On June 8, 1783, the earth split open along a 27-kilometer fissure in southern Iceland. Over the next eight months, the Laki volcanic system would pour out 14 cubic kilometers of basalt lava and release an estimated 120 million tons of sulfur dioxide into the atmosphere. The eruption itself killed no one directly. What came next killed tens of thousands across two continents and may have helped bring down one of Europe's oldest monarchies.
The toxic haze that drifted across the North Atlantic that summer became known as the "Laki haze" or, in France, the "brouillard sec"—the dry fog. It smelled of sulfur, corroded metal, wilted crops, and carried within it one of the most consequential natural disasters in modern European history. Yet today, outside Iceland, almost no one remembers it happened.
Eight Months of Fire and Poison
The eruption began without warning. Reverend Jón Steingrímsson, a Lutheran pastor in the village of Klaustur, watched the first fissures tear open the landscape and spent months documenting what he called "the Fires." His parish lay directly in the path of the lava flows, and his congregation prepared for the end.
"The flood of fire flowed with the speed of a great river swollen with meltwater on a spring day. In the middle and along the sides of the rivers of fire great cliffs and slabs of rock were swept along, tumbling about like large whales swimming."
Steingrímsson's account remains one of the most vivid primary sources for volcanic destruction ever written. On July 20, 1783, as lava advanced toward his church during Sunday services, he delivered what became known as the "Fire Mass," refusing to abandon his congregation. The lava stopped just short of the building—a fact locals attributed to divine intervention, though modern vulcanologists note the flow had simply exhausted itself.
The lava was devastating, but the gases proved far deadlier. The eruption released approximately 8 million tons of hydrogen fluoride, which settled on Iceland's grass and contaminated the island's water supply. Livestock died within days of eating the poisoned vegetation, their bones softening from fluorine toxicity. Within two years, over half of Iceland's cattle and nearly 80 percent of its sheep were dead. The resulting famine, known as the "Mist Hardships" (Móðuharðindin), killed approximately 10,000 Icelanders—roughly one-quarter of the population.
The Summer Europe Choked
By late June 1783, the volcanic haze had crossed the Atlantic. Benjamin Franklin, serving as American ambassador in Paris, was among the first to connect the strange atmospheric conditions to Iceland's volcanic activity. He observed that the summer sun appeared "pale" and gave "little heat," producing what he called a "constant fog." His paper on the subject, presented to the Manchester Literary and Philosophical Society in 1784, represents one of the earliest attempts to link volcanic eruptions to climate effects.
Across Europe, the summer of 1783 was marked by oppressive heat, dry fog, and a sun so dim that observers could stare directly at it. In England, naturalist Gilbert White described the haze as unlike anything he had witnessed in fifty years of weather observation. Workers in the fields collapsed from respiratory distress. The death rate in England during August and September 1783 was 30 percent higher than the average of the previous decade—an estimated 23,000 excess deaths that historians have attributed to the toxic aerosols.
The ecological effects rippled outward. Crops withered under the weakened sunlight. Grain harvests across Europe were poor in 1783 and disastrous in 1784 and 1785. The winter of 1783-1784 was among the coldest in recorded European history, with temperatures in parts of France dropping below minus 20 degrees Celsius. Rivers froze solid. When the thaw came, catastrophic flooding destroyed whatever crops had survived the cold.
Bread, Taxes, and the Road to Revolution
France in the 1780s was already a society under strain. The crown was effectively bankrupt from financing the American Revolution. The tax system was Byzantine, regressive, and deeply resented. The nobility and clergy enjoyed exemptions that placed the burden squarely on peasants and the emerging middle class. Into this volatile mix, Laki introduced hunger.
The connection between the eruption and the French Revolution remains debated among historians. What is documented is the sequence of crises that followed. Poor harvests in 1784 and 1785 drove bread prices upward. By 1788, another harvest failure—caused by drought followed by a devastating hailstorm—pushed prices to their highest levels in decades. By the spring of 1789, a Parisian worker might spend 88 percent of his wages on bread alone.
Historians like John D. Post and Emmanuel Le Roy Ladurie have traced direct connections between the climatic disruptions following Laki and the agricultural failures that preceded the Revolution. The volcanic winter contributed to a cascade of poor harvests that weakened the French economy, emptied the treasury of tax revenue, and brought desperate hunger to the peasantry. When Louis XVI convened the Estates-General in May 1789—the first meeting since 1614—he did so because the state was out of money and out of options.
The crowds that stormed the Bastille two months later were hungry. The women who marched on Versailles in October 1789, dragging the royal family back to Paris, chanted for bread. This does not mean Laki "caused" the French Revolution—the intellectual currents of the Enlightenment, the fiscal mismanagement of the crown, and the structural inequalities of the ancien régime would have produced crisis eventually. But the timing, the specific sequence of events that brought revolution in 1789 rather than 1799 or 1809, may owe something to a volcanic fissure erupting in a remote corner of Iceland six years earlier.
The Eruption History Forgot
The Laki eruption was, by several measures, the deadliest volcanic event in European history. It killed more Icelanders proportionally than any natural disaster in any European country in modern times. Its atmospheric effects contributed to excess mortality across England, France, and possibly as far as Egypt and Japan. Its climatic disruptions may have influenced events that reshaped the political order of the Western world.
Yet it remains largely unknown outside academic circles. The eruption had no Pompeii, no preserved bodies frozen in ash, no single dramatic moment of destruction. It was slow, diffuse, and continental in scale—exactly the kind of disaster that defies easy narrative. The suffering it caused was measured in failed harvests, in bread prices, in demographic statistics, not in dramatic eyewitness accounts of cities buried in fire.
This is perhaps the most unsettling lesson of Laki. We tend to remember disasters that arrive suddenly and visibly—earthquakes, tsunamis, the dramatic explosion of Vesuvius. We are less equipped to recognize catastrophes that unfold slowly, that work through chains of causation, that kill through hunger and political instability rather than direct violence. The haze that drifted over Europe in 1783 was visible to everyone. Almost no one understood what they were seeing.
The Laki fissures are quiet now, grassed over and visited mainly by tourists hiking Iceland's volcanic landscapes. But the system remains active. Another eruption on Laki's scale is not a question of if but when. When it happens, it will not care whether we remember the last time.