[Junior]

This one almost spelled the end for humanity:

SUPER VOLCANO TOBA 
Their is substantial evidence to show that within the time of the super volcano Toba's eruption in the Indonesian Pacific, the world's population of homo sapiens decreased from over one hundred thousand to less than two thousand, basically because global temperatures dropped five degrees for many years.  This was within the current interglacial and at its start.
 Toba, Indonesia, 75,000 years ago: The eruption of 2,800 cubic km of magma at Toba caldera 75,000 years ago was the largest eruption in the last 2 million years. The eruption may have release as much as 10¹² kg of sulfuric acid, an order of magnitude more than Laki in 1783 and Tambora in 1815, two of the greatest Holocene eruptions. The Toba eruption may have caused about 3 to 4 degree C cooling at the surface but this impact is hard to detect because of concurrent glacial conditions (Sigurdsson, 1990).
   

[#3Fan]

When Toba eropted, scientists estimate that there were only a few thousand human survivors out of millions, from studying mitochrondial DNA.