Craters have appeared on two glaciers in Iceland

Glacier subsidence at Bárðar­bunga. (source: Marco Nescher/
Glacier subsidence at Bárðar­bunga. (source: Marco Nescher/

The recent volcano eruptions in Iceland have created enormous circular depressions in two of the country’s glaciers. These dramatic features, which differ from each other in their origins and shape, are visible from the air.

A reconnaissance flight over Bárðar­bunga, the volcano where the first earthquakes were detected last month, shows that the ice over the caldera has fallen nearly 20 meters across an area about 7 kilometers long and 5 kilometers wide. This is a change in volume of 250 million cubic meters. The scientists at the University of Iceland attribute this shift to a movement of the base of the glacier rather than to melting. Magma has drained from a chamber under the glacier as it moves to the northeast and erupts onto the surface. As the chamber has emptied, the rock above it has shifted downward, carrying the glacier ice downward as well. This is the largest subsidence that has been observed in Iceland since measurements of the surface were begun over fifty years ago. This movement does not seem to be associated with geothermal activity at Bárðar­bunga, or of a higher likelihood of an eruption there. A recent photo from a helicopter flight shows the large extent and relative shallowness of this cauldron (the technical term for these craters).

Glacier subsidence at Dyngjujokull (source: Almannavarnir)
Glacier subsidence at Dyngjujokull (source: Almannavarnir)

Another flight travelled over Dyngjujokull Glacier, to the northeast of Bárðar­bunga. It showed two separate depressions, somewhat smaller in extent, but almost twice as deep, reaching down 35 meters. These are probably associated with small eruptions of lava below the surface of the ice. Such eruptions can cause the formation of cauldrons like these, without unleashing outburst floods. There is some risk of continued eruptions, including larger ones, at this site.

Bardarbunga glacier crater (source: University of Iceland Institute of Earth Sciences)

In recent days, the lava eruptions from the main fissure have been moving in two directions. The main flow from the eruptions is traveling to the northeast. It has recently reached the Jökulsá á Fjöl­lum River, releasing large quantities of steam. As this intrusion of lava into the river continues, explosive releases of gasses could occur, or a dam could be formed by the cooled lava, creating a lake and subsequent floods. A smaller branch of the fissure has opened close to Dyngjujokull. Should another branch open up a few kilometers to the south, under the glacier itself, there might be a flood or an explosive release of large quantities of ash. For the time being, though, the threat level remains at orange.

Lava near glacier (source: Morgenbladid Reykjavik)
(source: Morgenbladid Reykjavik)

The eruption and steam have created hazy skies over the area. The Icelandic Civil Protection Authority has issued alerts to people downwind of the eruption with respiratory conditions, since there are elevated concentrations of sulfur dioxide. They continue to monitor the entire region carefully.

Hazy skies near eruption (source: Iceland Review)
Hazy skies near eruption (source: Iceland Review)

15 Responses to “Craters have appeared on two glaciers in Iceland”

  1. Avatar

    Good report on the overall situation. I want to raise a question about a technicality or maybe philosophy of glaciology: Why do you say “two glaciers”?

    Aren’t both of them just parts of Vatnajökull ice cap? Dyngjujökull is its outlet/extension, while the glacier inside Bardarbunga caldera is just a bulge in main Vatnajökull – it’s one of the areas where the Dyngjujökull ice flow originates from. The way you write it sounds like they are two separate entities, like Eyjafjällajökull and Myrdalsjökull.

    This is a problem I’ve always had with naming different parts of glaciers, especially large ice caps and ice sheets. How do you define where one glacier ends and the other starts? It’s easy to find the ice divide, but where is the line between Dyngjujökull and Vatnajökull? Is it defined by speed of ice flow? Thickness? Surface slope? I know, I’m splitting hairs here, and defining definitions.

  2. GlacierHub

    Good points, Jake. You describe it well. Vatnajökull is an ice cap, large in area and flowing only very slowly in its center. Dyngjujökull is an outlet glacier that flows more quickly down from the edge of Vatnajökull. Bárðar­bunga is a volcano under the ice cap, a high point in it. You list several criteria for deciding whether a stretch of ice contains one or two glaciers. In a way, it’s like deciding whether a bumpy part of a range is one mountain with two peaks near each other, or two mountains. Sometimes it’s easy to say. And sometimes it seems arbitrary.

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