Lake Toba (Indonesian: Danau Toba) is a lake and supervolcano. The lake is 100 kilometres long, 30 kilometres wide, and up to 505 meters (1,666 ft) deep. Located in the middle of the northern part of the Indonesian island of Sumatra with a surface elevation of about 900 metres (2,953 ft). It is the largest lake in Indonesia and the largest volcanic lake in the World.
Lake Toba is the site of a massive supervolcanic eruption estimated at VEI 8 that occurred 69,000 to 77,000 years ago, representing a climate-changing event. It is the largest known explosive eruption on Earth in the last 25 million years. According to the Toba catastrophe theory, it had global consequences for human populations: it killed most humans living at that time and is believed to have created a population bottleneck in central east Africa and India, which affects the genetic make up of the human world-wide population to the present.
This hypothesis is not widely accepted because evidence is lacking for a decline or extinction of other animals, including species that are sensitive to changes in the environment. It has been accepted that the eruption of Toba led to a volcanic winter with a worldwide decrease in temperature between 3 to 5 °C (5.4 to 9.0 °F), and up to 15 °C (27 °F) in higher latitudes. Additional studies in Lake Malawi in East Africa show significant amounts of ash being deposited from the Toba eruptions, even at that great distance, but little indication of a significant climatic effect in East Africa.
The Toba eruption (the Toba event) occurred at what is now Lake Toba about 67,500 to 75,500 years ago. It was the last in a series of at least three caldera-forming eruptions at this location, with earlier calderas having formed around 700,000 and 840,000 years ago. This last eruption had an estimated VEI 8, making it possibly the largest explosive volcanic eruption within the last 25 million years.
Bill Rose and Craig Chesner of Michigan Technological University have estimated that the total amount of material released in the eruption was about 2,800 km3 (670 cu mi)- about 2,000 km3 (480 cu mi) of ignimbrite that flowed over the ground, and approximately 800 km3 (190 cu mi) that fell as ash mostly to the west. The pyroclastic flows of the eruption destroyed an area of 20,000 km2 (7,722 sq mi), with ash deposits as thick as 600 m (1,969 ft) by the main vent.