The Forgotten Volcano That Cooled the Planet and Turned the Sun Green

A little-known volcano on a remote Pacific island may have been the source of one of the 19th century’s most powerful eruptions.

Zavaritskogo, a caldera-ridden giant in the Kuril Islands, last erupted in 1957, but evidence now links it to a catastrophic 1831 explosion. That event injected enough sulfur into the stratosphere to cool the Northern Hemisphere and paint the skies strange colors.

The Striking Landscape of Zavaritskogo

In the remote northwestern Pacific, a chain of islands stretches between northern Japan and Russia’s Kamchatka Peninsula. This is the Kuril Archipelago — a sparsely populated region dominated by volcanoes.

One of its most striking features is the Zavaritskogo volcano (also known as Zavaritskii) on Simushir Island. This complex volcanic structure consists of steep-walled, nested calderas encircling a central lake. On September 12, 2024, the Operational Land Imager (OLI) on Landsat 8 captured detailed images of Zavaritskogo’s rugged terrain.

A History of Fiery Eruptions

At the heart of the volcano lies its youngest caldera, centered in the detailed image below, partially outlined by reddish, barren slopes. Since forming, it has seen small eruptions, beginning around 1910, that created cinder cones and lava domes within its boundaries. The last recorded eruption in 1957 ejected material that filled part of the lake, forming a dome 350 meters (1,150 feet) wide and 40 meters (130 feet) high.

A Cataclysmic 19th-Century Eruption

However, Zavaritskogo’s past eruptions were far more explosive. Recent research suggests that its inner caldera may have formed during one of the most powerful volcanic eruptions of the 19th century — a cataclysmic event that reshaped the landscape and possibly impacted global climate.

Previous analyses of polar ice cores indicated that a major eruption in 1831 had injected several metric tons of sulfur into the stratosphere, reflecting solar radiation back to space and causing the Northern Hemisphere to cool by up to 1 degree Celsius (2 degrees Fahrenheit). And historical accounts from that summer note the Sun appeared green, purple, and blue, which can occur when volcanic particles in the atmosphere scatter sunlight. The probable volcanic source of these phenomena, however, had long remained elusive.

Solving the Volcanic Mysteries of the Past

Scientists have now matched the chemical composition of volcanic material preserved in ice cores with that from the most recent major eruption of Zavaritskogo. Radiocarbon dating and estimates for the volume of material ejected from the volcano further implicated Zavaritskogo as the source of the major 1831 eruption.

More volcanic mysteries from that era are left to be solved, the study’s authors noted. The sources of two other eruptions in the early 19th century, signified by sulfur spikes in ice core data, have yet to be identified.

NASA Earth Observatory images by Wanmei Liang, using Landsat data from the U.S. Geological Survey.

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