The 1,080-square-mile Toba Lake Caldera in Indonesia is actually four enormous, overlapping craters and is sometimes described as Yellowstone's "big sister” – with the potential of even a larger blast. The most recent Toba supereruption, also called by geologists the “Youngest Toba Tuff” or simply “YTT” occurred between 69,000 and 77,000 years ago and is believed to have been one of the Earth's most catastrophic eruptions, plunging the planet into a 6-to-10-year volcanic winter and possibly an additional 1,000-year cooling episode. One theory says that it also resulted in the world's human population being reduced to as few as 2,000 adults, creating what anthropologists refer to as a “bottleneck” in human development in which our species almost suffered extinction.