Toba is a supervolcano in the middle of the Indonesia island of Sumatra.
A large lake, 100km long and 30 km wide, now sits in the calderas.
the Dutch geologist van Bemmelen, in 1949, first found that Lake Toba was surrounded by a vast layer of ignimbrite rocks.
Later researchers found rhyolite ash similar to that in the ignimbrite around Toba in Malaysia and 3000 km away in India. The total amount of volcanic material ejected was found to be about 2,800 cubic kilometres.
The Toba eruption was dated at 73,000 ± 4000 years ago and led to a decrease in the average global temperatures by 3 to 3.5 degrees Celsius for several years. This massive environmental change is believed to have created population bottlenecks in the various human species that existed at the time.
Genetic evidence suggests that all humans alive today are descended from a very small population, perhaps around 1,000 individuals that managed to survive.
From the records it seems that Toba produces major eruptions every 300-400,000 years.