Fire in the Hole


Fire in the Hole

Published in the 2014 October-December issue of Iceland Review & Atlantica – IR 05.14. Words by Haraldur Sigurðsson, Photos by Páll Stefánsson.

When Bárðarbunga volcano stirs, everyone in Iceland listens. It’s the country’s biggest volcano, and it’s located smack-bang in the middle of the Icelandic hotspot (volcanic regions thought to be fed by underlying anomalously hot mantle often near tectonic plate boundaries).

But it’s a difficult mountain to study, as it’s entirely buried underneath Vatnajökull, Europe’s largest glacier.

At some point in the distant past, the volcano collapsed during a catastrophic eruption, resulting in the formation of a caldera, or a huge, 10-km (6-mile) wide central cavity that is about 700 meters (2,300 feet) deep.

The cavity, or caldera, is filled with ice.

Somewhere within the caldera, now at a depth of over 100 meters in the ice, lies the wreck of a Skymaster DC-4 aircraft, Geysir, that crashed there in September 1950 during the early days of the Icelandic aviation pioneer Loftleiðir, now Icelandair.

It was a cargo flight and all six crew members were rescued.

Bárðarbunga began to shake violently on August 16, 2014, lasting two weeks. Then, the earthquakes migrated first to the southeast and quickly changed direction to the northeast.

Scientists determined that the earthquake activity was caused by the formation of a dike, or a magma-filled fissure, that was fed from the underground reservoir of the volcano.

Dikes are the plumbing system of Icelandic volcanoes, and they can carry molten rock or magma for a distance of tens of kilometers away from the volcano in vertical fractures within the crust.

This earthquake activity was focused in two areas. A series of large earthquakes, up to magnitude 5.7, occurred along the caldera margin of Bárðarbunga, while a series of earthquakes began to the east of the volcano.

This series created a line of earthquakes that stretched further and further to the north, up to a distance of about 70 km from Bárðarbunga and beyond the glacier’s edge.

These earthquakes represent the creation of a great fracture, or crack, in the earth’s crust north of the volcano. Through this vertical fracture, the volcano is sending a stream of molten rock or magma to the north within the crust.

Finally, at the end of August, the magma-filled dike reached the surface and a fissure eruption broke out in Holuhraun, first for a few hours on August 29, then again on August 31, and it has carried on since.

Holuhraun is an old lava field 50 km to the north of the volcano. For Icelanders, the eruption could not have happened in a better place: the region is a remote desert at the northern edge of the Vatnajökull icecap.

Red-hot magma at temperatures of 1,175°C (2,150°F) flowed from the 1.6-km (1-mile) long fissure, spreading lava over the sandy desert and over the old lava at Holuhraun, which formed in the exact same spot in 1797.

When the new eruption began, the floor of the caldera of Bárðarbunga began to subside, including the thick icecap sitting on top of it. It has been sinking at a rate of about 0.5 meters per day.

Although very remote, the eruption could potentially have two serious impacts. One of these is the threat of massive flooding if the fissure opens up beneath Vatnajökull.

In that case, the hot magma would cause melting in the icecap, suddenly releasing large volumes of meltwater. Fortunately, this situation has not come up so far.

Secondly, hazardous volcanic gases are released during eruptions of this type. They are a potent cocktail of sulfur, fluorine and chlorine, as well as carbon dioxide and steam.

Icelanders have been cautious about volcanic gas emission ever since the great Laki issure eruption in 1783. This massive eruption produced the largest lava flow in recorded history and released huge quantities of volcanic gas.

The gas emission produced a haze over all of Iceland, leading to a loss of about 75 percent of livestock from fluorosis and other effects. It also led to a decrease of 24 percent of the human population of Iceland.

No one is expecting such a catastrophic impact from the current eruption, but when it comes to Mother Nature, we don’t always know what to expect, especially as we’re dealing with Iceland’s largest volcano.

The gas plume from the current eruption has, however, already caused some discomfort for people in coastal regions to the east and north of the volcano.

Bárðarbunga deserves a lot of respect when we consider its history. Its eruption about 8,600 years ago produced the largest lava flow on earth since the end of the Ice Age. This lava stretched from central Iceland all the way 130 km to the south coast.

In 871 A.D., about one or two years before Iceland was officially settled by Norwegian Vikings, Bárðarbunga erupted again.

This time the volcano channeled a 50-km dike through the rocky crust to the south, until it intersected the magma reservoir of Torfajökull volcano. A violent explosion sent volcanic ash over all of Iceland, creating a marker in the soil that is known as the Settlement Layer, because it marks almost exactly the time of human settlement of Iceland.

Again, in 1477, a large fissure eruption took place south of Bárðarbunga, known as the Veiðivötn eruption. This time a 60-km long fissure erupted violently, sending volcanic ash over vast regions of the country.

But it’s neither the lava flow nor the volcanic ash that causes scientists most concern. It’s the prospect of a very large eruption that might emit huge quantities of hazardous volcanic gases.

Only time will tell whether Bárðarbunga will release a major eruption, or if the activity and the environmental impact will remain manageable, as it is at this time.

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