Toba: the Supervolcano

 Lake Toba is on the island of Sumatra, part of Indonesia. It is a very unusual lake: 100 km by 30 in area, with a large island in the middle, extremely deep, and with the steep slopes above containing large deposits of ash. Such a lake could not have been formed by normal geographical and geological forces, but is rather a huge hole blasted in the earth's crust. Deposits of similar volcanic ash have been found from Saudi Arabia to China, dating from about 75,000 years ago, and coinciding with massive quantities of sulphur dioxide found in ice cores in Greenland.

All of this points to an enormous volcanic explosion, with power equivalent to over 4,000 megatons, ten times the destructive power of the Tambora eruption in 1815, which resulted in a "year without a summer" and widespread famine in Europe and North America. The Toba eruption must have been by far the biggest in human history; perhaps one of the biggest ever. Perhaps 1,000 cubic kilometres of magma would have been released, in a column many miles high, with pyroclastic flows lasting two weeks or more, leaving a vast hole a kilometre deep. Any animal life within thousands of miles would have instantly choked. Enormous quantities of sulphur dioxide released into the atmosphere would have cut off the sunlight over much of the earth, leading to the death of plants and then of animals. Evidence of tiny molluscs in sea cores point to a fall in sea temperatures of 5 degrees. The eruption could thus have resulted in a thousand years of climate cooling; perhaps a mini-Ice Age. 

   The effects on the world's human population remains a matter of academic debate. At this time very few humans would have lived anywhere except in Africa and along the northern shores of the Indian Ocean. Scientists have long been aware of a genetic "bottleneck" around the time of the Toba eruption, suggesting very few people survived; but on the other hand, it has been suggested that the human population of Africa was not greatly affected by Toba. It is possible that the different so-called "races" of mankind resulted from just a few survivors remaining in small scattered communities, with consequent inbreeding. The biggest question, however, must be: could something as devastating as Toba happen again, and what would be its consequences? Is human civilisation merely something which has been able to develop in the interval between supervolcanic eruptions?