.6)(+0.5 degrees),consistent with the results of previous studies and current plate motion models including MORVEL2010 and GEODVEL2010. The horizontal velocity field reveals about 50 km wide stretching zone caused by the divergent plate movements. Glacial isostatic adjustment (GIA) induces uplift of over 20 mm/yr at the northern edge of Vatnajokull ice cap and 3-4 mm/yr horizontal motion directed away from the ice cap. Deformation in the NVZ between 2008 and 2014 can be reproduced by a combination of models relating to several different processes: (i) Mogi sources for volcanic and geothermal deformation at the Askja and Krafla volcanoes, (ii) scaled version of a velocity field derived from a glacial isostatic model, and (iii) simple arctangent-based model for secular plate spreading. We find the approximate location of the plate boundary spreading axis as well as its locking depth. The spreading axis lies through the Krafla, Fremrinamar, and Askja central volcanoes, the most active ones in the NVZ. It does not appear to follow the general direction of each fissure swarm but rather to change direction at the central volcanoes. The locking depth is on average within the 7-9 km range.
|
|
| 5. |
- Hreinsdottir, S, et al.
(författare)
-
A complex earthquake sequence captured by the continuous GPS network in SW Iceland
- 2009
-
Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 36:12, s. L12309-
-
Tidskriftsartikel (refereegranskat)abstract
- A complex sequence of earthquakes struck the western part of the South Iceland Seismic Zone (SISZ) on 29 May 2008. The sequence initiated with a M(w)6.3 (NEIC) earthquake in the western part of the SISZ. Aftershocks from the earthquake delineate two parallel N-S trending structures 4 km apart, in addition to activity along an E-W zone further westward. Continuous GPS measurements can best be explained by right-lateral strike-slip motion on two parallel N-S trending faults, with little slip occurring on other structures illuminated by earthquake activity. We estimate a total moment release of M(w)6.2, with M(w)6.1 on the first rupture and M(w)6.0 on the second rupture. High rate (1 Hz) CGPS data from a near-field station suggest that the main asperity on the Kross fault ruptured within 3 s of the initial mainshock on the Ingolfsfjall fault. Citation: Hreinsdottir, S., T. Amadottir, J. Decriem, H. Geirsson, A. Tryggvason, R. A. Bennett, and P. LaFemina (2009), A complex earthquake sequence captured by the continuous GPS network in SW Iceland, Geophys. Res. Lett., 36, L12309, doi: 10.1029/2009GL038391.
|
|
| 6. |
- Hreinsdottir, S., et al.
(författare)
-
Volcanic plume height correlated with magma-pressure change at Grimsvotn Volcano, Iceland
- 2014
-
Ingår i: Nature Geoscience. - : Springer Science and Business Media LLC. - 1752-0894 .- 1752-0908. ; 7:3, s. 214-218
-
Tidskriftsartikel (refereegranskat)abstract
- Magma flow during volcanic eruptions causes surface deformation that can be used to constrain the location, geometry and internal pressure evolution of the underlying magmatic source(1). The height of the volcanic plumes during explosive eruptions also varies with magma flow rate, in a nonlinear way(2,3). In May 2011, an explosive eruption at Grimsvotn Volcano, Iceland, erupted about 0.27 km(3) dense-rock equivalent of basaltic magma in an eruption plume that was about 20 km high. Here we use Global Positioning System (GPS) and tilt data, measured before and during the eruption at Grimsvotn Volcano, to show that the rate of pressure change in an underlying magma chamber correlates with the height of the volcanic plume over the course of the eruption. We interpret ground deformation of the volcano, measured by geodesy, to result from a pressure drop within a magma chamber at about 1.7 km depth. We estimate the rate of magma discharge and the associated evolution of the plume height by differentiating the co-eruptive pressure drop with time. The time from the initiation of the pressure drop to the onset of the eruption was about 60 min, with about 25% of the total pressure change preceding the eruption. Near-real-time geodetic observations can thus be useful for both timely eruption warnings and for constraining the evolution of volcanic plumes.
|
|
| 7. |
- Sigmundsson, F., et al.
(författare)
-
Intrusion triggering of the 2010 Eyjafjallajökull explosive eruption
- 2010
-
Ingår i: Nature. ; 468:7322, s. 426-430
-
Tidskriftsartikel (refereegranskat)abstract
- 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 reduced1–3. Less is known about the deformation style at moderately active volcanoes, such as Eyjafjallajo¨kull, 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 unrest4–9. 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 (.5mm 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 0.05km3 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. Eyjafjallajo¨kull’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.
|
|
