An unknown volcano erupted so explosively in 1831 that it cooled Earth’s climate. Now, almost 200 years later, scientists have identified the “mysterious 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 occurred during the last gasps of the Little Ice Age, one of the coldest periods on Earth in the last 10,000 years.
Although the year of this historic eruption was known, the location of the volcano was not. Researchers recently solved this puzzle by analyzing ice cores in Greenland, looking through the cores’ layers to examine sulfur isotopes, grains of ash and tiny fragments of volcanic glass deposited between 1831 and 1834.
Using geochemistry, radioactive dating and computer modeling to map the particles’ trajectories, scientists linked the 1831 eruption to an island volcano in the northwest Pacific Ocean, according to .
According to the analysis, the mysterious volcano was Zavaritskii (also spelled Zavaritsky) on Simushir Island, part of the Kuril Islands archipelago, an area disputed by Russia and Japan. Before scientists’ discoveries, the last known eruption of Zavaritskii 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 study lead author Dr. William Hutchison, principal investigator in the School of Earth and Environmental Sciences at the University of St. Andrews, in the United Kingdom.
“Zavaritskii is located on an extremely remote island between Japan and Russia. No one lives there and historical records are limited to a few diaries from ships that passed by these islands every few years,” Hutchison told CNN in an email.
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 considered volcanoes closer to the equator, such as the Babuyan Claro volcano in the Philippines, according to the study.
“This eruption had global climate impacts, but was wrongly attributed to a long-term tropical volcano,” said Dr. Stefan Brönnimann, leader of the climatology unit at the University of Bern in Switzerland. “Research now shows that the eruption occurred in the Kurils, not in the tropics,” said Brönnimann, who was not involved in the study.
“A genuine eureka moment”
Examination of ice cores from Greenland revealed that in 1831, sulfur precipitation – a sign of volcanic activity – was about 6.5 times greater in Greenland than in Antarctica. That discovery suggested the source was a large eruption from a mid-latitude volcano in the Northern Hemisphere, the researchers reported.
The study team also chemically analyzed ash and fragments of volcanic glass measuring no more than 0.0008 inch (0.02 millimeter) in length. When the scientists compared their results with geochemical datasets from volcanic regions, the closest matches 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 on the Kuril Islands provided samples that led researchers to a geochemical match with the Zavaritskii caldera.
“The moment in the lab analyzing the two ash together – one from the volcano and one from the ice core – was a genuine eureka moment,” Hutchison said in his email. Radiocarbon dating of tephra, or volcanic ash deposits, on Simushir Island has placed them within the last 300 years. Additionally, analysis of the caldera’s volume and sulfur isotopes suggests the crater formed after a massive eruption between 1700 and 1900. , making Zavaritskii “the leading candidate” for the mysterious eruption in 1831, the authors wrote.
“It still surprises me that an eruption of this size has not been reported,” Hutchison added. “Perhaps there are reports of ashfall or atmospheric phenomena that occurred in 1831 that reside in a dusty corner of a library in Russia or Japan. The follow-up work to delve into these records really excites me.”
The end of the Little Ice Age
Along with Zavaritskii, three other volcanoes erupted between 1808 and 1835. They marked the decline of the Little Ice Age, a climate anomaly that lasted from the early 1400s until about 1850. During this period, annual temperatures in the Northern Hemisphere fell an average of 1.1 degrees Fahrenheit (0.6 degrees Celsius). In some places, temperatures were 3.6 degrees Fahrenheit (2 degrees Celsius) colder than normal, and the cooling persisted for decades.
Two of the four eruptions have been previously identified: Mount Tambora in Indonesia exploded in 1815, and Cosegüina erupted in Nicaragua in 1835. The volcano that produced the 1808/1809 eruption remains unknown. The addition of Zavaritskii highlights the potential for volcanoes in the Kuril Islands to disrupt Earth’s climate, the study authors reported.
After the 1831 eruption, cooler and drier conditions emerged in the Northern Hemisphere. Reports of famine and widespread hardship soon followed, with famines ravaging India, Japan and Europe, affecting millions of people. “It seems plausible that volcanic climate cooling led to crop failure and famine,” Hutchison said. “A focus of ongoing research is to understand the extent to which these famines were caused by volcanic climate cooling or other sociopolitical factors.”
By providing a long-lost piece of information about the 19th-century volcanoes that cooled Earth’s climate, “the study perhaps strengthens our confidence in the role of volcanic eruptions for the last phase of the Little Ice Age,” Brönnimann said.
Like Zavaritskii, many volcanoes around the world are in isolated places and are poorly monitored, making it challenging to predict when and where the next large-magnitude eruption might occur, Hutchison added. If there is one lesson to be learned from the 1831 eruption, it is that volcanic activity in remote locations can have devastating global consequences—ones that people may not be prepared to face.
“We don’t really have a coordinated international community to spring into action when the next big eruption happens,” Hutchison said. “This is something we need to think about both as scientists and as a society.”
