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Volcano dykes: what scientists are watching out for

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Study shows how huge magma-filled cracks propagate near volcanoes

Thórdís Högnadóttir, University of Iceland

Volcanoes are misleading. For obvious reasons, their large, spectacular eruptions soak up most of our attention. But it's important to remember that there's actually a lot going on below the surface. For instance, many volcano eruptions are accompanied by the formation of dykes, magma-filled cracks below the Earth's surface. Unfortunately, because they're hard to observe in most parts of the world — dykes tend to form underwater — the science of how they propagate isn't very advanced. Thankfully, a group of researchers in Iceland are changing that. With the help of satellite technology, they were able to capture the formation of a 28 mile-long dyke in the two weeks prior to a volcano's main eruptive activity last August. And the resulting study offers precious clues about the origins of a rare volcanic phenomenon.

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"Such long dyke formations are characteristic for divergent plate boundaries on Earth, where two tectonic plates separate," says Freysteinn Sigmundsson, a volcanologist at The University of Iceland and a co-author of the study published today in Nature. That means that nearly every formation takes place several miles below the ocean. But there are exceptions to that rule — two exceptions, to be exact: the Afar region in Ethiopia, and Iceland.

Thórdís Högnadóttir, University of Iceland

In the study, the researchers observed a dyke as it formed alongside the Bárðarbunga central volcano in Iceland. They did so using satellite imagery and GPS measurements. They found that "the rate of dyke propagation was variable and slowed as the magma reached natural barriers," says Sigmundsson. The magma contained in the dyke was able to overcome these barriers, however, by building up pressure and creating a new segment. Moreover, the researchers found that the varying direction of dyke segments can be attributed to the interaction between the physical features of the ground and the stresses caused by divergent plate movements below the earth. Thanks to the study, Sigmundsson says, "we have a new understanding of subsurface magma movements prior to eruptions."

"precious clues about the origins of a rare volcanic phenomenon"

Dyke formations like the one in Iceland only occur once every few years. The last one appeared in 2005, and the one before that started in 1987. Still, the researchers hope to apply their findings to other volcanos in the near future, Sigmundsson says. "We hope that similar studies can be carried out to improve understanding and ability to forecast the evolution of lateral dykes in various volcanic settings around the world."