The map is uncannily similar to today’s: a spray of black dots showing the recorded sightings of a foul grey haze spreading across Europe, from Helsinki to Naples, from Heligoland to Majorca, and reaching eventually to Aleppo and Damascus – all of it caused by clouds of ash from an immense volcano erupting far across the sea in Iceland.But this was a map made from data collected in 1783. The volcano was called Laki, it erupted for eight dismal months without cease, ruined crops, lowered temperatures and drastically altered the weather. It killed 9000 people, drenched European forests in acid rain, caused skin lesions in children and the deaths of millions of cattle. And, by one account, it was a contributing factor (because of the hunger-inducing famines) to the outbreak six years later of the French revolution.Great volcanoes have a habit of prompting profound changes to the world – much greater in extent than the most savage of earthquakes and tsunamis, even though the immediate lethality of the latter is invariably much more cruel. Though ground-shaking events are generally fairly local in extent, their potential for killing can be terrific: 250,000 died after the Tangshan earthquake in China in 1975 and a similar number died in the Indian ocean tsunami of 2004. Volcanoes seem by contrast relatively benign: the accumulated total number of deaths in all of the great volcanoes of the past 300 years has probably not exceeded a quarter of a million: the total number of casualties from a hundred of the biggest recent eruptions has been no more than those from a single giant earthquake.But there is a significant difference. Earthquakes, once done, are done. Volcanoes, however, often trigger long-term and long-distance ill-effects, which generally far outweigh their immediate rain of death and destruction. Emanations of particles from the tiniest pinprick in the Earth’s crust, once lifted high into the skies by an explosive eruption, can wind themselves sinuously and menacingly around the planet, and leave all kinds of devastation in their train. They can disrupt and pollute and poison; they can darken skies and cause devastating changes in the weather; they can bring about the abrupt end to the existence of entire populations of animals and people.Earthquakes and tsunamis have never been known to cause extinctions but volcanoes and asteroid collisions have done so repeatedly – and since the Earth is still peppered with scores of thousands of volcanoes ever yearning to erupt, they and the dramatic long-term effects of their eruptions are in fact far more frequent, far more decisive, and far greater than those that are triggered by any other natural phenomenon on the planet.It is worth remembering that ours is a world essentially made from and by volcanoes. They are creatures that will continue to do their business over the aeons, quite careless of the fate of the myriad varieties of life that teems beneath them and on their flanks. Including, of course, ours.There is perhaps no better recent example of the havoc that a big eruption can cause than that which followed the explosive destruction of Mount Toba, in northern Sumatra, 72,000-74,000 years ago (which, in geological time, is very recent indeed). The relics of this mountain today are no more than a very large and beautiful lake, 100 kilometres long and 800 metres deep – the caldera left behind by what is by most reckonings the largest volcanic explosion known to have occurred on the planet in the past 25 million years.On the widely used volcanic explosivity index (VEI), Toba is thought to have been an eight – meaning that in the unusually flamboyant official language of vulcanology it was a super-plinian type eruption with mega-colossal characteristics (Iceland’s Eyjafjallajokull is by contrast listed as a strombolian type, with its characteristic regarded as merely gentle, and having a probable VEI rating of just two).About 2800 cubic kilometres of rock were instantly vaporised by the super-eruptive blast of Toba, all of which was hurled scores of thousands of metres into the air. This is what did the lasting damage, just as Iceland’s high-altitude rock-dust did in Europe. But while we merely suffered a large number of inconvenienced people and a weakening of the balance sheets of some airlines, the effect on the post-Toban world was catastrophic: as a result of the thick ash clouds the world’s ambient temperature plummeted, perhaps by as much as 5 degrees – and the cooling and the howling wave of deforestation and deaths of billions of animals and plants caused a sudden culling of the human population of the time, reducing it to maybe as few as 5000 people, perhaps 1000 breeding pairs. Many anthropologists believe that the event caused a sudden evolutionary bottleneck, with genetic implications that linger to this day. Put more crudely, humanity was nearly wiped out by Toba, and only by the merest hair’s breadth did our ancestors of 72,000 years ago manage to cling on and bequeath to us our existence.Mercifully, from humanity’s point of view, there have been very few Tobas known in history. They are probably so large that they reach the upper limit of the kind of eruptions that can physically occur on Earth – one VEI-8 event occurs only every 100,000 years or so. Yet of those known to have occurred, two have taken place in Britain (mainly because Britain has such a vast variety of geology, with almost every age of rock known in the world found somewhere between Cape Wrath and Dover). They are comfortingly ancient: both – the volcano that created Scafell in the Lake District, and the other that gave us Glen Coe in the Western Highlands – took place more than 400 million years ago.But others of the 47 known VEI-8 volcanoes are more alarmingly recent. Taupo in New Zealand erupted with mega-colossal force some 22,500 years ago. The newer of the great eruptions that helped form the mountains of today’s Yellowstone National Park in the United States took place just 640,000 years ago, and all the current signs – from such phenomena as the rhythmic slow rising and falling of the bed of the Yellowstone River, as if some giant creature is breathing far below – suggest another eruption is coming soon. When it does, it will be an American Armageddon: all of the north and west of the continent, from Vancouver to Oklahoma City, will be rendered uninhabitable, buried under scores of metres of ash. (I mentioned this once in a talk to a group of lunching ladies in Kansas City, soothing their apparent disquiet by adding that by ”soon” I was speaking in geologic time, and that meant about 250,000 years, by which time all humankind would be extinct. A woman in the front row exploded with a choleric and incredulous rage: ”What?” she said. ”Even Americans will be extinct?”)Ratcheting down the scale a couple of notches, to the only slightly less gigantic eruptions that are classified as VEI-7 and VEI-6, and a host of more familiar eruptions come into view. These include Santorini, the Aegean volcano whose destruction around 4000 years ago may have triggered the collapse of the Minoan civilisation; Laki, the 1783 Icelandic volcano mentioned above, and which most obviously parallels today’s events at Eyjafjallajokull; the Javan volcano of Krakatoa, which erupted so infamously in August 1883; and the rather more profoundly world-affecting eruption of 1815, also in the Dutch East Indies, of the huge stratovolcano on Sumbawa Island, known as Tambora. Each of these had massive effects, and all were global in their extent.Tambora is the most notorious, not least because it was so immense: almost 170 cubic kilometres of pulverised Sumbawan rock were hurled into the sky, which darkened, cooled and polluted a world that, unlike in Toba’s day, was already well populated and widely civilised. The consequences ranged from the dire – a lowering of temperature that caused frosts in Italy in June and snows in the US in July, and the failure of crops in immense swathes across Europe and the Americas – to the ludicrous: Irish migrants, promised better weather in New England, found it on landing to be every bit as grim as the Connemara and Cork they had left, and so either went home, or pressed on in hope to California.Krakatoa’s immediate aftermath was dominated initially by dramatic physical effects – a series of tsunamis that were measured as far away as Portland Bill and Biarritz, a detonation that was clearly heard (like naval gunfire, said the local police officer) 5000 kilometres away on Rodriguez Island, and a year’s worth of awe-inspiring evening beauty as the sky lit up with dazzling colours.There was an important legacy to Krakatoa’s eruption not shared by the other giant volcanoes of the time. Close mapping of the spread of the 1883 sunsets showed them girdling the Earth in a curious set of spirals, the stratospheric aerosols evidently being borne around the world on high-altitude winds that no one at the time knew existed. An atmospheric scientist in Hawaii mapped them and decided to call the air current the equatorial smoke stream. It later became, more elegantly and economically, the jet stream. There has to be some irony that the jet stream that drove this month’s Icelandic dust so dangerously over Britain and mainland Europe is a phenomenon that was first discovered as a direct consequence of the study of Krakatoa.And yet, of all the consequences of the truly great volcanoes of the past, the phenomenon of mass extinctions of life must surely be the most profound and world-changing of all. Between two and five major extinction events occur in the world every million years or so. Humans have not been privileged to observe one of them – hardly surprisingly, since they would probably occur so slowly as to be barely noticeable. However, with painstaking care, palaeontological evidence is being amassed to link sudden and catastrophic changes in world climate, changes that promote such extinction crises, with the known major eruptions of the past, and with what are known as flood basalt events (such as those that have been triggered specifically in the past by eruptions of Eyjafjallajokull and her neighbouring volcano in Iceland, Katla, which is itself well overdue for an eruption). It is a study that opens up a fascinating speculative possibility.For what if the kind of event that we have seen this month, and which caused such commercial inconvenience, is in fact not just a minor volcanic hiccup, but the beginning of an event that causes in time a mass extinction of some form of earthbound life? And, since we know from the history books that the massive eruption of Santorini once had the power to destroy one proud part of human society, what if the extinction we might be beginning to see turns out to be what will one day surely occur, and that is the extinction of us?Guardian News & MediaSimon Winchester is a journalist and author of Krakatoa: The Day The World Exploded.
Nanjing Night Net