Subglacial eruptions

Vatnajökull conceals a part of the neovolcanic zone and seven central volcanoes, including four of the most active ones in Iceland, Grímsvötn, Bárðarbunga, Kverkfjöll and Öræfajökull. Ice–volcano interactions produce various geological formations. Subglacial eruptions lead to explosive phreatomagmatic tephra production. The tephra is quickly glued together in the moist and hot environment at the eruption site to form breccia or hyaloclastite. Hyaloclastite mountains and ridges are characteristic for the neovolcanic zone of Iceland, but rare elsewhere in the world. During the Gjálp eruption in 1996, a 7 km long hyaloclastite ridge was formed, which is now buried by the glacier. The hyaloclastite formation in Iceland was mostly created by subglacial eruptive activity during the glacial intervals of the Ice Age, when a large ice sheet covered the country.

Meltwater that accumulates during subglacial eruptions can be released in catastrophic jökulhlaups, which may be hazardous to people and infrastructure. Eruptions and jökulhlaups from steep volcanoes like Öræfajökull destabilize the glacier itself, so that large blocks of ice break off and cascade downhill like an avalanche. Landforms created by such catastrophic events are found at the foothills of Öræfajökull and formed during the eruptions in 1362 and 1727.

 

Basal topography of Vatnajökull. Source: Glaciology Group, Institute of Earth Sciences, University of Iceland, Björnsson (2009).

Basal topography of Vatnajökull. Source: Glaciology Group, Institute of Earth Sciences, University of Iceland, Björnsson (2009).

 

The Gjálp eruption in 1996. Photo: Magnús Tumi Guðmundsson.

The Gjálp eruption in 1996. Photo: Magnús Tumi Guðmundsson.

 

The flood path of the jökulhlaup following the Gjálp eruption. Photo: Oddur Sigurðsson, 7th of November 1996.
The flood path of the jökulhlaup following the Gjálp eruption. Photo: Oddur Sigurðsson, 7th of November 1996.

 

Entering Grímsvötn volcano a year after the 2011 eruption. Photo: Hrafnhildur Hannesdóttir, 6th of June 2012.
Entering Grímsvötn volcano a year after the 2011 eruption.
Photo: Hrafnhildur Hannesdóttir, 6th of June 2012.

 

Field studies in Grímsvötn volcano a year after the 2011 eruption. Photo: Hrafnhildur Hannesdóttir, 8th of June 2012.

Field studies in Grímsvötn volcano a year after the 2011 eruption. Photo: Hrafnhildur Hannesdóttir, 8th of June 2012.