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), the lake stretches from 2.88°N 98.52°E to 2.35°N 99.1°E. 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 to 9 °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.