Which volcano's 1815 eruption caused the 'Year Without a Summer'?

Mount Tambora’s 1815 eruption caused the “Year Without a Summer.” The volcano, on Indonesia’s island of Sumbawa, produced the largest confirmed eruption in recorded human history and reached a Volcanic Explosivity Index of 7.

The climactic explosion occurred on 10 April 1815 after months of escalating activity. It blasted roughly 37–45 cubic kilometers of material into the atmosphere, collapsed the summit, and left a caldera about 6–7 kilometers wide. Tambora’s peak fell from approximately 4,300 meters to 2,851 meters.

Sulfur dioxide carried into the stratosphere formed sulfate aerosols that reflected sunlight and cooled the planet. In 1816, average global temperatures fell by roughly 0.4–0.7°C, with especially severe effects across the Northern Hemisphere. Snow fell during summer in parts of North America, while heavy rain and cold damaged crops in Europe and Asia.

A common mix-up is Krakatoa, whose 1883 eruption also produced spectacular atmospheric effects. Krakatoa was not responsible for the 1816 climate disaster; that event is chiefly associated with Tambora’s 1815 eruption.