in prehistory there was Toba, now lake toba, a huge caldera which is missing on this map.
they say that the human race was brought down to 4 digits numbers due to its eruption around 73,000 BP.
Yes, I first heard of that on the documentary “Supervolcano”.
http://www.youtube.com/watch?v=bqpOTJAAwBU&feature=related