Glacial Outburst Flood in Múlakvísl Expected Skip to content
Photo: Part of Route 1 in South Iceland. The bridge across Múlakvísl river could be closed by authorities..

Glacial Outburst Flood in Múlakvísl Expected

Measurements from Mýrdalsjökull glacier indicate that a glacial outburst flood could occur in Múlakvísl river in the next days or weeks. A relatively large flood is expected, the largest in the last eight years. Authorities do not expect to have to enforce closures on roads at this point in time, but they will follow developments in the area closely. Closure of Route 1 might occur. The Department of Civil Protection and Emergency Management reported this yesterday, and will continue to monitor the situation.

The results from The Institute of Earth Sciences at the University of Iceland indicate that enough water has collected below geothermal heat calderas in the eastern part of Mýrdalsjökull glacier. The water flow during the height of the glacial flood could be significantly more than the flood which took place in 2017, but likely less than the severe flood of 2011. The flood in 2011 destroyed the bridge on Route 1 crossing the Múlakvísl river east of Vík í Mýrdal.

Regular flooding of Múlakvísl
Small glacial floods have occurred in Múlakvísl river almost yearly in the last couple of years, close to or right after mid-summer when the thaw in Mýrdalsjökull glacier is at a high point. Those floods have most often been small enough that the river does not flow out of the riverbed, and have therefore not caused any damages. There was no glacial outburst flood in 2018. The flood in 2017 was considered significant although it did not cause any damages. However, the flood in 2017 caused significant air pollution due to the release of hydrogen sulphide. In the last 100 years, there have been at least two severe glacial outburst floods in Múlakvísl, in 1955 and 2011. In both of those floods, the bridge crossing Múlakvísl river was ruptured. For scale, the flood in 2017 is estimated to have been to the tune of 200 cubic metres per second near the Route 1 crossing, which was 20% of the maximum water flow in the 2011 flood in the same site.

“We’ve performed measurements in the same calderas four times since 2017. We can expect that the flood will be the largest flood which has occurred in Múlakvísl in the last eight years. In all likelihood, it will be significantly smaller than the 2011 flood which ruptured the bridge, but nonetheless, it would be the largest flood since then. The main explanation is the fact that there was no outburst from these calderas last summer,” said Eyjólfur Magnússon, a glacial research expert at The Institute of Earth Sciences at the University of Iceland in an interview with RÚV. The warmth in Iceland this summer could be causing an earlier flood than usual, according to Eyjólfur. “It could be causing that this flood will happen sooner than usual. These calderas often have outbursts in July or the beginning of August. That has been the main rule. It seems to be so that the summer thaw is starting this flood. So it seems to be often that these calderas empty when the summer thaw is at high-point up on the glacier, or soon after that.

There is considerable geothermal heat under Mýrdalsjökull glacier which creates about 20 calderas on the surface of the glacier. The heat melts the glacial ice and the meltwater collects under the geothermal calderas. In addition to this, thaw water from the surface of the glacier seeps through the glacier and is added to meltwater collecting below the glacier. When enough water has collected, it breaks out from under the glacier and causes the glacial outburst flood.

Members of the travel industry in the nearby area have been informed of the danger. If a flood should occur, they will be informed of further proceedings right away. Scientists believe that the flood will come with some prior warning, and they are now working on putting up a GPS measurement device in one of the sub-glacial calderas to measure proceedings more accurately.

At this point in time, it is believed that it is not necessary to close roads. That situation could change quickly, however, and authorities will step in if they believe a flood is about to occur.

What can happen, and how should travellers react?
Dangers which accompany a glacial outburst flood in Múlakvísl river:
– Floodwater can block the route from Route 1 towards Kötlujökull glacier west of Hafursey.
– Floodwater can flood over and block, or even rupture, Route 1 at the bridge crossing of Múlakvísl river.
– Floodwater can block the route into Þakgil.
– The gas hydrogen sulphide could be found in copious amounts close to Múlakvísl river. The gas can burn mucous membrane in the eyes and in the respiratory tract

– Respect road closures, as well as evacuations if they should occur.
– Keep away from the Múlakvísl river when a glacial outburst flood is occurring.
– Avoid places affected by gas pollution, such as along the river as well as in depressions nearby by it. Do not stop at the bridge crossing Múlakvísl or Skálm.

Travellers passing through the area are instructed to head to the website of the Icelandic Road and Coastal Administration,, for further information on road conditions, or call 1777.

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