Móðuharðinðin – “The Hardship of the Fog”: The Human and Environmental Disaster of the Laki Eruption, 1783-4

The central fissure at Laki. Photo: Petr Brož CC BY-SA 3.0

On 8 June 1873 the Laki mountain in the Grímsvötn volcanic system of southern Iceland was ripped apart by a volcanic eruption that opened a massive fissure and scores of craters. Over a period of 8 months to 7 February 1784 the Skaftáreldar, or Skaftár Fires, as they were known in Iceland , spewed out 14.7 cubic kilometres of basaltic lava, deposited 0.4 cubic kilometres of tephra, and a gas cloud that contained 122 million tons of sulphur dioxide, 7 million tons of hydrochloric acid, and 15 million tons of hydrofluoric acid. Such was the force of the eruption that between June and August of 1783 the eruption column is estimated to have reached 9 kilometres in height.

By any standards it was a monumental eruption and the effects were catastrophic, not only locally in Iceland but across much of the northern hemisphere. For several months a volcanic haze hung over the North Atlantic, Europe, North Africa and Asia, leading to an immediate and long lasting impact on the environment. This sulphuric aerosol cloud, known in Icelandic as the móða or ‘haze’, was observed to cover southeast Iceland by June 1873 and by 18 June all of Iceland was covered in a dark blue haze.

The force of the eruption carried the plume into the Atlantic Jet Stream and by 10 June it had been observed in the Faeroe Islands and possibly northern Scotland. By late June the haze had extended to cover nearly all of Europe, reaching St Petersburg by 26 June, and appearing in Tripoli and Syria towards the end of the month. By 1 July the haze had covered the sky above the Altai mountains in Central Asia, some 7,000 kilometres from its source in Iceland. By late July the haze covered the entire northern hemisphere from a latitude of 35 degrees North as far as the North Pole. While direct observation of the haze suggests that it was last seen in mid-September to late-October, other evidence from contemporary weather records suggests that at least a part of the Laki aerosol cloud remained in the atmosphere at lower stratosphere altitudes for at least one year after the eruption.

A schematic illustration showing the key features of the two-stage degassing in flood lava eruptions. (Thordarson & Self, 2003)

In Europe the haze caused sickness in humans and animals and withering of vegetation. In Holland people complained of headaches and breathing difficulties. In Norway, Denmark, Sweden and elsewhere vegetation withered leading to crop failures. English newspapers reported the yellowing of crops and the frequency of violent thunderstorms. In Switzerland there were reports of the haze discolouring paper as it came off the printing presses. Throughout Europe observers reported that the haze was thick enough that they could look directly on the sun without ill effect for several days.

In Iceland the effects were immediately obvious and far worse. The haze and volcanic ash falls were noticed across the island, most strongly in the southeast, and rapidly affected vegetation, animals and people. Acid rainfall on the first day of the eruption was strong enough to burn holes in vegetation and cause wounds on the skin of animals and humans. The toxic haze also affected people’s respiratory functions, irritated eyes and other soft tissues, and caused a general feeling of weakness and a throbbing of the heart.

Approximately 8 megatons of hydrogen fluoride was released into the Icelandic atmosphere with a large proportion of it settling on the island and poisoning the landscape. Throughout Iceland most of the birch trees, shrubs, and mosses died, many disappearing from Iceland for periods of up to 3 to 10 years, and in some areas vegetation never re-established itself. High concentrations of fluorine rapidly led to sickness in livestock which soon began to show symptoms of chronic fluorosis with softening and deformation of bones and joints, dental lesion and outgrowth on the molars. In southeast Iceland where the ash fall was most dense animal sickness developed rapidly leading to mass deaths of livestock within 8 to 14 days.

In the long term 79 per cent of the sheep, 76 per cent of the horses, and 50 per cent of the cattle died, mostly from chronic fluorosis exacerbated by the catastrophic effect on grass growth that left pastures withered and stunted. The human impact was terrible as a severe famine set in that lasted until 1786. Some 20 per cent of Iceland’s population of 50,000 died in this period. Had it not been for Iceland’s fishing economy it is certain that this figure would have been worse. As it was those inhabitants who lived inland experienced a higher death rate than those who lived on the coast.

While the summer of 1783 in Europe experienced higher than average temperatures the long-term effects of the haze cloud was a drop in the annual mean temperature in the northern hemisphere by 1.4 degrees centigrade, leading to several years of cold winters. Summers after 1784 were also cooler and irregular weather patterns between 1783 and 1790 led to frequent failure of the harvest and subsequent poverty and famine for large sectors of the European population.

Simplified cross section from Iceland to mainland Europe showing the
dispersal and development of the Laki plumes in the first 3–4 weeks of the eruption (Thordarson & Self, 2003)

An eruption on the same scale would undoubtedly cause far greater devastation today, not least due to the much higher population in Iceland. The much smaller Eyjafjallajökull eruption in 2010 gives us an idea of how air traffic and European business could be dramatically affected. Additionally, levels of industrial pollution are far higher today than in 1783 and in combination with Laki levels of sulphur dioxide, hydrochloric acid, and hydrofluoric acid could result in greater and more persistent environmental damage.

Unlike 1783 one would hope that the international response to the disaster would help to ameliorate the potential loss to life, if not the environmental damage. Following the Laki eruption Iceland found itself having to cope on its own with little support from Denmark. Today one would expect a major rescue effort and even complete evacuation, as in the cases of the town of Plymouth on the island of Montserrat, Tristan da Cunha, and the Cape Verde island of Fogo.

Which leaves us with the question, how likely is another Laki event? Statistically it’s unlikely to happen in the near future, but equally it could happen at any time. Laki is not the only potential Icelandic site for a major volcanic event and fissure eruptions are hard to predict. Evidence from Laki suggests that today we would have a three to four week period of precursor activity, mainly in the form of increased earth tremors and quakes.

Without constant monitoring, identifying a pending volcanic mega-event is nigh on impossible. Fortunately the Veðurstofa Íslands (Icelandic Meteorological Office) has a nationwide monitoring system that as well as monitoring the weather and hydrology has a 55-station seismic network with automatic, real-time data acquisition and earthquake location and a weather radar which can also monitor volcanic plumes. The Almannavarnir (Icelandic Civil Protection Department) also produces information and advice for specific eruptions in addition to general guidelines for Icelanders to follow in the event of volcanic activity. General evacuation measures are in place and specific plans are rapidly drawn up to deal with any new volcanic events such as the recent Eyjafjallajökull eruption.

To date such measures and evacuation plans have proved effective in protecting human life, though we should recognise that the Almannavarnir has not had to cope with anything near the severity of Laki. With a population of 329,000, Iceland is perhaps in a fortunate position, in that any mass evacuation of the entire population in a relatively short space of time would be logistically difficult but possible, given sufficient maritime support in terms of vessels capable of transporting high volumes of passengers in extremis. With Europe and North America within relatively quick sailing distance, and given Iceland’s membership of organizations such as the United Nations and NATO one would expect that rescue efforts would mean that the immediate death toll would be low, and that the famine that led to so many deaths following the eruption in 1783 would be averted.

The wider environmental and health impacts would be far more difficult to manage. The effect of a northern hemisphere wide aerosol cloud would exacerbate climate change and cause widespread pollution in Iceland and further afield. Europe would undoubtedly bear the brunt of the fallout of acid rain and toxic fumes, leading to extensive damage of vegetation and at the very least sickness in animals and humans. If assessments of the impact on England in 1783 are correct there could also be a death toll in the hundreds of thousands. In England alone some 20,000 people are estimated to have died in the Summer of 1783 as a direct consequence of the volcanic haze, the majority from respiratory conditions brought on or exacerbated by the toxic fumes. The sobering conclusion is that it seems unlikely that we could cope with the public health and environmental consequences of a Laki type eruption.