Geodetic investigation of Torfajokull Volcano, Iceland
Date
2009-05-29T07:30:30Z
Authors
Scheiber, Stephanie Elizabeth
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Abstract
The Mid-Atlantic ridge and North Atlantic mantle plume interaction is expressed in south
Iceland as two overlapping, subparallel spreading centres; the Western (WVZ) and
Eastern Volcanic Zones (EVZ). The South Iceland Seismic Zone (SISZ), a transform
fault, connects these systems. Plate motion is partitioned across these zones and is
accommodated by repeated lateral dyke injection from central volcanoes into fissure
swarms within the volcanic zones. South of the SISZ-EVZ intersection, also the location
of Torfajökull volcano, the EVZ is propagating to the southwest into the Eastern Volcanic
Flank Zone (EVFZ). The plate spreading south of Torfajökull appears to be partitioned
across the Reykjanes Peninsula (RP) in the west and the EVFZ.
This study investigates the complex interplay between plate spreading and volcano
deformation in the region surrounding Torfajökull volcano using space geodetic and
modelling techniques. We present a new horizontal velocity field based on episodic GPS
measurements collected between 2000 and 2006 in the southern part of the EVZ. This
velocity field is compared to a GPS-derived velocity field from 1994-2003 (LaFemina et
al. 2005) and elastic half-space plate spreading models. In a stable Eurasian reference
frame the horizontal signal is dominated by plate spreading through the caldera, in
agreement with known Holocene fissuring to the northeast along the Veidivötn fissure
swarm and southwest of the caldera. It is shown that spreading is occurring across the
EVFZ, with maximum strain accumulation during this inter-rifting period along the
western edge of the Eldgjá fissure swarm which was last active in 934 A.D. These locations have major implications for the location of future rifting events as it is
presumed that significant subsurface magma accumulation occurs along the centre of
spreading.
Spreading rates for this study show along strike variations, decreasing from 10-20 mm/yr
to the north of Torfajökull to 7-8 mm/yr in the south, which is in line with a simple
propagating ridge model and previous studies. Locking depths for these dyke models are
relatively shallow (<6 km). The horizontal velocity field also indicates the interaction of
Hekla volcano situated in the northwest of the study area, as the volcano has been
uplifting since its last eruption in 2000, as well as subsidence due to a possible slow
cooling magma chamber in the western part of Torfajökull which is supported by InSAR
and “dry-tilt” data.