The system erupted over an eight-month period between 1783 and 1784 from the Laki fissure and the adjoining Grímsvötn volcano, pouring out an estimated 14 km3 (3.4 cu mi) of basalt lava and clouds of poisonous hydrofluoric acid and sulfur dioxide compounds that killed over 50% of Iceland's livestock population, leading to a famine that killed approximately 25% of Iceland's human population.
The Laki eruption and its aftermath caused a drop in global temperatures, as sulfur dioxide was spewed into the Northern Hemisphere. This caused crop failures in Europe and may have caused droughts in India. The eruption has been estimated to have killed over six million people globally, making the eruption the deadliest in historical times.
On 8 June 1783, a fissure with 130 craters opened with phreatomagmatic explosions because of the groundwater interacting with the rising basaltmagma. Over a few days the eruptions became less explosive, Strombolian, and later Hawaiian in character, with high rates of lava effusion. This event is rated as 6 on the Volcanic Explosivity Index, but the eight-month emission of sulfuric aerosols resulted in one of the most important climatic and socially repercussive events of the last millennium.
The eruption, also known as the Skaftáreldar ("Skaftá fires") or Síðueldur, produced an estimated 14 km3 (3.4 cu mi) of basalt lava, and the total volume of tephra emitted was 0.91 km3 (0.2 cu mi).Lava fountains were estimated to have reached heights of 800 to 1,400 m (2,600 to 4,600 ft). The gases were carried by the convective eruption column to altitudes of about 15 km (10 mi).
The eruption continued until 7 February 1784, but most of the lava was ejected in the first five months. Grímsvötn volcano, from which the Laki fissure extends, was also erupting at the time, from 1783 until 1785. The outpouring of gases, including an estimated 8 million tons of hydrogen fluoride and an estimated 120 million tons of sulfur dioxide, gave rise to what has since become known as the "Laki haze" across Europe.
Consequences in Iceland
The consequences for Iceland, known as the "Móðuharðindin" (Mist Hardships), were catastrophic. An estimated 20–25% of the population died in the famine and fluoride poisoning after the fissure eruptions ceased. Around 80% of sheep, 50% of cattle and 50% of horses died because of dental and skeletal fluorosis from the 8 million tons of hydrogen fluoride that were released.
The parish priest and dean of Vestur-Skaftafellssýsla, Jón Steingrímsson (1728–1791), grew famous because of the eldmessa ("fire sermon") that he delivered on 20 July 1783. The people of the small settlement of Kirkjubæjarklaustur were worshipping while the village was endangered by a lava stream, which ceased to flow not far from town, with the townsfolk still in church.
"This past week, and the two prior to it, more poison fell from the sky than words can describe: ash, volcanic hairs, rain full of sulfur and saltpeter, all of it mixed with sand. The snouts, nostrils, and feet of livestock grazing or walking on the grass turned bright yellow and raw. All water went tepid and light blue in color and gravel slides turned gray. All the earth's plants burned, withered and turned gray, one after another, as the fire increased and neared the settlements."
Center of the Laki Fissure
Consequences in monsoon regions
There is evidence that the Laki eruption weakened African and Indianmonsoon circulations, leading to between 1 and 3 millimetres (0.04 and 0.12 in) less daily precipitation than normal over the Sahel of Africa, resulting in, among other effects, low flow in the River Nile. The resulting famine that afflicted Egypt in 1784 cost it roughly one-sixth of its population. The eruption was also found to have affected the southern Arabian Peninsula and India.
Consequences in Europe
An estimated 120,000,000 long tons (120,000,000 t) of sulphur dioxide was emitted, about three times the total annual European industrial output in 2006 (but delivered to higher altitudes, hence more persistent), and equivalent to six times the total 1991 Mount Pinatubo eruption. This outpouring of sulphur dioxide during unusual weather conditions caused a thick haze to spread across western Europe, resulting in many thousands of deaths throughout 1783 and the winter of 1784.
The summer of 1783 was the hottest on record and a rare high-pressure zone over Iceland caused the winds to blow to the south-east. The poisonous cloud drifted to Bergen in Denmark–Norway, then spread to Prague in the Kingdom of Bohemia (now the Czech Republic) by 17 June, Berlin by 18 June, Paris by 20 June, Le Havre by 22 June, and Great Britain by 23 June. The fog was so thick that boats stayed in port, unable to navigate, and the sun was described as "blood coloured".
Inhaling sulphur dioxide gas causes victims to choke as their internal soft tissue swells – the gas reacts with the moisture in lungs and produces sulfurous acid. The local death rate in Chartres was up by 5% during August and September, with more than 40 dead. In Great Britain, the records show that the additional deaths were among outdoor workers; the death rate in Bedfordshire, Lincolnshire and the east coast was perhaps two or three times the normal rate. It has been estimated that 23,000 British people died from the poisoning.
The weather became very hot, causing severe thunderstorms with large hailstones that were reported to have killed cattle, until the haze dissipated in the autumn. The winter of 1783/1784 was very severe; The naturalist Gilbert White in Selborne, Hampshire, reported 28 days of continuous frost. The extreme winter is estimated to have caused 8,000 additional deaths in the UK. During the spring thaw, Germany and Central Europe reported severe flood damage.
The meteorological impact of Laki continued, contributing significantly to several years of extreme weather in Europe. In France, the sequence of extreme weather events included a surplus harvest in 1785 that caused poverty for rural workers, as well as droughts, bad winters and summers, and a violent hailstorm in 1788 that destroyed crops. These events contributed significantly to an increase in poverty and famine that may have contributed to the French Revolution in 1789. Laki was only one factor in a decade of climatic disruption, as Grímsvötn was erupting from 1783 to 1785, and a 1998 study of El Niño patterns suggests that there was also an unusually strong El Niño effect from 1789 to 1793.
The summer of the year 1783 was an amazing and portentous one, and full of horrible phaenomena; for besides the alarming meteors and tremendous thunder-storms that affrighted and distressed the different counties of this kingdom, the peculiar haze, or smokey fog, that prevailed for many weeks in this island, and in every part of Europe, and even beyond its limits, was a most extraordinary appearance, unlike anything known within the memory of man. By my journal I find that I had noticed this strange occurrence from June 23 to July 20 inclusive, during which period the wind varied to every quarter without making any alteration in the air. The sun, at noon, looked as blank as a clouded moon, and shed a rust-coloured ferruginous light on the ground, and floors of rooms; but was particularly lurid and blood-coloured at rising and setting. All the time the heat was so intense that butchers' meat could hardly be eaten on the day after it was killed; and the flies swarmed so in the lanes and hedges that they rendered the horses half frantic, and riding irksome. The country people began to look, with a superstitious awe, at the red, louring aspect of the sun; [...]
During several of the summer months of the year 1783, when the effect of the sun's rays to heat the earth in these northern regions should have been greater, there existed a constant fog over all Europe, and a great part of North America. This fog was of a permanent nature; it was dry, and the rays of the sun seemed to have little effect towards dissipating it, as they easily do a moist fog, arising from water. They were indeed rendered so faint in passing through it, that when collected in the focus of a burning glass they would scarce kindle brown paper. Of course, their summer effect in heating the Earth was exceedingly diminished. Hence the surface was early frozen. Hence the first snows remained on it unmelted, and received continual additions. Hence the air was more chilled, and the winds more severely cold. Hence perhaps the winter of 1783–4 was more severe than any that had happened for many years.
The cause of this universal fog is not yet ascertained [...] or whether it was the vast quantity of smoke, long continuing, to issue during the summer from Hekla in Iceland, and that other volcano which arose out of the sea near that island, which smoke might be spread by various winds, over the northern part of the world, is yet uncertain.(According to contemporary records, Hekla did not erupt in 1783; its previous eruption was in 1766. The Laki fissure eruption was 45 miles (72 km) to the east and the Grímsvötn volcano was erupting about 75 miles (121 km) north east. Additionally Katla, only 31 miles (50 km) south east, was still renowned after its spectacular eruption 28 years earlier in 1755.)
...‘about six o’clock, that morning, I observed the air very much condensed in my chamber-window; and, upon getting up, was informed by a tenant that finding himself cold in bed, about three o’clock in the morning, he looked out at his window, and to his great surprise saw the ground covered with a white frost: and I was assured that two men at Barton, about 3 miles (4.8 km) off, saw in some shallow tubs, ice of the thickness of a crown-piece.’
Sir John goes on to describe the effect of this ‘frost’ on trees and crops:
‘The aristae of the barley, which was coming into ear, became brown and withered at their extremities, as did the leaves of the oats; the rye had the appearance of being mildewed; so that the farmers were alarmed for those crops…The larch, Weymouth pine, and hardy Scotch fir, had the tips of their leaves withered’.
Sir John’s vegetable garden did not escape; he noted that the plants looked ‘exactly as if a fire had been lighted near them, that had shrivelled and discoloured their leaves.’
^Gudmundsson, Magnús T.; Thórdís Högnadóttir (January 2007). "Volcanic systems and calderas in the Vatnajökull region, central Iceland: Constraints on crustal structure from gravity data". Journal of Geodynamics43 (1): 153–169. Bibcode:2007JGeo...43..153G. doi:10.1016/j.jog.2006.09.015.
^Gunnar Karlsson (2000), Iceland's 1100 Years, p. 181
Brayshay, M and Grattan, J. "Environmental and social responses in Europe to the 1783 eruption of the Laki fissure volcano in Iceland: a consideration of contemporary documentary evidence" in Firth, C. R. and McGuire, W. J. (eds) Volcanoes in the Quaternary. Geological Society, London, Special Publication 161, 173–187, 1999
Grattan, J., Brayshay, M. and Sadler, J. "Modelling the distal impacts of past volcanic gas emissions: Evidence of Europe-wide environmental impacts from gases emitted during the eruption of Italian and Icelandic volcanoes in 1783" in Quaternaire, 9, 25–35. 1998.
Grattan, D., Schütenhelm, R. and Brayshay, M. "Volcanic gases, environmental crises and social response" in Grattan, J. and Torrence, R. (eds) Natural Disasters and Cultural Change, Routledge, London 87–106. 2002.