O.K., it happened two hundred and twenty four years ago, but the point is it could happen again. A new piece of research has shown how a cloud of toxic gas emitted from the Laki volcano in Iceland killed 30,000 Britons 600 miles away, in 1783. According to Dr John Grattan from the University of Wales at Aberystwyth, "people died in such numbers because the volcanic cloud exacerbated their respiratory illnesses". The toxic cocktail appears to have been a combination of sulphur dioxide (SO2) and fine dust particles, and from problems of an associated hot climate. It is well known now that fine particles smaller than 2.5 microns (for comparison, the thickness of a human hair is about 70 microns) can trigger a spate of hospital admissions from heart attacks and lung complaints, caused by unexpectedly high levels of smog. These tiny particles are too small to be filtered-out in the higher respiratory tract and hence penetrate into the deep lung. Some of the smaller of them can cross the blood-tissue barrier, and through incompletely understood mechanisms cause the release of cytokines (molecules that instruct cells to communicate is particular ways, as part of their defense strategy) to combat them as foreign invaders. If airways are already inflamed the effect of SO2 is particularly deleterious, especially under hot humid conditions, as we saw in the record number of deaths across Europe in 2003, among the elderly and others suffering from respiratory and cardiovascular ailments.
Due to its location on the Mid-Atlantic Ridge (where the North American and Eurasian tectonic plates are pulling apart), Iceland has the greatest number of fissure-volcanoes, which erupt when huge cracks, some up to 35 miles long, open up in the ground. Icelandic fissure volcanoes can erupt for long periods - up to five years at a stretch. The 1783 event was caused by the eruption of a 15 mile long fissure, and lasted for seven months. Unlike the kind of volcanoes that we are more familiar with, fissure volcanoes release their debris more slowly and so the gas and ash from them are not cast into the higher atmosphere, but instead tend to circulate lower down, resulting in severe air pollution over a wide region. According to historical records, the major fissure eruptions in Iceland occurred for half of the 930's decade and then in the years 960, 1227, 1340, 1341, 1477, 1724, 1783 and 1975. One is always tempted to look for a pattern in such data, perhaps falsely as the Earth and its geology are unpredictable to our short point of view, but it is not unthinkable that another similar event of comparable magnitude could happen any time. These islands are far more extensively and densely populated than was the case in the late eighteenth century and simple reckoning of population numbers might suggest that the death toll would be nearer 100,000 than 30,000, but the exact number would depend closely on the prevailing climatic conditions as to where the major plume was finally received.
The 1783 event was only the second largest, and the 10th-century eruption lasted from 934 - 939 A.D., but for which the human effects are largely unknown. However, the event of 1783 had a further impact on the lives of those then living through its effect to initially raise local temperatures and cause severe damage to vegetation including crops. However, after several months of continuous eruption, the levels of sulphur in the atmosphere had reacted chemically to produce high levels of particles "sulphate aerosol" (sulphuric acid and its compounds including ammonium sulphate) which screened solar radiation from reaching the surface, which cooled alarmingly by several degrees. Quite a double-whammy.
There will be a B.B.C. "Timewatch" broadcast about the incident this Friday, in which Dr Gratton estimates that in addition to the U.K. casualty figure of 30,000, another 200,000 died in France, in the low countries (Netherlands etc.) and in northern Italy, while Iceland itself lost around 25% of its population. Should another such eruption occur, there is very little we could do about it, since we could neither stem the event itself, nor put millions of those vulnerable on "oxygen" say. God forbid, but such events of Nature which to us appear catastrophic are mere flicks of her fingertip, reminders of the consummate power of the planet. We should never forget it is Earth who is in control not us: we simply live as one of many species on her surface, at her pleasure or displeasure, and humankind might eventually become extinct as have so many others.