| 61. |
- Rymer, H., et al.
(författare)
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New mass increase beneath Askja volcano, Iceland – a precursor to renewed activity?
- 2010
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Ingår i: Terra Nova. - 0954-4879. ; 22:4
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Tidskriftsartikel (refereegranskat)abstract
- Askja is an active central volcano located on the NS trending en echelon rift zone marking the mid-Atlantic plate boundary in North Iceland. Between 2007 and 2009, we observed a gravity increase at the centre of the caldera. This contrasts with net gravity decreases recorded between 1988 and 2007 interpreted previously in terms of magma drainage. The recent gravity increase is rapid, but similar in terms of lateral extent to the preceding decrease. This gravity increase corresponds to a sub-surface mass increase of 0.68 × 1011 kg at about 3 km depth. It is possible that the new gravity increases observed at Askja reflect accumulation of magma beneath the caldera and thus may herald a new phase in the activity of this volcano, which last erupted in 1961.
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| 62. |
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| 63. |
- Sgattoni, G., et al.
(författare)
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Joint relative location of earthquakes without a pre-defined velocity model : an example from a peculiar seismic cluster on Katla volcano's south-flank (Iceland)
- 2016
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Ingår i: Geophysical Journal International. - : Oxford University Press (OUP). - 0956-540X .- 1365-246X. ; 207:2, s. 1244-1257
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Tidskriftsartikel (refereegranskat)abstract
- Relative location methods are commonly used to precisely locate earthquake clusters consisting of similar waveforms. Repeating waveforms are often recorded at volcanoes, where, however, the crust structure is expected to contain strong heterogeneities and therefore the 1-D velocity model assumption that is made in most location strategies is not likely to describe reality. A peculiar cluster of repeating low-frequency seismic events was recorded on the south flank of Katla volcano (Iceland) from 2011. As the hypocentres are located at the rim of the glacier, the seismicity may be due to volcanic or glacial processes. Information on the size and shape of the cluster may help constraining the source process. The extreme similarity of waveforms points to a very small spatial distribution of hypocentres. In order to extract meaningful information about size and shape of the cluster, we minimize uncertainty by optimizing the cross-correlation measurements and relative-location process. With a synthetic test we determine the best parameters for differential-time measurements and estimate their uncertainties, specifically for each waveform. We design a location strategy to work without a pre-defined velocity model, by formulating and inverting the problem to seek changes in both location and slowness, thus accounting for azimuth, take-off angles and velocity deviations from a 1-D model. We solve the inversion explicitly in order to propagate data errors through the calculation. With this approach we are able to resolve a source volume few tens of metres wide in horizontal directions and around 100 metres in depth. There is no suggestion that the hypocentres lie on a single fault plane and the depth distribution indicates that their source is unlikely to be related to glacial processes as the ice thickness is not expected to exceed few tens of metres in the source area. Our method is designed for a very small source region, allowing us to assume a constant slowness for the whole cluster and to include the effects of 3-D heterogeneity such as refraction. Similar circumstances may arise in other volcanic regions with a high level of heterogeneity and where densely clustered earthquakes are often recorded.
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| 64. |
- Sigmundsson, F., et al.
(författare)
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Intrusion triggering of the 2010 Eyjafjallajökull explosive eruption
- 2010
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Ingår i: Nature. ; 468:7322
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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.
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| 65. |
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| 66. |
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| 67. |
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| 68. |
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| 69. |
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| 70. |
- Sturkell, Erik, 1962, et al.
(författare)
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Katla and Eyjafjallajökull Volcanoes
- 2010
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Ingår i: Developments in Quaternary Sciences, Vol. 13: The Mýrdalsjökull Ice Cap, Iceland. Glacial processes, sediments and landforms on an active volcano (Edited by Anders Schomacker, Johannes Krüger and Kurt H. Kjær). - : Elsevier Ltd. - 9780444530455
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- The Katlavolcano is covered by the Mýrdalsjökull ice cap and is currently one of the most active volcanoes in Iceland. It has erupted twenty times the past 1,100 years. The neighbouring volcanoEyjafjallajökull has erupted twice, simultaneously with Katla. As glaciers cover both volcanoes, their eruptions are phreato-magmatic by nature. The volcanoes are located directly south of where surface expressions of the rift cease. Seismically, Katla is one of the most active volcanoes in Iceland, showing an annual cycle in activity, observed from at least 1960 and less pronounced since 2004. From 1999 to late 2004, GPS measurements revealed steady inflation of the volcano, showing uplift and outward horizontal displacement. Until 1990s, Eyjafjallajökull had been seismically quiet for several decades. Seismic activity there was high in 1994 and again in 1999, related to the emplacement of two intrusions.
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