An unknown volcano erupted to such an extent in 1831 that it cooled the Earth’s climate. Now, almost 200 years later, scientists have spotted the “mystery volcano”.

The eruption was one of the most powerful of the 19th century, spewing so much sulfur dioxide into the stratosphere that average annual temperatures in the Northern Hemisphere dropped by about 1 degree Celsius (1.8 degrees Fahrenheit). The event took place at the “exhalation” of the Little Ice Age, one of the coldest periods on Earth in the last 10,000 years.

While the year of this historic eruption was known, the location of the volcano was not. Researchers recently solved this puzzle by taking ice samples from Greenland, peering back in time through core layers to examine sulfur isotopes, ash grains and tiny volcanic glass fragments deposited between 1831 and 1834.

Using geochemistry, radioactive dating and computer modeling to map particle trajectories, scientists linked the 1831 eruption to a volcanic island in the northwest Pacific Ocean, they reported Monday in the journal Proceedings of the National Academy of Sciences.

According to the analysis, the mystery volcano was Zavaritskii (also spelled Zavaritsky) on Simushir Island, part of the Kuril Islands archipelago, an area disputed by Russia and Japan. Before the scientists’ findings, the last known Zavaritskii eruption was in 800 BC.

“For many of Earth’s volcanoes, particularly those in remote areas, we have a very poor understanding of their eruptive history“said lead study author Dr. William Hutchison, a principal investigator in the School of Earth and Environmental Sciences at the University of St. Andrews in the UK.

“Zavaritskii is located on an extremely remote island between Japan and Russia. No one lives there and historical records are limited to a handful of logbooks from ships that passed these islands every few yearsHutchison told CNN.

With little information available about Zavaritskii’s activity during the 19th century, no one previously suspected that it could be a candidate for the 1831 eruption. Instead, researchers looked at volcanoes closer to equator, such as the Babuyan Claro volcano in the Philippines, according to the study.

“This eruption had global climate effects, but was mistaken for a tropical volcano for a long time“said Dr. Stefan Brönnimann, head of the climatology unit at the University of Bern in Switzerland. “The research now shows that the eruption took place in the Kuriles, not in tropical islands,” said Brönnimann, who was not involved in the study.

Kuriles Islands

“Eureka!”

Examination of Greenland ice cores revealed that in 1831, sulfur fallout—a sign of volcanic activity—was about 6½ times greater in Greenland than in Antarctica. This finding suggests that the source was a large eruption from a mid-latitude volcano in the northern hemisphere, the researchers said.

The study team also chemically analyzed the ash and fragments of volcanic glass no larger than 0.0008 inches (0.02 millimeters) in length. When the scientists compared their results with geochemical datasets from volcanic regions, the closest results were in Japan and the Kuril Islands. Volcanic eruptions in 19th-century Japan were well documented, and there were no records of a major eruption in 1831. But colleagues who had previously visited volcanoes in the Kuril Islands provided samples that led researchers to a geochemical match to the Zavaritskii caldera.

“The moment in the lab analyzing the two ashes together – one from the volcano and one from the ice core – was a genuine eureka!Hutchison said. Radiocarbon dating of the ash, or volcanic ash, deposits on Simushir Island placed them within the last 300 years. Additionally, analysis of the caldera volume and sulfur isotopes suggested the crater formed after a massive eruption between 1700 and 1900, making the Zavaritskii caldera “the leading candidate” for the mysterious 1831 eruption, the authors wrote.

“I’m still surprised that an explosion of this magnitude went unreportedHutchison added. “Perhaps there are reports of ash fall or atmospheric phenomena that occurred in 1831 that are in a dusty corner of a library in Russia or Japan. Continuing to work on digging into these records really excites me».