Toba Catastrophe Theory - Supereruption


The Toba eruption or Toba event occurred at what is now Lake Toba about 73,000±4,000 years ago. The Toba eruption was the latest of the three major eruptions which occurred at Toba in the last 1 million years. The last eruption had an estimated Volcanic Explosivity Index of 8 (described as "mega-colossal"), or magnitude ≥ M8; it thus made a sizeable contribution to the 100 × 30 km2 caldera complex. Dense-rock equivalent estimates of eruptive volume for the eruption vary between 2,000 km3 and 3,000 km3, but the most frequently quoted DRE is 2,800 km3 (about 7×1015 kg) of erupted magma, of which 800 km3 was deposited as ash fall. It was two orders of magnitude greater in erupted mass than the largest volcanic eruption in historic times, in 1815 at Mount Tambora in Indonesia, which caused the 1816 "Year Without a Summer" in the northern hemisphere.

Although the Toba eruption took place in Indonesia, it deposited an ash layer approximately 15 centimetres thick over the entirety of South Asia. A blanket of volcanic ash was also deposited over the Indian Ocean, and the Arabian and South China Sea. Deep-sea cores retrieved from the South China Sea extended the known distribution of the eruption and suggest that the 2,800 km3 calculation of the eruption magnitude is a minimum value or even an underestimate.

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