Scientists Find the Mysterious Source of the Massive 1831 Volcanic Eruption That Cooled Earth and Made the Sun Appear Blue

In the summer of 1831, an enormous volcanic eruption spewed sulfur gas into Earth’s atmosphere. The particles scattered sunlight, making our star appear green, purple and blue. Its rays struggled to reach the planet’s surface, leading crops to fail and famines to spread. In the Northern Hemisphere, temperatures dropped by 1 degree Celsius.

That year, German composer Felix Mendelssohn traveled through the Alps on the way home from a sojourn in Italy. Though it was summer, he wrote that “it is as cold as in winter, there is already deep snow on the nearest hills.”

The blast that caused this darkness and cold was one of the largest volcanic eruptions of the 19th century, a brutal event toward the end of the Little Ice Age. But for nearly 200 years, scientists haven’t been sure exactly which volcano was responsible for the major climatic disruption.

Now, a study published last week in Proceedings of the National Academy of Sciences pins the blame on Zavaritskii caldera, “an extremely remote volcano” on Simushir Island in the Kuril archipelago, a disputed territory between Russia and Japan.

“For many of Earth’s volcanoes, particularly those in remote areas, we have a very poor understanding of their eruptive history,” study lead author Will Hutchison, a volcanologist at the University of St Andrews in Scotland, tells Mindy Weisberger of CNN. No one lives on Simushir Island, once home to a Soviet submarine base, Hutchison explains, and written sources of the island’s history, which usually offer a helpful guide for tracking past volcanic activity, are “limited to a handful of diaries from ships that passed these islands every few years.”

As a result, Zavaritskii was a thoroughly unknown candidate for the so-called “mystery volcano.”

Previous theories about the eruption indicated its source was much closer to the equator, and the Babuyan Claro volcano in the Philippines had been considered a leading candidate. “This eruption had global climatic impacts but was wrongly attributed to a tropical volcano for a long time period,” Stefan Brönnimann, a climatologist at the University of Bern in Switzerland who was unaffiliated with the study, tells CNN.

Hutchison and his team homed in on Zavaritskii after determining that ice cores from Greenland contained 6.5 times more sulfur fallout around 1831 than comparable samples from Antarctica. That meant the eruption likely took place in the Northern Hemisphere.

The Greenland ice cores included ash layers and microscopic volcanic glass—shards “roughly one-tenth the diameter of a human hair,” Hutchison says in a statement. Chemical analyses of these tiny remains matched best with existing data from Japan and the Kuril Islands. But an explosion of this magnitude—releasing around 13 million metric tons of sulfur into the atmosphere, per the study—could not have gone unnoticed in densely populated Japan.

That left the Kuril Islands as the most likely culprit—just near enough to obliterate Japanese crops and just far enough to remain unobserved. From there, they needed to find ash and glass from a local volcano with a chemical signature that matched the one seen in Greenland.

“Finding the match took a long time and required extensive collaboration with colleagues from Japan and Russia, who sent us samples collected from these remote volcanoes decades ago,” Hutchison adds in the statement.

He likens the work to crime scene forensics, calling the breakthrough when his team found a “perfect fingerprint match” between the Zavaritskii and Greenland ash samples “a genuine eureka moment.”

“It was really a terrific day,” Hutchison tells Live Science’s Patrick Pester. “One of the best days I’ve ever had in the lab.”

The team used radiocarbon dating to pinpoint the timeline of the volcanic ash on Simushir Island, and they took sulfur isotope readings and physical measurements of the volcano’s caldera. These data confirmed the match, leaving Zavaritskii “the prime candidate” for the seminal 1831 eruption, according to the study.

Brönnimann concurs with the research group’s findings, telling CNN that “the research now shows that the eruption took place on the Kurils, not in the tropics.”

Hutchison, for his part, remains amazed that such a massive, significant eruption could go unrecorded.

“Perhaps there are reports of ash fall or atmospheric phenomena occurring in 1831 that reside in a dusty corner of a library in Russia or Japan,” he tells CNN. “The follow-up work to delve into these records really excites me.”

Today, with our satellites and sensitive seismic monitors, a similar eruption would likely not be a mystery for long. But many remote volcanoes do not have instruments monitoring their activity. “This work shows how difficult it will be to predict when and where the next large magnitude eruption might come,” Hutchison tells Aristos Georgiou of Newsweek.

And the impacts of such a large eruption might be just as dire, if 1831 is any guide. It might lead to sparse sunlight, altered rainfall and dropping global temperatures, which would put stress on the food supply.

“There are so many volcanoes like this,” Hutchison adds in the statement. “As scientists and as a society, we need to consider how to coordinate an international response when the next large eruption, like the one in 1831, happens.”

Eli Wizevich | | READ MORE

Eli Wizevich is a history correspondent for Smithsonian. He studied history at the University of Chicago and previously wrote for the El Paso Times.