Laki, or Lakigígar, is a volcano in southern Iceland, it is a part of the Grímsvötn Volcanic Complex, which has been in the news this year. In June 1773 Laki erupted, not from its summit, but from a number of fissures in its side. These fissures produced a lava fountain that reached 1400 m into the air, and a column of ash and gasses ten times as high. This eruption persisted for eight months, during which time it is thought to have produced 14 km³ on lava, and clouds of ash and gas that reached around the globe, with devastating effects. The gasses produced by Laki were unusually rich in sulphur dioxide (SO₂), which is a lethal poison, and lead to many thousands of deaths in Iceland in Europe. In total Laki is thought to have killed around 6 million people worldwide, through a combination of sulphur dioxide poisoning, the climatic effects of the ash and aerosols and famine resulting from both, and to have contributed to the famine that triggered the French Revolution.
The French Revolution - an unusual side effect of a volcanic eruption. Image by Eugene Delacroix.
As a one-off event this would be historically interesting, if a little sad, but Laki was not a one-off event. Iceland is located on a divergent margin, where two of the Earth's larger tectonic plates (North America and Eurasia) are drawing apart and new crust is being formed. This makes it an extremely volcanically active environment, with eruptions, at least on a minor scale, happening more-or-less constantly. In the past two years there have been two eruptions large enough to cause major disruption to air-traffic in Europe - Eyjafjallajökull and Grímsvötn. Seen in this context it is not surprising to discover that there have been other Laki-type eruptions - four in the last 1150 years. This makes the likely-hood of another Laki-type eruption occurring in the foreseeable future worth worrying about; it is clearly a far more likely hazard than (for example) the danger of a major meteor strike, a scenario which has received considerable investigation in recent years.
The 20 September edition of the Proceedings of the National Academy of Sciences (vol. 108, no. 38), contains a paper by a team lead by Anja Schmidt of the School of Earth and Environment at the University of Leeds, in which they model the effects of a possible Laki-type eruption on modern day Europe.
Schmidt et al. begin by observing that the modern world is very different from the world of the late eighteenth century. Our scientific understanding of our environment and medical skills are far in advance of theirs, and we have the ability to respond to large scale problems in ways that simply not available then. Our populations are on the whole healthier than they were two centuries ago, but they are also older, making them vulnerable in different ways, and far larger, so that a lower fatality rate may well result in more deaths.
The country worst effected by the 1783-4 eruption was Iceland itself, with clouds of volcanic haze, rich in sulphur dioxide, covering much of the country, leading to the deaths of around 10 000 people, between 20 and 25% of the population. In addition between 50 and 75% of the island's livestock is thought to have perished. At the time nobody knew what sulphur dioxide was, so they were able to do little to respond to the problem. In modern Iceland the activities of all volcanoes are carefully monitored by the Icelandic Met Office, which also pays careful attention to air pollution arising from these activities. This should enable the country to take prompt action if confronted by a major volcanic haze problem, evacuating people where necessary and providing some protection to those who cannot be evacuated, though one on the scale of the 1783 Laki eruption would still cause considerable problems, so it is likely that there would still be fatalities.
Icelandic scientists monitoring emissions from Mount Eyjafjallajökull.
In addition to the poisoning by sulphur dioxide, it is likely that many of the deaths in Iceland in 1783-4 were caused by famine, as crops and livestock were smothered by ash, or poisoned by hydrofluoric acid (the ash was unusually rich in this lethal compound). This should be far less of a problem, as modern Iceland would be able to import food to get it through any crop failures, something which was not an option in the 1780s.
In total Schmidt et al. estimate that confronted with a modern Laki-type eruption on a similar scale to the 1783-4 eruption then they could potentially loose up to 400 people, which would be tragic, but is far less devastating than the eighteenth century losses.
From Iceland the volcanic haze drifted east to Europe, which was already suffering from an unprecedented heat-wave. Eighteenth century agriculture was far more labour intensive than modern farming, involving many more people working outdoors, doing hard physical labour in the hight of summer. These agricultural workers proved to be particularly vulnerable to the effects of sulphur dioxide poisoning.
In Britain it is estimated that 23 000 people died from poisoning in the summer of 1873, predominantly in the eastern English counties, where mortality rates reached three times normal. This was followed by an unusually severe winter, the result of volcanic aerosols, which tend to lower temperatures. This is thought to have lead to another 8000 deaths.
Schmidt et al. find that the modern UK is still vulnerable to the effects of a Laki-type eruption. By modeling the effects of sulphur dioxide from known pollution events on a population with the demographic make up of modern Britain, they estimate that approximately 20 900 additional deaths would be caused. This is comparable to the overall number of deaths in the eighteenth century, but represents a much smaller proportion of the population.
Across Western Europe they estimate that there would be between 77 500 and 81 900 additional deaths, with casualties particularly severe in the Netherlands and Belgium in addition to the UK. In the 1780s deaths were caused by famine in addition to poisoning. In modern Europe this is less likely to be a problem, but it is possible that if Europe needed to radically increase its food imports for a sustained period that this could cause famine in other, parts of the world.
The Schmidt et al. model does not attempt to make predictions beyond Europe, but the effects of the 1893-4 eruption much more far-reaching. It is thought to have interfered with the monsoon pattern in Africa and Asia, leading to famine in North Africa and the Sahel region (grasslands of West Africa), as well as India and Japan. It has also been linked to a particularly hard winter in North America.
These effects further afield are far harder to predict. The world has a far better ability to deal with famines than was formerly the case, with co-ordinated international efforts to help famine-hit countries. However it is difficult to predict what might happen in the event of widespread famine across several continents simultaneously. It is possible that developed nations with strong economies might hoard food at the expense of poorer nations, possibly leading to food shortages far from the regions effected by the eruption. It has been suggested that the recent political upheaval in North Africa was at least in part caused by rising food prices, and it is quite possible that a Laki-type eruption might cause widespread political change, just as it did in the eighteenth century.
The Egyptian Revolution of 2011 was probably caused at least in part by rising food prices, a result of the global financial crisis. It is possible that a Laki-type eruption could cause similar uprisings in many more countries.
See also The Hekla Volcano - is the Gateway to Hell about to open? The Grímsvötn Volcano and Volcanoes on Sciency Thoughts YouTube.