YVO is an interesting website. I said reflect on, not worry about it. The last such eruption (Mt. Toba, approx. 74,000 years ago) nearly wiped us out (nearly extinct). That should give a good approximation of the magnitude of a super volcano eruption.
What scientists call the 'main eruption' of Krakatoa, around 538 A.D., put us into the Dark Ages, via nearly 2 years without a growing season. Global temps dropped that far, and that eruption split the island in two. It is recorded in the Book of Kings. This is from a Nova episode, where scientists were tracing down the cause of the Dark Ages. They also mention that Krakatoa has a gigantic caldera on the ocean bottom (recent discovery).
Something stand in awe of the tremendous volcanic power, beneath your feet, while you are there. /ubbthreads/images/graemlins/wink.gif