April 10, 1815

1815 eruption of Mount Tambora

Tambora's climactic eruption and caldera collapse

At about 7 p.m., witnesses watched three separate columns of fire rise from the summit and merge. An hour later, falling material had hidden the mountain in darkness.

10 April 1815, on the Sanggar Peninsula

At about 7 p.m. local time on 10 April 1815, three eruption columns rose from Mount Tambora, on Sumbawa, and merged overhead. An account collected by Stamford Raffles says falling material had obscured the spectacle in darkness by about 8 p.m.

This was a climax, not a beginning. Major explosions had started on 5 April, and the climactic activity ran on into 11 April rather than stopping at midnight.

Flows to the sea, then a hole where the summit had been

The climactic phase sent pyroclastic flows to the sea around the Sanggar Peninsula, devastating nearby settlements and cropland and generating a tsunami.

Roughly 50 cubic kilometres of magma — about 140 gigatonnes, dense-rock equivalent — was expelled, with short-lived Plinian plumes reaching as high as 43 km. Emptying the chamber collapsed the summit, leaving the caldera visible today, about 6 km wide and 1,250 m deep.

Sulfur, and the counting of the dead

About 60 megatonnes of sulfur went into the stratosphere. Death tolls differ sharply between sources because they combine deaths during the eruption with famine and disease over the following months and years; the best-supported broad statement is more than 71,000 deaths on Sumbawa and Lombok during or after the eruption.

The region was then under the British interregnum in the former Dutch possessions. Lieutenant Owen Phillips travelled to Sumbawa with rice and gathered the local testimony — including the Rajah of Sanggar's account — that Raffles published.

Sources

Researched 23 Aug 2026 7 sources 2 audit passes

How this was checked

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What the sources leave uncertain

The local date of the climactic onset—10 April—is secure, but the most intense phase crossed into 11 April and later activity continued. It should not be described as a single instantaneous blast.
Death estimates differ substantially because they combine direct deaths with famine and disease occurring over subsequent months or years.