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.