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Ice–volcano interaction of the 1996 Gjálp subglacial eruption, Vatnajökull, Iceland


Volcanic eruptions under glaciers can cause dangerous floods and lahars1,2,3 and create hyaloclastite (fragmented glassy rock) mountains4,5,6,7,8. But processes such as the rate of heat transfer between ice and magma, edifice formation, and the response of the surrounding glacier are poorly understood, because of the lack of data. Here we present observations from the fissure eruption at Vatnajökull ice cap, Iceland, in October 1996. In the 13 days of the eruption 3 km3 of ice were melted and the erupted magma fragmented into glass forming a hyaloclastite ridge 6–7 km long and 200–300 m high under 500–750 m of ice. Meltwater of temperatures of 15–20 °C flowed along a narrow channel at the glacier bed into the Grímsvötn subglacial lake for five weeks, before draining in a sudden flood, or jökulhlaup. Subsidence and crevassing of the ice cap occurred over the eruptive fissure and the meltwater path, whereas elsewhere the glacier surface remained intact, suggesting that subglacial eruptions do not trigger widespread basal sliding in warm-based glaciers.

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Figure 1: Map of the northwest part of Vatnajökull showing the location of the 1996 eruptive fissure (solid line, in box), midway between the s.
Figure 2: Top, development of ice cauldrons at the eruption site.
Figure 3: Ice melting and heat transfer rate from 1 October 1996 until 3 January 1997.
Figure 4: Schematic sections showing how the eruption penetrated the ice cap, through a narrow chimney through the ice.


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We thank the Iceland Civil Aviation Authority, especially chief pilot S. Gudbjörnsson, the crews of the helicopters of the Icelandic Coast Guard and J. K. Björnsson of the Iceland Helicopter Service for enthusiastic cooperation during the monitoring of the eruption. F. Pálsson, H. Halldórsson, K. Pálsson, S. Jónsson and P. Símonarson took part in the GPS measurements and members of the Iceland Glaciological Society assisted in fieldwork in June 1997. The figures were prepared by Th. Högnadóttir. A review by D. Blankenship improved the paper.

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Correspondence to Magnú T. Gudmundsson.

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Gudmundsson, M., Sigmundsson, F. & Björnsson, H. Ice–volcano interaction of the 1996 Gjálp subglacial eruption, Vatnajökull, Iceland. Nature 389, 954–957 (1997).

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