On the evening of 5 April 1815, on the island of Sumbawa in what was then the British-occupied Dutch East Indies, a mountain that everyone assumed was extinct began to erupt. It made a noise the British Lieutenant-Governor on Java, sitting in his residence 1,250 kilometers away in Batavia, mistook for cannon fire. He sent dispatch boats to investigate which naval engagement had broken out off the coast.
The mountain was Tambora. It would continue erupting for ten days, with the climactic explosion coming on the evening of 10 April. The energy released would be approximately four times that of Krakatoa sixty-eight years later — itself the loudest sound in recorded history. Tambora would remove 1,500 meters of its own summit, eject 41 cubic kilometers of rock and ash into the upper atmosphere, kill roughly 10,000 people in the immediate vicinity from pyroclastic flows, kill perhaps another 60,000 from starvation and disease over the following year as ash blanketed crops across the Indonesian archipelago, and inject enough sulfur into the stratosphere to cool the entire planet by half a degree Celsius for two full years.
It was the largest volcanic eruption in 1,300 years. It is still, more than two centuries later, the largest eruption observed during the modern era. And almost nobody in Europe or North America had any idea it had happened.
What Raffles saw
The Lieutenant-Governor was Thomas Stamford Raffles, then thirty-three years old, an East India Company administrator in temporary charge of Java during the British occupation that had begun in 1811. After the dispatch boats came back and reported no naval engagement, Raffles wrote to his local British residents on Sumbawa, Lombok, and the nearby islands asking them to send detailed reports of whatever it was that had happened.
The reports came in over the next eight months. Raffles, who had a methodical mind, edited them into a long appendix that he published two years later in his book The History of Java. It is the most detailed contemporary account of the eruption that exists in English. The residents he had quoted — Owen Phillips on Sumbawa, the British resident on Lombok, others — were systematic. They counted dead in named villages. They described the ash falling in measured inches. They described the darkness.
Phillips’s account of the climactic evening of 10 April, observed from a ship at sea about thirty kilometers off the Sumbawa coast, reads:
“Three distinct columns of flame burst forth, near the top of the Tomboro mountain (all of them apparently within the verge of the crater), and, after ascending separately to a very great height, their tops united in the air in a troubled and confused manner. In a short time the whole mountain next Sang’ir appeared like a body of liquid fire, extending itself in every direction.”
The pyroclastic flows reached the sea. They killed every living thing on the slopes of the volcano and most of the population of the Sumbawan kingdom of Tambora, which had occupied the mountain’s western flank. The kingdom and its language — Tamboran, an Austronesian language unrelated to any other in the region — ceased to exist entirely. The dead included the kingdom’s rajah. The survivors, perhaps a few hundred out of an estimated twelve thousand, were absorbed into neighboring populations.
A pumice raft drifted west across the Indian Ocean for three years. Ships reported it as far as the Cape of Good Hope in 1818.
What the cooling did
Tambora put roughly sixty million tons of sulfur dioxide into the stratosphere. This combined with water vapor to form a fine sulfuric acid aerosol — the same mechanism Krakatoa would use sixty-eight years later, but on a larger scale. The aerosol veil spread north and south from the equator over the following six to ten months, reaching full hemispheric coverage by the spring of 1816.
It cooled the planet by about half a degree Celsius, on average, across 1816 and into 1817. In specific regions the cooling was much more dramatic — central Europe and New England saw average summer temperatures drop by 1 to 2 degrees. Frosts killed corn in Vermont in July 1816. Snow fell in Quebec in June. The wheat harvest across most of Europe failed for the second year in a row (the 1815 harvest had also been poor, for unrelated reasons — Napoleonic-war disruptions). Bread prices in 1816 reached the highest levels of the entire nineteenth century.
This was the Year Without a Summer. Famine swept through Switzerland, Ireland, Germany, and the New England states. Estimates of European deaths from the 1816 famine and the resulting typhus and dysentery epidemics run between 100,000 and 200,000. The 1817 cholera pandemic — the first global cholera epidemic in modern history — originated in Bengal in conditions of climate stress that were almost certainly Tambora-related, and went on to kill hundreds of thousands more across Asia, the Middle East, and Russia.
The trapped English Romantics at the Villa Diodati wrote Frankenstein and The Vampyre during the same wet summer. They had no idea why the weather was so strange.
Why nobody knew
The 1815 eruption was witnessed by a few thousand Europeans on Java and a million Indonesians on the surrounding islands. It was recorded in detail by Raffles. His History of Java was published in London in 1817 and the appendix on Tambora was read by exactly the people you would expect — a few East India Company officials, a few geologists, a few interested gentleman-scientists. It was not in the newspapers.
The British and European press of 1815 was focused on something else. The week of Tambora’s climactic eruption was the same week that Napoleon Bonaparte, having escaped from Elba, was marching on Paris during the Hundred Days. By the time Raffles’s reports could plausibly have reached Europe, the news was Waterloo and the second Bourbon restoration. By the time The History of Java was published, the Year Without a Summer was already over, and nobody connected the famines of 1816 to a volcano nobody had heard of in a colony nobody could find on a map.
The link between Tambora and the 1816 climate was not made in print, in any language, until the American climatologist William Humphreys proposed it in 1913. By then the famine was a footnote and the Indonesian eruption had been entirely forgotten outside specialist geology. Humphreys’s argument was essentially statistical and was widely rejected by his peers as speculative. It was confirmed only in the 1980s, when ice cores from Greenland and Antarctica showed a clear sulfate spike dated to 1815 — atmospheric evidence of a massive equatorial eruption — and the Stothers paper in Science in 1984 pulled together the contemporary accounts, the ice-core data, and the temperature reconstructions into a single argument.
The reconstruction is now uncontested. Tambora is in every textbook of historical climatology. It is the prototype example of how a single geological event can affect global agriculture, politics, and literature.
The mountain today
Tambora is still there, reduced from roughly 4,300 meters to about 2,850 meters by the 1815 eruption, with a caldera six kilometers across at the top. It has erupted in a small way three times since — 1819, 1880, and 1967 — without significant casualties. A team of Indonesian and American archaeologists excavated a buried village in the early 2000s, on the volcano’s western flank, beneath three meters of pyroclastic debris. They found a carbonized house, kitchen utensils, the bones of two people who had been sitting at a table, and a bronze bowl containing rice that had been turned to charcoal in the moment the flow reached them.
The bowl is in the National Museum of Indonesia in Jakarta. It is the only known artifact from the lost kingdom of Tambora.