The Day in History:

Iceland"s Laki Volcano Begins 9-Month-Long Eruption (1783)

Laki is part of a volcanic system, centering on the Grímsvötn volcano and including the Eldgjá canyon and Katla volcano, and lies between the glaciers of Mýrdalsjökull and Vatnajökul, in an area of fissures which run in a south-west to north-east direction.

In AD 934, the Laki system produced a very large volcanic eruption, as a flood basalt in the Eldgjá eruption, which released 19.6 cubic kilometres (4.7 cu mi) of lava.

In 1783-1784, the system erupted again, 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 fluorine/sulfur-dioxide compounds that killed over 50% of Iceland"s livestock population, leading to famine which killed approximately 25% of the population.

AD 934 eruptionThe A.D. 934 Eldgjá eruption of the Laki system released 19.6 km³ (4.7 cu mi) of flood basalt, one of the largest volcanic eruptions on earth in historical times.

1783 eruptionOn 8 June 1783, a fissure with 130 craters opened with phreatomagmatic explosions because of the groundwater interacting with the rising basalt magma. These are sometimes mistaken by non-volcanologists as being "plinian" but are not. 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 VEI 6 on the Volcanic Explosivity Index, but the eight month emission of sulphuric aerosols resulted in one of the most important climatic and socially repercussive events of the last millennium.

The eruption, also known as the Skaft?reldar ("Skaft? river fires") or S??ueldur, 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 800-1400 m (~2,600-4,600 ft). In Great Britain, the summer of 1783 was known as the "sand-summer" due to ash fallout.The gases were carried by the convective eruption column to altitudes of about 15 kilometres (10 mi). The aerosols built up caused a cooling effect in the Northern Hemisphere.

The eruption continued until 7 February 1784, but most of the lava was erupted in the first five months. Gr?msv?tn 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 fluorine and estimated 120 million tons of sulphur dioxide gave rise to what has since become known as the "Laki haze" across Europe.

Consequences in Iceland

The consequences for Iceland were catastrophic. An estimated 25% of the population died in the famine and fluorine 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 fluorine that were released.

The parish priest J?n Steingr?msson grew famous because of his eldmessa ("fire sermon"). The whole community of the small town of Kirkjub?jarklaustur was in church. At the same time the town was endangered by a lava stream. But while the people were in church, the lava stopped not far from town.

"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 salt peter, 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."

Consequences in Europe

An estimated 122 Tg (120 million tons) of sulphur dioxide were emitted into the atmosphere: approximately equivalent to three times the total annual European industrial output in 2006, and also equivalent to a Mount Pinatubo-1991 eruption every three days. This outpouring of sulphur dioxide during unusual weather conditions caused a thick sulphurous 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 Norway, then spread to Prague in the Province of Bohemia by 17 June, Berlin by 18 June, Paris by 20 June, Le Havre by 22 June, and to 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 sulphurous gas causes victims to choke as their internal soft tissue swells. The local death rate in Chartres was up by 5% during August and September, with over 40 dead. In Great Britain, the records show that the additional deaths were outdoor workers, and perhaps 2-3 times above the normal rate in Bedfordshire, Lincolnshire and the east coast. It has been estimated that 23,000 British people died from the poisoning in August and September.

The haze also heated up causing severe thunderstorms with hailstones that were reported to have killed cattle until it dissipated in the autumn. This disruption then led to a most severe winter in 1784, where Gilbert White at Selborne in Hampshire reported 28 days of continuous frost. The extreme winter is estimated to have caused 8,000 additional deaths in the UK. In the spring thaw, Germany and Central Europe then reported severe flood damage.

The meteorological impact of Laki resonated on, contributing significantly to several years of extreme weather in Europe. In France a sequence of extremes included a surplus harvest in 1785 that caused poverty for rural workers, accompanied by droughts, bad winters and summers, including a violent hailstorm in 1788 that destroyed crops. This in turn contributed significantly to the build up of poverty and famine that triggered the French Revolution in 1789. Laki was only a factor in a decade of climatic disruption, as Gr?msv?tn was erupting from 1783-1785 and a recent study of El Ni?o patterns also suggests an unusually strong El-Ni?o effect between 1789-93.

Consequences in North America

In North America, the winter of 1784 was the longest and one of the coldest on record. It was the longest period of below-zero temperatures in New England, the largest accumulation of snow in New Jersey, and the longest freezing over of Chesapeake Bay. There was ice skating in Charleston Harbor, a huge snowstorm hit the south, the Mississippi River froze at New Orleans, and there was ice in the Gulf of Mexico.

Other consequences

There is also evidence that the Laki eruption had effects beyond Europe, with weakened African and Indian monsoon circulations, leading to precipitation anomalies of -1 to -3 mm (-0.04 to -0.12 inch) per day over the Sahel of Africa, resulting in, amongst other effects, low flow in the River Nile. It may also have exacerbated the Tenmei famine in Japan.

Contemporary reports

Gilbert White recorded his perceptions of the event at Selborne:

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; [...]

Benjamin Franklin recorded his observations in a 1784 lecture:

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 Hecla 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.(It should be noted that, according to current records, Hekla did not erupt in 1783, its previous eruption was in 1766. The Laki fissure eruption was 45 miles to the east and the Gr?msv?tn volcano was erupting circa 75 miles north east. Additionally Katla, only 31 miles[19] south east, was still renowned after its spectacular eruption 28 years earlier in 1755.)

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