In 1831, the Earth shuddered. A massive volcano erupted with such ferocity that it dimmed the skies and cooled the planet. Crops failed, famine spread, and the Northern Hemisphere entered a climate-altered reality. Yet, for nearly two centuries, the identity of the volcano behind this global upheaval remained a mystery—a puzzle finally solved by a team of scientists armed with ice cores, volcanic ash, and a drive to uncover the past.

Their findings pinpoint the culprit: Zavaritskii, a remote volcano on Simushir Island, part of the Kuril Islands chain between Japan and Russia. Previously, the likely culprit was wrongly attributed to a tropical volcano. The eruption, one of the most powerful of the 19th century, spewed enough sulfur dioxide into the atmosphere to cool the Northern Hemisphere by approximately 1°C (1.8°F), leading to failed crops and a lot of human suffering.

The Smoking Gun

For centuries, hard evidence of the 1831 eruption existed only in fragments—ash buried in Greenland’s ice sheets, fleeting diary entries from sailors passing remote islands, and the fading effects of an extended chill during the Little Ice Age (a period of cooling after the so-called Medieval Warm Period). Without modern tools, volcanologists could only guess at its source.

Dr. William Hutchison, a principal research fellow at the University of St. Andrews, wasn’t satisfied with this. He spearheaded the investigation, which used samples from polar ice cores—time capsules of Earth’s climatic past— in order to trace the eruption to the Northern Hemisphere. The ash contained within these cores provided a “perfect fingerprint match” to Zavaritskii.

“The moment in the lab when we analyzed the two ashes together—one from the volcano and one from the ice core—was a genuine eureka moment,” Hutchison recalled. “I couldn’t believe the numbers were identical.”

The discovery came after painstaking efforts to compare the microscopic shards of volcanic glass in the ice—no larger than one-tenth the diameter of a human hair—to samples collected decades ago from the Kuril Islands. Eventually, the Zavaritskii caldera, with its striking red deposits from past eruptions, became the focal point of their investigation.

Unseen Devastation, Global Lessons

The eruption’s effects were dramatic and far-reaching. Cooling and drier conditions emerged across the Northern Hemisphere, leading to widespread crop failures. Famines swept through India, Japan, and Europe, affecting millions.

“It seems plausible that volcanic climate cooling led to crop failure and famine,” Hutchison said. “A focus of ongoing research is to understand to what extent these famines were caused by volcano climate cooling, or by other socio-political factors.”

Yet, as Hutchison noted, the 1831 eruption’s magnitude and impact went unnoticed for decades due to Zavaritskii’s extreme isolation. No one lives on Simushir Island, and historical records are sparse—limited to a handful of ship diaries from the era. Even today, many of Earth’s volcanoes remain poorly monitored, especially in remote regions like the Kurils.

“There are so many volcanoes like Zavaritskii, which highlights how difficult it will be to predict when or where the next large-magnitude eruption might occur,” Hutchison said. “We don’t really have a coordinated international community to kick into gear when the next big one happens. That is something we need to think about as both scientists and as a society.”

A Final Clue from the Ice Age

The 1831 eruption marked the waning days of the Little Ice Age, a centuries-long climate anomaly that cooled the Earth. Alongside three other significant eruptions between 1808 and 1835—including the infamous Mount Tambora in Indonesia—the event served as a final act in a period of unusual climatic upheaval.

As the world grapples with climate change and its own set of uncertainties, the lessons from 1831 remain stark. Volcanic eruptions, even in the planet’s most isolated corners, have the power to alter global systems and upend lives. Zavaritskii’s fury may have been forgotten for centuries, but its rediscovery offers a sobering reminder of nature’s unpredictable force.