n the remote northwest corner of the Pacific Ocean, where the Kuril Archipelago stretches between northern Japan and Russia’s Kamchatka Peninsula, lies a hidden geological marvel—Zavaritskogo Volcano. This volcanic structure, also known as Zavaritskii, stands prominently on Simushir Island, an uninhabited, rugged landmass in the middle of the archipelago. Though the region is sparsely populated by humans, it is a hotspot for volcanic activity, and Zavaritskogo is one of its most fascinating features.
Zavaritskogo is distinguished by its nested, steep-walled calderas, which encircle a serene central lake. This striking formation was captured in stunning detail by the Operational Land Imager (OLI) on Landsat 8 during a flyover on September 12, 2024.
The youngest of these calderas, featured prominently in satellite imagery, is outlined by reddish, unvegetated slopes, hinting at its relatively recent formation. Since around 1910, the volcano has experienced small eruptions that created cinder cones and lava domes within the caldera’s bounds. The last documented volcanic activity occurred in 1957, when an eruption filled part of the lake’s northwest section. This event formed a 350-meter-wide (1,150 feet) and 40-meter-high (130 feet) lava dome, still visible today.
While Zavaritskogo’s recent eruptions have been modest, new research suggests a much more explosive history. Scientists believe that the inner caldera may have formed during one of the largest volcanic eruptions of the 19th century.
Evidence for this theory comes from a surprising source: polar ice cores. These icy archives revealed that a major eruption in 1831 released vast quantities of sulfur into the stratosphere. The sulfur aerosols reflected sunlight back into space, leading to a cooling of up to 1°C (2°F) across the Northern Hemisphere. This sudden climatic shift was recorded in historical accounts from that summer, which described the Sun appearing in shades of green, purple, and blue—a phenomenon caused by volcanic particles scattering sunlight in the atmosphere.
For years, the exact source of this mysterious eruption remained unidentified. However, recent chemical analyses of volcanic materials preserved in ice cores have been matched with deposits from Zavaritskogo’s most significant eruption. Additionally, radiocarbon dating and volume estimates of ejected material point directly to Zavaritskogo as the culprit behind the 1831 eruption.
While this discovery solves a long-standing mystery, it also opens the door to further questions. The study’s authors note that two other significant eruptions from the early 19th century—also indicated by sulfur spikes in ice core data—remain unaccounted for. The search for their volcanic sources continues, promising more exciting revelations about the Kuril Archipelago’s fiery past.
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