Mystery volcano' that erupted and cooled Earth in 1831 has finally been identified

In 1831, an unknown volcano erupted violently, its impact so significant that it even cooled the Earth's climate. Nearly 200 years later, scientists have finally identified this "mystery volcano." This eruption was one of the most powerful volcanic events of the 19th century, injecting large amounts of sulfur dioxide into the stratosphere, causing the average annual temperature in the Northern Hemisphere to drop by approximately 1 degree Celsius (1.8 degrees Fahrenheit).

This event occurred towards the end of the Little Ice Age, one of the coldest periods on Earth in the past ten thousand years. Although the year of this historic eruption was known, the specific location of the volcano had remained a mystery. Recently, researchers solved this puzzle by analyzing ice cores from Greenland. Through the layered structure of the ice cores, they examined sulfur isotopes, volcanic ash particles, and tiny fragments of volcanic glass deposited between 1831 and 1834.

Using geochemistry, radiometric dating, and computer modeling to trace the particles’ trajectories, scientists linked the 1831 eruption to an island volcano in the Northwest Pacific. They reported in the Proceedings of the National Academy of Sciences that, based on their analysis, the mystery volcano is the Zavarytsky volcano on Simushir Island in the Kuril Islands, a region currently disputed by Russia and Japan. Prior to the scientists’ findings, the last known eruption of the Zavarytsky volcano was in 800 BC.

"For many volcanoes on Earth, especially those located in remote areas, our knowledge of their eruptive history is very limited," said Dr. William Hutchison, lead author of the study and principal investigator at the School of Earth and Environmental Sciences at the University of St Andrews in the UK. "Zavarytsky volcano is located on an extremely remote island between Japan and Russia. It is uninhabited, and historical records are limited to a few diary entries from ships that passed these islands every few years." Due to the scarcity of information about Zavarytsky volcano's activity in the 19th century, no one had previously suspected it as a candidate for the 1831 eruption. Instead, researchers considered volcanoes closer to the equator, such as the Babuyan Claro volcano in the Philippines.

An examination of the Greenland ice cores showed that in 1831, sulfur deposition in Greenland (an indicator of volcanic activity) was about 6.5 times higher than in Antarctica. This finding suggested that the source of the volcanic eruption was a large-scale eruption in the mid-latitudes of the Northern Hemisphere. The team also conducted chemical analysis of the volcanic ash and volcanic glass fragments, which were no more than 0.02 millimeters in length. When the scientists compared their results with geochemical datasets from volcanic regions, the closest match was Japan and the Kuril Islands. Volcanic eruptions in 19th-century Japan were well documented, but there was no record of a large-scale eruption in 1831.

However, colleagues who had previously visited volcanoes in the Kuril Islands provided samples that allowed researchers to geochemically match them with the caldera of the Zavarytsky volcano. "The moment in the lab when we analyzed the two ash samples – one from the volcano and one from the ice core – was a real 'aha' moment," Hutchison said in his email. Radiocarbon dating of ash deposits on Simushir Island indicated that they were formed within the last 300 years. Furthermore, analysis of the caldera's volume and sulfur isotopes suggested that it was formed after a large-scale eruption between 1700 and 1900, making the Zavarytsky volcano a "prime candidate" for the mysterious 1831 eruption.

In addition to the Zavarytsky volcano, three other volcanoes erupted between 1808 and 1835. These marked the decline of the Little Ice Age, a climate anomaly that lasted from the early 1400s to around 1850. During this period, the average annual temperature in the Northern Hemisphere decreased by an average of 0.6 degrees Celsius (1.1 degrees Fahrenheit). In some places, temperatures were 2 degrees Celsius (3.6 degrees Fahrenheit) lower than normal, and this cooling lasted for decades. Two of the four eruptions had been previously identified: Mount Tambora in Indonesia in 1815, and Cosigüina volcano in Nicaragua in 1835. The volcano that erupted in 1808/1809 remains unknown. The study authors reported that the addition of the Zavarytsky volcano highlights the potential of the Kuril Islands volcanoes to disrupt the Earth's climate.

Following the 1831 eruption, colder and drier conditions emerged in the Northern Hemisphere. Subsequently, widespread reports of hunger and suffering quickly surfaced, with famines sweeping through India, Japan, and Europe, affecting millions of people. "Volcanic climate cooling appears to have led to crop failures and famines," Hutchison said. "The current focus of research is to understand to what extent these famines were caused by volcanic climate cooling or by other socio-political factors." By providing long-missing information about the volcano that caused the Earth's climate to cool in the 19th century, "this research perhaps strengthens our confidence in the role of volcanic eruptions during the final stages of the Little Ice Age," said Brenneman.

Like the Zavarytsky volcano, many volcanoes in the world are located in remote areas and are poorly monitored, making it challenging to predict when and where the next large-scale eruption will occur, Hutchison added. If there is a lesson to be learned from the 1831 eruption, it is that volcanic activity in remote regions can have devastating global consequences, and people may not be prepared to face them. "When the next big event happens, we don't really have a coordinated international community to kick into action," Hutchison said. "This is something that we as scientists and as a society need to think about."