Grímsvötn Ice Shelf Drop Indicates Imminent Subglacial Outburst Flood Skip to content

Grímsvötn Ice Shelf Drop Indicates Imminent Subglacial Outburst Flood

By Gréta Sigríður Einarsdóttir

The Glaciological Society's spring trip to Grímsvötn on Vatnajökull glacier.
Photo: The Glaciological Society’s spring trip to Grímsvötn on Vatnajökull glacier..

The ice shelf above the subglacial lake Grímsvötn has dropped by almost 60 cm[23 in]. This indicates that a glacial run-off flood from Grímsvötn is imminent. Such floods occur regularly, and although they have in the past set off volcanic eruptions, at the moment, there is no seismic activity indicating a threat of eruption.

The Department of Civil Protection and Emergency Management’s Scientific Advisory Board met today to discuss the situation in Grímsvötn. The ice shelf over Grímsvötn has dropped by almost 60 cm[23 in] in the past few days, at an increasing speed. This would suggest that water is flowing from Grímsvötn and that we can expect a glacial run-off flood in Gígjukvísl river in southeast Iceland, not far from Skaftafell.

Based on earlier floods, the Met Office expects this one to surface at the glacier’s edge in the next two days and reach its peak 4-8 days later. At the moment, there’s no increase in Gígjukvísl river’s electrical conductivity, but an increase in electrical conductivity is the clearest indicator that a glacial run-off flood has begun. The Met Office also has gas detectors in place at the river’s source that would show when floodwater from the glacier is in the river.

The current Grímsvötn water levels would mean that the flood’s maximum flow was 5000 m3/s. A flood of that size is not likely to affect structures such as roads or bridges, although it is still too early to calculate the size of the flood.

It has happened before that a Grímsvötn glacial run-off flood is followed by a Grímsvötn eruption, the sudden loss of pressure when the water surface drops setting off the eruption. This last occurred in 2004, before that in 1934 and 1922. In 2004, a glacial run-off flood began on Oct 28, following a series of earthquakes indicating an impending eruption, which began three days later. No such seismic activity has been detected now. The last Grímsvötn eruption was in 2011.

The Met Office will continue to monitor the situation.

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