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Global Warming, Volcanic Eruptions

A Warmer World Could Be A More Explosive One

Much of the focus on global warming is always directed towards the obvious; food, water levels, animals. What makes the whole subject even more interesting though is the unexpected consequences of a warming planet. And if new research is to be believed, global warming may have an impact on volcanic eruptions. 

According to Carolina Pagli of the University of Leeds, UK, and Freysteinn Sigmundsson of the University of Iceland, Vatnajökull – the largest ice cap in Iceland – is disappearing at a rate of 5 cubic kilometers per year. Together, the two have calculated the effects that this will have on the crust and magma underneath.

Naturally, when ice disappears, the added weight it forced upon the crust below it disappears as well. As a result, according to Pagli and Sigmundsson, this is increasing the rate at which the rocks under the ice sheet melt in to magma. The melt to magma rate was found to be 0.014 km3/yr, which equated to a century average of 1.4 cubic kilometres produced since 1890; a 10% increase on the background rate.

(I spoke to Carolina Pagli via email, and she said that “One should be careful with the wording, because it’s the ice melting that causes decompression at depth and thus the mantle melting.” So the stats above refer to the rate of magma production, not ice melting.)

Iceland is home to several active volcanoes that exist underneath the ice, including Gjàlp, home of the last big eruption in 1996, and 58 years earlier in 1938. But according to Pagli and Sigmundsson the extra magma produced over the past century and more could reduce that time down to a gap of 30 years between each eruption.

Vatnajökull is somewhat unique in terms of its location, and is not necessarily an indicator for the rest of the world. Vatnajökull sits atop a boundary between tectonic plates, and as a result allows the release in pressure to have a much greater effect deep within the mantle.

But the thinning of ice over volcanic areas will have another effect, one which is more widespread. As the amount of weight on top of the crust diminishes – or at the very least changes – subsequent geological stresses will also change and increase the chance of eruptions. “Under the ice’s weight, the crust bends and as you melt the ice the crust will bounce up again,” explains Bill McGuire of University College London in the UK, who was not involved in the study.

Pagli points to Antarctica’s Mount Erebus, the Aleutian Islands and other Alaskan volcanoes as locations which will be at risk of similar increased volcanic activity. She adds that the shifting stresses could even cause eruptions in unexpected places. “We think that during the Gjàlp eruption, magma reached the surface at an unusual location, mid-way between two volcanoes, because of these stress changes,” says Pagli.

McGuire, who was speaking to New Scientist regarding the new research, added that “It’s not just unloading the crust that triggers volcanic activity but loading as well.” He and his team believe that rising sea-levels – also caused by melting ice caps – will increase volcanic activity. “We are going to see a massive increase in volcanic activity globally,” he told New Scientist. “If we look back at previous warm periods that is what happened.”