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By Jan Zalasiewicz

To a geologist, the presence of a volcano on Iceland isn’t at all surprising. After all, Iceland is literally, and continuously, splitting apart, as this island sits exactly on the Mid-Atlantic Ridge. That mighty planet-sized fracture is continuously oozing magma, as the Americas pull ever farther apart – by a couple of centimeters a year, maintained for over a hundred million years – from Africa and Europe.

What raised a few eyebrows, though (mine, for sure) was the sheer filthiness of the eruption, and the amount of ash that it hurled high into the atmosphere, to the alarm of airline companies just about everywhere. For volcanoes that sit astride mid-ocean ridges are by nature generally placid by nature. For sure, they produce what seem like spectacular firework displays for the TV cameras, and flowing lava can, here and there, play merry hell with real estate values.

This is nothing, though, compared to the paroxysmal eruptions – Krakatoa, Pinatubo and the like – that occur in those parts of the world where tectonic plates are colliding. The violence of such cataclysms can destroy a whole country (and even Krakatoa was small compared to the great eruptions of the deep geological past). So why was Eyjafjallajokull trying to behave like one of the bad boys?

One answer is ice. Lying far north, Iceland is a land not just of volcanoes but of glaciers too – one of which lies on top of Eyjafjallajokull. As the uprushing magma came into contact with this, the ice flashed into steam, the expansion of which added quite a bit of oomph to the eruption. The lava, in turn, rapidly chilled by the ice, solidified quickly as it emerged, the thermal stresses shattering it into countless tiny fragments. This produced lots of ash, to be carried high into the atmosphere in the steam-driven (turbo-charged, if you like) eruption plume. It’s a bit (only a bit, mind) like putting a lot of wet wood and leaves on to a bonfire. This was one smoky volcano, and it seriously annoyed the neighbours.

Volcanic ash, of course, is feared by airline pilots, and justifiably so. One of the scariest experiences in all of flight history took place in 1982 when a British Airways Boeing 747, carrying 263 people, flew into an ash cloud from an erupting Indonesian volcano, Mount Galunggung. Ash particles entered the jet engines, melted against the hot metal, and, in effect, clogged them with reconstituted magma. All four engines failed, and the airplane, now completely without power, began to plunge towards the Indian Ocean.

The pilots kept their nerve, and prepared to ditch into the sea, while at the same time trying to restart the engines. The attempts failed until, when just a few thousand meters above the sea, the engines – amazingly – coughed back into life. They were able to fly to Jakarta, and landed safely (though not without difficulty, as the windscreen was almost opaque through being sandblasted by the sharp ash particles).

They had been saved by the same phenomenon that made Eyjafjallajokull such a disruptive volcano: thermal shock. As the stricken airplane descended, the cold air rushing through the lifeless engines chilled the molten ash, freezing it into solid volcanic glass. The chilling was fast enough for thermal stresses to shatter this glass, causing enough of it to break off to allow the engines to re-start. It was a lucky squeak.

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Michelle Rafferty, Publicity Assistant

Jan Zalasiewicz is a field geologist, paleontologist and stratigrapher, as well as lecturer of geology and Earth history at the University of Leicester in Leicester, England.  He researches fossil ecosystems and environments across over half a billion years of geological time, and has published over a hundred papers in scientific journals. His latest book The Earth After Us: What Legacy Will Humans Leave in Rock? published this fall in paperback. In his Countdown to Copenhagen post, he talks about Anthropocene, the new human dominated epoch we live in, and whether our future legacy will look more like an apocalyptic science fiction novel or a modest geological footprint.

For the rest of the Countdown to Copenhagen posts, click here.

It seems like science-fiction. The Earth will, in a few short centuries – perhaps even decades – go back to the kind of world in which the dinosaurs lived. Ice caps will collapse, oceans will acidify, coral reefs will perish, coastlines will drown. Millions of species will go extinct. And we humans – who set all these events in train – will be in big, big trouble. As science-fiction, indeed, it may be no easier to accept such an idea. Imagine if  Terry Pratchett trashed the Discworld, drowned Ankh-Morpork – for ever? His readers wouldn’t stand for it.

Yet this scenario on our one and only Earth seems, on the evidence to hand, more likely than not. Such changes are not certain (perhaps, out there, there is the ecological equivalent of the cavalry over the hill, riding down to rescue us all). But these global changes are not just possible – they are probable. And their scale is not diminished by comparison with the great upheavals of the Earth’s multi-billion-year geological history. Rather, they are made to seem more stark by that comparison.

The enormous canvas of the Earth’s past shows drama, to be sure – the crazy climate switchbacks of the last million years, for instance. But it also shows long episodes of calm and stability. The most recent of these has been the last ten thousand years – our current epoch, the Holocene – since the most recent of the Earth’s glaciations receded. With both temperature and sea level holding remarkably steady, it’s no coincidence that human civilization has flowered over this time. But now, our civilisation has, over two centuries, poured hundreds of billions of tons of carbon into the atmosphere, taking CO2 levels higher than for millions of years. We are near – or perhaps already past – a tipping point, into a new climate regime.

But it is not just climate change, as immense and far-reaching a change as that is. As cities and farmland replace what was once forest and savannah, the Earth’s animals and plants are under siege as rarely before. Extinction rates are now likely somewhere between a hundred and a thousand times higher than is usual. Since we’ve discovered only a tenth or so of the species on Earth so far, it’s certain that many species will become