The 1815 volcanic eruption that caused the “Year Without Summer” and helped influence Frankenstein was Mount Tambora.
Tambora erupted on April 10, 1815, on Sumbawa in present-day Indonesia. It was one of the most powerful volcanic eruptions in recorded history, sending enormous quantities of ash and sulfur gases into the atmosphere. These particles reduced incoming sunlight and caused widespread cooling.
The climatic effects became especially severe in 1816, when Europe, North America, and other regions experienced unusually cold temperatures, heavy rain, frosts, crop failures, and food shortages. The year became known as the “Year Without Summer.”
Mary Shelley was staying near Lake Geneva with Percy Bysshe Shelley, Lord Byron, and John Polidori during the gloomy, stormy summer of 1816. Their indoor discussions and ghost-story challenge helped inspire Frankenstein. A common mix-up is Krakatoa, whose famous eruption occurred much later, in 1883.