Lake Toba (Indonesian: Danau Toba) is a large natural lake occupying the caldera of a supervolcano. The lake is about 100 kilometres (62 miles) long, 30 kilometres (19 mi) wide, and up to 505 metres (1,657 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°53′N 98°31′E / 2.88°N 98.52°E to 2°21′N 99°06′E / 2°21′N 99°06′E / 2.35; 99.1. It is the largest lake in Indonesia and also 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. Recent advances in dating methods suggest a more accurate identification of 74,000 years ago as the date. 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 worldwide population to the present. Debate exists regarding the catastrophe theory.
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.
On June 18, 2018, Lake Toba was the scene of a ferry disaster. A ferry loaded with three times the permitted number of people, and without enough life jackets, sank in bad weather. Around 190 people drowned and only 18 were saved, including the captain, who was also reportedly the owner.