The map is almost 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 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.
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 9,000 people, drenched the 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 – 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.