D44 Validation of VO-hydrological coupling models by application to SW-Iceland – NVI+NEA

Work within the workpackage has continued by applying software and procedures based on D43, presented in the paper by Zeeuw-van Dalfsen (2005a). Within the reporting period, VO-hydrological coupling models have been validated by applying them not only to a single area in SW-Iceland, but also to two additional areas in Iceland (expanded scope of work from initial description). This work forms the basis for D44, and additional work within the as well. It includes:

i) Application of a VO-hydrological coupling model to Krafla volcano in North Iceland. NVI has contributed to a collaborative study in this area lead by the Volcano Dynamics Group, Open University, UK, involving the Icelandic Meteorological Office as well. NEA has provided estimates of mass removal from the Krafla geothermal area by water extraction, as planned in the work description. This work is deliverable 44, presented in a manuscript by de Zeeuw-van Dalfsen et al. (submitted). New and previously published micro-gravity data were combined with InSAR data, precise levelling and GPS measurements to form an integrated model for processes operating at the Krafla volcano, discriminating between magmatic and hydrothermal processes. The data were divided into two periods: from 1990 to 1995 and from 1996 to 2003 and show that the rate of deflation at Krafla is decaying exponentially. Gravity and geodetic data demonstrate that both magmatic and hydrothermal processes are active. A net micro-gravity change at the centre of the caldera is shown, using the Free Air Gradient, to be -85 mGal for the first period and -100 mGal for the second period. After consideration of the effects of water extraction by a geothermal power station in the area the net gravity decreases are still -73 mGal for the first and -65 mGal for the second period. These decreases were then interpreted in terms of magma drainage at a rate of about 0.23 m³/s. The work suggests also coupling of shallow process at Krafla, to deep seated magmatic processes. Further analysis of InSAR geodetic data is presented in a separate paper (de Zeeuw-van Dalfsen et al., 2004). The InSAR data suggest deep seated accumulation of magma is taking place at Krafla, interpreted to be an important process taking place during inter-rifting periods at the plate boundary in Iceland.

ii) Application of a VO-hydrological coupling model to Reykjanes volcanic Peninsula, SW-Iceland. NEA conducted an extensive geodetic and gravity survey of the area in 2004, with the aim of understanding ongoing hydrothermal and magmatic processes taking place in the area. The results are still being analyzed, but indicate extensive deformation and little gravity changes relating to hydrothermal processes and tectonic deformation, but not direct involvement of magma. The data will be compared to detailed modeling of geothermal fields in the area (Thorhallson, 2005).

iii) VO-hydrological coupling has been studied at Grimsvotn volcano, central Iceland. This subglacial volcano in central Iceland erupted in late 2004. It provided an opportunity to study EQ-VO coupling (reported on in WP5100), but also a rare direct opportunity to study VO-hydrological coupling. This eruption was triggered by a hydrological process! The Grimsvotn caldera hosts a subglacial caldera lake that is maintained by geothermal heat melting ice. It is underlain by a shallow magma chamber that has been receiving inflow of magma in recent years, causing increasing magma pressure. The 2004 eruption that began on November 1? Was then preceded by glacial outburst flood, associated with draining of the caldera lake. Release of overburden pressure appears to have triggered the eruption. Initial study of the VO-hydrological coupling is presented in a series of internet reports including http://www.norvol.hi.is/html/grimsvotn2004/situationreport_nov2.html, and by Sigmundsson and Gudmundsson (2005).

iv) Deformation associated with one class of VO-hydrological coupling has been evaluated theoretically and applied in Iceland. This is the case of coupled deformation due to magma movement under subglacial volcanoes, and glacio-isostatic thinning of their overlying ice caps. This is of global relevance as many ice caps are thinning in response due to warmer climate. A method has been established to separate the two types of deformation fields, and applied to subglacial volcanoes in Iceland, both at Katla and Grimsvotn volcano (Sigmundsson et al., 2004).