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Less ice, more fire: Why shrinking glaciers could mean more volcanic eruptions

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AT THE end of the last ice age, around 11,700 years ago, Earth’s climate began warming rapidly. As the planet heated up, its vast glaciers fell back. Almost immediately afterwards (in geological terms, at least) volcanic activity surged. That was nothing new. The geological record has plenty of evidence of big glacial retreats that are followed by more frequent volcanic eruptions. Glaciers, in other words, seem to suppress volcanoes, which, by the same token, flourish in their absence.

This, at least, is the case for really big climatic swings. What has been less clear is whether more modest changes in ice cover might also affect the rate of eruptions. Given that humans are busy warming the planet, and therefore shrinking the few, relatively puny glaciers that still exist, this question matters. It would be good to know if more volcanic eruptions might be another consequence of global warming. In a paper just published in Geology, Graeme Swindles, a geographer at the University of Leeds, suggests that it will—eventually.

The fine details of how glaciers are linked to volcanic eruptions are unknown. But volcanologists theorise that pressure is key. The idea is that the weight of large ice sheets compresses the crust and mantle below. That closes up channels within the rock through which magma travels towards the surface. It also leaves less room for surface water to make its way down into the rocks, where, as steam, it can increase the pressure within magma chambers. Remove the ice, by contrast, and those processes go into reverse.

Dr Swindles and his colleagues studied layers of ash from Icelandic volcanoes that were deposited over Iceland and northern Europe during the relatively mild period since the end of the ice age, as well as volcanic sediments from Iceland itself. Their analysis revealed an unusual period between 5,500 and 4,500 years ago when no ash from Icelandic volcanoes found its way to Europe, and when the sediment record from Iceland suggests that no major eruptions took place. When Dr Swindles compared the volcanic record with the climate literature, he found that the absence of eruptions was preceded by a big change in atmospheric circulation patterns about 6,100 years ago. That would have encouraged Iceland’s glaciers to advance. When conditions changed again a thousand years later, this time to favour glacial retreat, volcanic activity picked up after a few hundred years.

Based upon these findings, Dr Swindles argues that even minor increases and decreases in glacier cover probably do affect volcanic activity, albeit with a time lag of perhaps five or six hundred years. The modern world is already recovering from its own miniature glaciation, the “Little Ice Age”, which lasted from about 1500 to 1850. Combine that with yet more glacial melt, caused this time by human-driven warming, and the centuries ahead may be noticeably fierier than those of the recent past.

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Julio Marchi ©

Publisher / Editor at BS News & Media Services
A free thinker, not labelled as anything, not associated with any party, not part of any group or engaged with any religion... A simple guy tired of the nowadays bullshit who decided to promote more serious debates about what is really happening hoping to bring back intelligence to the superficial and shallow news & headlines that unfortunately took over the existing media scene.
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