Saw this on CNN.
http://am.blogs.cnn.com/2011/01/27/physicist-michio-kaku-on-super-volcano-all-you-can-do-is-run/
Current scenario:
100 miles (160Km) near volcano instantly wiped out
500 miles (804.6Km) burning ash cloud
Smoke enters jet stream and cripples air traffic
Threatens world food...