Tambora: a deep dive into the eruption that caused a year without summer
Tambora is the largest volcanic eruption in recorded human history. In April 1815, this stratovolcano on the Indonesian island of Sumbawa exploded with an estimated VEI of 7, three times the size of Krakatoa. The mountain lost about a kilometre and a half of its height. The climate consequences were felt globally for years.
A stratovolcano on Sumbawa
Tambora rises on the Sanggar Peninsula of Sumbawa, in the Lesser Sunda Islands. Before 1815 it stood roughly 4,300 metres tall, one of the highest peaks in the East Indies. Today it reaches 2,850 metres and holds a six-kilometre-wide, one-kilometre-deep caldera at the top.
The build-up
Tambora had been emitting ash and small eruptions for several years before April 1815. The climactic phase began with a strong eruption on the 5th and culminated on 10–11 April with a series of paroxysmal explosions audible 2,000 kilometres away. Pyroclastic flows raced across the peninsula and out to sea.
The immediate death toll
Estimates of immediate deaths from the eruption itself range from roughly 10,000 to more than 70,000, depending on which sources are followed. Pyroclastic flows wiped out the Tambora kingdom on the mountain's slopes — a whole language and culture lost. Famine and disease in the following months killed many more across the region.
The year without a summer
About 100 cubic kilometres of magma was erupted, and a substantial sulphate aerosol layer entered the stratosphere. 1816 became "the year without a summer" in Europe and eastern North America. Snow fell in June in New England; crops failed across Europe; the lake-side holiday at Villa Diodati that summer gave the world both Frankenstein and the modern vampire story.
Tambora and global history
The 1816 famines triggered migrations, food riots and political unrest. Cholera in the Bay of Bengal worsened; the price of grain in Europe doubled. The eruption is one of the rare cases where a single geological event has measurably bent global political and demographic history.
The lost civilisation
Archaeologists have since uncovered the so-called "Pompeii of the East" beneath Tambora's pyroclastic deposits — wooden houses, rice in pots, charred bones. Excavations near Pekat continue. The Tambora language is preserved only in a brief word list collected before the eruption.
The caldera today
The Tambora caldera is one of the most accessible large volcanic calderas in the world. Multi-day treks lead up from the village of Pancasila to the rim, where the floor lies a kilometre below. Modest fumaroles still rise from the central cone.
Monitoring and present hazards
Tambora is monitored by the Indonesian Center for Volcanology and Geological Hazard Mitigation. Activity has been low for decades, but the caldera is alive — the same plumbing that produced 1815 has not been removed. A repeat is unlikely on human timescales but not geologically impossible.
Why Tambora matters
Tambora is the modern world's reminder of what a really big eruption looks like. It is the volcano against which Pinatubo, Mount St Helens and Krakatoa are scaled. And it is the volcano that briefly cooled the planet, scattered Mary Shelley's summer plans, and put "year without a summer" into the language.
On the map
Open the map and find Tambora on the Sanggar Peninsula of Sumbawa. Nearby Rinjani on Lombok and Agung on Bali continue the Sunda arc to the west; Krakatoa lies further west in the Sunda Strait.