The Laki eruption of 1783 killed about a fifth of everyone living in Iceland. Over eight months a single fissure 25 kilometres long, set with roughly 130 craters, poured out 14.7 cubic kilometres of lava, the largest flow from any eruption in recorded history. The lava was the smaller danger. The gas it released poisoned the grass, then the livestock, then the people, in a famine Icelanders still call the Moduhardindin, the Mist Hardships. The same haze drifted across Europe and turned the summer cold. This is the story of the Laki eruption, what it did to Iceland, and why scientists still treat it as a benchmark.
What and Where Laki Is
Laki, or Lakagigar in Icelandic, is a 25-kilometre row of craters torn along a fissure in the southern highlands, about 40 kilometres inland from the village of Kirkjubaejarklaustur. The name Lakagigar means the craters of Laki, after a small hill the fissure cut across. The eruption itself is called the Skaftareldar, the Skafta Fires, because the lava flooded down the gorge of the Skafta river.
The fissure belongs to the Grimsvotn volcanic system, whose central volcano sits under the Vatnajokull ice cap. Grimsvotn erupted at the same time in 1783, which tells geologists the two share a magma source. For how Laki fits among the country’s other systems, see our overview of volcanoes in Iceland.
The Eruption of 1783
The ground opened on 8 June 1783 and did not close until February 1784. The fissure unzipped in stages, each new section announced by earthquakes, until ten separate segments were active along its length. Fountains of lava rose hundreds of metres, and the first stream poured down the gorge of the Skafta river.
A second fissure tore open east of the hill Kaldbak on 29 July 1783 and sent a fresh stream down the gorge of the Hverfisfljot river. Between them the flows buried thirteen farms outright and forced families off about twenty-nine more holdings, as lava, ashfall, drifting sand and flooding ruined the ground. The new church at Holmar burned that same July.
By the time it ended, the lava covered close to 599 square kilometres. The 14.7 cubic kilometres it released is the largest basaltic lava flow produced by any single eruption in the historical record. For comparison, the much-reported 2014 Holuhraun eruption, the biggest in Iceland since the eighteenth century, produced under a sixth as much.
The flow left behind a lava field with its own name, Eldhraun, the fire lava. It spread across the lowland between the highlands and the coast, and Iceland’s Ring Road now runs straight over it east of Kirkjubaejarklaustur, under a deep blanket of grey-green moss. Drivers cross several kilometres of it without sensing they are on the largest lava flow in human history.
The Gases and the Mist Hardships
Laki’s lasting damage came from what it breathed out: an estimated 120 million tonnes of sulphur dioxide and around 8 million tonnes of fluorine. The fluorine settled on grass as the compound that causes fluorosis, which rots the bones and teeth of grazing animals. Livestock that ate the contaminated grass sickened and died through the following winter.
The numbers are stark. Iceland lost roughly half its cattle, about three quarters of its horses and nearly four fifths of its sheep. The national flock, around 357,000 sheep before the eruption, fell to about 50,000. With the animals gone, the people starved. The national census fell from 48,810 people in 1783 to 38,973 by 1786, a loss of close to one in five, almost all of it in the famine rather than from the lava. Nearest the craters the collapse ran deeper: the Sida district beside the eruption went from around 2,000 people to roughly 500 within two years.
- Sulphur dioxide released: around 120 million tonnes
- Fluorine released: about 8 million tonnes
- Sheep lost: roughly 80 percent of the national flock
- People lost: about 9,000, near a fifth of Iceland
Jon Steingrimsson and the Fire Mass
The eruption produced one of Iceland’s most retold pieces of history. Jon Steingrimsson, the parish minister at Kirkjubaejarklaustur, kept a detailed chronicle of the disaster that remains a key eyewitness source for any volcanologist studying Laki. He recorded the dates, the lava’s path and the suffering of his parish with unusual precision.
That chronicle, the Eldrit or fire writing, is read today as much for its prose as for its data, ranking among the founding works of Icelandic writing about a natural disaster. Steingrimsson stayed with his parish while other clergy fled, set the account down while burying his own parishioners, and lost his wife to the hardship that came after. He died in 1791.
On 20 July 1783, with a lava stream bearing down on the church, Steingrimsson gathered his congregation and delivered the sermon Icelanders remember as the Eldmessa, the Fire Mass. By the time the service ended, the lava had stopped just west of the rock pillar called Systrastapi and gone no further. The spot still carries the name Eldmessutangi, the Fire Mass point. Steingrimsson read it as divine mercy; later geologists found that water from the Holtsa and Fjadra rivers had chilled and stalled the flow front there. The memorial chapel that bears his name stands at Kirkjubaejarklaustur, on the ground the sermon is said to have saved.
The Haze Over Europe
The sulphur cloud spread fast across the continent. Contemporary records track it reaching Bergen, then Prague by 17 June 1783, Berlin by 18 June, Paris by 20 June and Britain by 23 June. People described a dry, acrid fog that dimmed the sun to a blood-red disc and made breathing hard.
That summer was unusually hot and still, which trapped the haze at ground level. Studies of parish burial records estimate that the polluted air caused around 23,000 excess deaths in Britain alone during the summer of 1783. Benjamin Franklin, then in Paris as the American envoy, later wrote in an essay of 1784 about a “constant fog over all Europe, and a great part of North America,” and wondered whether it had cooled the following winter, which proved among the harshest on record on both sides of the Atlantic.
In England people called it the sand summer for the gritty, sulphurous air. The naturalist Gilbert White, writing at Selborne, recorded a “peculiar haze, or smokey fog, that prevailed for many weeks” and a sun so dimmed it could be watched with a bare eye. The cold that followed reached North America as well, where the winter of 1784 was severe enough that ice was reported on the Mississippi as far south as New Orleans.
Did Laki Help Cause the French Revolution?
A popular claim links Laki to the French Revolution of 1789, and it deserves a careful answer rather than a flat yes. The chain of reasoning runs like this: the haze and the cold disrupted harvests, grain prices climbed through the 1780s, and hunger sharpened the anger that broke out in 1789.
Historians treat this as one contributing strand, not the cause. France’s crisis had deep political and financial roots, and the worst harvest failure came in 1788, five years after the eruption. Laki belongs in the background of bad weather and bad harvests across the decade, a real factor whose exact weight no one can measure.
Laki Today
The craters now sit quiet and green, their rough lava softened under a thick coat of grey-green moss, inside Vatnajokull National Park. The park became a UNESCO World Heritage Site in 2019, partly for this kind of active volcanic landscape. Reaching Lakagigar means a summer-only drive on the rough mountain road F206, which needs a high-clearance four-wheel drive and fords across glacial rivers.
The eruption even redrew the map. South of the new lava, wind-blown sand built up a fresh plain called Brunasandur, and the first farm on it, Orrustustadir, was not settled until 1822, almost forty years after the fires went out.
For modern Iceland, Laki is more than history. It is the worst-case scenario the Icelandic Meteorological Office models when it plans for a long fissure eruption: not an airport-closing ash cloud like Eyjafjallajokull, but a slow flood of lava and poison gas that could foul air and water for months. That is why the monitoring network watches the Grimsvotn system so closely.
Frequently Asked Questions
How many people did the Laki eruption kill?
In Iceland, about 9,000 people died, roughly a fifth of the population, almost all in the famine of 1784 rather than from the lava. Across Europe, the sulphur haze is linked to tens of thousands more deaths, including an estimated 23,000 in Britain in the summer of 1783.
How long did the Laki eruption last?
About eight months. The fissure opened on 8 June 1783 and activity continued until February 1784, with the heaviest lava and gas output in the first weeks.
Where is Laki in Iceland?
In the southern highlands, about 40 kilometres inland from Kirkjubaejarklaustur, inside Vatnajokull National Park. The crater row is reached by the F206 mountain track in summer with a four-wheel-drive vehicle.
Is Laki still active?
The Laki fissure itself has not erupted again since 1784, but it is part of the active Grimsvotn system, which still erupts regularly from under the Vatnajokull ice cap. A repeat fissure eruption somewhere in the system remains possible.
What is the Moduhardindin?
It is the Icelandic name for the famine that followed Laki, translating roughly as the Mist Hardships. It refers to the years of livestock death and starvation caused by the eruption’s fluorine and sulphur, not to the lava.
Sources and Further Reading
- Icelandic Meteorological Office – monitoring of the Grimsvotn system that feeds the Laki fissure
- Catalogue of Icelandic Volcanoes – technical profile of the Grimsvotn and Laki volcanic system
- Vatnajokull National Park – access and conservation detail for the Lakagigar crater row
- Smithsonian Global Volcanism Program – eruption record of Grimsvotn and the 1783 Laki event
- NHESS, Copernicus – 2024 study reassessing what people actually died of after Laki
- Reverend Jon Steingrimsson memorial chapel – the site of the Fire Mass at Kirkjubaejarklaustur
- Eldsveitir.is (Icelandic) – local heritage record of the fire districts, the farms lost and the lava’s path
- Visindavefur, University of Iceland (Icelandic) – scholarly account of the social and demographic effects of the Skaftareldar
