November 15, 2011

Anatomy of Iceland's Volcanoes:  Crustal Deformation and Magma Movements

Iceland has over 30 volcanic systems of different character, providing opportunities to study magma movements and associated crustal deformation in subaerial segments of the slow spreading Mid-Atlantic ridge. Space geodetic techniques, precise Global Positioning System geodesy as well as interferometric analysis of synthetic aperture radar images (InSAR) have been extensively used to reveal deformation patterns. These have been interpreted in terms of models of magma transport and storage; an integral element in understanding volcano dynamics.

Some of the most active central volcanoes in Iceland (including Grímsvötn, Hekla, Krafla, Askja) have persistent “reversible” deformation pattern of inter-eruptive gradual inflation (mm and cm/yr), and sudden co-eruptive deflation (typically tens of cm). This kind of deformation pattern is interpreted in terms of pressure change in crustal magma chambers at a depth of 2-20 km, which receive inflow of magma continuously or intermittently over years until a breaking limit is received; then an eruption or dike intrusion occurs. Deformation pattern at Grímsvötn prior to and in relation to its eruption in 1988, 2004 and 2011 are of this type.

Less active central volcanoes appear to have a different plumbing system, where one single magma chamber does not receive magma inflow; rather initial signs of renewed activity may be individual magmatic intrusions stalling at different locations. This was the case prior to the Eyjafjallajökull eruption in 2010; magma had been intruding intermittently over a period of 18 years prior to the catastrophic explosive eruption that caused the widespread airspace closure. That eruption was finally triggered when intruding basaltic magma interacted with residing more evolved magma under the summit area of the volcano.

Magmatic intrusions can occur outside the central volcanoes in still less active part of the plate boundary. A well documented case of such an intrusion occurred in 2007-2008 in the lower crust north of the Vatnajökull ice cap at 12-18 km depth, below the otherwise brittle-ductile boundary of the crust. In that case, the dike plane appears to have formed in direction perpendicular to the least compressive deviatoric stress setup in the crust due to present day glacial retreat, caused by warming climate. Magma movements in Iceland are therefore not only influenced by plate tectonic process; presently they are also influenced by retreating ice caps.

The observations of crustal movements and magma dynamics in Iceland are put into context of models for generation of the oceanic crust at slow spreading oceanic ridges in general.

If you have any questiions about the seminar, contact Freysteinn Sigmundsson, Nordic Volcanological Center, Institute of Earth Sciences, University of Iceland, This e-mail address is being protected from spambots. You need JavaScript enabled to view it