It was known as the “year without a summer.” In the medieval chronicles of Europe, the summer of 1258 was described as unseasonably cold, resulting in poor harvests that were devastated by heavy floods. That summer thousands of people were buried in mass graves in London, possibly a result of the bad weather and the lack of food. Think Game of Thrones, with its winters that last for years.
The reason behind the cold summer was the massive explosion of a volcano that would have thrown up as much as 10 cubic miles of rock and dust, creating a plume that would have reached as high as 25 miles above the ground. A dust plume that large would have had global effects, blocking out sunlight and exerting a dramatic cooling effect on the planet, leading to the year without summer. A similar effect was seen after the 1991 eruption of Mt. Pinatubo in the Philippines, which reduced the amount of sunlight reaching the Earth by 10% and a temporary drop of 0.7 F in global average temperatures. But Pinatubo threw up perhaps 2.4 cubic miles of rock—the medieval volcanic eruption was much, much greater.
Despite the size of the eruption, scientists didn’t know where the volcano actually was. (Medieval chroniclers didn’t exactly have access to satellite data in 1258.) But in a new study published in the Proceedings of the National Academy of the Sciences, researchers have identified the location: the Samalas volcano, in the Mount Rinjani Volcanic Complex on Indonesia’s Lombok Island.
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It makes sense that the mystery volcano would be found in Indonesia—the Southeast Asian country sits on the Ring of Fire, an arc that stretches along the Pacific from New Zealand to the eastern edge of Asia, and the Aleutian Islands in Alaska down the western coast of North and South America. The ring contains 75% of the world’s active and dormant volcanoes, and Indonesia is particularly active—the two biggest volcanic eruptions in the recent past, Kraktatau in 1883 and Tambora in 1815, both occurred in Indonesia.
Tambora in particular was a mega-eruption, and the resulting ash cloud created another year without summer for much of the world. But the medieval volcano was at least twice as strong, according to PNAS study, which matched sulfur and dust traces locked in polar ice to similar samples found near Samalas. (Ecuador’s Quilotoa volcano had long been considered a possible suspect, but the geochemical fingerprint didn’t match.) The researchers also made use of carbonized tree trunks and branches near the Samalas volcano, which allowed them to narrow down the likely time frame of the eruption to 1257.
There’s still more to be discovered. Old Indonesian records tell of a volcanic blast on Lombok that destroyed the city of Pamatan, capital of an ancient kingdom. It’s possible that city still exists, buried beneath the volcanic debris, waiting to be rediscovered like the Roman city of Pompeii. That would be an archeological achievement just as impressive as the geographic research that identified the volcano that caused the medieval year without summer.