Laki Eruption (1783): Iceland's Fissure That Poisoned Europe

The Laki eruption was a huge fissure eruption in southern Iceland that lasted from 8 June 1783 to 7 February 1784. It released vast amounts of lava and poisonous gas, causing a famine that killed about a fifth of Iceland’s people. Its sulphurous haze drifted across Europe, bringing illness, crop damage and unusual weather, and it is one of the deadliest volcanic events in recorded history.

Background

Iceland sits on the Mid-Atlantic Ridge, where the North American and Eurasian plates pull apart, and above a hotspot. Many of its eruptions come from long fissures rather than single mountains. The Laki fissure belongs to the Grímsvötn volcanic system beneath and near the Vatnajökull ice cap.

In the 1780s Iceland was a poor, thinly settled dependency of the Danish crown with a population of around 50,000. Most people were farmers who depended on sheep, cattle and horses, and on the hay needed to feed them through the long winter. This made the island extremely vulnerable to anything that poisoned its grass.

The eruption

Earthquakes shook the Síða district in late May 1783. On 8 June, Whit Sunday, a fissure opened on the south-west side of the mountain called Laki. Over the following months the crack extended to about 27 kilometres and more than 130 craters formed along it, in ten main eruptive episodes.

Lava fountains rose hundreds of metres high. The lava flowed down the valleys of the Skaftá and Hverfisfljót rivers, burying farms and churches. In total the eruption produced roughly 14 to 15 cubic kilometres of lava, covering about 600 square kilometres, one of the largest lava outpourings in historical times. Icelanders call the event Skaftáreldar, the Skaftá Fires.

The greater danger was invisible. The eruption released an estimated 120 million tonnes of sulphur dioxide, as well as large amounts of fluorine and other gases. Much of this rose high into the atmosphere, where it formed a haze of sulphuric acid droplets.

The fire sermon

The best eyewitness account comes from Jón Steingrímsson, the Lutheran pastor of Kirkjubæjarklaustur. He recorded the eruption in detail and later wrote a fuller account of it.

On 20 July 1783, as lava advanced towards his church, he held a service there that became known as the Eldmessa, or fire sermon. The lava stopped short of the church, an event many local people regarded as an answer to prayer. Geologists explain that the flow had reached a natural barrier, but the story remains central to the memory of the eruption in Iceland.

The Haze Famine in Iceland

Fluorine from the gas settled on grass and contaminated water. Animals that grazed on it developed fluorosis, with bone deformities and damaged teeth, and many starved or were poisoned. Acid rain and the haze also damaged crops and stunted the hay harvest.

Estimates suggest that about half of Iceland’s cattle and horses and around four-fifths of its sheep died. The famine that followed, known in Icelandic as Móðuharðindin, the Haze Famine or Mist Hardships, lasted until about 1785. Roughly 9,000 people died, about 20 to 25 per cent of the population, from starvation and disease.

The Danish government organised some relief, and officials in Copenhagen discussed the possibility of moving Icelanders to Denmark, but the idea was not carried out. Strong earthquakes in southern Iceland in August 1784 added to the suffering by destroying many farmhouses at the height of the famine.

Relief was slow and inadequate. Ships from Denmark could reach Iceland only in the sailing season, and the sums raised were small compared with the scale of the losses. In the worst-hit districts, such as Síða and the area around the Skaftá, whole farms were abandoned, and many survivors became beggars who wandered in search of food. Iceland’s population did not recover to its pre-eruption level for several decades.

The haze over Europe

By mid-June 1783 a strange dry fog had spread across much of Europe. Observers from Scandinavia to Italy reported a bluish haze that dimmed the sun, turned it blood-red at sunrise and sunset, and smelled of sulphur. Leaves withered and crops were damaged in places.

In England the naturalist Gilbert White described the summer as an “amazing and portentous one” in The Natural History of Selborne, recording the sun’s strange appearance. Benjamin Franklin, then in France, wrote a paper suggesting that the fog might come from a volcano in Iceland and might have caused the unusually cold winter that followed. His idea of a link between volcanoes and climate was ahead of its time.

The summer of 1783 was very hot in parts of western Europe and was followed by a severe winter in 1783–1784. Studies of English parish registers, including one by Alexandra Witham and Clive Oppenheimer, found a sharp rise in deaths in the summer and autumn of 1783 and again in the following winter; estimates of excess deaths in England range from about 10,000 to more than 20,000, many probably linked to the gas or the extreme weather. Similar increases in mortality have been found in France and elsewhere.

Wider effects

Climate scientists have linked the Laki aerosols to disruption of weather well beyond Europe. Research has suggested that the eruption weakened the African and Indian monsoons in 1783, and some studies connect it to low Nile floods and famine in Egypt in 1783–1784. North America also experienced an exceptionally cold winter. These links are supported by modelling but their precise scale is still debated.

Laki is now a standard case study for volcanologists. A similar fissure eruption in Iceland today could disrupt air travel and affect air quality across Europe, which is why the 1783 event features in national risk assessments, including in the United Kingdom.

Myths and facts

• Myth: Laki was a single huge volcano that exploded. Fact: It was a fissure eruption, in which lava welled out along a long crack. It was not especially explosive, and its deadliness came mainly from gas released over many months.
• Myth: The haze was caused only by smoke from forest fires or by the hot summer. Fact: Some contemporaries offered such explanations, but ice cores from Greenland contain a clear sulphate layer from Laki, confirming the volcanic origin of the aerosol.
• Myth: The eruption directly caused the French Revolution. Fact: Poor weather in the 1780s contributed to hardship, but the revolution had political and financial causes, and the bad harvest of 1788 is not attributed to Laki.

By the numbers

Timeline

• 1783, late May: Earthquakes are felt in southern Iceland.
• 1783, 8 June: The Laki fissure opens and the eruption begins.
• 1783, mid-June: Dry fog appears over much of Europe.
• 1783, 20 July: Jón Steingrímsson preaches the fire sermon at Kirkjubæjarklaustur.
• 1783, autumn: Livestock deaths spread across Iceland as famine sets in.
• 1783–1784, winter: A severe winter strikes Europe and North America.
• 1784, 7 February: The eruption ends.
• 1785: The Haze Famine eases after claiming about a fifth of Iceland’s people.

Why it matters

The Laki eruption showed that a volcano’s gas, not just its lava or ash, can kill on a continental scale. It devastated Iceland and contributed to a wave of deaths and poor weather across Europe, and it remains a key reference for understanding how eruptions affect climate and public health. It can be compared with the later Mount Tambora eruption, and in the same year southern Italy suffered the Calabrian earthquakes.