The map is almost uncannily similar to today’s: A spray of black dots showing the recorded sightings of a foul gray haze spreading across Europe, from Helsinki to Naples, from Heligoland to Mallorca, and reaching eventually to Aleppo and Damascus — and all of it caused by clouds of ash from an immense volcano erupting far across the sea in Iceland.
This was a map, however, 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 9,000 people, drenched the European forests in acid rain and 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 — very 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 last 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.
However, there is a signal difference. Earthquakes and their aftershocks, once done, are done. Volcanoes, however, often trigger long-term and long-distance ill-effects, which history indicates 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 entire 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 and they can and do 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 today 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 eons, 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 Mt Toba, in northern Sumatra, some 72,000 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, 100km long and 800m deep — the caldera that was left behind by what is by most reckonings the largest volcanic explosion known to have occurred on the planet in the last 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 (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 2,800 cubic kilometers of rock were instantly vaporized by the super-eruptive blast of Toba, all of which was hurled scores of thousands of meters into the air. This is what did the lasting damage, just as Iceland’s high-altitude rock-dust is doing today. However, while we today are merely suffering 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 5ºC — 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 5,000 people, perhaps 1,000 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 current existence.
Mercifully, from humanity’s point of view, there have been very few Tobas known in planetary 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 the Port of 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.
However, 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 Wyoming 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 meters 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 4,000 years ago may have triggered the collapse of the Minoan civilization; 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 present-day Indonesia, of the huge stratovolcano on Sumbawa Island, known as Tambora. Each of these had massive after-effects and all of the effects were global in their extent.
Tambora is the most notorious, not least because it was so immense: Almost 170 cubic kilometers of pulverized 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 civilized. The consequences ranged from the dire — a lowering of temperature that caused frosts in Italy in June and snows in Virginia in July and the failure of crops in immense swathes across Europe and the Americas — to the frankly 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.
And Tambora’s eruption had its effects on art also: A gloomy Byron wrote the gloomiest of poems, Darkness (“Morn came and went, and came, and brought no day/ And men forgot their passions in the dread/ Of this their desolation …”); Mary Shelley, it is said, became so fed up with the rain while visiting Byron in Geneva that she followed suit and wrote her exceptionally gloomy novel Frankenstein. Only J.M.W. Turner rose more cheerfully to the occasion: The lurid colors of many of his paintings, it is said, owe much to the flaming Tambora sunsets that had half the world astonished and Turner evidently inspired.
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 bang of detonation that was clearly heard (like naval gunfire, the local police officer said) 5,000km away on Rodriguez Island and a year’s worth of awe-inspiring evening beauty — astonishing sunsets of purple and passion fruit and salmon that had artists all around the world trying desperately to capture what they managed to see in the fleeting moments before dark. A Londoner named William Ascroft left behind almost 500 watercolors that he painted, one every 10 minutes like a human film camera, from his Thames-side flat in Chelsea; Frederic Church, of America’s so-called Hudson River School, captured the crepuscular skies over Lake Ontario in their full post-Krakatoan glory; and many now agree that Edvard Munch had the purple and orange skies over Oslo in mind when 10 years afterwards he painted, most hauntingly, The Scream.
Yet there was an important legacy to Krakatoa’s eruption that was 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 even 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 drives today’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. We humans have not thus far 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, paleontological evidence is currently 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 neighboring volcano in Iceland, Katla, which is herself currently 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 us all in Europe 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 further, 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?
Simon Winchester is a journalist and author; one of his books is Krakatoa: The Day The World Exploded.
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