| 1. |
- Árnadóttir, Thóra, et al.
(författare)
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Glacial rebound and plate spreading : results from the first countrywide GPS observations in Iceland
- 2009
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Ingår i: Geophysical Journal International. - 0956-540X .- 1365-246X. ; 177:2, s. 691-716
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Forskningsöversikt (refereegranskat)abstract
- Iceland is one of the few places on Earth where a divergent plate boundary can be observed on land. Direct observations of crustal deformation for the whole country are available for the first time from nationwide Global Positioning System (GPS) campaigns in 1993 and 2004. The plate spreading across the island is imaged by the horizontal velocity field and high uplift rates (>= 10 mm yr(-1)) are observed over a large part of central and southeastern Iceland. Several earthquakes, volcanic intrusions and eruptions occurred during the time spanned by the measurements, causing local disturbances of the deformation field. After correcting for the largest earthquakes during the observation period, we calculate the strain rate field and find that the main feature of the field is the extension across the rift zones, subparallel to the direction of plate motion. Kinematic models of the horizontal plate spreading signal indicate a slightly elevated rate of spreading in the Northern Volcanic Zone (NVZ) (23 +/- 2 mm yr(-1)), while the rates at the other plate boundary segments agree fairly well with the predicted rate of plate spreading (similar to 20 mm yr(-1)) across Iceland. The horizontal ISNET velocities across north Iceland therefore indicate that the excessive spreading rate (>30 mm yr(-1)) observed by GPS in 1987-1992 following the 1975-1984 Krafla rifting episode was significantly slower during 1993-2004. We model the vertical velocities using glacial isostatic adjustment (GIA) due to the recent thinning of the largest glaciers in Iceland. A layered earth model with a 10-km thick elastic layer, underlain by a 30-km thick viscoelastic layer with viscosity 1 x 10(20) Pa s, over a half-space with viscosity similar to 1 x 10(19) Pa s can explain the broad area of uplift in central and southeastern Iceland. A wide area of significant residual uplift ( up to 8 mm yr(-1)) is evident in north Iceland after we subtract the rebound signal from the observed rates, whereas the Reykjanes Peninsula and the Western Volcanic Zone (WVZ) appear to be subsiding at a rate of 4-8 mm yr(-1). We observe a coherent pattern of small but significant residual horizontal motion (up to 3 mm yr(-1)) away from Vatnajokull and the smaller glaciers that is most likely caused by glacial rebound. Our study demonstrates that the velocity field over a large part of Iceland is affected by deglaciation and that this effect needs to be considered when interpreting deformation data to monitor subglacial volcanoes in Iceland.
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| 2. |
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| 3. |
- Pagli, Carolina, et al.
(författare)
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Glacio-isostatic deformation around the Vatnajökull ice cap, Iceland, induced by recent climate warming : GPS observations and finite element modeling
- 2007
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 112:B8, s. B08405-
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Tidskriftsartikel (refereegranskat)abstract
- [1] Glaciers in Iceland began retreating around 1890, and since then the Vatnajokull ice cap has lost over 400 km 3 of ice. The associated unloading of the crust induces a glacio-isostatic response. From 1996 to 2004 a GPS network was measured around the southern edge of Vatnajokull. These measurements, together with more extended time series at several other GPS sites, indicate vertical velocities around the ice cap ranging from 9 to 25 mm/yr, and horizontal velocities in the range 3 to 4 mm/yr. The vertical velocities have been modeled using the finite element method (FEM) in order to constrain the viscosity structure beneath Vatnajokull. We use an axisymmetric Earth model with an elastic plate over a uniform viscoelastic half-space. The observations are consistent with predictions based on an Earth model made up of an elastic plate with a thickness of 10-20 km and an underlying viscosity in the range 4-10 x 10(18) Pa s. Knowledge of the Earth structure allows us to predict uplift around Vatnajokull in the next decades. According to our estimates of the rheological parameters, and assuming that ice thinning will continue at a similar rate during this century (about 4 km 3/year), a minimum uplift of 2.5 meters between 2000 to 2100 is expected near the current ice cap edge. If the thinning rates were to double in response to global warming (about 8 km 3/year), then the minimum uplift between 2000 to 2100 near the current ice cap edge is expected to be 3.7 meters.
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| 4. |
- Pinel, Virginie, et al.
(författare)
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Consequences of local surface load variations for volcanoes monitoring: Application to Katla subglacial volcano, Iceland
- 2009
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Ingår i: The VOLUME Project. VOLcanoes: Understanding subsurface mass moveMEnt. Edited by C.J. Bean, A.K. Braiden, I. Lokmer, F. Martini, G.S. O´Brien. - Dublin, Ireland. - 9781905254392 ; , s. 25-39
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Surface load variations occur frequently in the vicinity of volcanoes inducing deformation and stress field perturbations that can be recorded by geophysical monitoring. It is thus necessary to discriminate these perturbations from those caused by shallow magma movement and to understand their potential influence on themagmatic plumbing system. Discrimination can be performed by modelling the deformation induced by surface load variations using integration of Green's function. This method was applied to the Katla volcano located beneath the Mýrdalsjökull ice cap, Iceland, where an annual cycle in ice load occurs as well as a gradual ice retreat. We also estimated pressure changes induced by the seasonal ice load variation within a magma reservoir, and calculated the deformation field and the Coulomb stress changes induced by the combined effect of the ice load variation and the magma pressure re-equilibration. Seismicity rate response to the seasonal perturbation strongly depends on the shape and state of the magma reservoir. Finally, introducing a rupture criterion, we conclude that, in the case of spherical or horizontally elongated reservoir and a slow magma inflow, eruptions at Katla volcano are more likely during the summer period, which is consistent with historical observations.
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