Grimsvötn

Grimsvötn volcano (N 64.41°, W 17.33°), situated near the center of the Vatnajökull ice cap in central Iceland, is one of Iceland's most active volcanoes. It has a complex of calderas (Gudmundsson and Milsom, 1997), and a subglacial caldera lake sustained by geothermal heat. Small eruptions have occurred at the volcano in 1983 and 1998 (around 0.1 km3). In 1996, the Gjálp subglacial eruption occurred north of the volcano (Gudmundsson et al., 1997).

The Vatnajökull glacier is a temperate glacier covering about 8300 km2 in the SE part of Iceland. Volcanic fissure systems of the Mid-Atlantic Ridge plate boundary are partly covered by the western part of the ice sheet. Two major volcanic centers lie beneath the ice, the Bardarbunga volcanic centre and the Grimsvötn volcanic centre, both with large subglacial caldera depressions. The Bardarbunga centre is a part of a fissure system extending over 100 km to the south and some 50 km to the north of the glacier. The last eruption within the Bardarbunga centre occurred in 1910, but eruptions on the fissure system have occurred in 871 AD, 1477 AD and 1862 AD, all producing substantial amounts of lava.

The Grimsvötn centre is the more active of the two with an eruption frequency during past centuries close to one eruption per decade. The last eruption occurred in 2004. As Bardarbunga, the Grimsvötn centre is a part of a a fissure system which includes the Laki fissure, which in 1783 produced about 12-14 km3 of basaltic lava. Within the ice filled Grimsvötn caldera intense geothermal activity continuously melts the ice to form a subglacial lake, which at intervals of 5 to 10 years is emptied along subglacial channels to create large floods (jökulhlaup) on the sandur plain, Skeidararsandur, on the Icelandic south coast.

Reference list

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Björnsson, H. Jökulhlaups in Iceland: prediction, characteristics and simulation. Annals of Glaciology 16, 95-106, 1992.

Björnsson, H., S. Björnsson and Th. Sigurgeirsson. Penetration of water into hot rock boundaries of magma at Grímsvötn. Nature, 195, 580-581, 1982.

Björnsson, H., and H. Kristmannsdóttir. The Grímsvötn geothermal area, Vatnajökull, Iceland. Jökull, 34, 25-50, 1984.

Björnsson, H., and P. Einarsson. Volcanoes beneath Vatnajökull, Iceland: Evidence from radio-echo sounding, earthquakes and jökulhlaups. Jökull, 40, 147-168, 1991.

Björnsson, H., and M.T. Gudmundsson. Variations in the thermal output of the subglacial Grímsvötn caldera, Iceland. Geophys. Res. Lett. 20, 2127-2130, 1993.

Björnsson, H. 2002. Subglacial lakes and jökulhlaups in Iceland. Global and Planetary Change, 35, 255-271.

P. Einarsson and B. Brandsdóttir. Seismic Activity preceding and during the 1983 volcanic eruption in Grímsvötn, Iceland. Jökull 34, 13-23, 1984.

Páll Einarsson, Bryndís Brandsdóttir Magnús Tumi Gudmunsson, Helgi Björnsson, Karl Grönvold and Freysteinn Sigmundsson, 1997: Center of the Iceland Hotspot Experiences Volcanic Unrest. Eos,Transactions, American Geophysical Union, Vol. 78, No.35, Pages 369, 374-375.

Grönvold, K., and H. Jóhannesson. Eruption in Grímsvötn 1983; course of events and chemical studies of the tephra. Jökull 34, 1-11, 1984.

Gudmundsson, M.T. The Grímsvötn Caldera, Vatnajökull: Subglacial topography and structure of caldera infill. Jökull, 39, 1-20, 1989.

Gudmundsson, M.T., H. Björnsson, and F. Pálsson. Changes in jökulhlaup sizes in Grímsvötn, Vatnajökull, Iceland, 1934-91, deduced from in-situ measurements of subglacial lake volume. J. of Glaciology, 41, 263-272, 1995.

Gudmundsson, M. T., and J. Milsom, Gravity and magnetic studies of the subglacial Grimsvotn volcano, Iceland: Implications for crustal and thermal structure, J. Geophys. Res., 102, 7691-7704, 1997.

Gudmundsson, M. T., F. Sigmundsson, and H. Bjornsson, Ice-volcano interaction of the 1996 Gjalp subglacial eruption, Vatnajokull, Iceland, Nature, 389, 954-957, 1997.

Magnús T. Gudmunsson, Freysteinn Sigmundsson and Helgi Björnsson, 1997: Ice-volcano interaction of the 1996 Gjálp subglacial eruption, Vatnajökull, Iceland. Nature, vol. 389, 954-957.