volcano
Supervolcanoes can eject massive amounts of ash and gas, triggering global cooling.
An eruption could cause a new Ice Age and mass extinction.
Six known active supervolcanoes exist today, including Yellowstone and Lake Toba.
Signs of activity—earthquakes, gas emissions—suggest these calderas are far from dormant.
Yellowstone's last eruption ejected 8,000 times the ash of Mount St. Helens.
Lake Toba's eruption may have reduced humanity to a few thousand survivors.
Taupo, Aira, and Long Valley show ongoing volcanic activity and potential risk.
U.S. Geological Survey, Volcanology Research