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| Titel |
Volcanic unrest primed by ice cap melting: A case study of Snæfellsjökull volcano, Western Iceland |
| VerfasserIn |
Richard Bakker, Matteo Lupi, Marcel Frehner, Julien Berger, Florian Fuchs |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250097723
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| Publikation (Nr.) |
 EGU/EGU2014-13332.pdf |
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| Zusammenfassung |
| The most dramatic effect of global warming is the water level rise due to rapid melting of ice
sheets. In addition, recent studies suggest that accelerated glacial retreat and associated
lithospheric relaxation may enhance upwelling of magmatic fluids through the crust. Here,
we investigate whether, also at short geological timescales, shallow magmatic systems may
be affected by rapid melting of ice caps. As a case study, we chose the Snæfellsjökull
volcanic system in western Iceland, whose ice cap is rapidly melting with 1.25
m(w.e.)/year. To investigate the role of deglaciation in promoting volcanic unrest we use a
cross-disciplinary approach integrating geophysical field data, laboratory rheological rock
tests, and numerical finite-element analysis.
Initial results from seismic data acquisition and interpretation in 2011 show seismic activity
(occasionally in swarm sequences) at around a depth range of 8–13 km, indicating the
presence of a magmatic reservoir in the crust. In addition, a temporary seismic
network of 21 broad-band stations has been deployed in spring 2013 and continuously
collected data for several months, which will help better constrain the subsurface
geometry.
During summer 2013 we collected samples of Tertiary basaltic bedrock from the
flanks of Snæfellsjökull, which we assume to be representative for the subsurface
volcanic system. Cores drilled from these samples were tri-axially deformed in a
Paterson-type apparatus at a constant strain rate of 10-5 s-1, a confining pressure of 50
MPa (i.e. ~2 km depth), and a temperature ranging from 200 °C to 1000 °C (i.e.
various proximities to magma chamber). From the obtained stress-strain curves
the static Young’s modulus is calculated to be around 35 (±2) GPa, which is not
significantly influenced by increasing temperatures up to 800 °C. Beyond the elastic
domain, cataclastic shear bands develop, accommodating up to 7% strain before brittle
failure.
The subsurface geometrical constraints from geophysical field data and the rheological
parameters from laboratory testing are fed into a numerical finite-element model solving for
the pressure in the magma chamber and the stress field in the surrounding basement rock
before and after the retreat of an assumed 200 m thick ice cap. Preliminary results show that
ice unloading has two effects. First, it leads to significant stress release at the base of the
volcanic edifice, possibly resulting in a destabilization of the flanks, which in turn leads to
further unloading of the volcanic cone by means of landslides. Second, the pressure change
around the magma chamber is in the order of 0.5 MPa. This may be sufficient to induce
volatile exsolution and accelerated pressurization of the magmatic reservoir, ultimately
leading volcanic unrest, in particular in critically stressed environments prior to glacial
retreat.
We point out ice cap melting as a possible mechanism for triggering volcanic unrest of
shallow magmatic systems. |
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