6. Kirishima, Japan (51)
Sometimes being early in the year will hurt when it comes to the year-end voting and I think that the January/February eruption from the Shimnoedake cone at Kirishima might have felt just that. One of the first big volcanic events of 2011 saw some amazing ash plumes (see above) from one of the more active volcanoes in Japan when the Shinmoedake crater produced its first major eruption since 1991 (it had experienced a few smaller, steam-driven explosions in 2008-10). During the course of the activity, Kirishima was joined by nearby Sakurajima to produce two major ash plumes simultaneous in southern Japan.
Image: The ash plume from Kirishima in Japan seen in early February 2011. Image courtesy of James Reynolds - check out his year end video with shots from Kirishima erupting.