4. Etna, Italy (133)
If Grímsvötn was the "one hit wonder" for 2011, then Etna was the Beatles. The Italian volcano had 18 paroxysms over the course of the year, some of which produced lava flows, towering ash plumes and/or strombolian explosions. Thanks to Etna's location, each of these events were closely monitored by the likes of Dr. Boris Behncke at the Osservatario Etneo - along with many Eruptions readers who could catch the action of one of the many webcams pointed at the volcano.
Image: An explosion at Etna on August 29, 2011 as part of the 12th paroxysm of the year. Image courtesy of Dr. Boris Behncke.