Volcanoes rated at 8 ( the highest level ) on the Volcanic Explosivity Index are known as supervolcanoes . According to the Toba catastrophe theory , 75,000 to 80,000 years ago a supervolcanic eruption at what is now Lake Toba in Sumatra reduced the human population to 10,000 or even 1,000 breeding pairs , creating a bottleneck in human evolution , and killed three-quarters of all plant life in the northern hemisphere . However , there is considerable debate regarding the veracity of this theory . The main danger from a supervolcano is the immense cloud of ash , which has a disastrous global effect on climate and temperature for many years
Toba catastrophe theory
Toba catastrophe theory
Natural disaster