Toba volcano, on the island of Sumatra in Indonesia, produced one of the most powerful eruptions known. This eruption occurred about 74,000 years ago. Some scientists think that it caused worldwide cooling that killed off a large proportion of the human population. The volcano today has a large caldera (craterlike depression) on its summit. The caldera is filled by Lake Toba. The Toba caldera is one of the largest calderas known. It measures 20 miles by 60 miles (30 kilometers by 100 kilometers).
Toba’s ancient eruption was the largest known from the Quaternary Period. The Quaternary Period is a time that began about 2.6 million years ago. The eruption expelled about 670 cubic miles (2,800 cubic kilometers) of ejecta (ash and rock). The eruption was about 50 times as great as the largest in recorded history, the 1815 eruption of Mount Tambora, also in Indonesia.
Scientists rate the explosive power of an eruption using a scale called the Volcanic Explosivity Index (VEI). The VEI assigns eruptions a number from 0 through 8, with 8 being the most powerful. The eruption of Toba 74,000 years ago was a VEI 8. It was one of several large eruptions that created the Toba caldera.
Ash and gas placed into the atmosphere by the Toba eruption led to several years of global cooling. Some scientists believe that the colder weather helped reduce the number of humans on Earth to as few as several thousand. According to this theory, the dying was so severe that it contributed to a genetic bottleneck. A genetic bottleneck is an event survived by few individuals, reducing the diversity of genes (hereditary material) within a population. However, research published in 2018 indicated that the global cooling caused by the Toba eruption was not as severe as initial calculations suggested. Genetic studies also cast doubt that any bottleneck event occurred in human populations around the time of the eruption.
