Kate Humble on the giant volcano that’s starting to become restless…

The Volcano Live presenter discusses the "geological argy-bargy" and "volcanic farts" that indicate the next major volcanic eruption

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Volcanoes, in the words of my goddaughter, are cool. And she’s right, they are, in a hottish sort of way. Like dinosaurs, they have a mystique and a kind of glamour that belong to another era, but unlike dinosaurs they are still here, still very much active, still playing the crucial role they’ve been playing since the Earth was formed, of shaping and re-shaping our planet.

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Around the world there are about 20 volcanoes going off at any one time. Here in rather stable, benign Britain we may not think volcanoes have anything to do with us, but admirers of Scotland’s Western Isles, Northern Ireland’s Giant’s Causeway and the little island of Lundy have volcanic activity to thank for these natural British wonders. And then, of course, there was that time in April 2010, when for six whole days our skies were silent, and departure boards in airports throughout Europe and beyond just had CANCELLED all over them.

Why? Because in Iceland over 1,000 miles away from the UK there had been a volcanic eruption that caused not just unprecedented disruption to air travel but had every newscaster in the world tripping over its unpronounceable 16-letter name.

Today, Eyjafjallajokull (A-ya-fyat-la-yo-kuti and yes, after much practice I can pronounce it) looks the picture of innocence. It sits, dwarfed and rather insignificant in a landscape of almost unimaginable scale and grandeur, the product of 25 million years of frantic volcanic activity that hasn’t ended yet.

Iceland is the volcanic grout between two tectonic plates. On one side is the North American plate and on the other is the Eurasian plate. These two bits of our planet’s structure clearly don’t like each other very much and for millions of years have been trying to get further apart. This geological argy-bargy created the Highlands of Scotland and Snowdonia, but now the gap between Britain on the Eurasian plate and America on the North American plate is so wide that we’re both a long way from the volcanic action.

Further north it’s a different story, and it makes Iceland the most volcanically active place on Earth, with an eruption happening, on average, every five years. But you don’t need an eruption to be reminded that Iceland is one big hotbed of geothermal activity. Steam gushes from the ground; mud bubbles and oozes and smells of rotten eggs; hot water and central heating are really cheap.

So why, if all this has been going on constantly for 25 million years, did Eyjafjallajokull hit the headlines and the airlines in the way that it did? Why hadn’t it happened before?

The answer is that it has happened before, but in 1783, when there weren’t quite so many Easyjet flights carving up the skies. That year, a great fissure called Laki opened up, spilling 15 cubic kilometres of lava onto the surrounding countryside – the largest lava eruption in recorded history. The eruption lasted for months, but along with the lava came ash and toxic gas, which caused famine across Iceland.

Almost all the livestock perished and with it a fifth of the island’s people. An unusually high number of deaths were also recorded that year throughout northern Europe. There were reports of a fog that swept across the continent, but a fog that smelt foul and irritated the skin, eyes and back of the throat.

Back then no one knew where this fog had come from and why it was killing people. Now we know it was volcanic pollution – and far more devastating than thousands of cancelled flights.

Today volcanoes are much better understood and in developed countries like Iceland, studied and monitored 24 hours a day. Local volcanologist Bjorn Oddsson explains that the some of the ash created by Eyjafjallajokull’s eruption was dense and heavy, but other particles of ash were much finer and stayed in suspension in the air.

The wind blew it south, over the Atlantic, to the Scottish coast, and an unusually stable weather system kept it there. The weather in the UK that week was glorious, with forecasters talking about clear blue skies – but the problem was they weren’t clear. The sky was full of glass-like volcanic particles and no one was sure whether those particles would cause aeroplanes to fall out of the sky.

It is only from the air that I saw evidence that Eyjafjallajokull had ever erupted. There is a deep, black slash in the glacier that still steams and the air is thick with sulphur, but as Bjorn pointed out, Eyjafjallajokull is pretty insignificant when it comes to Iceland’s volcanic power.

It is surrounded by much bigger, much more active volcanoes, not least its immediate neighbour, Katla. Katla’s caldera, or crater, is 10km in diameter and covered in a layer of ice 750m deep. Last year some minor geothermal activity, a sort of volcanic fart beneath the ice sheet, caused enough ice to melt and sweep off the side of the mountain, down a river valley to wash away a bridge and part of a road. All eyes turned to Katla. Was it getting ready to blow?

Geologist Iain Stewart and I have been immersed in all things volcanic for the last few months. While I’ve been in Iceland, he’s been in Italy, another volcanic hotbed and one that has captured the human cost of living in the shadow of volcanoes more vividly than anywhere else.

We are now heading to Hawaii’s Big Island, home to the world’s most active volcano, Kilauea. Its open lava lake, the constant lava flow and smoking summit make it the perfect location to illustrate just how dynamic our planet is. We have eye-popping reports from field scientists working on volcanoes in Chile and the Congo, while webcams and a special volcanic map will give us minute-by-minute updates on what is happening throughout the world at any one time. But I know there’s one volcanic giant I’ll be paying particular attention to.

On the edge of Katla’s caldera are a series of instruments – seismographs and GPS systems that monitor every geothermal twitch. When I was there I stood with Benni, a scientist who spends his life watching this volcano, and looked at the alarmingly jagged line that bisected his computer screen.

“Are you expecting it to erupt any time soon?” I asked. “Well”, he said, “there’s been more activity lately. We’re keeping a close eye on it.”

On 21 June, those instruments picked up evidence of 26 minor earthquakes over a four-hour period. The tremors were shallow, but they’re signs that, just possibly, this giant volcano is starting to become restless. If the rumblings turn into something more significant there’s every chance our skies will fall silent again. And we’ll gape in amazement at the power of these incredible sleeping giants.

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Volcano Live is on BBC2, Monday-Thursday, at 8:00pm